Bibliographic Overview Update Biblio

30869852
- -

.

24501781
- -

.

31347571 Adult-onset leukodystrophy with homozygous AARS2 mutation located in the aminoacylation domain.
- - Neurology India

Uzun Gunes A.

20301462
- -

.

32308605 A New DARS2 Mutation Discovered in an Adult Patient.
- - Case reports in neurology

N'Gbo N'Gbo Ikazabo Rosy, Mostosi Christian, Jissendi Patrice, Labaisse Marie-Anne, Vandernoot Isabelle.

We report a case of an adult patient suffering from leukoencephalopathy with brainstem and spinal cord involvement and elevated white matter lactate (LBSL) caused by a DARS2 polymorphism. DARS2 mutation was identified by combining MRI and genetic analysis. Our patient was affected by compound heterozygosity for a pathogenic mutation and a common variant, but with reduced aspartyl-tRNA synthetase activity. Brain and spinal cord magnetic resonance imaging revealed extensive white matter abnormalities; spectroscopy revealed no lactate elevation. A new compound heterozygous DARS2 variant combined with a polymorphism in the other allele in an adult patient with LBSL was identified, resulting in reduced DARS2 activity. This combination is rare and has consequences on how we should consider benign variant polymorphisms in the future.

34104671 Perinatal Manifestations of DARS2-Associated Leukoencephalopathy With Brainstem and Spinal Cord Involvement and Lactate Elevation (LBSL).
- - Child neurology open

Ngo Julie, Prokop Jeremy W, Umfleet Jason, Seaver Laurie H.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a progressive disorder associated with deficiency of mitochondrial aspartyl-tRNA synthetase, a homodimer encoded by the gene DARS2. There is a wide range in age of onset of symptoms, typically from childhood to adulthood, with very few cases of infantile onset disease reported. We report a child at age 10 years with perinatal onset of symptoms evidenced by congenital microcephaly with progression to severe but non-lethal epileptic encephalopathy and spastic quadriplegia. A comprehensive epilepsy focused gene panel performed as a trio with parents detected a novel homozygous DARS2 variant. This variant is located at the dimer interface in a critical catalytic domain and is expected to result in markedly reduced enzyme activity which likely explains the severe and early onset symptoms in this case.

33962821 Remitting and exacerbating white matter lesions in leukoencephalopathy with thalamus and brainstem involvement and high lactate.
Aug 2021 Brain & development

Sawada Daisuke, Naito Sachiko, Aoyama Hiromi, Shiohama Tadashi, Ichikawa Tomohiko, Imagawa Eri, Miyake Noriko, Matsumoto Naomichi, Fujii Katsunori.

Leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL) is a hereditary disorder caused by biallelic variants in the EARS2 gene. Patients exhibit developmental delay, hypotonia, and hyperreflexia. Brain magnetic resonance imaging (MRI) reveals T2-hyperintensities in the deep white matter, thalamus, and brainstem, which generally stabilize over time. Herein, we report a case of LTBL, showing remitting and exacerbating white matter lesions.

33942428 Bi-allelic KARS1 pathogenic variants affecting functions of cytosolic and mitochondrial isoforms are associated with a progressive and multisystem disease.
Jun 2021 Human mutation

Cappuccio Gerarda, Ceccatelli Berti Camilla, Baruffini Enrico, Sullivan Jennifer, Shashi Vandana, Jewett Tamison, Stamper Tara, Maitz Silvia, Canonico Francesco, Revah-Politi Anya, Kupchik Gabriel S, Anyane-Yeboa Kwame, Aggarwal Vimla, Benneche Andreas, Bratland Eirik, Berland Siren, D'Arco Felice, Alves Cesar A, Vanderver Adeline, Longo Daniela, Bertini Enrico, Torella Annalaura, Nigro Vincenzo, , D'Amico Alessandra, van der Knaap Marjo S, Goffrini Paola, Brunetti-Pierri Nicola.

KARS1 encodes a lysyl-transfer RNA synthetase (LysRS) that links lysine to its cognate transfer RNA. Two different KARS1 isoforms exert functional effects in cytosol and mitochondria. Bi-allelic pathogenic variants in KARS1 have been associated to sensorineural hearing and visual loss, neuropathy, seizures, and leukodystrophy. We report the clinical, biochemical, and neuroradiological features of nine individuals with KARS1-related disorder carrying 12 different variants with nine of them being novel. The consequences of these variants on the cytosol and/or mitochondrial LysRS were functionally validated in yeast mutants. Most cases presented with severe neurological features including congenital and progressive microcephaly, seizures, developmental delay/intellectual disability, and cerebral atrophy. Oculo-motor dysfunction and immuno-hematological problems were present in six and three cases, respectively. A yeast growth defect of variable severity was detected for most variants on both cytosolic and mitochondrial isoforms. The detrimental effects of two variants on yeast growth were partially rescued by lysine supplementation. Congenital progressive microcephaly, oculo-motor dysfunction, and immuno-hematological problems are emerging phenotypes in KARS1-related disorder. The data in yeast emphasize the role of both mitochondrial and cytosolic isoforms in the pathogenesis of KARS1-related disorder and supports the therapeutic potential of lysine supplementation at least in a subset of patients.

33972171 Phenotypic diversity of brain MRI patterns in mitochondrial aminoacyl-tRNA synthetase mutations.
Jun 2021 Molecular genetics and metabolism

Roux Charles-Joris, Barcia Giulia, Schiff Manuel, Sissler Marie, Levy Raphaël, Dangouloff-Ros Volodia, Desguerre Isabelle, Edvardson Shimon, Elpeleg Orli, Rötig Agnès, Munnich Arnold, Boddaert Nathalie.

Mitochondrial aminoacyl-tRNA synthetases-encoded by ARS2 genes-are evolutionarily conserved enzymes that catalyse the attachment of amino acids to their cognate tRNAs, ensuring the accuracy of the mitochondrial translation process. ARS2 gene mutations are associated with a wide range of clinical presentations affecting the CNS.

34156427 Leber's Hereditary Optic Neuropathy Arising From the Synergy Between ND1 3635G>A Mutation and Mitochondrial YARS2 Mutations.
Jun 2021 Investigative ophthalmology & visual science

Jin Xiaofen, Zhang Juanjuan, Yi Qiuzi, Meng Feilong, Yu Jialing, Ji Yanchun, Mo Jun Q, Tong Yi, Jiang Pingping, Guan Min-Xin.

To investigate the mechanism underlying the synergic interaction between Leber's hereditary optic neuropathy (LHON)-associated ND1 and mitochondrial tyrosyl-tRNA synthetase (YARS2) mutations.

34088003 Generation of three human induced pluripotent stem cell lines, LUMCi024-A, LUMCi025-A, and LUMCi026-A, from two patients with combined oxidative phosphorylation deficiency 8 and a related control.
May 2021 Stem cell research

van Helden Ruben W J, Birket Matthew J, Freund Christian, Arendzen Christaan H, Mikkers Harald M, Orlova Valeria, de Coo René I, Mummery Christine L, Bellin Milena.

Combined Oxidative Phosphorylation Deficiency 8 (COXPD8) is an autosomal recessive disorder causing lethal childhood-onset hypertrophic cardiomyopathy. Homozygous or compound heterozygous mutations in the nuclear-encoded mitochondrial alanyl-tRNA synthetase 2 (AARS2) gene underly the pathology. We generated induced pluripotent stem cells (hiPSCs) from two patients carrying the heterozygous compound c.1774 C>T, c.2188 G>A and c.2872 C>T AARS2 mutations, as well as a related healthy control carrying the c.2872 C>T AARS2 mutation. All hiPSC-lines expressed pluripotency markers, maintained a normal karyotype, and differentiated towards the three germ layer derivatives in vitro. These lines can be used to model COXPD8 or mitochondrial dysfunction.

33977142 LBSL: Case Series and DARS2 Variant Analysis in Early Severe Forms With Unexpected Presentations.
Apr 2021 Neurology. Genetics

Stellingwerff Menno D, Figuccia Sonia, Bellacchio Emanuele, Alvarez Karin, Castiglioni Claudia, Topaloglu Pinar, Stutterd Chloe A, Erasmus Corrie E, Sanchez-Valle Amarilis, Lebon Sebastien, Hughes Sarah, Schmitt-Mechelke Thomas, Vasco Gessica, Chow Gabriel, Rahikkala Elisa, Dallabona Cristina, Okuma Cecilia, Aiello Chiara, Goffrini Paola, Abbink Truus E M, Bertini Enrico S, Van der Knaap Marjo S.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is regarded a relatively mild leukodystrophy, diagnosed by characteristic long tract abnormalities on MRI and biallelic variants in DARS2, encoding mitochondrial aspartyl-tRNA synthetase (mtAspRS). DARS2 variants in LBSL are almost invariably compound heterozygous; in 95% of cases, 1 is a leaky splice site variant in intron 2. A few severely affected patients, still fulfilling the MRI criteria, have been described. We noticed highly unusual MRI presentations in 15 cases diagnosed by WES. We examined these cases to determine whether they represent consistent novel LBSL phenotypes.

34085948 Refining the mutational spectrum and gene-phenotype correlates in pontocerebellar hypoplasia: results of a multicentric study.
Mar 2021 Journal of medical genetics

Nuovo Sara, Micalizzi Alessia, Romaniello Romina, Arrigoni Filippo, Ginevrino Monia, Casella Antonella, Serpieri Valentina, D'Arrigo Stefano, Briguglio Marilena, Salerno Grazia Gabriella, Rossato Sara, Sartori Stefano, Leuzzi Vincenzo, Battini Roberta, Ben-Zeev Bruria, Graziano Claudio, Mirabelli Badenier Marisol, Brankovic Vesna, Nardocci Nardo, Spiegel Ronen, Petković Ramadža Danijela, Vento Giovanni, Marti Itxaso, Simonati Alessandro, Dipresa Savina, Freri Elena, Mazza Tommaso, Bassi Maria Teresa, Bosco Luca, Travaglini Lorena, Zanni Ginevra, Bertini Enrico Silvio, Vanacore Nicola, Borgatti Renato, Valente Enza Maria.

Pontocerebellar hypoplasias (PCH) comprise a group of genetically heterogeneous disorders characterised by concurrent hypoplasia of the pons and the cerebellum and variable clinical and imaging features. The current classification includes 13 subtypes, with ~20 known causative genes. Attempts have been made to delineate the phenotypic spectrum associated to specific PCH genes, yet clinical and neuroradiological features are not consistent across studies, making it difficult to define gene-specific outcomes.

32879996 Distinctive diffusion-weighted imaging features in late-onset genetic leukoencephalopathies.
Jan 2021 Neuroradiology

De Cocker Laurens J L, Castillo Mauricio.

Genetic leukoencephalopathies are inherited disorders characterized by progressive white matter involvement. Although most are paediatric conditions, late-onset adult leukoencephalopathies are being increasingly recognized. Adult leukoencephalopathies may present as neurodegenerative diseases with cognitive decline and motor symptoms. Similar to their paediatric counterparts, different adult leukoencephalopathies often have distinctive MRI appearances. In particular, DWI has been recently shown to demonstrate specific patterns of persistent diffusion restriction in several adult-onset leukoencephalopathies. As such, DWI may provide important clues to the diagnosis of adult-onset leukoencephalopathy. The purpose of this review is to discuss characteristic DWI features in some late-onset leukoencephalopathies.

34277617 Mitochondrial Protein Translation: Emerging Roles and Clinical Significance in Disease.
- 2021 Frontiers in cell and developmental biology

Wang Fei, Zhang Deyu, Zhang Dejiu, Li Peifeng, Gao Yanyan.

Mitochondria are one of the most important organelles in cells. Mitochondria are semi-autonomous organelles with their own genetic system, and can independently replicate, transcribe, and translate mitochondrial DNA. Translation initiation, elongation, termination, and recycling of the ribosome are four stages in the process of mitochondrial protein translation. In this process, mitochondrial protein translation factors and translation activators, mitochondrial RNA, and other regulatory factors regulate mitochondrial protein translation. Mitochondrial protein translation abnormalities are associated with a variety of diseases, including cancer, cardiovascular diseases, and nervous system diseases. Mutation or deletion of various mitochondrial protein translation factors and translation activators leads to abnormal mitochondrial protein translation. Mitochondrial tRNAs and mitochondrial ribosomal proteins are essential players during translation and mutations in genes encoding them represent a large fraction of mitochondrial diseases. Moreover, there is crosstalk between mitochondrial protein translation and cytoplasmic translation, and the imbalance between mitochondrial protein translation and cytoplasmic translation can affect some physiological and pathological processes. This review summarizes the regulation of mitochondrial protein translation factors, mitochondrial ribosomal proteins, mitochondrial tRNAs, and mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) in the mitochondrial protein translation process and its relationship with diseases. The regulation of mitochondrial protein translation and cytoplasmic translation in multiple diseases is also summarized.

33327715 Biallelic IARS2 mutations presenting as sideroblastic anemia.
Dec 2020 Haematologica

Barcia Giulia, Pandithan Dinusha, Ruzzenente Benedetta, Assouline Zahra, Pennisi Alessandra, Ormieres Clothilde, Besmond Claude, Roux Charles-Joris, Boddaert Nathalie, Desguerre Isabelle, Thorburn David R, Bratkovic Drago, Munnich Arnold, Bonnefont Jean-Paul, Rötig Agnès, Steffann Julie.

Not available.

33385443 MUTATION IN KARS: A NOVEL MECHANISM FOR SEVERE ANAPHYLAXIS.
Dec 2020 The Journal of allergy and clinical immunology

Ribó Pau, Guo Yanru, Aranda Juan, Ainsua-Enrich Erola, Navinés-Ferrer Arnau, Guerrero Mario, Pascal Mariona, Cruz Cinthia de la, Orozco Modesto, Muñoz-Cano Rosa, Martin Margarita.

Anaphylaxis is a severe allergic reaction that can be lethal if not treated adequately. The underlying molecular mechanisms responsible for the severity are mostly unknown.

32725632 Whole-exome sequencing in adult patients with developmental and epileptic encephalopathy: It is never too late.
Nov 2020 Clinical genetics

Minardi Raffaella, Licchetta Laura, Baroni Maria Chiara, Pippucci Tommaso, Stipa Carlotta, Mostacci Barbara, Severi Giulia, Toni Francesco, Bergonzini Luca, Carelli Valerio, Seri Marco, Tinuper Paolo, Bisulli Francesca.

Developmental and epileptic encephalopathies (DEE) encompass rare, sporadic neurodevelopmental disorders and usually with pediatric onset. As these conditions are characterized by marked clinical and genetic heterogeneity, whole-exome sequencing (WES) represents the strategy of choice for the molecular diagnosis. While its usefulness is well established in pediatric DEE cohorts, our study is aimed at assessing the WES feasibility in adult DEE patients who experienced a diagnostic odyssey prior to the advent of this technique. We analyzed exomes from 71 unrelated adult DEE patients, consecutively recruited from an Italian cohort for the EPI25 Project. All patients underwent accurate clinical and electrophysiological characterization. An overwhelming percentage (90.1%) had already undergone negative genetic testing. Variants were classified according to the American College of Medical Genetics and Genomics guidelines. WES disclosed 24 (likely) pathogenic variants among 18 patients in epilepsy-related genes with either autosomal dominant, recessive or X-linked inheritance. Ten of these were novel. We obtained a diagnostic yield of 25.3%, higher among patients with brain malformations, early-onset epilepsy and dysmorphisms. Despite a median diagnostic delay of 38.7 years, WES analysis provided the long-awaited diagnosis for 18 adult patients, which also had an impact on the clinical management of 50% of them.

33204598 Utility of specific amino acid ratios in screening for pyruvate dehydrogenase complex deficiencies and other mitochondrial disorders associated with congenital lactic acidosis and newborn screening prospects.
Nov 2020 JIMD reports

Bedoyan Jirair K, Hage Rosemary, Shin Ha Kyung, Linard Sharon, Ferren Edwin, Ducich Nicole, Wilson Kirkland, Lehman April, Schillaci Lori-Anne, Manickam Kandamurugu, Mori Mari, Bartholomew Dennis, DeBrosse Suzanne, Cohen Bruce, Parikh Sumit, Kerr Douglas.

Pyruvate dehydrogenase complex deficiencies (PDCDs) and other mitochondrial disorders (MtDs) can (a) result in congenital lactic acidosis with elevations of blood alanine (Ala) and proline (Pro), (b) lead to decreased ATP production, and (c) result in high morbidity and mortality. With ~140,000 live births annually in Ohio and ~1 in 9,000 overall prevalence of MtDs, we estimate 2 to 3 newborns will have PDCD and 13 to 14 others likely will have another MtD annually. We compared the sensitivities of plasma amino acids (AA) Alanine (Ala), Alanine:Leucine (Ala:Leu), Alanine:Lysine and the combination of Ala:Leu and Proline:Leucine (Pro:Leu), in subjects with known primary-specific PDCD due to PDHA1 and PDHB mutations vs controls. Furthermore, in collaboration with the Ohio newborn screening (NBS) laboratory, we determined Ala and Pro concentrations in dried blood spot (DBS) specimens using existing NBS analytic approaches and evaluated Ala:Leu and Pro:Leu ratios from DBS specimens of 123,414 Ohio newborns in a 12-month period. We used the combined Ala:Leu ≥4.0 and Pro:Leu ≥3.0 ratio criterion from both DBS and plasma specimens as a screening tool in our retrospective review of newborn data. The screening tool applied on DBS and/or plasma (or serum) AA specimens successfully identified three unrelated females with novel de novoPDHA1 mutations, one male with a novel de novo X-linked HSD17B10 mutation, and a female with VARS2 mutations. This work lays the first step for piloting an NBS protocol in Ohio for identifying newborns at high risk for primary-specific PDCD and other MtDs who might benefit from neonatal diagnosis and early institution of known therapy and/or potential novel therapies for such disorders.

33228777 Two novel likely pathogenic variants of HARS2 identified in a Chinese family with sensorineural hearing loss.
Nov 2020 Hereditas

Yu Jing, Jiang Wei, Cao Li, Na Xiaoxue, Yang Jiyun.

Mutations in HARS2 are one of the genetic causes of Perrault syndrome, characterized by sensorineural hearing loss (SNHL) and ovarian dysfunction. Here, we identified two novel putative pathogenic variants of HARS2 in a Chinese family with sensorineural hearing loss including two affected male siblings, c.349G > A (p.Asp117Asn) and c.908 T > C (p.Leu303Pro), through targeted next-generation sequencing methods. The two affected siblings (13 and 11 years old) presented with early-onset, rapidly progressive SNHL. The affected siblings did not have any inner ear malformations or delays in gross motor development. Combined with preexisting clinical reports, Perrault syndrome may be latent in some families with non-syndromic deafness associated with HARS2 mutations. The definitive diagnosis of Perrault syndrome based on clinical features alone is a challenge in sporadic males, and preadolescent females with no signs of POI. Our findings further expanded the existing spectrum of HARS2 variants and Perrault syndrome phenotypes, which will assist in molecular diagnosis and genetic counselling of patients with HARS2 mutations.

33260297 Progressive Early-Onset Leukodystrophy Related to Biallelic Variants in the KARS Gene: The First Case Described in Latin America.
Nov 2020 Genes

Vargas Adriana, Rojas Jorge, Aivasovsky Ivan, Vergara Sergio, Castellanos Marianna, Prieto Carolina, Celis Luis.

The KARS gene encodes the aminoacyl-tRNA synthetase (aaRS), which activates and joins the lysin with its corresponding transfer RNA (tRNA) through the ATP-dependent aminoacylation of the amino acid. KARS gene mutations have been linked to diverse neurologic phenotypes, such as neurosensorial hearing loss, leukodystrophy, microcephaly, developmental delay or regression, peripheral neuropathy, cardiomyopathy, the impairment of the mitochondrial respiratory chain, and hyperlactatemia, among others. This article presents the case of a Colombian pediatric patient with two pathological missense variants in a compound heterozygous state in the KARS gene and, in addition to the case report, the paper reviews the literature for other cases of KARS1-associated leukodystrophy.

32802952 Late-onset leukoencephalopathy in a patient with recessive EARS2 mutations.
Oct 2020 Neurology. Genetics

Monfrini Edoardo, Ronchi Dario, Franco Giulia, Garbellini Manuela, Straniero Letizia, Scola Elisa, Arienti Federica, Duga Stefano, Comi Giacomo Pietro, Bresolin Nereo, Di Fonzo Alessio.

32399598 Genomic sequencing highlights the diverse molecular causes of Perrault syndrome: a peroxisomal disorder (PEX6), metabolic disorders (CLPP, GGPS1), and mtDNA maintenance/translation disorders (LARS2, TFAM).
Oct 2020 Human genetics

Tucker Elena J, Rius Rocio, Jaillard Sylvie, Bell Katrina, Lamont Phillipa J, Travessa André, Dupont Juliette, Sampaio Lurdes, Dulon Jérôme, Vuillaumier-Barrot Sandrine, Whalen Sandra, Isapof Arnaud, Stojkovic Tanya, Quijano-Roy Susana, Robevska Gorjana, van den Bergen Jocelyn, Hanna Chloe, Simpson Andrea, Ayers Katie, Thorburn David R, Christodoulou John, Touraine Philippe, Sinclair Andrew H.

Perrault syndrome is a rare heterogeneous condition characterised by sensorineural hearing loss and premature ovarian insufficiency. Additional neuromuscular pathology is observed in some patients. There are six genes in which variants are known to cause Perrault syndrome; however, these explain only a minority of cases. We investigated the genetic cause of Perrault syndrome in seven affected individuals from five different families, successfully identifying the cause in four patients. This included previously reported and novel causative variants in known Perrault syndrome genes, CLPP and LARS2, involved in mitochondrial proteolysis and mitochondrial translation, respectively. For the first time, we show that pathogenic variants in PEX6 can present clinically as Perrault syndrome. PEX6 encodes a peroxisomal biogenesis factor, and we demonstrate evidence of peroxisomal dysfunction in patient serum. This study consolidates the clinical overlap between Perrault syndrome and peroxisomal disorders, and highlights the need to consider ovarian function in individuals with atypical/mild peroxisomal disorders. The remaining patients had variants in candidate genes such as TFAM, involved in mtDNA transcription, replication, and packaging, and GGPS1 involved in mevalonate/coenzyme Q10 biosynthesis and whose enzymatic product is required for mouse folliculogenesis. This genomic study highlights the diverse molecular landscape of this poorly understood syndrome.

32938192 Recessive Inheritance of a Rare Variant in the Nuclear Mitochondrial Gene for AARS2 in Late-Onset Dilated Cardiomyopathy.
Oct 2020 Circulation. Genomic and precision medicine

Nielsen Søren K, Hansen Frederikke, Schrøder Henrik Daa, Wibrand Flemming, Gustafsson Finn, Mogensen Jens.

33209735 A term neonate with early myoclonic encephalopathy caused by RARS2 gene variants: a case report.
Oct 2020 Translational pediatrics

Xu Yan, Wu Bing-Bing, Wang Hui-Jun, Zhou Shui-Zhen, Cheng Guo-Qiang, Zhou Yuan-Feng.

The RARS2 gene encodes mitochondrial arginine-tRNA synthetase. Patients with variants of the RARS2 gene have pontocerebellar hypoplasia type 6 (PCH6), which is characterized by early onset seizures, progressive microcephaly, and developmental delay. PCH6 is a rare mitochondrial encephalopathy. To the best of our knowledge, the onset seizure type which the ictal video-electroencephalogram (VEEG) was compatible with early myoclonic encephalopathy (EME) has not been reported. Here we reported a term female neonate with EME caused by heterozygous variants of the RARS2 gene [NM_020320: exon10: c.773G>A (p. R258H) Maternal, NM_020320: exon4: c.282_285delAGAG Paternal]. Groan was the first symptom manifested, followed by metabolic disorders, and early marked cerebral atrophy. Metabolic disorders were corrected after feeding with extensively hydrolyzed protein formula. Seizures started at the 19th day of life. Interictal VEEG showed a suppression-burst (SB) pattern and ictal VEEG revealed myoclonic seizures that were compatible with early myoclonic encephalopathy (EME). She had frequent myoclonic seizures resistant to multi-antiepileptic drugs including phenobarbital, levetiracetam and oxcarbazepine, and soon developed into convulsive status epilepticus. At 7 months of age, she had severe developmental delay, and developed infantile spasms. Our case report expands the phenotypic spectrum of the PCH6, meanwhile, RARS2 should be considered be a causative gene in patients with EME.

32514400 PARS2-associated mitochondrial disease: A case report of a patient with prolonged survival and literature review.
Sep 2020 Molecular genetics and metabolism reports

A Almuqbil Mohammed, Vernon Hilary J, Ferguson Marcia, Kline Antonie D.

Biallelic pathogenic variants in mitochondrial aminoacyl-tRNA synthetase (mt-aaRS) PARS2 are associated with mitochondrial cytopathy. Here, we report the tenth case of an individual with biallelic PARS2 pathogenic variants, detected by exome sequencing (ES), and a literature review of ten cases of PARS2 mutations. Our patient displayed symptoms and clinical and laboratory findings similar to those reported previously with normal lactate levels. These symptoms included seizure disorder (which was managed with antiepileptics), developmental delay, and progressive cardiomyopathy which manifested at 19 years of age. The patient received a vitamin regimen including antioxidants as part of his treatment regimen. While further studies are required to conclusively establish the beneficial role of vitamin and cofactor administration on the mitochondria in PARS2-associated mitochondrial disease, these factors may have delayed the onset of cardiomyopathy.

32887222 Identification of a Novel Variant in EARS2 Associated with a Severe Clinical Phenotype Expands the Clinical Spectrum of LTBL.
Sep 2020 Genes

Barbosa-Gouveia Sofia, González-Vioque Emiliano, Hermida Álvaro, Suarez María Unceta, Martínez-González María Jesús, Borges Filipa, Wintjes Liesbeth, Kappen Antonia, Rodenburg Richard, Couce María-Luz.

The EARS2 nuclear gene encodes mitochondrial glutamyl-tRNA synthetase, a member of the class I family of aminoacyl-tRNA synthetases (aaRSs) that plays a crucial role in mitochondrial protein biosynthesis by catalyzing the charging of glutamate to mitochondrial tRNA(Glu). Pathogenic EARS2 variants have been associated with a rare mitochondrial disorder known as leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL). The targeted sequencing of 150 nuclear genes encoding respiratory chain complex subunits and proteins implicated in the oxidative phosphorylation (OXPHOS) function was performed. The oxygen consumption rate (OCR), and the extracellular acidification rate (ECAR), were measured. The enzymatic activities of Complexes I-V were analyzed spectrophotometrically. We describe a patient carrying two heterozygous EARS2 variants, c.376C>T (p.Gln126*) and c.670G>A (p.Gly224Ser), with infantile-onset disease and a severe clinical presentation. We demonstrate a clear defect in mitochondrial function in the patient's fibroblasts, suggesting the molecular mechanism underlying the pathogenicity of these EARS2 variants. Experimental validation using patient-derived fibroblasts allowed an accurate characterization of the disease-causing variants, and by comparing our patient's clinical presentation with that of previously reported cases, new clinical and radiological features of LTBL were identified, expanding the clinical spectrum of this disease.

32925487 Leukoencephalopathy With Brain Stem and Spinal Cord Involvement and Lactate Elevation (LBSL): A Case With Long-term Follow-up.
Sep 2020 The neurologist

Yazici Gencdal Isil, Dincer Alp, Obuz Oguzhan, Yapici Zuhal.

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) is caused by a recessive mutation in the DARS2 gene and can be recognized by specific magnetic resonance imaging patterns.

32842620 Novel Mutations in CLPP, LARS2, CDH23, and COL4A5 Identified in Familial Cases of Prelingual Hearing Loss.
Aug 2020 Genes

Zafar Saba, Shahzad Mohsin, Ishaq Rafaqat, Yousaf Ayesha, Shaikh Rehan S, Akram Javed, Ahmed Zubair M, Riazuddin Saima.

We report the underlying genetic causes of prelingual hearing loss (HL) segregating in eight large consanguineous families, ascertained from the Punjab province of Pakistan. Exome sequencing followed by segregation analysis revealed seven potentially pathogenic variants, including four novel alleles c.257G>A, c.6083A>C, c.89A>G, and c.1249A>G of CLPP, CDH23, COL4A5, and LARS2, respectively. We also identified three previously reported HL-causing variants (c.4528C>T, c.35delG, and c.1219T>C) of MYO15A, GJB2, and TMPRSS3 segregating in four families. All identified variants were either absent or had very low frequencies in the control databases. Our in silico analyses and 3-dimensional (3D) molecular modeling support the deleterious impact of these variants on the encoded proteins. Variants identified in MYO15A, GJB2, TMPRSS3, and CDH23 were classified as "pathogenic" or "likely pathogenic", while the variants in CLPP and LARS2 fall in the category of "uncertain significance" based on the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) variant pathogenicity guidelines. This paper highlights the genetic diversity of hearing disorders in the Pakistani population and reports the identification of four novel mutations in four HL families.

32775515 New AARS2 Mutations in Two Siblings With Tremor, Downbeat Nystagmus, and Primary Amenorrhea: A Benign Phenotype Without Leukoencephalopathy.
Aug 2020 Movement disorders clinical practice

De Michele Giovanna, Galatolo Daniele, Lieto Maria, Maione Luigi, Cocozza Sirio, Santorelli Filippo Maria, Filla Alessandro.

32442335 The expanding LARS2 phenotypic spectrum: HLASA, Perrault syndrome with leukodystrophy, and mitochondrial myopathy.
Aug 2020 Human mutation

Riley Lisa G, Rudinger-Thirion Joëlle, Frugier Magali, Wilson Meredith, Luig Melissa, Alahakoon Thushari Indika, Nixon Cheng Yee, Kirk Edwin P, Roscioli Tony, Lunke Sebastian, Stark Zornitza, Wierenga Klaas J, Palle Sirish, Walsh Maie, Higgs Emily, Arbuckle Susan, Thirukeswaran Shalini, Compton Alison G, Thorburn David R, Christodoulou John.

LARS2 variants are associated with Perrault syndrome, characterized by premature ovarian failure and hearing loss, and with an infantile lethal multisystem disorder: Hydrops, lactic acidosis, sideroblastic anemia (HLASA) in one individual. Recently we reported LARS2 deafness with (ovario) leukodystrophy. Here we describe five patients with a range of phenotypes, in whom we identified biallelic LARS2 variants: three patients with a HLASA-like phenotype, an individual with Perrault syndrome whose affected siblings also had leukodystrophy, and an individual with a reversible mitochondrial myopathy, lactic acidosis, and developmental delay. Three HLASA cases from two unrelated families were identified. All were males with genital anomalies. Two survived multisystem disease in the neonatal period; both have developmental delay and hearing loss. A 55-year old male with deafness has not displayed neurological symptoms while his female siblings with Perrault syndrome developed leukodystrophy and died in their 30s. Analysis of muscle from a child with a reversible myopathy showed reduced LARS2 and mitochondrial complex I levels, and an unusual form of degeneration. Analysis of recombinant LARS2 variant proteins showed they had reduced aminoacylation efficiency, with HLASA-associated variants having the most severe effect. A broad phenotypic spectrum should be considered in association with LARS2 variants.

32348839 Clinical and molecular characterization of pediatric mitochondrial disorders in south of China.
Aug 2020 European journal of medical genetics

Hu Chaoping, Li Xihua, Zhao Lei, Shi Yiyun, Zhou Shuizhen, Wu Bingbing, Wang Yi.

Mitochondrial disorders (MDs) are genetic ailments affecting all age groups. Epidemiological data and frequencies of gene mutations in pediatric patients in China are scarce. This retrospective study assessed 101 patients with suspected MDs treated at the Neurology Department of Children's Hospital, Fudan University, in 2011-2017. Mitochondrial (mtDNA) and nuclear (nDNA) samples were assessed by long-range polymerase chain reaction (PCR)-based whole mtDNA sequencing and whole exome sequencing (WES) for identifying pathogenic mutations. Muscle samples underwent various staining protocols and immunofluorescence for detecting selected proteins. Seventeen mutations in the MT-TL1, MT-COX2, MT-ND4, MT, tRNA TRNE, MT-TN, MT-TK, MT-ATP6, MT-ND6, MT-ND3 and MT-CO3 genes were identified in 39 patients, of which m.3243A > G, m.3303C > T, m.8993T > C/G, m.9176T > C, and m.10191T > C were most common. Mitochondrial myopathy and MELAS were most common for m.3243A > G mutation. Four novel mutations were detected, including m.9478insT, m.5666T > C, m.8265T > C, and m.8380-13600 deletion mutations related to Leigh syndrome, mitochondrial myopathy and KSS, respectively. Thirty-three mutations in the TK2, POLG, IBA57, HADHB, FBXL4, ALDH5A1, FOXRED1, TPK1, NDUFAF5, NDUFAF7, NDUFV1, CARS2, PDHA1, and HIBCH genes were identified in 19 patients, including 23 currently unknown. Higher rates of TK2, POLG, IBA57, and HADHB mutations were found in nDNA-mutated MD compared with the remaining individuals. Besides, IBA57 c.286T > C (p.Y96H), TK2 c.497A > T (p.D166V) founder mutations critically contributed to MDs. Comprehensive genomic analysis plays a critical role in pediatric MD diagnosis. These data summarize the relative frequencies of different gene mutations in a large Chinese population, and identified 23 novel MD-associated nDNA and 4 novel mtDNA mutations.

32189241 Hearing impairment-associated KARS mutations lead to defects in aminoacylation of both cytoplasmic and mitochondrial tRNALys.
Aug 2020 Science China. Life sciences

Wang Yong, Zhou Jing-Bo, Zeng Qi-Yu, Wu Siqi, Xue Mei-Qin, Fang Pengfei, Wang En-Duo, Zhou Xiao-Long.

Aminoacyl-tRNA synthetases (aaRSs) are ubiquitously expressed, essential enzymes, synthesizing aminoacyl-tRNAs for protein synthesis. Functional defects of aaRSs frequently cause various human disorders. Human KARS encodes both cytosolic and mitochondrial lysyl-tRNA synthetases (LysRSs). Previously, two mutations (c.1129G>A and c.517T>C) were identified that led to hearing impairment; however, the underlying biochemical mechanism is unclear. In the present study, we found that the two mutations have no impact on the incorporation of LysRS into the multiple-synthetase complex in the cytosol, but affect the cytosolic LysRS level, its tertiary structure, and cytosolic tRNA aminoacylation in vitro. As for mitochondrial translation, the two mutations have little effect on the steady-state level, mitochondrial targeting, and tRNA binding affinity of mitochondrial LysRS. However, they exhibit striking differences in charging mitochondrial tRNALys, with the c.517T>C mutant being completely deficient in vitro and in vivo. We constructed two yeast genetic models, which are powerful tools to test the in vivo aminoacylation activity of KARS mutations at both the cytosolic and mitochondrial levels. Overall, our data provided biochemical insights into the potentially molecular pathological mechanism of KARS c.1129G>A and c.517T>C mutations and provided yeast genetic bases to investigate other KARS mutations in the future.

32597768 Early-onset epileptic encephalopathy with migrating focal seizures associated with a FARS2 homozygous nonsense variant.
Jun 2020 Epileptic disorders : international epilepsy journal with videotape

Ville Dorothée, Lesca Gaetan, Labalme Audrey, Portes Vincent des, Arzimanoglou Alexis, de Bellescize Julitta.

Epilepsy of infancy with migrating focal seizures (EIMFS) is now a well-recognized early-onset syndrome included in the ILAE classification of the epilepsies. KCNT1 gain-of-function variants are identified in about half of patients. In the remaining cases, the underlying genetic component is far more heterogeneous with sporadic mutations occasionally reported in SCN1A, SCN2A, SLC12A5, TBC1D24, PLCB1, SLC25A22, and KCNQ2. Here, we report, for the first time, a homozygous deleterious variant in the FARS2 gene, identified using a 115-gene panel for monogenic epilepsies, in a patient with EIMFS. This boy was the second child born to healthy consanguineous parents. The first seizures occurred at six weeks of age. The patient rapidly developed severe epilepsy with focal discharges on EEG, migrating from one brain region to another, highly suggestive of EIMFS. At five months of age, he had daily multifocal clonic seizures and erratic myoclonic fits, which were not consistently related to spikes or spike-and-wave discharges. Neurological status was severely abnormal from onset and the patient died at 10 months of age from respiratory distress. Using the gene panel, a homozygous missense variant of FARS2 was identified, at Chr6 (GRCh37):g.5404829C>T, c.667C>T (NM_001318872.1), inherited from both parents, leading to an arginine-to-cysteine substitution, p.(Arg223Cys). FARS2 is a member of the mitochondrial aminoacyl tRNA transferase (ARS) enzymes. ARS variants are increasingly recognized causes of early-onset epileptic and neurodevelopmental encephalopathies, however, the associated epileptic phenotype is not completely described. This case shows that FARS2-related seizures can mimic EIMFS in the early stage of the disease. Furthermore, in the setting of migrating focal seizures of infancy, FARS2 should be considered as a further candidate gene, and increased lactate level and occurrence of refractory myoclonic seizures are possible key features to suspect FARS deficiency.

32319008 Mutations in aARS genes revealed by targeted next-generation sequencing in patients with mitochondrial diseases.
May 2020 Molecular biology reports

Felhi Rahma, Charif Majida, Sfaihi Lamia, Mkaouar-Rebai Emna, Desquiret-Dumas Valerie, Kallel Rim, Bris Céline, Goudenège David, Guichet Agnès, Bonneau Dominique, Procaccio Vincent, Reynier Pascal, Amati-Bonneau Patrizia, Hachicha Mongia, Fakhfakh Faiza, Lenaers Guy.

Mitochondrial diseases are a clinically heterogeneous group of multisystemic disorders that arise as a result of various mitochondrial dysfunctions. Autosomal recessive aARS deficiencies represent a rapidly growing group of severe rare inherited mitochondrial diseases, involving multiple organs, and currently without curative option. They might be related to defects of mitochondrial aminoacyl t-RNA synthetases (mtARS) that are ubiquitous enzymes involved in mitochondrial aminoacylation and the translation process. Here, using NGS analysis of 281 nuclear genes encoding mitochondrial proteins, we identified 4 variants in different mtARS in three patients from unrelated Tunisian families, with clinical features of mitochondrial disorders. Two homozygous variants were found in KARS (c.683C>T) and AARS2 (c.1150-4C>G), respectively in two patients, while two heterozygous variants in EARS2 (c.486-7C>G) and DARS2 (c.1456C>T) were concomitantly found in the third patient. Bio-informatics investigations predicted their pathogenicity and deleterious effects on pre-mRNA splicing and on protein stability. Thus, our results suggest that mtARS mutations are common in Tunisian patients with mitochondrial diseases.

32316520 Update Review about Metabolic Myopathies.
Apr 2020 Life (Basel, Switzerland)

Finsterer Josef.

The aim of this review is to summarize and discuss recent findings and new insights in the etiology and phenotype of metabolic myopathies. The review relies on a systematic literature review of recent publications. Metabolic myopathies are a heterogeneous group of disorders characterized by mostly inherited defects of enzymatic pathways involved in muscle cell metabolism. Metabolic myopathies present with either permanent (fixed) or episodic abnormalities, such as weakness, wasting, exercise-intolerance, myalgia, or an increase of muscle breakdown products (creatine-kinase, myoglobin) during exercise. Though limb and respiratory muscles are most frequently affected, facial, extra-ocular, and axial muscles may be occasionally also involved. Age at onset and prognosis vary considerably. There are multiple disease mechanisms and the pathophysiology is complex. Genes most recently related to metabolic myopathy include PGM1, GYG1, RBCK1, VMA21, MTO1, KARS, and ISCA2. The number of metabolic myopathies is steadily increasing. There is limited evidence from the literature that could guide diagnosis and treatment of metabolic myopathies. Treatment is limited to mainly non-invasive or invasive symptomatic measures. In conclusion, the field of metabolic myopathies is evolving with the more widespread availability and application of next generation sequencing technologies worldwide. This will broaden the knowledge about pathophysiology and putative therapeutic strategies for this group of neuromuscular disorders.

31827252 A recurrent missense variant in HARS2 results in variable sensorineural hearing loss in three unrelated families.
Mar 2020 Journal of human genetics

Demain Leigh A M, Gerkes Erica H, Smith Richard J H, Molina-Ramirez Leslie P, O'Keefe Raymond T, Newman William G.

HARS2 encodes mitochondrial histidyl-tRNA synthetase (HARS2), which links histidine to its cognate tRNA in the mitochondrial matrix. Biallelic variants in HARS2 are associated with Perrault syndrome, a rare recessive condition characterized by sensorineural hearing loss in both sexes and primary ovarian insufficiency in 46,XX females. Some individuals with Perrault syndrome have a broader phenotypic spectrum with neurological features, including ataxia and peripheral neuropathy. Here, we report a recurrent variant in HARS2 in association with sensorineural hearing loss. In affected individuals from three unrelated families, the variant HARS2 c.1439G>A p.(Arg480His) is present as a heterozygous variant in trans to a putative pathogenic variant. The low prevalence of the allele HARS2 c.1439G>A p.(Arg480His) in the general population and its presence in three families with hearing loss, confirm the pathogenicity of this variant and illustrate the presentation of Perrault syndrome as nonsyndromic hearing loss in males and prepubertal females.

31449985 Novel HARS2 missense variants identified in individuals with sensorineural hearing impairment and Perrault syndrome.
Mar 2020 European journal of medical genetics

Karstensen Helena Gásdal, Rendtorff Nanna Dahl, Hindbæk Lone Sandbjerg, Colombo Roberto, Stein Amelie, Birkebæk Niels Holtum, Hartmann-Petersen Rasmus, Lindorff-Larsen Kresten, Højland Allan Thomas, Petersen Michael Bjørn, Tranebjærg Lisbeth.

Biallelic variants in HARS2 have been associated with Perrault syndrome, characterized by sensorineural hearing impairment and premature ovarian insufficiency. Here we report three novel families, compound heterozygous for missense variants in HARS2 identified by next-generation sequencing, namely c.172A > G (p.Lys58Glu) and c.448C > T (p.Arg150Cys) identified in two sisters aged 13 and 16 years and their older brother, c.448C > T (p.Arg150Cys) and c.980G > A (p.Arg327Gln) identified in a seven year old girl, and finally c.137T > A (p.Leu46Gln) and c.259C > T (p.Arg87Cys) identified in a 32 year old woman. Clinically, all five individuals presented with early onset, rapidly progressive hearing impairment. Whereas the oldest female fulfilled the criteria of Perrault syndrome, the three younger females, aged 7, 13 and 16, all had apparently normal ovarian function, apart from irregular menstrual periods in the oldest female at age 16. The present report expands the list of HARS2 variants and helps gain further knowledge to the phenotype.

31970218 Mutation of the WARS2 Gene as the Cause of a Severe Hyperkinetic Movement Disorder.
Jan 2020 Movement disorders clinical practice

Hübers Annemarie, Huppertz Hans-Jürgen, Wortmann Saskia B, Kassubek Jan.

32071833 Phenotypes and genotypes of mitochondrial aminoacyl-tRNA synthetase deficiencies from a single neurometabolic clinic.
Jan 2020 JIMD reports

Al Balushi Aaisha, Matviychuk Diana, Jobling Rebekah, Salomons Gajja S, Blaser Susan, Mercimek-Andrews Saadet.

Mitochondrial aminoacyl-tRNA synthetases play a major role in protein translation, synthesis, and oxidative phosphorylation. We reviewed all patients diagnosed with mitochondrial aminoacyl-tRNA synthetase deficiencies diagnosed in a single neurometabolic clinic. We report five patients with mitochondrial aminoacyl-tRNA synthetase deficiencies including DARS2, EARS2, PARS2, and RARS2 deficiencies. Siblings with DARS2 deficiency presented with global developmental delay within the first year of life. DARS2, EARS2, PARS2, and RARS2 deficiencies were identified by whole exome sequencing. We report coagulation factor abnormalities in PARS2 deficiency for the first time. We also report symmetric increased signal intensity in globus pallidi in FLAIR images in brain MRI in EARS2 deficiency for the first time. One patient with RARS2 deficiency had compound heterozygous variants in RARS2. One of those variants was an intronic variant. We confirmed the pathogenicity by mRNA studies. Mitochondrial aminoacyl-tRNA synthetase deficiencies are diagnosed by molecular genetic investigations. Clinically available non-invasive biochemical investigations are non-specific for the diagnosis of mitochondrial aminoacyl-tRNA synthetase deficiencies. A combination of brain MRI features and molecular genetic investigations should be undertaken to confirm the diagnosis of mitochondrial aminoacyl-tRNA synthetase deficiencies.

31486067 Whole-exome sequencing identifies rare pathogenic and candidate variants in sporadic Chinese Han deaf patients.
02 2020 Clinical genetics

Zou Songfeng, Mei Xueshuang, Yang Weiqiang, Zhu Rvfei, Yang Tao, Hu Hongyi.

Genetic causes of hearing loss are highly heterogeneous and often ethnically specific. In recent years, a variety of next-generation sequencing (NGS) panels have been developed to target deafness-causative genes. Whole-exome sequencing (WES), on the other hand, was rarely used for genetic testing for deafness. In this study, we performed WES in 38 sporadic Chinese Han deaf patients who have been pre-excluded for mutations in common deafness genes GJB2, SLC26A4 and MT-RNR1. Non-synonymous variants have been filtered based on their minor allele frequencies in public databases and ethnically matched controls. Bi-allelic pathogenic mutations in eight deafness genes, OTOF, TRIOBP, ESPN, HARS2, CDH23, MYO7A, USH1C and TJP2, were identified in 10 patients, with 17 mutations identified in this study not being associated with deafness previously. For the rest 28 patients, possibly bi-allelic rare non-synonymous variants in an averaged 4.7 genes per patient were identified as candidate pathogenic causes for future analysis. Our study showed that WES may provide a unified platform for genetic testing of deafness and enables retro-analyzing when new causative genes are revealed.

31684799 Expanding the Phenotype: Neurodevelopmental Disorder, Mitochondrial, With Abnormal Movements and Lactic Acidosis, With or Without Seizures (NEMMLAS) Due to WARS2 Biallelic Variants, Encoding Mitochondrial Tryptophanyl-tRNA Synthase.
02 2020 Journal of child neurology

Tarnopolsky Mark, Kozenko Mariya, Jones Kevin.

32120303 Co-occurring WARS2 and CHRNA6 mutations in a child with a severe form of infantile parkinsonism.
03 2020 Parkinsonism & related disorders

Martinelli Simone, Cordeddu Viviana, Galosi Serena, Lanzo Ambra, Palma Eleonora, Pannone Luca, Ciolfi Andrea, Di Nottia Michela, Rizza Teresa, Bocchinfuso Gianfranco, Traversa Alice, Caputo Viviana, Farrotti Andrea, Carducci Claudia, Bernardini Laura, Cogo Susanna, Paglione Maria, Venditti Martina, Bentivoglio Annarita, Ng Joanne, Kurian Manju A, Civiero Laura, Greggio Elisa, Stella Lorenzo, Trettel Flavia, Sciaccaluga Miriam, Roseti Cristina, Carrozzo Rosalba, Fucile Sergio, Limatola Cristina, Di Schiavi Elia, Tartaglia Marco, Leuzzi Vincenzo.

To investigate the molecular cause(s) underlying a severe form of infantile-onset parkinsonism and characterize functionally the identified variants.

32007496 Two types of recessive hereditary spastic paraplegia in Roma patients in compound heterozygous state; no ethnically prevalent variant found.
03 2020 Neuroscience letters

Meszarosova Anna Uhrova, Seeman Pavel, Jencik Jan, Drabova Jana, Cibochova Renata, Stellmachova Julia, Safka Brozkova Dana.

Hereditary spastic paraplegia (HSP or SPG) is a group of rare upper motor neuron diseases. As some ethnically-specific, disease-causing homozygous variants were described in the Czech Roma population, we hypotesised that some prevalent HSP-causing variant could exist in this population. Eight Czech Roma patients were found in a large group of Czech patients with suspected HSP and were tested using gene panel massively parallel sequencing (MPS). Two of the eight were diagnosed with SPG11 and SPG77, respectively. The SPG77 patient manifests a pure HSP phenotype, which is unusual for this SPG type. Both patients are compound heterozygotes for two different variants in the SPG11 (c.1603-1G>A and del ex. 16-18) and FARS2 (c.1082C>T and del ex.1-2) genes respectively; the three variants are novel. In order to find a potential ethnically-specific, disease-causing variant for HSP, we tested the heterozygote frequency of these variants among 130 anonymised DNA samples of Czech Roma individuals without clinical signs of HSP (HPS-negative). A novel deletion of ex.16-18 in the SPG11 gene was found in a heterozygous state in one individual in the HSP-negative group. Haplotype analysis showed that this individual and the patient with SPG11 shared the same haplotype. This supports the assumption that the identified SPG11 deletion could be a founder mutation in the Czech Roma population. In some Roma patients the disease may also be caused by two different biallelic pathogenic mutations.

32048449 Clinical and genetic study of 12 Chinese Han families with nonsyndromic deafness.
04 2020 Molecular genetics & genomic medicine

Wu Di, Huang Weiyuan, Xu Zhenhang, Li Shuo, Zhang Jie, Chen Xiaohua, Tang Yan, Qiu Jinhong, Wang Zhixia, Duan Xuchu, Zhang Luping.

Nonsyndromic hearing loss is clinically and genetically heterogeneous. In this study, we characterized the clinical features of 12 Chinese Han deaf families in which mutations in common deafness genes GJB2, SLC26A4, and MT-RNR1 were excluded.

32020600 Genetic heterogeneity in Leigh syndrome: Highlighting treatable and novel genetic causes.
04 2020 Clinical genetics

Lee Jin Sook, Yoo Taekyeong, Lee Moses, Lee Youngha, Jeon Eunyoung, Kim Soo Yeon, Lim Byung Chan, Kim Ki Joong, Choi Murim, Chae Jong-Hee.

Leigh syndrome (LS), the most common childhood mitochondrial disorder, has characteristic clinical and neuroradiologic features. Mutations in more than 75 genes have been identified in both the mitochondrial and nuclear genome, implicating a high degree of genetic heterogeneity in LS. To profile these genetic signatures and understand the pathophysiology of LS, we recruited 64 patients from 62 families who were clinically diagnosed with LS at Seoul National University Children's Hospital. Mitochondrial genetic analysis followed by whole-exome sequencing was performed on 61 patients. Pathogenic variants in mitochondrial DNA were identified in 18 families and nuclear DNA mutations in 22. The following 17 genes analyzed in 40 families were found to have genetic complexity: MTATP6, MTND1, MTND3, MTND5, MTND6, MTTK, NDUFS1, NDUFV1, NDUFAF6, SURF1, SLC19A3, ECHS1, PNPT1, IARS2, NARS2, VPS13D, and NAXE. Two treatable cases had biotin-thiamine responsive basal ganglia disease, and another three were identified as having defects in the newly recognized genes (VPS13D or NAXE). Variants in the nuclear genes that encoded mitochondrial aminoacyl tRNA synthetases were present in 27.3% of cases. Our findings expand the genetic and clinical spectrum of LS, showing genetic heterogeneity and highlighting treatable cases and those with novel genetic causes.

32423379 LARS2-Perrault syndrome: a new case report and literature review.
05 2020 BMC medical genetics

Carminho-Rodrigues Maria Teresa, Klee Phillipe, Laurent Sacha, Guipponi Michel, Abramowicz Marc, Cao-van Hélène, Guinand Nils, Paoloni-Giacobino Ariane.

Perrault syndrome is a rare recessive and genetically heterogeneous disorder characterized by sensorineural hearing loss in males and females and gonadal dysgenesis in females. Mutations in seven different genes have been identified: HARS2, HSD17B4, CLLP, C10orf, ERAL1, TWNK and LARS2. To date, 19 variants have been reported in 18 individuals with LARS2-Perrault syndrome.

32767731 Perrault syndrome: Clinical report and retrospective analysis.
10 2020 Molecular genetics & genomic medicine

Pan Zhaoyu, Xu Hongen, Tian Yongan, Liu Danhua, Liu Huanfei, Li Ruijun, Dou Qian, Zuo Bin, Zhai Rongqun, Tang Wenxue, Lu Wei.

Perrault syndrome (PRLTS4; OMIM# 615300) is a rare autosomal recessive disorder and only a few cases have been reported worldwide. We report a Chinese female characterized by sensorineural hearing loss and premature ovarian insufficiency.

32774346 FARS2 Mutations: More Than Two Phenotypes? A Case Report.
- 2020 Frontiers in genetics

Hotait Mostafa, Nasreddine Wassim, El-Khoury Riyad, Dirani Maya, Nawfal Omar, Beydoun Ahmad.

FARS2, a nuclear gene, encodes the mitochondrial phenylalanyl-tRNA synthetase (mtPheRS). Previous reports have described two distinct phenotypes linked to FARS2 gene mutation: an early onset epileptic encephalopathy and spastic paraplegia. This report describes a distinctive phenotype of FARS2-linked, juvenile onset refractory epilepsy, caused by a hemizygous mutation in a compound heterozygous state (p.V197M and exon 2 microdeletion). A 17-year- old woman with normal development presented with a super refractory focal motor status epilepticus. Only an emergency life-saving surgery aborted her status after all therapeutic interventions, including anesthesia, failed to control her seizures. Pathological and biochemical activities on muscle biopsy showed mitochondrial proliferation with enhanced isolated activities of complexes II and IV, suggestive of a compensatory mechanism for the bioenergetic deficiency. Postoperatively, the patient started experiencing focal aware motor seizures originating from the contralateral hemisphere after being seizure free for a few months. This report suggests a third phenotypic manifestation of FARS2 gene mutation.

33426504 Mitochondrial translation defects and human disease.
- 2020 Journal of translational genetics and genomics

Webb Bryn D, Diaz George A, Prasun Pankaj.

In eukaryotic cells, mitochondria perform the essential function of producing cellular energy in the form of ATP via the oxidative phosphorylation system. This system is composed of 5 multimeric protein complexes of which 13 protein subunits are encoded by the mitochondrial genome: Complex I (7 subunits), Complex III (1 subunit),Complex IV (3 subunits), and Complex (2 subunits). Effective mitochondrial translation is necessary to produce the protein subunits encoded by the mitochondrial genome (mtDNA). Defects in mitochondrial translation are known to cause a wide variety of clinical disease in humans with high-energy consuming organs generally most prominently affected. Here, we review several classes of disease resulting from defective mitochondrial translation including disorders with mitochondrial tRNA mutations, mitochondrial aminoacyl-tRNA synthetase disorders, mitochondrial rRNA mutations, and mitochondrial ribosomal protein disorders.

31274036 Perrault syndrome with amenorrhea, infertility, Tarlov cyst, and degenerative disc.
Dec 2019 Gynecological endocrinology : the official journal of the International Society of Gynecological Endocrinology

Al-Jaroudi Dania, Enabi Saed, AlThagafi Malak Sameer.

Perrault syndrome is a rare autosomal recessive disorder that affects both males and females. The syndrome causes deafness in males, however females display gonadal dysgenesis along with sensorineural hearing loss. Herein, we present a 27-year-old female patient who is deaf and mute along with primary amenorrhea. Hormonal assays revealed hypergonadotropic hypogonadism and the karyotype was 46 XX. Pelvic ultrasound described a hypoplastic uterus and streak ovaries. MRI of the spine showed degenerative discs and Tarlov cysts. Whole exome sequencing identified a LARS2 mutation and the patient was diagnosed with Perrault syndrome type four (PRLTS4).

31429931 Whole exome and targeted gene sequencing to detect pathogenic recessive variants in early onset cerebellar ataxia.
Dec 2019 Clinical genetics

Shakya Sunil, Kumari Renu, Suroliya Varun, Tyagi Nishu, Joshi Aditi, Garg Ajay, Singh Inder, Kalikavil Puthanveedu Divya, Cherian Ajith, Mukerji Mitali, Srivastava Achal K, Faruq Mohammed.

Over 100 genetically distinct causal known loci for hereditary ataxia phenotype poses a challenge for diagnostic work-up for ataxia patients in a clinically relevant time and precision. In the present study using next-generation sequencing, we have investigated pathogenic variants in early-onset cerebellar ataxia cases using whole exome sequencing in singleton/family-designed and targeted gene-panel sequencing. A total of 98 index patients were clinically and genetically (whole exome sequencing (WES) in 16 patients and targeted gene panel of 41 ataxia causing genes in 82 patients) evaluated. Four families underwent WES in family based design. Overall, we have identified 24 variants comprising 20 pathogenic and four likely-pathogenic both rare/novel, variations in 21 early onset cerebellar ataxia patients. Among the identified variations, SACS (n = 7) and SETX (n = 6) were frequent, while ATM (n = 2), TTPA (n = 2) and other rare loci were observed. We have prioritized novel pathogenic variants in RARS2 and FA2H loci through family based design in two out of four families.

31685661 Contribution of a mitochondrial tyrosyl-tRNA synthetase mutation to the phenotypic expression of the deafness-associated tRNASer(UCN) 7511A>G mutation.
Dec 2019 The Journal of biological chemistry

Fan Wenlu, Zheng Jing, Kong Wanzhong, Cui Limei, Aishanjiang Maerhaba, Yi Qiuzi, Wang Min, Cang Xiaohui, Tang Xiaowen, Chen Ye, Mo Jun Qin, Sondheimer Neal, Ge Wanzhong, Guan Min-Xin.

Nuclear modifier genes have been proposed to modify the phenotypic expression of mitochondrial DNA mutations. Using a targeted exome-sequencing approach, here we found that the p.191Gly>Val mutation in mitochondrial tyrosyl-tRNA synthetase 2 (YARS2) interacts with the tRNASer(UCN) 7511A>G mutation in causing deafness. Strikingly, members of a Chinese family bearing both the YARS2 p.191Gly>Val and m.7511A>G mutations displayed much higher penetrance of deafness than those pedigrees carrying only the m.7511A>G mutation. The m.7511A>G mutation changed the A4:U69 base-pairing to G4:U69 pairing at the aminoacyl acceptor stem of tRNASer(UCN) and perturbed tRNASer(UCN) structure and function, including an increased melting temperature, altered conformation, instability, and aberrant aminoacylation of mutant tRNA. Using lymphoblastoid cell lines derived from symptomatic and asymptomatic members of these Chinese families and control subjects, we show that cell lines harboring only the m.7511A>G or p.191Gly>Val mutation revealed relatively mild defects in tRNASer(UCN) or tRNATyr metabolism, respectively. However, cell lines harboring both m.7511A>G and p.191Gly>Val mutations displayed more severe defective aminoacylations and lower tRNASer(UCN) and tRNATyr levels, aberrant aminoacylation, and lower levels of other tRNAs, including tRNAThr, tRNALys, tRNALeu(UUR), and tRNASer(AGY), than those in the cell lines carrying only the m.7511A>G or p.191Gly>Val mutation. Furthermore, mutant cell lines harboring both m.7511A>G and p.191Gly>Val mutations exhibited greater decreases in the levels of mitochondrial translation, respiration, and mitochondrial ATP and membrane potentials, along with increased production of reactive oxygen species. Our findings provide molecular-level insights into the pathophysiology of maternally transmitted deafness arising from the synergy between tRNASer(UCN) and mitochondrial YARS mutations.

31839000 Mitochondrial aminoacyl-tRNA synthetase disorders: an emerging group of developmental disorders of myelination.
Dec 2019 Journal of neurodevelopmental disorders

Fine Amena Smith, Nemeth Christina L, Kaufman Miriam L, Fatemi Ali.

The mitochondrial aminoacyl-tRNA synthetase proteins (mt-aaRSs) are a group of nuclear-encoded enzymes that facilitate conjugation of each of the 20 amino acids to its cognate tRNA molecule. Mitochondrial diseases are a large, clinically heterogeneous group of disorders with diverse etiologies, ages of onset, and involved organ systems. Diseases related to mt-aaRS mutations are associated with specific syndromes that affect the central nervous system and produce highly characteristic MRI patterns, prototypically the DARS2, EARS, and AARS2 leukodystrophies, which are caused by mutations in mitochondrial aspartyl-tRNA synthetase, mitochondria glutamate tRNA synthetase, and mitochondrial alanyl-tRNA synthetase, respectively. BODY: The disease patterns emerging for these leukodystrophies are distinct in terms of the age of onset, nature of disease progression, and predominance of involved white matter tracts. In DARS2 and EARS2 disorders, earlier disease onset is typically correlated with more significant brain abnormalities, rapid neurological decline, and greater disability. In AARS2 leukodystrophy cases reported thus far, there is nearly invariable progression to severe disability and atrophy of involved brain regions, often within a decade. Although most mutations are compound heterozygous inherited in an autosomal recessive fashion, homozygous variants are found in each disorder and demonstrate high phenotypic variability. Affected siblings manifest disease on a wide spectrum.

31887305 Neuronal ablation of mt-AspRS in mice induces immune pathway activation prior to severe and progressive cortical and behavioral disruption.
Dec 2019 Experimental neurology

Nemeth Christina L, Tomlinson Sophia N, Rosen Melissa, O'Brien Brett M, Larraza Oscar, Jain Mahim, Murray Connor F, Marx Joel S, Delannoy Michael, Fine Amena S, Wu Dan, Trifunovic Aleksandra, Fatemi Ali.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a rare, slowly progressive white matter disease caused by mutations in the mitochondrial aspartyl-tRNA synthetase (mt-AspRS, or DARS2). While patients show characteristic MRI T2 signal abnormalities throughout the cerebral white matter, brainstem, and spinal cord, the phenotypic spectrum is broad and a multitude of gene variants have been associated with the disease. Here, Dars2 disruption in CamKIIα-expressing cortical and hippocampal neurons results in slowly progressive increases in behavioral activity at five months, and culminating by nine months as severe brain atrophy, behavioral dysfunction, reduced corpus callosum thickness, and microglial morphology indicative of neuroinflammation. Interestingly, RNAseq based gene expression studies performed prior to the presentation of this severe phenotype reveal the upregulation of several pathways involved in immune activation, cytokine production and signaling, and defense response regulation. RNA transcript analysis demonstrates that activation of immune and cell stress pathways are initiated in advance of a behavioral phenotype and cerebral deficits. An understanding of these pathways and their contribution to significant neuronal loss in CamKII-Dars2 deficient mice may aid in deciphering mechanisms of LBSL pathology.

31529142 A combination of two novel VARS2 variants causes a mitochondrial disorder associated with failure to thrive and pulmonary hypertension.
Nov 2019 Journal of molecular medicine (Berlin, Germany)

Chin Hui-Lin, Goh Denise Li-Meng, Wang Furene Sijia, Tay Stacey Kiat Hong, Heng Chew Kiat, Donnini Claudia, Baruffini Enrico, Pines Ophry.

The VARS2 gene encodes a mitochondrial valyl-transfer RNA synthetase which is used in mitochondrial translation. To date, several patients with VARS2 pathogenic variants have been described in the literature. These patients have features of lactic acidosis with encephalomyopathy. We present a case of an infant with lactic acidosis, failure to thrive, and severe primary pulmonary hypertension who was found to be a compound heterozygote for two novel VARS2 variants (c.1940C>T, p.(Thr647Met) and c.2318G>A, p.(Arg773Gln)). The patient was treated with vitamin supplements and a carbohydrate-restricted diet. The lactic acidosis and failure to thrive resolved, and he showed good growth and development. Functional studies and molecular analysis employed a yeast model system and the VAS1 gene (yeast homolog of VARS2). VAS1 genes harboring either one of two mutations corresponding to the two novel variants in the VARS2 gene, exhibited partially reduced function in haploid yeast strains. A combination of both VAS1 variant alleles in a diploid yeast cell exhibited a more significant decrease in oxidative metabolism-dependent growth and in the oxygen consumption rate (reminiscent of the patient who carries two mutant VARS2 alleles). Our results demonstrate the pathogenicity of the biallellic novel VARS2 variants. KEY MESSAGES: • A case of an infant who is a compound heterozygote for two novel VARS2 variants. • This infant displayed lactic acidosis, failure to thrive, and pulmonary hypertension. • Treatment of the patient with a carbohydrate-restricted diet resulted in good growth and development. • Studies with the homologous yeast VAS1 gene showed reduced function of corresponding single mutant in haploid yeast strains. • A combination of both VAS1 variant alleles in diploid yeast exhibited a more significant decrease in function, thereby confirming the pathogenicity of the biallellic novel VARS2 variants.

31520968 Broad spectrum of clinical presentation in EARS2 beyond typical "leukoencephalopathy with thalamus and brain stem involvement".
Nov 2019 Journal of the neurological sciences

Prasun Pankaj, Mintz Cassie, Cork Emalyn, Naidich Thomas P, Webb Bryn D.

31451716 Identification of extremely rare mitochondrial disorders by whole exome sequencing.
Nov 2019 Journal of human genetics

Seo Go Hun, Oh Arum, Kim Eun Na, Lee Yeonmi, Park Jumi, Kim Taeho, Lim Young-Min, Kim Gu-Hwan, Kim Chong Jai, Yoo Han-Wook, Kang Eunju, Lee Beom Hee.

Whole exome sequencing (WES) is an effective tool for the genetic diagnosis of mitochondrial disorders due to various nuclear genetic defects. In this study, three patients affected by extremely rare mitochondrial disorders caused by nuclear genetic defects are described. The medical records of each patient were reviewed to obtain clinical symptoms, results of biochemical and imaging studies, and muscle biopsies. WES and massive parallel sequencing of whole mtDNA were performed for each patient. The oxygen consumption rate (OCR) and complex activity I and IV was measured. Patients 1 and 2 had exhibited global developmental delay and seizure since early infancy. Blood lactate, the lactate-to-pyruvate ratio, and urinary excretion of Krebs cycle intermediates were markedly elevated. Patient 1 also was noted for ophthalmoplegia. Patient 2 had left ventricular hypertrophy and ataxia. Patient 3 developed dysarthria, gait disturbance, and right-side weakness at age 29. Brain magnetic resonance imaging demonstrated abnormal signal intensity involving the bilateral thalami, midbrain, or pons. Based on WES, patient 1 had p.Glu415Gly and p.Arg484Trp variants in MTO1. In patient 2, p.Gln111ThrfsTer5 and RNA mis-splicing were identified in TSFM. Patient 3 carried p.Met151Thr and p.Met246Lys variants in AARS2. Skin fibroblasts of three patients exhibited decreased OCRs and complex 1 activity, and mitochondrial DNA was normal. These results demonstrate the utility of WES for identifying the genetic cause of extremely rare mitochondrial disorders, which has implications for genetic counseling.

31329004 A patient with juvenile-onset refractory status epilepticus caused by two novel compound heterozygous mutations in FARS2 gene.
Nov 2019 The International journal of neuroscience

Chen Zhongyun, Zhang Yan.

FARS2 encodes mitochondrial phenylalanyl transfer ribonucleic acid (RNA) synthetase and is implicated in autosomal recessive combined oxidative phosphorylation deficiency 14. The clinical manifestation can be divided into early onset epileptic phenotype and spastic paraplegia phenotype. The purpose of this study was to report a case of juvenile manifesting refractory epilepsy caused by two novel compound heterozygous mutations in the FARS2 gene. Microscopic and histochemical examination as well as next-generation sequencing and reconstruction of the three-dimensional structure of FARS2 protein were performed. A 17-year-old man with no developmental delays suffered from generalized tonic-clonic convulsion since 12 years of age and developed refractory status epilepticus 5 years later. No specific etiology was found following brain imaging, muscle biopsy and metabolic studies. DNA sequencing identified two novel compound heterozygous mutations in FARS2, (p.V197M and p.F402S), derived from each parents, respectively. These mutations affected the structure or thermodynamic stability of the protein. This is a case report of juvenile-onset refractory epilepsy caused by two novel compound heterozygous mutations in the FARS2 gene. This case confirms and expands the clinicalphenotype and the genotypic spectrum of the FARS2 gene.

31623496 A novel VARS2 gene variant in a patient with epileptic encephalopathy.
Nov 2019 Upsala journal of medical sciences

Ruzman Lucija, Kolic Ivana, Radic Nisevic Jelena, Ruzic Barsic Antonija, Skarpa Prpic Ingrid, Prpic Igor.

Background: Mitochondrial disorders are heterogeneous clinical syndromes caused by defective activity in the mitochondrial respiratory chain, resulting in a faulty oxidative phosphorylation system. These inherited disorders are individually rare, and furthermore they are phenotypic variables. The genetically characterized mitochondrial disorders are rarely associated with epileptic encephalopathies.Case presentation: We present the clinical phenotype, biochemical analysis, and electrographic and neuro-radiological features of a 5-month-old girl with epileptic encephalopathy, microcephaly, severe psychomotor delay, hypertrophic cardiomyopathy, and abnormal MRI scan. Using whole-genome sequencing technique, compound heterozygous mutations of the VARS2 gene were revealed, with one previously unreported frameshift mutation.Conclusion: Our report extends the phenotypic spectrum of VARS2-related disorders with an initial presentation of epileptic encephalopathy and early death due to malignant arrhythmia.

31680123 The genomic and clinical landscape of fetal akinesia.
Nov 2019 Genetics in medicine : official journal of the American College of Medical Genetics

Pergande Matthias, Motameny Susanne, Özdemir Özkan, Kreutzer Mona, Wang Haicui, Daimagüler Hülya-Sevcan, Becker Kerstin, Karakaya Mert, Ehrhardt Harald, Elcioglu Nursel, Ostojic Slavica, Chao Cho-Ming, Kawalia Amit, Duman Özgür, Koy Anne, Hahn Andreas, Reimann Jens, Schoner Katharina, Schänzer Anne, Westhoff Jens H, Schwaibold Eva Maria Christina, Cossee Mireille, Imbert-Bouteille Marion, von Pein Harald, Haliloglu Göknur, Topaloglu Haluk, Altmüller Janine, Nürnberg Peter, Thiele Holger, Heller Raoul, Cirak Sebahattin.

Fetal akinesia has multiple clinical subtypes with over 160 gene associations, but the genetic etiology is not yet completely understood.

31705293 Alanyl-tRNA Synthetase 2 (AARS2)-Related Ataxia Without Leukoencephalopathy.
Nov 2019 Cerebellum (London, England)

Kuo Molly E, Antonellis Anthony, Shakkottai Vikram G.

Mutations in the mitochondrial alanyl-tRNA synthetase gene, AARS2, have been reported to cause leukoencephalopathy associated with early ovarian failure, a clinical presentation described as "ovarioleukodystrophy." We present a sibling pair: one with cerebellar ataxia and one with vision loss and cognitive impairment in addition to ataxia. Neither shows evidence of leukoencephalopathy on MRI imaging. Exome sequencing revealed that both siblings are compound heterozygous for AARS2 variants (p.Phe131del and p.Ile328Met). Yeast complementation assays indicate that p.Phe131del AARS2 dramatically impairs gene function and that p.Ile328Met AARS2 is a hypomorphic allele. This work expands the phenotypic spectrum of AARS2-associated disease to include ataxia without leukoencephalopathy.

31388113 A novel compound heterozygous mutation in AARS2 gene (c.965?G?>?A, p.R322H; c.334?G?>?C, p.G112R) identified in a Chinese patient with leukodystrophy involved in brain and spinal cord.
Oct 2019 Journal of human genetics

Song Chengyuan, Peng Linliu, Wang Shengjun, Liu Yiming.

Leukodystrophies are genetic disorders leading to progressive white matter degeneration in the central nervous system. Mitochondrial aminoacyl tRNA synthase protein is encoded by the nuclear gene AARS2. An autosomal recessive mutation in this gene has been linked to AARS2 mutation-related adult-onset leukodystrophy (AARS2-L) or infantile mitochondrial cardiomyopathy. To date, only 16 AARS2-L cases have been reported in English literature. Thus, the clinical and genetic characteristics of this disease remain to be defined. Through whole-exome sequencing, we identified a Chinese patient with leukodystrophy related to two novel compounds heterozygous mutation in AARS2 (c.965 G > A, p.R322H; c.334 G > C, p.G112R). These two compounds heterozygous variants in AARS2 gene co-segregated with disease in his family. And pyramidal tracts in the spinal cord were involved. Our findings have important implications on genetic counseling for any case with leukodystrophy and extend the mutational spectrum in AARS2 gene.

30925032 The combination of whole-exome sequencing and clinical analysis allows better diagnosis of rare syndromic retinal dystrophies.
Sep 2019 Acta ophthalmologica

Abu Diab Alaa, AlTalbishi Ala'a, Rosin Boris, Kanaan Moien, Kamal Lara, Swaroop Anand, Chowers Itay, Banin Eyal, Sharon Dror, Khateb Samer.

To identify the accurate clinical diagnosis of rare syndromic inherited retinal diseases (IRDs) based on the combination of clinical and genetic analyses.

31106652 FARS2 Causing Complex Hereditary Spastic Paraplegia With Dysphonia: Expanding the Disease Spectrum.
Sep 2019 Journal of child neurology

Forman Eva B, Gorman Kathleen M, Ennis Sean, King Mary D.

Herein we present two siblings with hereditary spastic paraplegia caused by novel compound heterozygous variant and deletion in FARS2 and expansion of the disease spectrum to include dysphonia.

31536827 A patient with pontocerebellar hypoplasia type 6: Novel RARS2 mutations, comparison to previously published patients and clinical distinction from PEHO syndrome.
Sep 2019 European journal of medical genetics

Nevanlinna Viivi, Konovalova Svetlana, Ceulemans Berten, Muona Mikko, Laari Anni, Hilander Taru, Gorski Katarin, Valanne Leena, Anttonen Anna-Kaisa, Tyynismaa Henna, Courage Carolina, Lehesjoki Anna-Elina.

Pontocerebellar hypoplasia type 6 (PCH6) is a rare infantile-onset progressive encephalopathy caused by biallelic mutations in RARS2 that encodes the mitochondrial arginine-tRNA synthetase enzyme (mtArgRS). The clinical presentation overlaps that of PEHO syndrome (Progressive Encephalopathy with edema, Hypsarrhythmia and Optic atrophy). The proband presented with severe intellectual disability, epilepsy with varying seizure types, optic atrophy, axial hypotonia, acquired microcephaly, dysmorphic features and progressive cerebral and cerebellar atrophy and delayed myelination on MRI. The presentation had resemblance to PEHO syndrome but sequencing of ZNHIT3 did not identify pathogenic variants. Subsequent whole genome sequencing revealed novel compound heterozygous variants in RARS2, a missense variant affecting a highly conserved amino acid and a frameshift variant with consequent degradation of the transcript resulting in decreased mtArgRS protein level confirming the diagnosis of PCH6. Features distinguishing the proband's phenotype from PEHO syndrome were later appearance of hypotonia and elevated lactate levels in blood and cerebrospinal fluid. On MRI the proband presented with more severe supratentorial atrophy and lesser degree of abnormal myelination than PEHO syndrome patients. The study highlights the challenges in clinical diagnosis of patients with neonatal and early infantile encephalopathies with overlapping clinical features and brain MRI findings.

31280959 Novel alanyl-tRNA synthetase 2 (AARS2) homozygous mutation in a consanguineous Chinese family with premature ovarian insufficiency.
Jul 2019 Fertility and sterility

Zhou Yiran, Chen Beili, Li Lin, Pan Hong, Liu Beihong, Li Tengyan, Wang Ruyi, Ma Xu, Wang Binbin, Cao Yunxia.

To explore the candidate pathogenic gene in a premature ovarian insufficiency (POI) proband from a consanguineous marriage and detect the potential effects of mutation on cellular energy metabolism.

30920170 Mutations in the mitochondrial tryptophanyl-tRNA synthetase cause growth retardation and progressive leukoencephalopathy.
Jun 2019 Molecular genetics & genomic medicine

Maffezzini Camilla, Laine Isabelle, Dallabona Cristina, Clemente Paula, Calvo-Garrido Javier, Wibom Rolf, Naess Karin, Barbaro Michela, Falk Anna, Donnini Claudia, Freyer Christoph, Wredenberg Anna, Wedell Anna.

Mutations in mitochondrial aminoacyl tRNA synthetases form a subgroup of mitochondrial disorders often only perturbing brain function by affecting mitochondrial translation. Here we report two siblings with mitochondrial disease, due to compound heterozygous mutations in the mitochondrial tryptophanyl-tRNA synthetase (WARS2) gene, presenting with severe neurological symptoms but normal mitochondrial function in skeletal muscle biopsies and cultured skin fibroblasts.

31241862 Biophysical characterization of Alpers encephalopathy associated mutants of human mitochondrial phenylalanyl-tRNA synthetase.
Jun 2019 IUBMB life

Chakraborty Shruti, Ibba Michael, Banerjee Rajat.

Mutations in nucleus-encoded mitochondrial aminoacyl-tRNA synthetases (mitaaRSs) lead to defects in mitochondrial translation affecting the expression and function of 13 subunits of the respiratory chain complex leading to diverse pathological conditions. Mutations in the FARS2 gene encoding human mitochondrial phenylalanyl-tRNA synthetase (HsmitPheRS) have been found to be associated with two different clinical representations, infantile Alpers encephalopathy and spastic paraplegia. Here we have studied three pathogenic mutants (Tyr144Cys, Ile329Thr, and Asp391Val) associated with Alpers encephalopathy to understand how these variants affect the biophysical properties of the enzyme. These mutants have already been reported to have reduced aminoacylation activity. Our study established that the mutants are significantly more thermolabile compared to the wild-type enzyme with reduced solubility in vitro. The presence of aggregation-prone insoluble HsmitPheRS variants could have a detrimental impact on organellar translation, and potentially impact normal mitochondrial function.

31064326 VARS2-linked mitochondrial encephalopathy: two case reports enlarging the clinical phenotype.
May 2019 BMC medical genetics

Begliuomini Chiara, Magli Giorgio, Di Rocco Maja, Santorelli Filippo M, Cassandrini Denise, Nesti Claudia, Deodato Federica, Diodato Daria, Casellato Susanna, Simula Delia M, Dessì Veronica, Eusebi Anna, Carta Alessandra, Sotgiu Stefano.

Mitochondrial respiratory chain consists of five complexes encoded by nuclear and mitochondrial genomes. Mitochondrial aminoacyl-tRNA synthetases are key enzymes in the synthesis of such complexes. Bi-allelic variants of VARS2, a nuclear gene encoding for valyl-tRNA (Val-tRNA) synthetase, are associated to several forms of mitochondrial encephalopathies or cardiomyoencephalopathies. Among these, the rare homozygous c.1100C > T (p.Thr367Ile) mutation variably presents with progressive developmental delay, axial hypotonia, limbs spasticity, drug-resistant epilepsy leading, in some cases, to premature death. Yet only six cases, of which three are siblings, harbouring this homozygous mutation have been described worldwide.

31099476 Expansion of the clinical spectrum associated with AARS2-related disorders.
May 2019 American journal of medical genetics. Part A

Srivastava Siddharth, Butala Ankur, Mahida Sonal, Richter John, Mu Weiyi, Poretti Andrea, Vernon Hilary, VanGerpen Jay, Atwal Paldeep S, Middlebrooks Erik H, Zee David S, Naidu SakkuBai.

Biallelic pathogenic variants in AARS2, a gene encoding the mitochondrial alanyl-tRNA synthetase, result in a spectrum of findings ranging from infantile cardiomyopathy to adult-onset progressive leukoencephalopathy. In this article, we present three unrelated individuals with novel compound heterozygous pathogenic AARS2 variants underlying diverse clinical presentations. Patient 1 is a 51-year-old man with adult-onset progressive cognitive, psychiatric, and motor decline and leukodystrophy. Patient 2 is a 34-year-old man with childhood-onset progressive tremor followed by the development of polyneuropathy, ataxia, and mild cognitive and psychiatric decline without leukodystrophy on imaging. Patient 3 is a 57-year-old woman with childhood-onset tremor and nystagmus which preceded dystonia, chorea, ataxia, depression, and cognitive decline marked by cerebellar atrophy and white matter disease. These cases expand the clinical heterogeneity of AARS2-related disorders, given that the first and third case represent some of the oldest known survivors of this disease, the second is adult-onset AARS2-related neurological decline without leukodystrophy, and the third is biallelic AARS2-related disorder involving a partial gene deletion.

31106991 A homozygous mutation of alanyl-transfer RNA synthetase 2 in a patient of adult-onset leukodystrophy: A case report and literature review.
May 2019 Brain and behavior

Wang Jian-Yong, Chen Song-Fang, Zhang Hong-Qiu, Wang Meng-Yan, Zhu Jian-Hong, Zhang Xiong.

Leukodystrophy is a group of hereditary leukoencephalopathies predominantly affecting the white matter. Multiple genes and mutations have been reported to be associated with this disorder. Identification of pathogenic genes can facilitate diagnosis of leukodystrophy and development of therapeutic strategies.

31116475 Mutations in KARS cause a severe neurological and neurosensory disease with optic neuropathy.
May 2019 Human mutation

Scheidecker Sophie, Bär Séverine, Stoetzel Corinne, Geoffroy Véronique, Lannes Béatrice, Rinaldi Bruno, Fischer Frédéric, Becker Hubert D, Pelletier Valérie, Pagan Cécile, Acquaviva-Bourdain Cécile, Kremer Stéphane, Mirande Marc, Tranchant Christine, Muller Jean, Friant Sylvie, Dollfus Hélène.

Mutations in genes encoding aminoacyl-tRNA synthetases have been reported in several neurological disorders. KARS is a dual localized lysyl-tRNA synthetase and its cytosolic isoform belongs to the multiple aminoacyl-tRNA synthetase complex (MSC). Biallelic mutations in the KARS gene were described in a wide phenotypic spectrum ranging from nonsyndromic deafness to complex impairments. Here, we report on a patient with severe neurological and neurosensory disease investigated by whole-exome sequencing and found to carry biallelic mutations c.683C>T (p.Pro228Leu) and c.871T>G (p.Phe291Val), the second one being novel, in the KARS gene. The patient presented with an atypical clinical presentation with an optic neuropathy not previously reported. At the cellular level, we show that cytoplasmic KARS was expressed at a lower level in patient cells and displayed decreased interaction with MSC. In vitro, these two KARS variants have a decreased aminoacylation activity compared with wild-type KARS, the p.Pro228Leu being the most affected. Our data suggest that dysfunction of cytoplasmic KARS resulted in a decreased level of translation of the nuclear-encoded lysine-rich proteins belonging to the respiratory chain complex, thus impairing mitochondria functions.

31192300 Loss-of-function mutations in Lysyl-tRNA synthetase cause various leukoencephalopathy phenotypes.
Apr 2019 Neurology. Genetics

Sun Chong, Song Jie, Jiang Yanjun, Zhao Chongbo, Lu Jiahong, Li Yuxin, Wang Yin, Gao Mingshi, Xi Jianying, Luo Sushan, Li Meixia, Donaldson Kevin, Oprescu Stephanie N, Slavin Thomas P, Lee Sansan, Magoulas Pilar L, Lewis Andrea M, Emrick Lisa, Lalani Seema R, Niu Zhiyv, Landsverk Megan L, Walkiewicz Magdalena, Person Richard E, Mei Hui, Rosenfeld Jill A, Yang Yaping, Antonellis Anthony, Hou Ya-Ming, Lin Jie, Zhang Victor W.

To expand the clinical spectrum of lysyl-tRNA synthetase (KARS) gene-related diseases, which so far includes Charcot-Marie-Tooth disease, congenital visual impairment and microcephaly, and nonsyndromic hearing impairment.

30709774 The nuclear background influences the penetrance of the near-homoplasmic m.1630 A?>?G MELAS variant in a symptomatic proband and asymptomatic mother.
Apr 2019 Molecular genetics and metabolism

Uittenbogaard Martine, Wang Hao, Zhang Victor Wei, Wong Lee-Jun, Brantner Christine A, Gropman Andrea, Chiaramello Anne.

In this study, we report the metabolic consequences of the m.1630 A > G variant in fibroblasts from the symptomatic proband affected with the mitochondrial encephalomyopathy lactic acidosis and stroke-like episode Syndrome and her asymptomatic mother. By long-range PCR followed by massively parallel sequencing of the mitochondrial genome, we accurately measured heteroplasmy in fibroblasts from the proband (89.6%) and her mother (94.8%). Using complementary experimental approaches, we show a functional correlation between manifestation of clinical symptoms and bioenergetic potential. Our mitochondrial morphometric analysis reveals a link between defects of mitochondrial cristae ultrastructure and symptomatic status. Despite near-homoplasmic level of the m.1630A > G variant, the mother's fibroblasts have a normal OXPHOS metabolism, which stands in contrast to the severely impaired OXPHOS response of the proband's fibroblasts. The proband's fibroblasts also exhibit glycolysis at near constitutive levels resulting in a stunted compensatory glycolytic response to offset the severe OXPHOS defect. Whole exome sequencing reveals the presence of a heterozygous nonsense VARS2 variant (p.R334X) exclusively in the proband, which removes two thirds of the VARS2 protein containing key domains interacting with the mt-tRNAval and may play a role in modulating the penetrance of the m.1630A > G variant despite similar near homoplasmic levels. Our transmission electron microscopy study also shows unexpected ultrastructural changes of chromatin suggestive of differential epigenomic regulation between the proband and her mother that may explain the differential OXPHOS response between the proband and her mother. Future study will decipher by which molecular mechanisms the nuclear background influences the penetrance of the m.1630 A > G variant causing MELAS.

31687268 Recent advances in the genetics of frontotemporal dementia.
Mar 2019 Current genetic medicine reports

Sirkis Daniel W, Geier Ethan G, Bonham Luke W, Karch Celeste M, Yokoyama Jennifer S.

In this review we highlight recent advances in the human genetics of frontotemporal dementia (FTD). In addition to providing a broad survey of genes implicated in FTD in the last several years, we also discuss variation in genes implicated in both hereditary leukodystrophies and risk for FTD (e.g., TREM2, TMEM106B, CSF1R, AARS2, NOTCH3).

30737337 Biallelic variants in LARS2 and KARS cause deafness and (ovario)leukodystrophy.
Feb 2019 Neurology

van der Knaap Marjo S, Bugiani Marianna, Mendes Marisa I, Riley Lisa G, Smith Desiree E C, Rudinger-Thirion Joëlle, Frugier Magali, Breur Marjolein, Crawford Joanna, van Gaalen Judith, Schouten Meyke, Willems Marjolaine, Waisfisz Quinten, Mau-Them Frederic Tran, Rodenburg Richard J, Taft Ryan J, Keren Boris, Christodoulou John, Depienne Christel, Simons Cas, Salomons Gajja S, Mochel Fanny.

To describe the leukodystrophy caused by pathogenic variants in LARS2 and KARS, encoding mitochondrial leucyl transfer RNA (tRNA) synthase and mitochondrial and cytoplasmic lysyl tRNA synthase, respectively.

30799306 tRNAs and Aminoacyl-tRNA Synthetases in Human Disease: an introduction to the JBC Reviews thematic series.
Feb 2019 The Journal of biological chemistry

Musier-Forsyth Karin.

Aminoacyl-tRNA synthetases (ARSs) catalyze the attachment of specific amino acids to cognate tRNAs for use in protein synthesis. This historical function of ARSs and tRNAs is fairly well understood. However, ARSs and tRNAs also perform non-canonical functions that are continuing to be unveiled at a rapid pace. The expanded functions of these essential molecules of life range from roles in retroviral replication to stimulation of mTOR activity; DNA repair, splicing, transcriptional and translational regulation; and other aspects of cellular homeostasis. Furthermore, mutations in tRNAs and synthetases are known to drive human maladies, such as the neurodegenerative disorder Charcot-Marie-Tooth (CMT) disease along with other central nervous system dysfunctions, and cancer. This series of reviews focuses on the diseases that result from natural variations in human cytoplasmic tRNAs, as well as from mutations in mitochondrial tRNAs and ARSs. Ultimately, the exciting work in this rapidly emerging area may lead to new therapies for microbial and parasitic infections, cancer, and neurodegenerative diseases.

30389111 Genotype/Phenotype Issues of CARS2 Variants.
Feb 2019 Pediatric neurology

Finsterer Josef.

30098844 Avoid valproate in patients with IARS2 mutations.
Jan 2019 Brain & development

Finsterer Josef, Zarrouk-Mahjoub Sinda.

30253902 Reply to: Avoid valproate in patients with IARS2 mutations.
Jan 2019 Brain & development

Takezawa Yusuke, Fujie Hiromi, Kikuchi Atsuo, Kure Shigeo.

30635318 Leucoencephalopathy with brain stem and spinal cord involvement and lactate elevation: a novel mutation in the DARS2 gene.
Jan 2019 BMJ case reports

Yelam Anudeep, Nagarajan Elanagan, Chuquilin Miguel, Govindarajan Raghav.

Leucoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a very rare autosomal recessive, slowly progressive neurological disorder characterised by distinctive clinical findings including cerebellar, pyramidal and dorsal column dysfunction. This is caused by a mutation in the DARS2 gene, which encodes mitochondrial aspartyl-tRNA synthetase. MRI shows distinctive abnormalities in the cerebral white matter and specific brain stem and spinal cord tracts. Here, we present a case of LBSL, with a novel c.1192-2A>G mutation.

30642647 Cardiomyopathy in children with mitochondrial disease: Prognosis and genetic background.
Jan 2019 International journal of cardiology

Imai-Okazaki Atsuko, Kishita Yoshihito, Kohda Masakazu, Mizuno Yosuke, Fushimi Takuya, Matsunaga Ayako, Yatsuka Yukiko, Hirata Tomoko, Harashima Hiroko, Takeda Atsuhito, Nakaya Akihiro, Sakata Yasushi, Kogaki Shigetoyo, Ohtake Akira, Murayama Kei, Okazaki Yasushi.

Cardiomyopathy is a reported indicator of poor prognosis in children with mitochondrial disease. However, the association between prognosis and the genetic background of cardiomyopathy in children with mitochondrial disease has yet to be fully elucidated.

30647134 When a common biological role does not imply common disease outcomes: Disparate pathology linked to human mitochondrial aminoacyl-tRNA synthetases.
Jan 2019 The Journal of biological chemistry

González-Serrano Ligia Elena, Chihade Joseph W, Sissler Marie.

Mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) are essential components of the mitochondrial translation machinery. The correlation of mitochondrial disorders with mutations in these enzymes has raised the interest of the scientific community over the past several years. Most surprising has been the wide-ranging presentation of clinical manifestations in patients with mt-aaRS mutations, despite the enzymes' common biochemical role. Even among cases where a common physiological system is affected, phenotypes, severity, and age of onset varies depending on which mt-aaRS is mutated. Here we review work done thus far and propose a categorization of diseases based on tissue specificity that highlights emerging patterns. We further discuss multiple in vitro and in cellulo efforts to characterize the behavior of wildtype and mutant mt-aaRSs that have shaped hypotheses about the molecular causes of these pathologies. Much remains to do in order to complete our understanding of these proteins. We expect that futher work is likely to result in the discovery of new roles for the mt-aaRSs in addition to their fundamental function in mitochondrial translation, informing the development of treatment strategies and diagnoses.

30715177 Biallelic KARS pathogenic variants cause an early-onset progressive leukodystrophy.
03 2019 Brain : a journal of neurology

Itoh Masayuki, Dai Hongmei, Horike Shin-Ichi, Gonzalez John, Kitami Yoshikazu, Meguro-Horike Makiko, Kuki Ichiro, Shimakawa Shuichi, Yoshinaga Harumi, Ota Yoko, Okazaki Tetsuya, Maegaki Yoshihiro, Nabatame Shin, Okazaki Shin, Kawawaki Hisashi, Ueno Naoto, Goto Yu-Ichi, Kato Yoichi.

The leukodystrophies cause severe neurodevelopmental defects from birth and follow an incurable and progressive course that often leads to premature death. It has recently been reported that abnormalities in aminoacyl t-RNA synthetase (ARS) genes are linked to various unique leukodystrophies and leukoencephalopathies. Aminoacyl t-RNA synthetase proteins are fundamentally known as the first enzymes of translation, catalysing the conjugation of amino acids to cognate tRNAs for protein synthesis. It is known that certain aminoacyl t-RNA synthetase have multiple non-canonical roles in both transcription and translation, and their disruption results in varied and complicated phenotypes. We clinically and genetically studied seven patients (six male and one female; aged 2 to 12 years) from five unrelated families who all showed the same phenotypes of severe developmental delay or arrest (7/7), hypotonia (6/7), deafness (7/7) and inability to speak (6/7). The subjects further developed intractable epilepsy (7/7) and nystagmus (6/6) with increasing age. They demonstrated characteristic laboratory data, including increased lactate and/or pyruvate levels (7/7), and imaging findings (7/7), including calcification and abnormal signals in the white matter and pathological involvement (2/2) of the corticospinal tracts. Through whole-exome sequencing, we discovered genetic abnormalities in lysyl-tRNA synthetase (KARS). All patients harboured the variant [c.1786C>T, p.Leu596Phe] KARS isoform 1 ([c.1702C>T, p.Leu568Phe] of KARS isoform 2) either in the homozygous state or compound heterozygous state with the following KARS variants, [c.879+1G>A; c.1786C>T, p.Glu252_Glu293del; p.Leu596Phe] ([c.795+1G>A; c.1702C>T, p.Glu224_Glu255del; p.Leu568Phe]) and [c.650G>A; c.1786C>T, p.Gly217Asp; p.Leu596Phe] ([c.566G>A; c.1702C>T, p.Gly189Asp; p.Leu568Phe]). Moreover, similarly disrupted lysyl-tRNA synthetase (LysRS) proteins showed reduced enzymatic activities and abnormal CNSs in Xenopus embryos. Additionally, LysRS acts as a non-canonical inducer of the immune response and has transcriptional activity. We speculated that the complex functions of the abnormal LysRS proteins led to the severe phenotypes in our patients. These KARS pathological variants are novel, including the variant [c.1786C>T; p.Leu596Phe] (c.1702C>T; p.Leu568Phe) shared by all patients in the homozygous or compound-heterozygous state. This common position may play an important role in the development of severe progressive leukodystrophy. Further research is warranted to further elucidate this relationship and to investigate how specific mutated LysRS proteins function to understand the broad spectrum of KARS-related diseases.

30706699 AARS2 leukoencephalopathy: A new variant of mitochondrial encephalomyopathy.
04 2019 Molecular genetics & genomic medicine

Tang Yi, Qin Qi, Xing Yi, Guo Dongmei, Di Li, Jia Jianping.

Mutations in the mitochondrial alanyl-transfer (t)RNA synthetase 2 (AARS2,OMIM:612035) have been linked to leukoencephalopathy recently. Till now, there have been 19 cases reported so far. However, the clinical and genetic characteristics of this disease are not fully understood. We reported an adult-onset male leukoencephalopathy patient related to novel AARS2 gene mutations and reviewed all previous cases regarding the clinical and genetic features of AARS2 leukoencephalopathy.

30819764 Siblings with lethal primary pulmonary hypoplasia and compound heterozygous variants in the AARS2 gene: further delineation of the phenotypic spectrum.
06 2019 Cold Spring Harbor molecular case studies

Kiraly-Borri Catherine, Jevon Gareth, Ji Weizhen, Jeffries Lauren, Ricciardi Jamie-Lee, Konstantino Monica, Ackerman Kate G, Lakhani Saquib A.

Variants in the mitochondrial alanyl-tRNA synthetase 2 gene AARS2 (OMIM 612035) are associated with infantile mitochondrial cardiomyopathy or later-onset leukoencephalopathy with premature ovarian insufficiency. Here, we report two newborn siblings who died soon after birth with primary pulmonary hypoplasia without evidence of cardiomyopathy. Whole-exome sequencing detected the same compound heterozygous AARS2 variants in both siblings (c.1774C>T, p.Arg592Trp and c.647dup, p.Cys218Leufs*6) that have previously been associated with infantile mitochondrial cardiomyopathy. Segregation analysis in the family confirmed carrier status of the parents and an unaffected sibling. To our knowledge, this is the first report of primary pulmonary hypoplasia in the absence of cardiomyopathy associated with recessive AARS2 variants and further defines the phenotypic spectrum associated with this gene.

31282308 Expanding the Phenotype: Neurodevelopmental Disorder, Mitochondrial, With Abnormal Movements and Lactic Acidosis, With or Without Seizures (NEMMLAS) due to WARS2 Biallelic Variants, Encoding Mitochondrial Tryptophanyl-tRNA Synthase.
10 2019 Journal of child neurology

Virdee Manveen, Swarnalingam Eroshini, Kozenko Mariya, Tarnopolsky Mark, Jones Kevin.

WARS2 encodes a tryptophanyl tRNA synthetase, which is involved in mitochondrial protein synthesis. Biallelic mutations in WARS2 are rare and have been associated with a spectrum of clinical presentations, including neurodevelopmental disorder with abnormal movements, lactic acidosis with or without seizures (NEMMLAS).

31393557 Mitochondrial Dysfunction in Primary Ovarian Insufficiency.
10 2019 Endocrinology

Tiosano Dov, Mears Jason A, Buchner David A.

Primary ovarian insufficiency (POI) is defined by the loss or dysfunction of ovarian follicles associated with amenorrhea before the age of 40. Symptoms include hot flashes, sleep disturbances, and depression, as well as reduced fertility and increased long-term risk of cardiovascular disease. POI occurs in ∼1% to 2% of women, although the etiology of most cases remains unexplained. Approximately 10% to 20% of POI cases are due to mutations in a single gene or a chromosomal abnormality, which has provided considerable molecular insight into the biological underpinnings of POI. Many of the genes for which mutations have been associated with POI, either isolated or syndromic cases, function within mitochondria, including MRPS22, POLG, TWNK, LARS2, HARS2, AARS2, CLPP, and LRPPRC. Collectively, these genes play roles in mitochondrial DNA replication, gene expression, and protein synthesis and degradation. Although mutations in these genes clearly implicate mitochondrial dysfunction in rare cases of POI, data are scant as to whether these genes in particular, and mitochondrial dysfunction in general, contribute to most POI cases that lack a known etiology. Further studies are needed to better elucidate the contribution of mitochondria to POI and determine whether there is a common molecular defect in mitochondrial function that distinguishes mitochondria-related genes that when mutated cause POI vs those that do not. Nonetheless, the clear implication of mitochondrial dysfunction in POI suggests that manipulation of mitochondrial function represents an important therapeutic target for the treatment or prevention of POI.

31671122 Mitochondrial dysfunctions in leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL).
- 2019 PloS one

Lin Tsu-Kung, Chang Yung-Yee, Lin Hung-Yu, Liou Chia-Wei, Wang Pei-Wen, Chuang Jiin-Haur, Chen Shang-Der, Chuang Yao-Chung, Huang Sheng-Teng, Hsu Te-Yao, Peng Cheng-Huei, Lan Min-Yu.

Several inherited human diseases have been linked to mitochondrial aminoacyl-tRNA synthetases (mtARSs). Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a leukodystrophy caused by mutations in the DARS2 gene which encodes mitochondrial aspartyl-tRNA synthetase. As mitochondrial ARSs are key components of the mitochondrial translation apparatus, we investigated the effects of DARS2 mutations on mitochondrial functions and mitochondrial morphology in an LBSL patient. In fibroblasts from the patient with LBSL, biosynthesis of respiratory chain complex proteins encoded by mitochondrial DNA was decreased, while those encoded by nuclear DNA were not. Cellular oxygen consumption rates and respiratory control ratio were decreased in the LBSL patient; in addition, fragmentation of mitochondria was increased, while their tubular elongation and interconnectivity were decreased. Taken together, these findings suggest that DARS2 mutations impair translations of mitochondrial DNA-encoded respiratory chain complex proteins, consequently causing dysfunction of cellular respiration and impediment of mitochondrial dynamics, which highlights the role of mtARSs in the maintenance of normal mitochondrial bioenergetics and dynamics.

31920941 Novel Alanyl-tRNA Synthetase 2 Pathogenic Variants in Leukodystrophies.
- 2019 Frontiers in neurology

Wang Xingao, Wang Qun, Tang Hefei, Chen Bin, Dong Xiang, Niu Songtao, Li Shaowu, Shi Yuzhi, Shan Wei, Zhang Zaiqiang.

The white matter disease spectrum is associated with many genetic diseases, including AARS2, CADASIL, ALD, and others. In this study, to determine the novel alanyl-tRNA synthetase 2 mutation implicated in white matter disease, several families with an autosomal recessive inheritance pattern of white matter disease were analyzed by whole-exome sequencing. Variants were prioritized according to their rarity and pathogenic variants in genes already known to be associated with leukodystrophies and were confirmed by Sanger sequencing using standard protocols. We identified 5 rare variants (c.452T>C chr6:44279256 p.M151T, c.1871G>A chr6:44272054 p.W624X, c.802A>G chr6:44278128 p.M268V, c.1703-1704del chr6:-44272430-44272431 p.Q568fs, and c.179C>A chr6-44280882 p.P60H) with varying expression in 4 independent Chinese families with leukodystrophy. These single nucleotide variants (SNVs), or deletion mutations, each induced a frameshift, causing a missense mutation in alanyl-tRNA synthetase 2. These findings suggested that all mutations might contribute to the development of leukodystrophy in the examined family members. Combined with previous findings, our data confirmed that the novel mutations are located in leukodystrophy-related risk genes. We also summarized all the alanyl-tRNA synthetase 2 mutations related to the onset of leukodystrophies in adults.

30054184 Analysis of frontotemporal dementia, amyotrophic lateral sclerosis, and other dementia-related genes in 107 Korean patients with frontotemporal dementia.
Dec 2018 Neurobiology of aging

Kim Eun-Joo, Kim Young-Eun, Jang Ja-Hyun, Cho Eun-Hae, Na Duk L, Seo Sang Won, Jung Na-Yeon, Jeong Jee H, Kwon Jay C, Park Kee Hyung, Park Kyung Won, Lee Jae-Hong, Roh Jee Hoon, Kim Hee-Jin, Yoon Soo Jin, Choi Seong Hye, Jang Jae-Won, Ki Chang-Seok, Kim Seung Hyun.

To identify pathogenic variants in 107 Korean patients with sporadic frontotemporal dementia (FTD), 46 genes related to FTD, amyotrophic lateral sclerosis, and other dementias were screened by next-generation sequencing. Hexanucleotide repeats in C9orf72 gene were also tested by repeat-primed polymerase chain reaction. Next-generation sequencing revealed one known pathogenic variant (c.708+1G>A) in the GRN gene in a patient with behavioral variant FTD (bvFTD). In addition, a novel in-frame deletion (c.2675_2683del) in the CSF1R gene was identified in a patient with bvFTD who had severe bifrontal atrophy with frontal subcortical white matter changes. Novel compound heterozygous variants in the AARS2 gene, c.1040+1G>A and c.636G>A (p.Met212Ile), were found in a patient with bvFTD. Forty-six variants of uncertain significance were detected in other patients. None of the patients had expanded hexanucleotide repeats in C9orf72. These results show that pathogenic variants of known FTD genes are rare in Korean FTD patients but the CSF1R and AARS2 genes should be screened for a genetic diagnosis of FTD or other dementias.

30252186 Inhibition of mitochondrial translation in fibroblasts from a patient expressing the KARS p.(Pro228Leu) variant and presenting with sensorineural deafness, developmental delay, and lactic acidosis.
Dec 2018 Human mutation

Ruzzenente Benedetta, Assouline Zahra, Barcia Giulia, Rio Marlène, Boddaert Nathalie, Munnich Arnold, Rötig Agnès, Metodiev Metodi D.

Aminoacyl-tRNA synthetases are ubiquitous enzymes, which universally charge tRNAs with their cognate amino acids for use in cytosolic or organellar translation. In humans, mutations in mitochondrial tRNA synthetases have been linked to different tissue-specific pathologies. Mutations in the KARS gene, which encodes both the cytosolic and mitochondrial isoform of lysyl-tRNA synthetase, cause predominantly neurological diseases that often involve deafness, but have also been linked to cardiomyopathy, developmental delay, and lactic acidosis. Using whole exome sequencing, we identified two compound heterozygous mutations, NM_001130089.1:c.683C>T p.(Pro228Leu) and NM_001130089.1:c.1438del p.(Leu480TrpfsX3), in a patient presenting with sensorineural deafness, developmental delay, hypotonia, and lactic acidosis. Nonsense-mediated mRNA decay eliminated the truncated mRNA transcript, rendering the patient hemizygous for the missense mutation. The c.683C>T mutation was previously described, but its pathogenicity remained unexamined. Molecular characterization of patient fibroblasts revealed a multiple oxidative phosphorylation deficiency due to impaired mitochondrial translation, but no evidence of inhibition of cytosolic translation. Reintroduction of wild-type mitochondrial KARS, but not the cytosolic isoform, rescued this phenotype confirming the disease-causing nature of p.(Pro228Leu) exchange and demonstrating the mitochondrial etiology of the disease. We propose that mitochondrial translation deficiency is the probable disease culprit in this and possibly other patients with mutations in KARS.

30294545 Antiepileptic treatment may determine the outcome of FARS2 mutation carriers.
Dec 2018 Molecular genetics and metabolism reports

Finsterer Josef, Scorza Fulvio A, Scorza Carla A.

30566859 A Wars2 Mutant Mouse Model Displays OXPHOS Deficiencies and Activation of Tissue-Specific Stress Response Pathways.
Dec 2018 Cell reports

Agnew Thomas, Goldsworthy Michelle, Aguilar Carlos, Morgan Anna, Simon Michelle, Hilton Helen, Esapa Chris, Wu Yixing, Cater Heather, Bentley Liz, Scudamore Cheryl, Poulton Joanna, Morten Karl J, Thompson Kyle, He Langping, Brown Steve D M, Taylor Robert W, Bowl Michael R, Cox Roger D.

Mutations in genes essential for mitochondrial function have pleiotropic effects. The mechanisms underlying these traits yield insights into metabolic homeostasis and potential therapies. Here we report the characterization of a mouse model harboring a mutation in the tryptophanyl-tRNA synthetase 2 (Wars2) gene, encoding the mitochondrial-localized WARS2 protein. This hypomorphic allele causes progressive tissue-specific pathologies, including hearing loss, reduced adiposity, adipose tissue dysfunction, and hypertrophic cardiomyopathy. We demonstrate the tissue heterogeneity arises as a result of variable activation of the integrated stress response (ISR) pathway and the ability of certain tissues to respond to impaired mitochondrial translation. Many of the systemic metabolic effects are likely mediated through elevated fibroblast growth factor 21 (FGF21) following activation of the ISR in certain tissues. These findings demonstrate the potential pleiotropy associated with Wars2 mutations in patients.

30686629 Cerebral Infarction in CARS2 Mutation.
Dec 2018 Pediatric neurology

Samanta Debopam.

30177229 FARS2 deficiency; new cases, review of clinical, biochemical, and molecular spectra, and variants interpretation based on structural, functional, and evolutionary significance.
Nov 2018 Molecular genetics and metabolism

Almannai Mohammed, Wang Julia, Dai Hongzheng, El-Hattab Ayman W, Faqeih Eissa A, Saleh Mohammed A, Al Asmari Ali, Alwadei Ali H, Aljadhai Yaser I, AlHashem Amal, Tabarki Brahim, Lines Matthew A, Grange Dorothy K, Benini Ruba, Alsaman Abdulaziz S, Mahmoud Adel, Katsonis Panagiotis, Lichtarge Olivier, Wong Lee-Jun C.

An increasing number of mitochondrial diseases are found to be caused by pathogenic variants in nuclear encoded mitochondrial aminoacyl-tRNA synthetases. FARS2 encodes mitochondrial phenylalanyl-tRNA synthetase (mtPheRS) which transfers phenylalanine to its cognate tRNA in mitochondria. Since the first case was reported in 2012, a total of 21 subjects with FARS2 deficiency have been reported to date with a spectrum of disease severity that falls between two phenotypes; early onset epileptic encephalopathy and a less severe phenotype characterized by spastic paraplegia. In this report, we present an additional 15 individuals from 12 families who are mostly Arabs homozygous for the pathogenic variant Y144C, which is associated with the more severe early onset phenotype. The total number of unique pathogenic FARS2 variants known to date is 21 including three different partial gene deletions reported in four individuals. Except for the large deletions, all variants but two (one in-frame deletion of one amino acid and one splice-site variant) are missense. All large deletions and the single splice-site variant are in trans with a missense variant. This suggests that complete loss of function may be incompatible with life. In this report, we also review structural, functional, and evolutionary significance of select FARS2 pathogenic variants reported here.

30384889 Genetic Basis of Severe Childhood-OnsetCardiomyopathies.
Nov 2018 Journal of the American College of Cardiology

Vasilescu Catalina, Ojala Tiina H, Brilhante Virginia, Ojanen Simo, Hinterding Helena M, Palin Eino, Alastalo Tero-Pekka, Koskenvuo Juha, Hiippala Anita, Jokinen Eero, Jahnukainen Timo, Lohi Jouko, Pihkala Jaana, Tyni Tiina A, Carroll Christopher J, Suomalainen Anu.

Childhood cardiomyopathies are progressive and often lethal disorders, forming the most common cause of heart failure in children. Despite severe outcomes, their genetic background is still poorly characterized.

30394614 Novel GARS mutation presenting as autosomal dominant intermediate Charcot-Marie-Tooth disease.
Nov 2018 Journal of the peripheral nervous system : JPNS

Nan Haitian, Takaki Ryusuke, Hata Takanori, Ichinose Yuta, Tsuchiya Mai, Koh Kishin, Takiyama Yoshihisa.

We report the first family with a glycyl-tRNA synthetase (GARS) mutation with autosomal dominant intermediate Charcot-Marie-Tooth disease (DI-CMT). The proband and the proband's father presented with gait disturbance and hand weakness. Both patients displayed moderately decreased conduction velocities (MNCV) (ranging from 29.2 m/s to 37.8 m/s). A sural nerve biopsy of the father revealed evidence of both axonal loss and demyelination. On exome sequencing, in both the proband and his father we identified a novel missense mutation (c.643G>C, p.Asp215His) in the GARS gene in a heterozygous state, which is considered to be pathogenic for this DI-CMT family. The present study broadens current knowledge about intermediate CMT and the phenotypic spectrum of defects associated with GARS. This article is protected by copyright. All rights reserved.

30419932 Expanding the clinical phenotype of IARS2-related mitochondrial disease.
Nov 2018 BMC medical genetics

Vona Barbara, Maroofian Reza, Bellacchio Emanuele, Najafi Maryam, Thompson Kyle, Alahmad Ahmad, He Langping, Ahangari Najmeh, Rad Abolfazl, Shahrokhzadeh Sima, Bahena Paulina, Mittag Falk, Traub Frank, Movaffagh Jebrail, Amiri Nafise, Doosti Mohammad, Boostani Reza, Shirzadeh Ebrahim, Haaf Thomas, Diodato Daria, Schmidts Miriam, Taylor Robert W, Karimiani Ehsan Ghayoor.

IARS2 encodes a mitochondrial isoleucyl-tRNA synthetase, a highly conserved nuclear-encoded enzyme required for the charging of tRNAs with their cognate amino acid for translation. Recently, pathogenic IARS2 variants have been identified in a number of patients presenting broad clinical phenotypes with autosomal recessive inheritance. These phenotypes range from Leigh and West syndrome to a new syndrome abbreviated CAGSSS that is characterised by cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysplasia, as well as cataract with no additional anomalies.

30458719 A novel compound heterozygous mutation in VARS2 in a newborn with mitochondrial cardiomyopathy: a case report of a Chinese family.
Nov 2018 BMC medical genetics

Ma Keze, Xie Mingyu, He Xiaoguang, Liu Guojun, Lu Xiaomei, Peng Qi, Zhong Baimao, Li Ning.

Genetic defects in the mitochondrial aminoacyl-tRNA synthetase are important causes of mitochondrial disorders. VARS2 is one of the genes encoding aminoacyl-tRNA synthetases. Recently, an increasing number of pathogenic variants of VARS2 have been reported.

30467211 Practical approach to the diagnosis of adult-onset leukodystrophies: an updated guide in the genomic era.
Nov 2018 Journal of neurology, neurosurgery, and psychiatry

Lynch David S, Wade Charles, Paiva Anderson Rodrigues Brandão de, John Nevin, Kinsella Justin A, Merwick Áine, Ahmed Rebekah M, Warren Jason D, Mummery Catherine J, Schott Jonathan M, Fox Nick C, Houlden Henry, Adams Matthew E, Davagnanam Indran, Murphy Elaine, Chataway Jeremy.

Adult-onset leukodystrophies and genetic leukoencephalopathies comprise a diverse group of neurodegenerative disorders of white matter with a wide age of onset and phenotypic spectrum. Patients with white matter abnormalities detected on MRI often present a diagnostic challenge to both general and specialist neurologists. Patients typically present with a progressive syndrome including various combinations of cognitive impairment, movement disorders, ataxia and upper motor neuron signs. There are a number of important and treatable acquired causes for this imaging and clinical presentation. There are also a very large number of genetic causes which due to their relative rarity and sometimes variable and overlapping presentations can be difficult to diagnose. In this review, we provide a structured approach to the diagnosis of inherited disorders of white matter in adults. We describe clinical and radiological clues to aid diagnosis, and we present an overview of both common and rare genetic white matter disorders. We provide advice on testing for acquired causes, on excluding small vessel disease mimics, and detailed advice on metabolic and genetic testing available to the practising neurologist. Common genetic leukoencephalopathies discussed in detail include CSF1R, AARS2, cerebral arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and mitochondrial and metabolic disorders.

30583950 Management of NARS2-Related Mitochondrial Disorder is Complex.
Nov 2018 Pediatric neurology

Finsterer Josef.

30686630 Reply to Finsterer Regarding Lethal NARS2-Related Disorder Associated With Rapidly Progressive Intractable Epilepsy and Global Brain Atrophy.
Nov 2018 Pediatric neurology

Seaver Laurie H, DeRoos Steven, Betz Brad, Rajasekaran Surender.

30139652 Clinicopathologic Findings of CARS2 Mutation.
Oct 2018 Pediatric neurology

Samanta Debopam, Gokden Murat, Willis Erin.

We describe a 13-year-old girl with a past medical history of epilepsy, intellectual impairment, dysphagia with gastric tube dependence, and autism spectrum disorder who presented with focal status epilepticus.

30285085 Instability of the mitochondrial alanyl-tRNA synthetase underlies fatal infantile-onset cardiomyopathy.
Oct 2018 Human molecular genetics

Sommerville Ewen W, Zhou Xiao-Long, Oláhová Monika, Jenkins Janda, Euro Liliya, Konovalova Svetlana, Hilander Taru, Pyle Angela, He Langping, Habeebu Sultan, Saunders Carol, Kelsey Anna, Morris Andrew A M, McFarland Robert, Suomalainen Anu, Gorman Gráinne S, Wang En-Duo, Thiffault Isabelle, Tyynismaa Henna, Taylor Robert W.

Recessively-inherited variants in AARS2 (NM_020745.2) encoding mitochondrial alanyl-tRNA synthetase (mt-AlaRS) were first described in patients presenting with fatal infantile cardiomyopathy and multiple oxidative phosphorylation defects. To date, all described patients with AARS2-related fatal infantile cardiomyopathy are united by either a homozygous or compound heterozygous c.1774C>T (p.Arg592Trp) missense founder mutation that is absent in patients with other AARS2-related phenotypes. We describe the clinical, biochemical and molecular investigations of two unrelated boys presenting with fatal infantile cardiomyopathy, lactic acidosis and respiratory failure. Oxidative histochemistry showed cytochrome c oxidase (COX)-deficient fibres in skeletal and cardiac muscle. Biochemical studies showed markedly decreased activities of mitochondrial respiratory chain complexes I and IV with a mild decrease of complex III activity in skeletal and cardiac muscle. Using next-generation sequencing, we identified a c.1738C>T (p.Arg580Trp) AARS2 variant shared by both patients that was in trans with a loss-of-function heterozygous AARS2 variant; a c.1008dupT (p.Asp337*) nonsense variant or an intragenic deletion encompassing AARS2 exons 5-7. Interestingly, our patients did not harbour the p.Arg592Trp AARS2 founder mutation. In silico modelling of the p.Arg580Trp substitution suggested a deleterious impact on protein stability and folding. We confirmed markedly decreased mt-AlaRS protein levels in patient fibroblasts, skeletal and cardiac muscle, although mitochondrial protein synthesis defects were confined to skeletal and cardiac muscle. In vitro data showed that the p.Arg580Trp variant had a minimal effect on activation, aminoacylation or misaminoacylation activities relative to wild-type mt-AlaRS, demonstrating that instability of mt-AlaRS is the biological mechanism underlying the fatal cardiomyopathy phenotype in our patients.

30352563 Intra-familial phenotypic heterogeneity in a Sudanese family with DARS2-related leukoencephalopathy, brainstem and spinal cord involvement and lactate elevation: a case report.
Oct 2018 BMC neurology

Yahia Ashraf, Elsayed Liena, Babai Arwa, Salih Mustafa A, El-Sadig Sarah Misbah, Amin Mutaz, Koko Mahmoud, Abubakr Rayan, Idris Razaz, Taha Shaimaa Omer M A, Elmalik Salah A, Brice Alexis, Ahmed Ammar Eltahir, Stevanin Giovanni.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL, OMIM #611105) is a genetic disease of the central nervous system characterized by lower limb spasticity, cerebellar ataxia and involvement of the dorsal column. The disease is caused by mutations in the DARS2 gene but has never been reported in sub-Saharan Africa so far.

30237576 Autozygome and high throughput confirmation of disease genes candidacy.
Sep 2018 Genetics in medicine : official journal of the American College of Medical Genetics

Maddirevula Sateesh, Alzahrani Fatema, Al-Owain Mohammed, Al Muhaizea Mohammad A, Kayyali Husam R, AlHashem Amal, Rahbeeni Zuhair, Al-Otaibi Maha, Alzaidan Hamad I, Balobaid Ameera, El Khashab Heba Y, Bubshait Dalal K, Faden Maha, Yamani Suad Al, Dabbagh Omar, Al-Mureikhi Mariam, Jasser Abdulla Al, Alsaif Hessa S, Alluhaydan Iram, Seidahmed Mohammed Zain, Alabbasi Bashair Hamza, Almogarri Ibrahim, Kurdi Wesam, Akleh Hana, Qari Alya, Al Tala Saeed M, Alhomaidi Suzan, Kentab Amal Y, Salih Mustafa A, Chedrawi Aziza, Alameer Seham, Tabarki Brahim, Shamseldin Hanan E, Patel Nisha, Ibrahim Niema, Abdulwahab Firdous, Samira Menasria, Goljan Ewa, Abouelhoda Mohamed, Meyer Brian F, Hashem Mais, Shaheen Ranad, AlShahwan Saad, Alfadhel Majid, Ben-Omran Tawfeg, Al-Qattan Mohammad M, Monies Dorota, Alkuraya Fowzan S.

Establishing links between Mendelian phenotypes and genes enables the proper interpretation of variants therein. Autozygome, a rich source of homozygous variants, has been successfully utilized for the high throughput identification of novel autosomal recessive disease genes. Here, we highlight the utility of the autozygome for the high throughput confirmation of previously published tentative links to diseases.

30250868 FARS2 mutations presenting with pure spastic paraplegia and lesions of the dentate nuclei.
Sep 2018 Annals of clinical and translational neurology

Sahai Supreet K, Steiner Rebecca E, Au Margaret G, Graham John M, Salamon Noriko, Ibba Michael, Pierson Tyler M.

Mutations in FARS2, the gene encoding the mitochondrial phenylalanine-tRNA synthetase (mtPheRS), have been linked to a range of phenotypes including epileptic encephalopathy, developmental delay, and motor dysfunction. We report a 9-year-old boy with novel compound heterozygous variants of FARS2, presenting with a pure spastic paraplegia syndrome associated with bilateral signal abnormalities in the dentate nuclei. Exome sequencing identified a paternal nonsense variant (Q216X) lacking the catalytic core and anticodon-binding regions, and a maternal missense variant (P136H) possessing partial enzymatic activity. This case confirms and expands the phenotype related to FARS2 mutations with regards to clinical presentation and neuroimaging findings.

30006346 Three human aminoacyl-tRNA synthetases have distinct sub-mitochondrial localizations that are unaffected by disease-associated mutations.
Aug 2018 The Journal of biological chemistry

González-Serrano Ligia Elena, Karim Loukmane, Pierre Florian, Schwenzer Hagen, Rötig Agnès, Munnich Arnold, Sissler Marie.

Human mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) are key enzymes in the mitochondrial protein translation system and catalyze the charging of amino acids on their cognate tRNAs. Mutations in their nuclear genes are associated with pathologies having a broad spectrum of clinical phenotypes, but with no clear molecular mechanism(s). For example, mutations in the nuclear genes encoding mt-AspRS and mt-ArgRS are correlated with the moderate neurodegenerative disorder leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) and with the severe neurodevelopmental disorder pontocerebellar hypoplasia type 6 (PCH6), respectively. Previous studies have shown no or only minor impacts of these mutations on the canonical properties of these enzymes, indicating that the role of the mt-aaRSs in protein synthesis is mostly not affected by these mutations, but their effects on the mitochondrial localizations of aaRSs remain unclear. Here, we demonstrate that three human aaRSs, mt-AspRS, mt-ArgRS, and LysRS, each have a specific sub-mitochondrial distribution, with mt-ArgRS being exclusively localized in the membrane, LysRS exclusively in the soluble fraction, and mt-AspRS being present in both. Chemical treatments revealed that mt-AspRs is anchored in the mitochondrial membrane through electrostatic interactions, whereas mt-ArgRS uses hydrophobic interactions. We also report that novel mutations in mt-AspRS and mt-ArgRS genes from individuals with LBSL and PCH6, respectively, had no significant impact on the mitochondrial localizations of mt-AspRS and mt-ArgRS. The variable sub-mitochondrial locations for these three mt-aaRSs strongly suggest the existence of additional enzyme properties, requiring further investigation to unravel the mechanisms underlying the two neurodegenerative disorders.

30327238 Lethal NARS2-Related Disorder Associated With Rapidly Progressive Intractable Epilepsy and Global Brain Atrophy.
Aug 2018 Pediatric neurology

Seaver Laurie H, DeRoos Steven, Andersen Nicholas J, Betz Brad, Prokop Jeremy, Lannen Nick, Jordan Renee, Rajasekaran Surender.

Infantile epileptic encephalopathy is a heterogeneous condition that has been associated with variants in more than 200 genes. The variability in findings and prognosis creates challenges to making the correct diagnosis and initiating the appropriate therapy. Biallelic variants in NARS2, a mitochondrial aminoacyl-tRNA synthetase gene, were recently associated with neurodegenerative disorders that include epilepsy.

29954622 Ovarioleukodystrophy: Vanishing white matter versus AARS2-related ovarioleukodystrophy.
Aug 2018 Clinical neurology and neurosurgery

van der Knaap Marjo S, Abbink Truus E M.

30026338 The phenotypic spectrum of germline YARS2 variants: from isolated sideroblastic anemia to mitochondrial myopathy, lactic acidosis and sideroblastic anemia 2.
Jul 2018 Haematologica

Riley Lisa G, Heeney Matthew M, Rudinger-Thirion Joëlle, Frugier Magali, Campagna Dean R, Zhou Ronghao, Hale Gregory A, Hilliard Lee M, Kaplan Joel A, Kwiatkowski Janet L, Sieff Colin A, Steensma David P, Rennings Alexander J, Simons Annet, Schaap Nicolaas, Roodenburg Richard J, Kleefstra Tjitske, Arenillas Leonor, Fita-Torró Josep, Ahmed Rasha, Abboud Miguel, Bechara Elie, Farah Roula, Tamminga Rienk Yj, Bottomley Sylvia S, Sanchez Mayka, Swinkels Dorine W, Christodoulou John, Fleming Mark D.

YARS2 variants have previously been described in patients with myopathy, lactic acidosis and sideroblastic anemia 2 (MLASA2). YARS2 encodes the mitochondrial tyrosyl-tRNA synthetase, which is responsible for conjugating tyrosine to its cognate mt-tRNA for mitochondrial protein synthesis. Here we describe 14 individuals from 11 families presenting with sideroblastic anemia and with YARS2 variants that we identified using a sideroblastic anemia gene panel or exome sequencing. The phenotype of these patients ranged from MLASA to isolated congenital sideroblastic anemia. As in previous cases, inter- and intra-familial phenotypic variability was observed, however this report includes the first cases with isolated sideroblastic anemia and patients with biallelic YARS2 variants that have no clinically ascertainable phenotype. We identified ten novel YARS2 variants and three previously reported variants. In vitro amino-acylation assays of three five novel missense variants showed they that three had less effect on the catalytic activity of YARS2 than the most commonly reported variant, p.(Phe52Leu), associated with MLASA2, which may explain the milder phenotypes in patients with these variants. However, the other two missense variants had a more severe effect on YARS2 catalytic efficiency. Several patients carried the common YARS2 c.572 G>T, p.(Gly191Val) variant (minor allele frequency = 0.1259) in trans with a rare deleterious YARS2 variant. We have previously shown that the p.(Gly191Val) variant reduces YARS2 catalytic activity. Consequently, we suggest that biallelic YARS2 variants, including severe loss-of-function alleles in trans of the common p.(Gly191Val) variant, should be considered as a cause of isolated congenital sideroblastic anemia, as well as the MLASA syndromic phenotype.

30041933 Novel IARS2 mutations in Japanese siblings with CAGSSS, Leigh, and West syndrome.
Jul 2018 Brain & development

Takezawa Yusuke, Fujie Hiromi, Kikuchi Atsuo, Niihori Tetsuya, Funayama Ryo, Shirota Matsuyuki, Nakayama Keiko, Aoki Yoko, Sasaki Masayuki, Kure Shigeo.

IARS2 encodes isoleucine-tRNA synthetase, which is aclass-1 amino acyl-tRNA synthetase. IARS2 mutations are reported to cause Leigh syndrome or cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, and skeletal dysphasia syndrome (CAGSSS). To our knowledge, IARS2 mutations and diseases related to it have only been reported in three families. Here we report a case of two Japanese siblings with Leigh syndrome, some features of CAGSSS, and West syndrome that are found to have compound heterozygous novel IARS2 mutations.

29961496 A Newborn With Hyperlactatemia and Epileptic Encephalopathy.
Jul 2018 Seminars in pediatric neurology

Obeid Rawad, Sogawa Yoshimi, Naik Monica, Goldstein Amy, Gropman Andrea, Asato Miya.

The etiology of hyperlactatemia in newborns could be a challenging diagnosis. In this article we are discussing a diagnostic paradigm using the clinical history, laboratory results, and brain imaging that could be helpful in directing the work up.

29881806 Expanding spectrum of RARS2 gene disorders: Myoclonic epilepsy, mental retardation, spasticity, and extrapyramidal features.
Jun 2018 Epilepsia open

Mathew Thomas, Avati Amrutha, D'Souza Delon, Therambil Manjusha.

Pontocerebellar hypoplasia type 6 (PCH6) is an autosomal recessive mitochondrial disease, typically characterized by pontine atrophy, vermian hypoplasia, infantile encephalopathy, generalized hypotonia, and intractable seizures. The purpose of this study is to describe the seizures and other neurological manifestations of RARS2 gene mutations and to compare the clinical features with other causes of progressive myoclonic epilepsy. Detailed history, physical examination, and clinical and genetic work-up were performed in 2 siblings who presented with progressive myoclonic epilepsy. One sibling, a 20-year-old woman, and the other a 24-year-old man, had a homozygous missense variant (c.848T>A; p.Leu283Gln) in exon 10 of the RARS2 gene. The female patient had action and audiogenic myoclonic jerks, postural tremors, spastic dysarthria, and bradykinesia, and her male sibling had similar features with oculomotor apraxia. The RARS2 gene mutation can present with myoclonic epilepsy, mental retardation, and pyramidal and extrapyramidal features, and is an important differential for causes of progressive myoclonic epilepsy.

29915213 The genotypic and phenotypic spectrum of PARS2-related infantile-onset encephalopathy.
Jun 2018 Journal of human genetics

Yin Xiaomeng, Tang Beisha, Mao Xiao, Peng Jinxin, Zeng Sheng, Wang Yaqin, Jiang Hong, Li Nan.

Mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) are a family of enzymes that play critical roles in protein biosynthesis. Mutations in mt-aaRSs are associated with various diseases. As a member of the mt-aaRS family, PARS2 encoding prolyl-tRNA synthetase 2 was recently shown to be associated with Alpers syndrome and certain infantile-onset neurodegenerative disorders in four patients. Here, we present two patients in a pedigree with early developmental delay, epileptic spasms, delayed myelination combined with cerebellar white matter abnormalities, and progressive cortical atrophy. Whole-exome sequencing revealed pathogenic compound heterozygous variants [c.283 G > A (p.95 V > I)] and [c.604 G > C (p.202 R > G)] in PARS2. Nearly all patients had epileptic spasms with early response to treatment, early developmental delay and/or regression followed by generalized hypotonia, postnatal microcephaly, elevated lactate levels, and progressive cerebral atrophy. Our study provides further evidence for validating the role of PARS2 in the pathology of related infantile-onset encephalopathy, contributing to the phenotypic features of this condition, and providing clinical and molecular insight for the diagnosis of this disease entity.

29914532 Clinical and genetic characteristics of Chinese patients with familial or sporadic pediatric cataract.
Jun 2018 Orphanet journal of rare diseases

Li Jingyan, Leng Yunji, Han Shirui, Yan Lulu, Lu Chaoxia, Luo Yang, Zhang Xue, Cao Lihua.

Pediatric cataract is a clinically and genetically heterogeneous disease which is a significant cause of lifelong visual impairment and treatable blindness. Our study aims to investigate the genotype spectrum in a group of Chinese patients with pediatric cataract.

29749055 AARS2-related ovarioleukodystrophy: Clinical and neuroimaging features of three new cases.
May 2018 Acta neurologica Scandinavica

Taglia I, Di Donato I, Bianchi S, Cerase A, Monti L, Marconi R, Orrico A, Rufa A, Federico A, Dotti M T.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), previously known as hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) or pigmentary orthochromatic leukodystrophy (POLD), is the most frequent non-vascular adult-onset leukoencephalopathy. It is caused by autosomal dominant mutations in CSF1R gene. Recently, also autosomal recessive mutations in AARS2 gene were found to be the cause of an adult-onset leukodystrophy with axonal spheroids. Our aim was to achieve a genetic diagnosis in a cohort of CSF1R-negative patients, performing a sequence analysis of AARS2 gene.

29783990 Severe hepatopathy and neurological deterioration after start of valproate treatment in a 6-year-old child with mitochondrial tryptophanyl-tRNA synthetase deficiency.
May 2018 Orphanet journal of rare diseases

Vantroys Elise, Smet Joél, Vanlander Arnaud V, Vergult Sarah, De Bruyne Ruth, Roels Frank, Stepman Hedwig, Roeyers Herbert, Menten Björn, Van Coster Rudy.

The first subjects with deficiency of mitochondrial tryptophanyl-tRNA synthetase (WARS2) were reported in 2017. Their clinical characteristics can be subdivided into three phenotypes (neonatal phenotype, severe infantile onset phenotype, Parkinson-like phenotype).

29615062 KARS-related diseases: progressive leukoencephalopathy with brainstem and spinal cord calcifications as new phenotype and a review of literature.
Apr 2018 Orphanet journal of rare diseases

Ardissone Anna, Tonduti Davide, Legati Andrea, Lamantea Eleonora, Barone Rita, Dorboz Imen, Boespflug-Tanguy Odile, Nebbia Gabriella, Maggioni Marco, Garavaglia Barbara, Moroni Isabella, Farina Laura, Pichiecchio Anna, Orcesi Simona, Chiapparini Luisa, Ghezzi Daniele.

KARS encodes lysyl- transfer ribonucleic acid (tRNA) synthetase, which catalyzes the aminoacylation of tRNA-Lys in the cytoplasm and mitochondria. Eleven families/sporadic patients and 16 different mutations in KARS have been reported to date. The associated clinical phenotype is heterogeneous ranging from early onset encephalopathy to isolated peripheral neuropathy or nonsyndromic hearing impairment. Recently additional presentations including leukoencephalopathy as predominant cerebral involvement or cardiomyopathy, isolated or associated with muscular and cerebral involvement, have been reported. A progressive Leukoencephalopathy with brainstem and spinal cord calcifications was previously described in a singleton patient and in two siblings, without the identification of the genetic cause. We reported here about a new severe phenotype associated with biallelic KARS mutations and sharing some common points with the other already reported phenotypes, but with a distinct clinical and neuroimaging picture. Review of KARS mutant patients published to date will be also discussed.

29666464 An adolescence-onset male leukoencephalopathy with remarkable cerebellar atrophy and novel compound heterozygous AARS2 gene mutations: a case report.
Apr 2018 Journal of human genetics

Dong Qing, Long Ling, Chang Yan-Yu, Lin Yan-Jun, Liu Mei, Lu Zheng-Qi.

Mutations in the mitochondrial alanyl-transfer (t)RNA synthetase 2 (AARS2; OMIM 612035) have been linked to leukoencephalopathy recently. Until now, there have been only 13 cases reported in the literature. Hence, the clinical and genetic characteristics of this disease are not fully understood. Here, we reported an adolescence-onset male leukoencephalopathy patient characterized by progressive limb tremor at the age of 17 years. He had no signs of a cardiomyopathy. Magnetic resonance imaging scanning demonstrated severe cerebellar atrophy and white matter abnormalities involving descending tracts. Focused exome sequencing revealed he had novel compound heterozygous mutations in AARS2 gene (c.2265dupA; p.Arg756fs and c.650C>T; p.Pro217Leu). The patient was diagnosed with AARS2 mutation-related leukodystrophy (AARS2-L). We report a case with novel AARS2 gene mutations with developed striking cerebellar atrophy and leukoencephalopathy, which helps to further understand the clinical and genetic heterogeneity of AARS2-L.

29587458 Towards an Integrative Understanding of tRNA Aminoacylation-Diet-Host-Gut Microbiome Interactions in Neurodegeneration.
Mar 2018 Nutrients

Paley Elena L, Perry George.

Transgenic mice used for Alzheimer's disease (AD) preclinical experiments do not recapitulate the human disease. In our models, the dietary tryptophan metabolite tryptamine produced by human gut microbiome induces tryptophanyl-tRNA synthetase (TrpRS) deficiency with consequent neurodegeneration in cells and mice. Dietary supplements, antibiotics and certain drugs increase tryptamine content in vivo. TrpRS catalyzes tryptophan attachment to tRNAtrp at initial step of protein biosynthesis. Tryptamine that easily crosses the blood-brain barrier induces vasculopathies, neurodegeneration and cell death via TrpRS competitive inhibition. TrpRS inhibitor tryptophanol produced by gut microbiome also induces neurodegeneration. TrpRS inhibition by tryptamine and its metabolites preventing tryptophan incorporation into proteins lead to protein biosynthesis impairment. Tryptophan, a least amino acid in food and proteins that cannot be synthesized by humans competes with frequent amino acids for the transport from blood to brain. Tryptophan is a vulnerable amino acid, which can be easily lost to protein biosynthesis. Some proteins marking neurodegenerative pathology, such as tau lack tryptophan. TrpRS exists in cytoplasmic (WARS) and mitochondrial (WARS2) forms. Pathogenic gene variants of both forms cause TrpRS deficiency with consequent intellectual and motor disabilities in humans. The diminished tryptophan-dependent protein biosynthesis in AD patients is a proof of our model-based disease concept.

29410512 Clinical and molecular characteristics of newly reported mitochondrial disease entity caused by biallelic PARS2 mutations.
Feb 2018 Journal of human genetics

Ciara Elżbieta, Rokicki Dariusz, Lazniewski Michal, Mierzewska Hanna, Jurkiewicz Elżbieta, Bekiesińska-Figatowska Monika, Piekutowska-Abramczuk Dorota, Iwanicka-Pronicka Katarzyna, Szymańska Edyta, Stawiński Piotr, Kosińska Joanna, Pollak Agnieszka, Pronicki Maciej, Plewczyński Dariusz, Płoski Rafał, Pronicka Ewa.

Most of the 19 mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) involved in mitochondrial protein synthesis are already linked to specific entities, one of the exceptions being PARS2 mutations for which pathogenic significance is not finally validated. The aim of the study was to characterize the PARS2- related phenotype.Three siblings with biallelic PARS2 mutations presented from birth with infantile spasms, secondary microcephaly, and similar facial dysmorphy. Mental development was deeply impaired with speech absence and no eye contact. A dilated cardiomyopathy and multiorgan failure developed in childhood at the terminal stage, together with mitochondrial dysfunction triggered by valproate administration.Brain MRI showed progressive volume loss of the frontal lobes, both cortical and subcortical, with widening of the cortical sulci and frontal horns of the lateral ventricles. Hypoplasia of the corpus callosum and progressive demyelination were additional findings. Similar brain features were seen in three already reported PARS2 patients and seemed specific for this defect when compared with other mt-aaRSs defects (DARS2, EARS2, IARS2, and RARS2).Striking resemblance of the phenotype and Alpers-like brain MRI changes with predominance of frontal cerebral volume loss (FCVL-AS) in six patients from three families of different ethnicity with PARS2 mutations, justifies to distinguish the condition as a new disease entity.

29440775 Genetic defects in mtDNA-encoded protein translation cause pediatric, mitochondrial cardiomyopathy with early-onset brain disease.
Feb 2018 European journal of human genetics : EJHG

Kamps Rick, Szklarczyk Radek, Theunissen Tom E, Hellebrekers Debby M E I, Sallevelt Suzanne C E H, Boesten Iris B, de Koning Bart, van den Bosch Bianca J, Salomons Gajja S, Simas-Mendes Marisa, Verdijk Rob, Schoonderwoerd Kees, de Coo Irenaeus F M, Vanoevelen Jo M, Smeets Hubert J M.

This study aims to identify gene defects in pediatric cardiomyopathy and early-onset brain disease with oxidative phosphorylation (OXPHOS) deficiencies. We applied whole-exome sequencing in three patients with pediatric cardiomyopathy and early-onset brain disease with OXPHOS deficiencies. The brain pathology was studied by MRI analysis. In consanguineous patient 1, we identified a homozygous intronic variant (c.850-3A > G) in the QRSL1 gene, which was predicted to cause abnormal splicing. The variant segregated with the disease and affected the protein function, which was confirmed by complementation studies, restoring OXPHOS function only with wild-type QRSL1. Patient 2 was compound heterozygous for two novel affected and disease-causing variants (c.[253G > A];[938G > A]) in the MTO1 gene. In patient 3, we detected one unknown affected and disease-causing variants (c.2872C > T) and one known disease-causing variant (c.1774C > T) in the AARS2 gene. The c.1774C > T variant was present in the paternal copy of the AARS2 gene, the c.2872C > T in the maternal copy. All genes were involved in translation of mtDNA-encoded proteins. Defects in mtDNA-encoded protein translation lead to severe pediatric cardiomyopathy and brain disease with OXPHOS abnormalities. This suggests that the heart and brain are particularly sensitive to defects in mitochondrial protein synthesis during late embryonic or early postnatal development, probably due to the massive mitochondrial biogenesis occurring at that stage. If both the heart and brain are involved, the prognosis is poor with a likely fatal outcome at young age.

29478218 Mitochondrial Encephalopathy: First Portuguese Report of a VARS2 Causative Variant.
Feb 2018 JIMD reports

Pereira Sandra, Adrião Mariana, Sampaio Mafalda, Basto Margarida Ayres, Rodrigues Esmeralda, Vilarinho Laura, Teles Elisa Leão, Alonso Isabel, Leão Miguel.

Combined oxidative phosphorylation deficiency 20 (COXPD20) is a mitochondrial respiratory chain complex (RC) disorder, caused by disease-causing variants in the VARS2 gene, which encodes a mitochondrial aminoacyl-tRNA synthetase. Here we describe a patient with fatal mitochondrial encephalopathy caused by a homozygous VARS2 gene missense variant.

30325133 The first pediatric case of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) from Turkey.
Feb 2018 The Turkish journal of pediatrics

Çavuşoğlu Dilek, Olgaç-Dündar Nihal, Öztekin Özgür, Özdemir Taha Reşid, Arıcan Pınar, Gençpınar Pınar.

Çavuşoğlu D, Olgaç-Dündar N, Öztekin Ö, Özdemir TR, Arıcan P, Gençpınar P. The first pediatric case of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) from Turkey. Turk J Pediatr 2018; 60: 216-220. Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is defined as an autosomal recessive inheritance disorder characterized by slowly progressive cerebellar, pyramidal and dorsal column dysfunction. The diagnosis is based on specific magnetic resonance imaging abnormalities (MRI) in the cerebral and cerebellar white matter and selective involvement of white matter tracts in the brain stem and spinal cord. LBSL is caused by mutations in the DARS2 gene which encodes the mitochondrial aspartyl-tRNA synthetase. Herein, we report the first pediatric case from Turkey with a typical MRI course of LBSL associated with a compound heterozygous mutation in DARS2 gene.

29314548 Clinical, biochemical, and genetic features associated with VARS2-related mitochondrial disease.
Jan 2018 Human mutation

Bruni Francesco, Di Meo Ivano, Bellacchio Emanuele, Webb Bryn D, McFarland Robert, Chrzanowska-Lightowlers Zofia M A, He Langping, Skorupa Ewa, Moroni Isabella, Ardissone Anna, Walczak Anna, Tyynismaa Henna, Isohanni Pirjo, Mandel Hanna, Prokisch Holger, Haack Tobias, Bonnen Penelope E, Enrico Bertini, Pronicka Ewa, Ghezzi Daniele, Taylor Robert W, Diodato Daria.

In recent years, an increasing number of mitochondrial disorders have been associated with mutations in mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs), which are key enzymes of mitochondrial protein synthesis. Bi-allelic functional variants in VARS2, encoding the mitochondrial valyl tRNA-synthetase, were first reported in a patient with psychomotor delay and epilepsia partialis continua associated with an oxidative phosphorylation (OXPHOS) Complex I defect, before being described in a patient with a neonatal form of encephalocardiomyopathy. Here we provide a detailed genetic, clinical, and biochemical description of 13 patients, from nine unrelated families, harboring VARS2 mutations. All patients except one, who manifested with a less severe disease course, presented at birth exhibiting severe encephalomyopathy and cardiomyopathy. Features included hypotonia, psychomotor delay, seizures, feeding difficulty, abnormal cranial MRI, and elevated lactate. The biochemical phenotype comprised a combined Complex I and Complex IV OXPHOS defect in muscle, with patient fibroblasts displaying normal OXPHOS activity. Homology modeling supported the pathogenicity of VARS2 missense variants. The detailed description of this cohort further delineates our understanding of the clinical presentation associated with pathogenic VARS2 variants and we recommend that this gene should be considered in early-onset mitochondrial encephalomyopathies or encephalocardiomyopathies.

29434700 Distinct magnetic resonance imaging features in a patient with novelRARS2mutations: A case report and review of the literature.
Jan 2018 Experimental and therapeutic medicine

Zhang Jie, Zhang Zhongbin, Zhang Yao, Wu Ye.

Pontocerebellar hypoplasia type 6 (PCH6) is a rare autosomal recessive disease that occurs due to mutations in the mitochondrial arginyl-tRNA synthetase 2 (RARS2) gene. To the best of our knowledge, 23 cases with relatively complete clinical data have been reported thus far. In the present study, a case with PCH6 caused by novel RARS2 mutations is described, in which distinct magnetic resonance imaging (MRI) features were identified. In addition, 23 PCH6 cases found in the literature were reviewed. Early onset hypotonia (43.48%), epileptic seizures (34.78%), encephalopathy (26.08%) and feeding difficulties (17.39%) were common initial symptoms of PCH6. During disease progression, the patients presented refractory epileptic seizures (94.12%), feeding problems (60.87%), severe developmental delay (100%), microcephaly (88.89%) and hyperlactacidemia (76.47%). The clinical features of the present patient were suggestive of PCH6, with early onset epilepsy, feeding difficulties, severe developmental delay, microcephaly, hearing loss and hyperlactacidemia. According to available MRI data from 20 reported cases with PCH6, the characteristic finding in MRI was pontocerebellar dysplasia or progressive cerebral/pontocerebellar atrophy in 16 cases, while 4 cases did not present pontocerebellar hypoplasia, and no basal ganglia involvement was observed in any of the cases. Distinctive MRI features were also identified in the present case, including pontocerebellar preservation after 1 year of age, as well as a high diffusion-weighted imaging signal suggesting intracellular edema in the cerebellar hemispheres, basal ganglia, thalamus and corpus callosum. Progressive loss of cerebral white matter and cortical volume were common features shared by all patients. In conclusion, in the present study, two novel heterozygous mutations were identified in RARS2, namely c.1718C>T(p.Thr573Ile) and c.991A>G (p.Ile331Val). Thus, the present case enriched the phenotypic and genotypic spectrum of the RARS2 mutations.

30272204 AARS2 Compound Heterozygous Variants in a Case of Adult-Onset Leukoencephalopathy With Axonal Spheroids and Pigmented Glia.
11 2018 Journal of neuropathology and experimental neurology

Wang Danqing, Yu Meng, Zhang Wei, Wang Zhaoxia, Yuan Yun.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), usually referred to as hereditary diffuse leukoencephalopathy with spheroids or pigmentary orthochromatic leukodystrophy, is genetically caused by CSF1R mutations. AARS2 was recently confirmed to be another causative gene in a series of CSF1R-negative ALSP cases. We report a case of adult-onset leukoencephalopathy with ALSP with AARS2 variants. A 34-year-old woman presented with 2 years of motor and cognitive deterioration with severely impaired cortical functions and rigid spasticity. Brain magnetic resonance imaging showed a confluent, patchy, and predominantly frontoparietal, periventricular pattern of white matter lesions, with relatively preserved subcortical U-fibers. Brain biopsy revealed axonal spheroids, severe demyelination and pigmented macrophages. Genetic analyses revealed compound heterozygous c.1691T>C and c.179C>A variants in the AARS2 gene. CSF1R mutation testing was negative. Our findings proved adult-onset leukoencephalopathy with spheroids and pigmented glia to be a genetically heterogeneous disease entity. The selective brain involvement without ovarian failure might be a new subtype in AARS2 mutations related to ALSP.

29976739 Sideroblastic anemia with myopathy secondary to novel, pathogenic missense variants in the YARS2 gene.
12 2018 Haematologica

Smith Frances, Hopton Sila, Dallabona Cristina, Gilberti Micol, Falkous Gavin, Norwood Fiona, Donnini Claudia, Gorman Gráinne S, Clark Barnaby, Taylor Robert W, Kulasekararaj Austin G.

29205794 Biallelic mutations in LARS2 can cause Perrault syndrome type 2 with neurologic symptoms.
Dec 2017 American journal of medical genetics. Part A

Kosaki Rika, Horikawa Reiko, Fujii Eriko, Kosaki Kenjiro.

Perrault syndrome represents a genetically heterogeneous disorder characterized by sensorineural hearing loss in males and females and ovarian dysfunction in females. Causative genes include HARS2, HSD17B4, CLPP, C10orf2, and LARS2. Some patients with Perrault syndrome exhibit neurologic features including learning disability, cerebellar ataxia, and peripheral neuropathy and are classified as type 2 and are clinically separate from those without neurological symptoms other than a hearing loss (type 1). To date, all reported patients with LARS2 mutations (15 patients in 8 families) have been classified as type 1. Here, we report female siblings with biallelic mutations in LARS2, p.Glu294Lys, and p.Thr519Met, who were classified as type 2. The proposita developed progressive sensorineural hearing loss at 18 months and pervasive developmental disorder at 8 years, with repetitive behavior, insistence on sameness, attention deficit, tic, irritability, and an ataxic gait. At age 15 years, she was diagnosed as having primary amenorrhea with elevated FSH and LH and a decreased estradiol; ultrasound and magnetic resonance imaging examinations revealed a small uterus and no detectable ovaries. The proposita's younger sister presented with neonatal sensorineural hearing loss and a mild delay in motor and speech development. She was diagnosed as having primary amenorrhea with endocrinologic and radiographic findings that were comparable to those of her sister. She had difficulty with reading comprehension, and had trouble with open-ended test questions at 12 years of age. We concluded that Perrault syndrome patients with LARS2 mutations are at risk for neurologic problems, despite previous notions otherwise.

29288497 The role of tRNA synthetases in neurological and neuromuscular disorders.
Dec 2017 FEBS letters

Boczonadi Veronika, Jennings Matthew J, Horvath Rita.

Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed enzymes responsible for charging tRNAs with their cognate amino acids, therefore essential for the first step in protein synthesis. Although the majority of protein synthesis happens in the cytosol, an additional translation apparatus is required to translate the 13 mitochondrial DNA-encoded proteins important for oxidative phosphorylation. Most ARS genes in these cellular compartments are distinct, but two genes are common, encoding aminoacyl-tRNA synthetases of glycine (GARS) and lysine (KARS) in both mitochondria and the cytosol. Mutations in the majority of the 37 nuclear-encoded human ARS genes have been linked to a variety of recessive and dominant tissue-specific disorders. Current data indicate that impaired enzyme function could explain the pathogenicity, however not all pathogenic ARSs mutations result in deficient catalytic function; thus, the consequences of mutations may arise from other molecular mechanisms. The peripheral nerves are frequently affected, as illustrated by the high number of mutations in cytosolic and bifunctional tRNA synthetases causing Charcot-Marie-Tooth disease (CMT). Here we provide insights on the pathomechanisms of CMT-causing tRNA synthetases with specific focus on the two bifunctional tRNA synthetases (GARS, KARS).

29120065 Biallelic Mutations in Mitochondrial Tryptophanyl-tRNA Synthetase Cause Levodopa-Rresponsive Infantile-Onset Parkinsonism.
Nov 2017 Clinical genetics

Burke E A, Frucht S J, Thompson K, Wolfe L A, Yokoyama T, Bertoni M, Huang Y, Sincan M, Adams D R, Taylor R W, Gahl W A, Toro C, Malicdan M C V.

Mitochondrial aminoacyl-tRNA synthetases (mtARSs) are essential, ubiquitously expressed enzymes that covalently attach amino acids to their corresponding tRNA molecules during translation of mitochondrial genes. Deleterious variants in the mtARS genes cause a diverse array of phenotypes, many of which involve the nervous system. Moreover, distinct mutations in mtARSs often cause different clinical manifestations. Recently, the gene encoding mitochondrial tryptophanyl tRNA synthetase (WARS2) was reported to cause two different neurological phenotypes, a form of autosomal recessive intellectual disability and a syndrome of severe infantile-onset leukoencephalopathy. Here, we present the case of a 17 year-old boy with compound heterozygous mutations in WARS2 (p.Trp13Gly, p.Ser228Trp) who presented with infantile-onset, Levodopa responsive parkinsonism at the age of 2 years. Analysis of patient-derived dermal fibroblasts revealed decreased steady state WARS2 protein and normal OXPHOS content. Muscle mitochondrial studies suggested mitochondrial proliferation without obvious respiratory chain deficiencies at age 9 years. This case expands the phenotypic spectrum of WARS2 deficiency and emphasizes the importance of mitochondrial protein synthesis in the pathogenesis of parkinsonism.

29126765 New insights into the phenotype of FARS2 deficiency.
Oct 2017 Molecular genetics and metabolism

Vantroys Elise, Larson Austin, Friederich Marisa, Knight Kaz, Swanson Michael A, Powell Christopher A, Smet Joél, Vergult Sarah, De Paepe Boel, Seneca Sara, Roeyers Herbert, Menten Björn, Minczuk Michal, Vanlander Arnaud, Van Hove Johan, Van Coster Rudy.

Mutations in FARS2 are known to cause dysfunction of mitochondrial translation due to deficient aminoacylation of the mitochondrial phenylalanine tRNA. Here, we report three novel mutations in FARS2 found in two patients in a compound heterozygous state. The missense mutation c.1082C>T (p.Pro361Leu) was detected in both patients. The mutations c.461C>T (p.Ala154Val) and c.521_523delTGG (p.Val174del) were each detected in one patient. We report abnormal in vitro aminoacylation assays as a functional validation of the molecular genetic findings. Based on the phenotypic data of previously reported subjects and the two subjects reported here, we conclude that FARS2 deficiency can be associated with two phenotypes: (i) an epileptic phenotype, and (ii) a spastic paraplegia phenotype.

28887846 Mutations in KARS cause early-onset hearing loss and leukoencepha lopathy: Potential pathogenic mechanism.
Sep 2017 Human mutation

Zhou Xiao-Long, He Long-Xia, Yu Li-Jia, Wang Yong, Wang Xi-Jin, Wang En-Duo, Yang Tao.

Leukoencephalopathies are a broad class of common neurologic deterioration for which the etiology remain unsolved in many cases. In a Chinese Han family segregated with sensorineural hearing loss and leukoencephalopathy, candidate pathogenic variants were identified by targeted next-generation sequencing of 144 genes associated with deafness and 108 genes with leukoencephalopathy. Novel compound heterozygous mutations p.R477H and p.P505S were identified in KARS, which encodes lysyl-tRNA synthetase (LysRS), as the only candidate causative variants. These two mutations were functionally characterized by enzymatic assays, immunofluorescence, circular dichroism analysis and gel filtration chromatography. Despite no alteration in the dimer-tetramer oligomerization and cellular distribution by either mutation, the protein structure was notably influenced by the R477H mutation, which subsequently released the protein from the multiple-synthetase complex (MSC). Mutant LysRSs with the R477H and P505S mutations had decreased tRNA(Lys) aminoacylation and displayed a cumulative effect when introduced simultaneously. Our studies showed that mutations in KARS lead to a newly defined subtype of leukoencephalopathy associated with sensorineural hearing impairment. The combined effect of reduced aminoacylation and release of LysRS from the MSC likely underlies the pathogenesis of the KARS mutations identified in this study. This article is protected by copyright. All rights reserved.

28905505 Biallelic variants in WARS2 encoding mitochondrial tryptophanyl-tRNA synthase in six individuals with mitochondrial encephalopathy.
Sep 2017 Human mutation

Wortmann Saskia B, Timal Sharita, Venselaar Hanka, Wintjes Liesbeth T, Kopajtich Robert, Feichtinger René G, Onnekink Carla, Mühlmeister Mareike, Brandt Ulrich, Smeitink Jan A, Veltman Joris A, Sperl Wolfgang, Lefeber Dirk, Pruijn Ger, Stojanovic Vesna, Freisinger Peter, V Spronsen Francjan, Derks Terry Gj, Veenstra-Knol Hermine E, Mayr Johannes A, Rötig Agnes, Tarnopolsky Mark, Prokisch Holger, Rodenburg Richard J.

Mitochondrial protein synthesis involves an intricate interplay between mitochondrial DNA encoded RNAs and nuclear DNA encoded proteins, such as ribosomal proteins and aminoacyl-tRNA synthases. Eukaryotic cells contain 17 mitochondria-specific aminoacyl-tRNA synthases. WARS2 encodes mitochondrial tryptophanyl-tRNA synthase (mtTrpRS), a homodimeric class Ic enzyme (mitochondrial tryptophan-tRNA ligase; EC 6.1.1.2). Here, we report six individuals from five families presenting with either severe neonatal onset lactic acidosis, encephalomyopathy and early death or a later onset, more attenuated course of disease with predominating intellectual disability. Respiratory chain enzymes were usually normal in muscle and fibroblasts, while a severe combined respiratory chain deficiency was found in the liver of a severely affected individual. Exome sequencing revealed rare biallelic variants in WARS2 in all affected individuals. An increase of uncharged mitochondrial tRNA(Trp) and a decrease of mtTrpRS protein content were found in fibroblasts of affected individuals. We hereby define the clinical, neuroradiological and metabolic phenotype of WARS2 defects. This confidently implicates that mutations in WARS2 cause mitochondrial disease with a broad spectrum of clinical presentation. This article is protected by copyright. All rights reserved.

28822227 Inborn errors of metabolism in a cohort of pregnancies with non-immune hydrops fetalis: a single center experience.
Aug 2017 Journal of perinatal medicine

Bruwer Zandrè, Al Riyami Nihal, Al Dughaishi Tamima, Al Murshedi Fathiya, Al Sayegh Abeer, Al Kindy Adila, Meftah Douja, Al Kharusi Khalsa, Al Foori Amel, Al Yarubi Naeema, Scott Patrick, Al-Thihli Khalid.

The purpose of this study was to determine the frequency of non-immune hydrops fetalis (NIHF) among all pregnancies referred for prenatal care at Sultan Qaboos University Hospital (SQUH) during the study period and to evaluate the underlying etiologies of NIH.

28820624 Retinopathy and optic atrophy: Expanding the phenotypic spectrum of pathogenic variants in the AARS2 gene.
Aug 2017 Ophthalmic genetics

Peragallo Jason H, Keller Stephanie, van der Knaap Marjo S, Soares Bruno P, Shankar Suma P.

Optic atrophy may be the sequela of optic nerve injury due to any insult, including isolated and syndromic genetic diseases. Alanyl-tRNA synthetase 2 (AARS2) pathogenic variants have been reported to cause leukodystrophy with ovarian failure, and cardiomyopathy (#615889) as well as combined oxidative phosphorylation deficiency-8 (#614096). We report a young child who presented with decreased vision due to optic atrophy and was found to harbor missense variants in the AARS2 gene expanding the phenotypic expression of the AARS2 gene.

28832386 Marfanoid habitus is a nonspecific feature of Perrault syndrome.
Aug 2017 Clinical dysmorphology

Zerkaoui Maria, Demain Leigh A M, Cherkaoui Jaouad Imane, Ratbi Ilham, Amjoud Karima, Urquhart Jill E, O'Sullivan James, Newman William G, Sefiani Abdelaziz.

The objective of this study was to report the clinical and biological characteristics of two Perrault syndrome cases in a Moroccan family with homozygous variant c.1565C>A in the LARS2 gene and to establish genotype-phenotype correlation of patients with the same mutation by review of the literature. Whole-exome sequencing was performed. Data analysis was carried out and confirmed by Sanger sequencing and segregation. The affected siblings were diagnosed as having Perrault syndrome with sensorineural hearing loss at low frequencies; the female proband had primary amenorrhea and ovarian dysgenesis. Both affected individuals had a marfanoid habitus and no neurological features. Both patients carried the homozygous variant c.1565C>A; p.Thr522Asn in exon 13 of the LARS2 gene. This variant has already been reported as a homozygous variant in three other Perrault syndrome families. Both affected siblings of a Moroccan consanguineous family with LARS2 variants had low-frequency sensorineural hearing loss, marfanoid habitus, and primary ovarian insufficiency in the affected girl. According to the literature, this variant, c.1565C>A; p.Thr522Asn, can be correlated with low-frequency hearing loss. However, marfanoid habitus was been considered a nonspecific feature in Perrault syndrome, but we believe that it may be more specific than considered previously. This diagnosis allowed us to provide appropriate management to the patients and to provide more accurate genetic counseling to this family.

28985337 DARS2 protects against neuroinflammation and apoptotic neuronal loss, but is dispensable for myelin producing cells.
Aug 2017 Human molecular genetics

Aradjanski Marijana, Dogan Sukru Anil, Lotter Stephan, Wang Shuaiyu, Hermans Steffen, Wibom Rolf, Rugarli Elena, Trifunovic Aleksandra.

Although mitochondria are ubiquitous, each mitochondrial disease has surprisingly distinctly different pattern of tissue and organ involvement. Congruently, mutations in genes encoding for different mitochondrial tRNA synthetases result in the development of a very flamboyant group of diseases. Mutations in some of these genes, including aspartyl-tRNA synthetase (DARS2), lead to the onset of a white matter disease-leukoencephalopathy with brainstem and spinal cord involvement, and lactate elevation (LBSL) characterized by progressive spastic ataxia and characteristic leukoencephalopathy signature with multiple long-tract involvements. Puzzled by the white matter disease phenotypes caused by DARS2 deficiency when numerous other mutations in the genes encoding proteins involved in mitochondrial translation have a detrimental effect predominantly on neurons, we generated transgenic mice in which DARS2 was specifically depleted in forebrain-hippocampal neurons or myelin-producing cells. Our results now provide the first evidence that loss of DARS2 in adult neurons leads to strong mitochondrial dysfunction and progressive loss of cells. In contrast, myelin-producing cells seem to be resistant to cell death induced by DARS2 depletion despite robust respiratory chain deficiency arguing that LBSL might originate from the primary neuronal and axonal defect. Remarkably, our results also suggest a role for early neuroinflammation in the disease progression, highlighting the possibility for therapeutic interventions of this process.

28675565 Compound heterozygosity for loss-of-function GARS variants results in a multi-system developmental syndrome that includes severe growth retardation.
Jul 2017 Human mutation

Oprescu Stephanie N, Chepa-Lotrea Xenia, Takase Ryuichi, Golas Gretchen, Markello Thomas C, Adams David R, Toro Camilo, Gropman Andrea L, Hou Ya-Ming, Malicdan May Christine V, Gahl William A, Tifft Cynthia J, Antonellis Anthony.

Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed enzymes that ligate amino acids onto tRNA molecules. Genes encoding ARSs have been implicated in myriad dominant and recessive disease phenotypes. Glycyl-tRNA synthetase (GARS) is a bi-functional ARS that charges tRNA(Gly) in the cytoplasm and mitochondria. GARS variants have been associated with dominant Charcot-Marie-Tooth disease but have not been convincingly implicated in recessive phenotypes. Here we describe a patient from the NIH Undiagnosed Diseases Program with a multi-system, developmental phenotype. Whole-exome sequence analysis revealed that the patient is compound heterozygous for one frameshift (p.Glu83Ilefs*6) and one missense (p.Arg310Gln) GARS variant. Using in vitro and in vivo functional studies, we show that both GARS variants cause a loss-of-function effect: the frameshift variant results in depleted protein levels and the missense variant reduces GARS tRNA charging activity. In support of GARS variant pathogenicity, our patient shows striking phenotypic overlap with other patients having ARS-related recessive diseases, including features associated with variants in both cytoplasmic and mitochondrial ARSs; this observation is consistent with the essential function of GARS in both cellular locations. In summary, our clinical, genetic, and functional analyses expand the phenotypic spectrum associated with GARS variants. This article is protected by copyright. All rights reserved.

28716624 Mitochondrial Aminoacyl-tRNA Synthetases in Human Disease.
Jul 2017 Trends in molecular medicine

Sissler Marie, González-Serrano Ligia Elena, Westhof Eric.

Dysfunctions in mitochondria - the powerhouses of the cell - lead to several human pathologies. Because mitochondria integrate nuclear and mitochondrial genetic systems, they are richly intertwined with cellular activities. The nucleus-encoded mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs) are key components of the mitochondrial translation apparatus. Mutations in these enzymes predominantly affect the central nervous system (CNS) but also target other organs. Comparable mutations in mt-aaRSs can lead to vastly diverse diseases, occurring at different stages in life, and within different tissues; this represents a confounding issue. With newer information available, we propose that the pleiotropy and tissue-specificity of mt-aaRS-associated diseases result from the molecular integration of mitochondrial translation events within the cell; namely, through specific crosstalk between the cellular program and the energy demands of the cell. We place particular focus on neuronal cells.

28496994 Novel Causative Variants in DYRK1A, KARS, and KAT6A Associated with Intellectual Disability and Additional Phenotypic Features.
Jun 2017 Journal of pediatric genetics

Murray Clark R, Abel Samantha N, McClure Matthew B, Foster Joseph, Walke Maria I, Jayakar Parul, Bademci Guney, Tekin Mustafa.

Patients with unclear patterns of developmental and cognitive delay may go years without a definitive diagnosis despite extensive testing due to overlapping phenotypes of many genetic disorders. In this study, we identified causative variants in DYRK1A, KARS, or KAT6A in four individuals with global developmental delay and various findings including microcephaly and sensorineural hearing loss using whole exome sequencing. We present the cognitive, neurologic, and physical findings of four individuals to expand the clinical knowledge of possible features of the phenotypes of three rare genetic disorders. Through this process, we provide support for the use of whole exome sequencing in the setting of severe, intellectual disability or in those in whom a genetic disorder is suspected despite initial negative testing.

28650581 Deficiency of WARS2, encoding mitochondrial tryptophanyl tRNA synthetase, causes severe infantile onset leukoencephalopathy.
Jun 2017 American journal of medical genetics. Part A

Theisen Benjamin E, Rumyantseva Anastasia, Cohen Julie S, Alcaraz Wendy A, Shinde Deepali N, Tang Sha, Srivastava Siddarth, Pevsner Jonathan, Trifunovic Aleksandra, Fatemi Ali.

Pathogenic variants in the mitochondrial aminoacyl tRNA synthetases lead to deficiencies in mitochondrial protein synthesis and are associated with a broad range of clinical presentations usually with early onset and inherited in an autosomal recessive manner. Of the 19 mitochondrial aminoacyl tRNA synthetases, WARS2, encoding mitochondrial tryptophanyl tRNA synthetase, was as of late the only one that had not been associated with disease in humans. A case of a family with pathogenic variants in WARS2 that caused mainly intellectual disability, speech impairment, aggressiveness, and athetosis was recently reported. Here we substantially extend and consolidate the symptomatology of WARS2 by presenting a patient with severe infantile-onset leukoencephalopathy, profound intellectual disability, spastic quadriplegia, epilepsy, microcephaly, short stature, failure to thrive, cerebral atrophy, and periventricular white matter abnormalities. He was found by whole-exome sequencing to have compound heterozygous variants in WARS2, c.938A>T (p.K313M) and c.298_300delCTT (p.L100del). De novo synthesis of proteins inside mitochondria was reduced in the patient's fibroblasts, leading to significantly lower steady-state levels of respiratory chain subunits compared to control and resulting in lower oxygen consumption rates.

28431594 Phenotypic spectrum of DARS2 mutations.
May 2017 Journal of the neurological sciences

Finsterer Josef, Zarrouk-Mahjoub Sinda.

28534666 Human aminoacyl-tRNA synthetases in diseases of the nervous system.
May 2017 RNA biology

Ognjenović Jana, Simonović Miljan.

Aminoacyl-tRNA synthetases (AaRSs) are ubiquitously expressed enzymes that ensure accurate translation of the genetic information into functional proteins. These enzymes also execute a variety of non-canonical functions that are significant for regulation of diverse cellular processes and that reside outside the realm of protein synthesis. Associations between faults in AaRS-mediated processes and human diseases have been long recognized. Most recent research findings strongly argue that 10 cytosolic and 14 mitochondrial AaRSs are implicated in some form of pathology of the human nervous system. The advent of modern whole-exome sequencing makes it all but certain that similar associations between the remaining 15 ARS genes and neurological illnesses will be defined in future. It is not surprising that an intense scientific debate about the role of translational machinery, in general, and AaRSs, in particular, in the development and maintenance of the healthy human neural cell types and the brain is sparked. Herein, we summarize the current knowledge about causative links between mutations in human AaRSs and diseases of the nervous system and briefly discuss future directions.

27875839 Severe Metabolic Acidosis and Hepatopathy due to Leukoencephalopathy with Thalamus and Brainstem Involvement and High Lactate.
Apr 2017 Neuropediatrics

Sellars Elizabeth A, Balmakund Tonya, Bosanko Katherine, Nichols Brandi L, Kahler Stephen G, Zarate Yuri A.

Leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL) is a recently described autosomal recessive mitochondrial disease characterized by early onset of neurological symptoms, a biphasic clinical course, and distinctive neuroimaging. Pathogenic variants in the EARS2 gene that encode for mitochondrial glutamyl-tRNA synthetase are responsible for LTBL. Here, we describe the clinical course of an infant diagnosed with an acute crisis of LTBL and severe liver disease. This article illustrates the utility of blood lactate quantification in addition to basic metabolic testing and brain imaging in a child with low tone and poor growth. In addition, this case demonstrates the utility of current genetic diagnostic testing, in lieu of more invasive procedures, in obtaining rapid answers in this very complicated group of disorders.

28243630 Redefining the phenotype of ALSP and AARS2 mutation-related leukodystrophy.
Apr 2017 Neurology. Genetics

Lakshmanan Rahul, Adams Matthew E, Lynch David S, Kinsella Justin A, Phadke Rahul, Schott Jonathan M, Murphy Elaine, Rohrer Jonathan D, Chataway Jeremy, Houlden Henry, Fox Nick C, Davagnanam Indran.

To provide an overview of the phenotype of 2 clinically, radiologically, and pathologically similar leukodystrophies, adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) and alanyl-transfer RNA synthetase 2 mutation-related leukodystrophy (AARS2-L), and highlight key differentiating features.

28328135 Confirmation of CAGSSS syndrome as a distinct entity in a Danish patient with a novel homozygous mutation in IARS2.
Apr 2017 American journal of medical genetics. Part A

Moosa Shahida, Haagerup Annette, Gregersen Pernille Axel, Petersen Karin Kastberg, Altmüller Janine, Thiele Holger, Nürnberg Peter, Cho Tae-Joon, Kim Ok-Hwa, Nishimura Gen, Wollnik Bernd, Vogel Ida.

Since the original description of the IARS2-related cataracts, growth hormone deficiency, sensory neuropathy, sensorineural hearing loss, skeletal dysplasia syndrome (CAGSSS; OMIM 616007) in an extended consanguineous family of French-Canadian descent, no further patients have been reported. IARS2 (OMIM 612801) encodes the mitochondrial isoleucine-tRNA synthetase which belongs to the class-I aminoacyl-tRNA synthetase family, and has been implicated in CAGSSS and a form of Leigh syndrome. Here, we report on a female Danish patient with a novel homozygous IARS2 mutation, p.Gly874Arg, who presented at birth with bilateral hip dislocation and short stature. At 3 months, additional dysmorphic features were noted and at 18 months her radiographic skeletal abnormalities were suggestive of an underlying spondyloepimetaphyseal dysplasia (SEMD). Retrospective analysis of the neonatal radiographs confirmed that the skeletal changes were present at birth. It was only with time that several of the other manifestations of the CAGSSS emerged, namely, cataracts, peripheral neuropathy, and hearing loss. Growth hormone deficiency has not (yet) manifested. We present her clinical features and particularly highlight her skeletal findings, which confirm the presence of a primary SEMD skeletal dysplasia in a growing list of mitochondrial-related disorders including CAGSSS, CODAS, EVEN-PLUS, and X-linked SEMD-MR syndromes.

28322004 Two Korean siblings with recently described ovarioleukodystrophy related to AARS2 mutations.
Apr 2017 European journal of neurology

Lee J-M, Yang H-J, Kwon J-H, Kim W-J, Kim S-Y, Lee E-M, Park J-Y, Weon Y C, Park S H, Gwon B-J, Ryu J-C, Lee S-T, Kim H-J, Jeon B.

28395030 Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy.
Apr 2017 JAMA neurology

Sommerville Ewen W, Ng Yi Shiau, Alston Charlotte L, Dallabona Cristina, Gilberti Micol, He Langping, Knowles Charlotte, Chin Sophie L, Schaefer Andrew M, Falkous Gavin, Murdoch David, Longman Cheryl, de Visser Marianne, Bindoff Laurence A, Rawles John M, Dean John C S, Petty Richard K, Farrugia Maria E, Haack Tobias B, Prokisch Holger, McFarland Robert, Turnbull Douglass M, Donnini Claudia, Taylor Robert W, Gorman Gráinne S.

YARS2 mutations have been associated with a clinical triad of myopathy, lactic acidosis, and sideroblastic anemia in predominantly Middle Eastern populations. However, the identification of new patients expands the clinical and molecular spectrum of mitochondrial disorders.

28419689 Kinetic and structural changes in HsmtPheRS, induced by pathogenic mutations in human FARS2.
Apr 2017 Protein science : a publication of the Protein Society

Kartvelishvili Ekaterine, Tworowski Dmitry, Vernon Hilary, Moor Nina, Wang Jing, Wong Lee-Jun, Chrzanowska-Lightowlers Zofia, Safro Mark.

Mutations in the mitochondrial aminoacyl-tRNA synthetases (mtaaRSs) can cause profound clinical presentations, and have manifested as diseases with very selective tissue specificity. To date most of the mtaaRS mutations could be phenotypically recognized, such that clinicians could identify the affected mtaaRS from the symptoms alone. Among the recently reported pathogenic variants are point mutations in FARS2 gene, encoding the human mitochondrial PheRS. Patient symptoms range from spastic paraplegia to fatal infantile Alpers encephalopathy. How clinical manifestations of these mutations relate to the changes in three-dimensional structures and kinetic characteristics remains unclear, although impaired aminoacylation has been proposed as possible etiology of diseases. Here, we report four crystal structures of HsmtPheRS mutants, and extensive MD simulations for wild-type and nine mutants to reveal the structural changes on dynamic trajectories of HsmtPheRS. Using steady-state kinetic measurements of phenylalanine activation and tRNA(Phe) aminoacylation, we gained insight into the structural and kinetic effects of mitochondrial disease-related mutations in FARS2 gene.

27862672 Clinical and genetic spectra of Charcot-Marie-Tooth disease in Chinese Han patients.
Mar 2017 Journal of the peripheral nervous system : JPNS

Sun Bo, Chen Zhaohui, Ling Li, Yang Fei, Huang Xusheng.

Charcot-Marie-Tooth disease (CMT) is a common hereditary motor and sensory neuropathy. Epidemiological data for Chinese CMT patients are few. This study aimed to analyze the electrophysiological and genetic characteristics of Chinese Han patients. A total of 106 unrelated patients with the clinical diagnosis of CMT were included. Clinical examination, nerve conduction studies (NCS), next-generation sequencing (NGS), and bioinformatic analyses were performed. Genetic testing was performed for 82 patients; 27 (33%) patients carried known CMT-associated gene mutations. PMP22 duplication was detected in 10 (12%) patients and GJB1 mutations in 9 (11%) patients. The mutation rate was higher in patients with a positive family history than in the sporadic cases (50% vs. 27%, p < 0.05). Six novel CMT-associated gene mutations including BSCL2 (c.461C>T), LITAF (c.32C>G), MFN2 (c.497C>T), GARS (c.794C>T), NEFL (c.280C>T), and MPZ (c.440T>C) were discovered. All except the LITAF (c.32C>G) mutation were identified as "disease causing" via bioinformatic analyses. In this Chinese Han population, the frequency of PMP22 gene duplication in those with CMT1 was slightly (50% vs. 70%-80%) less than in Western/Caucasian populations. The novel CMT-associated gene mutations broaden the mutation diversity of CMT1. NGS should be considered for genetic analyses in CMT patients.

28263850 Laser-capture micro dissection combined with next-generation sequencing analysis of cell type-specific deafness gene expression in the mouse cochlea.
Mar 2017 Hearing research

Nishio Shin-Ya, Takumi Yutaka, Usami Shin-Ichi.

Cochlear implantation (CI), which directly stimulates the cochlear nerves, is the most effective and widely used medical intervention for patients with severe to profound sensorineural hearing loss. The etiology of the hearing loss is speculated to have a major influence of CI outcomes, particularly in cases resulting from mutations in genes preferentially expressed in the spiral ganglion region. To elucidate precise gene expression levels in each part of the cochlea, we performed laser-capture micro dissection in combination with next generation-sequencing analysis and determined the expression levels of all known deafness-associated genes in the organ of Corti, spiral ganglion, lateral wall, and spiral limbs. The results were generally consistent with previous reports based on immunocytochemistry or in situ hybridization. As a notable result, the genes associated with many kinds of syndromic hearing loss (such as Clpp, Hars2, Hsd17b4, Lars2 for Perrault syndrome, Polr1c and Polr1d for Treacher Collins syndrome, Ndp for Norrie Disease, Kal for Kallmann syndrome, Edn3 and Snai2 for Waardenburg Syndrome, Col4a3 for Alport syndrome, Sema3e for CHARGE syndrome, Col9a1 for Sticker syndrome, Cdh23, Cib2, Clrn1, Pcdh15, Ush1c, Ush2a, and Whrn for Usher syndrome and Wfs1 for wolfram syndrome) showed higher levels of expression in the spiral ganglion than in other parts of the cochlea. This dataset will provide a base for more detailed analysis in order to clarify gene functions in the cochlea as well as predict CI outcomes based on gene expression data.

28334938 Clinical and genetic characterization of leukoencephalopathies in adults.
Mar 2017 Brain : a journal of neurology

Lynch David S, Rodrigues Brandão de Paiva Anderson, Zhang Wei Jia, Bugiardini Enrico, Freua Fernando, Tavares Lucato Leandro, Macedo-Souza Lucia Inês, Lakshmanan Rahul, Kinsella Justin A, Merwick Aine, Rossor Alexander M, Bajaj Nin, Herron Brian, McMonagle Paul, Morrison Patrick J, Hughes Deborah, Pittman Alan, Laur Matilde, Reilly Mary M, Warren Jason D, Mummery Catherine J, Schott Jonathan M, Adams Matthew, Fox Nick C, Murphy Elaine, Davagnanam Indran, Kok Fernando, Chataway Jeremy, Houlden Henry.

Leukodystrophies and genetic leukoencephalopathies are a rare group of disorders leading to progressive degeneration of cerebral white matter. They are associated with a spectrum of clinical phenotypes dominated by dementia, psychiatric changes, movement disorders and upper motor neuron signs. Mutations in at least 60 genes can lead to leukoencephalopathy with often overlapping clinical and radiological presentations. For these reasons, patients with genetic leukoencephalopathies often endure a long diagnostic odyssey before receiving a definitive diagnosis or may receive no diagnosis at all. In this study, we used focused and whole exome sequencing to evaluate a cohort of undiagnosed adult patients referred to a specialist leukoencephalopathy service. In total, 100 patients were evaluated using focused exome sequencing of 6100 genes. We detected pathogenic or likely pathogenic variants in 26 cases. The most frequently mutated genes were NOTCH3, EIF2B5, AARS2 and CSF1R. We then carried out whole exome sequencing on the remaining negative cases including four family trios, but could not identify any further potentially disease-causing mutations, confirming the equivalence of focused and whole exome sequencing in the diagnosis of genetic leukoencephalopathies. Here we provide an overview of the clinical and genetic features of these disorders in adults.

28202951 Erratum: PARS2 and NARS2 mutations in infantile-onset neurodegenerative disorder.
Feb 2017 Journal of human genetics

Mizuguchi Takeshi, Nakashima Mitsuko, Kato Mitsuhiro, Yamada Keitaro, Okanishi Tohru, Ekhilevitch Nina, Mandel Hanna, Eran Ayelet, Toyono Miyuki, Sawaishi Yukio, Motoi Hirotaka, Shiina Masaaki, Ogata Kazuhiro, Miyatake Satoko, Miyake Noriko, Saitsu Hirotomo, Matsumoto Naomichi.

28236339 Mutations of the aminoacyl-tRNA-synthetases SARS and WARS2 are implicated in the aetiology of autosomal recessive intellectual disability.
Feb 2017 Human mutation

Musante Luciana, Püttmann Lucia, Kahrizi Kimia, Garshasbi Masoud, Hu Hao, Stehr Henning, Lipkowitz Bettina, Otto Sabine, Jensen Lars R, Tzschach Andreas, Jamali Payman, Wienker Thomas, Najmabadi Hossein, Ropers Hans Hilger, Kuss Andreas W.

Intellectual disability (ID) is the hallmark of an extremely heterogeneous group of disorders that comprises a wide variety of syndromic and non-syndromic phenotypes. Here we report on mutations in two aminoacyl-tRNA synthetases that are associated with ID in two unrelated Iranian families. In the first family, we identified a homozygous missense mutation (c.514G>A, p.Asp172Asn) in the cytoplasmic seryl-tRNA synthetase (SARS) gene. The mutation affects the enzymatic core domain of the protein and impairs its enzymatic activity, probably leading to reduced cytoplasmic tRNA(Ser) concentrations. The mutant protein was predicted to be unstable, which could be substantiated by investigating ectopic mutant SARS in transfected HEK293T cells. In the second family, we found a compound heterozygous genotype of the mitochondrial tryptophanyl-tRNA synthetase (WARS2) gene, comprising a nonsense mutation (c.325delA, p.Ser109Alafs*15), which very likely entails nonsense-mediated mRNA decay, and a missense mutation (c.37T>G, p.Trp13Gly). The latter affects the mitochondrial localization signal of WARS2, causing protein mislocalization. Including AIMP1, which we have recently implicated in the aetiology of ID, three genes with a role in tRNA-aminoacylation are now associated with this condition. We therefore suggest that the functional integrity of tRNAs in general is an important factor in the development and maintenance of human cognitive functions. This article is protected by copyright. All rights reserved.

28017220 Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) with a novel DARS2 mutation and isolated progressive spastic paraparesis.
Jan 2017 Journal of the neurological sciences

Lan Min-Yu, Chang Yung-Yee, Yeh Tu-Hseuh, Lin Tsu-Kung, Lu Chin-Song.

28077841 PARS2 and NARS2 mutations in infantile-onset neurodegenerative disorder.
Jan 2017 Journal of human genetics

Mizuguchi Takeshi, Nakashima Mitsuko, Kato Mitsuhiro, Yamada Keitaro, Okanishi Tohru, Ekhilevitch Nina, Mandel Hanna, Eran Ayelet, Toyono Miyuki, Sawaishi Yukio, Motoi Hirotaka, Shiina Masaaki, Ogata Kazuhiro, Miyatake Satoko, Miyake Noriko, Saitsu Hirotomo, Matsumoto Naomichi.

Here we present four unrelated families with six individuals that have infantile-onset developmental delay/regression and epilepsy. Whole-exome sequencing revealed compound heterozygous mutations, c.[283G>A];[607G>A] in a gene encoding prolyl-tRNA synthetase (PARS2) in one family. Two pairs of compound heterozygous mutations, c.[151C>T];[1184T>G] and c.[707T>G];[594+1G>A], and a homozygous mutation, c.[500A>G];[500A>G], in a gene encoding asparaginyl-tRNA synthetase (NARS2) were also identified in the other three families. Mutations in genes encoding aminoacyl-tRNA synthetases cause gene-specific mitochondrial disorders. Biallelic PARS2 or NARS2 mutations are reported to cause Alpers' syndrome, which is an autosomal recessive neurodegenerative disorder characterized by psychomotor regression and epilepsy with variable degree of liver involvement. Moreover, it is known that NARS2 mutations cause various clinical phenotypes, including non-syndromic hearing loss, Leigh syndrome, intellectual disability with epilepsy and severe myopathy. The individuals with PARS2 and NARS2 mutations, we have reported here demonstrate similar neurological features as those previously reported, with diversity in clinical presentation such as hearing loss and seizure type. Our data broaden the clinical and mutational spectrum of PARS2- and NARS2-related disorders.Journal of Human Genetics advance online publication, 12 January 2017; doi:10.1038/jhg.2016.163.

28594869 Compound heterozygous mutations in glycyl-tRNA synthetase (GARS) cause mitochondrial respiratory chain dysfunction.
- 2017 PloS one

Nafisinia Michael, Riley Lisa G, Gold Wendy A, Bhattacharya Kaustuv, Broderick Carolyn R, Thorburn David R, Simons Cas, Christodoulou John.

Glycyl-tRNA synthetase (GARS; OMIM 600287) is one of thirty-seven tRNA-synthetase genes that catalyses the synthesis of glycyl-tRNA, which is required to insert glycine into proteins within the cytosol and mitochondria. To date, eighteen mutations in GARS have been reported in patients with autosomal-dominant Charcot-Marie-Tooth disease type 2D (CMT2D; OMIM 601472), and/or distal spinal muscular atrophy type V (dSMA-V; OMIM 600794). In this study, we report a patient with clinical and biochemical features suggestive of a mitochondrial respiratory chain (MRC) disorder including mild left ventricular posterior wall hypertrophy, exercise intolerance, and lactic acidosis. Using whole exome sequencing we identified compound heterozygous novel variants, c.803C>T; p.(Thr268Ile) and c.1234C>T; p.(Arg412Cys), in GARS in the proband. Spectrophotometric evaluation of the MRC complexes showed reduced activity of Complex I, III and IV in patient skeletal muscle and reduced Complex I and IV activity in the patient liver, with Complex IV being the most severely affected in both tissues. Immunoblot analysis of GARS protein and subunits of the MRC enzyme complexes in patient fibroblast extracts showed significant reduction in GARS protein levels and Complex IV. Together these studies provide evidence that the identified compound heterozygous GARS variants may be the cause of the mitochondrial dysfunction in our patient.

29138691 A novel DARS2 mutation in a Japanese patient with leukoencephalopathy with brainstem and spinal cord involvement but no lactate elevation.
- 2017 Human genome variation

Shimojima Keiko, Higashiguchi Takafumi, Kishimoto Kanako, Miyatake Satoko, Miyake Noriko, Takanashi Jun-Ichi, Matsumoto Naomichi, Yamamoto Toshiyuki.

The mitochondrial aspartyl-tRNA synthetase 2 gene (DARS2) is responsible for leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL). A Japanese patient with LBSL showed compound heterozygous DARS2 mutations c.358_359delinsTC (p.Gly120Ser) and c.228-15C>G (splicing error). This provides further evidence that most patients with LBSL show compound heterozygous mutations in DARS2 in association with a common splicing mutation in the splicing acceptor site of intron 2.

28043061 FARS2 mutation and epilepsy: Possible link with early-onset epileptic encephalopathy.
Dec 2016 Epilepsy research

Cho Jae So, Kim Seung Hyo, Kim Ha Young, Chung Taesu, Kim Dongsup, Jang Sesong, Lee Seung Bok, Yoo Seung Keun, Shin Jongyeon, Kim Jong-Il, Kim Hunmin, Hwang Hee, Chae Jong-Hee, Choi Jieun, Kim Ki Joong, Lim Byung Chan.

Early-onset epileptic encephalopathy (EOEE) consists of a heterogeneous group of epilepsy phenotypes. Recent technological advances in molecular biology have also rapidly expanded the genotype of EOEE. Genes involved in diverse molecular pathways, including ion channels, synaptic structure, transcription regulation, and cellular growth, have been implicated in EOEE. Mitochondrial aminoacyl tRNA synthetase, which plays a key role in mitochondrial protein synthesis by attaching 20 different amino acids to the tRNA tail, has been recently linked with the epilepsy phenotype. Here, we report a novel homozygous c.925G>A (G309S) missense mutation in the gene that encodes the human mitochondrial phenylalanyl-tRNA synthetase (FARS2) in four patients from two nonconsanguineous Korean families. All four patients suffered from intractable seizures that started at the age of 3 and 4 months. Seizure types were variable, including infantile spasms and myoclonic seizures, and often prolonged. Although their initial development seemed to be normal, relentless regression after seizure onset occurred in all patients. An etiologic investigation, including brain imaging and metabolic studies, did not reveal a specific etiology. We reviewed the epilepsy phenotypes of six additional FARS2 mutation-positive patients and suggest that FARS2 can be considered one of the genetic causes of EOEE.

27839525 Thymidine kinase 2 and alanyl-tRNA synthetase 2 deficiencies cause lethal mitochondrial cardiomyopathy: case reports and review of the literature.
Nov 2016 Cardiology in the young

Mazurova Stella, Magner Martin, Kucerova-Vidrova Vendula, Vondrackova Alzbeta, Stranecky Viktor, Pristoupilova Anna, Zamecnik Josef, Hansikova Hana, Zeman Jiri, Tesarova Marketa, Honzik Tomas.

Cardiomyopathy is a common manifestation in neonates and infants with mitochondrial disorders. In this study, we report two cases manifesting with fatal mitochondrial hypertrophic cardiomyopathy, which include the third known patient with thymidine kinase 2 deficiency and the ninth patient with alanyl-tRNA synthetase 2 deficiency. The girl with thymidine kinase 2 deficiency had hypertrophic cardiomyopathy together with regression of gross motor development at the age of 13 months. Neurological symptoms and cardiac involvement progressed into severe myopathy, psychomotor arrest, and cardiorespiratory failure at the age of 22 months. The imaging methods and autoptic studies proved that she suffered from unique findings of leucoencephalopathy, severe, mainly cerebellar neuronal degeneration, and hepatic steatosis. The girl with alanyl-tRNA synthetase 2 deficiency presented with cardiac failure and underlying hypertrophic cardiomyopathy within 12 hours of life and subsequently died at 9 weeks of age. Muscle biopsy analyses demonstrated respiratory chain complex I and IV deficiencies, and histological evaluation revealed massive mitochondrial accumulation and cytochrome c oxidase-negative fibres in both cases. Exome sequencing in the first case revealed compound heterozygozity for one novel c.209T>C and one previously published c.416C>T mutation in the TK2 gene, whereas in the second case homozygozity for the previously described mutation c.1774C>T in the AARS2 gene was determined. The thymidine kinase 2 mutations resulted in severe mitochondrial DNA depletion (to 12% of controls) in the muscle. We present, for the first time, severe leucoencephalopathy and hepatic steatosis in a patient with thymidine kinase 2 deficiency and the finding of a ragged red fibre-like image in the muscle biopsy in a patient with alanyl-tRNA synthetase 2 deficiency.

27891585 Novel mutations in KARS cause hypertrophic cardiomyopathy and combined mitochondrial respiratory chain defect.
Nov 2016 Clinical genetics

Verrigni Daniela, Diodato Daria, Di Nottia Michela, Torraco Alessandra, Bellacchio Emanuele, Rizza Teresa, Tozzi Giulia, Verardo Margherita, Piemonte Fiorella, Tasca Giorgio, D'Amico Adele, Bertini Enrico, Carrozzo Rosalba.

Mutations in KARS, which encodes for both mitochondrial and cytoplasmic lysyl-tRNA synthethase, have been so far associated with three different phenotypes: the recessive form of Charcot Mary-Tooth polyneuropathy, the autosomal recessive non-syndromic hearing loss and the last recently described condition related to congenital visual impairment and progressive microcephaly. Here we report the case of a 14-years-old-girl with severe cardiomyopathy associated to mild psychomotor delay and mild myopathy; moreover, a diffuse reduction of cytochrome C oxidase (COX, complex IV) and a combined enzymatic defect of complex I (CI) and IV (CIV) was evident in muscle biopsy. Using the TruSight One sequencing panel we identified two novel mutations in KARS. Both mutations, never reported previously, occur in a highly conserved region of the catalytic domain and had a dramatic effect on KARS stability. Structural analysis confirmed the pathogenic role of the identified variants. Our findings confirm and emphasize that mt-ARSs enzymes are related to a broad clinical spectrum due to their multiple and still unknown functions.

27251004 The first Japanese case of leukodystrophy with ovarian failure arising from novel compound heterozygous AARS2 mutations.
Oct 2016 Journal of human genetics

Hamatani Mio, Jingami Naoto, Tsurusaki Yoshinori, Shimada Shino, Shimojima Keiko, Asada-Utsugi Megumi, Yoshinaga Kenji, Uemura Norihito, Yamashita Hirofumi, Uemura Kengo, Takahashi Ryosuke, Matsumoto Naomichi, Yamamoto Toshiyuki.

Even now, only a portion of leukodystrophy patients are correctly diagnosed, though various causative genes have been identified. In the present report, we describe a case of adult-onset leukodystrophy in a woman with ovarian failure. By whole-exome sequencing, a compound heterozygous mutation consisting of NM_020745.3 (AARS2_v001):c.1145C>A and NM_020745.3 (AARS2_v001):c.2255+1G>A was identified. Neither of the mutations has been previously reported, and this is the first report of alanyl-transfer RNA synthetase 2 mutation in Asia. We anticipate that further studies of the molecular basis of leukodystrophy will provide insight into its pathogenesis and hopefully lead to sophisticated diagnostic and treatment strategies.

27734837 Novel AARS2 gene mutation producing leukodystrophy: a case report.
Oct 2016 Journal of human genetics

Szpisjak Laszlo, Zsindely Nora, Engelhardt Jozsef I, Vecsei Laszlo, Kovacs Gabor G, Klivenyi Peter.

AARS2 gene (NM_020745.3) mutations result in two different phenotypic diseases: infantile mitochondrial cardiomyopathy and late-onset leukoencephalopathy. The patient's first symptoms appeared at the age of 18 years with behavioral changes and psychiatric problems. Some years later, extrapyramidal symptoms, cognitive impairment, nystagmus, dysarthria and pyramidal symptoms also developed. The brain magnetic resonance imaging (MRI) indicated extensive white matter abnormalities. The diagnosis of AARS2 gene mutations causing leukodystrophy was confirmed by genetic testing. Segregation analysis confirmed the compound heterozygous state of the patient. Histological examination of the biopsy did not prove specific pathological alterations. The clinical phenotype of our patient was compared with seven previously described patients suffering from leukoencephalopathy caused by AARS2 mutations. We have documented a new, nonsense AARS2 gene mutation (c.578T>G, p.Leu193*) and a known missense mutation (c.595C>T, p.Arg199Cys) associated with leukoencephalopathy in a male patient. Clinical features, imaging characteristics and genetic testing are presented, and histological data from an AARS2-related leukodystrophy patient are described for the first time.Journal of Human Genetics advance online publication, 13 October 2016; doi:10.1038/jhg.2016.126.

27769281 Novel homozygous RARS2 mutation in two siblings without pontocerebellar hypoplasia - further expansion of the phenotypic spectrum.
Oct 2016 Orphanet journal of rare diseases

Lühl S, Bode H, Schlötzer W, Bartsakoulia M, Horvath R, Abicht A, Stenzel M, Kirschner J, Grünert S C.

Pontocerebellar hypoplasia type 6 (PCH6) is a mitochondrial disease caused by mutations in the RARS2 gene. RARS2 encodes mitochondrial arginyl transfer RNA synthetase, an enzyme involved in mitochondrial protein translation. A total of 27 patients from 14 families have been reported so far. Characteristic clinical features comprise neonatal lactic acidosis, severe encephalopathy, intractable seizures, feeding problems and profound developmental delay. Most patients show typical neuroradiologic abnormalities including cerebellar hypoplasia and progressive pontocerebellar atrophy.

27749956 Analysis of Mutations in AARS2 in a Series of CSF1R-Negative Patients With Adult-Onset Leukoencephalopathy With Axonal Spheroids and Pigmented Glia.
Oct 2016 JAMA neurology

Lynch David S, Zhang Wei Jia, Lakshmanan Rahul, Kinsella Justin A, Uzun Günes Altiokka, Karbay Merih, Tüfekçioglu Zeynep, Hanagasi Hasmet, Burke Georgina, Foulds Nicola, Hammans Simon R, Bhattacharjee Anupam, Wilson Heather, Adams Matthew, Walker Mark, Nicoll James A R, Chataway Jeremy, Fox Nick, Davagnanam Indran, Phadke Rahul, Houlden Henry.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a frequent cause of adult-onset leukodystrophy known to be caused by autosomal dominant mutations in the CSF1R (colony-stimulating factor 1) gene. The discovery that CSF1R mutations cause ALSP led to more accurate prognosis and genetic counseling for these patients in addition to increased interest in microglia as a target in neurodegeneration. However, it has been known since the discovery of the CSF1R gene that there are patients with typical clinical and radiologic evidence of ALSP who do not carry pathogenic CSF1R mutations. These patients include those in whom the pathognomonic features of axonal spheroids and pigmented microglia have been found. Achieving a genetic diagnosis in these patients is important to our understanding of this disorder.

27650058 An Application of NGS for Molecular Investigations in Perrault Syndrome: Study of 14 Families and Review of the Literature.
Sep 2016 Human mutation

Lerat Justine, Jonard Laurence, Loundon Natalie, Christin-Maitre Sophie, Lacombe Didier, Goizet Cyril, Rouzier Cécile, Van Maldergem Lionel, Gherbi Souad, Garabedian Eréa-Nöel, Bonnefont Jean-Paul, Touraine Philippe, Mosnier Isabelle, Munnich Arnold, Denoyelle Françoise, Marlin Sandrine.

Perrault syndrome (PS) is a rare autosomal recessive condition characterized by deafness and gonadic dysgenesis. Recently, mutations in five genes have been identified: C10orf2, CLPP, HARS2, HSD17B4, and LARS2. Probands included are presented with sensorineural deafness associated with gonadic dysgenesis. DNA was sequenced using next-generation sequencing (NGS) with a panel of 35 deafness genes including the five Perrault genes. Exonic variations known as pathogenic mutations or detected with <1% frequency in public databases were extracted and subjected to segregation analysis within each family. Both mutations and low coverage regions were analyzed by Sanger sequencing. Fourteen female index patients were included. The screening in four cases has been extended to four family members presenting with PS phenotype. For four unrelated patients (28.6%), causative mutations were identified: three homozygous mutations in C10orf2, CLPP, and HARS2, and one compound heterozygous mutation in LARS2. Three additional heterozygous mutations in LARS2 and HSD17B4 were found in three independent familial cases. All these missense mutations were verified by Sanger sequencing. Familial segregation analyses confirmed the molecular diagnosis in all cases carrying biallelic mutations. Because of NGS, molecular analysis confirmed the clinical diagnosis of PS in 28.6% of our cohort and four novel mutations were found in four Perrault genes. For the unsolved cases, exome sequencing should be performed to search for a sixth unknown PS gene.

27683254 RARS2 Mutations: Is Pontocerebellar Hypoplasia Type 6 a Mitochondrial Encephalopathy?
Sep 2016 JIMD reports

van Dijk Tessa, van Ruissen Fred, Jaeger Bregje, Rodenburg Richard J, Tamminga Saskia, van Maarle Merel, Baas Frank, Wolf Nicole I, Poll-The Bwee Tien.

Mutations in the mitochondrial arginyl tRNA synthetase (RARS2) gene are associated with Pontocerebellar Hypoplasia type 6 (PCH6). Here we report two patients, compound heterozygous for RARS2 mutations, presenting with early onset epileptic encephalopathy and (progressive) atrophy of both supra- and infratentorial structures. Early pontocerebellar hypoplasia was virtually absent and respiratory chain (RC) defects could not be detected in muscle biopsies. Both patients carried a novel missense mutation c.1544A>G (p.(Asp515Gly)) in combination with either a splice site (c.297+2T>G) or a frameshift (c.452_454insC) mutation. The splice site mutation induced skipping of exon 4.These two patients expand the phenotypical spectrum associated with RARS2 mutations beyond the first report of PCH6 by Edvardson and colleagues. We propose to classify RARS2-associated phenotypes as an early onset mitochondrial encephalopathy, since this is more in agreement with both clinical presentation and underlying genetic cause.

27502409 Neonatal encephalocardiomyopathy caused by mutations in VARS2.
Aug 2016 Metabolic brain disease

Baertling Fabian, Alhaddad Bader, Seibt Annette, Budaeus Sonja, Meitinger Thomas, Strom Tim M, Mayatepek Ertan, Schaper Jörg, Prokisch Holger, Haack Tobias B, Distelmaier Felix.

VARS2 encodes a mitochondrial aminoacyl-tRNA-synthetase. Mutations in VARS2 have recently been identified as a cause of mitochondrial encephalomyopathy in three individuals. However, clinical information remained scarce. Exome sequencing lead us to identify compound heterozygous pathogenic VARS2 variants in a boy presenting with severe lactic acidosis, hypertrophic cardiomyopathy, epilepsy, and abnormalities on brain imaging including hypoplasia of corpus callosum and cerebellum as well as a massive lactate peak on MR-spectroscopy. Studies in patient-derived fibroblasts confirmed the functional relevance of the identified VARS2 variants. Our report expands the phenotypic spectrum associated with this rare mitochondrial defect, in that VARS2 deficiency may also cause severe neonatal presentations with cardiac involvement and structural brain abnormalities.

27549011 Clinical findings in a patient with FARS2 mutations and early-infantile-encephalopathy with epilepsy.
Aug 2016 American journal of medical genetics. Part A

Raviglione Federico, Conte Giorgio, Ghezzi Daniele, Parazzini Cecilia, Righini Andrea, Vergaro Raffaella, Legati Andrea, Spaccini Luigina, Gasperini Serena, Garavaglia Barbara, Mastrangelo Massimo.

The FARS2 gene encodes the mitochondrial phenylalanyl-tRNA synthetase and is implicated in autosomal recessive combined oxidative phosphorylation deficiency 14, a clinical condition characterized by infantile onset epilepsy and encephalopathy. Mutations in FARS2 have been reported in only few patients, but a detailed description of seizures, electroencephalographic patterns, magnetic resonance imaging findings, and long-term follow-up is still needed. We provide a clinical report of a child with FARS2-related disease manifesting drug-resistant infantile spasms associated with focal seizures. By comparative genomic hybridization analysis we identified a heterozygous microdeletion in the short arm of chromosome 6, inherited from the mother, that encompasses the first coding exon of FARS2. By sequencing of the FARS2 gene we identified a variant c.1156C>G; p.(R386G), inherited from the father. By using standard spectrophotometric techniques in skin fibroblasts, we found a combined abnormality of complexes I and IV of the mitochondrial respiratory chain. The main clinical features of the patient included axial hypotonia, mild distal hypertonia, and psychomotor delay. The magnetic resonance imaging showed microcephaly, frontal cerebral atrophy, and signal changes of dentate nuclei. At the age of 3 years and 6 months, the patient was still under treatment with vigabatrin and he has been seizure free for the last 23 months. © 2016 Wiley Periodicals, Inc.

27571996 Lethal Neonatal LTBL Associated with Biallelic EARS2 Variants: Case Report and Review of the Reported Neuroradiological Features.
Aug 2016 JIMD reports

Oliveira Renata, Sommerville Ewen W, Thompson Kyle, Nunes Joana, Pyle Angela, Grazina Manuela, Chinnery Patrick F, Diogo Luísa, Garcia Paula, Taylor Robert W.

Mitochondrial translation defects are important causes of early onset mitochondrial disease. Although the biochemical (combined respiratory chain deficiency) signature and neuroimaging are usually distinctive, they are not diagnostic as the genetic origin of mitochondrial translation defects is heterogeneous. We report a female child, born at term to non-consanguineous parents, who exhibited global hypotonia, failure to thrive, persistent and progressive hyperlactacidaemia with lactic acidosis, liver dysfunction and encephalopathy and died at the age of 5 months. Brain MRI revealed hypogenesis of the corpus callosum, T2 signal abnormalities in the medulla oblongata, pons, midbrain, thalami, cerebellar white matter, and a lactate peak on MRS. Muscle histochemistry showed cytochrome c oxidase (COX)-deficient and ragged-red fibres, while muscle biochemical studies showed decreased activities of mitochondrial respiratory chain complexes I and IV. Whole exome sequencing (WES) identified biallelic EARS2 (NM_001083614) variants, a previously reported start-loss (c.1>G, p.Met1?) variant and a novel missense (c.184A>T, p.Ile62Phe) variant. Patient fibroblasts and muscle homogenate displayed markedly decreased EARS2 protein levels, although decreased steady-state levels of complex I (NDUFB8) and complex IV (MT-CO1 and MT-CO2) subunits were only observed in muscle. Pathogenic variants in EARS2, encoding mitochondrial glutamyl-tRNA synthetase (mtGluR), are associated with Leukoencephalopathy involving the Thalamus and Brainstem with high Lactate (LTBL), a mitochondrial disorder characterised by a distinctive brain MRI pattern and a biphasic clinical course. We further outline the unique phenotypic spectrum of LTBL and review the neuroradiological features reported in all patients documented in the literature.

27206875 Leukoencephalopathy with thalamus and brainstem involvement and high lactate caused by novel mutations in the EARS2 gene in two siblings.
Jun 2016 Journal of the neurological sciences

Şahin Sevim, Cansu Ali, Kalay Ersan, Dinçer Tuba, Kul Sibel, Çakır İsmet Miraç, Kamaşak Tülay, Budak Gülden Yorgancıoğlu.

Leukoencephalopathy with thalamus and brainstem involvement, and high lactate (LTBL) is a recently identified disease related to mutations in the EARS2 gene encoding glutamyl-tRNA synthetase. We report clinical and radiological findings for two siblings with new pathogenic mutations in the EARS2 gene. Both patients showed symptoms of mild-type disease, but there were clinical differences between the two siblings. While the older brother had hypotonia and delayed developmental milestones, the younger brother had seizures and spasticity in the lower extremities. Brain magnetic resonance imaging (MRI) findings were quite similar for the two siblings. MRI findings were specific to LTBL. MRI lesions of the older sibling had regressed over time. Clinical and radiological improvement, as in the previously reported patients with LTBL, may be an important clue for diagnosis.

27279129 Splicing Defect in Mitochondrial seryl-tRNA Synthetase Gene Causes Progressive Spastic Paresis Instead of HUPRA Syndrome.
Jun 2016 Human mutation

Linnankivi Tarja, Neupane Nirajan, Richter Uwe, Isohanni Pirjo, Tyynismaa Henna.

Mitochondrial aminoacyl-tRNA synthetases are an important group of disease genes typically underlying either a disorder affecting an isolated tissue or a distinct syndrome. Missense mutations in the mitochondrial seryl-tRNA synthetase gene, SARS2, have been identified in HUPRA syndrome (hyperuricemia, pulmonary hypertension, renal failure in infancy and alkalosis). We report here a homozygous splicing mutation in SARS2 in a patient with progressive spastic paresis. We show that the mutation leads to diminished levels of the synthetase in patient's fibroblasts. This has a destabilizing effect on the tRNASer(AGY) isoacceptor, but to a lesser degree than in HUPRA syndrome patients. tRNASer(UCN) is largely unaffected in both phenotypes. In conclusion, the level of tRNASer(AGY) instability may be a factor in determining tissue manifestation in patients with SARS2 mutations. This finding exemplifies the sensitivity of the nervous system to partially reduced aminoacylation, which is sufficient in other tissues to maintain respiratory chain function. This article is protected by copyright. All rights reserved.

27290639 New perspective in diagnostics of mitochondrial disorders: two years' experience with whole-exome sequencing at a national paediatric centre.
Jun 2016 Journal of translational medicine

Pronicka Ewa, Piekutowska-Abramczuk Dorota, Ciara Elżbieta, Trubicka Joanna, Rokicki Dariusz, Karkucińska-Więckowska Agnieszka, Pajdowska Magdalena, Jurkiewicz Elżbieta, Halat Paulina, Kosińska Joanna, Pollak Agnieszka, Rydzanicz Małgorzata, Stawinski Piotr, Pronicki Maciej, Krajewska-Walasek Małgorzata, Płoski Rafał.

Whole-exome sequencing (WES) has led to an exponential increase in identification of causative variants in mitochondrial disorders (MD).

27234911 Genetic causes of hypomagnesemia, a clinical overview.
May 2016 Pediatric nephrology (Berlin, Germany)

Viering Daan H H M, de Baaij Jeroen H F, Walsh Stephen B, Kleta Robert, Bockenhauer Detlef.

Magnesium is essential to the proper functioning of numerous cellular processes. Magnesium ion (Mg(2+)) deficits, as reflected in hypomagnesemia, can cause neuromuscular irritability, seizures and cardiac arrhythmias. With normal Mg(2+) intake, homeostasis is maintained primarily through the regulated reabsorption of Mg(2+) by the thick ascending limb of Henle's loop and distal convoluted tubule of the kidney. Inadequate reabsorption results in renal Mg(2+) wasting, as evidenced by an inappropriately high fractional Mg(2+) excretion. Familial renal Mg(2+) wasting is suggestive of a genetic cause, and subsequent studies in these hypomagnesemic families have revealed over a dozen genes directly or indirectly involved in Mg(2+) transport. Those can be classified into four groups: hypercalciuric hypomagnesemias (encompassing mutations in CLDN16, CLDN19, CASR, CLCNKB), Gitelman-like hypomagnesemias (CLCNKB, SLC12A3, BSND, KCNJ10, FYXD2, HNF1B, PCBD1), mitochondrial hypomagnesemias (SARS2, MT-TI, Kearns-Sayre syndrome) and other hypomagnesemias (TRPM6, CNMM2, EGF, EGFR, KCNA1, FAM111A). Although identification of these genes has not yet changed treatment, which remains Mg(2+) supplementation, it has contributed enormously to our understanding of Mg(2+) transport and renal function. In this review, we discuss general mechanisms and symptoms of genetic causes of hypomagnesemia as well as the specific molecular mechanisms and clinical phenotypes associated with each syndrome.

27215512 [Clinicopathological characteristics of colorectal carcinoma in the elderly].
May 2016 Zhonghua wei chang wai ke za zhi = Chinese journal of gastrointestinal surgery

Tao Kaixiong, Gao Jinbo, Wang Guobin.

Elderly patients with colorectal cancer have different clincopathological characteristics from younger patients. Colorectal cancers tend to localize in the proximal colon, from cecum to the splenic flexure in the elderly patients. Changes in the stools, rectal bleeding or black stool, abdominal pain, fatigue, weight loss and anemia are the common symptoms. Analysis showed that age is one of independent risk factors for lower completion rates of colonoscopy. Therefore, the choice of diagnosis methods in elderly patients should be careful. Achieving a clear diagnosis and avoiding complications should be considered at the same time. Most colorectal cancers in elderly are highly and moderately differentiated adenocarcinomas and locally advanced, and have less lymphatic and blood metastasis. The proportion of poorly differentiated adenocarcinoma increases with the increase of age, which should be concerned. Multiple colorectal cancers and colorectal cancer with extra-colorectal malignancy are not rare in the elderly patients. The common extra-colorectal tumors consist of gastric cancer, lung cancer, biliary carcinoma, pancreas cancer and malignancy from blood system. Molecular events, such as mutations of KARS, BRAF, TP53 and deficiency of DNA mismatch repair, are more frequent in elderly colorectal cancer patients. Many factors have impact on treatment decision in elderly patients with colorectal cancer, including age, comorbidities, physiological functions of organs and willingness of patients and their relatives. Although surgery is still the main treatment, the proportion of radical surgery is lower and emergency surgery is higher as compared to younger patients. With the development of minimally invasive surgical techniques and advances in anesthesia and perioperative management, laparoscopic surgery has become widespread in elderly patients with colorectal cancer. In addition, more attention should be paid to adjuvant therapy. Comprehensive individualized treatment plan should be taken to improve outcomes.

27061686 RARS2 mutations in a sibship with infantile spasms.
Apr 2016 Epilepsia

Ngoh Adeline, Bras Jose, Guerreiro Rita, Meyer Esther, McTague Amy, Dawson Eleanor, Mankad Kshitij, Gunny Roxana, Clayton Peter, Mills Philippa B, Thornton Rachel, Lai Ming, Forsyth Robert, Kurian Manju A.

Pontocerebellar hypoplasia is a group of heterogeneous neurodevelopmental disorders characterized by reduced volume of the brainstem and cerebellum. We report two male siblings who presented with early infantile clonic seizures, and then developed infantile spasms associated with prominent isolated cerebellar hypoplasia/atrophy on magnetic resonance imaging (MRI). Using whole exome sequencing techniques, both were found to be compound heterozygotes for one previously reported and one novel mutation in the gene encoding mitochondrial arginyl-tRNA synthetase 2 (RARS2). Mutations in this gene have been classically described in pontocerebellar hypoplasia type six (PCH6), a phenotype characterized by early (often intractable) seizures, profound developmental delay, and progressive pontocerebellar atrophy. The electroclinical spectrum of PCH6 is broad and includes a number of seizure types: myoclonic, generalized tonic-clonic, and focal clonic seizures. Our report expands the characterization of the PCH6 disease spectrum and presents infantile spasms as an associated electroclinical phenotype.

27078007 Recessive Mutation in a Nuclear-Encoded Mitochondrial tRNA Synthetase Associated With Infantile Cataract, Congenital Neurotrophic Keratitis, and Orbital Myopathy.
Apr 2016 Cornea

Jabbour Samir, Harissi-Dagher Mona.

To report the ocular findings of a rare case of mutation in the nuclear-encoded mitochondrial aminoacyl-tRNA synthetase IARS2.

27095821 Novel Compound Heterozygous Mutations Expand the Recognized Phenotypes of FARS2-Linked Disease.
Apr 2016 Journal of child neurology

Walker Melissa A, Mohler Kyle P, Hopkins Kyle W, Oakley Derek H, Sweetser David A, Ibba Michael, Frosch Matthew P, Thibert Ronald L.

Mutations in mitochondrial aminoacyl-tRNA synthetases are an increasingly recognized cause of human diseases, often arising in individuals with compound heterozygous mutations and presenting with system-specific phenotypes, frequently neurologic.FARS2encodes mitochondrial phenylalanyl transfer ribonucleic acid (RNA) synthetase (mtPheRS), perturbations of which have been reported in 6 cases of an infantile, lethal disease with refractory epilepsy and progressive myoclonus. Here the authors report the case of juvenile onset refractory epilepsy and progressive myoclonus with compound heterozygousFARS2mutations. The authors describe the clinical course over 6 years of care at their institution and diagnostic studies including electroencephalogram (EEG), brain magnetic resonance imaging (MRI), serum and cerebrospinal fluid analyses, skeletal muscle biopsy histology, and autopsy gross and histologic findings, which include features shared with Alpers-Huttenlocher syndrome, Leigh syndrome, and a previously published case ofFARS2mutation associated infantile onset disease. The authors also present structure-guided analysis of the relevant mutations based on published mitochondrial phenylalanyl transfer RNA synthetase and related protein crystal structures as well as biochemical analysis of the corresponding recombinant mutant proteins.

27117034 A compound heterozygous EARS2 mutation associated with mild leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL).
Apr 2016 Brain & development

Güngör Olcay, Özkaya Ahmet Kağan, Şahin Yavuz, Güngör Gülay, Dilber Cengiz, Aydın Kürşad.

Mitochondrial glutamyl-tRNA synthetase is a major component of protein biosynthesis that loads tRNAs with cognate amino acids. Mutations in the gene encoding this enzyme have been associated with a variety of disorders related to oxidative phosphorylation. Here, we present a case of leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL) presenting a biphasic clinical course characterized by delayed psychomotor development and seizure. High-throughput sequencing revealed a novel compound heterozygous mutation in mitochondrial glutamyl-tRNA synthetase 2 (EARS2), which appears to be causative of disease symptoms.

27121845 Novel mutations in WWOX, RARS2, and C10orf2 genes in consanguineous Arab families with intellectual disability.
Apr 2016 Metabolic brain disease

Alkhateeb Asem M, Aburahma Samah K, Habbab Wesal, Thompson I Richard.

Intellectual disability is a heterogeneous disease with many genes and mutations influencing the phenotype. Consanguineous families constitute a rich resource for the identification of rare variants causing autosomal recessive disease, due to the effects of inbreeding. Here, we examine three consanguineous Arab families, recruited in a quest to identify novel genes/mutations. All the families had multiple offspring with non-specific intellectual disability. We identified homozygosity (autozygosity) intervals in those families through SNP genotyping and whole exome sequencing, with variants filtered using Ingenuity Variant Analysis (IVA) software. The families showed heterogeneity and novel mutations in three different genes known to be associated with intellectual disability. These mutations were not found in 514 ethnically matched control chromosomes. p.G410C in WWOX, p.H530Y in RARS2, and p.I69F in C10orf2 are novel changes that affect protein function and could give new insights into the development and function of the central nervous system.

26866824 Does IARS2 Deficiency Cause an Intrinsic Disorder of Bone Development (Skeletal Dysplasia) or Are the Reported Skeletal Changes Secondary to Growth Hormone Deficiency and Neuromuscular Involvement?
Mar 2016 Hum. Mutat.

Mordaunt Dylan A, Savarirayan Ravi.

26970254 Expanding the Genotypic Spectrum of Perrault syndrome.
Mar 2016 Clinical genetics

Demain Leigh A M, Urquhart Jill E, O'Sullivan James, Williams Simon G, Bhaskar Sanjeev S, Jenkinson Emma M, Lourenco Charles M, Heiberg Arvid, Pearce Simon H, Shalev Stavit A, Yue Wyatt W, Mackinnon Sabrina, Munro Kevin J, Newbury-Ecob Ruth, Becker Kristen, Kim Min Jeong, O' Keefe Raymond T, Newman William G.

Perrault syndrome is a rare autosomal recessive disorder characterised by sensorineural hearing loss (SNHL) in both sexes and primary ovarian insufficiency in 46, XX karyotype females. Biallelic variants in five genes are reported to be causative: HSD17B4, HARS2, LARS2, CLPP and C10orf2. Here we present eight families affected by Perrault syndrome. In five families we identified novel or previously reported variants in HSD17B4, LARS2, CLPP and C10orf2. The proband from each family was whole exome sequenced and variants confirmed by Sanger sequencing. A female was compound heterozygous for a known, p.(Gly16Ser) and novel, p.(Val82Phe) variant in D-bifunctional protein (HSD17B4). A family was homozygous for mtLeuRS (LARS2) p.(Thr522Asn), previously associated with Perrault syndrome. A further family was compound heterozygous for mtLeuRS, p.(Thr522Asn) and a novel variant, p.(Met117Ile). Affected individuals with LARS2 variants had low frequency SNHL, a feature previously described in Perrault syndrome. A female with significant neurological disability was compound heterozygous for p.(Arg323Gln) and p.(Asn399Ser) variants in Twinkle (C10orf2). A male was homozygous for a novel variant in CLPP, p.(Cys144Arg). In three families there were no putative pathogenic variants in these genes confirming additional disease-causing genes remain unidentified. We have expanded the spectrum of disease-causing variants associated with Perrault syndrome.

26970947 RARS2 mutations cause early onset epileptic encephalopathy without ponto-cerebellar hypoplasia.
Mar 2016 European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society

Nishri Daniella, Goldberg-Stern Hadassa, Noyman Iris, Blumkin Lubov, Kivity Sara, Saitsu Hirotomo, Nakashima Mitsuko, Matsumoto Naomichi, Leshinsky-Silver Esther, Lerman-Sagie Tally, Lev Dorit.

Early onset epileptic encephalopathies (EOEEs) are a group of devastating diseases, manifesting in the first year of life with frequent seizures and/or prominent interictal epileptiform discharges on the electroencephalogram, developmental delay or regression and usually a poor prognosis. There are numerous causes for EOEEs making the diagnostic workup time consuming and costly.

26979109 Mitochondrial DNA homeostasis is essential for nigrostriatal integrity.
Mar 2016 Mitochondrion

Tzoulis Charalampos, Schwarzlmüller Thomas, Biermann Martin, Haugarvoll Kristoffer, Bindoff Laurence A.

Mitochondrial involvement in the pathogenesis of Parkinson's disease has been suggested by multiple studies, but the mechanisms involved remain unresolved. Here, we sought to identify which mitochondrial defects are associated with degeneration of the nigrostriatal system. Nigrostriatal integrity was assessed in vivo by dopamine transporter (DAT) imaging in twenty-one patients with mitochondrial disorders of different molecular etiology including: maternally inherited mitochondrial DNA (mtDNA) point mutations, primary single mtDNA deletions, nuclear-encoded disorders of mtDNA replication and maintenance due to mutations in POLG or C10orf2 (Twinkle), and mutations in other nuclear mitochondrial genes including the mitochondrial aspartyl-tRNA synthetase (DARS2) and ADCK3 genes. Patients with mitochondrial disease were compared with twenty patients with Parkinson's disease and eighteen controls. Nigrostriatal degeneration occurred exclusively in patients with defective mtDNA replication and maintenance. In these patients, nigrostriatal degeneration was progressive and at least as severe as in patients with advanced Parkinson's disease. None of the patients with other mitochondrial defects showed evidence of nigral involvement. Our findings demonstrate that dopaminergic neurons of the substantia nigra are specifically vulnerable to defective mtDNA replication/repair or quality control and not to primary point mutations of mtDNA. These results support the hypothesis that accumulating somatic mtDNA damage plays an important role in neurodegeneration.

26893310 Early-Onset Mild Type Leukoencephalopathy Caused by a Homozygous EARS2 Mutation.
Feb 2016 Journal of child neurology

Taskin Birce Dilge, Karalok Zeynep Selen, Gurkas Esra, Aydin Kursad, Aydogmus Ummu, Ceylaner Serdar, Karaer Kadri, Yilmaz Cahide, Pearl Phillip Lawrence.

Childhood leukoencephalopathies are a broad class of diseases, which are extremely rare. The treatment and classification of these disorders are both challenging. Nearly half of children presenting with a leukoencephalopathy remain without a specific diagnosis. Leukoencephalopathy with thalamus and brain stem involvement and high lactate (LTBL) is a newly described childhood leukoencephalopathy caused by mutations in the gene encoding a mitochondrial aminoacyl-tRNA synthetase specific for glutamate, EARS2. Magnetic resonance images show a characteristic leukoencephalopathy with thalamic and brain stem involvement. Here, we report a different clinical course of LTBL supported by typical MRI features in a Turkish patient who presented with a history of failure to walk. The EARS2 gene mutation analysis identified a c.322C>T transition, predicting a p.R108W change. This is the first reported early-onset mild type LTBL caused by a homozygous EARS2 mutation case in the literature.

26780086 EARS2 mutations cause fatal neonatal lactic acidosis, recurrent hypoglycemia and agenesis of corpus callosum.
Jan 2016 Metabolic brain disease

Danhauser Katharina, Haack Tobias B, Alhaddad Bader, Melcher Marlen, Seibt Annette, Strom Tim M, Meitinger Thomas, Klee Dirk, Mayatepek Ertan, Prokisch Holger, Distelmaier Felix.

Mitochondrial aminoacyl tRNA synthetases are essential for organelle protein synthesis. Genetic defects affecting the function of these enzymes may cause pediatric mitochondrial disease. Here, we report on a child with fatal neonatal lactic acidosis and recurrent hypoglycemia caused by mutations in EARS2, encoding mitochondrial glutamyl-tRNA synthetase 2. Brain ultrasound revealed agenesis of corpus callosum. Studies on patient-derived skin fibroblasts showed severely decreased EARS2 protein levels, elevated reactive oxygen species (ROS) production, and altered mitochondrial morphology. Our report further illustrates the clinical spectrum of the severe neonatal-onset form of EARS2 mutations. Moreover, in this case the live-cell parameters appeared to be more sensitive to mitochondrial dysfunction compared to standard diagnostics, which indicates the potential relevance of fibroblast studies in children with mitochondrial diseases.

26811336 A Human Disease-causing Point Mutation in Mitochondrial Threonyl-tRNA Synthetase Induces both Structural and Functional Defects.
Jan 2016 The Journal of biological chemistry

Wang Yong, Zhou Xiao-Long, Ruan Zhi-Rong, Liu Ru-Juan, Eriani Gilbert, Wang En-Duo.

Mitochondria require all translational components, including aminoacyl-tRNA synthetases (aaRSs), to complete organelle protein synthesis. Some aaRS mutations cause mitochondrial disorders, including human mitochondrial threonyl-tRNA synthetase (hmtThrRS; encoded by TARS2), whose P282L mutation causes mitochondrial encephalomyopathies. However, its catalytic and structural consequences remain unclear. Herein, we cloned TARS2 and purified the wild-type and P282L mutant hmtThrRS. HmtThrRS mis-activates non-cognate Ser and uses post-transfer editing to clear erroneously synthesized products. In vitro and in vivo analyses revealed that the mutation induces decrease of Thr activation, aminoacylation and proofreading activities, and a change in the protein structure and/or stability that might cause reduced catalytic efficiency. We also identified a splicing variant of TARS2 mRNA lacking exons 8 and 9, whose protein product is targeted into mitochondria. In HEK293T cells, the variant does not dimerize and cannot complement the ThrRS-knockout strain in yeast, suggesting that the truncated protein is inactive and might have a non-canonical function, as observed for other aaRSs fragments. The present study describes the aminoacylation and editing properties of hmtThrRS, clarifies the molecular consequences of the P282L mutation and shows that the yeast ThrRS-deletion model is suitable to test pathology-associated point mutations or alternative splicing variants of mammalian aaRS mRNAs.

27348859 Chronic Rhinosinusitis Patients Show Accumulation of Genetic Variants in PARS2.
- 2016 PloS one

Henmyr Viktor, Lind-Halldén Christina, Halldén Christer, Säll Torbjörn, Carlberg Daniel, Bachert Claus, Cardell Lars-Olaf.

Genetic studies of chronic rhinosinusitis (CRS) have identified a total of 53 CRS-associated SNPs that were subsequently evaluated for their reproducibility in a recent study. The rs2873551 SNP in linkage disequilibrium with PARS2 showed the strongest association signal. The present study aims to comprehensively screen for rare variants in PARS2 and evaluate for accumulation of such variants in CRS-patients. Sanger sequencing and long-range PCR were used to screen for rare variants in the putative promoter region and coding sequence of 310 CRS-patients and a total of 21 variants were detected. The mutation spectrum was then compared with data from European populations of the 1000Genomes project (EUR) and the Exome Aggregation Consortium (ExAC). The CRS population showed a significant surplus of low-frequency variants compared with ExAC data. Haplotype analysis of the region showed a significant excess of rare haplotypes in the CRS population compared to the EUR population. Two missense mutations were also genotyped in the 310 CRS patients and 372 CRS-negative controls, but no associations with the disease were found. This is the first re-sequencing study in CRS research and also the first study to show an association of rare variants with the disease.

26647310 The exome sequencing identified the mutation in YARS2 encoding the mitochondrial tyrosyl-tRNA synthetase as a nuclear modifier for the phenotypic manifestation of Leber's hereditary optic neuropathy-associated mitochondrial DNA mutation.
Dec 2015 Human molecular genetics

Jiang Pingping, Jin Xiaofen, Peng Yanyan, Wang Meng, Liu Hao, Liu Xiaoling, Zhang Zhenjun, Ji Yanchun, Zhang Juanjuan, Liang Min, Zhao Fuxin, Sun Yan-Hong, Zhang Minglian, Zhou Xiangtian, Chen Ye, Mo Jun Qin, Huang Taosheng, Qu Jia, Guan Min-Xin.

Leber's hereditary optic neuropathy (LHON) is the most common mitochondrial disorder. Nuclear modifier genes are proposed to modify the phenotypic expression of LHON-associated mitochondrial DNA (mtDNA) mutations. By using an exome sequencing approach, we identified a LHON susceptibility allele (c.572G>T, p.191Gly>Val) in YARS2 gene encoding mitochondrial tyrosyl-tRNA synthetase, which interacts with m.11778G>A mutation to cause visual failure. We performed functional assays by using lymphoblastoid cell lines derived from members of Chinese families (asymptomatic individuals carrying m.11778G>A mutation, or both m.11778G>A and heterozygous p.191Gly>Val mutations, and symptomatic subjects harboring m.11778G>A and homozygous p.191Gly>Val mutations) and controls lacking these mutations. The 191Gly>Val mutation reduced the YARS2 protein level in the mutant cells. The aminoacylated efficiency and steady-state level of tRNA(Tyr) were markedly decreased in the cell lines derived from patients both carrying homozygous YARS2 p.191Gly>Val and m.11778G>A mutations. The failure in tRNA(Tyr) metabolism impaired mitochondrial translation, especially for polypeptides with high content of tyrosine codon such as ND4, ND5, ND6 and COX2 in cells lines carrying homozygous YARS2 p.191Gly>Val and m.11778G>A mutations. The YARS2 p.191Gly>Val mutation worsened the respiratory phenotypes associated with m.11778G>A mutation, especially reducing activities of complex I and IV. The respiratory deficiency altered the efficiency of mitochondrial ATP synthesis and increased the production of reactive oxygen species. Thus, mutated YARS2 worsens mitochondrial dysfunctions associated with the m.11778G>A mutation, exceeding the threshold for the expression of blindness phenotype. Our findings provided new insights into the pathophysiology of LHON that were manifested by interaction between mtDNA mutation and mutated nuclear-modifier YARS2.

26657938 First independent replication of the involvement of LARS2 in Perrault syndrome by whole-exome sequencing of an Italian family.
Dec 2015 Journal of human genetics

Sold Giulia, Caccia Sonia, Robusto Michela, Chiereghin Chiara, Castorina Pierangela, Ambrosetti Umberto, Duga Stefano, Asselta Rosanna.

Perrault syndrome (MIM #233400) is a rare autosomal recessive disorder characterized by ovarian dysgenesis and primary ovarian insufficiency in females, and progressive hearing loss in both genders. Recently, mutations in five genes (HSD17B4, HARS2, CLPP, LARS2 and C10ORF2) were found to be responsible for Perrault syndrome, although they do not account for all cases of this genetically heterogeneous condition. We used whole-exome sequencing to identify pathogenic variants responsible for Perrault syndrome in an Italian pedigree with two affected siblings. Both patients were compound heterozygous for two novel missense variants within the mitochondrial leucyl-tRNA synthetase (LARS2): NM_015340.3:c.899C>T(p.Thr300Met) and c.1912G>A(p.Glu638Lys). Both variants cosegregated with the phenotype in the family. p.Thr300 and p.Glu638 are evolutionarily conserved residues, and are located, respectively, within the editing domain and immediately before the catalytically important KMSKS motif. Homology modeling using as template the E. coli leucyl-tRNA synthetase provided further insights on the possible pathogenic effects of the identified variants. This represents the first independent replication of the involvement of LARS2 mutations in Perrault syndrome, contributing valuable information for the further understanding of this disease.Journal of Human Genetics advance online publication, 10 December 2015; doi:10.1038/jhg.2015.149.

26620921 Neurodegenerative disease-associated mutants of a human mitochondrial aminoacyl-tRNA synthetase present individual molecular signatures.
Dec 2015 Scientific reports

Sauter Claude, Lorber Bernard, Gaudry Agnès, Karim Loukmane, Schwenzer Hagen, Wien Frank, Roblin Pierre, Florentz Catherine, Sissler Marie.

Mutations in human mitochondrial aminoacyl-tRNA synthetases are associated with a variety of neurodegenerative disorders. The effects of these mutations on the structure and function of the enzymes remain to be established. Here, we investigate six mutants of the aspartyl-tRNA synthetase correlated with leukoencephalopathies. Our integrated strategy, combining an ensemble of biochemical and biophysical approaches, reveals that mutants are diversely affected with respect to their solubility in cellular extracts and stability in solution, but not in architecture. Mutations with mild effects on solubility occur in patients as allelic combinations whereas those with strong effects on solubility or on aminoacylation are necessarily associated with a partially functional allele. The fact that all mutations show individual molecular and cellular signatures and affect amino acids only conserved in mammals, points towards an alternative function besides aminoacylation.

26537577 LARS2 Variants Associated with Hydrops, Lactic Acidosis, Sideroblastic Anemia, and Multisystem Failure.
Nov 2015 JIMD reports

Riley Lisa G, Rudinger-Thirion Joëlle, Schmitz-Abe Klaus, Thorburn David R, Davis Ryan L, Teo Juliana, Arbuckle Susan, Cooper Sandra T, Campagna Dean R, Frugier Magali, Markianos Kyriacos, Sue Carolyn M, Fleming Mark D, Christodoulou John.

Pathogenic variants in mitochondrial aminoacyl-tRNA synthetases result in a broad range of mitochondrial respiratory chain disorders despite their shared role in mitochondrial protein synthesis. LARS2 encodes the mitochondrial leucyl-tRNA synthetase, which attaches leucine to its cognate tRNA. Sequence variants in LARS2 have previously been associated with Perrault syndrome, characterized by premature ovarian failure and hearing loss (OMIM #615300). In this study, we report variants in LARS2 that are associated with a severe multisystem metabolic disorder. The proband was born prematurely with severe lactic acidosis, hydrops, and sideroblastic anemia. She had multisystem complications with hyaline membrane disease, impaired cardiac function, a coagulopathy, pulmonary hypertension, and progressive renal disease and succumbed at 5 days of age. Whole exome sequencing of patient DNA revealed compound heterozygous variants in LARS2 (c.1289C>T; p.Ala430Val and c.1565C>A; p.Thr522Asn). The c.1565C>A (p.Thr522Asn) LARS2 variant has previously been associated with Perrault syndrome and both identified variants are predicted to be damaging (SIFT, PolyPhen). Muscle and liver samples from the proband did not display marked mitochondrial respiratory chain enzyme deficiency. Immunoblotting of patient muscle and liver showed LARS2 levels were reduced in liver and complex I protein levels were reduced in patient muscle and liver. Aminoacylation assays revealed p.Ala430Val LARS2 had an 18-fold loss of catalytic efficiency and p.Thr522Asn a 9-fold loss compared to wild-type LARS2. We suggest that the identified LARS2 variants are responsible for the severe multisystem clinical phenotype seen in this baby and that mutations in LARS2 can result in variable phenotypes.

26553276 A Newly Identified Missense Mutation in FARS2 Causes Autosomal Recessive Spastic Paraplegia.
Nov 2015 Human mutation

Yang Ying, Liu Wei, Fang Zhipeng, Shi Juan, Che Fengyu, He Chunxia, Yao Libo, Wang Enduo, Wu Yuanming.

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by spasticity of the lower limbs due to pyramidal tract dysfunction. Here we report that a missense homozygous mutation c.424G>T (p.D142Y) in the FARS2 gene, which encodes a mitochondrial phenylalanyl tRNA synthetase (mtPheRS), causes HSP in a Chinese consanguineous family by using combination of homozygous mapping and whole exome sequencing. Immunohistochemical experiments were performed showing that the FARS2 protein was highly expressed in the Purkinje cells of rat cerebellum. The aminoacylation activity of mtPheRS was severely disrupted by the p.D142Y substitution in vitro not only in the first aminoacylation step but also in the last transfer step. Taken together, our results indicate a missense mutation in FARS2 contributes to HSP, which has the clinical significance of the regulation of tRNA synthetases in human neurodegenerative diseases. This article is protected by copyright. All rights reserved.

26619324 Absent Thalami Caused by a Homozygous EARS2 Mutation: Expanding Disease Spectrum of LTBL.
Nov 2015 Neuropediatrics

Kevelam Sietske H, Klouwer Femke C C, Fock Johanna M, Salomons Gajja S, Bugiani Marianna, van der Knaap Marjo S.

Leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL) is caused by autosomal recessive EARS2 mutations. Onset is most often in infancy, but in severe cases in the neonatal period. Patients typically have magnetic resonance imaging (MRI) signal abnormalities involving the thalamus, brainstem, and deep cerebral white matter. Most signal abnormalities resolve, but in severe cases at the expense of tissue loss. Here, we report a patient with an encephalopathy of antenatal onset. His early MRI at 8 months of age showed signal abnormalities in the deep cerebral white matter that improved over time. The thalami were absent with the configuration of a developmental anomaly, without evidence of a lesion. We hypothesized that this was a case of LTBL in which the thalamic damage occurred antenatally and was incorporated in the normal brain development. The diagnosis was confirmed by a novel homozygous EARS2 mutation. Our case adds to the phenotypic and genetic spectrum of LTBL.

26000875 A novel mutation of the glycyl-tRNA synthetase (GARS) gene associated with Charcot-Marie-Tooth type 2D in a Chinese family.
Sep 2015 Neurological research

Sun Aping, Liu Xiangyi, Zheng Mei, Sun Qingli, Huang Yu, Fan Dongsheng.

To explore the clinical features of a novel glycyl-tRNA synthetase (GARS) gene mutation in a family with Charcot-Marie-Tooth disease type 2D (CMT2D).

26327357 Early-onset leukoencephalopathy due to a homozygous missense mutation in the DARS2 gene.
Aug 2015 Molecular and cellular probes

Köhler Cornelia, Heyer Christoph, Hoffjan Sabine, Stemmler Susanne, Lücke Thomas, Thiels Charlotte, Kohlschütter Alfried, Löbel Ulrike, Horvath Rita, Kleinle Stephanie, Benet-Pages Anna, Abicht Angela.

Mutations in the DARS2 gene are known to cause leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL), a rare autosomal recessive neurological disorder. It was originally described as juvenile-onset slowly progressive ataxia and spasticity, but recent reports suggest a broader clinical spectrum. Most patients were found to carry compound heterozygous DARS2 mutations, and only very few patients with homozygous mutations have been described so far. We present here an 8-month-old boy carrying a homozygous missense mutation in DARS2 who clinically showed severe neurological deterioration after a respiratory tract infection, followed by an almost complete remission of symptoms. This report further extends the knowledge about the clinical and molecular genetic spectrum of LBSL.

26083569 Neuropathologic Characterization of Pontocerebellar Hypoplasia Type 6 Associated With Cardiomyopathy and Hydrops Fetalis and Severe Multisystem Respiratory Chain Deficiency due to Novel RARS2 Mutations.
Jul 2015 Journal of neuropathology and experimental neurology

Lax Nichola Z, Alston Charlotte L, Schon Katherine, Park Soo-Mi, Krishnakumar Deepa, He Langping, Falkous Gavin, Ogilvy-Stuart Amanda, Lees Christoph, King Rosalind H, Hargreaves Iain P, Brown Garry K, McFarland Robert, Dean Andrew F, Taylor Robert W.

Autosomal recessive mutations in the RARS2 gene encoding the mitochondrial arginyl-transfer RNA synthetase cause infantile-onset myoencephalopathy pontocerebellar hypoplasia type 6 (PCH6). We describe 2 sisters with novel compound heterozygous RARS2 mutations who presented perinatally with neurologic features typical of PCH6 but with additional features including cardiomyopathy, hydrops, and pulmonary hypoplasia and who died at 1 day and 14 days of age. Magnetic resonance imaging findings included marked cerebellar hypoplasia, gyral immaturity, punctate lesions in cerebral white matter, and unfused deep cerebral grey matter. Enzyme histochemistry of postmortem tissues revealed a near-global cytochrome c oxidase-deficiency; assessment of respiratory chain enzyme activities confirmed severe deficiencies involving complexes I, III, and IV. Molecular genetic studies revealed 2 RARS2 gene mutations: a c.1A>G, p.? variant predicted to abolish the initiator methionine, and a deep intronic c.613-3927C>T variant causing skipping of exons 6-8 in the mature RARS2 transcript. Neuropathologic investigation included low brain weights, small brainstem and cerebellum, deep cerebral white matter pathology, pontine nucleus neuron loss (in 1 sibling), and peripheral nerve pathology. Mitochondrial respiratory chain immunohistochemistry in brain tissues confirmed an absence of complexes I and IV immunoreactivity with sparing of mitochondrial numbers. These cases expand the clinical spectrum of RARS2 mutations, including antenatal features and widespread mitochondrial respiratory chain deficiencies in postmortem brain tissues.

25330800 Congenital Visual Impairment and Progressive Microcephaly Due to Lysyl-Transfer Ribonucleic Acid (RNA) Synthetase (KARS) Mutations: The Expanding Phenotype of Aminoacyl-Transfer RNA Synthetase Mutations in Human Disease.
Jul 2015 Journal of child neurology

McMillan Hugh J, Humphreys Peter, Smith Amanda, Schwartzentruber Jeremy, Chakraborty Pranesh, Bulman Dennis E, Beaulieu Chandree L, , Majewski Jacek, Boycott Kym M, Geraghty Michael T.

Aminoacyl-transfer ribonucleic acid (RNA) synthetases (ARSs) are a group of enzymes required for the first step of protein translation. Each aminoacyl-transfer RNA synthetase links a specific amino acid to its corresponding transfer RNA component within the cytoplasm, mitochondria, or both. Mutations in ARSs have been linked to a growing number of diseases. Lysyl-transfer RNA synthetase (KARS) links the amino acid lysine to its cognate transfer RNA. We report 2 siblings with severe infantile visual loss, progressive microcephaly, developmental delay, seizures, and abnormal subcortical white matter. Exome sequencing identified mutations within the KARS gene (NM_005548.2):c.1312C>T; p.Arg438Trp and c.1573G>A; p.Glu525Lys occurring within a highly conserved region of the catalytic domain. Our patients' phenotype is remarkably similar to a phenotype recently reported in glutaminyl-transfer RNA synthetase (QARS), another bifunctional ARS gene. This finding expands the phenotypic spectrum associated with mutations in KARS and draws attention to aminoacyl-transfer RNA synthetase as a group of enzymes that are increasingly being implicated in human disease.

25851414 Mutations in FARS2 and non-fatal mitochondrial dysfunction in two siblings.
May 2015 American journal of medical genetics. Part A

Vernon Hilary J, McClellan Rebecca, Batista Denise As, Naidu Sakkubai.

Recently, mutations in FARS2, which encodes for mitochondrial phenylalanyl-tRNA synthetase, have been implicated in autosomal recessive combined oxidative phosphorylation deficiency 14. Associated clinical features in three previously reported patients with confirmed FARS2 mutations include infantile onset epilepsy, and a fatal Alpers-like encephalopathy. Herein, we report on two siblings with global developmental delay, dysarthria and tremor and compound heterozygous FARS2 abnormalities. They have a heterozygous missense mutation, c.1255C>T which predicts p.Arg419Cys in exon 7 of FARS2, inherited from their father and uncovered on exome sequencing, and an interstitial deletion of chromosome 6p25.1 inherited from their mother and uncovered on SNP array. This interstitial deletion includes all of exon 6 and parts of introns 5 and 6 of FARS2. Biochemical studies were also consistent with a mitochondrial disorder. While these siblings had considerable developmental difficulties, they are making consistent developmental progress and appear to be considerably less severely affected than the other patients reported in the literature with FARS2 associated mitochondrial disease. Thus, this study expands the phenotypic spectrum of FARS2 related disease and emphasizes intragenic deletion in the list of causative mutations. © 2015 Wiley Periodicals, Inc.

25809939 A novel mutation in the promoter of RARS2 causes pontocerebellar hypoplasia in two siblings.
Mar 2015 Journal of human genetics

Li Zejuan, Schonberg Rhonda, Guidugli Lucia, Johnson Amy Knight, Arnovitz Stephen, Yang Sandra, Scafidi Joseph, Summar Marshall L, Vezina Gilbert, Das Soma, Chapman Kimberly, Del Gaudio Daniela.

Pontocerebellar hypoplasia (PCH) is characterized by hypoplasia and atrophy of the cerebellum, variable pontine atrophy, microcephaly, severe mental and motor impairments and seizures. Mutations in 11 genes have been reported in 8 out of 10 forms of PCH. Recessive mutations in the mitochondrial arginyl-transfer RNA synthetase gene (RARS2) have been recently associated with PCH type 6, which is characterized by early-onset encephalopathy with signs of oxidative phosphorylation defect. Here we describe the clinical presentation, neuroimaging findings and molecular characterizations of two siblings with a clinical diagnosis of PCH who displayed a novel variant (c.-2A>G) in the 5'-UTR of the RARS2 gene in the homozygous state. This variant was identified through next-generation sequencing testing of a panel of nine genes known to be involved in PCH. Gene expression and functional studies demonstrated that the c.-2A>G sequence change directly leads to a reduced RARS2 messenger RNA expression in the patients by decreasing RARS2 promoter activity, thus providing evidence that mutations in the RARS2 promoter are likely to represent a new causal mechanism of PCH6.Journal of Human Genetics advance online publication, 26 March 2015; doi:10.1038/jhg.2015.31.

25787132 Mutations in the mitochondrial cysteinyl-tRNA synthase gene, CARS2, lead to a severe epileptic encephalopathy and complex movement disorder.
Mar 2015 Journal of medical genetics

Coughlin Curtis R, Scharer Gunter H, Friederich Marisa W, Yu Hung-Chun, Geiger Elizabeth A, Creadon-Swindell Geralyn, Collins Abigail E, Vanlander Arnaud V, Coster Rudy Van, Powell Christopher A, Swanson Michael A, Minczuk Michal, Van Hove Johan L K, Shaikh Tamim H.

Mitochondrial disease is often suspected in cases of severe epileptic encephalopathy especially when a complex movement disorder, liver involvement and progressive developmental regression are present. Although mutations in either mitochondrial DNA or POLG are often present, other nuclear defects in mitochondrial DNA replication and protein translation have been associated with a severe epileptic encephalopathy.

25771765 Response to: does IARS2 deficiency cause an intrinsic disorder of bone development (skeletal dysplasia) or are the reported skeletal changes secondary to growth hormone deficiency and neuromuscular involvement?
Mar 2015 Hum. Mutat.

Samuels Mark E, Alos Nathalie, Deal Cheri L.

25771764 Does IARS2 deficiency cause an intrinsic disorder of bone development (skeletal dysplasia) or are the reported skeletal changes secondary to growth hormone deficiency and neuromuscular involvement?
Mar 2015 Hum. Mutat.

Mordaunt Dylan A, Savaririyan Ravi.

25754315 Novel, Compound Heterozygous, Single-Nucleotide Variants in MARS2 Associated with Developmental Delay, Poor Growth, and Sensorineural Hearing Loss.
Mar 2015 Human mutation

Webb Bryn D, Wheeler Patricia G, Hagen Jacob J, Cohen Ninette, Linderman Michael D, Diaz George A, Naidich Thomas P, Rodenburg Richard J, Houten Sander M, Schadt Eric E.

Novel, single-nucleotide mutations were identified in the mitochondrial methionyl amino-acyl tRNA synthetase gene (MARS2) via whole exome sequencing in two affected siblings with developmental delay, poor growth, and sensorineural hearing loss.We show that compound heterozygous mutations c.550C>T:p.Gln 184* and c.424C>T:p.Arg142Trp in MARS2 lead to decreased MARS2 protein levels in patient lymphoblasts. Analysis of respiratory complex enzyme activities in patient fibroblasts revealed decreased complex I and IV activities. Immunoblotting of patient fibroblast and lymphoblast samples revealed reduced protein levels of NDUFB8 and COXII, representing complex I and IV, respectively. Additionally, overexpression of wild-type MARS2 in patient fibroblasts increased NDUFB8 and COXII protein levels. These findings suggest that recessive single-nucleotide mutations in MARS2 are causative for a new mitochondrial translation deficiency disorder with a primary phenotype including developmental delay and hypotonia. Identification of additional patients with single-nucleotide mutations in MARS2 is necessary to determine if pectus carinatum is also a consistent feature of this syndrome.

25807530 Mutations of human NARS2, encoding the mitochondrial asparaginyl-tRNA synthetase, cause nonsyndromic deafness and Leigh syndrome.
Feb 2015 PLoS genetics

Simon Mariella, Richard Elodie M, Wang Xinjian, Shahzad Mohsin, Huang Vincent H, Qaiser Tanveer A, Potluri Prasanth, Mahl Sarah E, Davila Antonio, Nazli Sabiha, Hancock Saege, Yu Margret, Gargus Jay, Chang Richard, Al-Sheqaih Nada, Newman William G, Abdenur Jose, Starr Arnold, Hegde Rashmi, Dorn Thomas, Busch Anke, Park Eddie, Wu Jie, Schwenzer Hagen, Flierl Adrian, Florentz Catherine, Sissler Marie, Khan Shaheen N, Li Ronghua, Guan Min-Xin, Friedman Thomas B, Wu Doris K, Procaccio Vincent, Riazuddin Sheikh, Wallace Douglas C, Ahmed Zubair M, Huang Taosheng, Riazuddin Saima.

Here we demonstrate association of variants in the mitochondrial asparaginyl-tRNA synthetase NARS2 with human hearing loss and Leigh syndrome. A homozygous missense mutation ([c.637G>T; p.Val213Phe]) is the underlying cause of nonsyndromic hearing loss (DFNB94) and compound heterozygous mutations ([c.969T>A; p.Tyr323*] + [c.1142A>G; p.Asn381Ser]) result in mitochondrial respiratory chain deficiency and Leigh syndrome, which is a neurodegenerative disease characterized by symmetric, bilateral lesions in the basal ganglia, thalamus, and brain stem. The severity of the genetic lesions and their effects on NARS2 protein structure cosegregate with the phenotype. A hypothetical truncated NARS2 protein, secondary to the Leigh syndrome mutation p.Tyr323* is not detectable and p.Asn381Ser further decreases NARS2 protein levels in patient fibroblasts. p.Asn381Ser also disrupts dimerization of NARS2, while the hearing loss p.Val213Phe variant has no effect on NARS2 oligomerization. Additionally we demonstrate decreased steady-state levels of mt-tRNAAsn in fibroblasts from the Leigh syndrome patients. In these cells we show that a decrease in oxygen consumption rates (OCR) and electron transport chain (ETC) activity can be rescued by overexpression of wild type NARS2. However, overexpression of the hearing loss associated p.Val213Phe mutant protein in these fibroblasts cannot complement the OCR and ETC defects. Our findings establish lesions in NARS2 as a new cause for nonsyndromic hearing loss and Leigh syndrome.

25385316 Two siblings with homozygous pathogenic splice-site variant in mitochondrial asparaginyl-tRNA synthetase (NARS2).
Feb 2015 Human mutation

Vanlander Arnaud V, Menten Björn, Smet Joél, De Meirleir Linda, Sante Tom, De Paepe Boel, Seneca Sara, Pearce Sarah F, Powell Christopher A, Vergult Sarah, Michotte Alex, De Latter Elien, Vantomme Lies, Minczuk Michal, Van Coster Rudy.

A homozygous missense mutation (c.822G>C) was found in the gene encoding the mitochondrial asparaginyl-tRNA synthetase (NARS2) in two siblings born to consanguineous parents. These siblings presented with different phenotypes: one had mild intellectual disability and epilepsy in childhood, whereas the other had severe myopathy. Biochemical analysis of the oxidative phosphorylation (OXPHOS) complexes in both siblings revealed a combined complex I and IV deficiency in skeletal muscle. In-gel activity staining after blue native-polyacrylamide gel electrophoresis confirmed the decreased activity of complex I and IV, and, in addition, showed the presence of complex V subcomplexes. Considering the consanguineous descent, homozygosity mapping and whole-exome sequencing were combined revealing the presence of one single missense mutation in the shared homozygous region. The c.822G>C variant affects the 3' splice site of exon 7, leading to skipping of the whole exon 7 and a part of exon 8 in the NARS2 mRNA. In EBV-transformed lymphoblasts, a specific decrease in the amount of charged mt-tRNA(Asn) was demonstrated as compared with controls. This confirmed the pathogenic nature of the variant. To conclude, the reported variant in NARS2 results in a combined OXPHOS complex deficiency involving complex I and IV, making NARS2 a new member of disease-associated aaRS2.

25629079 Whole exome sequencing reveals mutations in NARS2 and PARS2, encoding the mitochondrial asparaginyl-tRNA synthetase and prolyl-tRNA synthetase, in patients with Alpers syndrome.
Jan 2015 Molecular genetics & genomic medicine

Sofou Kalliopi, Kollberg Gittan, Holmström Maria, Dávila Marcela, Darin Niklas, Gustafsson Claes M, Holme Elisabeth, Oldfors Anders, Tulinius Már, Asin-Cayuela Jorge.

Alpers syndrome is a progressive neurodegenerative disorder that presents in infancy or early childhood and is characterized by diffuse degeneration of cerebral gray matter. While mutations in POLG1, the gene encoding the gamma subunit of the mitochondrial DNA polymerase, have been associated with Alpers syndrome with liver failure (Alpers-Huttenlocher syndrome), the genetic cause of Alpers syndrome in most patients remains unidentified. With whole exome sequencing we have identified mutations in NARS2 and PARS2, the genes encoding the mitochondrial asparaginyl-and prolyl-tRNA synthetases, in two patients with Alpers syndrome. One of the patients was homozygous for a missense mutation (c.641C>T, p.P214L) in NARS2. The affected residue is predicted to be located in the stem of a loop that participates in dimer interaction. The other patient was compound heterozygous for a one base insertion (c.1130dupC, p.K378 fs*1) that creates a premature stop codon and a missense mutation (c.836C>T, p.S279L) located in a conserved motif of unknown function in PARS2. This report links for the first time mutations in these genes to human disease in general and to Alpers syndrome in particular.

25854774 Expanding the Clinical and Magnetic Resonance Spectrum of Leukoencephalopathy with Thalamus and Brainstem Involvement and High Lactate (LTBL) in a Patient Harboring a Novel EARS2 Mutation.
- 2015 JIMD reports

Biancheri Roberta, Lamantea Eleonora, Severino Mariasavina, Diodato Daria, Pedemonte Marina, Cassandrini Denise, Ploederl Alexandra, Trucco Federica, Fiorillo Chiara, Minetti Carlo, Santorelli Filippo M, Zeviani Massimo, Bruno Claudio.

Leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL) is a novel mitochondrial disease caused by mutations in EARS2, which encodes the mitochondrial glutamyl-tRNA synthetase (mtGluRS). A distinctive brain MRI pattern is the hallmark of the disease.A 6-year-old boy presented at 3 months with feeding difficulties and muscle hypotonia. Brain MRI, at 8 months, showed hyperintensity of the deep cerebral and cerebellar white matter, thalamus, basal ganglia, brainstem, and thin corpus callosum. From the second year of life onward, the child reported global clinical improvement, parallel to partial resolution of brain MRI pattern. However, the last neuroimaging assessment revealed novel lesions within the left caudate and pallidum nuclei. DNA genomic sequencing analysis identified a novel EARS2 mutation.This case expands the clinical and neuroradiological phenotype of LTBL presenting intermediate clinical manifestations between the severe and milder forms of the disease and previously unreported brain MRI features.

25705216 Structural modeling of tissue-specific mitochondrial alanyl-tRNA synthetase (AARS2) defects predicts differential effects on aminoacylation.
- 2015 Frontiers in genetics

Euro Liliya, Konovalova Svetlana, Asin-Cayuela Jorge, Tulinius Már, Griffin Helen, Horvath Rita, Taylor Robert W, Chinnery Patrick F, Schara Ulrike, Thorburn David R, Suomalainen Anu, Chihade Joseph, Tyynismaa Henna.

The accuracy of mitochondrial protein synthesis is dependent on the coordinated action of nuclear-encoded mitochondrial aminoacyl-tRNA synthetases (mtARSs) and the mitochondrial DNA-encoded tRNAs. The recent advances in whole-exome sequencing have revealed the importance of the mtARS proteins for mitochondrial pathophysiology since nearly every nuclear gene for mtARS (out of 19) is now recognized as a disease gene for mitochondrial disease. Typically, defects in each mtARS have been identified in one tissue-specific disease, most commonly affecting the brain, or in one syndrome. However, mutations in the AARS2 gene for mitochondrial alanyl-tRNA synthetase (mtAlaRS) have been reported both in patients with infantile-onset cardiomyopathy and in patients with childhood to adulthood-onset leukoencephalopathy. We present here an investigation of the effects of the described mutations on the structure of the synthetase, in an effort to understand the tissue-specific outcomes of the different mutations. The mtAlaRS differs from the other mtARSs because in addition to the aminoacylation domain, it has a conserved editing domain for deacylating tRNAs that have been mischarged with incorrect amino acids. We show that the cardiomyopathy phenotype results from a single allele, causing an amino acid change R592W in the editing domain of AARS2, whereas the leukodystrophy mutations are located in other domains of the synthetase. Nevertheless, our structural analysis predicts that all mutations reduce the aminoacylation activity of the synthetase, because all mtAlaRS domains contribute to tRNA binding for aminoacylation. According to our model, the cardiomyopathy mutations severely compromise aminoacylation whereas partial activity is retained by the mutation combinations found in the leukodystrophy patients. These predictions provide a hypothesis for the molecular basis of the distinct tissue-specific phenotypic outcomes.

25638461 A Novel Homozygous YARS2 Mutation in Two Italian Siblings and a Review of Literature.
- 2015 JIMD reports

Ardissone Anna, Lamantea Eleonora, Quartararo Jade, Dallabona Cristina, Carrara Franco, Moroni Isabella, Donnini Claudia, Garavaglia Barbara, Zeviani Massimo, Uziel Graziella.

YARS2 encodes the mitochondrial tyrosyl-tRNA synthetase that catalyzes the covalent binding of tyrosine to its cognate mt-tRNA. Mutations in YARS2 have been identified in patients with myopathy, lactic acidosis, and sideroblastic anemia type 2 (MLASA2). We report here on two siblings with a novel mutation and a review of literature. The older patient presented at 2 months with marked anemia and lactic acidemia. He required periodic blood transfusions until 14 months of age. Cognitive and motor development was normal. His younger sister was diagnosed at birth, presenting with anemia and lactic acidosis at 1 month of age requiring periodical transfusions. She is now 14 months old and doing well. For both our patients, there was no clinical evidence of muscle involvement. We found a new homozygous mutation in YARS2, located in the α-anticodon-binding (αACB) domain, involved in the interaction with the anticodon of the cognate mt-tRNA(Tyr).Our study confirms that MLASA must be considered in patients with congenital sideroblastic anemia and underlines the importance of early diagnosis and supportive therapy in order to prevent severe complications. Clinical severity is variable among YARS2-reported patients: our review of the literature suggests a possible phenotype-genotype correlation, although this should be confirmed in a larger population.

26244500 Two Novel De Novo GARS Mutations Cause Early-Onset Axonal Charcot-Marie-Tooth Disease.
- 2015 PloS one

Liao Yi-Chu, Liu Yo-Tsen, Tsai Pei-Chien, Chang Chia-Ching, Huang Yen-Hua, Soong Bing-Wen, Lee Yi-Chung.

Mutations in the GARS gene have been identified in a small number of patients with Charcot-Marie-Tooth disease (CMT) type 2D or distal spinal muscular atrophy type V, for whom disease onset typically occurs during adolescence or young adulthood, initially manifesting as weakness and atrophy of the hand muscles. The role of GARS mutations in patients with inherited neuropathies in Taiwan remains elusive.

25361775 A homozygous splice-site mutation in CARS2 is associated with progressive myoclonic epilepsy.
Dec 2014 Neurology

Hallmann Kerstin, Zsurka Gábor, Moskau-Hartmann Susanna, Kirschner Janbernd, Korinthenberg Rudolf, Ruppert Ann-Kathrin, Ozdemir Ozkan, Weber Yvonne, Becker Felicitas, Lerche Holger, Elger Christian E, Thiele Holger, Nürnberg Peter, Sander Thomas, Kunz Wolfram S.

We report a consanguineous family with 2 affected individuals whose clinical symptoms closely resembled MERRF (myoclonus epilepsy with ragged red fibers) syndrome including severe myoclonic epilepsy, progressive spastic tetraparesis, progressive impairment of vision and hearing, as well as progressive cognitive decline.

25326399 Intermediate Charcot-Marie-Tooth disease.
Dec 2014 Neuroscience bulletin

Liu Lei, Zhang Ruxu.

Charcot-Marie-Tooth (CMT) disease is a common neurogenetic disorder and its heterogeneity is a challenge for genetic diagnostics. The genetic diagnostic procedures for a CMT patient can be explored according to the electrophysiological criteria: very slow motor nerve conduction velocity (MNCV) (<15 m/s), slow MNCV (15-25 m/s), intermediate MNCV (25-45 m/s), and normal MNCV (>45 m/s). Based on the inheritance pattern, intermediate CMT can be divided into dominant (DI-CMT) and recessive types (RI-CMT). GJB1 is currently considered to be associated with X-linked DI-CMT, and MPZ, INF2, DNM2, YARS, GNB4, NEFL, and MFN2 are associated with autosomal DI-CMT. Moreover, GDAP1, KARS, and PLEKHG5 are associated with RI-CMT. Identification of these genes is not only important for patients and families but also provides new information about pathogenesis. It is hoped that this review will lead to a better understanding of intermediate CMT and provide a detailed diagnostic procedure for intermediate CMT.

25476837 Evolutionary and structural annotation of disease-associated mutations in human aminoacyl-tRNA synthetases.
Dec 2014 BMC genomics

Datt Manish, Sharma Amit.

Mutation(s) in proteins are a natural byproduct of evolution but can also cause serious diseases. Aminoacyl-tRNA synthetases (aaRSs) are indispensable components of all cellular protein translational machineries, and in humans they drive translation in both cytoplasm and mitochondria. Mutations in aaRSs have been implicated in a plethora of diseases including neurological conditions, metabolic disorders and cancer.

25289895 Neuropathologic features of pontocerebellar hypoplasia type 6.
Nov 2014 Journal of neuropathology and experimental neurology

Joseph Jeffrey T, Innes A Micheil, Smith Amanda C, Vanstone Megan R, Schwartzentruber Jeremy A, Bulman Dennis E, Majewski Jacek, Daza Ray A, Hevner Robert F, Michaud Jean, Boycott Kym M, .

Pontocerebellar hypoplasia is a group of severe developmental disorders with prenatal onset affecting the growth and function of the brainstem and cerebellum. The rarity and genetic heterogeneity of this group of disorders can make molecular diagnosis challenging. We report 3 siblings who were born to nonconsanguineous parents, were hypotonic at birth, developed seizures, had repeated apneic spells, and died within 2 months of life. Neuroimaging showed that all had profound cerebellar hypoplasia and simplified cortical gyration. Genetic analysis by whole-exome sequencing demonstrated compound heterozygous mutations in the mitochondrial arginyl transfer RNA synthetase gene RARS2, indicating that the children had pontocerebellar hypoplasia type 6. Autopsies on the younger twin siblings revealed small and immature cerebella at an approximate developmental age of less than 18 weeks. The basis pontis showed regressive changes, and the medulla had marked inferior olivary hypoplasia. The brains of both twins were microencephalic and had simplified gyri; cortices were immature, and deep white matter had extensive astrocytosis. The findings suggest a near-normal embryologic period followed by midgestation developmental slowing or cessation and later regression in select anatomic regions. This is the first detailed description of neuropathologic findings associated with pontocerebellar hypoplasia type 6 and demonstrates the profound effects of RARS2 disruption during early neurodevelopment.

25130867 Mutation in the nuclear-encoded mitochondrial isoleucyl-tRNA synthetase IARS2 in patients with cataracts, growth hormone deficiency with short stature, partial sensorineural deafness, and peripheral neuropathy or with Leigh syndrome.
Nov 2014 Human mutation

Schwartzentruber Jeremy, Buhas Daniela, Majewski Jacek, Sasarman Florin, Papillon-Cavanagh Simon, Thiffault Isabelle, Thiffaut Isabelle, Sheldon Katherine M, Massicotte Christine, Patry Lysanne, Simon Mariella, Zare Amir S, McKernan Kevin J, , Michaud Jacques, Boles Richard G, Deal Cheri L, Desilets Valerie, Shoubridge Eric A, Samuels Mark E.

Mutations in the nuclear-encoded mitochondrial aminoacyl-tRNA synthetases are associated with a range of clinical phenotypes. Here, we report a novel disorder in three adult patients with a phenotype including cataracts, short-stature secondary to growth hormone deficiency, sensorineural hearing deficit, peripheral sensory neuropathy, and skeletal dysplasia. Using SNP genotyping and whole-exome sequencing, we identified a single likely causal variant, a missense mutation in a conserved residue of the nuclear gene IARS2, encoding mitochondrial isoleucyl-tRNA synthetase. The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes. IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation. Compound heterozygous mutations in IARS2 were independently identified in a previously unreported patient with a more severe mitochondrial phenotype diagnosed as Leigh syndrome. This is the first report of clinical findings associated with IARS2 mutations.

25614874 The allelic spectrum of Charcot-Marie-Tooth disease in over 17,000 individuals with neuropathy.
Nov 2014 Molecular genetics & genomic medicine

DiVincenzo Christina, Elzinga Christopher D, Medeiros Adam C, Karbassi Izabela, Jones Jeremiah R, Evans Matthew C, Braastad Corey D, Bishop Crystal M, Jaremko Malgorzata, Wang Zhenyuan, Liaquat Khalida, Hoffman Carol A, York Michelle D, Batish Sat D, Lupski James R, Higgins Joseph J.

We report the frequency, positive rate, and type of mutations in 14 genes (PMP22, GJB1, MPZ, MFN2, SH3TC2, GDAP1, NEFL, LITAF, GARS, HSPB1, FIG4, EGR2, PRX, and RAB7A) associated with Charcot-Marie-Tooth disease (CMT) in a cohort of 17,880 individuals referred to a commercial genetic testing laboratory. Deidentified results from sequencing assays and multiplex ligation-dependent probe amplification (MLPA) were analyzed including 100,102 Sanger sequencing, 2338 next-generation sequencing (NGS), and 21,990 MLPA assays. Genetic abnormalities were identified in 18.5% (n = 3312) of all individuals. Testing by Sanger and MLPA (n = 3216) showed that duplications (dup) (56.7%) or deletions (del) (21.9%) in the PMP22 gene accounted for the majority of positive findings followed by mutations in the GJB1 (6.7%), MPZ (5.3%), and MFN2 (4.3%) genes. GJB1 del and mutations in the remaining genes explained 5.3% of the abnormalities. Pathogenic mutations were distributed as follows: missense (70.6%), nonsense (14.3%), frameshift (8.7%), splicing (3.3%), in-frame deletions/insertions (1.8%), initiator methionine mutations (0.8%), and nonstop changes (0.5%). Mutation frequencies, positive rates, and the types of mutations were similar between tests performed by either Sanger (n = 17,377) or NGS (n = 503). Among patients with a positive genetic finding in a CMT-related gene, 94.9% were positive in one of four genes (PMP22, GJB1, MPZ, or MFN2).

24604904 Application of whole exome sequencing in undiagnosed inherited polyneuropathies.
Nov 2014 Journal of neurology, neurosurgery, and psychiatry

Klein Christopher J, Middha Sumit, Duan Xiaohui, Wu Yanhong, Litchy William J, Gu Weihong, Dyck P James B, Gavrilova Ralitza H, Smith David I, Kocher Jean-Pierre, Dyck Peter J.

Inherited polyneuropathies often go undiagnosed. We investigated whole exome sequencing (WES) in utility to identify the genetic causes of diverse forms of inherited polyneuropathies without genetic diagnosis.

24827421 VARS2 and TARS2 mutations in patients with mitochondrial encephalomyopathies.
Aug 2014 Human mutation

Diodato Daria, Melchionda Laura, Haack Tobias B, Dallabona Cristina, Baruffini Enrico, Donnini Claudia, Granata Tiziana, Ragona Francesca, Balestri Paolo, Margollicci Maria, Lamantea Eleonora, Nasca Alessia, Powell Christopher A, Minczuk Michal, Strom Tim M, Meitinger Thomas, Prokisch Holger, Lamperti Costanza, Zeviani Massimo, Ghezzi Daniele.

By way of whole-exome sequencing, we identified a homozygous missense mutation in VARS2 in one subject with microcephaly and epilepsy associated with isolated deficiency of the mitochondrial respiratory chain (MRC) complex I and compound heterozygous mutations in TARS2 in two siblings presenting with axial hypotonia and severe psychomotor delay associated with multiple MRC defects. The nucleotide variants segregated within the families, were absent in Single Nucleotide Polymorphism (SNP) databases and are predicted to be deleterious. The amount of VARS2 and TARS2 proteins and valyl-tRNA and threonyl-tRNA levels were decreased in samples of afflicted patients according to the genetic defect. Expression of the corresponding wild-type transcripts in immortalized mutant fibroblasts rescued the biochemical impairment of mitochondrial respiration and yeast modeling of the VARS2 mutation confirmed its pathogenic role. Taken together, these data demonstrate the role of the identified mutations for these mitochondriopathies. Our study reports the first mutations in the VARS2 and TARS2 genes, which encode two mitochondrial aminoacyl-tRNA synthetases, as causes of clinically distinct, early-onset mitochondrial encephalopathies.

25120326 Neuropathic pain model of peripheral neuropathies mediated by mutations of glycyl-tRNA synthetase.
Aug 2014 Journal of Korean medical science

Lee Seo Jin, Seo Ah Jung, Park Byung Sun, Jo Hyun Woo, Huh Youngbuhm.

Charcot-Marie-Tooth disease (CMT) is the most common inherited motor and sensory neuropathy. Previous studies have found that, according to CMT patients, neuropathic pain is an occasional symptom of CMT. However, neuropathic pain is not considered to be a significant symptom associated with CMT and, as a result, no studies have investigated the pathophysiology underlying neuropathic pain in this disorder. Thus, the first animal model of neuropathic pain was developed by our laboratory using an adenovirus vector system to study neuropathic pain in CMT. To this end, glycyl-tRNA synthetase (GARS) fusion proteins with a FLAG-tag (wild type [WT], L129P and G240R mutants) were expressed in spinal cord and dorsal root ganglion (DRG) neurons using adenovirus vectors. It is known that GARS mutants induce GARS axonopathies, including CMT type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V). Additionally, the morphological phenotypes of neuropathic pain in this animal model of GARS-induced pain were assessed using several possible markers of pain (Iba1, pERK1/2) or a marker of injured neurons (ATF3). These results suggest that this animal model of CMT using an adenovirus may provide information regarding CMT as well as a useful strategy for the treatment of neuropathic pain.

25058219 Use of whole-exome sequencing to determine the genetic basis of multiple mitochondrial respiratory chain complex deficiencies.
Jul 2014 JAMA

Taylor Robert W, Pyle Angela, Griffin Helen, Blakely Emma L, Duff Jennifer, He Langping, Smertenko Tania, Alston Charlotte L, Neeve Vivienne C, Best Andrew, Yarham John W, Kirschner Janbernd, Schara Ulrike, Talim Beril, Topaloglu Haluk, Baric Ivo, Holinski-Feder Elke, Abicht Angela, Czermin Birgit, Kleinle Stephanie, Morris Andrew A M, Vassallo Grace, Gorman Grainne S, Ramesh Venkateswaran, Turnbull Douglass M, Santibanez-Koref Mauro, McFarland Robert, Horvath Rita, Chinnery Patrick F.

Mitochondrial disorders have emerged as a common cause of inherited disease, but their diagnosis remains challenging. Multiple respiratory chain complex defects are particularly difficult to diagnose at the molecular level because of the massive number of nuclear genes potentially involved in intramitochondrial protein synthesis, with many not yet linked to human disease.

24860141 Reply: DARS2 gene clinical spectrum: new ideas regarding an underdiagnosed leukoencephalopathy.
Jul 2014 Brain

van der Knaap Marjo S, Hamilton Eline M, van Berge Laura.

24860140 DARS2 gene clinical spectrum: new ideas regarding an underdiagnosed leukoencephalopathy.
Jul 2014 Brain

Pinto Wladimir Bocca Vieira de Rezende, de Souza Paulo Victor Sgobbi.

24808023 Novel (ovario) leukodystrophy related to AARS2 mutations.
Jun 2014 Neurology

Dallabona Cristina, Diodato Daria, Kevelam Sietske H, Haack Tobias B, Wong Lee-Jun, Salomons Gajja S, Baruffini Enrico, Melchionda Laura, Mariotti Caterina, Strom Tim M, Meitinger Thomas, Prokisch Holger, Chapman Kim, Colley Alison, Rocha Helena, Ounap Katrin, Schiffmann Raphael, Salsano Ettore, Savoiardo Mario, Hamilton Eline M, Abbink Truus E M, Wolf Nicole I, Ferrero Ileana, Lamperti Costanza, Zeviani Massimo, Vanderver Adeline, Ghezzi Daniele, van der Knaap Marjo S.

The study was focused on leukoencephalopathies of unknown cause in order to define a novel, homogeneous phenotype suggestive of a common genetic defect, based on clinical and MRI findings, and to identify the causal genetic defect shared by patients with this phenotype.

24407472 Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation: high outcome variation between two siblings.
Jun 2014 Neuropediatrics

Tylki-Szymanska Anna, Jurkiewicz Elzbieta, Zakharova Ekaterina Y, Bobek-Billewicz Barbara.

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation is a rare disorder caused by mutations in the gene encoding a mitochondrial aspartyl-tRNA synthetase, DARS2. Clinical features include childhood or adolescent onset, slowly progressive ataxia, spasticity, and dorsal column dysfunction with or without mild cognitive decline. Magnetic resonance (MR) images show a characteristic leukoencephalopathy with multiple long tract involvement. MR spectroscopy shows elevated levels of lactate. We present strikingly different clinical courses and discrepant MR images findings for a pair of brothers. It cannot be excluded that in the cases presented, the different clinical outcome is related to a varicella infection in infancy in the younger brother.

24566671 Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation: clinical and genetic characterization and target for therapy.
Apr 2014 Brain : a journal of neurology

van Berge Laura, Hamilton Eline M, Linnankivi Tarja, Uziel Graziella, Steenweg Marjan E, Isohanni Pirjo, Wolf Nicole I, Krägeloh-Mann Ingeborg, Brautaset Nils J, Andrews P Ian, de Jong Brigit A, al Ghamdi Malak, van Wieringen Wessel N, Tannous Bakhos A, Hulleman Esther, Würdinger Thomas, van Berkel Carola G M, Polder Emiel, Abbink Truus E M, Struys Eduard A, Scheper Gert C, van der Knaap Marjo S, .

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is a disorder caused by recessive mutations in the gene DARS2, which encodes mitochondrial aspartyl-tRNA synthetase. Recent observations indicate that the phenotypic range of the disease is much wider than initially thought. Currently, no treatment is available. The aims of our study were (i) to explore a possible genotype-phenotype correlation; and (ii) to identify potential therapeutic agents that modulate the splice site mutations in intron 2 of DARS2, present in almost all patients. A cross-sectional observational study was performed in 78 patients with two DARS2 mutations in the Amsterdam and Helsinki databases up to December 2012. Clinical information was collected via questionnaires. An inventory was made of the DARS2 mutations in these patients and those previously published. An assay was developed to assess mitochondrial aspartyl-tRNA synthetase enzyme activity in cells. Using a fluorescence reporter system we screened for drugs that modulate DARS2 splicing. Clinical information of 66 patients was obtained. The clinical severity varied from infantile onset, rapidly fatal disease to adult onset, slow and mild disease. The most common phenotype was characterized by childhood onset and slow neurological deterioration. Full wheelchair dependency was rare and usually began in adulthood. In total, 60 different DARS2 mutations were identified, 13 of which have not been reported before. Except for 4 of 42 cases published by others, all patients were compound heterozygous. Ninety-four per cent of the patients had a splice site mutation in intron 2. The groups of patients sharing the same two mutations were too small for formal assessment of genotype-phenotype correlation. However, some combinations of mutations were consistently associated with a mild phenotype. The mitochondrial aspartyl-tRNA synthetase activity was strongly reduced in patient cells. Among the compounds screened, cantharidin was identified as the most potent modulator of DARS2 splicing. In conclusion, the phenotypic spectrum of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is wide, but most often the disease has a relatively slow and mild course. The available evidence suggests that the genotype influences the phenotype, but because of the high number of private mutations, larger numbers of patients are necessary to confirm this. The activity of mitochondrial aspartyl-tRNA synthetase is significantly reduced in patient cells. A compound screen established a 'proof of principle' that the splice site mutation can be influenced. This finding is promising for future therapeutic strategies.

24430573 A novel homozygous YARS2 mutation causes severe myopathy, lactic acidosis, and sideroblastic anemia 2.
Apr 2014 Journal of human genetics

Nakajima Junya, Eminoglu Tuba F, Vatansever Goksel, Nakashima Mitsuko, Tsurusaki Yoshinori, Saitsu Hirotomo, Kawashima Hisashi, Matsumoto Naomichi, Miyake Noriko.

Mitochondrial diseases are associated with defects of adenosine triphosphate production and energy supply to organs as a result of dysfunctions of the mitochondrial respiratory chain. Biallelic mutations in the YARS2 gene encoding mitochondrial tyrosyl-tRNA synthetase cause myopathy, lactic acidosis, and sideroblastic anemia 2 (MLASA2), a type of mitochondrial disease. Here, we report a consanguineous Turkish family with two siblings showing severe metabolic decompensation including recurrent hypoglycemia, lactic acidosis, and transfusion-dependent anemia. Using whole-exome sequencing of the proband and his parents, we identified a novel YARS2 mutation (c.1303A>G, p.Ser435Gly) that was homozygous in the patient and heterozygous in his parents. This mutation is located at the ribosomal protein S4-like domain of the gene, while other reported YARS2 mutations are all within the catalytic domain. Interestingly, the proband showed more severe symptoms and an earlier onset than previously reported patients, suggesting the functional importance of the S4-like domain in tyrosyl-tRNA synthetase.

24669931 Compound heterozygous mutations in glycyl-tRNA synthetase are a proposed cause of systemic mitochondrial disease.
Mar 2014 BMC medical genetics

McMillan Hugh J, Schwartzentruber Jeremy, Smith Amanda, Lee Suzie, Chakraborty Pranesh, Bulman Dennis E, Beaulieu Chandree L, Majewski Jacek, Boycott Kym M, Geraghty Michael T.

Glycyl-tRNA synthetase (GARS) is an aminoacyl-tRNA synthetase (ARS) that links the amino acid glycine to its corresponding tRNA prior to protein translation and is one of three bifunctional ARS that are active within both the cytoplasm and mitochondria. Dominant mutations in GARS cause rare forms of Charcot-Marie-Tooth disease and distal spinal muscular atrophy.

24558666 Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL): assessment of the involved white matter tracts by MRI.
Jan 2014 European journal of radiology

Kassem Hassan, Wafaie Ahmed, Abdelfattah Sherif, Farid Tarek.

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) is a recently identified autosomal recessive disorder with early onset of symptoms and slowly progressive pyramidal, cerebellar and dorsal column dysfunction. LBSL is characterized by distinct white matter abnormalities and selective involvement of brainstem and spinal cord tracts. The purpose of this study is to assess the imaging features of the involved white matter tracts in cases of LBSL by MRI.

24161539 Mutation of the human mitochondrial phenylalanine-tRNA synthetase causes infantile-onset epilepsy and cytochrome c oxidase deficiency.
Jan 2014 Biochimica et biophysica acta

Almalki Abdulraheem, Alston Charlotte L, Parker Alasdair, Simonic Ingrid, Mehta Sarju G, He Langping, Reza Mojgan, Oliveira Jorge M A, Lightowlers Robert N, McFarland Robert, Taylor Robert W, Chrzanowska-Lightowlers Zofia M A.

Mitochondrial aminoacyl-tRNA synthetases (aaRSs) are essential enzymes in protein synthesis since they charge tRNAs with their cognate amino acids. Mutations in the genes encoding mitochondrial aaRSs have been associated with a wide spectrum of human mitochondrial diseases. Here we report the identification of pathogenic mutations (a partial genomic deletion and a highly conserved p. Asp325Tyr missense variant) in FARS2, the gene encoding mitochondrial phenylalanyl-tRNA synthetase, in a patient with early-onset epilepsy and isolated complex IV deficiency in muscle. The biochemical defect was expressed in myoblasts but not in fibroblasts and associated with decreased steady state levels of COXI and COXII protein and reduced steady state levels of the mt-tRNA(Phe) transcript. Functional analysis of the recombinant mutant p. Asp325Tyr FARS2 protein showed an inability to bind ATP and consequently undetectable aminoacylation activity using either bacterial tRNA or human mt-tRNA(Phe) as substrates. Lentiviral transduction of cells with wildtype FARS2 restored complex IV protein levels, confirming that the p.Asp325Tyr mutation is pathogenic, causing respiratory chain deficiency and neurological deficits on account of defective aminoacylation of mt-tRNA(Phe).

25420567 [A novel mutation in glycyl-tRNA synthetase caused Charcot-Marie-Tooth disease type 2D with facial and respiratory muscle involvement].
- 2014 Rinsho shinkeigaku = Clinical neurology

Kawakami Nobuko, Komatsu Kenichi, Yamashita Hirofumi, Uemura Kengo, Oka Nobuyuki, Takashima Hiroshi, Takahashi Ryosuke.

Charcot-Marie-Tooth disease (CMT) is a hereditary peripheral neuropathy; symptoms include distal wasting and weakness, usually with some sensory impairment. The clinical course is typically benign and the disease is not life threatening; however, in some cases, severe phenotypes include serious respiratory distress.

24917879 Transfer RNA and human disease.
- 2014 Frontiers in genetics

Abbott Jamie A, Francklyn Christopher S, Robey-Bond Susan M.

Pathological mutations in tRNA genes and tRNA processing enzymes are numerous and result in very complicated clinical phenotypes. Mitochondrial tRNA (mt-tRNA) genes are "hotspots" for pathological mutations and over 200 mt-tRNA mutations have been linked to various disease states. Often these mutations prevent tRNA aminoacylation. Disrupting this primary function affects protein synthesis and the expression, folding, and function of oxidative phosphorylation enzymes. Mitochondrial tRNA mutations manifest in a wide panoply of diseases related to cellular energetics, including COX deficiency (cytochrome C oxidase), mitochondrial myopathy, MERRF (Myoclonic Epilepsy with Ragged Red Fibers), and MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). Diseases caused by mt-tRNA mutations can also affect very specific tissue types, as in the case of neurosensory non-syndromic hearing loss and pigmentary retinopathy, diabetes mellitus, and hypertrophic cardiomyopathy. Importantly, mitochondrial heteroplasmy plays a role in disease severity and age of onset as well. Not surprisingly, mutations in enzymes that modify cytoplasmic and mitochondrial tRNAs are also linked to a diverse range of clinical phenotypes. In addition to compromised aminoacylation of the tRNAs, mutated modifying enzymes can also impact tRNA expression and abundance, tRNA modifications, tRNA folding, and even tRNA maturation (e.g., splicing). Some of these pathological mutations in tRNAs and processing enzymes are likely to affect non-canonical tRNA functions, and contribute to the diseases without significantly impacting on translation. This chapter will review recent literature on the relation of mitochondrial and cytoplasmic tRNA, and enzymes that process tRNAs, to human disease. We explore the mechanisms involved in the clinical presentation of these various diseases with an emphasis on neurological disease.

25254289 Perrault Syndrome.
- 2014

.

24344687 Phenotypic variability and identification of novel YARS2 mutations in YARS2 mitochondrial myopathy, lactic acidosis and sideroblastic anaemia.
Dec 2013 Orphanet journal of rare diseases

Riley Lisa G, Menezes Minal J, Rudinger-Thirion Joëlle, Duff Rachael, de Lonlay Pascale, Rotig Agnes, Tchan Michel C, Davis Mark, Cooper Sandra T, Christodoulou John.

Mutations in the mitochondrial tyrosyl-tRNA synthetase (YARS2) gene have previously been identified as a cause of the tissue specific mitochondrial respiratory chain (RC) disorder, Myopathy, Lactic Acidosis, Sideroblastic Anaemia (MLASA). In this study, a cohort of patients with a mitochondrial RC disorder for who anaemia was a feature, were screened for mutations in YARS2.

24047924 Subdural effusions and lack of early pontocerebellar hypoplasia in siblings with RARS2 mutations.
Dec 2013 Archives of disease in childhood

Kastrissianakis Katherina, Anand Geetha, Quaghebeur Gerardine, Price Sue, Prabhakar Prab, Marinova Jasmina, Brown Garry, McShane Tony.

Mutations in the recently described RARS2 gene encoding for mitochondrial arginyl-transfer RNA synthetase give rise to a disorder characterised by early onset seizures, progressive microcephaly and developmental delay. The disorder was named pontocerebellar hypoplasia type 6 (PCH6) based on the corresponding radiological findings observed in the original cases. We report two siblings with the RARS2 mutation who displayed typical clinical features of PCH6, but who had distinct neuroimaging features. Early scans showed marked supratentorial, rather than infratentorial, atrophy, and the pons remained preserved throughout. One sibling also had bilateral subdural effusions at presentation. The deceleration in head growth pointed to an evolving genetic/metabolic process giving rise to cerebral atrophy and secondary subdural effusions. RARS2 mutations should be considered in infants presenting with seizures, subdural effusions, decelerating head growth and evidence of cerebral atrophy even in the absence of pontocerebellar hypoplasia on imaging.

24003969 Pathophysiology and genetic mutations in congenital sideroblastic anemia.
Dec 2013 Pediatrics international : official journal of the Japan Pediatric Society

Fujiwara Tohru, Harigae Hideo.

Sideroblastic anemias are heterogeneous congenital and acquired disorders characterized by anemia and the presence of ringed sideroblasts in the bone marrow. Congenital sideroblastic anemia (CSA) is a rare disease caused by mutations of genes involved in heme biosynthesis, iron-sulfur [Fe-S] cluster biosynthesis, and mitochondrial protein synthesis. The most common form is X-linked sideroblastic anemia, due to mutations in the erythroid-specific δ-aminolevulinate synthase (ALAS2), which is the first enzyme of the heme biosynthesis pathway in erythroid cells. Other known etiologies include mutations in the erythroid specific mitochondrial transporter (SLC25A38), adenosine triphosphate (ATP) binding cassette B7 (ABCB7), glutaredoxin 5 (GLRX5), thiamine transporter SLC19A2, the RNA-modifying enzyme pseudouridine synthase (PUS1), and mitochondrial tyrosyl-tRNA synthase (YARS2), as well as mitochondrial DNA deletions. Due to its rarity, however, there have been few systematic pathophysiological and genetic investigations focusing on sideroblastic anemia. Therefore, a nationwide survey of sideroblastic anemia was conducted in Japan to investigate the epidemiology and pathogenesis of this disease. This review will cover the findings of this recent survey and summarize the current understanding of the pathophysiology and genetic mutations involved in CSA.

24030952 Next generation sequencing for molecular diagnosis of neurological disorders using ataxias as a model.
Oct 2013 Brain : a journal of neurology

Németh Andrea H, Kwasniewska Alexandra C, Lise Stefano, Parolin Schnekenberg Ricardo, Becker Esther B E, Bera Katarzyna D, Shanks Morag E, Gregory Lorna, Buck David, Zameel Cader M, Talbot Kevin, de Silva Rajith, Fletcher Nicholas, Hastings Rob, Jayawant Sandeep, Morrison Patrick J, Worth Paul, Taylor Malcolm, Tolmie John, O'Regan Mary, , Valentine Ruth, Packham Emily, Evans Julie, Seller Anneke, Ragoussis Jiannis.

Many neurological conditions are caused by immensely heterogeneous gene mutations. The diagnostic process is often long and complex with most patients undergoing multiple invasive and costly investigations without ever reaching a conclusive molecular diagnosis. The advent of massively parallel, next-generation sequencing promises to revolutionize genetic testing and shorten the 'diagnostic odyssey' for many of these patients. We performed a pilot study using heterogeneous ataxias as a model neurogenetic disorder to assess the introduction of next-generation sequencing into clinical practice. We captured 58 known human ataxia genes followed by Illumina Next-Generation Sequencing in 50 highly heterogeneous patients with ataxia who had been extensively investigated and were refractory to diagnosis. All cases had been tested for spinocerebellar ataxia 1-3, 6, 7 and Friedrich's ataxia and had multiple other biochemical, genetic and invasive tests. In those cases where we identified the genetic mutation, we determined the time to diagnosis. Pathogenicity was assessed using a bioinformatics pipeline and novel variants were validated using functional experiments. The overall detection rate in our heterogeneous cohort was 18% and varied from 8.3% in those with an adult onset progressive disorder to 40% in those with a childhood or adolescent onset progressive disorder. The highest detection rate was in those with an adolescent onset and a family history (75%). The majority of cases with detectable mutations had a childhood onset but most are now adults, reflecting the long delay in diagnosis. The delays were primarily related to lack of easily available clinical testing, but other factors included the presence of atypical phenotypes and the use of indirect testing. In the cases where we made an eventual diagnosis, the delay was 3-35 years (mean 18.1 years). Alignment and coverage metrics indicated that the capture and sequencing was highly efficient and the consumable cost was ∼£400 (€460 or US$620). Our pathogenicity interpretation pathway predicted 13 different mutations in eight different genes: PRKCG, TTBK2, SETX, SPTBN2, SACS, MRE11, KCNC3 and DARS2 of which nine were novel including one causing a newly described recessive ataxia syndrome. Genetic testing using targeted capture followed by next-generation sequencing was efficient, cost-effective, and enabled a molecular diagnosis in many refractory cases. A specific challenge of next-generation sequencing data is pathogenicity interpretation, but functional analysis confirmed the pathogenicity of novel variants showing that the pipeline was robust. Our results have broad implications for clinical neurology practice and the approach to diagnostic testing.

24034276 A new mutation in the gene encoding mitochondrial seryl-tRNA synthetase as a cause of HUPRA syndrome.
Sep 2013 BMC nephrology

Rivera Henry, Martín-Hernández Elena, Delmiro Aitor, García-Silva María Teresa, Quijada-Fraile Pilar, Muley Rafael, Arenas Joaquín, Martín Miguel A, Martínez-Azorín Francisco.

HUPRA syndrome is a rare mitochondrial disease characterized by hyperuricemia, pulmonary hypertension, renal failure in infancy and alkalosis. This syndrome was previously described in three patients with a homozygous mutation c.1169A > G (p.D390G) in SARS2, encoding the mitochondrial seryl-tRNA synthetase.

23918765 A distinct mitochondrial myopathy, lactic acidosis and sideroblastic anemia (MLASA) phenotype associates with YARS2 mutations.
Sep 2013 American journal of medical genetics. Part A

Shahni Rojeen, Wedatilake Yehani, Cleary Maureen A, Lindley Keith J, Sibson Keith R, Rahman Shamima.

Nuclear-encoded disorders of mitochondrial translation are clinically and genetically heterogeneous. Genetic causes include defects of mitochondrial aminoacyl-tRNA synthetases, and factors required for initiation, elongation and termination of protein synthesis as well as ribosome recycling. We report on a new case of myopathy, lactic acidosis and sideroblastic anemia (MLASA) syndrome caused by defective mitochondrial tyrosyl aminoacylation. The patient presented at 1 year with anemia initially attributed to iron deficiency. Bone marrow aspirate at 5 years revealed ringed sideroblasts but transfusion dependency did not occur until 11 years. Other clinical features included lactic acidosis, poor weight gain, hypertrophic cardiomyopathy and severe myopathy leading to respiratory failure necessitating ventilatory support. Long-range PCR excluded mitochondrial DNA rearrangements. Clinical diagnosis of MLASA prompted direct sequence analysis of the YARS2 gene encoding the mitochondrial tyrosyl-tRNA synthetase, which revealed homozygosity for a known pathogenic mutation, c.156C>G;p.F52L. Comparison with four previously reported cases demonstrated remarkable clinical homogeneity. First line investigation of MLASA should include direct sequence analysis of YARS2 and PUS1 (encoding a tRNA modification factor) rather than muscle biopsy. Early genetic diagnosis is essential for counseling and to facilitate appropriate supportive therapy. Reasons for segregation of specific clinical phenotypes with particular mitochondrial aminoacyl tRNA-synthetase defects remain unknown.

23652419 Impaired information-processing speed and working memory in leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate (LBSL) and DARS2 mutations: a report of three adult patients.
Aug 2013 Journal of neurology

Martikainen Mika H, Ellfolk Ulla, Majamaa Kari.

Leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate (LBSL) is clinically characterized by progressive pyramidal and cerebellar dysfunction, dorsal column dysfunction and sometimes with axonal neuropathy. Magnetic resonance imaging of brain and the spinal cord reveals characteristic findings. LBSL is caused by mutations in the DARS2 gene that encodes the mitochondrial aspartyl-tRNA synthetase. The presentation and clinical course of LBSL is not uniform, and there is lack of longitudinal data on these patients. In addition, the existing data on the prevalence and characteristics of cognitive abnormalities in patients with LBSL are scarce and somewhat conflicting. Here we report long-term data of neurological and cognitive functioning in three non-related adult patients with LBSL. Cognitive impairment seems to be common among patients with LBSL and DARS2 mutations. The cognitive profile in LBSL shares similarities with that reported in multiple sclerosis, as information-processing speed and working memory are especially affected. In addition, our results and the previously reported carrier frequencies of common pathogenic DARS2 mutations suggest that LBSL may be underdiagnosed in the population.

23768514 Mutations in KARS, encoding lysyl-tRNA synthetase, cause autosomal-recessive nonsyndromic hearing impairment DFNB89.
Jul 2013 Am. J. Hum. Genet.

Santos-Cortez Regie Lyn P, Lee Kwanghyuk, Azeem Zahid, Antonellis Patrick J, Pollock Lana M, Khan Saadullah, Irfanullah , Andrade-Elizondo Paula B, Chiu Ilene, Adams Mark D, Basit Sulman, Smith Joshua D, , Nickerson Deborah A, McDermott Brian M, Ahmad Wasim, Leal Suzanne M.

Previously, DFNB89, a locus associated with autosomal-recessive nonsyndromic hearing impairment (ARNSHI), was mapped to chromosomal region 16q21-q23.2 in three unrelated, consanguineous Pakistani families. Through whole-exome sequencing of a hearing-impaired individual from each family, missense mutations were identified at highly conserved residues of lysyl-tRNA synthetase (KARS): the c.1129G>A (p.Asp377Asn) variant was found in one family, and the c.517T>C (p.Tyr173His) variant was found in the other two families. Both variants were predicted to be damaging by multiple bioinformatics tools. The two variants both segregated with the nonsyndromic-hearing-impairment phenotype within the three families, and neither mutation was identified in ethnically matched controls or within variant databases. Individuals homozygous for KARS mutations had symmetric, severe hearing impairment across all frequencies but did not show evidence of auditory or limb neuropathy. It has been demonstrated that KARS is expressed in hair cells of zebrafish, chickens, and mice. Moreover, KARS has strong localization to the spiral ligament region of the cochlea, as well as to Deiters' cells, the sulcus epithelium, the basilar membrane, and the surface of the spiral limbus. It is hypothesized that KARS variants affect aminoacylation in inner-ear cells by interfering with binding activity to tRNA or p38 and with tetramer formation. The identification of rare KARS variants in ARNSHI-affected families defines a gene that is associated with ARNSHI.

23596069 Targeted exome sequencing of suspected mitochondrial disorders.
May 2013 Neurology

Lieber Daniel S, Calvo Sarah E, Shanahan Kristy, Slate Nancy G, Liu Shangtao, Hershman Steven G, Gold Nina B, Chapman Brad A, Thorburn David R, Berry Gerard T, Schmahmann Jeremy D, Borowsky Mark L, Mueller David M, Sims Katherine B, Mootha Vamsi K.

To evaluate the utility of targeted exome sequencing for the molecular diagnosis of mitochondrial disorders, which exhibit marked phenotypic and genetic heterogeneity.

23589646 Teaching NeuroImages: MRI guides genetics: leukoencephalopathy with brainstem and spinal cord involvement (LBSL).
Apr 2013 Neurology

Schicks Julia, Schöls Ludger, van der Knaap Marjo S, Synofzik Matthis.

23541342 Mutations in LARS2, encoding mitochondrial leucyl-tRNA synthetase, lead to premature ovarian failure and hearing loss in Perrault syndrome.
Apr 2013 American journal of human genetics

Pierce Sarah B, Gersak Ksenija, Michaelson-Cohen Rachel, Walsh Tom, Lee Ming K, Malach Daniel, Klevit Rachel E, King Mary-Claire, Levy-Lahad Ephrat.

The genetic causes of premature ovarian failure (POF) are highly heterogeneous, and causative mutations have been identified in more than ten genes so far. In two families affected by POF accompanied by hearing loss (together, these symptoms compose Perrault syndrome), exome sequencing revealed mutations in LARS2, encoding mitochondrial leucyl-tRNA synthetase: homozygous c.1565C>A (p.Thr522Asn) in a consanguineous Palestinian family and compound heterozygous c.1077delT and c.1886C>T (p.Thr629Met) in a nonconsanguineous Slovenian family. LARS2 c.1077delT leads to a frameshift at codon 360 of the 901 residue protein. LARS2 p.Thr522Asn occurs in the LARS2 catalytic domain at a site conserved from bacteria through mammals. LARS2 p.Thr629Met occurs in the LARS2 leucine-specific domain, which is adjacent to a catalytic loop critical in all species but for which primary sequence is not well conserved. A recently developed method of detecting remote homologies revealed threonine at this site in consensus sequences derived from multiple-species alignments seeded by human and E. coli residues at this region. Yeast complementation indicated that LARS2 c.1077delT is nonfunctional and that LARS2 p.Thr522Asn is partially functional. LARS2 p.Thr629Met was functional in this assay but might be insufficient as a heterozygote with the fully nonfunctional LARS2 c.1077delT allele. A known C. elegans strain with the protein-truncating alteration LARS-2 p.Trp247Ter was confirmed to be sterile. After HARS2, LARS2 is the second gene encoding mitochondrial tRNA synthetase to be found to harbor mutations leading to Perrault syndrome, further supporting a critical role for mitochondria in the maintenance of ovarian function and hearing.

23433712 Mitochondrial aminoacyl-tRNA synthetases in human disease.
Apr 2013 Molecular genetics and metabolism

Konovalova Svetlana, Tyynismaa Henna.

Mitochondrial aminoacyl-tRNA synthetases (mtARSs) are essential in the process of transferring genetic information from mitochondrial DNA to the complexes of the oxidative phosphorylation system. These synthetases perform an integral step in the initiation of mitochondrial protein synthesis by charging tRNAs with their cognate amino acids. All mtARSs are encoded by nuclear genes, nine of which have recently been described as disease genes for mitochondrial disorders. Unexpectedly, the clinical presentations of these diseases are highly specific to the affected synthetase. Encephalopathy is the most common manifestation but again with gene-specific outcomes. Other clinical presentations include myopathy with anemia, cardiomyopathy, tubulopathy and hearing loss with female ovarian dysgenesis. Here we review the described mutation types and the associated patient phenotypes. The identified mutation spectrum suggests that only mutation types that allow some residual tRNA-charging activity can result in the described mtARS diseases but the molecular mechanisms behind the selective tissue involvement are not currently understood.

22677571 Neuropathology of leukoencephalopathy with brainstem and spinal cord involvement and high lactate caused by a homozygous mutation of DARS2.
Apr 2013 Brain & development

Yamashita Sumimasa, Miyake Noriko, Matsumoto Naomichi, Osaka Hitoshi, Iai Mizue, Aida Noriko, Tanaka Yukichi.

We diagnosed three siblings from consanguineous east Asian parents with leukoencephalopathy with brainstem and spinal cord involvement and high lactate (LBSL) from characteristic MRI, MRS findings and a homozygous mutation in the DARS2 gene. The neurological symptoms of the three patients consisted of psychomotor developmental delay, cerebellar ataxia since infancy, spasticity in the initial phase and peripheral neuropathy in later stages. Their mental development was delayed, but did not deteriorate. MRI signal abnormalities included the same abnormalities reported previously but tended to be more extensive. Signal abnormalities in the cerebral and cerebellar white matter were homogeneous and confluent from early stages. In addition, other tract such as the central tegmental tract was involved. Furthermore, an atrophic change in the cerebral white matter was observed on follow-up in one case. Two of the patients were autopsied and neuropathological findings revealed characteristic vacuolar changes in the white matter of the cerebrum, cerebellum and the nerve tracts of the brain stem and spinal cord. The central myelin sheath showed intralamellar splitting by electron microscopy. These findings were consistent to a spongy degeneration in the diffuse white matter of the brain, or spongiform leukoencephalopathy. In addition, peripheral nerves showed both axonal degeneration and abnormal myelin structures. We discussed the relationship between deficits in mitochondrial aspartyl-tRNA synthetase activity and the neuropathology observed.

23644316 Adult-onset leukoencephalopathy with brain stem and spinal cord involvement in Chinese Han population: a case report and literature review.
Mar 2013 Neurology India

Cheng Fu-Bo, Shen Ping-Ping, Zhou Hong-Wei, Meng Hong-Mei, Yang Yu, Feng Jia-Chun.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a recently described disorder with an autosomal recessive mode of inheritance. We report a case of rare adult-onset LBSL with typical magnetic resonance imaging (MRI) features. The DARS2 gene mutation analysis has identified a c. 228-20_21delTTinsC (p.R76SfsX5) mutation and a c. 850G > A (p. 284E > K) mutation. With glucocorticosteroid treatment the patient has had improvement in bladder symptoms. This is the first reported adult-onset LBSL case in the Chinese Han population. A review of the literature suggests that brain lactate elevation in adult-onset LBSL is lower than early-onset cases (P < 0.01), and early-onset cases show mild intelligence and cognition decline. These observations suggest that age of onset and brain lactate levels probably influence the prognosis of LBSL.

23216004 Pathogenic mutations causing LBSL affect mitochondrial aspartyl-tRNA synthetase in diverse ways.
Mar 2013 The Biochemical journal

van Berge Laura, Kevenaar Josta, Polder Emiel, Gaudry Agnès, Florentz Catherine, Sissler Marie, van der Knaap Marjo S, Scheper Gert C.

The autosomal recessive white matter disorder LBSL (leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation) is caused by mutations in DARS2, coding for mtAspRS (mitochondrial aspartyl-tRNA synthetase). Generally, patients are compound heterozygous for mutations in DARS2. Many different mutations have been identified in patients, including several missense mutations. In the present study, we have examined the effects of missense mutations found in LBSL patients on the expression, enzyme activity, localization and dimerization of mtAspRS, which is important for understanding the cellular defect underlying the pathogenesis of the disease. Nine different missense mutations were analysed and were shown to have various effects on mtAspRS properties. Several mutations have a direct effect on the catalytic activity of the enzyme; others have an effect on protein expression or dimerization. Most mutations have a clear impact on at least one of the properties of mtAspRS studied, probably resulting in a small contribution of the missense variants to the mitochondrial aspartylation activity in the cell.

23008233 Multisystem fatal infantile disease caused by a novel homozygous EARS2 mutation.
Feb 2013 Brain

Talim Beril, Pyle Angela, Griffin Helen, Topaloglu Haluk, Tokatli Aysegul, Keogh Michael J, Santibanez-Koref Mauro, Chinnery Patrick F, Horvath Rita.

22569581 Pontocerebellar hypoplasia type 6 caused by mutations in RARS2: definition of the clinical spectrum and molecular findings in five patients.
Jan 2013 Journal of inherited metabolic disease

Cassandrini Denise, Cilio Maria Roberta, Bianchi Marzia, Doimo Mara, Balestri Martina, Tessa Alessandra, Rizza Teresa, Sartori Geppo, Meschini Maria Chiara, Nesti Claudia, Tozzi Giulia, Petruzzella Vittoria, Piemonte Fiorella, Bisceglia Luigi, Bruno Claudio, Dionisi-Vici Carlo, D'Amico Adele, Fattori Fabiana, Carrozzo Rosalba, Salviati Leonardo, Santorelli Filippo M, Bertini Enrico.

Recessive mutations in the mitochondrial arginyl-transfer RNA synthetase (RARS2) gene have been associated with early onset encephalopathy with signs of oxidative phosphorylation defects classified as pontocerebellar hypoplasia 6. We describe clinical, neuroimaging and molecular features on five patients from three unrelated families who displayed mutations in RARS2. All patients rapidly developed a neonatal or early-infantile epileptic encephalopathy with intractable seizures. The long-term follow-up revealed a virtual absence of psychomotor development, progressive microcephaly, and feeding difficulties. Mitochondrial respiratory chain enzymes in muscle and fibroblasts were normal in two. Blood and CSF lactate was abnormally elevated in all five patients at early stages while appearing only occasionally abnormal with the progression of the disease. Cerebellar vermis hypoplasia with normal aspect of the cerebral and cerebellar hemispheres appeared within the first months of life at brain MRI. In three patients follow-up neuroimaging revealed a progressive pontocerebellar and cerebral cortical atrophy. Molecular investigations of RARS2 disclosed the c.25A>G/p.I9V and the c.1586+3A>T in family A, the c.734G>A/p.R245Q and the c.1406G>A/p.R469H in family B, and the c.721T>A/p.W241R and c.35A>G/p.Q12R in family C. Functional complementation studies in Saccharomyces cerevisiae showed that mutation MSR1-R531H (equivalent to human p.R469H) abolished respiration whereas the MSR1-R306Q strain (corresponding to p.R245Q) displayed a reduced growth on non-fermentable YPG medium. Although mutations functionally disrupted yeast we found a relatively well preserved arginine aminoacylation of mitochondrial tRNA. Clinical and neuroimaging findings are important clues to raise suspicion and to reach diagnostic accuracy for RARS2 mutations considering that biochemical abnormalities may be absent in muscle biopsy.

23279345 Two novel mutations of GARS in Korean families with distal hereditary motor neuropathy type V.
Dec 2012 Journal of the peripheral nervous system : JPNS

Lee Hye Jin, Park Jin, Nakhro Khriezanou, Park Jin Mo, Hur Yoon-Mi, Choi Byung-Ok, Chung Ki Wha.

Glycyl-tRNA synthetase (GARS), which encodes the enzyme responsible for charging tRNA(Gly) with glycine in both the cytoplasm and mitochondria, is implicated to Charcot-Marie-Tooth disease 2D (CMT2D) and distal hereditary motor neuropathy type V (dHMN-V). We performed whole exome sequencing (WES) to identify the genetic defects in the two dHMN families. WES revealed several decades of non-synonymous variants in the CMT and aminoacyl-tRNA synthetase genes. The subsequent capillary sequencing for family members and controls revealed two novel causative mutations, c.598G>A (D200N) and c.794C>T (S265F), in the GARS gene in each dHMN family. Both mutations were cosegregated with affected individuals in each family, and were not found in the 200 controls. The mutation sites were well conserved between the different species and in silico analysis predicted that both mutations may affect protein function. Therefore, we believe that these two novel GARS mutations are the underlying causes of the dHMN phenotype.

22833457 Mitochondrial phenylalanyl-tRNA synthetase mutations underlie fatal infantile Alpers encephalopathy.
Oct 2012 Human molecular genetics

Elo Jenni M, Yadavalli Srujana S, Euro Liliya, Isohanni Pirjo, Götz Alexandra, Carroll Christopher J, Valanne Leena, Alkuraya Fowzan S, Uusimaa Johanna, Paetau Anders, Caruso Eric M, Pihko Helena, Ibba Michael, Tyynismaa Henna, Suomalainen Anu.

Next-generation sequencing has turned out to be a powerful tool to uncover genetic basis of childhood mitochondrial disorders. We utilized whole-exome analysis and discovered novel compound heterozygous mutations in FARS2 (mitochondrial phenylalanyl transfer RNA synthetase), encoding the mitochondrial phenylalanyl transfer RNA (tRNA) synthetase (mtPheRS) in two patients with fatal epileptic mitochondrial encephalopathy. The mutations affected highly conserved amino acids, p.I329T and p.D391V. Recently, a homozygous FARS2 variant p.Y144C was reported in a Saudi girl with mitochondrial encephalopathy, but the pathogenic role of the variant remained open. Clinical features, including postnatal onset, catastrophic epilepsy, lactic acidemia, early lethality and neuroimaging findings of the patients with FARS2 variants, resembled each other closely, and neuropathology was consistent with Alpers syndrome. Our structural analysis of mtPheRS predicted that p.I329T weakened ATP binding in the aminoacylation domain, and in vitro studies with recombinant mutant protein showed decreased affinity of this variant to ATP. Furthermore, p.D391V and p.Y144C were predicted to disrupt synthetase function by interrupting the rotation of the tRNA anticodon stem-binding domain from a closed to an open form. In vitro characterization indicated reduced affinity of p.D391V mutant protein to phenylalanine, whereas p.Y144C disrupted tRNA binding. The stability of p.I329T and p.D391V mutants in a refolding assay was impaired. Our results imply that the three FARS2 mutations directly impair aminoacylation function and stability of mtPheRS, leading to a decrease in overall tRNA charging capacity. This study establishes a new genetic cause of infantile mitochondrial Alpers encephalopathy and reports a new mitochondrial aminoacyl-tRNA synthetase as a cause of mitochondrial disease.

22504945 A novel mutation in YARS2 causes myopathy with lactic acidosis and sideroblastic anemia.
Aug 2012 Human mutation

Sasarman Florin, Nishimura Tamiko, Thiffault Isabelle, Shoubridge Eric A.

Mutations in the mitochondrial aminoacyl-tRNA synthetases (ARSs) are associated with a strikingly broad range of clinical phenotypes, the molecular basis for which remains obscure. Here, we report a novel missense mutation (c.137G>A, p.Gly46Asp) in the catalytic domain of YARS2, which codes for the mitochondrial tyrosyl-tRNA synthetase, in a subject with myopathy, lactic acidosis, and sideroblastic anemia (MLASA). YARS2 was undetectable by immunoblot analysis in subject myoblasts, resulting in a generalized mitochondrial translation defect. Retroviral expression of a wild-type YARS2 complementary DNA completely rescued the translation defect. We previously demonstrated that the respiratory chain defect in this subject was only present in fully differentiated muscle, and we show here that this likely reflects an increased requirement for YARS2 as muscle cells differentiate. An additional, heterozygous mutation was detected in TRMU/MTU1, a gene encoding the mitochondrial 2-thiouridylase. Although subject myoblasts and myotubes contained half the normal levels of TRMU, thiolation of mitochondrial tRNAs was normal. YARS2 eluted as part of high-molecular-weight complexes of ∼250 kDa and 1 MDa by gel filtration. This study confirms mutations in YARS2 as a cause of MLASA and shows that, like some of the cytoplasmic ARSs, mitochondrial ARSs occur in high-molecular-weight complexes.

22492562 Leukoencephalopathy with thalamus and brainstem involvement and high lactate 'LTBL' caused by EARS2 mutations.
May 2012 Brain : a journal of neurology

Steenweg Marjan E, Ghezzi Daniele, Haack Tobias, Abbink Truus E M, Martinelli Diego, van Berkel Carola G M, Bley Annette, Diogo Luisa, Grillo Eugenio, Te Water Naudé Johann, Strom Tim M, Bertini Enrico, Prokisch Holger, van der Knaap Marjo S, Zeviani Massimo.

In the large group of genetically undetermined infantile-onset mitochondrial encephalopathies, multiple defects of mitochondrial DNA-related respiratory-chain complexes constitute a frequent biochemical signature. In order to identify responsible genes, we used exome-next-generation sequencing in a selected cohort of patients with this biochemical signature. In an isolated patient, we found two mutant alleles for EARS2, the gene encoding mitochondrial glutamyl-tRNA synthetase. The brain magnetic resonance imaging of this patient was hallmarked by extensive symmetrical cerebral white matter abnormalities sparing the periventricular rim and symmetrical signal abnormalities of the thalami, midbrain, pons, medulla oblongata and cerebellar white matter. Proton magnetic resonance spectroscopy showed increased lactate. We matched this magnetic resonance imaging pattern with that of a cohort of 11 previously selected unrelated cases. We found mutations in the EARS2 gene in all. Subsequent detailed clinical and magnetic resonance imaging based phenotyping revealed two distinct groups: mild and severe. All 12 patients shared an infantile onset and rapidly progressive disease with severe magnetic resonance imaging abnormalities and increased lactate in body fluids and proton magnetic resonance spectroscopy. Patients in the 'mild' group partially recovered and regained milestones in the following years with striking magnetic resonance imaging improvement and declining lactate levels, whereas those of the 'severe' group were characterized by clinical stagnation, brain atrophy on magnetic resonance imaging and persistent lactate increases. This new neurological disease, early-onset leukoencephalopathy with thalamus and brainstem involvement and high lactate, is hallmarked by unique magnetic resonance imaging features, defined by a peculiar biphasic clinical course and caused by mutations in a single gene, EARS2, expanding the list of medically relevant defects of mitochondrial DNA translation.

22283595 Mitochondrial disease and epilepsy.
May 2012 Developmental medicine and child neurology

Rahman Shamima.

Mitochondrial respiratory chain disorders are relatively common inborn errors of energy metabolism, with a combined prevalence of one in 5000. These disorders typically affect tissues with high energy requirements, and cerebral involvement occurs frequently in childhood, often manifesting in seizures. Mitochondrial diseases are genetically heterogeneous; to date, mutations have been reported in all 37 mitochondrially encoded genes and more than 80 nuclear genes. The major genetic causes of mitochondrial epilepsy are mitochondrial DNA mutations (including those typically associated with the mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes [MELAS] and myoclonic epilepsy with ragged red fibres [MERRF] syndromes); mutations in POLG (classically associated with Alpers syndrome but also presenting as the mitochondrial recessive ataxia syndrome [MIRAS], spinocerebellar ataxia with epilepsy [SCAE], and myoclonus, epilepsy, myopathy, sensory ataxia [MEMSA] syndromes in older individuals) and other disorders of mitochondrial DNA maintenance; complex I deficiency; disorders of coenzyme Q(10) biosynthesis; and disorders of mitochondrial translation such as RARS2 mutations. It is not clear why some genetic defects, but not others, are particularly associated with seizures. Epilepsy may be the presenting feature of mitochondrial disease but is often part of a multisystem clinical presentation. Mitochondrial epilepsy may be very difficult to manage, and is often a poor prognostic feature. At present there are no curative treatments for mitochondrial disease. Individuals with mitochondrial epilepsy are frequently prescribed multiple anticonvulsants, and the role of vitamins and other nutritional supplements and the ketogenic diet remain unproven.

22086604 Further delineation of pontocerebellar hypoplasia type 6 due to mutations in the gene encoding mitochondrial arginyl-tRNA synthetase, RARS2.
May 2012 Journal of inherited metabolic disease

Glamuzina Emma, Brown Ruth, Hogarth Kieran, Saunders Dawn, Russell-Eggitt Isabelle, Pitt Matthew, de Sousa Carlos, Rahman Shamima, Brown Garry, Grunewald Stephanie.

Pontocerebellar hypoplasia type 6 (PCH6) (MIM #611523) is a recently described disorder caused by mutations in RARS2 (MIM *611524), the gene encoding mitochondrial arginyl-transfer RNA (tRNA) synthetase, a protein essential for translation of all mitochondrially synthesised proteins. This case confirms that progressive cerebellar and cerebral atrophy with microcephaly and complex epilepsy are characteristic features of PCH6. Additional features of PCH subtypes 2 and 4, including severe dystonia, optic atrophy and thinning of the corpus callosum, are demonstrated. Congenital lactic acidosis can be present, but respiratory chain dysfunction may be mild or absent, suggesting that disordered mitochondrial messenger RNA (mRNA) translation may not be the only mechanism of impairment or that a secondary mechanism exists to allow some translation. We report two novel mutations and expand the phenotypic spectrum of this likely underdiagnosed PCH variant, where recognition of the characteristic neuroradiological phenotype could potentially expedite genetic diagnosis and limit invasive investigations.

22037954 Perrault syndrome: further evidence for genetic heterogeneity.
May 2012 J. Neurol.

Jenkinson Emma M, Clayton-Smith Jill, Mehta Sarju, Bennett Christopher, Reardon Willie, Green Andrew, Pearce Simon H S, De Michele Giuseppe, Conway Gerard S, Cilliers Deirdre, Moreton Natalie, Davis Julian R E, Trump Dorothy, Newman William G.

22499341 Genomic analysis of mitochondrial diseases in a consanguineous population reveals novel candidate disease genes.
Apr 2012 Journal of medical genetics

Shamseldin Hanan E, Alshammari Muneera, Al-Sheddi Tarfa, Salih Mustafa A, Alkhalidi Hisham, Kentab Amal, Repetto Gabriela M, Hashem Mais, Alkuraya Fowzan S.

To investigate the utility of autozygome analysis and exome sequencing in a cohort of patients with suspected or confirmed mitochondrial encephalomyopathy.

22422207 Mitochondrial syndromes with leukoencephalopathies.
Feb 2012 Seminars in neurology

Wong Lee-Jun C.

White matter involvement has recently been recognized as a common feature in patients with multisystem mitochondrial disorders that may be caused by molecular defects in either the mitochondrial genome or the nuclear genes. It was first realized in classical mitochondrial syndromes associated with mitochondrial DNA (mtDNA) mutations, such as mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), Leigh's disease, and Kearns-Sayre's syndrome. Deficiencies in respiratory chain complexes I, II, IV, and V often cause Leigh's disease; most of them are due to nuclear defects that may lead to severe early-onset leukoencephalopathies. Defects in a group of nuclear genes involved in the maintenance of mtDNA integrity may also affect the white matter; for example, mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) caused by thymidine phosphorylase deficiency, Navajo neurohepatopathy (NNH) due to MPV17 mutations, and Alpers syndrome due to defects in DNA polymerase gamma (POLG). More recently, leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) has been reported to be caused by autosomal recessive mutations in a mitochondrial aspartyl-tRNA synthetase, DARS2 gene. A patient with leukoencephalopathy and neurologic complications in addition to a multisystem involvement warrants a complete evaluation for mitochondrial disorders. A definite diagnosis may be achieved by molecular analysis of candidate genes based on the biochemical, clinical, and imaging results.

22023289 Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation is associated with cell-type-dependent splicing of mtAspRS mRNA.
Feb 2012 The Biochemical journal

van Berge Laura, Dooves Stephanie, van Berkel Carola G M, Polder Emiel, van der Knaap Marjo S, Scheper Gert C.

LBSL (leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation) is an autosomal recessive white matter disorder with slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction. Magnetic resonance imaging shows characteristic abnormalities in the cerebral white matter and specific brain stem and spinal cord tracts. LBSL is caused by mutations in the gene DARS2, which encodes mtAspRS (mitochondrial aspartyl-tRNA synthetase). The selective involvement of specific white matter tracts in LBSL is striking since this protein is ubiquitously expressed. Almost all LBSL patients have one mutation in intron 2 of DARS2, affecting the splicing of the third exon. Using a splicing reporter construct, we find cell-type-specific differences in the sensitivity to these mutations: the mutations have a larger effect on exon 3 exclusion in neural cell lines, especially neuronal cell lines, than in non-neural cell lines. Furthermore, correct inclusion of exon 3 in the normal mtAspRS mRNA occurs less efficiently in neural cells than in other cell types, and this effect is again most pronounced in neuronal cells. The combined result of these two effects may explain the selective vulnerability of specific white matter tracts in LBSL patients.

21792730 Leukoencephalopathy with brainstem and spinal cord involvement caused by a novel mutation in the DARS2 gene.
Feb 2012 Journal of neurology

Tzoulis Charalampos, Tran Gia Tuong, Gjerde Ivar Otto, Aasly Jan, Neckelmann Gesche, Rydland Jana, Varga Viktoria, Wadel-Andersen Pia, Bindoff Laurence A.

Leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate (LBSL) is a rare, autosomal recessive disorder caused by mutations in the gene encoding a mitochondrial aspartyl-tRNA synthetase, DARS2. The disease is characterized by progressive spastic ataxia and magnetic resonance imaging (MRI) shows a highly characteristic leukoencephalopathy with multiple long tract involvement. We describe the clinical and radiological features of two new cases of LBSL and report a novel pathogenic mutation in the DARS2 gene. Both patients had typical clinical and radiological findings, although no elevated lactate was found. The severity of MRI changes did not correlate with clinical course and severity suggesting that, although of highly specific diagnostic value, MRI does not necessarily reflect clinical activity and should not be used to assess disease severity or prognosis in LBSL.

22456076 [Clinical and genetic analysis of a family with leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation].
Jan 2012 Zhonghua er ke za zhi = Chinese journal of pediatrics

Huang Qiong-hui, Xiao Jiang-xi, Wang Jing-min, Jiang Yu-wu, Wu Ye.

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) is a rare autosomal recessive disease. Affected individuals are invariably compound heterozygous for two mutations in DARS2. No reports of LBSL patients have been published in the mainland of China. The aim of this study was to explore the clinical and genetic features of a family with LBSL, which may contribute to definite diagnosis, genetic counseling and prenatal diagnosis of this rare disease in China.

22448145 Mutations in the mitochondrial methionyl-tRNA synthetase cause a neurodegenerative phenotype in flies and a recessive ataxia (ARSAL) in humans.
- 2012 PLoS biology

Bayat Vafa, Thiffault Isabelle, Jaiswal Manish, Tétreault Martine, Donti Taraka, Sasarman Florin, Bernard Geneviève, Demers-Lamarche Julie, Dicaire Marie-Josée, Mathieu Jean, Vanasse Michel, Bouchard Jean-Pierre, Rioux Marie-France, Lourenco Charles M, Li Zhihong, Haueter Claire, Shoubridge Eric A, Graham Brett H, Brais Bernard, Bellen Hugo J.

An increasing number of genes required for mitochondrial biogenesis, dynamics, or function have been found to be mutated in metabolic disorders and neurological diseases such as Leigh Syndrome. In a forward genetic screen to identify genes required for neuronal function and survival in Drosophila photoreceptor neurons, we have identified mutations in the mitochondrial methionyl-tRNA synthetase, Aats-met, the homologue of human MARS2. The fly mutants exhibit age-dependent degeneration of photoreceptors, shortened lifespan, and reduced cell proliferation in epithelial tissues. We further observed that these mutants display defects in oxidative phosphorylation, increased Reactive Oxygen Species (ROS), and an upregulated mitochondrial Unfolded Protein Response. With the aid of this knowledge, we identified MARS2 to be mutated in Autosomal Recessive Spastic Ataxia with Leukoencephalopathy (ARSAL) patients. We uncovered complex rearrangements in the MARS2 gene in all ARSAL patients. Analysis of patient cells revealed decreased levels of MARS2 protein and a reduced rate of mitochondrial protein synthesis. Patient cells also exhibited reduced Complex I activity, increased ROS, and a slower cell proliferation rate, similar to Drosophila Aats-met mutants.

22006980 Leucoencephalopathy with brainstem and spinal cord involvement and high lactate: quantitative magnetic resonance imaging.
Nov 2011 Brain : a journal of neurology

Steenweg Marianne E, Pouwels Petra J W, Wolf Nicole I, van Wieringen Wessel N, Barkhof Frederik, van der Knaap Marjo S.

Leucoencephalopathy with brainstem and spinal cord involvement and elevated lactate is a white matter disorder caused by DARS2 mutations. The pathology is unknown. We observed striking discrepancies between improvement on longitudinal conventional magnetic resonance images and clinical deterioration and between large areas of high signal on diffusion-weighted imaging and small areas with low apparent diffusion coefficient values. These observations prompted a longitudinal and quantitative magnetic resonance imaging study. We investigated eight patients (two males, mean age 27 years). Maps of T(2) relaxation times, fractional anisotropy, apparent diffusion coefficients, signal on diffusion-weighted imaging, and axial and radial diffusivities were generated. Brain metabolites, obtained by chemical shift imaging, were quantified. Data analysis focused on: (i) white matter with low apparent diffusion coefficient; (ii) white matter with high T(2) values; (iii) white matter with intermediate T(2) values; and (iv) normal-appearing white matter. The areas were compared with similarly located areas in eight matched controls. In five patients, T(2)-weighted images, spectroscopy, apparent diffusion coefficient maps and diffusion-weighted imaging maps were compared with those obtained 5-7 years ago. In white matter with low apparent diffusion coefficient, axial and radial diffusivities were decreased and fractional anisotropy was high. T(2) values were intermediate. These areas with truly restricted diffusion were small and often observed at the periphery of areas with high T(2) values. In the white matter with high and intermediate T(2) values, apparent diffusion coefficients and axial and radial diffusivities were increased and fractional anisotropy decreased. The signal on diffusion-weighted imaging was highest in white matter with high T(2) values, an effect of T(2) shinethrough. Chemical shift imaging in both white matter types showed increased lactate, increased myo-inositol and decreased N-acetylaspartate, most pronounced in white matter with high T(2) values. Normal-appearing white matter was comparable with white matter of control subjects. Over time, mild decreases in T(2) signal intensities, signal on diffusion-weighted imaging and in extent of the low apparent diffusion coefficient areas were seen. In conclusion, the disease process in leucoencephalopathy with brainstem and spinal cord involvement and elevated lactate is extremely slow. We hypothesize that diffusion restriction is the first stage of the disease caused by intramyelinic water accumulation, followed by slow shift and then loss of the surplus of water. On conventional T(2) images this leads to improvement. We hypothesize that it is loss of water rather than structural restoration that causes the change in T(2) signal intensity, which would be in better agreement with the slow clinical deterioration.

21749991 Acetazolamide-responsive exercise-induced episodic ataxia associated with a novel homozygous DARS2 mutation.
Oct 2011 Journal of medical genetics

Synofzik Matthis, Schicks Julia, Lindig Tobias, Biskup Saskia, Schmidt Thorsten, Hansel Jochen, Lehmann-Horn Frank, Schöls Ludger.

Leukoencephalopathy with brain stem and spinal cord involvement and brain lactate elevation (LBSL) was recently shown to be caused by mutations in the DARS2 gene, encoding a mitochondrial aspartyl-tRNA synthetase. So far, affected individuals were invariably compound heterozygous for two mutations in DARS2, and drug treatments have remained elusive.

21277128 Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation in the first Polish patient.
Oct 2011 Brain & development

Mierzewska Hanna, van der Knaap Marjo S, Scheper Gert C, Bekiesinska-Figatowska Monika, Szczepanik Elzbieta, Jurkiewicz Elzbieta.

Leukoencephalopathy with brain stem and spinal cord involvement and elevated white matter lactate (LBSL) is a very rare autosomal recessive mitochondrial disorder. Clinically patients have slowly progressive ataxia, pyramidal syndrome and dorsal column dysfunction. The disease is defined on the basis of characteristic abnormalities observed on magnetic resonance imaging such as inhomogeneous, spotty involvement of the cerebral white matter, selective involvement of brain stem and spinal cord tracts as well as lactate elevation in the affected white matter on spectroscopy. We present the first identified Polish patient suffering from LBSL confirmed molecularly.

21815884 A novel homozygous mutation of DARS2 may cause a severe LBSL variant.
Sep 2011 Clin. Genet.

Miyake N, Yamashita S, Kurosawa K, Miyatake S, Tsurusaki Y, Doi H, Saitsu H, Matsumoto N.

21427441 Spinal cord calcification in an early-onset progressive leukoencephalopathy.
Jul 2011 Journal of child neurology

Orcesi Simona, La Piana Roberta, Uggetti Carla, Tonduti Davide, Pichiecchio Anna, Pasin Moreno, Viselner Gisela, Comi Giacomo P, Del Bo Roberto, Ronchi Dario, Bastianello Stefano, Balottin Umberto.

Spinal cord calcifications are an unusual finding in pediatric neurology. We here describe a young child who presented severe psychomotor delay, tetraplegia, deafness, and anemia. Neuroradiological investigations revealed severe leukodystrophy and unusual calcifications in the cerebral white matter and all along the medullary pathways. Common infectious and metabolic diseases were ruled out. A mild reduction in the activity of several respiratory chain complexes was documented on muscle biopsy. Of interest, we found an intronic variant in DARS2, a gene involved in mitochondrial DNA translation, responsible for the syndrome of leukoencephalopathy with brainstem and spinal cord involvement and high brain lactate. In our opinion, our case, and probably 2 previously reported Japanese siblings with a picture very similar to that of our patient, could represent a new, progressive leukoencephalomyelopathy.

21493805 Leukoencephalopathy with brain stem and spinal cord involvement and high lactate: a genetically proven case without elevated white matter lactate.
Jun 2011 Journal of child neurology

Sharma Suvasini, Sankhyan Naveen, Kumar Atin, Scheper Gert C, van der Knaap Marjo S, Gulati Sheffali.

A 17-year-old Indian boy with gradually progressive ataxia with onset at 12 years of age is described. Magnetic resonance imaging (MRI) of the brain revealed extensive, inhomogeneous signal abnormalities in the cerebral white matter, with involvement of selected tracts in the brain stem and spinal cord. The imaging findings were characteristic of leukoencephalopathy with brain stem and spinal cord involvement and high lactate, a recently described leukodystrophy. Interestingly, magnetic resonance spectroscopy of the abnormal white matter did not reveal elevated lactate. The patient was compound heterozygous for 2 new mutations in DARS2, genetically confirming the diagnosis.

21549344 Exome sequencing identifies mitochondrial alanyl-tRNA synthetase mutations in infantile mitochondrial cardiomyopathy.
May 2011 American journal of human genetics

Götz Alexandra, Tyynismaa Henna, Euro Liliya, Ellonen Pekka, Hyötyläinen Tuulia, Ojala Tiina, Hämäläinen Riikka H, Tommiska Johanna, Raivio Taneli, Oresic Matej, Karikoski Riitta, Tammela Outi, Simola Kalle O J, Paetau Anders, Tyni Tiina, Suomalainen Anu.

Infantile cardiomyopathies are devastating fatal disorders of the neonatal period or the first year of life. Mitochondrial dysfunction is a common cause of this group of diseases, but the underlying gene defects have been characterized in only a minority of cases, because tissue specificity of the manifestation hampers functional cloning and the heterogeneity of causative factors hinders collection of informative family materials. We sequenced the exome of a patient who died at the age of 10 months of hypertrophic mitochondrial cardiomyopathy with combined cardiac respiratory chain complex I and IV deficiency. Rigorous data analysis allowed us to identify a homozygous missense mutation in AARS2, which we showed to encode the mitochondrial alanyl-tRNA synthetase (mtAlaRS). Two siblings from another family, both of whom died perinatally of hypertrophic cardiomyopathy, had the same mutation, compound heterozygous with another missense mutation. Protein structure modeling of mtAlaRS suggested that one of the mutations affected a unique tRNA recognition site in the editing domain, leading to incorrect tRNA aminoacylation, whereas the second mutation severely disturbed the catalytic function, preventing tRNA aminoacylation. We show here that mutations in AARS2 cause perinatal or infantile cardiomyopathy with near-total combined mitochondrial respiratory chain deficiency in the heart. Our results indicate that exome sequencing is a powerful tool for identifying mutations in single patients and allows recognition of the genetic background in single-gene disorders of variable clinical manifestation and tissue-specific disease. Furthermore, we show that mitochondrial disorders extend to prenatal life and are an important cause of early infantile cardiac failure.

21326314 Molecular diagnosis and clinical onset of Charcot-Marie-Tooth disease in Japan.
May 2011 Journal of human genetics

Abe Akiko, Numakura Chikahiko, Kijima Kazuki, Hayashi Makiko, Hashimoto Taeko, Hayasaka Kiyoshi.

To study the genetic background of Japanese Charcot-Marie-Tooth disease (CMT) patients, we analyzed qualitative and quantitative changes in the disease-causing genes mainly by denaturing high performance liquid chromatography and multiplex ligation-dependent probe analysis in 227 patients with demyelinating CMT and 127 patients with axonal CMT. In demyelinating CMT, we identified 53 patients with PMP22 duplication, 10 patients with PMP22 mutations, 20 patients with MPZ mutations, eight patients with NEFL mutations, 19 patients with GJB1 mutations, one patient with EGR2 mutation, five patients with PRX mutations and no mutations in 111 patients. In axonal CMT, we found 14 patients with MFN2 mutations, one patient with GARS mutation, five patients with MPZ mutations, one patient with GDAP1 mutation, six patients with GJB1 mutations and no mutations in 100 patients. Most of the patients carrying PMP22, MPZ, NEFL, PRX and MFN2 mutations showed early onset, whereas half of the patients carrying PMP22 duplication and all patients with GJB1 or MPZ mutations showing axonal phenotype were adult onset. Our data showed that a low prevalence of PMP22 duplication and high frequency of an unknown cause are features of Japanese CMT. Low prevalence of PMP22 duplication is likely associated with the mild symptoms due to genetic and/or epigenetic modifying factors.

21464306 Mutations in mitochondrial histidyl tRNA synthetase HARS2 cause ovarian dysgenesis and sensorineural hearing loss of Perrault syndrome.
Apr 2011 Proceedings of the National Academy of Sciences of the United States of America

Pierce Sarah B, Chisholm Karen M, Lynch Eric D, Lee Ming K, Walsh Tom, Opitz John M, Li Weiqing, Klevit Rachel E, King Mary-Claire.

Perrault syndrome is a genetically heterogeneous recessive disorder characterized by ovarian dysgenesis and sensorineural hearing loss. In a nonconsanguineous family with five affected siblings, linkage analysis and genomic sequencing revealed the genetic basis of Perrault syndrome to be compound heterozygosity for mutations in the mitochondrial histidyl tRNA synthetase HARS2 at two highly conserved amino acids, L200V and V368L. The nucleotide substitution creating HARS2 p.L200V also created an alternate splice leading to deletion of 12 codons from the HARS2 message. Affected family members thus carried three mutant HARS2 transcripts. Aminoacylation activity of HARS2 p.V368L and HARS2 p.L200V was reduced and the deletion mutant was not stably expressed in mammalian mitochondria. In yeast, lethality of deletion of the single essential histydyl tRNA synthetase HTS1 was fully rescued by wild-type HTS1 and by HTS1 p.L198V (orthologous to HARS2 p.L200V), partially rescued by HTS1 p.V381L (orthologous to HARS2 p.V368L), and not rescued by the deletion mutant. In Caenorhabditis elegans, reduced expression by RNAi of the single essential histydyl tRNA synthetase hars-1 severely compromised fertility. Together, these data suggest that Perrault syndrome in this family was caused by reduction of HARS2 activity. These results implicate aberrations of mitochondrial translation in mammalian gonadal dysgenesis. More generally, the relationship between HARS2 and Perrault syndrome illustrates how causality may be demonstrated for extremely rare inherited mutations in essential, highly conserved genes.

21273289 Impairment of the tRNA-splicing endonuclease subunit 54 (tsen54) gene causes neurological abnormalities and larval death in zebrafish models of pontocerebellar hypoplasia.
Apr 2011 Human molecular genetics

Kasher Paul R, Namavar Yasmin, van Tijn Paula, Fluiter Kees, Sizarov Aleksander, Kamermans Maarten, Grierson Andrew J, Zivkovic Danica, Baas Frank.

Pontocerebellar hypoplasia (PCH) represents a group (PCH1-6) of neurodegenerative autosomal recessive disorders characterized by hypoplasia and/or atrophy of the cerebellum, hypoplasia of the ventral pons, progressive microcephaly and variable neocortical atrophy. The majority of PCH2 and PCH4 cases are caused by mutations in the TSEN54 gene; one of the four subunits comprising the tRNA-splicing endonuclease (TSEN) complex. We hypothesized that TSEN54 mutations act through a loss of function mechanism. At 8 weeks of gestation, human TSEN54 is expressed ubiquitously in the brain, yet strong expression is seen within the telencephalon and metencephalon. Comparable expression patterns for tsen54 are observed in zebrafish embryos. Morpholino (MO) knockdown of tsen54 in zebrafish embryos results in loss of structural definition in the brain. This phenotype was partially rescued by co-injecting the MO with human TSEN54 mRNA. A developmental patterning defect was not associated with tsen54 knockdown; however, an increase in cell death within the brain was observed, thus bearing resemblance to PCH pathophysiology. Additionally, N-methyl-N-nitrosourea mutant zebrafish homozygous for a tsen54 premature stop-codon mutation die within 9 days post-fertilization. To determine whether a common disease pathway exists between TSEN54 and other PCH-related genes, we also monitored the effects of mitochondrial arginyl-tRNA synthetase (rars2; PCH1 and PCH6) knockdown in zebrafish. Comparable brain phenotypes were observed following the inhibition of both genes. These data strongly support the hypothesis that TSEN54 mutations cause PCH through a loss of function mechanism. Also we suggest that a common disease pathway may exist between TSEN54- and RARS2-related PCH, which may involve a tRNA processing-related mechanism.

21255763 Mutations in the mitochondrial seryl-tRNA synthetase cause hyperuricemia, pulmonary hypertension, renal failure in infancy and alkalosis, HUPRA syndrome.
Feb 2011 American journal of human genetics

Belostotsky Ruth, Ben-Shalom Efrat, Rinat Choni, Becker-Cohen Rachel, Feinstein Sofia, Zeligson Sharon, Segel Reeval, Elpeleg Orly, Nassar Suheir, Frishberg Yaacov.

An uncharacterized multisystemic mitochondrial cytopathy was diagnosed in two infants from consanguineous Palestinian kindred living in a single village. The most significant clinical findings were tubulopathy (hyperuricemia, metabolic alkalosis), pulmonary hypertension, and progressive renal failure in infancy (HUPRA syndrome). Analysis of the consanguineous pedigree suggested that the causative mutation is in the nuclear DNA. By using genome-wide SNP homozygosity analysis, we identified a homozygous identity-by-descent region on chromosome 19 and detected the pathogenic mutation c.1169A>G (p.Asp390Gly) in SARS2, encoding the mitochondrial seryl-tRNA synthetase. The same homozygous mutation was later identified in a third infant with HUPRA syndrome. The carrier rate of this mutation among inhabitants of this Palestinian isolate was found to be 1:15. The mature enzyme catalyzes the ligation of serine to two mitochondrial tRNA isoacceptors: tRNA(Ser)(AGY) and tRNA(Ser)(UCN). Analysis of amino acylation of the two target tRNAs, extracted from immortalized peripheral lymphocytes derived from two patients, revealed that the p.Asp390Gly mutation significantly impacts on the acylation of tRNA(Ser)(AGY) but probably not that of tRNA(Ser)(UCN). Marked decrease in the expression of the nonacylated transcript and the complete absence of the acylated tRNA(Ser)(AGY) suggest that this mutation leads to significant loss of function and that the uncharged transcripts undergo degradation.

20878420 Clinically asymptomatic adult patient with extensive LBSL MRI pattern and DARS2 mutations.
Feb 2011 J. Neurol.

Labauge Pierre, Dorboz Imen, Eymard-Pierre Eleonore, Dereeper Olivier, Boespflug-Tanguy Odile.

21121901 A human pathology-related mutation prevents import of an aminoacyl-tRNA synthetase into mitochondria.
Feb 2011 The Biochemical journal

Messmer Marie, Florentz Catherine, Schwenzer Hagen, Scheper Gert C, van der Knaap Marjo S, Maréchal-Drouard Laurence, Sissler Marie.

Mutations in the nuclear gene coding for the mitochondrial aspartyl-tRNA synthetase, a key enzyme for mitochondrial translation, are correlated with leukoencephalopathy. A Ser⁴⁵ to Gly⁴⁵ mutation is located in the predicted targeting signal of the protein. We demonstrate in the present study, by in vivo and in vitro approaches, that this pathology-related mutation impairs the import process across mitochondrial membranes.

20952379 Clinical, neuroradiological and genetic findings in pontocerebellar hypoplasia.
Jan 2011 Brain : a journal of neurology

Namavar Yasmin, Barth Peter G, Kasher Paul R, van Ruissen Fred, Brockmann Knut, Bernert Günther, Writzl Karin, Ventura Karen, Cheng Edith Y, Ferriero Donna M, Basel-Vanagaite Lina, Eggens Veerle R C, Krägeloh-Mann Ingeborg, De Meirleir Linda, King Mary, Graham John M, von Moers Arpad, Knoers Nine, Sztriha Laszlo, Korinthenberg Rudolf, , Dobyns William B, Baas Frank, Poll-The Bwee Tien.

Pontocerebellar hypoplasia is a group of autosomal recessive neurodegenerative disorders with prenatal onset. The common characteristics are cerebellar hypoplasia with variable atrophy of the cerebellum and the ventral pons. Supratentorial involvement is reflected by variable neocortical atrophy, ventriculomegaly and microcephaly. Mutations in the transfer RNA splicing endonuclease subunit genes (TSEN54, TSEN2, TSEN34) were found to be associated with pontocerebellar hypoplasia types 2 and 4. Mutations in the mitochondrial transfer RNA arginyl synthetase gene (RARS2) were associated with pontocerebellar hypoplasia type 6. We studied a cohort of 169 patients from 141 families for mutations in these genes, of whom 106 patients tested positive for mutations in one of the TSEN genes or the RARS2 gene. In order to delineate the neuroradiological and clinical phenotype of patients with mutations in these genes, we compared this group with 63 patients suspected of pontocerebellar hypoplasia who were negative on mutation analysis. We found a strong correlation (P < 0.0005) between TSEN54 mutations and a dragonfly-like cerebellar pattern on magnetic resonance imaging, in which the cerebellar hemispheres are flat and severely reduced in size and the vermis is relatively spared. Mutations in TSEN54 are clinically associated with dyskinesia and/or dystonia and variable degrees of spasticity, in some cases with pure generalized spasticity. Nonsense or splice site mutations in TSEN54 are associated with a more severe phenotype of more perinatal symptoms, ventilator dependency and early death. In addition, we present ten new mutations in TSEN54, TSEN2 and RARS2. Furthermore, we show that pontocerebellar hypoplasia type 1 together with elevated cerebrospinal fluid lactate may be caused by RARS2 mutations.

20501884 Leukoencephalopathy with brainstem and spinal cord involvement and normal lactate: a new mutation in the DARS2 gene.
Nov 2010 Journal of child neurology

Lin Jaime, Chiconelli Faria Eliete, Da Rocha Antônio José, Rodrigues Masruha Marcelo, Pereira Vilanova Luiz Celso, Scheper Gert C, Van der Knaap Marjo S.

Leukoencephalopathy with brainstem and spinal cord involvement and elevated brain lactate diagnosis is based on its highly characteristic pattern of abnormalities observed by magnetic resonance imaging and spectroscopy. Clinically, affected patients develop slowly progressive cerebellar ataxia, spasticity, and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. In 2007, the pathophysiology of this disorder was elucidated with the discovery of mutations in the DARS2 gene, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals. Here, the authors present a case of leukoencephalopathy with brainstem and spinal cord involvement with normal brain lactate, in which genetic analysis revealed a new mutation in the DARS2 gene not previously described.

20920668 Compound heterozygosity for loss-of-function lysyl-tRNA synthetase mutations in a patient with peripheral neuropathy.
Oct 2010 American journal of human genetics

McLaughlin Heather M, Sakaguchi Reiko, Liu Cuiping, Igarashi Takao, Pehlivan Davut, Chu Kristine, Iyer Ram, Cruz Pedro, Cherukuri Praveen F, Hansen Nancy F, Mullikin James C, , Biesecker Leslie G, Wilson Thomas E, Ionasescu Victor, Nicholson Garth, Searby Charles, Talbot Kevin, Vance Jeffrey M, Züchner Stephan, Szigeti Kinga, Lupski James R, Hou Ya-Ming, Green Eric D, Antonellis Anthony.

Charcot-Marie-Tooth (CMT) disease comprises a genetically and clinically heterogeneous group of peripheral nerve disorders characterized by impaired distal motor and sensory function. Mutations in three genes encoding aminoacyl-tRNA synthetases (ARSs) have been implicated in CMT disease primarily associated with an axonal pathology. ARSs are ubiquitously expressed, essential enzymes responsible for charging tRNA molecules with their cognate amino acids. To further explore the role of ARSs in CMT disease, we performed a large-scale mutation screen of the 37 human ARS genes in a cohort of 355 patients with a phenotype consistent with CMT. Here we describe three variants (p.Leu133His, p.Tyr173SerfsX7, and p.Ile302Met) in the lysyl-tRNA synthetase (KARS) gene in two patients from this cohort. Functional analyses revealed that two of these mutations (p.Leu133His and p.Tyr173SerfsX7) severely affect enzyme activity. Interestingly, both functional variants were found in a single patient with CMT disease and additional neurological and non-neurological sequelae. Based on these data, KARS becomes the fourth ARS gene associated with CMT disease, indicating that this family of enzymes is specifically critical for axon function.

20635367 Pontocerebellar hypoplasia type 6: A British case with PEHO-like features.
Aug 2010 American journal of medical genetics. Part A

Rankin Julia, Brown Ruth, Dobyns William B, Harington Judith, Patel Jay, Quinn Michael, Brown Garry.

Six subtypes of autosomal recessive pontocerebellar hypoplasia (PCH) have been identified and the genetic basis of four of these (PCH1, PCH2, PCH4, and PCH6) is known. PCH6 is associated with cerebral atrophy and multiple but variable respiratory chain defects in muscle and has been reported in one consanguineous Sephardic Jewish family. It is caused by mutations in the RARS2 gene which encodes mitochondrial arginine-transfer RNA synthetase. Here we describe a female patient born to nonconsanguineous British parents. She presented in the neonatal period with increased respiratory rate, poor feeding and transiently elevated blood and CSF lactate levels. She went on to manifest profound developmental delay and severe microcephaly. Edema of the hands, feet, and face were suggestive of a PEHO-like condition (progressive encephalopathy, edema, hypsarrhythmia and optic atrophy), although optic atrophy and hypsarrhythmia were absent. Cranial MRI at age 14 months showed generalized cerebral atrophy, thinning of the pons and gross atrophy and flattening of the cerebellar hemispheres. Muscle biopsies on two occasions were normal with normal respiratory chain studies. Despite the absence of respiratory chain defects, the phenotype was felt to be consistent with PCH6 and indeed two novel pathogenic RARS2 mutations were identified. Ours is the second report of PCH6 due to RARS2 mutations and demonstrates that respiratory chain abnormalities are not obligatory, whereas some features of PEHO might be present.

20598274 Mutation of the mitochondrial tyrosyl-tRNA synthetase gene, YARS2, causes myopathy, lactic acidosis, and sideroblastic anemia--MLASA syndrome.
Jul 2010 American journal of human genetics

Riley Lisa G, Cooper Sandra, Hickey Peter, Rudinger-Thirion Joëlle, McKenzie Matthew, Compton Alison, Lim Sze Chern, Thorburn David, Ryan Michael T, Giegé Richard, Bahlo Melanie, Christodoulou John.

Mitochondrial respiratory chain disorders are a heterogeneous group of disorders in which the underlying genetic defect is often unknown. We have identified a pathogenic mutation (c.156C>G [p.F52L]) in YARS2, located at chromosome 12p11.21, by using genome-wide SNP-based homozygosity analysis of a family with affected members displaying myopathy, lactic acidosis, and sideroblastic anemia (MLASA). We subsequently identified the same mutation in another unrelated MLASA patient. The YARS2 gene product, mitochondrial tyrosyl-tRNA synthetase (YARS2), was present at lower levels in skeletal muscle whereas fibroblasts were relatively normal. Complex I, III, and IV were dysfunctional as indicated by enzyme analysis, immunoblotting, and immunohistochemistry. A mitochondrial protein-synthesis assay showed reduced levels of respiratory chain subunits in myotubes generated from patient cell lines. A tRNA aminoacylation assay revealed that mutant YARS2 was still active; however, enzyme kinetics were abnormal compared to the wild-type protein. We propose that the reduced aminoacylation activity of mutant YARS2 enzyme leads to decreased mitochondrial protein synthesis, resulting in mitochondrial respiratory chain dysfunction. MLASA has previously been associated with PUS1 mutations; hence, the YARS2 mutation reported here is an alternative cause of MLASA.

20169446 Charcot-Marie-Tooth disease type 2D with a novel glycyl-tRNA synthetase gene (GARS) mutation.
Jul 2010 Journal of neurology

Hamaguchi Ayumi, Ishida Chiho, Iwasa Kazuo, Abe Akiko, Yamada Masahito.

20506600 Leukoencephalopathy with Brain Stem and Spinal Cord Involvement and Lactate Elevation.
May 2010

.

19592391 DARS2 mutations in mitochondrial leucoencephalopathy and multiple sclerosis.
Jan 2010 Journal of medical genetics

Isohanni P, Linnankivi T, Buzkova J, Lönnqvist T, Pihko H, Valanne L, Tienari P J, Elovaara I, Pirttilä T, Reunanen M, Koivisto K, Marjavaara S, Suomalainen A.

Leucoencephalopathy with brain stem and spinal cord involvement and high brain lactate (LBSL) was first defined by characteristic magnetic resonance imaging and spectroscopic findings. The clinical features include childhood or juvenile onset slowly progressive ataxia, spasticity, and dorsal column dysfunction, occasionally accompanied by learning difficulties. Mutations in DARS2, encoding mitochondrial aspartyl-tRNA synthetase, were recently shown to cause LBSL. The signs and symptoms show some overlap with the most common leucoencephalopathy of young adults, multiple sclerosis (MS).

19770827 [Clinical and molecular genetic diagnosis of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation in children].
- 2009 Zhurnal nevrologii i psikhiatrii imeni S.S. Korsakova

Mikhaĭlova S V, Zakharova E Iu, Banin A V, Demushkina A A, Petrukhin A S.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a recently described disorder with autosomal recessive model of inheritance. Mutations in the DARS2 gene, which encode mitochondrial aspartyl-tRNA synthetase, have been found. We present 31 cases with characteristic clinical and neuroimaging findings of this disorder. Patients have been stratified into two groups (early and late forms) by age-at-onset and clinical symptoms. The early form was characterized clinically by progressive pyramidal dysfunction, cerebellar and intellectual problems appeared later. Patients with the late form had cerebellar and sensitive ataxia, disturbances of muscle tonus, spastic type, mostly in the low extremities, polyneuropathic and rarely - psychoorganic syndrome. The brain MRI of all patients was characterized by inhomogeneous T2W signal abnormalities in the periventricular and deep white matter and a strikingly selective involvement of certain brainstem and spinal tracts. Most of the patients were compound-heterozygous for common mutations in the DARS2. We found 4 new mutations associated with LBSL. This is the first clinical and molecular-genetic investigation of this rare leukoencephalopathy in Russia.

18619624 Leukoencephalopathy with brain stem and spinal cord involvement and high lactate: a genetically proven case with distinct MRI findings.
Oct 2008 Journal of the neurological sciences

Uluc Kayihan, Baskan Ozdil, Yildirim Kadriye Agan, Ozsahin Selda, Koseoglu Mesrure, Isak Baris, Scheper G C, Gunal Dilek Ince, van der Knaap M S.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a recently described disorder with autosomal recessive mode of inheritance. Lately, mutations in the DARS2 gene, which encodes mitochondrial aspartyl-tRNA synthetase, have been found as the underlying defect. We report a 19-year-old male patient with cerebellar, pyramidal and dorsal column dysfunctions and specific magnetic resonance imaging (MRI) and characteristic magnetic resonance spectroscopy (MRS) abnormalities. The patient was compound-heterozygous for two mutations in DARS2. MRI showed selective involvement of cerebral and cerebellar white matter and superior and inferior cerebellar peduncles, without contrast enhancement. The U-fibers were spared. The sensory and the pyramidal tracts were affected over their entire length. Involvement of the intraparenchymal trajectories of the trigeminal nerves and mesencephalic trigeminal tracts was demonstrated. In the spinal cord, signal abnormalities were identified in the dorsal columns and the lateral corticospinal tracts. Proton-MRS of the frontal and cerebellar white matter showed elevated lactate, reduced N-acetylaspartate, increased myoinositol and mildly elevated choline. In LBSL, distinct MRI findings should lead to the diagnosis, which can be confirmed by the analysis of the disease gene DARS2.

17847012 Deleterious mutation in the mitochondrial arginyl-transfer RNA synthetase gene is associated with pontocerebellar hypoplasia.
Oct 2007 American journal of human genetics

Edvardson Simon, Shaag Avraham, Kolesnikova Olga, Gomori John Moshe, Tarassov Ivan, Einbinder Tom, Saada Ann, Elpeleg Orly.

Homozygosity mapping was performed in a consanguineous Sephardic Jewish family with three patients who presented with severe infantile encephalopathy associated with pontocerebellar hypoplasia and multiple mitochondrial respiratory-chain defects. This resulted in the identification of an intronic mutation in RARS2, the gene encoding mitochondrial arginine-transfer RNA (tRNA) synthetase. The mutation was associated with the production of an abnormally short RARS2 transcript and a marked reduction of the mitochondrial tRNA(Arg) transcript in the patients' fibroblasts. We speculate that missplicing mutations in mitochondrial aminoacyl-tRNA synthethase genes preferentially affect the brain because of a tissue-specific vulnerability of the splicing machinery.

17384640 Mitochondrial aspartyl-tRNA synthetase deficiency causes leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation.
Apr 2007 Nature genetics

Scheper Gert C, van der Klok Thom, van Andel Rob J, van Berkel Carola G M, Sissler Marie, Smet Joél, Muravina Tatjana I, Serkov Sergey V, Uziel Graziella, Bugiani Marianna, Schiffmann Raphael, Krägeloh-Mann Ingeborg, Smeitink Jan A M, Florentz Catherine, Van Coster Rudy, Pronk Jan C, van der Knaap Marjo S.

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) has recently been defined based on a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy. LBSL is an autosomal recessive disease, most often manifesting in early childhood. Affected individuals develop slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. We performed linkage mapping with microsatellite markers in LBSL families and found a candidate region on chromosome 1, which we narrowed by means of shared haplotypes. Sequencing of genes in this candidate region uncovered mutations in DARS2, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals from all 30 families. Enzyme activities of mutant proteins were decreased. We were surprised to find that activities of mitochondrial complexes from fibroblasts and lymphoblasts derived from affected individuals were normal, as determined by different assays.