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Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy.

ABSTRACT: Importance: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. Objectives:To review the clinical, molecular, and genetic features of YARS2-related mitochondrial disease and to demonstrate a new Scottish founder variant. Design, Setting, and Participants:An observational case series study was conducted at a national diagnostic center for mitochondrial disease in Newcastle upon Tyne, England, and review of cases published in the literature. Six adults in a well-defined mitochondrial disease cohort and 11 additional cases described in the literature were identified with YARS2 variants between January 1, 2000, and January 31, 2015. Main Outcome and Measures:The spectrum of clinical features and disease progression in unreported and reported patients with pathogenic YARS2 variants. Results:Seventeen patients (median [interquartile range] age at onset, 1.5 [9.8] years) with YARS2-related mitochondrial myopathy were identified. Fifteen individuals (88%) exhibited an elevated blood lactate level accompanied by generalized myopathy; only 12 patients (71%) manifested with sideroblastic anemia. Hypertrophic cardiomyopathy (9 [53%]) and respiratory insufficiency (8 [47%]) were also prominent clinical features. Central nervous system involvement was rare. Muscle studies showed global cytochrome-c oxidase deficiency in all patients tested and severe, combined respiratory chain complex activity deficiencies. Microsatellite genotyping demonstrated a common founder effect shared between 3 Scottish patients with a p.Leu392Ser variant. Immunoblotting from fibroblasts and myoblasts of an affected Scottish patient showed normal YARS2 protein levels and mild respiratory chain complex defects. Yeast modeling of novel missense YARS2 variants closely correlated with the severity of clinical phenotypes. Conclusions and Relevance:The p.Leu392Ser variant is likely a newly identified founder YARS2 mutation. Testing for pathogenic YARS2 variants should be considered in patients presenting with mitochondrial myopathy, characterized by exercise intolerance and muscle weakness even in the absence of sideroblastic anemia irrespective of ethnicity. Regular surveillance and early treatment for cardiomyopathy and respiratory muscle weakness is advocated because early treatment may mitigate the significant morbidity and mortality associated with this genetic disorder.

SUBMITTER: Sommerville EW

PROVIDER: S-EPMC5822212 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy.

Sommerville Ewen W EW Ng Yi Shiau YS Alston Charlotte L CL Dallabona Cristina C Gilberti Micol M He Langping L Knowles Charlotte C Chin Sophie L SL Schaefer Andrew M AM Falkous Gavin G Murdoch David D Longman Cheryl C de Visser Marianne M Bindoff Laurence A LA Rawles John M JM Dean John C S JCS Petty Richard K RK Farrugia Maria E ME Haack Tobias B TB Prokisch Holger H McFarland Robert R Turnbull Douglass M DM Donnini Claudia C Taylor Robert W RW Gorman Gráinne S GS

JAMA neurology 20170601 6

<h4>Importance</h4>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.<h4>Objectives</h4>To review the clinical, molecular, and genetic features of YARS2-related mitochondrial disease and to demonstrate a new Scottish founder variant.<h4>Design, setting, and participants</h4>A ...[more]

PMID: 28395030

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Project description:BackgroundMutations 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.MethodsTwelve patients were screened for YARS2 mutations by Sanger sequencing. Clinical data were compared. Functional assays were performed to confirm the pathogenicity of the novel mutations and to investigate tissue specific effects.ResultsPathogenicYARS2 mutations were identified in three of twelve patients screened. Two patients were found to be homozygous for the previously reported p.Phe52Leu mutation, one severely and one mildly affected. These patients had different mtDNA haplogroups which may contribute to the observed phenotypic variability. A mildly affected patient was a compound heterozygote for two novel YARS2 mutations, p.Gly191Asp and p.Arg360X. The p.Gly191Asp mutation resulted in a 38-fold loss in YARS2 catalytic efficiency and the p.Arg360X mutation did not produce a stable protein. The p.Phe52Leu and p.Gly191Asp/p.Arg360X mutations resulted in more severe RC deficiency of complexes I, III and IV in muscle cells compared to fibroblasts, but had relatively normal YARS2 protein levels. The muscle-specific RC deficiency can be related to the increased requirement for RC complexes in muscle. There was also a failure of mtDNA proliferation upon myogenesis in patient cells which may compound the RC defect. Patient muscle had increased levels of PGC1-? and TFAM suggesting mitochondrial biogenesis was activated as a potential compensatory mechanism.ConclusionIn this study we have identified novel YARS2 mutations and noted marked phenotypic variability among YARS2 MLASA patients, with phenotypes ranging from mild to lethal, and we suggest that the background mtDNA haplotype may be contributing to the phenotypic variability. These findings have implications for diagnosis and prognostication of the MLASA and related phenotypes.

Dataset Information

Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy.

Publications

Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy.

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