Biallelic variants in WARS2 encoding mitochondrial tryptophanyl-tRNA synthase in six individuals with mitochondrial encephalopathy

Hum Mutat. 2017 Dec;38(12):1786-1795. doi: 10.1002/humu.23340. Epub 2017 Oct 6.

Abstract

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 tRNATrp 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.

Keywords: COX deficiency; lactic acidosis; liver; mitochondrial disorder.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acyl-tRNA Synthetases / genetics*
  • Amino Acyl-tRNA Synthetases / metabolism
  • Exome / genetics
  • Female
  • Genetic Variation*
  • Humans
  • Infant, Newborn
  • Intellectual Disability / enzymology
  • Intellectual Disability / genetics*
  • Male
  • Mitochondrial Diseases / enzymology
  • Mitochondrial Diseases / genetics*
  • Mitochondrial Encephalomyopathies / enzymology
  • Mitochondrial Encephalomyopathies / genetics*
  • Mitochondrial Encephalomyopathies / pathology
  • Models, Molecular
  • Mutation
  • Pedigree
  • Phenotype
  • Pregnancy
  • Sequence Alignment
  • Whole Exome Sequencing

Substances

  • Amino Acyl-tRNA Synthetases

Supplementary concepts

  • Mitochondrial encephalopathy