Mitochondrial tRNA ^Gly A10055G mutation contributes to non-syndromic hearing loss: a study of three Han Chinese pedigrees

Mutations in mitochondrial tRNA (mt-tRNA) genes are associated with non-syndromic hearing loss (NSHL), though their detailed molecular mechanisms and pathogenic potential remain unclear. In this study, we reported three Han Chinese pedigrees exhibiting maternally transmitted NSHL. Mitochondrial genomes from probands were sequenced and compared to revised Cambridge reference sequence (rCRS), followed by phylogenetic analysis to assess pathogenicity. We further established cybrid cell lines to measure mtDNA copy number, ATP levels, mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and 8-OHdG, we also screened mutations in nuclear deafness genes including GJB2, GJB3, GJB6, and TRMU. Affected individuals displayed a wide range of age at onset (mean 40.5 years) of deafness. A homoplasmic m.A10055G mutation was identified in the tRNAGly gene, which disrupted a conserved base pair. Compared to controls, mutant cybrids showed significantly reduced mtDNA copy number, ATP, and MMP, along with increased levels of 8-OHdG and ROS, whereas no pathogenic nuclear variants were detected. Collectively, these findings indicated that the m.A10055G mutation contributed to NSHL pathogenesis by impairing mitochondrial functions, most likely through defective tRNA metabolism and by increasing oxidative stress.