Extremely low penetrance of deafness associated with the mitochondrial 12S rRNA T1095C mutation in three Chinese families.

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic, and molecular characterization of three Chinese pedigrees (a total of 43 matrilineal relatives) with aminoglycoside-induced impairment. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects, although these subjects shared some common features: being bilateral and sensorineural hearing impairment. Strikingly, only probands of these Chinese pedigrees exhibited severe to profound hearing loss. Mutational analysis of the mtDNA in these pedigrees showed the presence of homoplasmic 12S rRNA T1095C mutation, which has been associated with hearing impairment in several families. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the identical homoplasmic T1095C mutation and distinct sets of mitochondrial DNA (mtDNA) variants belonging to haplogroups M11C. Despite the presence of several highly evolutionarily conservative variants in protein-encoding genes and 16S rRNA gene, the extremely low penetrance of hearing loss with the T1095C mutation implies that the mitochondrial variants may not play an important role in the phenotypic expression of the T1095C mutation in these Chinese families. However, the history of exposure to aminoglycosides in these three hearing-impaired subjects suggested that the aminoglycosides very likely are the cause of hearing loss.