Unique penetrance of hearing loss in a five-generation Chinese family with the mitochondrial 12S rRNA 1555A > G mutation.

CONCLUSIONS: Analysis of the complete mtDNA genome and X-linkage of this five-generation Chinese family revealed that the 1555A > G mutation may lead to deafness.

OBJECTIVES: Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. However, the variable clinical phenotype and incomplete penetrance of mtDNA 1555A > G-induced hearing loss complicate our understanding of this mutation. We aimed to identify whether nuclear genes, mitochondrial haplotypes/variants, and a possible threshold effect are involved in its manifestation in the pedigree.

METHODS: We performed clinical, genetic, and X-linkage analysis of a five-generation Chinese family in which all the affected individuals were male.

RESULTS: Clinical evaluation revealed that affected individuals with or without aminoglycoside exposure developed hearing loss extending gradually from 8000 Hz to 4000 Hz and then to 1000 Hz. Using X-linkage analysis and sequencing, we detected an identical homoplasmic 1555A > G mutation in nine individuals, and a previously unreported variant 14163C > T in mtDNA. The new variant 14163C > T coexisted with the 1555A > G mutation in six affected subjects of our pedigree. The previously unreported variant 14163C > T and aminoglycoside exposure may synergize the development of this deafness.