Maternally transmitted aminoglycoside-induced and non-syndromic hearing loss caused by the 1494C > T mutation in the mitochondrial 12S rRNA gene in two Chinese families.

OBJECTIVE

To explore the molecular genetic characterization of two Chinese families with aminoglycoside-induced and non-syndromic hearing loss (NSHL).

DESIGN

Clinical evaluations, sequence analysis of mitochondrial DNA (mtDNA) as well as two nuclear genes TRMU and MTO1 encoding mitochondrial proteins.

STUDY SAMPLE

Two Chinese families with aminoglycoside-induced and NSHL.

RESULTS

Clinical evaluations revealed incomplete penetrance (28.6% vs. 40.0%) and variable phenotype of hearing losses between two families. When the effect of aminoglycosides was excluded, the penetrances were both 0%. Sequence analysis of mitochondrial genomes showed a homoplasmic 1494C > T mutation in the12S rRNA gene (MT-RNR1) in all maternal relatives, as well as distinct sets of mtDNA polymorphism belonging to Eastern Asian haplogroups D4j and D5a2, respectively. However, none of these mtDNA variants was highly evolutionarily conserved and implicated to have functional significance. No mutations were identified in either TRMU or MTO1 gene.

CONCLUSIONS

Mitochondrial 1494C> T mutation is the molecular basis responsible for the NSHL of two families, and the use of aminoglycoside antibiotics can worsen the hearing of the mutation carriers. Our results indicate the importance of a systematic screening for the mitochondrial 1494C > T mutation in Chinese subjects in the prevention of aminoglycoside-induced and non-syndromic hearing loss.