Hearing loss with a mitochondrial gene mutation is highly prevalent in Japan

Objectives/Hypothesis: Mutations in the mitochondrial genome may predispose people to sensorineural hearing loss. An adenine to guanine point mutation in the tRNA(Leu(UUR)) gene at nucleotide 3,243 is one of the deaf-related mutations. This mutation is reported to be associated with 0.9% of diabetes mellitus patients. However, the prevalence of this mutation in hearing-imp aired patients still remains unknown. The aim of this study was to determin e the prevalence of this mutation among bilaterally sensorineural hearing-i mpaired patients in Japan. Study Design: Retrospective survey of 100 patien ts with bilateral sensorineural hearing loss without any evident causes. Me thods: Mitochondrial DNA fragments from the patients were amplified by poly merase chain reaction, followed by a restriction enzyme fragment length pol ymorphism method. Results: Three patients with this mutation were identifie d. Their clinical profiles were different from the category which had been considered as hearing loss caused by this mitochondrial gene mutation. Conc lusions: The mutation is associated with approximately 3% of bilateral sens orineural hearing loss cases of unknown origin and is possibly distributed widely in sensorineural hearing-impaired patients in Japan.