['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-impaired patients still remains unknown. The aim of this study was to determine the prevalence of this mutation among bilaterally sensorineural hearing-impaired patients in Japan.', 'Retrospective survey of 100 patients with bilateral sensorineural hearing loss without any evident causes.', 'Mitochondrial DNA fragments from the patients were amplified by polymerase chain reaction, followed by a restriction enzyme fragment length polymorphism method.', 'Three patients with this mutation were identified. Their clinical profiles were different from the category which had been considered as hearing loss caused by this mitochondrial gene mutation.'] Is hearing loss with a mitochondrial gene mutation highly prevalent in Japan?