Several point mutations of mitochondrial DNA have recently been identified as a cause of hearing loss. In Japan, there are considerable number of patients with A-to-G mutations at nucleotide position 3243 and at 1555. We investigated the prevalence of these mutations in patients with hearing loss using polymerase chain reaction method (PCR). We identified 3243 point mutation in 2 of 72 patients (2.8%) and 1555 point mutation in one of 57 patients (1.8%). The clinical neuro-otologic findings in patients with point mutations were consistent with those previously reported. The number of patients examined was composed of 9% of a total in our outpatient clinic. Therefore, we estimated 0.4% of patients in our clinic have a point mutation at nucleotide position 3243 or 1555.
