Abstract
An A to G mutation at nucleotide position 3243 of mitochondrial DNA is associated with mitochondrial encephalomyopathy, diabetes mellitus, and/or sensorineural hearing loss, which is maternally inherited. It is observed in about 1% of the patients with diabetes mellitus in Japan. Therefore, it is highly probable that otolaryngologists will encounter patients with hearing loss caused by the 3243 mutation. In this paper, we studied the audiovestibular characteristics of 8 patients who were identified as having the 3243 mutation (4 cases of mitochondrial encephalomyopathy and 4 cases of diabetes mellitus). Six of these patients had sensorineural hearing loss. The average age of onset of hearing loss was 30 years. The hearing loss was bilateral and symmetric, and was equivalent in all frequencies or increased from low to high frequencies. The hearing loss gradually deteriorated and the progression rate was 3.6dB per year on average. Hearing deterioration in patients with mitochondrial encephalomyopathy was faster than that in patients with diabetes mellitus. The audiologic examinations suggested both cochlear and retrocochlear impairment. Equilibrium function tests presented no significant characteristics, even in cases of severe hearing loss.
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