Sensorineural hearing loss is a common symptom in patients with myoclonic epilepsy associated with ragged-red fibres (MERRF), one of the mitochondrial encephalomyopathies, although the lesion causing hearing loss in such cases remains unknown. Here we describe the audiological features in three MERRF patients, all of whom exhibited a point mutation in their mitochondrial DNA at nucleotide 8344. Pure-tone threshold audiometry revealed bilateral, sloping-type, sensorineural hearing loss in all three patients. Distortion product otoacoustic emissions, electrocochleography, and auditory brainstem responses were variable, even differing between the right and left ears of the same patient. Taken together, our findings suggest that the primary lesion underlying hearing loss in MERRF patients is in the cochlea, although a retrocochlear lesion may be involved in some patients.
