Clinical and audiological follow up of a family with the 8363G > A mutation in the mitochondrial DNA

Hearing loss is relatively common in mtDNA-related disorders. While auditory function has been assessed fully in the syndrome of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes, few studies have investigated the degree of progressive hearing deficit in individuals bearing other mtDNA mutations. We performed a 4-year clinical and audiological follow up in a family carrying the 8363G > A mutation in the mitochondrial transfer ribonucleic acid lysine (tRNA^Lys) gene who displayed a progressive neuromuscular disease. In addition to pure tone audiometry, we considered distortion products of otoacoustic emissions, a sensitive indicator of cochlear dysfunction, as well as brainstem auditory evoked responses. A generalized increase in the auditory threshold at follow up, indicating a cochlear impairment in three cases, was noted. Distortion products of otoacoustic emissions may reveal sub-clinical cochlear dysfunction, even in oligosymptomatic patients. A complete and periodical assessment of the hearing function should be encouraged in asymptomatic relatives of patients carrying the tRNA^Lys 8363G > A mutation.