Nonsyndromic hearing loss caused by a mitochondrial T7511C mutation

Abstract

Objectives: The aims of the present study were to identify a mutation in a Japanese family showing nonsyndromic sensorineural hearing loss and to relate the mutation to characteristics of patients, including audiovestibular findings. Study Design: Familial cohort study. Methods: Mutation analysis was performed using genomic DNA extracted from blood samples. Subjects underwent audiovestibular examinations, including pure-tone audiograms, tympanometry, self-recording audiometry, acoustic reflex threshold, speech discrimination testing, evoked and distortion-product otoacoustic emissions, auditory brainstem responses, and caloric testing. Results: We identified a T7511C mutation in the mitochondrial tRNASer(UCN) gene previously reported in one other family. The degree of heteroplasmy for the T7511C mutation ranged from 84% to 92%, and did not correlate with age at examination or severity of hearing loss. Extensive audiologic evaluation suggested both cochlear and retrocochlear involvement. Conclusion: Families with maternally transmitted nonsyndromic hearing loss should be investigated for mutations in the tRNASer(UCN) gene.