Isolated hearing loss associated with T7511C mutation in mitochondrial DNA.

Conclusion: The T7511C mutation is considered responsible for maternally inherited, isolated sensorineural hearing loss of cochlear origin. This mutation should be screened for in cases of nonsyndromic, familial sensorineural hearing loss compatible with maternal transmission.

Objectives: To clarify the audiovestibular phenotype characteristics associated with a T7511C mutation in mitochondrial DNA and determine whether it causes isolated sensorineural hearing loss unaccompanied by other neuromuscular symptoms or signs.

Subjects and methods: A proband and affected members of a Japanese family harboring a T7511C mutation in the mitochondrial tRNA(Ser(UCN)) gene were enrolled. Mutation analysis was done on genomic DNA extracted from blood samples. Auditory pathways involved were investigated in examinations that included pure-tone audiograms, acoustic reflexes, speech discrimination testing, distortion-product otoacoustic emissions, and auditory brainstem responses. The presence of other signs and symptoms, including vestibular ones, was investigated.

Results: We identified a homoplasmic T7511C mutation in the mitochondrial tRNA(Ser(UCN)) gene in this family. No other pathogenic mutations associated with hearing loss or common mitochondrial diseases were found. Hearing loss of cochlear origin mainly developed at mid to high frequencies. Vestibular systems were well preserved. No symptoms or signs characteristic of mitochondrial diseases were present in any family members.