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Auditory Findings in Patients with Maternally Inherited Diabetes and Deafness Harboring a Point Mutation in the Mitochondrial Transfer RNA Leu (UUR) Gene
Author(s) -
Yamasoba Tatsuya,
Oka Yoshitomo,
Tsukuda Katsunori,
Nakamura Masaichi,
Kaga Kimitaka
Publication year - 1996
Publication title -
the laryngoscope
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.181
H-Index - 148
eISSN - 1531-4995
pISSN - 0023-852X
DOI - 10.1097/00005537-199601000-00010
Subject(s) - heteroplasmy , hearing loss , mitochondrial dna , point mutation , genetics , cochlea , biology , sensorineural hearing loss , transfer rna , melas syndrome , mutant , gene , mutation , medicine , audiology , mitochondrial myopathy , rna , anatomy
Five patients with sensorineural hearing loss, who harbored a point mutation in the mitochondrial transfer RNA (tRNA) gene tRNA Leu (UUR) , from five unrelated family pedigrees were examined. In these families diabetes and deafness were maternally inherited. Bilateral hearing was more severely impaired at higher frequencies. Audiometric test results revealed that hearing loss involved the cochlea. Hearing gradually deteriorated; the progression rate ranged from 1.5 to 7.9 dB per year. Proportion of mutant mitochondrial DNAs (mtDNAs) in the leukocytes was not related to the rate or degree of hearing loss, although hearing loss appeared at a younger age in patients with higher heteroplasmy. We speculate that after the proportion of damaged mtDNAs, mostly as a result of mutation, exceeds the expression threshold for deficiencies in mitochondrial protein synthesis and oxygen consumption, a drop in adenosine triphosphate level could lead to an imbalance of ion concentration, resulting in cell death in the cochlea.