The Frequency of Mitochondrial Gene Point Mutations in Korean Non-syndromic Sensorineural Hearing Loss / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Mitochondrial point mutations have been shown to be responsible for syndromic and non-syndromic hearing impairment. Among these mitochondrial point mutations, 1555 A-->G, 3243 A-->G, and 7445 A-->G mutations are detected more frequently in sensorineural hearing loss (SNHL). In the present study, we evaluated the frequency of these three mitochondrial mutations among the non-syndromic SNHL population in Korea. SUBJECTS AND METHOD: To determine the frequency of three mitochondrial point mutation 1555 A-->G, 3243 A-->G, and 7445 A-->G, we examined 129 unrelated SNHL outpatients using restriction fragment length polymorphism. And to confirm these point mutations, we analyzed mitochondrial DNA with point mutations by direct sequence analysis. RESULTS: The frequency of mitochondrial gene mutation in the unrelated sensorineural hearing impaired patients in the Korean population was 1555 A-->G: 2.3% (3/129), 3243 A-->G: 0.7% (1/129), 7445 A-->G: 0% (0/129). CONCLUSION: These results regarding Koreans are similar to those of Japanese. Each member in a family with 1555 A-->G mitochondrial point mutation had variable hearing levels (different phenotype) in spite of the same mitochondrial point mutation. The pathogenesis of these mitochondrial point mutations in hearing should be further investigated and a study should be performed using large number of families and functional experiments to elucidate the meaning of these point mutations.

Familial Hearing Loss Associated with mtDNA A1555G Mutation in Korea: 1 Pedigree / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Familial aminoglycoside-induced deafness has been described in a number of Chinese and Japanese pedigrees. Recently, the familial aminoglycoside-induced ototoxicity is proved to be associated with a mutation in mitochondrial (mt) 12S ribosomal RNA (rRNA) gene at nucleotide position 1555 in some families. In this study, we analyzed mt 12S rRNA gene to find out this particular mutation in Korean pedigrees who had a family history of hearing loss. MATERIALS AND METHODS: Peripherial blood was obtained from 91 individuals of 30 families, and total genomic DNA (gDNA) was extracted. A fragment of DNA including a part of mt 12S rRNA gene was amplified by polymerase chain reaction (PCR). The PCR products were analyzed by restriction digestion with Bsm A1 and DNA sequencing. RESULTS: We found one family of mtDNA A1555G. Six family members had mutant genotype and three of them showed severe sensorineural hearing loss or deafness. The mutation was homoplasmic in all affected family members, and the genotype revealed maternal transmission. CONCLUSION: We found the first case of familial hearing loss genetically proved to be associated with the mt 12S rRNA gene mutation, in Korea. Because it is possible that an individual with this mutation shows a progressive sensorineural hearing loss, a screening of mtDNA A1555G mutation for the familial members who have a maternal inheritant hearing loss might be necessary.