|Budget Amount *help
¥2,700,000 (Direct Cost : ¥2,700,000)
Fiscal Year 1999 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1998 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Mitochondrial mutations have been found to cause syndromic or non-syndromic sensorineural hearing loss(SNHL). In the present study, the frequency of three mitochondrial point mutations, 1555A->G, 3243A->G, and 7445A->G, known to be associated with hearing impairment, was examined using restriction fragment length polymorphism (RFLP) analysis in two Japanese groups: 1) 319 unrelated SNHL outpatients (including 21 with aminoglycoside antibiotic injection history), and 2) 140 cochlear implantation patients (including 22 with aminoglycoside-induced hearing loss). Approximately 3% of the outpatients and 10% of the cochlear implantation patients had the 1555A->G mutation. The frequency was higher in the patients with a history of aminoglycoside injection (outpatient group 33%; cochlear implantation group 59%). One outpatient (0.314%)had the 3243A->G mutation, but no outpatients had the 7445A->G mutation and neither were found in the cochlear implantation group. The significance of the 1555A->G mutation, the most prevalent mitochondrial mutation found in this study of a hearing impaired population in Japan, among subjects with specific backgrounds, such as aminoglycoside-induced hearing loss, is evident. Among them, the 1555A->G point mutation is associated with a susceptibility to aminoglycoside antibiotics, and is of particular interest as it may cause hearing loss even without aminoglycoside exposure. There may be a considerably large high-risk population in Japan and to avoid possible side effects in this group, a rapid mass screening system and careful counseling is recommended. We are currently using the MASA (Mutant Allele Specific Amplification)method to detect the 1555A->G mitochondrial mutation and we distribute a warning card to subjects found to bear this mutation.