Prevalence of mitochondrial gene mutations among hearing impaired patients

The frequency of three mitochondrial point mutations, 1555A-->G, 3243A-->G, and 7445A-->G, known to be associated with hearing impairment, was examine d using restriction fragment length polymorphism (RFLP) analysis in two Jap anese groups: (1) 319 unrelated SNHL outpatients (including 21 with aminogl ycoside antibiotic injection history), and (2) 140 cochlear implantation pa tients (including 22 with aminoglycoside induced hearing lass). Approximate ly 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 his tory of aminoglycoside injection (outpatient group 33%, cochlear implantati on group 59%). One outpatient (0.314%) had the 3243A-->G mutation, but no o utpatients had the 7445A-->G mutation and neither were found in the cochlea r 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 amin oglycoside induced hearing loss, is evident.