Seiko Murai

Audiologic features of hearing loss due to the 1,555 mutation of mitochondrial DNA

We proved a 1,555 mutation of mitochondrial DNA in one member of each of three families with familial streptomycin hearing loss, and report the pedigrees and audiologic features. DNA was extracted by the standard method. The 1,555 A to G mutation was identified in all three patients and confirmed by direct sequencing of the polymerase chain reaction products by a cycle sequencing method. On audiograms, the hearing loss was sensorineural, bilateral, and symmetric, showing a high-tone loss or a profound loss particularly in the high-tone range, and the “symmetry law” of Langenbeck was applicable. The superimposed audiograms of members of one family did not cross themselves, proving the applicability of the “never-cross principle of audiograms.”

HEARING TEST FOR EIGHTEEN THOUSAND SCHOOL CHILDREN

A scheduled survey was carried out to obtain the incidence of children with defective hearing and individual records of the auditory function of all school children living in Morioka City. Almost all the children of all primary schools in Morioka City were surveyed. The program consisted of four steps: the first step was a group pure tone screening test, the second and third were individual screening tests and the fourth was ordinary pure tone audiometry. The first and second steps were performed at each school and the third and fourth at Iwate Medical University Hospital. In the first step, the authors employed a new test method for group screening, in which 40 testees were tested at the same time. Among 18,422 school children tested, 388 were judged as having defective hearing. The incidence was 2.1 %. No essential difference was found among school grades one (6 years old) to six (11 years old). Two notable findings were (1) a prevalence of perceptive against conductive hearing loss and (2) relatively high incidence of 4 KHz dip.