RESUMO
OBJECTIVE: Many factors, hereditary and environmental, may cause deafness. The aim of the present study was to analyze data on the etiology of bilateral sensorineural hearing impairment in children born in the Jerusalem area during 1978-1991, and to compare the results to those of a previous survey (1968-1977) in the same area. METHODS: The study included 150 Jewish children (139 families) with hearing loss, born during 1978-1991. Information was obtained on prenatal, perinatal and postnatal events, history of hearing loss in the family, the parents' communities and consanguinity. Children with a sensorineural hearing impairment of 56 dB HL or greater in the better ear, within the frequency range of 0.5-4 kHz were included in the study. The hearing loss was classified as moderate-severe (56-70 dB HL), severe (71-90 dB HL) and profound (91 dB HL or more) in the better ear. Mutations in the coding sequence of the connexin 26 (C x 26) and the connexin 30 genes were examined in some of the families. RESULTS: The hearing impairment was hereditary in 66 (44%) of the children, environmental in 31 (21%) and four children (3%) had multiple malformations. The cause was unknown in 49 (33%) children. Sixty-two families were of European origin (Ashkenazim) and 62 of Afro-Asian origin (Sephardim). Consanguinity was in 7% of the families. Mutations in connexin 26 and the deletion in connexin 30 were diagnosed in 9/18 families tested. The incidence of hearing loss decreased from 1.28 per thousand during 1968-1977 to 1.06 per thousand during 1978-1991. The rate of environmental causes decreased over the years together with an increase in the rate of unknown causes. The rate of hearing loss among Sephardim decreased significantly and increased among Ashkenazim. CONCLUSIONS: The rate of hearing impairment in Israel is as that found in other countries, as was the distribution of the causes of deafness. The decrease in the rates of hearing impairment among the Sephardim may be due to a continuing decrease in consanguineous marriages among Sephardim. It is expected that the group of unknown causes will become smaller in future with the availability of more molecular genetic tests.
