Incidence of genetic factors in the causation of deafness in childhood.

Routine investigations of 1568 children with severe-profound hearing loss, during a 15 years' period, revealed the following classification: Hereditary Deafness 25%, Acquired Deafness 43% (prenatally 11%, perinatally 16%, postnatally 16%), Unknown Deafness 32%. This group of unknown causes is usually large in any surgery of deafness and in many of these children deafness is believed to have a genetic basis. In the light of this premise, we performed more careful genetic and clinical investigation in 268 children coming under observation in the 3 last years. Moreover, we examined a group of 44 asymptomatic parental pairs of these children to determine if any were carriers of genes for deafness. The criteria used for identification were: pure tone audiometry, speech discrimination score, threshold of the acoustic reflex, Lüscher test, loudness discomfort level for 1-2-4 kHz, continuous Bekesy audiometry. Children follow-up enabled us to place 14 cases in the range of hereditary syndromes. Therefore, the group of unknown deafness decreased from 32% to 27%. The audiological investigation, performed on the parental pairs, pointed out an abnormal auditory function in 30.6% of subjects, who for these reasons should be considered as heterozygous carriers.