Causes of childhood deafness at a Dutch school for the hearing impaired.

This study was conducted on 162 hearing-impaired school pupils who were investigated as to the cause of their hearing loss. In 64 pupils (40%) a hereditary cause was recognized, and in 43 (27%), an acquired cause; in 55 (34%) the cause remained unknown, according to the criteria we used for defining a cause. Special attention was paid to the differences between the hereditary and acquired forms of deafness in relation to the degree of hearing loss. The study population therefore was divided into groups per 10 dB of hearing loss. Using this method we found that an autosomal dominant hearing loss occurred significantly more frequently among the less severe hearing disorders. This finding, which has not been seen in the literature, is important in genetic counseling for the deaf. Another remarkable finding was that Usher's syndrome, especially type 2 with a moderate hearing loss, was more frequent among the hearing-impaired subjects than we had expected.