Nonsyndromal profound genetic deafness in childhood.

About one-half of children with profound deafness have an autosomal recessive or autosomal dominant inherited type of deafness. The X-linked inherited types of deafness are rare. About one out of three profoundly deaf children has an autosomal recessive form of inherited deafness. At sometime during their life a syndromal diagnosis can be made in one out of four cases with an autosomal recessive form of deafness. Therefore in about 25% of all the children with profound deafness, a nonsyndromal autosomal recessive type of genetic deafness will be involved. It is still not clear how many different genes are responsible for this. The more severe the deafness in a child, the greater the chance that an autosomal recessive etiology is involved. The autosomal dominant inherited types of deafness are significantly more frequent in cases where the hearing loss in the best ear is less than 80-90 db. About one-half of the autosomal dominant inherited cases show a classical syndromal type of deafness based on clinical features. In the other half, some audiometrically recognizable types of deafness can be diagnosed after an autosomal dominant pattern of inheritance has been established. Additional genetic knowledge based on gene-linkage studies is needed to provide better tools for the more accurate diagnosis of genetic etiology in a profoundly deaf child. Adequate pedigrees are quite rare and such pedigrees are expected to become even more scarce as a result of a diminishing ratio of consanguineous marriages. It is necessary to start gene-linkage studies in these existing pedigrees to trace the genes responsible for this nonsyndromal type of profound genetic deafness in childhood.