[Personal experience with genetic study of the hearing-impaired]

In 1988-1990 the authors examined on account of impaired hearing in the family 78 families, which were divided into two groups. The first group comprises 48 families of actively invited pupils from schools with children with impaired hearing in Prague, the second group comprises 30 families examined in the framework of common counselling and consultation services. On the first group a genetic aetiology of the disorder was revealed in 75% and in the second group in 73.3% of the cases. An autosomal recessive type of heredity was proved unequivocally in 31.3% in group 1 and in 20.0% in group 2. An autosomal dominant type of heredity was found in 6.25% in group 1 and in 6.7% in group 2. X-linked deafness was proved only in group 1 in 4.2% and sporadic syndromes only in group 2 in 13.3%. In 33.3% in both groups it was not possible to differentiate the type of heredity (most frequently the child and both parents were affected). In the first group three genetic syndromes were detected and in group 2 seven genetic syndromes. As the percentage of genetically conditioned hearing disorders in both groups is relatively high, the authors consider active screening of deaf children more useful so far.