A genetic study of otosclerosis in a population living in the north of Tunisia.

The frequency of otosclerosis has been estimated to be 0.6 per 100 inhabitants in a population living in the North of Tunisia. The sex ratio in probands is 0.73 with clinical otosclerosis being approximately twice as frequent in females than in males, an observation which could be due to hormonal factors. The main risk period for otosclerosis is between 25 and 35 years of age in both sexes. Segregation analysis was performed in 193 nuclear families belonging to 65 pedigrees of otosclerosis. The pattern of the disease is due to a rare dominant major gene with a high polygenic component. This finding was unexpected since otosclerosis is usually considered to be a disease with simple dominant inheritance and incomplete penetrance. The authors have estimated that only 13% of affected patients are carriers of the rare dominant gene. This gene has strong penetrance which, however, varies according to age and sex.