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 inh abitants in a population living in the North of Tunisia. The sex ratio in probands is 0.73 with clinical otosclerosis being approximately tw ice as frequent in females than in males, an observation which could b e due to hormonal factors. The main risk period for otosclerosis is be tween 25 and 35 years of age in both sexes. Segregation analysis was p erformed in 193 nuclear families belonging to 65 pedigrees of otoscler osis. The pattern of the disease is due to a rare dominant major gene with a high polygenic component. This finding was unexpected since oto sclerosis is usually considered to be a disease with simple dominant i nheritance 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 ag e and sex.