Consanguinity and endogamy in Northern Tunisia and its impact on non-syndromic deafness

Deafness is an important health problem in the Tunisian population, especially in isolates where the prevalence ranges from 2 to 8%. To evaluate the effect of inbred unions on deafness, a study was conducted on 5,020 individuals (160 are deaf) between 2000 and 2002 in the North of Tunisia. The coefficient of inbreeding for all individuals and the levels of inbreeding in ten districts were computed. The higher levels were obtained in the rural districts. Our study revealed that geographic isolation, social traditions, and parental involvement in mode selection all contribute to increase consanguinity in these regions. The mean inbreeding seems to be similar to those estimated in highly inbred isolates in the world. The relative risk of the 35delG mutation, the single most frequent allele for non-syndromic recessive deafness in Tunisia, was estimated from the observed inbreeding coefficient and found to be 10.76 (SD 7.74) for first-cousin marriages, which are the most common form of consanguineous marriage encountered. Our knowledge of the risk rate of deafness and our understanding of consanguinity is required for the prevention of genetic deafness in the Tunisian population.