Saguenay-Lac-St-Jean is a geographically isolated region located in northeastern Quebec. Opened to the white settlement in 1838, its immigrants mainly came from Charlevoix, another isolated region of Quebec. The prevalence and/or incidence of several autosomal dominant and recessive disorders are very high. The overall birth prevalence of the recessive disorders was calculated at 1/207 living births and the overall carrier rate at 1/7 inhabitants. This situation may be explained by migration and social factors.