Cluster of cystic fibrosis cases in a limited area of Brittany (France).

Cystic fibrosis in the northern sector of the French “departement” of Finistere is 1:1787 live births. Within this sector a concentration of the disease was found in a small area. The minimal frequency in this area, from 1946 to 1972, was calculated as 1 per 377 live births, the gene frequency being 0.0515. Genealogic analysis, going back to the beginning of the 18th century, showed a relationship between 8 of the 10 families to which the patients belonged. The origin of the deleterious genes may be explained by at least five primary ancestral couples living in the 18th century. Random drift is the most probable explanation for the concentration of cystic fibrosis in this region.