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 a 
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. 