Cystic fibrosis in the Ohio Amish: gene frequency and founder effect

A high incidence of cystic fibrosis (CF), 1/569 live births (0.00176), was found among 10 816 live births in an Ohio Amish isolate. The minimum gene frequency calculated from this incidence was 0.042. In marked contrast, a second Amish isolate was described with no occurrence of CF among 4448 live births. Founder effect is the most probable explanation for the difference in the CF gene frequency between the two communities. Pedigree analysis identified a single ancestral couple born in the 1700s common to all obligate heterozygotes.