Cystic fibrosis mutations in North American populations of French ancestry: analysis of Quebec French-Canadian and Louisiana Acadian families. A 3-bp deletion (delta F508) in the cystic fibrosis (CF) gene is the mutation on the majority of CF chromosomes. We studied 112 CF families from North American populations of French ancestry: French-Canadian families referred from hospitals in three cities in Quebec and from the Saguenay-Lac St. Jean region of northeastern Quebec and Acadian families living in Louisiana. delta F508 was present on 71%, 55%, and 70% of the CF chromosomes from the major-urban Quebec, Saguenay-Lac St. Jean, and Louisiana Acadian families, respectively. A weighted estimate of the proportion of delta F508 in the French-Canadian patient population of Quebec was 70%. We found that 95% of the CF chromosomes with delta F508 had D7S23 haplotype B, the most frequent haplotype on CF chromosomes. In the Saguenay-Lac St. Jean families, 86% of the CF chromosomes without delta F508 had the B haplotype, compared with 31% for the major-urban Quebec and Louisiana Acadian families. The incidence of CF in the Saguenay-Lac St. Jean population was 1/895 live-born infants. 