[Analysis of 112 haplotypes carrying the cystic fibrosis gene. Applications in genetic counseling].

Cystic fibrosis (CF) is always a common lethal genetic disease. The locus is localized to human chromosome 7q22-7q31. Genetic linkage between the CF locus and polymorphic DNA marker is used to realize family studies. We have genotyped 56 families (352 patients) with a CF child. The informativeness with the six markers (Met D/Taq I, Met H/Taq I, Met H/Msp 1, XV2c/Taq 1, km19/pst pJ 3.11/Msp 1) is important (96%). The linkage desequilibrium between alleles detected by XV2 c and Km 19 described by Estivill and al, is also showed in our population. The haplotype B (Km 19 = 6.6 kb, XV2 c = 2.1 kb) is present on 84% of our 112 CF chromosomes. We have established the frequencies of the 10 possible genotypes in the pool of the 112 CF chromosomes and in the pool of the normal chromosome and according to Bayes obtained the predictive positive value to be heterozygote. It is possible to precise the genetic counselling in these families.