CA/GT MICROSATELLITE ALLELES WITHIN THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR (CFTR) GENE ARE NOT GENERATED BY UNEQUAL CROSSINGOVER

The gene responsible for cystic fibrosis (CF) has recently been identified, and a three-nucleotide deletion (ΔF508 mutation) that results in the loss of a phenylalanine residue in the first putative ATP-binding domain of the predicted protein (CF transmembrane conductance regulator, CFTR) has been found to be the major CF mutation. Although several other mutations have been identified in the CFTR gene, most of them are very rare, making their application to genetic diagnosis difficult. While characterizing the genomic region encompassing the CF locus, we have identified three CA GT blocks that flank exon 9 of the CF gene. One of the CA GT blocks exhibits a highly informative variable number of dinucleotide repeats (VNDR) polymorphism. This intragenic VNDR microsatellite should, by itself, provide full information for genetic analysis in approximately 80% of CF families and will help elucidate the associations between DNA polymorphism haplotypes and specific gene mutations. Haplotype analyses of CF chromosomes with and without the ΔF508 mutation suggest that the different alleles are generated by slipped-strand mispairing within the dinucleotide repeat during DNA replication, rather than by unequal crossingover within a recombination hot spot. © 1991.