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Three intragenic microsatellites of the CFTR gene, a TA and a CA repeats, namely IVS17bTA and IVS17bCA, located in intron 17b and a CA repeat (IVS8CA) located in intron 8 of the CFTR gene, were analyzed in a large sample of Italian cystic fibrosis (CF) and normal chromosomes. Linkage disequilibrium was evaluated between each marker and difference CF mutations on a total of 377 CF and 358 normal chromosomes. Our results are consistent with the hypothesis that all delta F508 chromosomes derive from a single mutational event. The same hypothesis is valid for mutations G542X, N1303K, 1717-1G-->A, which might have been originated more recently than delta F508.

The delta 508 mutation accounts for about 53% of the molecular defects causing cystic fibrosis (CF) in Italy. The numerous additional mutations detected so far are all relatively rare, and about 30% of CF chromosomes carries unknown mutations in our patients. In order to identify the non-delta F508 mutations causing CF in our population, we performed GC-clamped denaturing gradient gel electrophoresis (DGGE) on 9 exons of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in a sample of 86 Italian CF patients carrying unknown mutations on at least one chromosome. Direct sequencing of 17 samples showing an altered electrophoretic mobility allowed the identification of four new mutations (541delC, R347H, R352Q, and E585X), five mutations already known (G85E, I148T, G178R, 1078delT, and R347P), and one rare variant (1898 + 3A-->G). The strategy based on GC-clamped DGGE represents an efficient and rapid approach for mutation detection for those genetic diseases, such as CF, in which a large number of rare molecular defects has been described.