MILD CYSTIC-FIBROSIS-DISEASE IN 3 MEXICAN DELTA-F508 G551S COMPOUND HETEROZYGOUS SIBLINGS/

We describe three delta-F508/G551S compound heterozygous siblings with a mild CF phenotype, characterized by mild chronic pulmonary disease, pancreatic sufficiency and increased sweat chloride levels. PCR-media ted site-directed mutagenesis detected the delta-F508 mutation on one allele, and the G551S mutation was detected by SSCP and sequence analy sis of exon 11. Two previously described sisters who were homozygous f or the G551S mutation had a very mild phenotype with normal sweat chlo ride concentrations. In our patients the mild phenotype resulted from the combined effect of the mild G551S allele with the severe delta-F50 8 allele.