CFTR and cystic fibrosis: Given the diversity of mutations, it is perhaps not surprising that there is a wide range of phenotypic variability in CF simply due to variation in CFTR. Many reports of correlations between CFTR genotype and clinical phenotype exist (Kerem et al., 1990a; Stuhrmann et al., 1991; The Cystic Fibrosis Genotype-Phenotype Consortium, 1993; Tsui and Durie, 1997; Zielenski, 2000), with the most extensive catalog to date carried out as an international effort2 and currently includes data on over 35,000 patients.