Clinical Implications of Cystic Fibrosis Transmembrane Conductance Regulator Mutations

Cystic fibrosis (CF) is a lethal autosomal recessive disorder characterized by obstructive pulmonary disease, pancreatic exocrine deficiency, high content of sodium and chloride in the sweat, and male infertility (Table 1) . The CF phenotype is highly variable among unrelated individuals and within families, although certain manifestations, such as pancreatic status, are similar among affected siblings. At least three factors contribute to variability of the CF phenotype: mutations in the CF gene, genetic background, and environment. 26 , 133 First, mutations in the CF gene correlate with specific features of the CF phenotype. These include pancreatic function and the degree of sweat chloride abnormality. Second, genetic background may contribute to the variable manifestations of CF in different populations. Animal models of CF have uncovered modifying genes in different genetic backgrounds that influence phenotype. 101 Third, environmental factors, such as second-hand exposure to cigarette smoke, have been shown to influence phenotype. 76 Accordingly, patients with CF show a wide range in clinical severity, particularly with regard to lung disease.