CFTR and cystic fibrosis: Cystic Fibrosis (CF) is a genetic disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in a dysfunctional or absent CFTR protein on the apical membrane of epithelial cells in all exocrine organs in the body (e.g., sweat glands, salivary glands, exocrine pancreas, genital tract, gut and lung).