CFTR and cystic fibrosis: CF is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) channel protein, located in the secretory glandular epithelium of multiple organ systems such as the airways, sweat glands, gastrointestinal tract, hepatobiliary system, reproductive system, and pancreas, where it plays an important role in epithelial bicarbonate and chloride transport.