Overview Cystic fibrosis (CF) occurs when a patient carries 2 deleterious mutations in the CF transmembrane conductance regulator (CFTR) gene, leading to CFTR protein malfunction in the epithelia of various organs. The CFTR protein is an ion channel, whose malfunction causes impaired chloride ion channel movement, resulting in abnormal secretions in the sweat glands, lungs, liver, pancreas ....