A defect, or mutation in the CFTR gene is what causes CF or (Cystic Fibrosis). This gene makes a protein that controls the movement of salt and water in and out of your body’s cells. In people who have CF, the gene makes a protein that doesn’t work well. This causes thick, sticky mucus and very salty sweat. Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane protein and chloride channel in vertebrates that is encoded by the CFTR gene. The CFTR gene codes for an ABC transporter-class ion channel protein that conducts chloride and thiocyanate ions across epithelial cell membranes.