CFTR and cystic fibrosis: CF is an autosomal recessive disorder characterized by a defect in cystic fibrosis transmembrane conductance regulator (CFTR) that regulates chloride and bicarbonate secretion across the pulmonary epithelium (Poulsen et al., 1994; Mall and Hartl, 2014; Elborn, 2016; Kunzelmann et al., 2017).