CFTR and cystic fibrosis: A prominent example is the ΔF508-CFTR (cystic fibrosis transmembrane conductance regulator) deletion mutation (Riordan et al., 1989), which is present in the majority of cystic fibrosis (CF) patients and causes defective folding, thereby inhibiting trafficking of the protein to the plasma membrane (Cheng et al., 1990).