CFTR and cystic fibrosis: As expected, the genotypes including premature termination codon (PTC) (Y122X, G542X), deletion generating PTC (394delTT), severe splicing mutations (711 + 1 G > T, 1717 1 G > A), and the misfolding N1303K mutation, did not display CFTR-dependent Cl− transport, whereas the terminally truncated mutation (E1418X), the mild splicing mutation (2789 + 5 G > A), and mutations associated with atypical CF such as D1152H, displayed residual function (Fig. 2, x-axis).