When the changes in PD induced by CFTR inhibition in the presence of a 100% gradient are normalized to donor‐matched epithelia analyzed in the absence of a gradient, the fold difference between these conditions is greater in non‐CF epithelia than in F508del CFTR epithelia, even with the correction of the F508del gating defect using VX‐770 (Figure 4). The gene discussed is CFTR; the disease is cystic fibrosis.