This is why the CFTR potentiator drug, VX-770 (ivacaftor, Kalydeco)[54] is markedly effective in G551D-CFTR patients, while the CF corrector drug, VX-809, corrects/rescues ΔF-CFTR from ER quality control and is without effect on G551D-CFTR patients[55,56]. Here, CFTR is linked to cystic fibrosis.