Table 1.

CFTR mutation classes and required strategies for treating cystic fibrosis.

Classification	CFTR defect	Mutation examples	Required approaches	Drug required (Approved?)
Class I	No functional CFTR protein/mRNA	G542X, W1282X, R553X	Salvage protein synthesis	Bypass therapy (no), Read through agents (no)
Class II	CFTR trafficking defect	ΔF508, ΔI507, N1303K	Correct protein folding	Corrector (yes)
Class III	Impaired gating	G551D, V520F, S549N	Recover channel conductance	Potentiator (yes)
Class IV	Decreased channel conductance	R334W, R117H, S1235R	Recover channel conductance	Potentiator (only for R117H)
Class V	Reduced production of CFTR	A455E, 1680-886A→G	Improve maturation/correct splicing	Antisense oligonucleotides (no), Corrector (no), Amplifier (no)
Class VI	Decreased CFTR stability	Q1412X, 4279 insA	Promote protein stability	Stabilisers (no)

CFTR, cystic fibrosis transmembrane conductance regulator.