Table 1.

Classification of CFTR mutations based on the impact of the CFTR protein

Class	How CFTR protein is affected	Examples
I	No functional CFTR protein is made	G542X, W1282X, 621 + 1G>T
II	CFTR protein is misfolded and does not reach the cell membrane	F508del, G85E
III	CFTR protein reaches the cell membrane but the channel gate does not open	G551D
IV	CFTR protein reaches the cell membrane but the channel does not move chloride efficiently	R117H, R334W, R347P
V	The CFTR protein is made and works properly but the amount is insufficient	3849 + 10kb C>T, 2789 +5 G>A
VI	The CFTR protein is made and is in the correct location but has reduced stability and accelerated turnover	rF508del, 4326del, 4279insTC

rF508 denotes the rescued protein after drug treatment.