Table 1.

CFTR Gene Mutation Classes

Class	Effect on protein	Key example of disease-causing mutations
I	Defective protein production	G542X
II	Defective protein processing	F508del
III	Defective protein regulation	G551D
IV	Defective protein conductance	R117H
V	Reduced protein synthesis	A455E
VI	Reduced protein surface retention	c.120del23

CFTR, cystic fibrosis transmembrane conductance regulator gene. Of note: a large number of known CFTR mutations are currently unclassified with respect to mutation class.