Table 1.

Depicting various classes of mutations, the primary defect and the outcome with examples

Mutation class	Defect	Outcome	Common mutations
I	Protein production	Complete absence of CFTR protein due to premature mRNA termination (nonsense or frame shift mutation) [18, 21, 22]	G542X, W1282X, R553X, 621+G>T
II	Protein processing	Inability of protein to localize to correct cellular location due to abnormal post-translational modifications [18]	F508del, N1303K, A455E
III	Protein regulation	Decreased activity of protein (chloride channel) in response to ATP due to abnormalities of the nuclear binding fold regions [18]	G551D
IV	Protein conduction	Frequency of flow of ions and channel opening duration are reduced though there is generation of chloride currents on stimulation with cAMP [18]	R117H
V	Reduced amount of functional CFTR	Stability of mRNA and/or mature protein is compromised [19, 20]	A455E
VI	Normal amount of functional CFTR	Enhanced turnover due to C-terminus abnormalities	Q1412X