TABLE 1.

Classification of gene mutations that cause cystic fibrosis (CF)

Class	Mutation examples	Mutation mechanism
I	G542X, W1282X	No functional CFTR protein is synthesised due to the presence of premature termination codons
II	F508del	CFTR protein is synthesised but misfolded, keeping it from reaching the apical cell surface
III	G551D, G1349D	Full-length CFTR protein reaching the apical cell surface exhibits abnormal gating (channel persists in the closed state)
IV	R117H, R334W, R347P	Full-length CFTR protein reaches the apical cell surface but transport of chloride ions is reduced due to channel pore defect
V	2789+5G>A, 3849+10kbC>T	Reduced number of CFTR transcripts due to promoter or splicing abnormalities
VI	4326delTC, 4279insA	Defective CFTR stability at the cell surface; C-terminus mutations result in accelerated turnover

CFTR: CF transmembrane conductance regulator.