Although frequencies of F508C did not vary significantly between 850 individuals undergoing cystic fibrosis</span> carrier screening and those submitted for diagnostic testing on suspicion of cystic fibrosis, the frequency of F508C in the congenital bilateral absence of the vas deferens population was significantly higher than expected (chi2 = 6.95, corrected P = 0.0486).
Both patients with the complex allele F508C-S1251N are carrying delta F508 on the other CF chromosome and are suffering from severe pulmonary and gastrointestinal CF disease.