Third component of complement in cystic fibrosis.

In a study of C3 levels and phenotypes in 64 cystic fibrosis 
(CF) patients, 92 CF parents, 64 normal siblings, and 126 healthy 
controls, significant elevations of mean C3 levels were found in CF 
patients, their parents, and in one genetic sub-group of their siblins 
(SS females). C3 concentration in CF patients correlated with the degree 
of clinical impairment as measured by Shwachman-Kulczycki (S-K) score. No significant 
differences were found in the prevalences of C3 phenotypes or the 
S and F gene frequencies among the groups studied. 