Cystic fibrosis heterozygote detection: a study on a normal population.

Detection of the cystic fibrosis (CF) heterozygote by testing for cystic fibrosis 
factor activity (CFFA) in serum samples using bioassays had been reported 
to give unreliable results. The present study was undertaken to find 
whether the use of medium from short term white blood cell 
or skin fibroblast cultures, rather than serum, as the test sample 
would eliminate such inconsistencies. Short term white blood cell cultures were 
established from 107 normal, healthy individuals. Cultures from 97 had no 
CFFA, six (No. 1-6) showed variable results and four (No. 7-10) 
had activity in all four tests done on a single sample. 
When the assays were repeated 3 months later on new cultures 
from these four positive CFFA individuals, two showed activity (Nos. 7 
& 9) and two did not (Nos. 8 & 10). All 
10 individuals whose cultures showed CFFA has histories of allergies. The 
association of CFFA in the culture medium derived from individuals having 
allergies with the intermittent presence of this activity suggested that environmental 
factors induced a CFF-like activity in such white blood cell cultures. 
The oyster ciliary assay, using medium from white blood cell cultures, 
cannot be used for screening for the CF heterozygote since the 
substitution of culture medium for serum did not eliminate inconsistent results 
and CFFA was not specific by this assay for the CF 
gene. Of the fibroblast lines established from the four persons whose 
initial white blood cell cultures consistently showed CFFA, only one (No. 
7) showed the CF culture phenotype (CFFA positive and metachromasia). 