Isoelectric focusing of serum in cystic fibrosis: failure to distinguish between homozygote and heterozygote sera.

Thin-layer isoelectric focusing was performed on samples of sera from patients with 
Cystic Fibrosis, siblings and obligate heterozygotes (parents), and children without cystic 
fibrosis (controls). The protein band with an isoelectric point of pH 
5.48, previously reported to be absent in homozygote cystic fibrosis sera, 
was found to have a pI of 5.25. It was present 
in approximately one-half of the homozygote and heterozygote sera tested, and 
absent from 18 percent of control sera. The presence of this 
band is not therefore a reliable marker for the normal gene, 
and cannot be used to identify the heterozygous carrier for cystic 
fibrosis. 