Studies on cystic fibrosis using isoelectric focusing. I. An assay for detection of cystic fibrosis homozygotes and heterozygote carriers from serum.

We have developed a standardized biophysical assay for the rapid detection of 
individuals homozygous or heterozygous for cystic fibrosis (C/F). The assay employs 
isoelectric focusing in thin layer polyacrylamide gels to analyze microliter quantities 
of whole serum for the presence of a C/F factor protein 
and for deletions in a group of proteins called proteins B, 
C, and D (Fig, 1). A pH 5-10 gradient is used 
(Fig. 2) and each sample is screened using a serum volume 
which contains 300 g immunoglobulin G (IgG). Individuals homozygous or heterozygous 
for C/F are distinguished from normal unaffected individuals on the basis 
of the presence of a C/F factor protein band (Table 1). 
Heterozygous carriers for C/F are distinguished from C/F homozygotes 75 percent 
of the time, on the basis of a deletion in either 
band B, C, or D (Table 2). On the basis of 
screening 65 patients with cystic fibrosis, 61 heterozygous carriers for C/F, 
and 105 normal control subjects, it was concluded that no obvious 
correlation existed between either sex, age, or severity of the disease 
in the individual C/F patient, and the absolute presence or absence 
of the C/F factor. In addition, no correlation existed between sex 
or age and the presence of the C/F factor or deletions 
in proteins B, C, and D in the individual heterozygous carrier 
for C/F or normal control subjects. Analysis of serum samples from 
68 patients with a variety of other diseases, many with clinical 
symptoms resembling those seen in the patient with cystic fibrosis (Table 
3), indicated that the C/F factor protein described in this study 
appears to be diagnostic for C/F genotypes, with the possible exception 
of patients with certain types of leukemia. 