4-methylumbelliferylguanidinobenzoate reactive plasma "protease" in cystic fibrosis is albumin

Carrier detection in cystic fibrosis

We evaluated four methods purported to distinguish between individuals homozygous or heterozygous for cystic fibrosis (CF) and normal controls: (1) detection of a protein in the serum by isoelectric focusing at pH 8.5, (2) detection of a lectinlike factor in the serum by hemagglutination, (3) isolation of CF-lectin from the serum by affinity chromatography, and (4) measurement of MUGB-reactive proteases in the plasma. The results were disappointing. The detection of CF protein by isoelectric focusing was unreliable; it could be identified in only 46% of heterozygotes and 66% of homozygotes, with a false positive rate of 17%. Detection of a lectinlike factor by hemagglutination was also found to be unreliable and irreproducible. The lectin isolated by affinity chromatography was not specific for the CF gene. No significant differences were found in the MUGB titers of the three populations tested. However, low titers (MU less than 200 nmol/ml) were found in 33% of homozygotes and heterozygotes and in 17% of normal controls. We conclude that none of these methods is suitable for carrier detection in cystic fibrosis.

Immunoreactive trypsin and the prenatal diagnosis of cystic fibrosis

Immunoreactive trypsin (IRT) was measured by radioimmunoassay in a series of amniotic fluids obtained at between 15 and 19 weeks from pregnancies with a 1-in-4 risk of fetal cystic fibrosis. IRT concentrations were significantly depressed in nine affected pregnancies, but the degree of overlap with the normal range was too great for this to be useful in early prenatal diagnosis. Furthermore, in one fetus, presumed to have cystic fibrosis, the fetal plasma IRT concentration was within the normal range.

Prenatal diagnosis of cystic fibrosis by assay of amniotic fluid microvillar enzymes

Activities of the microvillar enzymes gamma-glutamyltranspeptidase (GGTP), aminopeptidase M (APM), phosphodiesterase and maltase have been examined in second-trimester amniotic fluid as possible aids to the early prenatal diagnosis of cystic fibrosis (CF). The two peptidases, GGTP and APM, gave best results. If the fifth percentile of the normal range is used as an action line, the sensitivity of a positive test (low GGTP value) is 78% and the predictability 84%. At the tenth percentile the sensitivity is 100% and the predictability 77%. These approximate figures apply only to pregnancies where there has been a previous affected child. Until the primary protein defect in CF is discovered, this may prove an acceptable form of prenatal diagnosis to the high-risk mother.

Amniotic fluid protease activity and the prenatal detection of cystic fibrosis

Changes in the protease activity in amniotic fluid has been proposed as a valid method for the prenatal detection of cystic fibrosis (CF). We have studied by quantitative and qualitative procedures, sixty four amniotic fluids: two of them from CF-affected fetuses. Interpretation of the benzoyl arginine ethyl ester (BAEE)-staining patterns after isoelectric focusing was often difficult, and repeated experiments gave variable results. In order to improve gel discrimination, we performed amniotic fluid electrofocusing in the presence of detergents: 0.1 per cent Triton X-100, 0.1 per cent DOC, or 0.1 per cent SDS. In these conditions, the pattern revealed by BAEE was modified, but no differences were observed between CF and normal amniotic fluids.

Microvillar peptidase activity in amniotic fluid: possible use in the prenatal diagnosis of cystic fibrosis

The activities of two microvillar peptidases, gamma-glutamyl transpeptidase (GGTP) and aminopeptidase M (APM), have been measured in 132 samples of mid-trimester amniotic fluid. These included samples from 16 pregnancies at risk for cystic fibrosis. The activities of both peptidases were significantly below the normal range in amniotic fluids from the 6 affected pregnancies. This points to early pathological changes in fetal tissues in which microvilli are prominent. In contrast, 4-methylumbelliferylguanidinobenzoate-reactive protease activity in amniotic fluid from the 6 affected pregnancies was normal. Correlation of individual values between GGTP and APM was close in all cases examined, so that when a further 7 samples from cases at risk became available they were tested for GGTP alone. Of these, the 3 affected pregnancies had significantly reduced GGTP activity, particularly in the early weeks of gestation. It is suggested that early amniocentesis and examination of gamma-glutamyl-transpeptidase isoenzyme constitution might make possible the reliable early diagnosis of cystic fibrosis.