Methylumbelliferylguanidinobenzoate-reactive proteases in human amniotic fluid: Promising marker for the intrauterine detection of cystic fibrosis.

Over 1,000 specimens of midtrimester human amniotic fluid have been analyzed for 4-methylumbelliferylguanidinobenzoate (MUGB) reactivity. The mean specific activity value (nanomoles of methylumbelliferone (MU) formed per milligram of protein) for the control population (1,037) was 2.37 +/- 0.41. The mean specific activity values from a series of specimens of amniotic fluid derived from abnormal pregnancies (chromosomal and biochemical abnormalities, confirmed neural tube defects, abortions/stillbirths) were found not to vary significantly from value in the control population. The mean specific activity value of blood-tinged samples centrifuged to remove the red blood cell contaminants prior to freezing at -20 degrees C did not vary from the value for the control group, in contrast to the value for samples containing hemolyzed red blood cells (1.76 +/- 0.30). The mean specific activity values for all four groups (control, abnormal, spun and unspun) were found to be significantly different (p less than 0.001) from the mean specific activity value of 1.24 +/- 0.12 for the four cystic fibrosis (CF) amniotic fluids. In addition, upon isoelectric focusing of the control and CF fluids on polyacrylamide gels, pH 5-7, subsequently stained for alpha-N-benzoyl-L-arginine ethyl ester activity, the controls gave a pattern of five activity bands with a pl of 5.1 to 5.4, whereas the CF fluids consistently gave only four. These data suggest the potential value of the MUGB-reactive protease assay for the intrauterine detection of cystic fibrosis.