Protocol for prenatal diagnosis of cystic fibrosis based on studies of alkaline phosphatase isoenzymes

Amniotic fluid analysis of microvillar enzymes, including alkaline phosphatase (ALP) total activity and ALP isoenzymes, has been widely experimented with and used for the prenatal diagnosis of cystic fibrosis in the second trimester of gestation. Since the development of cystic fibrosis molecular analysis, interest in these biochemical tests has been maintained for those instances in which the pregnancy is not fully informative by restriction fragment length polymorphism analysis or DNA is not available from the index-affected child. However, recommended biochemical protocols do not provide clear-cut diagnostic results in a minority of cases. We have tested the reliability of cystic fibrosis biochemical prediction by ALP high-resolution electrophoresis and ALP kinetic studies after inactivation by urea. With this approach, all the amniotic fluid samples that had not been unambiguously classified as affected or unaffected by standard microvillar enzymes analysis were definitely categorized. The proposed method seems to improve the diagnostic accuracy in pregnancies with a one in four risk of resulting in a child with cystic fibrosis.