PRENATAL-DIAGNOSIS OF OPEN NEURAL-TUBE DEFECTS USING THE AMNIOTIC-FLUID ACETYLCHOLINESTERASE ASSAY

The most reliable tool at present for the prenatal detection of [human] open neural tube defects is the amniotic fluid .alpha.-fetoprotein assay. Its nonspecificity and false-positive results produced by fetal blood admixture and other less well-defined causes have spurred the search for a more specific test. Increased amniotic fluid acetylcholinesterase activity has been reported in association with open neural tube defects. Acetylcholinesterase was assayed in 2nd-trimester amniotic fluid samples with previously determined .alpha.-fetoprotein values from 200 pregnancies with 96.5% of the outcomes known. These pregnancies were selected because of known fetal abnormalities or difficulties in prenatal diagnosis. High .alpha.-fetoprotein and acetylcholinesterase activity was detected in all 66 cases of open neural tube defects. Of normal pregnancies with spuriously high .alpha.-fetoprotein, 89% were reclassified by demonstrating no acetylcholinesterase band after slab gel electrophoresis. Nine cases with a normal outcome but high .alpha.-fetoprotein values and acetylcholinesterase activity constitute the remaining false-positive results. Notwithstanding the false-positive results, which may have been due to undetected fetal blood admixture, the acetylcholinesterase gel electrophoresis assay is a valuable adjunctive test to the .alpha.-fetoprotein assay for the prenatal detection of neural tube defects. Although not specific for open neural tube defects, acetylcholinesterase analysis by gel electrophoresis of amniotic fluid is significantly less influenced by fetal blood than is .alpha.-fetoprotein and may prove as reliable a diagnostic test for open neural tube defect.