An Investigation of Amniotic Fluid Microvillar Fragments in Autosomal Trisomy Pregnancies

Reduced levels of microvillar enzymes in amniotic fluid have been reported in association with several foetal abnormalities, including urinary tract and gastro-intestinal anomalies, chromosomal disorders and cystic fibrosis. Trisomies 21, 18 and 13 have been reported, by several authors, to show reduced levels of gamma glutamyl transferase (GGT), aminopeptidase M (APM), alkaline phosphatase (ALP) and the disaccharidases; maltase, sucrase, trehalase and lactase. The reasons for this are not understood. Possible explanations include; (a) reduced amounts of enzyme on the microvillar membranes, (b) reduced numbers of microvillar fragments, with the normal complement of enzyme, reaching the amniotic fluid, or (c) normal microvillar fragments present in normal amount but subjected to an abnormal rate of enzyme inactivation in the amniotic fluid