2ND TRIMESTER AMNIOTIC-FLUID PLACENTAL ALKALINE-PHOSPHATASE LEVELS ARE LOW IN DOWNS-SYNDROME BUT NOT IN OTHER FETAL ABNORMALITIES

Second trimester amniotic fluid placental alkaline phosphatase (FLAP) immunoreactivity was measured in 756 normal pregnancies, 63 Down's syndrome pregnancies and 42 pregnancies associated with other chromosomal abnormalities. FLAP levels were significantly reduced in cases of Down's syndrome (MoM = 0.72, U = 17 565, P = 0.0002, 95% Cl = 0.63-0.88). However, there was no significant difference between other aneuploid conditions and the normals (MoM = 0.88, U = 13 289, P = 0.35, 95% CI = 0.77-1.08). FLAP is the carrier protein for immunoglobulin G. Neonates with Downs syndrome but not other chromosomal abnormalities are associated with a deficiency of IgG. These data therefore support the theory that the low IgG levels in Downs syndrome are a result of a defect in FLAP transport.