Correlation Between Down Syndrome and the Level of Placental Alkaline Phosphatase in Amniotic Fluid

Authors: CANAN UÇAR, SEVİM BALCI, ERGÜL TUNÇBİLEK, İBRAHİM ÜNSAL

Abstract: The aim of this study was to investigate the correlation between Down syndrome and the level of placental alkaline phosphatase (PLAP) in amniotic fluid. A total of 279 amniotic fluid samples taken between 14 and 24 gestational weeks were investigated in this study. Karyotype analysis was made in all samples. In 10 samples trisomy 21 was determined, in one sample trisomy 18, in two samples 47,XXY, in six samples various structural chromosomal anomalies and in 260 samples normal karyotype. PLAP was measured using a fluorometric heat inactivation assay. Mean PLAP multiples of normal gestational median (MOM) value in samples with Down syndrome was 0.44 MOM, and in those with normal karyotype was 1.14 MOM. In fetuses with Down syndrome, amniotic fluid PLAP levels were significantly reduced (p = 0.002). There was no difference between mean PLAP MOM values in samples with normal karyotype and in those with structural chromosomal abnormality (p = 0.47). When 0.37 MOM was accepted as a cut-off value of PLAP activity in amniotic fluid, detection rate (sensitivity) of the test was 50%, specificity was 94%, and false-positive rate was 5.8%. We conclude that PLAP levels are reduced in the amniotic fluid of women carrying a fetus with Down syndrome.

Keywords: PLAP (placental alkaline phosphatase), Down syndrome, amniotic fluid

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