HCG concentration and receptor gene expression in placental tissue from trisomy 18 and 21

Trisomy 21 is associated with high maternal serum concentrations of intact human chorionic gonadotrophin alpha(HCG) and free beta-HCG whereas these co ncentrations are markedly decreased in trisomy 18. In this study, we invest igated the effect of trisomy 21 and 18 on endogenous HCG concentrations and luteinizing hormone (LH)/HCG receptor expression in placental villous tiss ue in eight trisomy 21, six trisomy 18 and 42 chromosomally normal samples, collected at 12-16 weeks gestation. The tissue concentrations of intact HC G, free alpha-HCG and free beta-HCG subunits were measured using solid-phas e two-site immunoradiometric assay. LH/HCG receptor expression was evaluate d with immunohistochemistry and in-situ hybridization. Villous tissue in tr isomy 21 contained higher beta-HCG concentrations than the controls (P < 0. 05). In trisomy 18 cases, the beta-HCG concentration was lower than in the control group (P < 0.01). Both immunocytochemistry and in-situ hybridizatio n demonstrated a more intense staining of the trophoblast in cases of triso my 21 and 18, compared with controls with the strongest signal in cases of trisomy 18 (P < 0.01). We concluded that in trisomy 21 the high tissue HCG concentration and expression of LH/HCG receptor in the trophoblast may refl ect the relative immaturity of the trophoblastic tissue whereas in trisomy 18, the very low concentration of endogenous HCG, associated with an over-e xpression of LH/HCG receptor in the trophoblast, is probably secondary to t he poor differentiation of the cytotrophoblast.