TOTAL AMOUNT OF CIRCULATING HUMAN CHORIONIC-GONADOTROPIN ALPHA-SUBUNIT AND BETA-SUBUNIT IN FIRST TRIMESTER TRISOMY-21 AND TRISOMY-18

The aim of this study was to evaluate the variations in the balance be tween total (free and combined) circulating a and beta subunits of hum an chorionic gonadotrophin (hCG) in trisomy 21 and 18. Maternal serum samples were collected at 10 and 11 weeks of gestation from 22 singlet on pregnancies with trisomy 21 (n=17) and trisomy 18 (n=5) and 66 chro mesomally normal controls, matched for gestational age. The hCG and fr ee alpha and beta subunits circulating levels were measured using spec ific immunoradiometric assays and converted in a common unit system ob tained using calibration of the assays with intact and thermally disso ciated purified hCG preparation. In trisomy 21, the only significant d ifference from controls was in the flee beta hCG level which was incre ased. In trisomy 18, intact hCG, free beta hCG as well as total alpha hCG and total beta hCG levels were significantly lower whereas the fre e alpha hCG level was significantly higher than in controls. The decre ase in total beta hCG was more pronounced than the decrease in total a lpha hCG resulting in a significant increase in the total alpha- to be ta hCG subunit ratio in trisomy 18. These findings suggest some modifi cations in the biosynthesis and/or release rates of the hCG subunits i n these trisomies.