Serum expression of sialyltransferase in normal and Down's syndrome-affected pregnancy

Human chorionic gonadotrophin (hCG) has been used as a serum biochemical ma rker of Down's syndrome (DS) pregnancies, and recent studies have reported an increase in a hyperglycosylated form of the protein associated with DS. In the present study, the activity of the combined soluble serum sialyltran sferase (ST) enzymes was examined as a potential marker for the hyperglycos ylated form of hCG. There were no changes in total ST activity during the c ourse of the pregnancy in normal mothers and there was no difference in enz yme activity in the DS pregnancies when compared with controls. These resul ts suggest that, although there may be an alteration in the activities of o ne or more of the glycosyltransferase enzymes in the placenta resulting in an alteration in hCG glycosylation, this is not reflected in the serum solu ble enzyme activity.