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

Human chorionic gonadotrophin (hCG) has been used as a serum biochemical marker 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 sialyltransferase (ST) enzymes was examined as a potential marker for the hyperglycosylated form of hCG. There were no changes in total ST activity during the course of the pregnancy in normal mothers and there was no difference in enzyme activity in the DS pregnancies when compared with controls. These results suggest that, although there may be an alteration in the activities of one or more of the glycosyltransferase enzymes in the placenta resulting in an alteration in hCG glycosylation, this is not reflected in the serum soluble enzyme activity.