Prediction and prevention of thrombosis during pregnancy and oestrogen use

Abstract number: P0021

Ivey^* L. M., Staton† J. M., Maslen† K. E., Sayer^* M. S., Hughes^* Q. W., Barden^* A. E., Singh^* R., Beilin^* L. J., Baker^* R. I.

†Department of Haematology Royal Perth Hospital, Australia ^*Royal Perth Hospital, Australia;

It is well established that a deficiency in protein S, a cofactor to activated protein C (APC) in the degradation of activated clotting factors V and VIII, results in an increased risk of thrombosis. Of particular interest is the four-fold increased risk of venous thromboembolism in women during pregnancy, use of oral contraceptives or hormone replacement therapy. In addition, pre-eclampsia is a relatively common and serious complication of pregnancy, which often involves thrombosis of the foetomaternal circulation, leading to foetal death. All women develop ‘acquired’ protein S deficiency by the third trimester of pregnancy, however, 30% become severely protein S deficient. We hypothesised that this severe protein S deficiency is due to underlying mutations within the protein S gene (PROS1) resulting in exaggerated reduction of protein S levels in high oestrogen conditions. This hypothesis was tested by screening 125 pregnant women who had experienced either a normal pregnancy (n = 46), pre-eclampsia (n = 38), gestational diabetes (n = 33), or essential hypertension (n = 8). Mutations within the PROS1 gene were detected by PCR/SSCP analysis and specifically identified by sequencing. Plasma levels of total, free and functional protein S were measured at 32 weeks gestation and at least six weeks post partum on the STA-R coagulation analyser (Diagnostica Stago, France). Several mutations were detected within the PROS1 gene including three that were previously unreported, one in the APC binding domain (T101A), one within the C4BP binding domain (N457N) and the third (G340C) having implications for protein folding. In addition to these novel mutations, 68% of women were found to have the previously described a to g substitution at nucleotide 2148 with an over-representation of the g allele in the pre-eclampsia group (P < 0.05). Previous reports have demonstrated a reduction in circulating plasma levels of protein S associated with this polymorphism. Our studies confirm that individuals with the ag or gg alleles have significantly lower levels of circulating proteins S in all samples, but were more pronounced at 32 weeks gestation when measured by total [P < 0.05 (ag); P < 0.02 (gg)], and functional [P < 0.03 (ag); P < 0.01 (gg)] assays. In conclusion, we have shown the 2148 g allele results in reduced protein S levels and is associated with higher risk of suffering pre-eclampsia.