British Journal of Haematology , 2001, 114, 641±646 Mutations in the thrombomodulin and endothelial protein C receptor genes in women with late fetal loss Franca Franchi, 1 Eugenia Biguzzi, 1 Irene Cetin, 2 Floriana Facchetti, 1 Tatjana Radaelli, 2 Maddalena Bozzo 2 Giorgio Pardi 2 and Elena M. Faioni 1 1 The Angelo Bianchi Bonomi Haemophilia and Thrombosis Centre, I.R.C.C.S. Maggiore Hospital and Department of Internal Medicine, University of Milan, and 2 Department of Obstetrics and Gynaecology, DMCO Ospedale San Paolo, University of Milan, Italy Received 30 January 2001; accepted for publication 18 April 2001 Summary. Late fetal loss can be associated with placental insufficiency and coagulation defects. Thrombomodulin (TM) and the endothelial protein C receptor (EPCR) are glycoprotein receptors expressed mainly on the endothelial surface of blood vessels and also in the placenta; they both play a key physiological role in the protein C anticoagulant pathway. Defects in these proteins might play an important role in the pathogenesis of late fetal loss. We performed a case±control study in 95 women with unexplained late fetal loss (. 20 weeks), to elucidate whether TM or EPCR gene mutations were associated with an increased risk for this complication of pregnancy. The control group comprised 236 women who gave birth to at least one healthy baby and had no history of late fetal death or obstetrical complica- tions. The entire TM and EPCR genes, including the promoter region, were screened. In total, five mutations were identified in the TM gene in 95 patients and three in 236 control subjects, and two mutations were identified in the EPCR gene in 95 patients and one in 236 control subjects. The relative risk for late fetal loss when having a mutation in the TM or EPCR gene was estimated by an odds ratio of 4´0 (95% CI 1´1±14´9). In conclusion, identified mutations in the TM and EPCR genes of women with unexplained fetal loss are more prevalent compared with women with no obstetrical complications. Keywords: thrombomodulin, endothelial protein C receptor, late fetal loss, gene mutations, thrombosis. Late fetal loss is relatively common, and it is estimated to occur in around 1 in 200 pregnancies (Stirrat, 1990; Samueloff et al, 1993; Gris et al, 1999). It is often associated with placental insufficiency, (Davies & Arroyo, 1985) and a number of risk factors for this complication are known. These include uterine malformations and abnormal placental insertion, drug or alcohol abuse, abnormal fetal karyotype or congenital abnormality, and previous fetal death from erythroblastosis or hydrops caused by Rh incompatibility (Pitkin, 1987). Recently, inherited conditions associated with an increased risk of venous thromboembolism, such as deficiencies of the naturally occurring anticoagulants (antithrombin, protein C, protein S), the G/A 1691 mutation in the factor V gene (factor V R506Q or factor V Leiden), the G/A 20210 mutation in the prothrombin gene and homozygosity for the C/T 677 mutation in the methylenetetrahydrofolate reductase gene, have been associated with obstetrical complications (Sanson et al, 1996; Brenner et al, 1999; Kupferminc et al, 1999) including late fetal loss, suggesting that thrombophilia might play an important role in the pathogenesis of these complications. Thrombomodulin (TM) is a glycoprotein receptor com- posed of 559 amino acid residues and expressed mainly on the endothelial surface of blood vessels and in the placental syncytiotrophoblast, where its expression and functional activity increase with gestational age (Maruyama et al, 1985). It is composed of different structural domains: an N-terminal lectin-like module, a hydrophobic region, six EGF-like repeats, a Ser/Thr-rich region, a trans-membrane region and a short cytoplasmic tail (Dittman & Majerus 1990). TM forms a high-affinity complex with thrombin, increasing its catalytic efficiency in the activation of protein C (Sadler, 1997). Activated protein C (APC) inactivates blood coagulation cofactors Va and VIIIa, thereby limiting thrombin production. Moreover, TM abrogates all of the procoagulant activities of thrombin (Esmon et al, 1982; Esmon, 1995). Because of the key physiological role of TM in the protein C pathway, it has been suggested that an impaired TM q 2001 Blackwell Science Ltd 641 Correspondence: Elena M. Faioni, MD, Haemophilia and Thrombosis Centre, Via Pace 9, 20122 Milano, Italy. E-mail: elena.faioni@ unimi.it