Thrombomodulin gene polymorphisms or haplotypes as potential risk factors for venous thromboembolism: a population-based case-control study

Effect of thrombomodulin gene polymorphisms on venous thromboembolism: An analysis of evidence involving 6,629 patients

BACKGROUD

The association between thrombomodulin gene (THBD) c.1418 C>T polymorphisms and the risk of venous thromboembolism (VTE) is controversial. The purpose of this meta-analysis was to evaluate THBD c.1418 C>T polymorphisms and the risk of VTE.

METHODS

Computer searches were performed on the CNKI, Wanfang database, VIP database, PubMed, Embase, Web of Science, and Cochrane Library databases. The retrieval time limit was from the establishment of the database to June 2022. Case-control studies and cohort studies of THBD c.1418 C>T polymorphisms associated with VTE were included. The literature was screened according to inclusion and exclusion criteria, data extraction and literature quality evaluation. Meta-analysis was performed using STATA 14.0 software.

RESULTS

A total of 12 literature were included, including 2980 cases in the case group and 3649 cases in the control group. The meta-analysis results showed no significant association of the THBD c.1418 C> T polymorphisms with the occurrence of VTE (T vs C: OR = 1.17, 95%CI = 0.93-1.48; TT vs CT+CC: OR = 1.00, 95%CI = 0.75-1.33; TT+CT vs CC: OR = 1.22, 95%CI = 0.94-1.59). Subgroup analyses revealed an increased risk of VTE in Asian populations due to THBD c.1418 C>T polymorphisms (T vs C: OR = 1.48, 95%CI = 1.06-2.07; TT vs CT+CC: OR = 1.80, 95%CI = 1.13-2.85; TT+CT vs CC: OR = 1.58, 95%CI = 1.07-2.32). THBD c.1418 C>T polymorphisms increased the risk of DVT (T vs C: OR = 1.51, 95%CI = 1.24-1.85; TT vs CT+CC: OR = 1.85, 95%CI = 1.10-3.12; TT+CT vs CC: OR = 1.64, 95%CI = 1.28-2.11). THBD c.1418 C>T polymorphisms reduced the risk of VTE in non-Asian populations (TT vs CT+CC: OR = 0.66, 95%CI = 0.45-0.98).

CONCLUSION

THBD c.1418 C>T polymorphisms is associated with VTE in Asian population, which may be a factor in the occurrence of VTE in Asian population. THBD c.1418 C>T polymorphisms increases the risk of DVT. Given the limitations of this meta-analysis, the conclusions require being further supported by large-scale and high-quality studies.

Markers of Hereditary Thrombophilia with Unclear Significance

Thrombophilia leads to an increased risk of venous thromboembolism. Widely accepted risk factors for thrombophilia comprise deficiencies of protein C, protein S, and antithrombin, as well as the factor V "Leiden" mutation, the prothrombin G20210A mutation, dysfibrinogenemia, and, albeit less conclusive, increased levels of factor VIII. Besides these established markers of thrombophilia, risk factors of unclear significance have been described in the literature. These inherited risk factors include deficiencies or loss-of-activity of the activity of ADAMTS13, heparin cofactor II, plasminogen, tissue factor pathway inhibitor (TFPI), thrombomodulin, protein Z (PZ), as well as PZ-dependent protease inhibitor. On the other hand, thrombophilia has been linked to the gain-of-activity, or elevated levels, of α2-antiplasmin, angiotensin-converting enzyme, coagulation factors IX (FIX) and XI (FXI), fibrinogen, homocysteine, lipoprotein(a), plasminogen activator inhibitor-1 (PAI-1), and thrombin-activatable fibrinolysis inhibitor (TAFI). With respect to the molecular interactions that may influence the thrombotic risk, more complex mechanisms have been described for endothelial protein C receptor (EPCR) and factor XIII (FXIII) Val34Leu. With focus on the risk for venous thrombosis, the present review aims to give an overview on the current knowledge on the significance of the aforementioned markers for thrombophilia screening. According to the current knowledge, there appears to be weak evidence for a potential impact of EPCR, FIX, FXI, FXIII Val34Leu, fibrinogen, homocysteine, PAI-1, PZ, TAFI, and TFPI on the thrombotic risk.

Thrombomodulin (THBD) gene variants and thrombotic risk in a population-based cohort study

BACKGROUND

The protein C anticoagulant system plays a key role in maintaining the hemostatic balance. Although several studies have identified thrombomodulin gene (THBD) variants among venous thromboembolism (VTE) patients, the role of THBD in relation to VTE in humans remains to be clarified.

OBJECTIVES

This study aimed to determine the thrombotic risk of rare and common THBD variants in a large population-based cohort of middle-aged and older adults.

PATIENTS/METHODS

The exome sequence of THBD was analyzed for qualifying variants in 28,794 subjects (born 1923-1950, 60% women), who participated in the Malmö Diet and Cancer study (1991-1996). Patients were followed from baseline until the first event of VTE, death, or 2018. Qualifying variants were defined as loss-of-function or non-benign (PolyPhen-2) missense variants with minor allele frequency <0.1%.

RESULTS

The single common coding variant rs1042579 was not associated with incident VTE. Sixteen rare variants were classified as qualifying and included in collapsing analysis. Seven individuals with VTE compared to 24 individuals without VTE carried one qualifying variant. Cox multivariate regression analysis adjusted for age, sex, body mass index, systolic blood pressure, smoking and alcohol consumption, rs6025, rs1799963, and the top two eigenvectors from a principal components analysis showed a hazard ratio of 3.0 (95% confidence interval 1.4-6.3) for the rare qualifying variants. The distributions of qualifying variants in THBD showed a difference for individuals with and without incident VTE indicating a possible position effect.

CONCLUSIONS

Rare qualifying THBD variants were associated with VTE, suggesting that rare variants in THBD contribute to development of VTE.

Rare Defects: Looking at the Dark Face of the Thrombosis

Venous thromboembolism (VTE) constitutes a serious and potentially fatal disease, often complicated by pulmonary embolism and is associated with inherited or acquired factors risk. A series of risk factors are known to predispose to venous thrombosis, and these include mutations in the genes that encode anticoagulant proteins as antithrombin, protein C and protein S, and variants in genes that encode instead pro-coagulant factors as factor V (FV Leiden) and factor II (FII G20210A). However, the molecular causes responsible for thrombotic events in some individuals with evident inherited thrombosis remain unknown. An improved knowledge of risk factors, as well as a clear understanding of their role in the pathophysiology of VTE, are crucial to achieve a better identification of patients at higher risk. Moreover, the identification of genes with rare variants but a large effect size may pave the way for studies addressing new antithrombotic agents in order to improve the management of VTE patients. Over the past 20 years, qualitative or quantitative genetic risk factors such as inhibitor proteins of the hemostasis and of the fibrinolytic system, including fibrinogen, thrombomodulin, plasminogen activator inhibitor-1, and elevated concentrations of factors II, FV, VIII, IX, XI, have been associated with thrombotic events, often with conflicting results. The aim of this review is to evaluate available data in literature on these genetic variations to give a contribution to our understanding of the complex molecular mechanisms involved in physiologic and pathophysiologic clot formation and their role in clinical practice.

Increased Activated Protein C Response Rates Reduce the Thrombotic Risk of Factor V Leiden Carriers But Not of Prothrombin 20210G>A Carriers

RATIONALE

Carriers of the most common prothrombotic mutations FVL (factor V Leiden) and FII (prothrombin) 20210G>A show a highly variable clinical phenotype. Using standardized in vivo coagulation activation followed by activity pattern analysis we have recently shown, that the FVL mutation accelerates thrombin and APC (activated protein C) formation in carriers without a history of venous thromboembolism (VTE).

OBJECTIVE

The aim of this prospective cohort study was to investigate, if the FII 20210G>A mutation induces a similar reaction pattern, and if the response rates differ in FVL and FII 20210G>A mutation carriers with prior VTE (VTE+).

METHODS AND RESULTS

We comparatively analyzed 30 FVL carriers, 28 FII 20210G>A carriers (thereof 13 VTE+ each) and 15 healthy controls. Changes in plasma levels of thrombin, prothrombin activation fragment 1+2 (F1+2), TAT (thrombin-antithrombin complex), APC, and D-dimer were monitored over 8 hours after infusion of recombinant factor VIIa (15 µg/kg). An increase of F1+2 and TAT levels was observed, that did neither differ between FVL and FII 20210G>A carriers nor between asymptomatic and VTE+ carriers of these mutations. Median plasma levels of APC increased more (P=0.008) in FVL carriers (from 1.39 to 7.79 pmol/L) than in FII 20210G>A carriers (from 1.03 to 5.79 pmol/L), and more in FII 20210G>A carriers (P=2×10^-4) than in healthy controls (from 0.86 to 3.00 pmol/L). Most importantly, however, the APC response was greater (P=0.015) in asymptomatic (n=13) than in VTE+ (n=12) heterozygous FVL carriers, with an increase of APC levels from 1.44 to 8.11 pmol/L versus 1.27 to 5.62 pmol/L.

CONCLUSIONS

These in vivo data demonstrate that the FII 20210G>A and FVL mutations share an intermediate phenotype that is characterized by increased thrombin formation after coagulation activation. Furthermore, our data support the conclusion that the APC activating capacity of FVL carriers modifies the thrombotic risk of this common prothrombotic mutation.

Rare thrombophilic conditions

Thrombophilia, either acquired or inherited, can be defined as a predisposition to developing thromboembolic complications. Since the discovery of antithrombin deficiency in the 1965, many other conditions have been described so far, which have then allowed to currently detect an inherited or acquired predisposition in approximately 60-70% of patients with thromboembolic disorders. These prothrombotic risk factors mainly include qualitative or quantitative defects of endogenous coagulation factor inhibitors, increased concentration or function of clotting proteins, defects in the fibrinolytic system, impaired platelet function, and hyperhomocysteinemia. In this review article, we aim to provide an overview on epidemiologic, clinic and laboratory aspects of both acquired and inherited rare thrombophilic risk factors, especially including dysfibrinogenemia, heparin cofactor II, thrombomodulin, lipoprotein(a), sticky platelet syndrome, plasminogen activator inhibitor-1 apolipoprotein E, tissue factor pathway inhibitor, paroxysmal nocturnal haemoglobinuria and heparin-induced thrombocytopenia.

Genetics in thrombophilia

Venous thromboembolism (VTE) poses a worldwide health burden affecting millions of people each year. The annual incidence of symptomatic VTE, the collective term used here for deep venous thrombosis, pulmonary embolism or both, is 2–3 per thousand inhabitants. The one-year mortality is 20% after a first VTE. Of the surviving patients 15–25% will experience a recurrent episode of VTE in the three years after the first event. Primary and secondary prevention is key to reducing death and disability from VTE. How to make use of our current knowledge of inherited risk of VTE for primary and secondary disease prevention is not straightforward. This despite the fact that in the past two or three decades we have made major strides in enlarging our understanding of inherited VTE risk, and that new inherited risk factors continue to be identified.

For primary prevention of VTE genetic testing is not likely to play a role in the future. Genetic variations also determine recurrence risk, albeit that the effect sizes for individual genetic variations are invariably lower than those for first VTE events. Multilocus genetic risk scores improve risk classification, and it is now possible to stratify patients who have had a first venous thrombosis, into subgroups with a high and low risk of recurrence. Whether this approach can be used to tailor intensity and duration of treatment remains to be established.

THBD sequence variants potentially related to recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a frequently occurring disease, which is classified as idiopathic in more than 50% of cases. THBD, the endothelial cell receptor for thrombin, has been associated with distinct biological processes and considered a coherent RPL-related candidate gene. In the present study, we have sequenced the complete coding region of THBD in 262 patients affected by RPL. Bioinformatics analysis and screening of controls strongly suggested that the THBD-p.Trp153Gly mutation might be related to RPL aetiology. It could be used, after its validation by functional assays, as a molecular marker for diagnostic/prognostic purposes.

Uncertain thrombophilia markers

The development of venous thromboembolism (VTE), which includes deep-vein thrombosis and pulmonary embolism, may be associated with inherited or acquired risk factors that can be measured in plasma or DNA testing. The main inherited thrombophilias include the plasma deficiencies of the natural anticoagulants antithrombin, protein C and S; the gain-of-function mutations factor V Leiden and prothrombin G20210A; some dysfibrinogenaemias and high plasma levels of coagulation factor VIII. Besides these established biomarkers, which usually represent the first-level laboratory tests for thrombophilia screening, a number of additional abnormalities have been less consistently associated with an increased VTE risk. These uncertain causes of thrombophilias will be discussed in this narrative review, focusing on their clinical impact and the underlying pathogenetic mechanisms. Currently, there is insufficient ground to recommend their inclusion within the framework of conventional thrombophilia testing.

Variable phenotypic penetrance of thrombosis in adult mice after tissue-selective and temporally controlled Thbd gene inactivation

Thrombomodulin (Thbd) exerts pleiotropic effects on blood coagulation, fibrinolysis, and complement system activity by facilitating the thrombin-mediated activation of protein C and thrombin-activatable fibrinolysis inhibitor and may have additional thrombin- and protein C (pC)-independent functions. In mice, complete Thbd deficiency causes embryonic death due to defective placental development. In this study, we used tissue-selective and temporally controlled Thbd gene ablation to examine the function of Thbd in adult mice. Selective preservation of Thbd function in the extraembryonic ectoderm and primitive endoderm via the Meox2Cre-transgene enabled normal intrauterine development of Thbd-deficient (Thbd^-/-) mice to term. Half of the Thbd^-/- offspring expired perinatally due to thrombohemorrhagic lesions. Surviving Thbd^-/- animals only rarely developed overt thrombotic lesions, exhibited low-grade compensated consumptive coagulopathy, and yet exhibited marked, sudden-onset mortality. A corresponding pathology was seen in mice in which the Thbd gene was ablated after reaching adulthood. Supplementation of activated PC by transgenic expression of a partially Thbd-independent murine pC zymogen prevented the pathologies of Thbd^-/- mice. However, Thbd^-/- females expressing the PC transgene exhibited pregnancy-induced morbidity and mortality with near-complete penetrance. These findings suggest that Thbd function in nonendothelial embryonic tissues of the placenta and yolk sac affects through as-yet-unknown mechanisms the penetrance and severity of thrombosis after birth and provide novel opportunities to study the role of the natural Thbd-pC pathway in adult mice and during pregnancy.

Thrombomodulin gene c.1418C>T polymorphism and risk of recurrent venous thromboembolism

Thrombomodulin gene (THBD) is a critical cofactor in protein C anticoagulant system. THBD c.1418C>T polymorphism is reported to be associated with higher risk of primary venous thromboembolism (VTE) but its role in VTE recurrence is unknown. The aim of this study was to investigate the role of THBD polymorphism in VTE recurrence. THBD c.1418C>T polymorphism was genotyped by using Taqman polymerase chain reaction in a prospective population based study of 1465 consecutive objectively verified VTE patients. Uni- and multivariate Cox regression were performed for the risk assessment of VTE recurrence. Patients who had VTE before inclusion or had recurrence or died during anticoagulant treatment were excluded. Among the remaining (N = 1046) patients, 126 (12.05 %) had VTE recurrence during the follow up period (from 1998 to 2008). THBD polymorphism was not significantly associated with risk of VTE recurrence in the univariate [Hazard ratio (HR) 1.11, 95 % confidence interval (CI) 0.78-1.59, p = 0.55] as well as the multivariate analysis adjusted for age, sex and thrombophilia (HR 1.11, 95 % CI 0.78-1.59, p = 0.54). Similarly, in unprovoked first VTE (n = 614), no association was observed between THBD polymorphism and risk of VTE recurrence (HR 1.22 and 95 % CI 0.78-1.89, p = 0.38). In this prospective study, our results do not suggest a predictive role for THBD c.1418C>T polymorphism in VTE recurrence.

Identification of Genetic Aberrations in Thrombomodulin Gene in Patients With Recurrent Venous Thromboembolism

Thrombomodulin (THBD) serves as a cofactor for thrombin-mediated activation of anticoagulant protein C pathway. Genetic aberrations in THBD have been studied in arterial and venous thrombosis. However, genetic changes in THBD and their role in the risk assessment of recurrent venous thromboembolism (VTE) are not well understood. The aim of the present study was to identify the genetic aberrations in THBD and their association with the risk of VTE recurrence in a prospective population-based study. We sequenced the entire THBD gene, first in selected patients with VTE (n = 95) by Sanger sequencing and later validated those polymorphisms with minor allele frequency (MAF) ≥5% in the whole study population (n = 1465 with the follow-up period of 1998-2008) by Taqman polymerase chain reaction. In total, we identified 8 polymorphisms in THBD, and 3 polymorphisms with MAF ≥5% were further validated. No significant association between THBD polymorphisms and risk of VTE recurrence on univariate or multivariate Cox regression analysis was found (hazard ratio [HR] = 0.89, 95% confidence interval [CI] = 0.62-1.28, HR = 1.27, 95% CI = 0.88-1.85, and HR = 1.15, 95% CI = 0.80-1.66 for THBD rs1962, rs1042580, and rs3176123 polymorphisms, respectively), adjusted for family history, acquired risk factors for VTE, location of deep vein thrombosis, and risk of thrombophilia. Subanalysis of patients with unprovoked first VTE also showed no significant association of identified THBD polymorphisms with the risk of VTE recurrence. Our results show that aberrations in the THBD gene may not be useful for the assessment of VTE recurrence; however, further studies with large sample size are needed to confirm these findings.

Genetic basis of ethnic disparities in VTE risk

In this issue of Blood, Hernandez et al identify and replicate single-nucleotide polymorphisms on chromosome 20 (and putatively on the THBD gene for thrombomodulin) that increased the risk of venous thromboembolism (VTE) by about 2.3-fold in African Americans (AAs) in the United States.

Novel genetic predictors of venous thromboembolism risk in African Americans

Venous thromboembolism (VTE) is the third most common life-threatening cardiovascular condition in the United States, with African Americans (AAs) having a 30% to 60% higher incidence compared with other ethnicities. The mechanisms underlying population differences in the risk of VTE are poorly understood. We conducted the first genome-wide association study in AAs, comprising 578 subjects, followed by replication of highly significant findings in an independent cohort of 159 AA subjects. Logistic regression was used to estimate the association between genetic variants and VTE risk. Through bioinformatics analysis of the top signals, we identified expression quantitative trait loci (eQTLs) in whole blood and investigated the messenger RNA expression differences in VTE cases and controls. We identified and replicated single-nucleotide polymorphisms on chromosome 20 (rs2144940, rs2567617, and rs1998081) that increased risk of VTE by 2.3-fold (P< 6 × 10(-7)). These risk variants were found in higher frequency among populations of African descent (>20%) compared with other ethnic groups (<10%). We demonstrate that SNPs on chromosome 20 are cis-eQTLs for thrombomodulin (THBD), and the expression of THBD is lower among VTE cases compared with controls (P= 9.87 × 10(-6)). We have identified novel polymorphisms associated with increased risk of VTE in AAs. These polymorphisms are predominantly found among populations of African descent and are associated with THBD gene expression. Our findings provide new molecular insight into a mechanism regulating VTE susceptibility and identify common genetic variants that increase the risk of VTE in AAs, a population disproportionately affected by this disease.

Ethnic diversity in the genetics of venous thromboembolism

Genetic susceptibility is considered as a crucial factor for the development of venous thromboembolism (VTE). Epidemiologic and genetic studies have revealed clear disparities in the incidence of VTE and the distribution of genetic factors for VTE in populations stratified by ethnicity worldwide. While gain-of-function polymorphisms in the procoagulant genes are common inherited factors in European-origin populations, the most prevalent molecular basis for venous thrombosis in Asians is confirmed to be dysfunctional variants in the anticoagulant genes. With the breakthrough of genomic technologies, a set of novel common alleles and rare mutations associated with VTE have also been identified, in different ethnic groups. Several putative pathways contributing to the pathogenesis of thrombophilia in populations of African-ancestry are largely unknown, as current knowledge of hereditary and acquired risk factors do not fully explain the highest risk of VTE in Black groups. In-depth studies across diverse ethnic populations are needed to unravel the whole genetics of VTE, which will help developing individual risk prediction models and strategies to minimise VTE in all populations.

Dysfunction of protein C anticoagulant system, main genetic risk factor for venous thromboembolism in northeast Asians

Venous thromboembolism (VTE) is a life threatening medical disorder worldwide. A great deal of evidence suggests that prevalence of VTE varies significantly among ethnic populations, with consistently lower incidence found in Asians. While the distribution of genetic risk factors may vary among races, genetic risk factors can play a major role among individuals with different genetic backgrounds. Two clinically evaluated low-frequency genetic mutations that predispose to VTE--the factor V Leiden mutation and prothrombin G20210A mutation--are found predominantly in Caucasians, and virtually never in Asians. The findings of a recent genetic study of VTE in northeast Asians, which greatly advanced our knowledge in this area, indicate that the most frequent genetic risk factors for VTE in northeast Asians can be attributed to a dysfunction of the protein C anticoagulant system. Several low-frequency genetic mutations, PROS1 p.Lys196Glu in Japanese and PROC p.Arg189Trp and p.Lys193del in Chinese, are significantly associated with increased risk for VTE, with odds ratio more than 2 through the reduced protein C anticoagulant activity. Construction of a multifactorial model based on the genetic risk factors in the protein C anticoagulant system could facilitate genetic counseling for VTE risk in these populations. The influence of prevalent genetic mutations on the risk of VTE should be further investigated in Asian countries.

Association of the Thrombomodulin Gene c.1418C>T Polymorphism With Thrombomodulin Levels and With Venous Thrombosis Risk

Objective—

To investigate the association of the THBD c.1418C>T polymorphism, which encodes for the replacement of Ala455 by Val in thrombomodulin (TM), with venous thromboembolism (VTE), plasma soluble TM, and activated protein C levels. In addition, human umbilical vein endothelial cells (HUVEC) isolated from 100 umbilical cords were used to analyze the relation between this polymorphism and THBD mRNA and TM protein expression.

Approach and Results—

The THBD c.1418C>T polymorphism was genotyped in 1173 patients with VTE and 1262 control subjects. Levels of soluble TM and activated protein C were measured in 414 patients with VTE (not on oral anticoagulants) and 451 controls. HUVECs were genotyped for the polymorphism and analyzed for THBD mRNA and TM protein expression and for the ability to enhance protein C activation by thrombin. The 1418T allele frequency was lower in patients than in controls ( P <0.001), and its presence was associated with a reduced VTE risk, reduced soluble TM levels, and increased circulating activated protein C levels ( P <0.001). In cultured HUVEC, the 1418T allele did not influence THBD expression but was associated with increased TM in cell lysates, increased rate of protein C activation, and reduced soluble TM levels in conditioned medium.

Conclusions—

The THBD 1418T allele is associated with lower soluble TM, both in plasma and in HUVEC-conditioned medium, and with an increase in functional membrane–bound TM in HUVEC, which could explain the increased activated protein C levels and the reduced VTE risk observed in individuals carrying this allele.

Common genetic risk factors for venous thrombosis in the Chinese population

Venous thrombosis is a major medical disorder caused by both genetic and environmental factors. Little is known about the genetic background of venous thrombosis in the Chinese population. A total of 1,304 individuals diagnosed with a first venous thrombosis and 1,334 age- and sex-matched healthy participants were enrolled in this study. Resequencing of THBD (encoding thrombomodulin) in 60 individuals with venous thrombosis and 60 controls and a functional assay showed that a common variant, c.-151G>T (rs16984852), in the 5' UTR significantly reduced the gene expression and could cause a predisposition to venous thrombosis. Therefore, this variant was genotyped in a case-control study, and results indicated that heterozygotes had a 2.80-fold (95% confidence interval = 1.88-4.29) increased risk of venous thrombosis. The THBD c.-151G>T variant was further investigated in a family analysis involving 176 first-degree relatives from 38 index families. First-degree relatives with this variant had a 3.42-fold increased risk of venous thrombosis, and their probability of remaining thrombosis-free was significantly lower than that of relatives without the variant. In addition, five rare mutations that might be deleterious were also identified in thrombophilic individuals by sequencing. This study is the largest genetic investigation of venous thrombosis in the Chinese population. Further study on genetics of thrombosis should focus on resequencing of THBD and other hemostasis genes in different populations.

Polymorphisms in antithrombin and in tissue factor pathway inhibitor genes are associated with recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a multifactorial condition. The effect of antithrombin (SERPINC1), protein C (PROC), thrombomodulin (THBD) and tissue factor pathway inhibitor (TFPI) single nucleotide polymorphisms (SNPs) on the risk of RPL is thus far unknown. Our objective was to determine the association of SNPs in the above mentioned genes with RPL. We included 117 non-pregnant women with three or more consecutive losses prior to 20 weeks of pregnancy without a previous history of carrying a fetus to viability, and 264 healthy fertile non-pregnant women who had at least two term deliveries and no known pregnancy losses. The PROC (rs1799809 and rs1799808), SERPINC1 (rs2227589), THBD (rs1042579) and TFPI (rs10931292, rs8176592 and rs10153820) SNPs were analysed by Real Time PCR. Genotype frequencies for PROC 2418A>G, PROC 2405C>T, THBD 1418C>T, TFPI (T-33C and TFPI C-399T) SNPs were similar in cases and controls. The carriers of SERPINC1 786A allele (GA + AA genotypes) had an increased risk for RPL (odds ratio [OR]: 1.77, 95% confidence interval [CI]: 1.05-3.00, p= 0.034) while women carrying the TFPI -287C allele (TC + CC genotypes) had a protection effect on having RPL (OR: 0.46, 95% CI: 0.26-0.83, p= 0.009). The TCC haplotype for TFPI T-33C/ TFPI T-287C/ TFPI C-399T SNPs was less frequent in cases (5.7%) than in controls (11.6%) (OR: 0.45, 95% CI: 0.23-0.90, p= 0.025). In conclusion, our data indicate that SERPINC1 786G>A variant increases the risk for RPL, while TFPI T-287C variant is protective; however, further studies are required to confirm our findings.

A genome-wide association study of venous thromboembolism identifies risk variants in chromosomes 1q24.2 and 9q

OBJECTIVES

To identify venous thromboembolism (VTE) disease-susceptibility genes.

PATIENTS AND METHODS

We performed in silico genome wide association scan (GWAS) analyses using genotype data imputed to approximately 2.5 million single-nucleotide polymorphisms (SNPs) from adults with objectively-diagnosed VTE (n=1503), and controls frequency matched on age and gender (n=1459; discovery population). Single-nucleotide polymorphisms exceeding genome-wide significance were replicated in a separate population (VTE cases, n=1407; controls, n=1418). Genes associated with VTE were re-sequenced.

RESULTS

Seven SNPs exceeded genome-wide significance (P<5×10(-8)): four on chromosome 1q24.2 (F5 rs6025 [factor V Leiden], BLZF1 rs7538157, NME7 rs16861990 and SLC19A2 rs2038024) and three on chromosome 9q34.2 (ABO rs2519093 [ABO intron 1], rs495828, rs8176719 [ABO blood type O allele]). The replication study confirmed a significant association of F5, NME7 and ABO with VTE. However, F5 was the main signal on 1q24.2 as only ABO SNPs remained significantly associated with VTE after adjusting for F5 rs6025. This 1q24.2 region was shown to be inherited as a haplotype block. ABO re-sequencing identified 15 novel single nucleotide variations (SNV) in ABO intron 6 and the ABO 3' UTR that were strongly associated with VTE (P<10(-4)) and belonged to three distinct linkage disequilibrium (LD) blocks; none were in LD with ABO rs8176719 or rs2519093. Our sample size provided 80% power to detect odds ratios (ORs)=2.0 and 1.51 for minor allele frequencies=0.05 and 0.5, respectively (α=1×10(-8); 1% VTE prevalence).

CONCLUSIONS

Apart from F5 rs6025, ABO rs8176719, rs2519093 and F2 rs1799963, additional common and high VTE-risk SNPs among whites are unlikely.

Thrombomodulin as a regulator of the anticoagulant pathway: implication in the development of thrombosis

Thrombomodulin is a cell surface-expressed glycoprotein that serves as a cofactor for thrombin-mediated activation of protein C (PC), an event further amplified by the endothelial cell PC receptor. The PC pathway is a major anticoagulant mechanism that downregulates thrombin formation and hedges thrombus formation. The objectives of this review were to review recent findings regarding thrombomodulin structure, its involvement in the regulation of hemostasis and further discuss the implication, if any, of the genetic polymorphisms in the thrombomodulin gene in the risk of development of thrombosis. We performed a literature search by using electronic bibliographic databases. Although the direct evaluation of risk situations associated with thrombomodulin mutations/polymorphisms could be of clinical significance, it appears that mutations that affect the function of thrombomodulin are rarely associated with venous thromboembolism. However, several polymorphisms are reported to be associated with increased risk for arterial thrombosis. Additionally studies on knock out mice as well studies on humans bearing rare mutations suggest that thrombomodulin dysfunction may be implicated in the pathogenesis of myocardial infraction.

Human thrombomodulin knock-in mice reveal differential effects of human thrombomodulin on thrombosis and atherosclerosis

OBJECTIVE

We sought to develop a murine model to examine the antithrombotic and antiinflammatory functions of human thrombomodulin in vivo.

METHODS AND RESULTS

Knock-in mice that express human thrombomodulin from the murine thrombomodulin gene locus were generated. Compared with wild-type mice, human thrombomodulin knock-in mice exhibited decreased protein C activation in the aorta (P<0.01) and lung (P<0.001). Activation of endogenous protein C following infusion of thrombin was decreased by 90% in knock-in mice compared with wild-type mice (P<0.05). Carotid artery thrombosis induced by photochemical injury occurred more rapidly in knock-in mice (12±3 minutes) than in wild-type mice (31±6 minutes; P<0.05). No differences in serum cytokine levels were detected between knock-in and wild-type mice after injection of endotoxin. When crossed with apolipoprotein E-deficient mice and fed a Western diet, knock-in mice had a further decrease in protein C activation but did not exhibit increased atherosclerosis.

CONCLUSION

Expression of human thrombomodulin in place of murine thrombomodulin produces viable mice with a prothrombotic phenotype but unaltered responses to systemic inflammatory or atherogenic stimuli. This humanized animal model will be useful for investigating the function of human thrombomodulin under pathophysiological conditions in vivo.

Thrombomodulin mutations in atypical hemolytic-uremic syndrome

BACKGROUND

The hemolytic-uremic syndrome consists of the triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. The common form of the syndrome is triggered by infection with Shiga toxin-producing bacteria and has a favorable outcome. The less common form of the syndrome, called atypical hemolytic-uremic syndrome, accounts for about 10% of cases, and patients with this form of the syndrome have a poor prognosis. Approximately half of the patients with atypical hemolytic-uremic syndrome have mutations in genes that regulate the complement system. Genetic factors in the remaining cases are unknown. We studied the role of thrombomodulin, an endothelial glycoprotein with anticoagulant, antiinflammatory, and cytoprotective properties, in atypical hemolytic-uremic syndrome.

METHODS

We sequenced the entire thrombomodulin gene (THBD) in 152 patients with atypical hemolytic-uremic syndrome and in 380 controls. Using purified proteins and cell-expression systems, we investigated whether thrombomodulin regulates the complement system, and we characterized the mechanisms. We evaluated the effects of thrombomodulin missense mutations associated with atypical hemolytic-uremic syndrome on complement activation by expressing thrombomodulin variants in cultured cells.

RESULTS

Of 152 patients with atypical hemolytic-uremic syndrome, 7 unrelated patients had six different heterozygous missense THBD mutations. In vitro, thrombomodulin binds to C3b and factor H (CFH) and negatively regulates complement by accelerating factor I-mediated inactivation of C3b in the presence of cofactors, CFH or C4b binding protein. By promoting activation of the plasma procarboxypeptidase B, thrombomodulin also accelerates the inactivation of anaphylatoxins C3a and C5a. Cultured cells expressing thrombomodulin variants associated with atypical hemolytic-uremic syndrome had diminished capacity to inactivate C3b and to activate procarboxypeptidase B and were thus less protected from activated complement.

CONCLUSIONS

Mutations that impair the function of thrombomodulin occur in about 5% of patients with atypical hemolytic-uremic syndrome.

Genetic variations and their influence on risk and treatment of venous thrombosis

Venous thrombosis (VT) is a highly prevalent disease. Risk factors can be genetic or acquired. The well-established genetic polymorphisms predisposing to thrombophilic disorders can be divided into rare 'loss-of-function mutations' in anticoagulant proteins and common 'gain-of-function mutations' in procoagulant proteins, which are weaker risk factors. In addition to functional polymorphisms, defects in common pathways affecting biosynthesis or clearance of plasma coagulation factors and their relations to VT risk have been detected. Recently, investigations regarding genetic variations and response to drug treatment, relevant for the pathogenesis as well as therapy of venous thromboembolism have been performed. The methodical advances in genetic research have led to the identification of a number of new variants with still unclear association to VT. This review aims to discuss the established genetic risk factors as well as some candidate predictors of VT. Further, the recent developments in pharmacogenomics are reviewed.

Predictive genetic variants for venous thrombosis: what's new?

Various pathways lead to the development of venous thrombosis. Risk factors are common and can be genetic or acquired. Since the identification of factor V Leiden and prothrombin 20210 G-->A, the field of genetic epidemiology has developed rapidly and many new genetic variants have been described in the past decade. However, the association with venous thrombosis is often unclear and conflicting results have been reported in various studies. The aim of this review is to describe these candidate predictors of venous thrombosis and to put these in perspective.

Haplotype of thrombomodulin gene associated with plasma thrombomodulin level and deep vein thrombosis in the Japanese population

INTRODUCTION

Thrombomodulin (TM) is an essential cofactor in protein C activation by thrombin. Here, we evaluated the contribution of genetic variations in the TM gene to soluble TM (sTM) level and deep vein thrombosis (DVT) in Japanese.

PATIENTS AND METHODS

We sequenced the TM putative promoter, exon, and 3'-untranslated region in DVT patients (n=118). Among 17 genetic variations we identified, two missense mutations (R385K, D468Y) and three common single nucleotide polymorphisms (-202G>A, 2487A>T, 2729A>C) were genotyped in a general population of 2247 subjects (1032 men and 1215 women) whose sTM levels were measured. We then compared the frequency of these mutations in DVT patients with that in the age, body mass index-adjusted population-based controls.

RESULTS

We identified one neutral mutation (H381) and three missense mutations (R385K; n=2, A455V; n=53 heterozygous, n=14 homozygous, D468Y; n=2) of TM in the DVT patients. Age-adjusted mean values of sTM were lower in C-allele carriers of 2729A>C than in noncarriers in the Japanese general population (women: 16.7+/-0.3 U/ml vs. 17.9+/-0.2 U/ml, p<0.01, men: 19.4+/-0.3 U/ml vs. 20.4+/-0.3 U/ml, p=0.03). Additionally, the CC genotype of this mutation was more common in the male DVT patients than in the male individuals of the general population (odds ratio=2.76, 95% confidence interval=1.14-6.67; p=0.02). This mutation was in linkage disequilibrium (r-square>0.9) with A455V mutation.

CONCLUSIONS

TM mutations, especially those with a haplotype consisting of 2729A>C and A455V missense mutation, affect sTM levels, and may be associated with DVT in Japanese.