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Genetic determinants of venous thromboembolism (VTE) in the African-American population are poorly characterised. It was recently shown that fibrinogen gamma gene (FGG) polymorphisms 10034C>T and 9340T>C influence VTE risk in the Caucasian population. In the African-American population these polymorphisms are common, with allele frequencies above 25%. Here we evaluated whether these and other FGG 3'-end polymorphisms were associated with VTE risk in the African-American population and aimed to replicate the association in the Caucasian population. We examined 557 Caucasian patients and 678 Caucasian controls, and 537 African-American patients and 586 African-American controls from the ;Genetic Attributes and Thrombosis Epidemiology' (GATE) study. In the African-American population, 10034C>T and 9340T>C marginally influenced VTE-risk, with a 20% increase in risk for 10034TT carriers and a 20% reduction in risk for 9340CC carriers. In the Caucasian population, 10034TT was associated with a 1.7-fold increase in risk, which increased to 2.1-fold for idiopathic VTE patients. 9340CC significantly reduced VTE risk approximately two-fold. In conclusion, both FGG polymorphisms 10034C>T and 9340T>C influence VTE-risk, with the strongest effects observed in the Caucasian population, confirming previous data on these polymorphisms in this population.

ABO blood group is a genetic determinant of von Willebrand factor (VWF) levels. We investigated the effect of ABO genotypes on VWF and factor VIII (FVIII) levels and on the degree to which VWF is loaded with A- and B-antigens, expressed as normalized ratios, nA-ratio and nB-ratio, respectively, in the Leiden Thrombophilia Study, a large case-control study on venous thrombosis. We found that the ABO locus had an allele-specific, dosage dependent effect on VWF and FVIII levels and on the loading of VWF with A-antigen and B-antigen. The highest mean nA- and nB-ratios were found in A(1)A(1) and BB genotypes, respectively. Four A(1)O carriers had four 43-bp repeats in the minisatellite region of the ABO gene in stead of the expected one repeat. All had a reduced nA-ratio compared to A(1)O carriers with one repeat in their A(1) allele. The amount of A- and B-antigens expressed onVWF (nA-ratio and nB-ratio) explained about 18% (R(2)) of the variation in VWF levels.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are considered to be two forms of the same disease, however it is not fully understood what determines their clinical presentation. Proteins encoded by the FXIIIA and TAFI genes are involved in stabilizing the fibrin clot and in making it more lysis resistant. The FXIIIA 34Leu and TAFI -438A alleles might protect against DVT. Information on such an association with PE is either contradictory or missing. We hypothesized that both polymorphisms might influence the formation and fate of emboli and accordingly the risk of PE. We determined the frequencies of both polymorphisms in patients with objectively demonstrated PE. The frequency of FXIIIA Leu34Leu in PE patients and non-PE patients was 4.5% and 8.8%, [OR 0.5 (95% CI: 0.1 to 1.9)], respectively. For -438 A/A TAFI genotype the frequency was 1.5% and 8.1% [OR 0.1 (95% CI: 0.02 to 1.1)], respectively.

Elevated levels of procoagulant proteins factor II, factor VIII, factor IX, factor XI and fibrinogen are associated with an increased risk of venous thrombosis. In a population-based case-control study on venous thrombosis (Leiden Thrombophilia Study, LETS) we investigated whether elevated coagulation factor X (FX) levels are a risk factor for venous thrombosis and whether FX levels are determined by polymorphisms in the promoter region of the FX gene. We found that subjects with high FX levels (above the 90th percentile, > or = 126 U/dl) had a 1.6-fold increased risk of venous thrombosis. The highest risk (OR = 4.3, 95% confidence interval: 1.5-12) was found in the subgroup of premenopausal women who are not using oral contraceptives. However, these estimated risks disappeared after adjustment for other vitamin K-dependent coagulation factors II, VII and IX. To study the influence of genotypic variation on plasma FX levels we assessed four polymorphisms in the promoter region of the FX gene: a TTGTGA insertion between position -343A and -342G, a C/T polymorphism at position -222, a C/A polymorphism at position -220 and a C/T polymorphism at position -40. No relationship between these investigated genotypes and FX levels was observed. We conclude that high FX levels predict risk of thrombosis, but are not a risk factor for venous thrombosis when the levels of other vitamin K-dependent proteins are taken into account.

The HR2 haplotype of the factor V gene, which contains the histidine to arginine substitution at position 1299, has been reported to be associated with reduced factor V levels. Because high factor V levels have been found to be associated with an increased risk of myocardial infarction, we examined how the presence of the R2 allele affected the risk of myocardial infarction in the case-control "Study of Myocardial Infarctions Leiden". Among 560 men with a first myocardial infarction before the age of 70 years, 9.5% were heterozygous carriers of the R2 allele. The control group consisted of 646 men, in which 9.9% were heterozygous and 0.2% homozygous carriers of the R2 allele. The risk of myocardial infarction in the presence of the R2 allele was not increased (odds ratio, 0.9; 95% confidence interval 0.6 to 1.4). Exclusion of factor V Leiden carriers did not change this result. The risk was 4.4-fold increased for smokers who carried the R2 allele compared to non-smoking noncarriers. No synergy was found between metabolic risk factors and the presence of the R2 allele. We conclude that the risk of myocardial infarction for men in the presence of the R2 allele of the His1299Arg polymorphism is neither increased nor decreased.

We studied the HR2 haplotype of the factor V gene in a case-control study for venous thrombosis including 474 patients with a first deep-vein thrombosis and 474 age- and sex-matched healthy controls (Leiden Thrombophilia Study, LETS). We investigated both the original His1299Arg (A4070G) polymorphism and the Met385Thr (T1328C) polymorphism. This latter polymorphism, located in exon 8 (heavy chain), is always present in the HR2 haplotype, but also occurs on its own in a His1299 (wt) background. The HR2 haplotype was not associated with an increased risk of venous thrombosis (OR = 1.2, 95% confidence interval: 0.8-2.0). We did not find an association between the HR2 haplotype and a reduced sensitivity for activated protein C (APC) in non-carriers of factor V Leiden (FVL). However, in compound heterozygous FVL/HR2 carriers the sensitivity for APC was reduced. The HR2 haplotype was also associated with reduced factor V antigen levels in both patients and controls. Sequence analysis of the promoter region of factor V in HR2 homozygotes did not reveal any sequence variations that could explain the reduced FV levels. Our results show that the HR2 haplotype is not associated with an increased risk of venous thrombosis or with a reduced sensitivity for APC in non-FVL carriers. However, the HR2 haplotype is associated with a reduced sensitivity for APC in carriers of FVL and with reduced factor V antigen levels.