The factor VIII D1241E polymorphism is associated with decreased factor VIII activity and not with activated protein C resistance levels.

Elevated factor VIII (FVIII) levels are a recognized risk factor for venous thrombosis. Recently, family studies suggested that the G allele of the 3951C/G (D1241E) FVIII polymorphism is associated to lower FVIII activity. We investigated in case-control studies both biological effects (FVIII levels and activated protein C sensitivity ratio) and clinical associations (venous thromboembolism) of the D1241E change. Among 145 healthy and 150 thrombotic women, not carriers of known thrombophilic defects, the 1241E allele was associated with 11% reduced (t-test, P<0.05) FVIII levels. The effect on activated protein C sensitivity ratio was not statistically significant. Carriership of the 1241E allele, potentially conferring protection from thrombosis, was found in 22.8% of controls and in 15.3% of cases. In an additional cohort of factor V Leiden carriers (n=283), carriership of the 1241E allele was 25.2% among 143 asymptomatic subjects and 17.1% among 140 thrombotic patients. Our data do not indicate a specific interaction with factor V Leiden. These genotype distributions suggest a mild protective effect from venous thrombosis conferred by 1241E FVIII, masked by other genetic and/or environmental components, and detectable only in very large population studies. Our findings point toward the presence of genetic determinant of coagulation factor levels with a biologically significant role, but with a poor predictive value to estimate thrombotic risk beyond established risk factors.

Influence of factor VII gene polymorphisms and environmental factors on plasma coagulation factor VII concentrations in middle-aged women with and without manifest coronary heart disease.

Plasma concentrations of coagulation factorVII (FVII) are determined by environmental and genetic factors. The influence of functional polymorphisms in the FVII gene (-670A>C, -402G>A, -401G>T and R353Q) and of established cardiovascular risk factors on plasma concentrations of FVII were investigated in a representative sample of middle-aged women with (n=238) and without (n=220) coronary heart disease (CHD). Specific and sensitive assays were used to measure FVII antigen (VIIag) and activated factorVII (VIIa). The effect of genotypes was markedly stronger on VIIa than on VIIag, with the percentage variation in FVII levels accounted for by genotypes being greater in controls than in patients. Of the four polymorphisms examined, only the R353Q contributed to the variation inVIIa (24.1% in patients and 30.3% in controls). The -401G>T and -670A>C promoter polymorphisms together accounted for 12.2% of the variation in VIIag amongst patients whereas the -401G>T polymorphism alone contributed 19.7% of the variation in VIIag in controls. Serum triglycerides exerted a major influence onVIIag in both patients (13.0%) and controls (7.2%). Three main haplotypes emerged from the four polymorphisms which accounted for 98% of all haplotypes. Large-scale prospective studies of CHD including FVII haplotypes and sensitive and specific FVII measurements are needed in women.

Modulation of factor V levels in plasma by polymorphisms in the C2 domain.

OBJECTIVE: Functional polymorphisms contributing to coagulation factor levels are preferential markers for association studies aimed at identifying prothrombic genetic components. METHODS AND RESULTS: Factor V (FV) microsatellite genotypes were found to be associated with FV levels (P=0.003). Single nucleotide polymorphisms analysis and sequencing of the promoter and of coding regions identified two polymorphisms (Met2120Thr, Asp2194Gly) present in 20% of the population (n=1013) that are responsible for genotype-phenotype associations. The effect of the Met2120Thr polymorphism, both in plasma (mean reduction of FV level in the heterozygous condition: 25%) and in recombinant FV studies (34% reduction), was comparable to that of the Asp2194Gly change (20% and 34%, respectively). The study of 10 subjects with a rare genotype indicated that the Asp2194Gly substitution is the functional determinant of the reduced FV levels associated with the FVHR2 haplotype. Among Leiden carriers, the doubly heterozygous condition for FV2120Thr was found to be associated with a significantly increased activated protein-C resistance (APCR) (P<0.05), and the doubly heterozygous condition for FV2194Gly was found to be more frequent (P=0.009) in symptomatic than in asymptomatic subjects. CONCLUSIONS: Extensive analysis of FV polymorphisms indicated that changes in the C2 domain modulate FV levels and might increase APCR and thrombotic risk in FV Leiden carriers through a pseudohomozygous mechanism.

A FV multiallelic marker detects genetic components of APC resistance contributing to venous thromboembolism in FV Leiden carriers.

Activated protein C resistance (APCR) is a major risk factor for venous thromboembolism (VTE). Although the factor V (FV) Leiden mutation accounts for the vast majority of APCR cases, other polymorphisms may contribute to the APCR phenotype. Genetic components of APCR and thrombophilia were investigated by two dinucleotide repeats, characterized in introns 2 and 11 of the FV gene. Only the intron 11 marker was genetically stable and thus suitable for further analysis. Its allelic frequencies were found to differ significantly (P=0.003) between subjects selected for increased APCR in the absence of the FV R506Q mutation (n=70, normalized ratios /=1.31). Genotype differences were also found (P=0.017) between FV R506Q heterozygotes (n=100) who had experienced previous VTE and those (n=100), who were still asymptomatic for VTE. Significance was mostly driven by the relative over-representation of the 12R allele and to a minor extent by the under-representation of the 15R allele among the symptomatic versus the asymptomatic FV Leiden carriers. Two SNPs (4070A/G and 2391A/G) were found to underlie the 12R and 15R alleles respectively, and marked extended haplo-types, previously (HR2) or newly (HT2) identified. Only the FV HR2 differed (P=0.002) in frequency between the two groups of FV R506Q heterozygotes, suggesting that it represents the most relevant FV genetic component of APCR or VTE detectable by this experimental and clinical approach. Our analysis indicates that frequent FV genetic components might contribute to shape the risk for VTE in FV Leiden carriers.

Relationships of plasma factor VIIa-antithrombin complexes to manifest and future cardiovascular disease.

BACKGROUND: Low levels of free activated coagulation factor VII (VIIa) are normally present in plasma to prime the coagulation of blood in normal hemostasis and during thrombus formation. VIIa also circulates in inactive form, in complex with antithrombin (VIIaAT) formed when VIIa is bound to tissue factor (TF). This study evaluated VIIaAT in relation to cardiovascular disease (CVD). METHODS: We determined the plasma VIIaAT concentration in samples from the Stockholm Coronary Atherosclerosis Risk Factor (SCARF) study, a population-based case-control study of myocardial infarction (MI) and in samples from the Stockholm study of 60-years-old individuals, a prospective study of CVD. VIIaAT was measured with a sandwich ELISA that captures the complex between a monoclonal antibody to VIIa and a polyclonal antibody to AT. RESULTS: In the SCARF study (200 post-MI cases, 340 controls), VIIaAT was statistically significantly associated with patient status [odds ratio (95% confidence interval (CI)] 1.51 (1.09-2.08), p=0.0126). The case-control differences were however small, with VIIaAT values that largely overlap between the two groups. When a nested case-control design (211 incident CVD cases and 633 matched controls) was applied on 5- to 7-year follow-up results of the Stockholm prospective study of 60-year-olds, plasma VIIaAT concentration was not associated with incident CVD (odds ratio (95% CI) 1.001 (0.997-1.005), p=0.5447). CONCLUSIONS: Plasma VIIaAT concentration had no predictive value for future CVD in our study population. Slightly increased plasma VIIaAT concentrations observed after MI may reflect processes that occur in connection with the acute event when TF and VIIa availability is increased.