The factor V gene A4070G mutation and the risk of venous thrombosis

The A4070G polymorphism in exon 13 of the factor V (FV) gene, which replaces His by Arg at position 1299 of the B domain, was recently shown to influence circulating FV levels and to contribute to the activated protein C (APC) resistance phenotype. We examined the impact of this polymorphism in a population of unselected patients with venous thromboembolic disease (VTE). The prevalence of the G4070 (R2) allele was determined in 205 patients and 394 healthy subjects of similar age and sex distribution. Thirty-seven patients (18%) were heterozygous for the R2 allele and 1 (0.5%) was homozygous. Forty-four controls (11.2%) were heterozygous for the R2 allele and 1 (0.2%) was homozygous. Thus, the allelic frequency was significantly higher in the patients with VTE than in the healthy controls, with respective values of 9.5% and 5.8%. The odds ratio was 1.8 (95% CI: 1.1-2.8, p = 0.02), pointing to an increased risk of VTE in carriers of the R2 allele. After excluding subjects with putative or confirmed gene defects (mainly the FV R506Q mutation), the R2 allele was still a risk factor for VTE in the remaining patients, with an odds ratio of 2.0 (95% CI: 1.2-3.5, p = 0.01), demonstrating that this polymorphism is itself a risk factor. This study also confirms that the R2 allele influences APC resistance (APCR) in the absence of the FV R506Q mutation.     

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.     

High prevalence of factor V Leiden in healthy Jordanian Arabs

The prevalence of APC resistance in healthy Jordanian Arabs was studied. Between October 1996 through September 1997 a total of 400 healthy subjects were studied. There were 212 males and 188 females. APC resistance was studied by functional and DNA methods. There were a total of 52 subjects (13%) who were APC resistant by the functional test. There were 49 subjects (12.25%) who had FV Q506 by DNA test. Of these there were 42 heterozygous and 7 homozygous (allele frequency 0.07). None of the subjects had clinical thrombosis. It is concluded that the prevalence of APC resistance due to FV Q506 is high in Jordanian Arabs.     

Factor V Q506 (resistance to activated protein C) and prognosis after acute coronary syndrome.

Factor V:Q506 causing resistance to activated protein C (APC-resistance), is a risk factor for venous thrombosis. Some studies have indicated an association with arterial disease, especially in women. We investigated the prevalence of the FV:Q506 allele prospectively in 295 patients with acute coronary syndrome. Mortality and myocardial infarction rate were evaluated after 30 days and after 2 years. The FV:Q506 allele was found in 38 patients. In a Cox proportional hazards model, smokers carrying FV:Q506 had a higher risk of infarction or death within 30 days, compared to non-smokers with a normal genotype (relative risk 2.9 [95% CI 1.2-7.0]). The difference remained significant after 2 years (relative risk 2.8 [95% CI 1.2-6.5]). The effect of the FV:Q506 allele on clinical outcome in acute coronary syndrome has not previously been described. Our results demonstrate a gene-environment interaction between smoking and the FV:Q506 allele, with an increased risk of early complications after an acute ischemic event.     

Venous thromboembolic disease and the prothrombin, methylene tetrahydrofolate reductase and factor V genes

The prevalence of the A20210 allele of the prothrombin (PT) gene and the T677 allele of the methylene tetrahydrofolate reductase (MTHFR) gene was determined in 205 patients with venous thromboembolism (VTE) and in 398 healthy subjects of similar age and sex distribution. We also determined the frequency of these two candidate risk alleles in subjects carrying the factor V (FV) Q506 allele, to identify a possible interaction. Forty patients (19.5%) and 14 control subjects (3.5%) were heterozygous for the FV R506Q mutation. Twenty-one patients (10.2%) and 11 controls (2.8%) were heterozygous for the PT A20210 allele (odds ratio (OR) 4.02, 95% confidence interval (CI): 1.90-8.50, p <0.001). This confirmed that the PT A20210 allele was a risk factor for VTE in our population. Among the FV Q506 allele carriers, 9 patients (22.5%) and no control also had the PT gene G20210A mutation. The absence of the combined abnormality in the control group made it impossible to calculate the relevant ORs but the lower bound of the 95% CI was 3.94, suggesting that individuals bearing the two mutations have a higher risk than those with a single mutation. Twenty-six patients (12.7%) and 49 controls (12.3%) were homozygous for the MTHFR T677 allele (OR 1.04, 95% CI: 0.62-1.72, not significant). Four patients and 1 control were also heterozygous for the FV R506Q mutation (OR 9.33, 95% CI: 1.03-84.23). However, the ORs for carriers of the FV R506Q mutation were not significantly influenced by MTHFR gene C677T homozygosity.     

Activated protein C resistance and the FV:R506Q mutation in a random population sample--associations with cardiovascular risk factors and coagulation variables.

Activated protein C (APC) resistance, defined as a low APC ratio, is associated with the factor V mutation R506Q (factor V Leiden). APC ratio may also be influenced by other clinical and coagulation variables, which we studied in 460 men and 495 women aged 25-74 years, from a random population sample (Glasgow MONICA Survey). APC ratio correlated positively with APTT; and inversely with factor VIIIc, factor IXc, antithrombin activity, prothrombin F1+2 fragment, and thrombin-antithrombin complexes; but not with other coagulation variables. APC ratio decreased with age, but APTT did not. APC ratio and APTT were significantly lower in women versus men, and were significantly lower in users of oral contraceptives or hormone replacement therapy. The FV:R506Q mutation (prevalence 2.5%) was associated with lower APC ratio and protein C and S activities and with higher factor VIIIc levels; but not with increases in F1+2 fragment or thrombin-antithrombin complexes. APC ratio correlated inversely with total cholesterol and diastolic blood pressure; and in women with triglycerides, systolic blood pressure, and body mass index. Obesity was associated with a significantly lower APC ratio. In contrast, smoking markers correlated positively with APC ratio in men. These associations of APC ratio may be relevant to the increased risks of venous thrombosis with age, female sex, oestrogen use, obesity and high factor VIIIc levels. The association of APC resistance with elevated plasma levels of coagulation markers suggests that this phenotype represents an in vivo hypercoagulable state.     

Oral contraceptive use in women with poor anticoagulant response to activated protein C but not carrying the factor V Leiden mutation increases the risk of venous thrombosis

The factor V Leiden mutation (FVL), associated with reduced sensitivity to activated Protein C (APC), is a risk factor for venous thromboembolism (VTE) and displays a strong interaction with oral contraceptives (OC). The aim of this study was to evaluate the risk of VTE in OC users with reduced APC sensitivity unrelated to the FVL. APC sensitivity was measured by an original aPTT-based test (without sample pre-dilution in factor V-deficient plasma) in 195 women who suffered from VTE in reproductive age and in 487 healthy women with results being expressed as normalized ratio. Subjects with currently known clinically relevant thrombophilic alterations were excluded. APC normalized ratios were stratified into quartiles. The adjusted ORs of subjects in the lower quartile (>/= 0.90) was 2.46 (95%CI: 1.02-5.95). Of the 195 patients, 89 had suffered VTE during OC. The 181 healthy women who had used OC for at least 6 months in the two year period before presentation but who had stopped OC at least 3 months before blood sampling were considered OC users. The risk of VTE in subjects using OC with APC normalized ratio in the lower quartile was increased 4.9-fold (95% CI: 1.92-12.6). In conclusion, our results showed that altered APC resistance in women not carrying the FVL significantly increased the VTE risk, albeit to a lesser extent than in women also carrying the FVL. Our data also showed that OC use in women with altered APC resistance further increased the risk of VTE in a way that exceeded the additive expectation.     

No association between thrombosis and factor V gene polymorphisms in Chinese Han population

Activated protein C resistance (APCR) is the most common hereditary condition of thrombosis in Western countries. And it is significantly linked to a single nucleotide polymorphisms (SNPs) in the coagulation factor V gene that results in the mutations at R506, R306 and HR2 alleles. To determine the prevalence of APCR and its association with the factor V gene SNPs in Chinese Han thrombotic patients, we investigated a total of 346 Chinese thrombotic patients and 140 normal controls for APCR using the APTT-based assays, according to manufacturer's instructions, APC ratio 相似文献   

The incidence and risk factors of recurrent venous thromboembolism during pregnancy

Introduction

Recurrent venous thromboembolism (VTE) during pregnancy is a challenging topic with relatively few publications. The aim of this study was to identify the incidence and the risk factors of recurrent antepartum VTE in women with a history of at least one previous VTE episode.

Materials and Methods

This observational cohort study involved 270 pregnant women (369 pregnancies) with at least one previous episode of VTE. The risk factors of recurrent antepartum VTE were identified by using group A (women without recurrent venous thromboembolism VTE) as a control group for group B (women with recurrent VTE despite LMWH (low molecular weight heparin) prophylaxis) and C (women with VTE recurrence in early pregnancy before the planned initiation of LMWH prophylaxis).

Results and Conclusions

The incidence of recurrent VTE was 7.6% (n = 28).Twelve recurrent VTEs in ten women (3.3%) developed during early pregnancy before initiation of LMWH and sixteen recurrent VTEs (4.3%) developed in 15 women despite LMWH prophylaxis.In women with recurrent antepartum VTE, the incidence of a history of two or more previous VTEs (group A vs. B: 5.7% vs. 40.0%, p < 0.001; group A vs. C: 5.7% vs. 30.0%, p = 0.022), previous VTE in connection with antiphospholipid antibody syndrome (group A vs. B: 2.6% vs. 20.0%, p = 0.012) and a history of VTE related to hormonal risk factors (group A vs. B: 60.4% vs. 93.3%, p = 0.011) was significantly higher compared to those with successful LMWH-prophylaxis. The percentage of the women with long-term anticoagulation was also significantly higher among the women with recurrent antepartum VTE (group A vs. B: 7.6% vs. 46.7%, p < 0.001) compared to those with successful LMWH-prophylaxis. The risk of antepartum recurrent VTE is considerable in women with a history of two or more previous VTEs, antiphospholipid antibody syndrome or long-term anticoagulation. The antepartum prophylaxis with prophylactic dose of LMWH or even with intermediate dose of LMWH might not be sufficient in this high-risk population.     

A Novel Mutation (G2172→C) in the Factor V Gene in a Chinese Family with Hereditary Activated Protein C Resistance

BackgroundActivated protein C resistance (APC-R) was a major risk factor for venous thromboembolism(VTE) in Caucasians, and at least 90% of APC-R were associated with the point mutation of factor V (FV) gene (Arg506 → Gln, FV Leiden). However, this genetic defect was extremely rare in Asian population.ObjectiveTo identify the genetic defect of FV in a Chinese family with APC-R associated with VTE.MethodsWe describe a Chinese family with a history of venous thrombosis. Blood samples were obtained from five family members (including the proband) for screening APC-R by coagulation assay and the genetic defect of FV using direct sequencing.ResultsFour out of five members had APC-R. We identified a novel mutation (G2172→C) in exon 13 of the FV gene, which was present in all the individuals with APC-R but was absent in the individual without APC-R. This mutation is predicted to result in the replacement of glutamate by aspartate at position 666, close to one of the APC cleavage sites.ConclusionsWe have identified, for the first time, a novel mutation (G2172→C) of FV that was associated with APC-R in a Chinese family with VTE. We speculate that this mutation interferes with cleavage at Arg679 by APC. The incomplete penetrance of thrombotic phenotype in this family, similar to that conferred by FV Leiden, suggests that it might be a weak risk factor for VTE.     

ACTIVATED PROTEIN C RESISTANCE CAUSED BY A COMMON FACTOR V MUTATION HAS A SINGLE ORIGIN.

A point mutation (FV:R506Q) in the human coagulation factor V gene is associated with resistance to activated protein C and life-long increased risk of venous thrombosis. The mutation is common in populations of Caucasian origin but virtually absent among other populations. In this study of 140 healthy Swedish volunteers and 110 homozygotes for the FV:R506Q mutation, we determined the allele frequencies of the FV:R506Q mutation and four other dimorphisms, C/T at nucleotide positions 2298 and 2325, and A/G at nucleotide positions 2379 and 2391. Manifest linkage disequilibrium was found between the FV:R506Q mutation and the four different dimorphisms. The finding of a single FV:R506Q haplotype in all homozygotes constitutes strong evidence of a common ancestor of Swedish individuals with the FV:R506Q mutation. Copyright © 1997 Elsevier Science Ltd     

Association of elevated soluble P-selectin levels with fetal loss in women with a history of venous thromboembolism

Introduction

An association between pregnancy complications such as fetal loss with inherited and acquired thrombophilic defects has frequently been reported. Recently, the cell adhesion molecule P-selectin has been identified to be a strong risk factor for venous thromboembolism (VTE).

Patients and Methods

The aim of our study was to investigate whether soluble P-selectin (sP-selectin) is also associated with fetal loss (e.g. miscarriage or stillbirth) in 304 women (median age [25th-75th percentile]: 45 [37-54] years) with a history of VTE, in whom data on pregnancy-associated complications had been evaluated. At the time of sP-selectin measurement none of the women was pregnant or had an acute VTE.

Results

The prevalence of miscarriage was 21.4% and that of stillbirth was 4.6%. The median sP-selectin level of the total study population was 38.0 [31.7-44.4] ng/mL. In subjects with elevated sP-selectin levels (defined as sP-selectin ≥ 44.4 ng/mL, representing the 75th percentile of levels in the study population) the prevalence of stillbirth was significantly higher compared to those with lower levels (10.5% vs. 2.6%, p = 0.008), whereas no statistically significant difference in the prevalence of miscarriage was observed between women with and without elevated sP-selectin (17.1% vs. 22.9%, p = 0.303). The odds ratio [95% CI] of elevated sP-selectin was 4.2 [1.5-12.7] for stillbirth and 0.7 [0.4-1.3] for miscarriage.

Conclusions

Elevated sP-selectin plasma levels were associated with a 4.2-fold risk for stillbirth in women with a history of VTE. Our data support a possible role of P-selectin in late pregnancy loss.     

Association of factor V gene polymorphisms (Leiden; Cambridge; Hong Kong and HR2 haplotype) with recurrent idiopathic pregnancy loss in Tunisia. A case-control study

Inherited thrombophilia has been shown to be linked with fetal loss. We performed a case-control study on the association between thrombosis-related polymorphisms in the factor V (FV) gene (Leiden, Cambridge, Hong Kong; HR2 haplotype) and idiopathic recurrent pregnancy loss (RPL) in Tunisian women. A total of 348 women with RPL, and 203 control women were studied, corresponding to 1,250 pregnancy losses and 1,200 successful pregnancies. FV Leiden was seen in 19.4% of patients (4.3% in the homozygous state) and in 5.5% of controls. The prevalence of the FV HR2 haplotype was similar in patients and controls, but with 7 homozygous patients for 1 control. FV Cambridge and Hong Kong were absent from both patients and controls. The study of all pregnancy losses evidenced that the frequency of the factor V Leiden polymorphism was zero in women who had mis-carried before 7 weeks of gestation, and then sharply increased to a plateau. After categorization of pregnancy losses (before 8 weeks of gestation; weeks 8 and 9; weeks 10 to 12; from the 13th week of gestation onwards), heterozygous and homozygous factor V Leiden polymorphisms, and homozygous FV HR2 haplotype, were associated with significant and independent risks of pregnancy loss during weeks 8 and 9, which increased during weeks 10 to 12, then culminated after week 12. In Tunisian women with idiopathic RPL, factor V Leiden polymorphism and homozygous FV HR2 haplotype are not a risk factor for very early pregnancy loss, before 8 weeks of gestation, but are thereafter associated with significant clinical risks, which gradually increase from the 8th week onwards.     

Effects of hereditary and acquired risk factors of venous thrombosis on a thrombin generation-based APC resistance test

BACKGROUND: Several hereditary and acquired risk factors for venous thromboembolism (VTE) are associated with impaired down-regulation of thrombin formation via the protein C pathway. To identify individuals at risk, functional tests are needed that estimate the risk to develop venous thrombosis. METHOD: We determined the effects of hereditary and acquired risk factors of venous thrombosis on an APC resistance test that quantifies the influence of APC on the time integral of thrombin formation (the endogenous thrombin potential, ETP) initiated in plasma via the extrinsic coagulation pathway. APC sensitivity ratios (APCsr) were determined in plasma from carriers of factor V(Leiden) (n = 56) or prothrombin G20210A (n = 18), of individuals deficient in antithrombin (n = 9), protein C (n = 7) or protein S (n = 14) and of women exposed to acquired risk factors such as hormone replacement therapy (n = 49), oral contraceptive use (n = 126) or pregnancy (n = 35). We also analysed combinations of risk factors (n = 60). RESULTS: The thrombin generation-based APC resistance test was sensitive for the factor V(Leiden) and prothrombin G20210A mutation, to protein S deficiency, hormone replacement therapy, oral contraceptive use and pregnancy. The assay was not influenced by antithrombin or protein C deficiency. The presence of more than one risk factor of venous thrombosis resulted in more pronounced APC resistance. The APCsr of individuals with a single or combined risk factors of VTE correlated well with reported risk increases. INTERPRETATION: The thrombin generation-based APC resistance test identifies individuals at risk for venous thrombosis due to acquired risk factors and/or hereditary thrombophilic disorders that affect the protein C pathway.     

The value of 64-detector row computed tomography for the exclusion of pulmonary embolism

Identification of patients at high risk of recurrence after a first event of venous thromboembolism (VTE) remains difficult. Resistance to activated protein C (APC) is a known risk factor for VTE, but data on the risk of recurrence is controversial. We wanted to investigate whether APC resistance in the absence of factor V Leiden, determined with global coagulation test such as the thrombin generation assay, could be used as a marker for increased risk of recurrent VTE among women 18-65 years old after a first event of VTE. In a cohort of 243 women with a first event of VTE, plasma was collected after discontinuation of anticoagulant treatment and the patients were followed up for 46 months (median). Thrombin generation was measured via calibrated automated thrombography, at 1 pM and 10 pM of tissue factor (TF). In women without factor V Leiden (n=117), samples were analysed in the absence and in the presence of APC. Increase in ETP (endogenous thrombin potential) and peak height analysed in the presence of APC correlated significantly with higher risk of recurrence. At 1 pM, peak height correlated with increased risk of recurrence. In conclusion, high thrombin generation in the presence of APC, in women after a first event of VTE is indicative for an increased risk of a recurrence. We also found that thrombin generation at low TF (1 pM) is correlated with the risk of recurrence. Our data suggest that APC resistance in the absence of factor V Leiden is a risk factor for recurrent VTE.     

Low level of circulating activated protein C is a risk factor for venous thromboembolism.

The levels of circulating activated protein C (APC) reflect in vivo protein C activation. The aim of this study was to determine whether a low APC level is an independent risk factor for venous thromboembolism (VTE). We measured APC in 160 patients with a history of VTE and without recognized thrombophilic defects, and in 199 healthy individuals. The mean (+/- SD) APC level was lower in patients (0.99 +/- 0.44 ng/ml) than in controls (1.19 +/- 0.41 ng/ml) (p < 0.0001), and showed a different distribution in the two groups. Thirty-eight patients (23.7%) had APC levels below the 5th percentile of the control group (<0.69 ng/ml) and 57 patients (35.6%) had APC levels below the 10th percentile (<0.77 ng/ml). APC levels <0.69 ng/ml increased the risk of a single or recurrent episode of VTE 4.2-fold (95% confidence interval, 2.0-9.0) or 6.9-fold (2.6-17.9). respectively, and APC levels <0.77 ng/ml increased these risks 3.4-fold (1.9-6.2) or 5.1-fold (2.3-11.2), respectively, compared with controls. Familial studies revealed that in some cases the low APC phenotype seems to be hereditary. We conclude that a low level of circulating APC in individuals without any of the most recognized thrombophilic defects is a prevalent, independent risk factor for VTE, and that it predisposes to recurrent VTE.     

The Glasgow Outcome, APCR and Lipid (GOAL) Pregnancy Study: significance of pregnancy associated activated protein C resistance

Activated protein C (APC) resistance secondary to Factor V Leiden (FVL) is associated with pregnancy failure and pre-eclampsia (PET). In non-pregnant subjects, the degree of resistance to APC relates to venous thrombosis risk. In pregnancy, resistance to APC occurs in the absence of FVL. We investigated, in an unselected prospective longitudinal study of 1,671 pregnant, non-FVL subjects, the relationship of the APC sensitivity ratio (APC:SR) with demographic variables and pregnancy outcome. Lower APC:SR values at 7-16 weeks gestation were observed in subjects who subsequently developed PET (median APC:SR 2.55, IQR 2.29-2.70 vs 2.69, IQR 2.48-2.93, Mann-Whitney U-test p = 0.003) in the current pregnancy. An APC:SR < the median (2.69) at 7-16 weeks was associated with a 2.95-fold increased risk (CI95 1.2-7.4) of PET in the current pregnancy. No relationship between the APC:SR, at any gestation, and fetal loss was observed. An inverse correlation between the APC:SR and birth weight was noted. Higher APC:SRs were observed in blood group O subjects and smokers. An inverse relationship of the APC:SR with age, diastolic blood pressure and total serum cholesterol was observed.     

The anticoagulant function of coagulation factor V

Almost two decades ago an anticoagulant function of factor V (FV) was discovered, as an anticoagulant cofactor for activated protein C (APC). A natural mutant of FV in which the R506 inactivation site was mutated to Gln (FV(Leiden)) was inactivated slower by APC, but also could not function as anticoagulant cofactor for APC in the inactivation of activated factor VIII (FVIIIa). This mutation is prevalent in populations of Caucasian descent, and increases the chance of thrombotic events in carriers. Characterisation of the FV anticoagulant effect has elucidated multiple properties of the anticoagulant function of FV: 1) Cleavage of FV at position 506 by APC is required for anticoagulant function. 2) The C-terminal part of the FV B domain is required and the B domain must have an intact connection with the A3 domain of FV. 3) FV must be bound to a negatively charged phospholipid membrane. 4) Protein S also needs to be present. 5) FV acts as a cofactor for inactivation of both FVa and FVIIIa. 6) The prothrombotic function of FV(Leiden) is a function of both reduced APC cofactor activity and resistance of FVa to APC inactivation. However, detailed structural and mechanistic properties remain to be further explored.