The risk of pregnancy-related venous thromboembolism in women who are homozygous for factor V Leiden

The risk of venous thromboembolism (VTE) is increased in pregnancy and during the post-partum period. The absolute risk for pregnancy-related VTE in heterozygous women with the factor V Leiden mutation is approximately 2%, but studies on this risk for homozygous women show conflicting results. In a retrospective family study, we found that the risk of pregnancy-related VTE in women with a symptomatic first-degree relative was 17% per pregnancy (95%CI 4.7-37.4). Anticoagulant prophylaxis during the post-partum period appears to be indicated in asymptomatic homozygous women from symptomatic kindred, whereas this could be decided on an individual basis during pregnancy.     

Factor XIII Val34Leu and the risk of venous thromboembolism in factor V Leiden carriers

A mutation in factor XIII (Val34Leu) was reported to protect against venous thromboembolism. We evaluated the effect of Val34Leu on thrombotic risk in 352 factor V Leiden carriers who were first-degree relatives of 132 thrombotic propositi carrying factor V Leiden. The total observation period was 2,594 years in 92 Val34Leu carriers and 7,444 years in 260 non-carriers. The annual incidence of a first episode of venous thromboembolism was 0.31% in Val34Leu carriers and 0.44% in non-carriers [relative risk (RR) for venous thromboembolism: 0.7, 95% CI 0.3-1.5]. Age-specific RR for venous thromboembolism were (for Val34Leu carriers and non-carriers respectively): 1.0 (95% CI 0.3-3.2) in the age group of 15-30 years, 0.4 (95%, CI 0.05-3.0) in the age group of 30-45 years, 0.6 (95% CI 0.1-2.9) in the group aged 45-60 years and 0.5 (95% CI 0.06-4.5) in relatives older than 60 years. In conclusion, the impact of FXIII Val34Leu on the venous thromboembolic risk is modest, suggesting that screening for this mutation in factor V Leiden carriers is not justified.     

Factor V Leiden: the venous thrombotic risk in thrombophilic families

Factor V Leiden (FVL) leads to a sevenfold increased risk of venous thrombosis and is present in 50% of individuals from families referred because of unexplained familial thrombophilia. We assessed the association of FVL with venous thromboembolism (VTE) in 12 thrombophilic families of symptomatic probands with FVL in a retrospective follow-up study. We screened 182 first- and second-degree relatives of the 12 unrelated propositi for the FVL mutation and the occurrence of VTE. The incidence rate of VTE in carriers of FVL (0.56%/year) was about six times the incidence for the Dutch population (0.1%/year). The incidence rate in non-carriers also appeared to be higher (0.15% per year). At the age of 50 years, the probability of not being affected by VTE was reduced to 75% for carriers and to 93% for non-carriers (P = 0.009). Identification of carriers of FV Leiden may be worthwhile in young symptomatic individuals and their relatives with a strong positive family history of venous thromboembolism or a history of recurrent venous thrombosis who may be at risk (e.g. pregnancy, use of oral contraceptives). After adjustment for prothrombin G20210A (present in two families), even higher thrombotic incidence rates were found in carriers and non-carriers of FVL. This makes the presence of other unknown prothrombotic risk factors more probable in these families.     

The factor V Leiden mutation in children with cancer and thrombosis

Thromboembolic phenomena, frequently observed in children with cancer who are undergoing chemotherapy, can cause significant morbidity and, less frequently, mortality. Many contributory factors have been identified. Whether the recently identified and most common coagulation defect predisposing to thrombosis, factor V Leiden, is associated with thrombosis in this setting, has not been explored. The current study was undertaken to determine the prevalence of the factor V Leiden mutation in children with cancer who developed thromboembolic phenomena as compared to those with cancer who did not. Genomic DNA was amplified using the polymerase chain reaction (PCR), followed by digestion of the amplification product with the restriction enzyme Mnl I. The digested PCR products were then size-fractionated to classify samples as heterozygous, homozygous or normal for the factor V Leiden mutation. 67 children with cancer were evaluated for the factor V Leiden mutation. One of 32 children with cancer and thrombosis, and none of 35 who had not experienced thrombotic problems, was found heterozygous for this mutation. We conclude that the factor V Leiden mutation does not play a significant role in the overall incidence of thromboses that occur in children with cancer.     

Risk of recurrent venous thromboembolism in patients with the factor V Leiden (FVR506Q) mutation: effect of warfarin and prediction by precipitating factors

Three cohorts of patients with the factor V Leiden mutation were recruited independently (heterozygotes, homozygotes and combined thrombophilia). The antithrombotic efficacy of oral anticoagulation and the predictive value for recurrence of an idiopathic as opposed to a precipitated first event were determined. Idiopathic first events occurred at an older age than precipitated events (43 v 26 years, LR = 23.31, P  < 0.001). None of the patients had a recurrent event while on warfarin but the median time to recurrence after stopping warfarin was 9 years (95%CI 0.7–17.3 years). The time to recurrence was shorter when the first event was idiopathic as opposed to precipitated (3.5 v 13 years, LR = 4.76, P  = 0.029). A calculation of benefit to risk of oral anticoagulation with a target INR of 2.5 does not support the use of long-term therapy in all patients with the factor V Leiden mutation following a first thrombotic event.     

Risk of venous thromboembolism in carriers of factor V Leiden with a concomitant inherited thrombophilic defect: a retrospective analysis.

Factor V Leiden is the most common genetic defect associated with venous thromboembolism. Its clinical expression is limited and shows a wide intrafamilial and interfamilial variation, which might be explained by the influence of other genetic risk factors. We retrospectively studied 226 patients with factor V Leiden and documented venous thromboembolism (probands) and 400 first-degree carrier relatives to assess the contribution of concomitant genetic risk factors to the occurrence of venous thromboembolism. The prothrombin G20210A mutation was found in 8.3%, homozygosity of factor V Leiden in 7.2%, and inherited deficiencies of antithrombin, protein C or protein S in 4.7% of symptomatic carriers (probands and relatives), as compared with 6.0, 3.4 and 0.9% of asymptomatic carriers, respectively. The total follow-up time in relatives was 11 049 years. Prevalences of venous thromboembolism were 10.8% in single heterozygous factor V Leiden carrier relatives, 16.0% in double-heterozygotes for factor V Leiden and the prothrombin mutation, 36.8% in homozygotes for factor V Leiden, and 40.0% in double-heterozygotes for factor V Leiden and an inherited deficiency of protein C or protein S. Annual incidences in these groups were 0.39, 0.57, 1.41, and 4.76%, respectively. Multivariate analysis showed a small, non-significant additional effect of the prothrombin mutation on the risk of venous thromboembolism in heterozygotes for factor V Leiden [adjusted hazard ratio, 1.3; 95% confidence interval (CI), 0.5-3.8]. This effect was more pronounced for homozygosity of factor V Leiden (adjusted hazard ratio, 3.9; 95% CI, 1.7-9.0) and inherited protein C or protein S deficiencies (adjusted hazard ratio, 17.5; 95% CI, 3.8-81.2). Our data provide evidence of clustering of the evaluated genetic thrombophilic defects in symptomatic factor V Leiden carriers and support the assumption that the clinical expression of factor V Leiden depends on clustering in a part of carriers.     

High factor VIII levels contribute to the thrombotic risk in families with factor V Leiden

Factor V Leiden (FVL)-carrying relatives of selected patients with venous thromboembolism (VTE) have much higher venous thrombotic risks than FVL-carrying relatives of unselected consecutive patients with VTE. To find an explanation for this, we explored other risk factors of VTE, in particular the presence of high factor VIII levels, in a retrospective follow-up study. We assessed levels of factor VIII, factor IX, fibrinogen, protein C, protein S, antithrombin, the presence of prothrombin 20210A, and the occurrence of VTE in 61 first-degree relatives of 12 selected thrombophilic families harbouring FVL, and 183 first-degree relatives of 47 unselected families of FVL carriers with a first VTE. In all families, FVL appeared to be an independent risk factor for VTE. Higher thrombosis incidence rates were found in carriers of both FVL and high factor VIII levels (> or = 150 IU/dl), while high levels of factor VIII appeared to be an independent thrombotic risk factor only in selected thrombophilic families. The fraction of individuals with more than one prothrombotic coagulation disorder was 10% higher in selected families. These results and the higher thrombotic risks we found in the thrombophilic families favour the hypothesis that other unknown co-existing genetic defects contribute to thrombophilia.     

The risk of recurrent venous thromboembolism in heterozygous carriers of factor V Leiden and a first spontaneous venous thromboembolism

BACKGROUND: Factor V (FV) Leiden is a risk factor for venous thrombosis (VT). Data on its influence on the risk of recurrent venous thromboembolism (VTE) are controversial owing to different study designs and patient cohorts. METHODS: We reevaluated the risk of recurrence among heterozygous carriers and noncarriers of FV Leiden with a first spontaneous proximal VT of the leg and/or pulmonary embolism. Patients with secondary VTE, homozygous FV Leiden, natural inhibitor deficiencies, lupus anticoagulant, cancer, or long-term anticoagulation were excluded. The study end point was objectively documented, symptomatic, recurrent VTE. RESULTS: After discontinuation of oral anticoagulant therapy for a first VTE, we prospectively observed 287 patients, 83 (29%) of whom were heterozygous for FV Leiden. Recurrent VTE was seen in 17 (20%) of 83 patients with and 44 (21.6%) of 204 without FV Leiden. The probability of recurrence among heterozygotes was 12% (95% confidence interval [CI], 8%-16%), 27% (95% CI, 21%-33%), and 27% (95% CI, 21%-33%) after 2, 4, and 6 years, respectively, and was not higher than that among patients without the mutation (16%, 23%, and 34%, respectively). The relative risk of recurrence in heterozygotes was 0.9 (95% CI, 0.5-1.6; P =.60) after adjustment for confounding variables. The risk of recurrence among patients with and without FV Leiden was not different when sex distribution or duration of anticoagulation therapy was taken into account. CONCLUSIONS: The risk of recurrence is similar among carriers and noncarriers of FV Leiden. Heterozygous patients should receive secondary thromboprophylaxis for a similar length of time as patients without FV Leiden.     

Evaluation of a tissue factor dependent factor V assay to detect factor V Leiden: demonstration of high sensitivity and specificity for a generally applicable assay for activated protein C resistance

Resistance to the anticoagulant effects of activated protein C (APC) is now considered the most prevalent cause of inherited thrombophilia. The great majority of patients with activated protein C resistance (APCR) have a missense mutation in the factor V molecule (factor V Leiden, FVR506Q) resulting in defective inactivation of factor Va due to a loss of an APC cleavage site. The diagnosis of APCR has been based upon the inability of APC to prolong the activated partial thromboplastin (aPTT) clotting time in subjects with APCR. However, this assay has a number of deficiencies which limit its general use. We have evaluated a newly described one-stage tissue factor dependent factor V coagulation assay for APCR in 117 patients and controls and compared the results of this assay in a blinded manner to a polymerase chain reaction (PCR) based assay for the molecular defect of factor V Leiden. 43% (50 /117) of the patients studied were receiving coumadin or heparin, or had a lupus anticoagulant. The tissue factor dependent factor V assay had 100% specificity and sensitivity for factor V Leiden and successfully predicted a homozygous state in the three documented homozygotes. The PCR-based assay for factor V Leiden resulted in a single false positive assay due to a silent A to C transition at nucleotide 1692 resulting in the loss of the Mnl restriction endonuclease cleavage site. The single-stage tissue factor dependent factor V assay is a highly sensitive and generally applicable assay for APCR.     

Factor V HR2 haplotype: a risk factor for venous thromboembolism in individuals with absence of Factor V Leiden

Venous thromboembolism (VTE), including deep venous thrombosis (DVT) and pulmonary embolism (PE), occurs secondary to a number of hereditary and acquired disorders of hemostasis. A recently recognized polymorphism in Factor V (FV) gene H1299R (also named HR2) has been reported to be a possible risk factor for the development of VTE. The aim of this study is to evaluate the role of HR2 polymorphism in VTE in a group of Lebanese patients. Seventy-three VTE patients and 125 healthy subjects were examined for HR2. The average ages for the patients and controls were 45.0 ± 19.1 years and 35.4 ± 18.6 years, respectively. Sixty patients (82.2%) had DVT, eight patients (11%) had PE, and five patients (6.8%) had both. There was significant association between FV Leiden and VTE (p < 0.001). HR2 haplotype had a prevalence of 16.4% in patients. VTE patients with normal FV were 2.7 times more likely to have the HR2 haplotype as compared to controls with normal FV (p = 0.036, 95% CI = 1.04–7.06). We conclude that the FV HR2 haplotype significantly affects the risk of VTE in subjects with normal FV. This finding entails that screening for the HR2 haplotype should be done in VTE patients with normal FV Leiden results. No conflicts of interest. No source of funding.     

Resistance to activated protein C is a risk factor for pregnancy-related venous thrombosis in the absence of the F5 rs6025 (factor V Leiden) polymorphism

Resistance to activated protein C (aPC) is most commonly due to the F5 rs6025 (factor V Leiden) polymorphism, which increases the risk of venous thrombosis. In the present population-based study of 313 cases and 353 controls, we investigated whether reduced sensitivity to aPC was associated with a history of pregnancy-related venous thrombosis. Calibrated automated thrombography was used to determine the sensitivity to aPC, and normalized aPC sensitivity ratio (n-aPC-sr) was calculated. Pregnant women and women using oral contraceptives and/or anticoagulants were excluded due to the effect on the n-aPC-sr. In women without the F5 rs6025 polymorphism, free tissue factor pathway inhibitor (TFPI), free protein S and protein C activity were associated with n-aPC-sr. Unadjusted odds ratio for venous thrombosis for women with n-aPC-sr in the 4th quartile as compared with n-aPC-sr below the 4th quartile was 2·4 (95% confidence interval 1·7-3·6). Adjusting for free protein S, free TFPI and age did not influence the odds ratios. Also in carriers of the F5 rs6025 polymorphism the risk for venous thrombosis was increased for women with higher n-aPC-sr. Our findings substantiate the importance of the aPC resistant phenotype as a risk factor for pregnancy-related venous thrombosis.     

Activated protein C resistance: a comparison between two clotting assays and their relationship to the presence of the factor V Leiden mutation

Resistance to the anticoagulant effect of activated protein C (APC resistance), a frequent abnormality in patients with a history of venous thrombosis, is known to be due, in the large majority of cases, to the presence of an abnormal factor V: the factor V Leiden. It is reasonable to surmise that screening for this abnormality should be performed with a clotting method for APC resistance, before submitting the patients with abnormal results to DNA analysis. The present study was performed on 216 individuals enrolled at the Bologna centre, of which 189 were unrelated patients with a history of juvenile venous thromboembolism and 27 were relatives with or without thrombosis. APC resistance was first measured in Bologna by a standard commercial method and then, in Leiden, by an in-house method; DNA analysis was performed in those cases in which at least one of the clotting methods was abnormal. The data obtained confirm the good performance and the optimal positive predictive value for the Leiden mutation (100%) of the Leiden in-house clotting method. Performance of the commercial method was less satisfactory but markedly improved by expressing the data in relation to the values simultaneously obtained with a normal plasma pool. Even with optimal data expression, however, the positive predictive value of the commercial method, versus DNA analysis, did not exceed 88%.
It is concluded that further standardization of the commercial method here evaluated is necessary before it can be widely adopted for the screening of APC resistance and prediction of the presence of factor V Leiden.     

Inherited combined deficiency of factor V and factor VIII: report of a case with normal factor VIII antigen and ristocetin-induced platelet aggregation

A patient with inherited combined deficiency of factor V and factor VIII is reported, who demonstrated normal levels of factor VIII antigen and plasma cofactor for ristocetin-induced platelet aggregation. The relationship of this condition to classical hemophilia and von Willebrand's disease is discussed. The data presented suggest that multiple loci on at least 2 chromosomes are necessary for the normal expression of factor VIII activity.     

Phenotypic homozygous activated protein C resistance associated with compound heterozygosity for Arg506Gln (factor V Leiden) and His1299Arg substitutions in factor V

Two patients from two unrelated families with a history of thrombosis showed severe plasma activated protein C (APC) resistance. However, genotypic analysis demonstrated that the patients were heterozygous for factor V (FV) Leiden mutation. Coagulation studies revealed that FV clotting activity and antigen were similarly reduced at about 50% of normal in the patients. One brother of propositus A also showed the same abnormalities. Genetic analysis showed that, in addition to FV Leiden mutation in exon 10 of the FV gene (G1691A), these patients had a transition in exon 13 of the FV gene (A4070G; R2 allele) predicting His1299Arg substitution in the mature FV. Study by RT-PCR of platelet FV mRNA indicated that the mRNA produced by the FV gene, marked by the R2 allele, was reduced in amount in both pseudohomozygous patients of family A. The R2 allele has previously been demonstrated to be significantly associated with plasma FV deficiency in the Italian population. The presence of FV deficiency did not protect the propositi from thrombosis. These data confirm that genotypic analysis is mandatory in patients with phenotypic severe APC resistance before these patients are definitely classified as homozygotes for FV Leiden and that further genotypic analysis is advisable.     

Venous thrombosis: factor V G1691A genotyping related to APC resistance as measured by 2 methods

Abstract: Blood samples were collected from consecutive unrelated patients with venous thrombosis. The patients originate from the middle part of Sweden. We investigated the presence of the reported point mutation at nt 1691 of factor V which renders the protein resistant to cleavage by activated protein C (APC). Thirty-seven per cent of the patients were heterozygote carriers, and 4.5% were homozygotes for a mutated factor V gene. In addition, resistance to coagulation induced by APC was measured, both by the conventional APTT assay and by a modified APTT assay which has been reported to have an increased resolution. Compared to a control group of healthy people, the mean value was significantly lower in the patient group. A strong correlation between low APC ratio and presence of the factor V mutation was found. By using the modified method, a complete resolution of carriers of the factor V mutation and people with normal factor V alleles was found. However, there was still an overlap between heterozygote carriers and people homozygous for the mutation. The modified method was also found useful in patients treated with warfarin. Among 40 healthy blood donors 7% were found to be heterozygous.     

A prospective study of asymptomatic carriers of the factor V Leiden mutation to determine the incidence of venous thromboembolism

BACKGROUND: The factor V Leiden mutation is a common genetic defect associated with an increased risk for venous thromboembolism. The clinical implications for asymptomatic carriers of this mutation and, consequently, the usefulness of screening families in which a proband has both the mutation and venous thromboembolism are unclear. OBJECTIVE: To determine the incidence of venous thromboembolism in asymptomatic carriers of the factor V Leiden mutation. DESIGN: Prospective cohort study. SETTING: University hospitals in the Netherlands. PARTICIPANTS: 470 asymptomatic carriers of the factor V Leiden mutation (234 men, 236 women; mean age, 43 years [range, 15 to 88 years]), 12 of whom were homozygous. Carriers were identified by screening the first-degree relatives (>15 years of age) of 247 symptomatic probands. MEASUREMENTS: Objectively diagnosed episodes of venous thromboembolism and the relationship between incidence and exposure to high-risk situations. RESULTS: Nine venous thromboembolic events were observed in 1564 observation-years, resulting in an annual incidence of 0.58% (95% CI, 0.26% to 1.10%). The incidence of spontaneous venous thromboembolism was 0.26% (CI, 0.07% to 0.65%) per year; 3.5% (CI, 0.1% to 17.8%) per episode of surgery, trauma, or immobilization; 0.0% (CI, 0.0% to 19.5%) per pregnancy; 1.8% (CI, 0.4% to 5.2%) per year of oral contraceptive use; and 2.9% (CI, 0.8% to 15.3%) per year of use of hormone replacement therapy. CONCLUSIONS: The absolute annual incidence of spontaneous venous thromboembolism in asymptomatic carriers of the factor V Leiden mutation is low and does not justify routine screening of the families of symptomatic patients.     

The risk of venous thromboembolism in family members with mutations in the genes of factor V or prothrombin or both

Factor V Leiden and the G20210A mutation in the prothrombin gene are the most frequent abnormalities associated with venous thromboembolism. It is unknown whether the risks due to the presence of either mutation are of the same magnitude. We compared the prevalence and incidence rate of venous thromboembolism in relatives with either mutation or both. The finding of different rates might influence the strategies for primary prevention of thrombosis in carriers of these mutations. The study population included 1076 relatives of probands with the prothrombin gene mutation, factor V Leiden or both who underwent screening for inherited thrombophilia and were found to be carriers of single mutations or double mutations or who were non-carriers. The prevalence of venous thromboembolism was 5.7% in relatives with the prothrombin gene mutation, 7.8% in those with factor V Leiden, 17.1% in those with both mutations and 2.5% in non-carriers. Annual incidences of thrombosis were 0.13% [95% confidence interval (CI) 0.06-0.24], 0.19% (0.13-0.25), 0.42% (0.15-0.83) and 0.066% (0.03-0.11), respectively, and the relative risk of thrombosis was two times higher in carriers of the prothrombin gene mutation, three times higher in those with factor V Leiden and six times higher in double carriers than in non-carriers. The incidence of venous thromboembolism in carriers of the prothrombin gene mutation is slightly lower than that observed in carriers of factor V Leiden, whereas in carriers of both mutations it is two or three times higher. These findings suggest that lifelong primary anticoagulant prophylaxis of venous thromboembolism is not needed in asymptomatic carriers of single or double mutations. Anticoagulant prophylaxis seems to be indicated only when transient risk factors for thrombosis coexist with mutations.     

FV Leiden mutation and risk of recurrent venous thromboembolism in Serbian population

The absolute rate of recurrence of venous thromboembolism (VTE) is approximately 5% per year. There is a lower rate of recurrence in provoked VTE, and higher in idiopathic one. So far, there is no consensus whether hereditary thrombophilia should be considered as a persistent risk factor, and whether it requires long-term anticoagulant therapy. The aim of our study was to estimate the risk of recurrent VTE in patients carrying FV Leiden mutation in Serbian population.In retrospective study (1994-2006), we have evaluated the risk of recurrent VTE in 56 patients who are carriers of FV Leiden mutation, in comparison to group consisting of 56 patients non-carriers of FV Leiden mutation. Patients with FII G20210A and MTHFR C677T mutations, antiphospholipid antibodies, antithrombin III, protein C or protein S deficiency, malignancies and diabetes were excluded from the study.Recurrent VTE occurred in 44.6% of the patients, carriers of the FV Leiden mutations, vs. 26.7% in non-carriers group (P<0.05). The incidence rate was 3.7 and 2.2% per year, respectively. The estimated relative risk of recurrence for FV Leiden carriers was 1.67 (95% CI 0.99-2.81, P=0.049). The 60% of patients with mutation and only 13% without mutation develop rethrombosis during first year after discontinuance of therapy (P<0.01).In our study patients with symptomatic VTE who are carriers of the FV Leiden gene mutations have a higher risk of recurrent VTE than non-carriers. Our data suggest the importance of the FV Leiden mutation detection and the estimation of the clinical condition for successful secondary prophylaxis of VTE.     

Prevalence of factor V Leiden and prothrombin G20210A mutations in unselected patients with venous thromboembolism

We determined the prevalence of factor V Leiden and of prothrombin G20210A mutations in a cohort of unselected outpatients (n = 748) referred for suspected deep vein thrombosis (DVT) and/or pulmonary embolism (PE) and a pooled analysis of similar studies was also performed. Based on the clinical presentation, the prevalence of factor V Leiden was 15.7% in the 83 patients with DVT and 14.1% in the 99 patients with PE compared with 5.3% in patients without DVT and/or PE (control group). The prevalence of the prothrombin G20210A mutation did not differ among the three groups (3.9% for controls, 4. 8% for DVT and 3.9% for PE patients). We then divided the 99 patients with PE by separately analysing those with PE but without DVT (n = 57) and those with PE and DVT (n = 42). Compared with the control group, the prevalence of factor V Leiden was 10.5%, odds ratio (OR) 2.10 [95% confidence interval (95% CI) 0.68-5.45] in patients with primary PE and 19.1%, OR 4.20 (95% CI 1.54-10.30) in patients with DVT and PE. For the prothrombin G20210A mutation, no statistically significant differences were found between the control group and the three other groups. In conclusion, our data and the pooled analysis indicate that patients with primary PE are less often affected by the factor V Leiden mutation. No statistically significant differences were observed between patients and controls for the prothrombin G20210A mutation.