Low risk of venous thrombosis in two families with combined type I plasminogen deficiency and factor V R506Q mutation

Two families with type I plasminogen deficiency and APC resistance are reported. The proposita of family A suffered from ischemic stroke when taking estrogen-progesterone-containing oral contraceptive. Several hemostatic challenges in the past (ovariectomy, appendectomy, and two pregnancies) were without thrombosis. Plasminogen activity and antigen (60 and 58%, normal range 72–136 and 69–135%, respectively) were reduced, and an increased APC resistance (APC-SR = 1.55; normal range 1.8–3.00) associated with G → A change at 1,691 nucleotide position in exon 10 of FV gene (FV Leiden) was observed. The asymptomatic son had isolated plasminogen deficiency (activity 57% and antigen 60%) whereas the asymptomatic daughter had isolated APC resistance (APC-SR = 1.61) and FV Leiden mutation. The proposita of family B, referred for superficial thrombophlebitis, had low plasminogen levels (activity 55% and antigen 53%) and APC resistance (APC-SR = 1.5) whereas the asymptomatic mother and the brother had isolated APC resistance (APC-SR = 1.62 and 1.8, respectively) and the asymptomatic father isolated plasminogen deficiency (activity 61% and antigen 62%). These data suggest that the combination of plasminogen deficiency and APC resistance probably does not significantly increase the risk of venous thrombosis. However, larger experience with additional cases is needed to definitely assess the magnitude of thrombotic risk in these families. Am. J. Hematol. 57:344–347, 1998. © 1998 Wiley-Liss, Inc.     

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.     

Pregnancy-associated venous thromboembolism (VTE) in combined heterozygous factor V Leiden (FVL) and prothrombin (FII) 20210 A mutation and in heterozygous FII single gene mutation alone

The risk of venous thromboembolism (VTE) in the absence of prophylaxis was evaluated in a retrospective study of 47 women (84 pregnancies) with combined thrombophilia [heterozygous factor V Leiden (FVL) plus prothrombin (FII) 20210A mutation (group I)] and in 82 women (193 pregnancies) with the FII alone (group II). VTE was more frequent in group I than in group II [17.8% versus 6.2%, P = 0.003, relative risk (RR) 2.9, 95% confidence interval (CI) 1.4-5.9], ante partum (7.1% and 2.1%) and post partum (11.5% and 4.2%). The risk was higher in index cases than in family members (RR 2.5, 95% CI 1.2-5.2 and RR 2.1, 95% CI 0.2-22.3 respectively) Even women who had no history of VTE before pregnancy had an increased risk (RR 2.2, 95% CI 1.0-4.8). Our results suggest that, during ante partum, prophylaxis is indicated in women with combined thrombophilia and with a VTE before pregnancy. In those without VTE before pregnancy, prophylaxis might be decided for each individual case, taking into consideration all risk factors. In women with the FII mutation alone, the low risk may not justify prophylaxis in the absence of previous VTE. In post partum, prophylaxis is indicated in all cases.     

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.     

Thrombophilic risk of individuals with rare compound factor V Leiden and prothrombin G20210A polymorphisms: an international case series of 100 individuals

The risk of thrombosis in individuals with rare compound thrombophilias, homozygous factor V Leiden (FVL) plus heterozygous prothrombin G20210A (PTM), homozygous PTM plus heterozygous FVL, and homozygous FVL plus homozygous PTM, is unknown. We identified, worldwide, individuals with these compound thrombophilias, predominantly through mailing members of the International Society on Thrombosis and Haemostasis. Physicians were sent a clinical questionnaire. Confirmatory copies of the genetic results were obtained. One hundred individuals were enrolled; 58% were female. Seventy‐one individuals had a venous thrombosis (includes superficial and deep vein thrombosis, and pulmonary embolism), 4 had an arterial thrombosis and 6 had both. Nineteen individuals had never had a thrombotic event. Thrombosis‐free survival curves demonstrated that 50% of individuals had experienced a thrombotic event by 35 yrs of age, while 50% had a first venous thromboembolic event (VTE; includes all venous thrombosis except superficial thrombosis) by 41 yrs of age; 38.2% of first VTEs were unprovoked. 37% of patients had at least one VTE recurrence. Seventy percent of first pregnancies carried to term and not treated with anticoagulation were thrombosis‐free. In conclusion, patients with these rare compound thrombophilias are not exceedingly thrombogenic, even though they have a substantial risk for VTE.     

Two common genetic thrombotic risk factors: factor V Leiden and prothrombin G20210A in adult Turkish patients with thrombosis

The prevalence of genetic risk factors for thrombosis varies greatly in different parts of the world, both in patients with thrombosis and in the general population. Factor V Leiden (FVL) and prothrombin G20210A (PT G20210A) mutations are the most common genetic defects leading to thrombosis. We have previously reported that those two thrombotic risk alleles are frequently found in Turkish children with thrombosis. The aim of the present study was to investigate the frequency of FVL and PT G20210A and their clinical manifestations in adult Turkish patients with thrombosis. Between January 1997 and February 2000, 146 patients with documented thrombosis were investigated in our center for the presence of the FVL and PT G20210A mutations. Forty-five of 146 patients with thrombosis (30.8%) were detected to have FVL mutation. Among those cases with the FVL mutation, seven (4.8%) had homozygote and 38 (26%) had heterozygote mutation. The PT G20210A mutation was detected in 10 of the 146 patients with thrombosis (6.8%). Another six cases (4.1%) had both FVL and PT G20210A mutations. The overall frequency of these two common risk alleles in our adult population with thrombosis was 41.6%. Our findings reveal that FVL and PT G20210A mutations are significant genetic risk factors contributing to the pathophysiology of thrombosis in the Turkish population.     

Pseudohomozygosity for activated protein C resistance is a risk factor for venous thrombosis

Pseudohomozygosity for activated protein C resistance (APC-r) is a rare condition due to the association of heterozygous FV Leiden mutation and partial type I FV deficiency. To assess the risk of venous thromboembolism in these subjects, seven families including 11 pseudohomozygotes and 45 relatives were examined. Among the relatives, 16 were heterozygous FV Leiden carriers, nine showed partial FV deficiency and 20 no abnormalities. Deep vein thrombosis occurred in 4/11 (36.3%) pseudohomozygous patients versus 6/16 (37. 4%) FV Leiden carriers and 1/20 (5%) normal relatives. Pseudohomozygotes and FV Leiden carriers had a significantly increased risk of venous thrombosis in comparison to normal relatives (RR 8.8 and 5.7, respectively). There was no difference between the thrombotic risk of pseudohomozygous subjects and of FV Leiden carriers (RR 1.6, 95% CI 0.43-5.7). Furthermore, there was no difference in thrombosis-free survival between pseudohomozygotes and 45 consecutive FV Leiden heterozygous outpatients, suggesting that a referral bias may explain the apparent younger age of thrombosis in the pseudohomozygotes in comparison to relatives with FV Leiden heterozygosity (27 years v 54 years; P = 0.01). Pseudohomozygosity for APC resistance carries a significantly higher risk for venous thromboembolism in comparison to normal subjects, but probably not in comparison to heterozygous FV Leiden carriers.     

An overview of methods for detection of factor V Leiden and the prothrombin G20210A mutations

Venous thromboembolism, represented by deep venous thrombosis and pulmonary embolism, is a common disease with high mortality and morbidity. Within the last 25 years, risk factors for venous thromboembolism have been linked to mutations in the genes of the coagulation/anticoagulation system. Factor V Leiden and the prothrombin G20210A mutations are the most prevalent inherited risk factors predisposing to venous thromboembolism in the Western world. Tests to detect these mutations are carried out when investigating a personal or family history of venous thromboembolism. At the present, there are several different methods available for the detection of these mutations in the laboratory. The choice of the method will depend on many variables. This article is aimed at reviewing the available methods for the detection of factor V Leiden and prothrombin G20210A mutations, their principle, applicability, advantages and disadvantages of use.     

A novel ELISA-based primer extension assay for the detection of the factor V Leiden mutation

We describe an enzyme-linked immunosorbent assay (ELISA) based primer extension method for the detection of the factor V Leiden (FVL) mutation. The wild-type nucleotide at position 1691 or the mutant nucleotide at the complementary position on the antisense strand were detected by the incorporation of biotinylated complementary bases onto fluorescein isothiocyanate (FITC) labelled mini-sequence primers with specificity for the sense and antisense gene segments downstream from the bases adjacent to position 1691. The reactions took place in pairs of tubes containing the complementary bases to either the wild-type or mutant nucleotide respectively. Primer extension products from each reaction tube pair which have incorporated biotinylated bases were then captured in streptavidin-coated microtitre plate wells and detected colourimetrically using an ELISA procedure. 200 patient samples were tested to validate the assay and there was complete genotypic agreement between the ELISA method and restriction site analysis using Mnl I (137 wild type, 55 FVL heterozygotes and eight homozygotes). The method utilizes non-radioactive reagents and does not require electrophoretic techniques. It is therefore a safe, simple and rapid assay which lends itself to automation.     

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 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.     

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.     

Prothrombin fragment 1+2 and thrombin–antithrombin complex levels in patients with inherited APC resistance due to factor V Leiden mutation

Inherited activated protein C (APC) resistance is a newly described pathological condition associated with familial thrombophilia. A recent report on a family with APC resistance showed increased levels of prothrombin fragment 1+2 (F1+2) in the affected individuals. No data concerning thrombin–antithrombin complex (TAT) levels in patients with inherited APC resistance are presently available. The aim of this study was to assess the plasma levels of F1+2 and TAT in patients with inherited APC resistance due to factor V (F.V) Leiden mutation and to evaluate F1+2 and TAT levels in symptomatic and asymptomatic patients with the defect (‘carriers’) as compared to their family members having no evidence of F.V Leiden mutation (‘non-carriers’). One hundred and twenty-nine individuals belonging to 30 families with inherited APC resistance due to F.V Leiden mutation were studied. F1+2 and TAT levels were determined using two commercially available ELISA kits and cut-off values were defined as the higher limits of normal ranges obtained in healthy volunteers. Out of the 129 family members investigated, 36 were non-carriers, 85 were heterozygous and eight homozygous for F.V Leiden mutation. Thrombosis had occurred in 2/36 (6%) non-carriers, in 36/85 (42.3%) heterozygous and in 5/8 (63%) homozygous. Median levels of F1+2 and TAT were above cut-off values in carriers, whereas they were below in non-carriers. An overall percentage of 68.8% of carriers exhibited F1+2 levels above the cut-off value as compared to 38.9% of non-carriers. For TAT, an overall percentage of 63.4% of carriers presented with levels above the cut-off compared with 28% of non-carriers. In conclusion, patients with inherited F.V Leiden mutation may exhibit increased levels of F1+2 and TAT. There are no differences in F1+2 and TAT median levels among symptomatic and asymptomatic carriers. The percentage of carriers of F.V Leiden with levels of F1+2 and TAT above cut-off appears to be higher than that found in other clotting inhibitors defects and in this respect the defect might be considered different. However, these findings and the presence of a high percentage of non-carriers presenting with increased F1+2 and TAT levels may suggest the possible coexistence in these families of other unknown defects predisposing to 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.     

Factor V Leiden, prothrombin 20210A and the risk of venous thrombosis among cancer patients

Cancer patients have an increased risk of venous thrombosis (VT). The association of factor V Leiden (FVL) and the prothrombin 20210A variant with VT in cancer patients is not established. We genotyped 101 cancer patients with VT and 101 cancer patients without VT for these polymorphisms. Five cases and three controls were heterozygous for FVL, yielding an odds ratio of 1.7 (95% confidence interval (CI) 0.3-10.7). Five cases and no controls were heterozygous for prothrombin 20210A, for an odds ratio of 6.7 (95% CI 0.9-infinity). Prothrombin 20210A may be associated with VT risk among cancer patients.     

Effect of the MTHFRC677T variant on risk of venous thromboembolism: interaction with factor V Leiden and prothrombin (F2G20210A) mutations

Odds ratios for the MTHFR C677T variant were determined in a large case–control study of 558 unselected patients with venous thromboembolism and 500 control subjects. The odds ratios for MTHFR C677T heterozygosity and homozygosity were 1.07 (95%CI 0.84–1.36) and 0.71 (95%CI 0.48–1.03). In patients with the factor V Leiden or the F2 G20210A mutations there was no apparent increase in risk of venous thromboembolism due to the MTHFR C677T polymorphism.
Thrombophilia testing should not include genotyping for the MTHFR C677T polymorphism.     

Heritability of elevated factor VIII antigen levels in factor V Leiden families with thrombophilia

Factor VIII activity (factor VIII:C) and factor VIII antigen (factor VIII:Ag) levels above 150 IU/dl are associated with a five- to sixfold increased risk of venous thrombosis compared with levels < 100 IU/dl. These high levels are present in 25% of patients with a first episode of deep-vein thrombosis and in 11% of healthy controls. von Willebrand factor (VWF) and blood group are important determinants of the factor VIII level in plasma and therefore contribute to thrombotic risk, while factor VIII appears to be the final effector. Previously, we found familial clustering of factor VIII:C levels in women, which remained after adjustment for VWF and blood group. In the present study, we analysed the familial influence on factor VIII:Ag levels exceeding 150 IU/dl in 12 large families with thrombophilia in which high factor VIII:Ag levels contribute to thrombotic risk. As expected, blood group was a main determinant of the plasma factor VIII level: 58 relatives (32%) had factor VIII levels above 150 IU/dl and 50 (86%) of these had blood group non-O. After adjustment for blood group and age, we found an association between factor VIII:Ag levels in sister pairs (0.35, P = 0.003), brother pairs (0.35, P = 0.003), brother-sister pairs (0.35, P < 0.001) and in mother-son pairs (0.45, P = 0.02), but not in father-daughter or father-son pairs. The familial aggregation test was strongly positive for factor VIII:Ag levels (P < 0.001) and remained so after adjustment for the influence of blood group. We conclude that high factor VIII:Ag levels are a highly prevalent risk factor for venous thrombosis and contribute to risk in families with thrombophilia, and that these high levels are likely to be genetically determined by factors other than just blood group.     

R255h amino acid substitution of protein Z identified in patients with factor V Leiden mutation

The clinical significance of diminished protein Z in plasma is controversial. Studies in mice demonstrated that deficiency of protein Z dramatically increases the prothrombotic tendency of factor V Leiden mutation. This finding was confirmed by initial results in humans, indicating that thromboembolism in factor V Leiden patients with lowered protein Z level occurs earlier than in patients with normal protein Z levels. Consequently, the aim of our present study was to find out whether genetic alterations of protein Z were demonstrated in patients with factor V Leiden mutation and early onset of thromboembolic disease. DNA-sequencing of the protein Z gene was performed in two patients with factor V Leiden mutation, early onset of thromboembolism, and lowered protein Z levels. In both patients, R255H substitution of the protein Z gene was identified. Subsequently, the R255H substitution was also found in 12 of 132 additional patients. Patients presenting with the R255H substitution in addition to factor V Leiden mutation showed thromboembolic events more frequently than factor V Leiden patients without R255H substitution of the protein Z gene. In conclusion, R255H substitution of the protein Z gene seems to influence clinical symptoms of thromboembolism in factor V Leiden patients.