Clinical and analytical relevance of the combination of prothrombin 20210A/A and factor V Leiden: results from a large family

We analysed the clinical and analytical features of 18 subjects from a Spanish family who bear several combinations of two prothrombotic mutations, factor V Leiden (FVL) and prothrombin 20210A. We identified three subjects homozygous for the 20210A prothrombin mutation which additionally were heterozygous for FVL. The combination of both mutations increases the risk of developing venous thrombotic episodes at the earlier age. However, even in association with FVL, the homozygous condition of the prothrombin 20210A mutation requires additional risk factors to induce a thrombotic event. Finally, the plasma level of factor II showed a significant relationship with the prothrombin genotype.     

Diagnosis strategies in activated protein C resistance: is genotyping still necessary?

Resistance to activated protein C (APC) is due, in most cases, to a G to A mutation at nucleotide 1691 of factor V (FV) gene (the Leiden mutation). This inherited abnormality is now considered to be the major hereditary cause associated with an elevated risk of thrombosis. For this reason, laboratories are faced with an increasing number of samples referred for APC resistance diagnosis. This could have serious economic consequences and a comprehensive laboratory screening strategy for APC resistance is necessary. An original DNA assay based on denaturing gradient gel electrophoresis (DGGE) was designed in our laboratory. During a first period we systematically performed DNA analysis and compared the results with phenotypic assays. Using the modified functional test with a 1 : 5 predilution of plasmas, the cut-off value for APC resistance ratio was 2.6 in our sample. Among 94 consecutive patients referred to our laboratory we found a clear cut-off between the APC resistance ratio obtained for normal and abnormal individuals. The modified test had a predictive value of 1.0 found by a cut-off ≤2.6 for the heterozygote FV Leiden. This obviates the necessity of genotyping subjects with a normal phenotype. Among patients with an abnormal phenotype we were able to fully discriminate between homozygous and heterozygous patients using a cut-off value of 1.5. Nevertheless, our results demonstrate that, because of false-positive results such as lupus anticoagulant, genotyping is still indicated for patients with an abnormal ratio determined with the modified APC resistance test. The strategy described here allows us to safely lower the number of samples analysed by DGGE.     

Prevalence of hyperhomocysteinaemia, activated protein C resistance and prothrombin gene mutation in inflammatory bowel disease

BACKGROUND: Thromboembolic disease is a significant cause of morbidity and mortality in patients with inflammatory bowel disease (IBD). A hypercoagulable state exists in IBD that may involve many components of haemostasis and is closely linked to the disease pathogenesis. It has been proposed that microvascular thrombosis and infarction may trigger the underlying inflammatory process. AIM: To determine the prevalence of prothrombotic factors including hyperhomocysteinaemia, activated protein C (APC) resistance and prothrombin gene mutations as well as vitamin levels in the local IBD population. METHOD: A total of 68 patients (37 men and 31 women) attending the IBD clinic were enrolled into the study. Citrated and ethylenediamine tetraacetic acid blood samples were collected from all patients as well as from 30 controls. Homocysteine levels were measured using the IMX immunoassay. APC resistance was measured using an unmodified activated partial thromboplastin time-based clotting assay. Prothrombin mutations were determined using polymerase chain reaction with the HB-gene factor II detection system. RESULTS: Mean homocysteine levels were significantly higher and APC resistance ratios significantly lower in IBD patients compared with controls. No significant difference was detected between patients with ulcerative colitis or Crohn's disease. There was no significant increase in the incidence of prothrombin mutation in IBD patients. IBD patients had lower vitamin B12 and higher serum folate levels than controls. CONCLUSION: High homocysteine and high serum folate may be associated with low vitamin B12 levels in IBD patients. We did not find any association between a low APC ratio and the factor V Leiden mutation or high factor VIII levels. Both hyperhomocysteinaemia and a low APC ratio may contribute to an increased risk of thromboembolic disease in IBD patients.     

Factor V Leiden and prothrombin G20210A mutations in Thai patients awaiting kidney transplant

Renal transplantation provides the best long-term treatment for chronic renal failure, but thrombosis of the transplanted renal artery or renal vein is one of the causes of kidney failure in the early postoperative period. Factor V Leiden (FVL) and prothrombin G20210A mutation are the most frequent genetic abnormalities associated with venous thrombosis. We investigated the prevalence of FVL and prothrombin G20210A by polymerase chain reaction with restriction fragment length polymorphism in 75 Thai patients awaiting renal transplant, and a control group of 106 healthy blood donors. Of those awaiting renal transplant, none was found to carry FVL or prothrombin G20210A mutations. Neither the heterozygous nor the homozygous FVL mutation nor the prothrombin G20210A mutation was detected in the 106 healthy volunteers. Although we failed to detect FVL and prothrombin G20210A mutation among those waiting for a kidney transplant, the population size was small. Further studies need to be performed in order to ascertain if these coagulation mutations are of relevance in predicting patients at risk of early transplant failure.     

The impact of oral anticoagulant therapy, factor VIII level and quality of factor V-deficient plasma on three commercial methods for activated protein C resistance.

Several methods are now available for the laboratory assessment of activated protein C resistance (APCR). In this study, we evaluated two activated partial thromboplastin time-based assays [Coatest activated protein C (APC) and Diagen protein C activator (PCA)], with and without predilution of test plasma in factor V-deficient plasma (FVdp) and an amidolytic assay (Immuno Ltd, Vienna, Austria). Testing plasmas from normal volunteers who had received 1-deamino-8-D-arginine vasopressin (DDAVP) also assessed the effect of elevated factor VIII on APCR. In the unmodified clotting tests, the Coatest kit gave overlapping results for normal and heterozygous FV:Q506 samples; some FV:Q506 samples on oral anticoagulant therapy (OAT) were misclassified as normal, and some normal samples with high factor VIII levels would be classified as APC resistant. The unmodified Diagen kit correctly classified these three types of sample, but had the disadvantage that prolonged PCA clotting times gave serious problems with instrument end-point detection. Both kits modified by diluting the samples in FVdp correctly classified all the samples, as well as samples from patients with lupus anticoagulant (LA) and patients receiving heparin. The Immunochrom kit correctly classified the normal and FV:Q506 samples, but would have misclassified most normal persons on OAT as well as some patients with LA or receiving heparin therapy as APC resistant.     

Venous thromboembolism at a young age in a brother and sister with coinheritance of homozygous 20210A/A prothrombin mutation and heterozygous 1691G/A factor V Leiden mutation.

We report on members of a Turkish thrombophilic family with coinheritance of the prothrombin mutation PT20210A and the factor V Leiden mutation. The 23-year-old propositus and his elder sister both had episodes of venous theomboembolism at a young age (23 years and 26 years, respectively) and are homozygous for the PT20210A mutation and heterozygous for the factor V Leiden mutation. The 51-year-old father is suffering from coronary heart disease and is heterozygous for both thrombophilic mutations. The asymptomatic 43-year-old mother is heterozygous for the PT20210A mutation, but without activated protein C resistance. Two other children, a 20-year-old girl who is homozygous for the PT20210A mutation and a 13-year-old boy who is heterozygous for the PT20210A mutation, are both free from activated protein C resistance and thrombosis. This report provides further evidence for an early onset of thromboembolic disorders in individuals with an homozygous state of the prothrombin variant 20210A/A and coinheritance of another thrombophilic mutation. Consensus guidelines are required for the treatment and prophylaxis of patients and subjects who remain asymptomatic with homozygous or more than one heterozygous genetic defect associated with thrombophilia.     

Use of a generally applicable tissue factor--dependent factor V assay to detect activated protein C-resistant factor Va in patients receiving warfarin and in patients with a lupus anticoagulant

The original activated partial thromboplastin time-based assay for activated protein C (APC)-resistant factor Va (FVa) requires carefully prepared fresh plasma and cannot be used in patients receiving warfarin or in patients with antiphospholipid antibodies. A new test is described here that circumvents these limitations and distinguishes without overlap heterozygotes for APC-resistant FVa from persons with normal FV. A diluted test plasma is incubated with an FV-deficient substrate plasma and tissue factor and then clotted with Ca2+ or Ca2+ plus APC. Test results are independent of the FV level or the dilution of the test plasma used. Of 39 controls, 37 gave normal results. Two controls (5%) gave results indicative of APC resistant FVa and on DNA analysis were found to be heterozygous for FV R506Q. Twenty of 21 randomly selected patients receiving warfarin gave normal results. In the single patient with abnormal results, heterozygous FV R506Q was confirmed by DNA analysis. Two of 15 patients with protein S deficiency and 5 of 29 patients with a lupus anticoagulant had abnormal results. APC resistance caused by FV R506Q was confirmed in the five of these seven patients available for DNA analysis. APC-resistant FVa was also detected in 10 of 21 (46%) stored plasma from unrelated patients with venous thrombosis and negative earlier evaluation for a lupus anticoagulant or a deficiency of protein C, protein S, or antithrombin, which confirms a high incidence of this defect among patients with venous thrombosis.     

Low frequency of factor V Leiden and prothrombin G20210A mutations in patients with hepatic venous outflow tract obstruction in northern India: a case-control study.

BACKGROUND: Factor V Leiden (FVL) and prothrombin gene (G20210A) mutations are known to be associated with venous thromboembolism. Several studies have shown an association of these mutations with hepatic venous outflow tract obstruction (HVOTO). We studied the prevalence of these mutations among patients with HVOTO in northern India in comparison with healthy population. METHODS: Genomic DNA from patients with HVOTO and healthy controls was analyzed for the presence of FVL and prothrombin gene G20210A mutations, using PCR and restriction-fragment length polymorphism. RESULTS: Fifty-nine patients with HVOTO (age 5-69 years, median 27; 39 male) and 49 unrelated healthy controls from the same geographic region were studied. Of the 59 patients, 19 had a block in the hepatic vein, 7 in inferior vena cava, and 33 had mixed block. Presentation was with acute thrombosis in 9 patients and with long-standing obstruction in 50 patients. Among 49 controls, heterozygous and homozygous FVL mutations were observed in 2 and 0 subjects, respectively, with an allele frequency of 2% (2 of 98). In comparison, among 59 patients with HVOTO, four had heterozygous and none had homozygous FVL mutation, with an allele frequency of 3.4% (p=ns versus controls). The G20210A prothrombin gene mutation was not found in any of the patients or controls. CONCLUSION: FVL and prothrombin G20210A mutations appear to have no role in the pathogenesis of HVOTO in our patients with Budd-Chiari syndrome, consisting largely of those with long-standing obstruction of the inferior vena cava.     

Contribution of the glycoprotein Ia 807TT, methylene tetrahydrofolate reductase 677TT and prothrombin 20210GA genotypes to prothrombotic risk among factor V 1691GA (Leiden) carriers

The cooperative effects of the GPIa 807TT, MTHFR 677TT and prothrombin 20210GA genotypes with the FV Leiden 1691GA (FVL) genotype were evaluated by comparing these genotype frequencies in 77 asymptomatic and 156 symptomatic heterozygous FVL carriers. The GPIa 807TT and MTHFR 677TT genotypes did not segregate within the symptomatic FVL carrier group and did not contribute to venous thrombotic risk in this patient cohort. There was no difference in the prothrombin 20210GA genotype frequency between asymptomatic FVL carriers and a random Caucasian control group; however, the prothrombin 20210GA genotype was nearly 5 times as prevalent (19/156 v 2/77; P < 0.02) in the symptomatic FVL carriers (odds ratio 5.21; 95% confidence interval 1.20-47.62), demonstrating that this important prothrombotic risk factor acts synergistically with FVL.     

An investigation of the association of the factor V Leiden mutation and inflammatory bowel disease

BACKGROUND: A thrombotic aetiology for inflammatory bowel disease (IBD) has been proposed as a result of its association with thrombo-embolic complications, smoking, the oral contraceptive pill and the response of ulcerative colitis (UC) patients to heparin. The factor V Leiden (FVL) mutation is the commonest inherited risk factor for thrombo-embolism. AIM: The aim of the study was to investigate the hypothesis that the pro-thrombotic state associated with the FVL mutation is involved in the aetiology of IBD. PATIENTS AND METHODS: A prospective cohort study of patients attending the Bristol Royal Infirmary IBD outpatient clinic was performed. Fifty-four patients with IBD (30 with Crohn's disease (CD) and 24 with UC) and 55 historical controls were screened for the presence of FVL using the activated protein C (APC) ratio. Abnormal APC ratios were confirmed to be due to FVL using a heteroduplex-based polymerase chain reaction (PCR) technique. RESULTS: Five patients had the FVL mutation, compared to two controls. One of the patients was homozygous. Two of the patients had CD and three UC. The differences between controls and IBD patients was significant when the allelic frequency of the FVL mutation in patients with UC was compared with controls, with a risk ratio of 2.27, but with limited data. CONCLUSION: There appears to be a weak association between FVL and UC. This association is not strong enough to imply a causal relationship, but may be responsible for some of the thrombo-embolic complications.     

Method-dependent influence of certain polymorphisms in the factor V B-domain on the response to activated protein C.

The factor V (FV) B-domain is extremely important to the cofactor function of native FV for activated protein C (APC) in the inactivation of factor VIII (FVIII). In a previous study, we found that in the B-domain coding portion of DNA, the polymorphisms at nucleotide positions 2391, 2663, 2684, and 2863 were associated. In the major allele, all bases are A (A allele) and those in the minor allele are G (G allele). This study concerns itself with the question of whether or not there are differences in the APC response between the A allele and the G allele in plasma samples from persons without the FV Leiden. The APC ratios of homozygous carriers of the major A allele and the minor G allele do not differentiate themselves in classical activated partial thromboplastin time-based assays. In contrast, a test based on the deactivation of FVIII in the tenase complex in homozygous carriers of the minor G allele showed significantly lower APC ratios (P = 0.001) in comparison with the major A allele. The results of the investigation after modification of the test indicate that mutative changes in the B-domain apparently influence the interaction among phospholipids, APC, FV, and protein S. An increase in FVIII through the introduction of the FVIII concentrate Kogenate to the plasma samples was associated with a drop in the APC ratios of both genotypes. After defining 59 age- and sex-based matched pairs without the FV Leiden, the observed frequency of the minor G allele was higher in the non-thrombotic group (33.0%) than in the thrombotic group (22.8%). However, the difference did not reach the level of significance (odds ratio, 0.53; 95% confidence interval, 0.26-1.12). It does, nevertheless, appear possible that a homozygous condition for the minor allele in combination with a defect known to be associated with thrombophilia represents an additional thrombogenetic risk factor.     

History of non-fatal cardiovascular disease in a cohort of Dutch and British patients with haemophilia

Protein C (PC) deficiency is an autosomal dominant inherited disorder associated with spontaneous and recurrent thrombotic events. Factor V Leiden (FVL) increases the risk of thrombosis in PC-deficient type I families. We have investigated the relationship between PC deficiency genotype and clinical phenotype in a large four-degree Italian family followed since 1988. Methods: PC activity and antigen levels were quantified; sequencing of PC DNA was performed to identify polymorphism. FVL and factor II (G20210A) polymorphism were screened. Results: PC activity ranged from 5% to 9%, and PC antigen levels were 5,3% in two homozygous for PROC missense mutation Arg32Cys; PC activity ranged from 18% to 60% and antigen levels from 21% to 64%, respectively, in 11 heterozygous for Arg32Cys; PC activity was 99% and 120% in two wild type. Of 15, eight were heterozygous for FVL. The two subjects with PC < 6%, homozygous for Arg32Cys and heterozygous for FVL, suffered from thrombosis during childhood. Of 11, six subjects with PC deficiency and heterozygous for FVL showed the first thrombosis at an age between 21 and 54. None of the five PC-deficient subjects, who were wild type for FVL, showed thrombosis. Two subjects with PC > 70%, both heterozygous for FVL developed thrombosis in the presence of another risk factor. This study suggests that FVL and PROC mutations increase the risk of thrombosis in subjects with PC deficiency, which could be considered as a 'variable' risk factor. The thrombosis-prone PC-deficient families carry additional risk factors for thrombosis.     

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.     

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.     

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.     

The APC-independent anticoagulant activity of protein S in plasma is decreased by elevated prothrombin levels due to the prothrombin G20210A mutation

Protein S exhibits anticoagulant activity independent of activated protein C (APC). An automated factor Xa-based one-stage clotting assay was developed that enables quantification of the APC-independent activity of protein S in plasma from the ratio of clotting times (protein S ratio [pSR]) determined in the absence and presence of neutralizing antibodies against protein S. The pSR was 1.62 +/- 0.16 (mean +/- SD) in a healthy population (n = 60), independent of plasma levels of factors V, VIII, IX, and X; protein C; and antithrombin, and not affected by the presence of factor V Leiden. The pSR strongly correlates with the plasma level of protein S and is modulated by the plasma prothrombin concentration. In a group of 16 heterozygous protein S-deficient patients, the observed mean pSR (1.31 +/- 0.09) was significantly lower than the mean pSR of the healthy population, as was the pSR of plasma from carriers of the prothrombin G20210A mutation (1.47 +/- 0.21; n = 46). We propose that the decreased APC-independent anticoagulant activity of protein S in plasma with elevated prothrombin levels may contribute to the thrombotic risk associated with the prothrombin G20210A mutation.     

Modification of the ProC Global assay using dilution of patient plasma in factor V-depleted plasma as a screening assay for factor V Leiden mutation.

The activated protein C (APC) resistant-factor V (factor V Leiden) has emerged as the most common inherited risk factor for thrombosis in the Caucasian population. Beside DNA analysis, the laboratory diagnosis is often based on the detection of a poor anticoagulant response to exogenous APC. The ProC Global assay (Dade Behring, Marburg, Germany) is a global clotting assay, which was primarily developed to evaluate the functionality of the protein C anticoagulant pathway. It is based on the ability of endogenous APC, generated by activation of protein C by an extract from Agkistrodon contortrix contortrix venom, to prolong an activated partial thromboplastin time. It was previously found to be highly sensitive for the factor V Leiden mutation and for protein C deficiency, but only moderately sensitivity for protein S deficiency. Here, we evaluated the performance of a modification of the ProC Global assay using a 1 : 5 pre-dilution of patient plasma in factor V-depleted plasma in the screening of the factor V Leiden mutation-related APC resistance. For that purpose, we investigated selected frozen plasma samples from 341 patients with a history of venous thromboembolism. The sensitivity for the factor V Leiden mutation of the modified assay was found to be 100%, as all the carriers of that mutation (five homozygotes and 77 heterozygotes) had a decreased response to the assay, i.e. a normalized ratio below 0.80. Its specificity was also 100% since none of the other tested patients had a decreased response, i.e. isolated protein C (n = 3) or protein S deficiency (n = 50), or without any abnormality of the protein C pathway (n = 143), even those on oral anticoagulant treatment (n = 76). However, it would be preferable that each laboratory defines both its reference range and its cut-off level. Finally, even if larger-scale multicentre studies are needed before definite recommendations could be made, these results suggest that the ProC Global performed using a 1 : 5 pre-dilution of the patient plasma in factor V-depleted plasma could be validly used as a screening assay of the factor V Leiden mutation-related APC resistance in patients with a history of thrombosis.     

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.     

The frequency of factor V Leiden and concomitance of factor V Leiden with prothrombin G20210A mutation and methylene tetrahydrofolate reductase C677T gene mutation in healthy population of Denizli, Aegean region of Turkey.

Factor V Leiden causing activated protein C resistance is the most common inherited form of thrombophilia leading to thrombosis. Its frequency shows great ethnic and geographic variations. The aim of this study was to determine the frequency of FV Leiden and coinheritance of FV Leiden with two other frequent hereditary thrombophilia causes, namely, prothrombin G20210A and methylene-tetrahydrofolate reductase (MTHFR) C677T mutation in the Aegean region of Turkey. The study population consisted of 1030 (500 men and 530 women) apparently healthy subjects. Functional resistance to activated protein C (APC) was measured by using the test kit STA staclot APC-R ((Diagnostica Stago, Asnieres, France, Cat. No. 00721). In subjects with APC resistance, molecular analyses of FV Leiden and of prothrombin G20210A and MTHFR C677T mutation were performed by using FV-PTH-MTHFR StripA (Vienna Lab, Labordiagnostika GmbH, Austria) kit, which was based on hybridization of polymerase chain reaction (PCR) amplified DNA products with mutation-specific oligonucleotide probes. Functional APC resistance was present in 93 subjects (9%). FV Leiden mutation was found in 87 of 93 subjects with APC resistance by PCR method. The FV Leiden carrier frequency was found to be 8.4% (87/1030). Seventy-six individuals were heterozygous (7.3%), and 11 were homozygous (1.06%). Among the 87 subjects with FV Leiden mutation, 45 subjects had MTHFR C677T gene mutation (7 homozygous, 38 heterozygous) and 4 subjects had heterozygote prothrombin G20210A gene mutation. A combination of FV Leiden and prothrombin G20210A and MTHFR C677T gene mutation was detected in 3 subjects. The results indicate that FV Leiden prevalence is quite high and coexistence of FV Leiden with other hereditary causes of thrombosis such as prothrombin G20210A mutation and MTHFR enzyme defect is not rare in healthy population of Aegean region of Turkey.     

Thrombophilia: 2009 update

As venous thrombosis is mostly caused by disturbances in the plasma coagulation system, abnormalities of coagulation factors are mostly risk factors for venous thromboembolism (VTE). Relatively little is known about thrombophilias that predispose to arterial thromboembolism. Although some abnormalities in the fibrinolytic pathway appear to predispose to arterial thrombosis, the associations are weak and often inconsistent between studies. At present, there is not enough consistent and clinically meaningful information to include fibrinolytic parameters in a clinical thrombophilia workup. Controversy exists as to which patients and family members to test for thrombophilia. Several testing guidelines exist. Routine screening for inherited thrombophilias is not indicated in patients with VTE provoked by immobility, surgery, and malignancy, or in those with arterial thrombosis with arteriosclerosis risk factors. Heterozygous factor V Leiden (FVL) and prothrombin 20210 mutations increase the risk for recurrent VTE only slightly once anticoagulation is stopped. Therefore, decisions regarding the length of anticoagulant therapy typically are not influenced by finding one of these heterozygous mutations. The main reason to perform thrombophilia testing in a patient is to detect a strong thrombophilia (ie, antithrombin deficiency, antiphospholipid antibody syndrome, homozygous FVL, double-heterozygous FVL plus prothrombin 20210 mutation, protein C deficiency, and maybe protein S deficiency). The finding of a strong thrombophilia has several clinical consequences: it decreases the threshold to recommend long-term anticoagulation in a patient with unprovoked VTE; facilitates discussion regarding whether anticoagulant or antiplatelet therapy is the preferred empiric treatment for a patient who had an unexplained arterial, nonarteriosclerotic thromboembolic event; and leads to the consideration of testing asymptomatic female family members for the identified thrombophilia(s) so they can be counseled on their risk of thromboembolism, the use of hormonal therapies, and the potential benefit of pre- and postpartum anticoagulant therapy.