Rapid multiplex analysis for the factor V Leiden and prothrombin G20210A mutations associated with hereditary thrombophilia

Thromboembolic episodes are common events and affect approximately one in 1,000 persons annually. Pulmonary embolism alone accounts for 50,000 to 100,000 deaths per year in the United States with > 50% of those being elderly persons. Resistance to activated protein C is the most common inherited disorder associated with hereditary thrombophilia. A missense mutation has been identified in the gene coding for coagulation factor V (codon 506) which renders this procoagulant factor resistant to inactivation by activated protein C resulting in an increased risk for venous thrombosis. Recently, a second polymorphism was identified in the prothrombin gene (factor II) which is also associated with increased risk for venous thrombosis. Because of the high prevalence of these two mutations in the general population as well as in specific patient populations, the ability readily to detect these two mutations must be feasible. In this study, we evaluated 303 patients for the prothrombin mutatin (G20210A) which were previously tested for the factor V mutation using established polymerase chain reaction-mediated restriction fragment length polymorphism assays. In these patients, 30 (9.9%) were found to be heterozygous for the factor V Leiden mutation with no homozygous mutants identified. Twenty individuals (6.6%) were heterozygous for the prothrombin G20210A mutation, and we identified two individuals (0.66%) who were homozygous for the 20210A allele. Of the total 303 individuals screened, two were double heterozygotes for both the factor V Leiden and the prothrombin gene mutations. We also describe a multiplex polymerase chain reaction-mediated restriction fragment length polymorphism assay for detecting both mutations in a single-tube double-enzyme digestion reaction making identification of these two mutations easily achievable.     

Multigenic thrombophilia: genetic anomaly of factor II and mutation of factor V Leiden. Study in a French family

BACKGROUND: A genetic variation of the prothrombin (factor II) gene, a G to A transition at nucleotide position 20210, was recently found in patients with familial thrombophilia (predisposition to venous thrombosis). It seems to be frequent in patients with the factor V Leiden mutation. We report a family with the factor V Leiden and/or the genetic variation of prothrombin in 3 members. CASE REPORT: The patient had repeated episodes of deep vein thromboses starting at the age of 30 during the 4th pregnancy. She is a heterozygous carrier of both the factor V Leiden nutation and the prothrombin mutation 20210 A. She has 4 asymptomatic children, aged 28 to 32 and 3 of them have been explored: one son has the prothrombin mutation, one daughter the factor V Leiden and one has none of them. DISCUSSION: This case report illustrates the polygenic nature of thrombophilia which may explain the heterogeneity of clinical expression observed in isolated congenital abnormalities, especially in factor V Leiden mutation.     

Activated-protein-C resistance in cancer patients

BACKGROUND: Resistance to activated protein C (aPC) is usually linked to factor V Leiden, but may occur in other disorders associated with hypercoagulability. In this study, we investigated the frequency of resistance to aPC in patients with advanced cancer and examined the relationship of aPC resistance to other markers of coagulation activation. METHODS: Patients (n = 39) had established diagnosis of advanced cancer; controls (n = 20) were healthy persons. aPC resistance was measured as the ratio of activated partial thromboplastin times with and without aPC (aPC-sensitivity ratio, aPC-SR). The factor V Leiden mutation was detected by a polymerase-chain-reaction based technique. Other assays were performed by standard laboratory methods. Data were analyzed using t tests and the Pearson correlation. RESULTS: aPC-SR was below 2 SD for 5 of the cancer patients (13%), but none of the controls; only 1 of the 5 had the factor V Leiden mutation. aPC-SR was inversely correlated (p < 0.01) with factor VIII and fibrinogen in patients and with prothrombin activation fragment 1.2 (F1.2) in controls. Patient factor VIII, von Willebrand factor, (vWF), fibrinogen, F1.2 and D dimer were all significantly increased (p < 0.01; antithrombin III, protein C and proteins were similar to controls. Factor VIII correlated with vWF (p < 0.001) and F1.2 with d-dimer (p < 0.001). Other associations (p < 0.05) were observed between factor V and protein C, fibrinogen and protein C, factor V and antithrombin III and protein C and antithrombin III. Four cancer patients had a history of thromboembolism; their aPC-SR was similar to that of patients without thrombosis. Of the several coagulation measures examined, only vWF was higher in the patients with thrombosis (p = 0.01). INTERPRETATION: Cancer patients have evidence of intravascular coagulation and increases in procoagulants and may have aPC resistance. The aPC resistance is not due to factor V Leiden, but is rather associated with elevated levels of factor VIII and fibrinogen, and in itself does not predict thrombosis.     

Activated protein C resistance--a recently discovered hereditary thrombophilia

Activated protein C resistance is an inherited thrombophilia caused by a point mutation in the factor V gene (G to A transition in nucleotide 1691 in the factor V gene with replacement of arginine (R) 506 by glutamine (Q) in the factor V molecule). The mutation is commonly named factor V R506Q or factor V Leiden. The mutation results in a poor anticoagulant response to activated protein C. APC resistance is inherited autosomally, and approximately 5-10% of the Norwegian population are carriers of the mutation. It is present in 20-50% of all cases of venous thromboembolism. Among asymptomatic heterozygous family members of affected individuals there is a five to eight-fold increase in the risk of venous thromboembolism, whereas there may be a 100-fold increased risk among homozygous individuals. The risk for asymptomatic carriers without a family history is yet not known. Activated protein C resistance is a major risk factor for venous thromboembolism, and the detection of activated protein C resistance is vital for proper prophylaxis and treatment of this disorder. It is essential therefore that as many medical specialists as possible acquire knowledge of activated protein C resistance. This report describes a family with activated protein C resistance and the main indications for screening for inherited thrombophilia.     

Clinical application of hepatitis C virus core protein in early diagnosis of acute hepatitis C

OBJECTIVE: To investigate the prevalence of currently recognised inherited prothrombotic states in a population of children with arterial stroke. METHODS: Children with arterial stroke presenting to a tertiary level paediatric neurology centre between 1990 and 1996 were investigated for inherited prothrombotic states. RESULTS: Sixty seven children with arterial stroke were investigated. Abnormalities were initially identified in 16 patients; however, only eight children (12%) had an inherited prothrombotic state. This was type 1 protein S deficiency in one patient, the factor V Leiden mutation in six, and activated protein C resistance (without the factor V Leiden mutation) in one. The prevalence of the factor V Leiden mutation was not significantly higher in children with arterial stroke (12%) than in a control population of children without thrombosis attending the same institution (5.2%; Fisher's exact test, p=0.19; difference in prevalence between patients and controls (95% confidence interval)=6.8% (-2.78% to 16.8%)). CONCLUSIONS: Currently recognised inherited prothrombotic tendencies were rarely associated with stroke in this group of children, although larger numbers of patients would be needed to confirm this. Age appropriate normal values should be used when interpreting the results of a prothrombotic screen. Prothrombotic abnormalities seen acutely are as often transient as inherited. Longitudinal assessment and family studies are required before low concentrations of an anticoagulant protein found acutely can be attributed to an inherited abnormality.     

The prothrombin gene G20210A variant: prevalence in a U.K. anticoagulant clinic population

We have investigated the prevalence of a recently reported genetic variation in the prothrombin gene (G20210A) in patients with an objectively confirmed history of venous thrombosis, 12/219 patients (5.5%) were found to be heterozygous carriers of the 20210A allele. The incidence of the 20210A allele in a group of 164 healthy controls was 1.2% (allele frequency 0.61%, 95% CI 0.08-2.19). When patients with a known alternative hereditary risk factor for venous thrombosis (factor V Leiden mutation or deficiency of antithrombin, protein C or protein S) were excluded, the G20210A variant was found to increase the risk for venous thrombosis by approximately 5-fold (odds ratio 5.4, 95% CI 1.16-25.0). This prothrombin gene sequence variation adds further to the list of recognized genetic risk factors for thrombophilia.     

C677T MTHFR mutation and factor V Leiden mutation in patients with TIA/minor stroke: a case-control study

A common C677T mutation in the gene for the enzyme 5,10-methylenetetrahydrofolate reductase (5,10-MTHFR) has been linked to elevated levels of homocysteine and was therefore suspected to be a candidate genetic risk factor for arterial occlusive disease. Another mutation, factor V Leiden, has been established as a common hereditary risk factor for venous thrombosis, but its role in arterial disease remains controversial. We investigated the prevalence of both the C677T MTHFR mutation and the factor V Leiden mutation in 81 patients with transient ischemic attack (TIA) or minor stroke (MS) and in 81 age- and sex-matched control subjects free from clinically manifest vascular disease. We further compared clinical and laboratory data as well as clinical course of patients carrying the factor V Leiden mutation alone or in combination with the C677T MTHFR mutation and mutation-free patients. The prevalence of the MTHFR mutation did not differ between patients and control subjects with 11.1% homozygous carriers in both groups (OR for homozygous carriers 1.0; 95% CI 0.38-2.66). However, there was a trend towards a higher prevalence of carriers of factor V Leiden in patients (12.3%) than in control subjects (4.9%) (OR 2.75; 95% CI 0.83-9.17;p=0.09). Furthermore, we found some evidence that the combined occurrence of the C677T MTHFR mutation and factor V Leiden might unfavorably affect the clinical course of the disease, but the number of respective patients was small. Larger studies with a greater number of carriers of both the C677T MTHFR mutation and factor V Leiden seem therefore warranted.     

The factor V Leiden mutation increases the risk of venous thrombosis in patients with inflammatory bowel disease

BACKGROUND & AIMS: Thromboembolic disease is a significant cause of morbidity and mortality in patients with inflammatory bowel disease (IBD). The aim of this study was to determine the incidence and possible association of the factor V Leiden mutation with the development of thrombosis in patients with IBD. METHODS: This retrospective study included 11 patients with IBD and arterial or venous thrombosis and 51 patients with IBD and no history of thrombosis who were matched for age, sex, ethnic/racial origin, and type of IBD (controls). The presence of the factor V Leiden mutation was determined by coagulation assay and confirmed by a polymerase chain reaction method. RESULTS: Four of 11 IBD patients (36%) with thrombosis and 2 of 51 IBD controls (4%) were heterozygotes for the factor V Leiden mutation (relative risk, 14.00; 95% confidence interval, 1.55-169.25; P = 0.009, Fisher exact test). All thrombotic events in the patients with activated protein C resistance were venous with a calculated prevalence of 50% (4 of 8 patients) and a relative risk of venous thrombosis in IBD patients with factor V Leiden of 23 (95% confidence interval, 2-294; P = 0.005). CONCLUSIONS: In patients with IBD, inheritance of the factor V Leiden mutation results in a significant increased risk of venous thrombosis.     

Resistance to activated protein C caused by the factor VR506Q mutation is a common risk factor for venous thrombosis

In 1993, inherited resistance to activated protein C (APC) was described as a novel risk factor for venous thrombosis. APC-resistance is present in 20-60% of venous thrombosis cases. It is caused by a single point mutation in the factor V gene which substitutes arginine (R) at position 506 with a glutamine (Q). The mutation is common in Caucasians with up to 15% prevalence in the population, whereas it is not found among other human races. Mutated factor V (FVR506Q, FV:Q506 or FV Leiden) is partially resistant to APC which results in a hypercoagulable state conferring a life-long increased risk of thrombosis. Individuals having FV:Q506 combined with other anticoagulant defects have a high risk of thrombosis, and it is now generally accepted that severe thrombophilia is a multigenetic disease. Easy functional and genetic tests for inherited APC-resistance will profoundly influence the development of prophylactic regimens and hopefully result in a decreased incidence of thrombosis.     

Factor V Leiden and other coagulation factor mutations affecting thrombotic risk

Five genetic defects have been established as risk factors for venous thrombosis. Three are protein C, protein S, and antithrombin deficiencies, defects in the anticoagulant pathways of blood coagulation. Together they can be found in approximately 15% of families with inherited thrombophilia. Their laboratory diagnosis is hampered by the large genetic heterogeneity of these defects. The other two genetic risk factors, resistance to activated protein C associated with the factor V Leiden mutation and increased prothrombin associated with the prothrombin 20210 A allele, are much more prevalent and together can be found in 63% of the thrombophilia families. Because both defects are caused by a single mutation, DNA analysis is the basis of their laboratory diagnosis.     

Geographic distribution of the 20210 G to A prothrombin variant

A variant in prothrombin (clotting factor II), a G to A transition at nucleotide position 20210, has recently been shown to be associated with the prothrombin plasma levels and the risk of both venous and arterial thrombosis. The purpose of this study was to investigate the prevalence of carriership of this mutation in various populations. We combined data from 11 centres in nine countries, where tests for this mutation had been performed in groups representing the general population. We calculated an overall prevalence estimate, by a precision-weighted method, and, since the distribution of the prevalences did not appear homogeneous, by an unweighted average of the prevalences. We examined differences in the prevalences by geographical location and ethnic background as a possible explanation for the heterogeneity. Among a total of 5527 individuals who had been tested, 111 heterozygous carriers of the 20210A mutation were found. The prevalence estimates varied from 0.7 to 4.0 between the centres. The overall prevalence estimate was 2.0 percent (CI95 1.4-2.6%). The variation around the summary estimate appeared more than was expected by chance alone, and this heterogeneity could be explained by geographic differences. In southern Europe, the prevalence was 3.0 percent (CI95 2.3 to 3.7%), nearly twice as high as the prevalence in northern Europe (1.7%, CI95 1.3 to 2.2%). The prothrombin variant appeared very rare in individuals from Asian and African descent. The 20210A prothrombin variant is a common abnormality, with a prevalence of carriership between one and four percent. It is more common in southern than in northern Europe. Since this distribution within Europe is very different to that of another prothrombotic mutation (factor V Leiden or factor V R506Q), founder effects are the most likely explanation for the geographical distribution of both mutations.     

The prevalence of factor V Leiden (1691 G-->A) mutation in Turkey

Resistance to activated protein C (APC), which is caused by a single point mutation in the gene for factor V, is a common risk factor for thrombosis. In this study, we screened factor V (FV) Leiden mutation in 81 subjects. The mutation in the heterozygous form was found in 7.1 percent of our normal population. This high frequency suggests that screening for the FV mutation should be considered in patients with a family history of thrombosis.     

Genetic susceptibility to pregnancy-related venous thromboembolism: roles of factor V Leiden, prothrombin G20210A, and methylenetetrahydrofolate reductase C677T mutations

OBJECTIVE: This study's objective was to evaluate the association between venous thromboembolism during pregnancy and the postpartum period and the factor V Arg 506 Gln (factor V Leiden), the prothrombin G20210A, and methylenetetrahydrofolate reductase C677T polymorphisms. STUDY DESIGN: In this case-control study 42 case patients and 213 control subjects (parous age-matched women without history of thrombosis) were genotyped for all the polymorphisms. Moreover, antiphospholipid antibodies and protein C, protein S, and antithrombin III deficiencies were investigated in each case. RESULTS: Ten case patients (23.8%) and 4 control subjects (1.9%; odds ratio 16.3, 95% confidence interval 4.8-54.9) carried the factor V Leiden mutation; 13 case patients (31.0%) and 9 control subjects (4.2%; odds ratio 10.2, 95% confidence interval 4.0-25.9) were carriers of the prothrombin G20210A allele. Finally, 12 case patients (28.6%) and 34 control subjects (16.0%; odds ratio 2.1, 95% confidence interval 1.0-4.5) were homozygotes for methylenetetrahydrofolate reductase C677T. Overall, mutations were found in 25 case patients (59.5%) and 47 control patients (22.2%; odds ratio 5.2, 95% confidence interval 4.9-19.6). One patient carried the antithrombin III deficiency and 1 the protein S deficiency, whereas 2 women had a primary antiphospholipid syndrome. CONCLUSIONS: The significant risk estimates of having a pregnancy-related venous thromboembolism in the presence of the prothrombotic genetic risk factors analyzed suggest to screen for these mutations women with a personal history of thromboembolic events during pregnancy or the postpartum period.     

Inherited prethrombotic disorders and infectious purpura

Patients with severe meningococcal infection are characterized by extensive microvascular thrombosis, consumption coagulopathy and secondary hemorrhages. The contribution of the inherited prethrombotic disorders to the severity of the disease course is not established yet. Here, we report on the levels of protein C, protein S, antithrombin and the presence of the factor V Leiden mutation (R506Q) in 50 patients with meningococcal disease, as determined 6 to 58 months after hospital discharge. In addition, we recalled the parents of 16 deceased patients to screen for the mutation in factor V, an abnormality which results in resistance to activated protein C. Among the patients, the prevalence of the genetic risk factors for thrombosis was not higher than expected on the basis of their prevalence in the general population. Moreover, the prevalence of the factor V Leiden mutation was not increased among the parents of the deceased patients. The individual plasma levels of protein C, protein S, and antithrombin did not differ between the patients with or without severe purpura. The present data constitute circumstantial evidence that primary defects in the natural anticoagulant systems do not play a major role in the severity of the disease course. Screening of patients with infectious purpura for inherited thrombotic risk factors is therefore not indicated.     

Factor V Leiden and genetic defects of thrombophilia in childhood porencephaly

AIMS: To determine to what extent the Arg506 to Gln point mutation in the factor V gene and further genetic factors of thrombophilia affect the risk of porencephaly in neonates and infants. METHODS: The Arg506 to Gln mutation, factor V, protein C, protein S, antithrombin, antiphospholipid antibodies and lipoprotein (a) (Lp(a)) were retrospectively measured in neonates and children with porencephaly (n = 24). RESULTS: Genetic risk factors for thrombophilia were diagnosed in 16 of these 24 patients: heterozygous factor V Leiden (n = 3); protein C deficiency type I (n = 6); increased Lp (a) (n = 3); and protein S type I deficiency (n = 1). Three of the 16 infants had two genetic risk factors of thrombophilia: factor V Leiden mutation combined with increased familial Lp (a) was found in two, and factor V Leiden mutation with protein S deficiency type I in one. CONCLUSIONS: The findings indicate that deficiencies in the protein C anticoagulant pathway have an important role in the aetiology of congenital porencephaly.     

Factor V Leiden: who should be tested?

Resistance to activated protein C resulting from the genetic point mutation known as factor V Leiden is the most frequently found genetic risk factor associated with familial predisposition to venous thrombosis. Factor V Leiden is also frequent among people with nonfamilial venous thrombosis and appears to have a relatively high prevalence rate in the general population. The author comments on the findings of the first Canadian prevalence study of factor V Leiden, reported in this issue by Dr. David H. Lee and associates (see pages 285 to 289). She notes that although certain hereditary and clinical variables are known to modulate the risk of venous thrombosis in people with factor V Leiden, explanations for the relatively high prevalence of this mutation and the wide spectrum of risk associated with it are still speculative. Management guidelines for affected patients are quickly evolving but are still limited by a lack of clinical data. It is clear that further research into factor V Leiden will have considerable importance for the understanding and management of thrombotic risk.     

Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families

Deficiency of the naturally occurring anticoagulant proteins, such as antithrombin, protein C and protein S, and activated protein C resistance due to the factor V Leiden gene mutation is associated with inherited thrombophilia. So far, no direct comparison of the thrombotic risk associated with these genetic defects is available. In this study, we wish to compare the lifetime probability of developing thrombosis, the type of thrombotic symptoms, and the role of circumstantial triggering factors in 723 first- and second-degree relatives of 150 index patients with different thrombophilic defects. We found higher risks for thrombosis for subjects with antithrombin (risk ratio 8.1, 95% confidence interval [CI], 3.4 to 19.6), protein C (7.3, 95% CI, 2.9 to 18.4) or protein S deficiency (8.5, 95% CI, 3. 5 to 20.8), and factor V Leiden (2.2, 95% CI, 1.1 to 4.7) than for individuals with normal coagulation. The risk of thrombosis for subjects with factor V Leiden was lower than that for those with all three other coagulation defects (0.3, 95% CI, 0.1 to 1.6), even when arterial and superficial vein thromboses were excluded and the analysis was restricted to deep vein thrombosis (0.3, 95% CI, 0.2 to 0.5). No association between coagulation defects and arterial thrombosis was found. The most frequent venous thrombotic manifestation was deep vein thrombosis with or without pulmonary embolism (90% in antithrombin, 88% in protein C, 100% in protein S deficiency, and 57% in factor V Leiden), but a relatively mild manifestation such as superficial vein thrombosis was common in factor V Leiden (43%). There was a predisposing factor at the time of venous thromboembolism in approximately 50% of cases for each of the four defects. In conclusion, factor V Leiden is associated with a relatively small risk of thrombosis, lower than that for antithrombin, protein C, or protein S deficiency. In addition, individuals with factor V Leiden develop less severe thrombotic manifestations, such as superficial vein thrombosis.     

Clinical studies and thrombin generation in patients homozygous or heterozygous for the G20210A mutation in the prothrombin gene

A genetic variation in the prothrombin gene, the G-->A transition at nucleotide 20210, is a risk factor for venous thrombosis in heterozygotes and is associated with increased prothrombin activity. The homozygous phenotype and the extent of thrombin generation in heterozygous and homozygous subjects are unknown. We investigated a family that included 2 homozygous and 5 heterozygous carriers of the 20210 A allele. The homozygous propositus and his presumably heterozygous father suffered from deep-vein thrombosis. His presumably heterozygous mother and his homozygous sister had recurrent phlebitis at a young age. The remaining 5 affected family members are still asymptomatic. We studied thrombin generation in the family and in 22 unrelated carriers of the 20210 A allele by measuring (1) prothrombin fragment F1+2 (F1+2) as an index of ongoing thrombin generation and (2) the endogenous thrombin potential (ETP) as an index of the possible thrombin-forming capacity. Their F1+2 levels were not different from those of age-matched controls, and thus, ongoing hemostatic system activation was not detectable. A significantly increased ETP was found in the heterozygous carriers of the 20210A allele compared with the controls (527.8+/-114.9 versus 387+/-50.1 nmol/L x min, P<0.0001). In the 2 homozygotes, the ETP was almost twice (639 and 751 nmol/L x min, respectively) as high as in the controls. We conclude that homozygosity for the G20210A mutation in the prothrombin gene is associated with a severe, albeit more benign, thrombotic diathesis compared with homozygosity for deficiencies of antithrombin, protein C, or protein S. In carriers of the 20210 A allele, the pathomechanisms leading to thrombosis should be sought in the higher amounts of thrombin that may be formed once thrombin generation is triggered, rather than in ongoing thrombin generation in vivo.     

Intrathecal vincristine: an analysis of reasons for recurrent fatal chemotherapeutic error with recommendations for prevention

Activated protein C (APC) is a naturally occurring anticoagulant that interacts with factor V and VIII to inhibit the clotting cascade. The prevalence of APC resistance among Korean patients with deep vein thrombosis is ill defined. The aim of the present study was to investigate the prevalence of APC resistance and factor V Leiden mutation in Korean patients with deep vein thrombosis. The presence of factor V Leiden mutation was determined in 49 patients who visited Asan Medical Center. APC ratio was performed in 33 individuals from the above 49 patients. Three patients were excluded from the analysis because their baseline aPTT was prolonged. Resistance to APC was diagnosed when the APC ratio was below 2.55. APC resistance was documented in 8 individuals, representing 27% (8/30) of the patients on whom APC resistance test was performed. The 2 patients, who showed APC resistance, were positive for lupus anticoagulant. None of the 49 patients demonstrated factor V Leiden mutation. These findings indicate that factor V Leiden mutation is rare and APC resistance is less prevalent in Korean patients with deep vein thrombosis than in Caucasians. APC resistance not caused by factor V Leiden mutation may be a risk factor for deep vein thrombosis in this population.     

Angiographic embolization of intrahepatic arterioportal fistula

BACKGROUND: Patients with venous thromboembolic disease may present with different clinical manifestations. Factor V Leiden mutation leading to resistance to activated protein C is associated with a sevenfold increased risk for presenting with deep-vein thrombosis. It is not yet established whether carriers of the mutation have a similarly increased risk for manifesting with pulmonary embolism. METHODS: From an Anticoagulation Clinic monitoring coumarin therapy, a consecutive series of patients with a first thromboembolic event (objectively proven by current radiological methods) were enrolled. All patients were interviewed and blood was drawn for genotyping. From the hospital charts and the personal interview, information was obtained on acquired risk factors and the signs and symptoms on hospital admission. RESULTS: 45 patients presented with symptoms of pulmonary embolism only, 211 had only symptoms of deep-vein thrombosis whereas 23 had clinical features of both. In about half of the patients acquired risk factors for venous thromboembolism were present which did not differ between the three groups of patients. Recent surgery had been performed more often in patients presenting with pulmonary embolism than in other patients (33.3% vs. 18.5%, p < 0.05). Factor V Leiden was present in 9% of the patients presenting with pulmonary embolism (relative risk: 3.3 95% CI: 1.0-10.6) and 17% of the patients presenting with deep-vein thrombosis (relative risk: 6.9 95% CI: 3.6-12.8). The prevalence of factor V Leiden was intermediate in patients with both clinical characteristics. CONCLUSION: These data suggest that patients with venous thromboembolism have different clinical presentation depending on the risk factor profile. Factor V Leiden may preferentially lead to manifest deep-vein thrombosis. Differences in structure of venous thrombi could underlie differences in embolic tendency.