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.     

Thrombophilia and inflammatory bowel disease: does factor V mutation have a role?

BACKGROUND: An increased tendency for thromboembolism is a well known problem of inflammatory bowel disease (IBD). Microvascular thrombosis has also been claimed as a pathogenic factor in IBD. Recently a point mutation in the gene coding factor V (FV Leiden) has been identified in various thromboembolic diseases, but the role in IBD is unknown. OBJECTIVE: To determine the frequency of FV Leiden in IBD patients and compare with a group of controls. METHODS: Sixty-three IBD patients [43 ulcerative colitis (UC) patients and 20 Crohn's disease (CD) patients] and 36 healthy controls were included in the study. Only one of the UC patients had a history of cerebral thromboembolism. The extracted DNA from frozen blood was subjected to polymerase chain reaction for the amplification of FV gene. The amplicons were hybridized both with the mutant and wild-type probes to detect FV mutation. Readings of optical density above 0.3 were considered as positive results. According to the patterns of ELISA, heterozygosity and homozygosity for normal and mutant alleles were determined. RESULTS: Eight (18%) of UC patients were heterozygous normal and one (2%) patient had homozygous mutation. Eight (45%) of the 20 CD patients had a heterozygous pattern and one (5%) had a homozygous pattern. In the control group four (11%) subjects showed a heterozygous genotype. FV Leiden was found to be statistically more frequent in CD patients (P < 0.005) (odds ratio 6.5, 95% confidence interval 1.3-18.), but not in the UC patients as compared with controls (P> 0.05). There was no significant correlation between FV Leiden presence and disease activity, gender or disease duration for both UC and CD. CONCLUSION: The results suggest that FV Leiden is more frequent in CD patients, but not in the UC patients as compared with controls. The high rate of factor V mutation in our CD patients suggests the need for further studies to confirm a relationship between this mutation and aetiology of the disease.     

Factor V Leiden mutation is a risk factor for cerebral venous thrombosis: a case-control study of 55 patients

BACKGROUND and PURPOSE: Different coagulation disorders have been associated with cerebral venous thrombosis (CVT). Until now, fewer than 50 patients have been reported with CVT and the factor V Leiden (FVL) mutation. Although the prevalence of FVL-positive patients with CVT ranged from 10% to 25%, it was as low as 0.5% to 3% in the control groups. Most other studies had not systematically searched for concomitant risk factors or previous thromboembolic events. To better define the relevance of the FVL mutation in conjunction with additional risk factors in CVT, we conducted the present case-control study. METHODS: Fifty-five patients with CVT were compared with 272 healthy controls. A standardized interview regarding established risk factors for venous thrombosis and the patients' and their families' histories for thromboembolic events was performed. The presence of the FVL mutation was determined by polymerase chain reaction on DNA obtained from peripheral blood leukocytes. RESULTS: Of 55 patients, 8 (14.5%) were heterozygous for the FVL mutation compared with 17 of 272 controls (6.25%). The relative risk for the presence of FVL was 2.55 (95% confidence interval, 1.04 to 6.26; P=0.04). Additional risk factors for CVT were frequently found in both the presence and absence of FVL. Recurrence of venous thromboembolic events was more frequent in patients with the FVL mutation (5 of 8 patients, 62.5%) than in those without this anomaly (8 of 47 patients, 17%; P<0.005). CONCLUSIONS: Our study confirms the FVL mutation as the most relevant hereditary risk factor for CVT. Coexisting risk factors are usually involved in the initiation of CVT. Patients with the FVL mutation are at an increased risk for recurrent venous thrombosis.     

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.     

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.     

Association of factor V Leiden with Beh?et's disease

OBJECTIVE: Studies show an association between factor V Leiden and venous thrombosis. Since venous thrombosis is common in Beh?et's disease (BD), we looked for an association between thrombosis in BD and the presence of factor V Leiden. METHODS: Twenty-three patients with BD according to International Study Group criteria and 22 patients with rheumatoid arthritis by American College of Rheumatology criteria as controls participated in the study. Patients with BD and controls were tested for the presence of factor V Leiden by polymerase chain reaction (PCR) amplification of genomic DNA and by restriction enzymatic analysis of PCR products. RESULTS: Three of 23 patients with BD were positive for factor V Leiden (13%). Among BD patients without thrombosis 0/15 were positive; among those with thrombosis 3 of 8 were positive (37.5%) for factor V. Only one patient with RA was positive for factor V Leiden. CONCLUSION. The presence of factor V Leiden in patients with BD may markedly increase the risk of thrombosis.     

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 mutation Ala677-->Val in the methylene tetrahydrofolate reductase gene: a risk factor for arterial disease and venous thrombosis

Mild hyperhomocysteinemia has been identified as a risk factor for arterial disease and for venous thrombosis. Individuals homozygous for the thermolabile variant of the methylene tetrahydrofolate reductase gene (MTHFR) which results from a common mutation Ala677-->Val and is found in 5-15% of the general population, have significantly elevated plasma homocysteine levels and may account for one of the genetic risk factors in vascular disease. We have analyzed the prevalence of MTHFR-T homozygotes in patients with arterial disease or venous thrombosis. We studied 191 patients with arterial disease and 127 individuals with venous thrombosis and compared with 296 unmatched controls. The results showed that there was a high prevalence of homozygotes for the mutated MTHFR-T allele among a group of patients with arterial disease (19%) in the absence of hyperlipoproteinemia, hypertension, and diabetes mellitus when compared to controls (4%), odds ratio of 5.52 (95% C.I., 2.27 to 13.51). The prevalence of homozygotes among patients with venous thrombosis was 11%, odds ratio of 2l93 (95% C.I., 1.23 to 7.01). The risk of venous thrombosis remained high, odds ratio of 2.63, even after we excluded 27 patients with hereditary thrombophilia (e.g. factor V Leiden, dysfibrinogenemia, deficiency of protein C, protein S, antithrombin III, or factor XII) from the 127 overall cases with venous thrombosis. These data support the hypothesis that being a homozygote for the MTHFR-T is a risk factor for the development of arterial disease and also for venous thrombosis.     

Case-control study of risk of cerebral sinus thrombosis in oral contraceptive users and in [correction of who are] carriers of hereditary prothrombotic conditions. The Cerebral Venous Sinus Thrombosis Study Group

OBJECTIVE: To investigate whether users of oral contraceptives and in [corrected] carriers of a hereditary prothrombotic condition (factor V Leiden mutation, protein C, S, or antithrombin deficiency) have an increased risk of cerebral sinus thrombosis. DESIGN: Comparison of a prospective series of cases of cerebral sinus thrombosis with population data. SETTING: Neurological teaching hospitals from different regions in the Netherlands (cases) and a representative sample of the non-institutionalised Dutch population (controls). SUBJECTS: 40 women aged 18-54 years with cerebral sinus thrombosis (cases) and 2248 women aged 18-49 years (controls). MAIN OUTCOME MEASURE: Current use of oral contraceptives at the time of the thrombosis (cases) or at the time of the questionnaire (controls). Prevalences of a hereditary prothrombotic condition in patients and in the population with odds ratios. RESULTS: 34 of 40 (85%) women with cerebral sinus thrombosis used oral contraceptives, versus 1007 of 2248 (45%) of the control women; the age adjusted odds ratio was 13 (95% confidence interval 5 to 37). Seven of 36 patients (19%) had a prothrombotic deficiency, versus 7% expected in the population; this corresponds to a threefold to fourfold increase in risk. In women who used oral contraceptives and also carried a prothrombotic defect, the odds ratio for cerebral sinus thrombosis was about 30 relative to women who had neither risk factor. CONCLUSION: The use of oral contraceptives and being a carrier of a hereditary prothrombotic condition increase the risk of and interact in a multiplicative way in the development of cerebral sinus thrombosis.     

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.     

Mechanical thrombolysis of acute occlusion of both the superficial and the deep femoral arteries using a thrombectomy device

Substantial evidence suggests that thrombosis contributes to the pathogenesis of primary pulmonary hypertension (PPH). An abnormal factor V (factor V Leiden) may contribute to thrombosis in the pulmonary microcirculation of PPH patients. A point mutation in which adenine is substituted for guanine at nucleotide 1691 (1691A) alters factor V so that it resists cleavage by activated protein C. Heterozygosity for the 1691A mutation is more common (2-8%) in Caucasian Europeans and Americans than in Africans (1%) and Asians (<1%). The aim of the study was to examine the prevalence of the mutation that codes for factor V Leiden in individuals with PPH. We identified 42 Caucasians diagnosed with PPH. We extracted deoxyribonucleic acid (DNA) from whole blood and assayed DNA samples for the point mutation (1691 A) that codes for factor V Leiden. One out of 42 (2.4%; 95% confidence interval=0.1-12.6) Caucasians diagnosed with PPH was heterozygous for the normal 1691G and mutant 1691A allele. All 10 individuals with familial PPH were homozygous for the normal 1691G allele. The prevalence of heterozygosity for the 1691A allele and the normal 1691G allele does not differ from that observed in reference (control) populations. The low prevalence of the 1691A mutation among individuals diagnosed with primary pulmonary hypertension provides evidence that factor V Leiden does not contribute to the pathogenesis of the disease in most patients.     

Interaction between oral contraceptive use and coagulation factor levels in deep venous thrombosis

Deep venous thrombosis is a multicausal disease, i.e. more than one risk factor needs to be present to cause the disease. Oral contraceptive use increases the risk of venous thrombosis but since not all women using oral contraceptives develop thrombosis, the presence of additional risk factors in patients is likely. The aim of this study was to assess the joint effect of oral contraceptive use and the levels of procoagulant factors (F)(FII, FV, FVII, FVIII, FIX, FX, FXI, FXII, FXIII and fibrinogen). Data of premenopausal women were re-analyzed in the Leiden Thrombophilia Study. The highest relative risks were observed for the combination of oral contraceptive use and high levels (>90th percentile) of FII (Odds Ratio [OR]OC+FII 10.1; 95% confidence interval [CI] 3.5-29.0), FV (OROC+FV 12.6; 95% CI 3.8-41.5), and FXI (OROC+FXI 11.9; 95% CI 3.6-39.2) and low levels (< 10th percentile) of FXII (OROC+FXII 12.3; 95% CI 2.4-63.0). No interaction was observed between oral contraceptive use and high levels of the other coagulation factors, i.e. the joint effect of these risk factors did not exceed the sum of the separate effects. The results of this study indicate that the risk for the joint effects of oral contraceptive use and coagulation factor levels are minor compared with the joint effect of oral contraceptive use and the FV Leiden mutation (RR > 30).     

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.     

Uterine rhabdomyosarcoma metastatic to mediastinal lymph nodes: diagnosis by transbronchial needle aspiration

An inherited tendency to hypercoagulability has been suggested as a cause of vascular thrombosis resulting in Legg-Calvé-Perthes disease (LCPD). Here we carried out an investigation of the most common inherited risk factors for hypercoagulability including the mutation in the factor V gene (factor V Leiden), the transition 20.210G-->A in the prothrombin gene, and also the homozygosity for the 677C-->T transition in the methylenetetrahydrofolate reductase gene (MTHFR). The investigation was carried out among 61 Brazilian children with LCPD, who were compared with 296 individuals from the general population. The prevalence of the factor V Leiden mutation was higher in LCPD patients than in the controls (4.9 vs. 0.7%; p = 0.03). However, no patient had the prothrombin gene variant, and no difference was found between patients and controls when homozygosity for MTHFR-T (3.2 vs. 2.6%: p = 0.64) was determined. These data suggest that in our population, the heterozygosity for factor V Leiden was the only inherited risk factor associated with the development of LCPD.     

Risk of venous thromboembolism associated with a G to A transition at position 20210 in the 3'-untranslated region of the prothrombin gene

The odds ratio for the FII 20210G/A mutation in 504 patients with venous thromboembolism compared to controls was 2.0 (95% CI 1.0-4.0) and, for factor V Leiden, 5.8 (95% CI 3.3-10.3). 3/504 patients were heterozygous for both mutations. None of the patients had combined natural anticoagulant deficiency and the FII 20210G/A mutation. We conclude that the FII 20210G/A mutation is present in 2.6% of the population and the relative risk of venous thromboembolism in carriers is 2.0.     

A common mutation in the methylenetetrahydrofolate reductase gene (C677T) increases the risk for deep-vein thrombosis in patients with mutant factor V (factor V:Q506)

Hyperhomocysteinemia is a frequent risk factor for deep-vein thrombosis. A common mutation (C677T) in the gene encoding for methylenetetrahydrofolate reductase (MTHFR) is responsible, in the homozygous state, for decreased enzyme activity and mild hyperhomocysteinemia and is associated with increased risk for cardiovascular disease. We studied the prevalence of C677T MTHFR in 77 patients with deep-vein thrombosis and in 154 age- and sex-matched healthy control subjects. In the same individuals, we also evaluated the frequency of the coexistence of C677T MTHFR with mutant factor V:Q506, a common risk factor for deep-vein thrombosis. Sixteen patients (20.8%) and 35 control subjects (22.7%) were homozygous for the C677T MTHFR mutation (odds ratio [OR] = 0.8, 95% confidence interval [CI] = 0.4-2.0). Sixteen patients (20.8%) and 4 control subjects (2.6%) had factor V:Q506; of them, 10 patients and 3 control subjects had isolated factor V:Q506 (adjusted OR = 6.3, 95% CI = 1.6-25.3) and 6 patients and 1 control subject also had C677T MTHFR (adjusted OR = 17.3, 95% CI = 2.0-152.9). The OR for the coexistence of the two mutations was 65% to 75% higher than the expected joint effect calculated by either an additive (OR = 6.0) or multiplicative (OR = 4.4) model. The homozygous C677T mutation of MTHFR per se is not a risk factor for deep-vein thrombosis but increases the risk associated with factor V:Q506. Due to the high prevalence of C677T MTHFR, it is likely that previous studies, which did not look for this mutation, overestimated the relative risk of thrombosis associated with factor V:Q506 alone.     

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 (G1691A), the prothrombin 3'-untranslated region variant (G20210A) and thermolabile methylenetetrahydrofolate reductase (C677T): a single genetic test genotypes all three loci--determination of frequencies in the S. Wales population of the UK

Simultaneous genetic diagnosis of factor V (FV) Leiden (G1691A), the prothrombin variant (G20210A) and the thermolabile methylenetetrahydrofolate reductase (MTHFR) variant (C677T) has been achieved using multiplex heteroduplex analysis. All three loci are amplified in a single polymerase chain reaction (PCR) containing test DNA and three heteroduplex generators, respectively detecting the three nucleotide substitutions. After PCR, the products are analysed directly without further manipulation and the resulting heteroduplex profiles permit straightforward interpretation of the respective genotypes. The multiplex test has been used to assess the prevalence and allele frequency of each of the three nucleotide substitutions in 300 individuals (150 males and 150 females) from the local (S. Wales) population. A prevalence of 8% and an allele frequency of 0.040 +/- 0.015 (95% confidence interval) was obtained for FV Leiden; the prothrombin variant showed a prevalence of 1% and an allele frequency of 0.007 +/- 0.006 (95% confidence interval); the MTHFR mutation showed a prevalence of 60% and an allele frequency of 0.377 +/- 0.039 (95% confidence interval). This method is applicable to investigation of large cohorts of patients with arterial or venous thrombotic disease.