Premature ischaemic heart disease and the gene for coagulation factor V

State-of-the-Art Review: Activated Protein C Resistance: Clinical Implications

The discovery of inherited resistance to activated protein C (APC) as a major risk factor for venous thrombosis has dramatically improved our understanding of the pathogenesis of venous thrombosis. In a majority of cases, APC resistance is associated with a single point mutation in the factor V gene (FV) that results in substitution of arginine, R, at position 506 by glutamine, Q. (FV:Q506). The mutation renders factor Va partially resistant to degradation by APC. A functional APC resistance test, which includes predilution of the patient plasma with factor V-deficient plasma, is found to be 100% sensitive and specific for the presence of FV:Q506and is useful as a screening assay. Carriers of the FV:Q506allele have increased thrombin generation, resulting in hypercoagulability and a lifelong increased risk of venous thrombosis. In Western countries, APC resistance due to the FV mutation is present in 20-60% of thrombosis patients and in 1-15% of healthy controls, whereas the mutation is virtually absent from ethnic groups other than Caucasians. This may explain the high incidence of venous thrombosis in Western countries. The thrombotic risk in APC-resistant individuals may be further increased by other genetic defects, e.g., protein C or protein S deficiency, and by exposure to circumstantial risk factors, e.g., oral contraceptives, pregnancy, immobilization, and surgery. The question is thus raised as to whether general screening for APC resistance before circumstantial risk factors occur is warranted in Western countries. Key Words: Factor V—APC resistance-Protein C-Protein S—Thrombosis—Mutation.

Factor VLeiden and prothrombin G20210A gene polymorphisms in patients with coronary artery disease

PURPOSE

The precise molecular mechanisms culminating in coronary artery disease (CAD) are not well understood, despite a wealth of knowledge on predisposing risk factors and pathomechanisms. CAD and myocardial infarction (MI) are complex genetic diseases; neither the environment alone, nor a single gene, cause disease, rather, a mix of environmental and genetic factors lead to atherosclerosis of the coronary arteries.

MATERIALS AND METHODS

In the present study, our aim was to investigate the roles of prothrombin G20210A mutation and Factor VLeiden mutation in atherosclerotic coronary artery disease. 287 subjects (106 control subjects, who were angiographically normal, and 181 angiographically documented coronary atherosclerotic patients who exhibited coronary artery narrowing to a degree of >or=50%) were included in this study. The mutations were assessed with LightCycler Real-Time PCR mutation detection kits (Roche Diagnostics, GmbH, Germany).

RESULTS

6.6% of control subjects, and 6.1% of patients with (50% coronary artery narrowing were determined to have the Factor VLeiden heterozygote mutation. 6.6% of control subjects had the Prothrombin G20210A heterozygote mutation, while 7.7% of patients with (50% coronary artery narrowing had this mutation. The OR for Factor VLeiden was 1.52 (CI: 0.240-9.602) and for Prothrombin G20210A mutation, the OR was 1.415 (CI: 0.287-6.962).

CONCLUSION

Although both the heterozygote Factor VLeiden and Prothrombin gene mutations were more frequent in patients with CAD than in control subjects, there was no statistical relationship found to exist between coronary artery disease and the Factor VLeiden and Prothrombin G20210A mutations.

Homozygous factor V Leiden mutation in two siblings presenting with acute myocardial infarction: a rare cause of myocardial infarction in the young

Although factor V Leiden mutation, is the most common established genetic risk factor for venous thrombosis, its effect on the development of myocardial infarction remains unclear. We describe a family case of homozygous factor V Leiden mutation in two siblings presenting with acute myocardial infarction as a rare cause of myocardial infarction in the young.

The haematology of indigenous Australians

Prior to European settlement indigenous Australians were hunter-gatherers who lived in geographically isolated small clan groups, also separated by elaborate totemic rules. Today they still reside in isolated communities throughout Australia but many have moved to the cities. They share a high incidence of a range of health problems including cardiovascular disease, renal disease and infectious diseases largely attributed to a change to a more sedentary lifestyle. This paper reviews the haematology of indigenous Australians, including blood count, frequency and causes of anaemia, inherited risk factors for thrombophilia, blood groups and the incidence and types of haematological malignancies. There are some significant genetic differences between indigenous and non-indigenous Australians particularly in the frequency of blood groups, factor V Leiden and prothrombin mutations and presence of -alpha3.7 kb thalassaemia. These findings may have practical therapeutic implications (e.g. HPA phenotype for transfusion therapy and pregnancy risk) and in predicting disease risk. Other differences are acquired, related to lifestyle and living conditions (e.g. eosinophilia secondary to parasitic infections; iron and folate deficiencies), and are largely preventable.

Prevalence of resistance against activated protein C resulting from factor V Leiden is significantly increased in myocardial infarction: investigation of 507 patients with myocardial infarction

BACKGROUND

A point mutation in the gene encoding coagulation factor V is a cause of resistance against activated protein C. The presence of factor V Leiden is linked to 50% of congenital defects causing venous thrombosis. Its relationship to arterial thrombosis, particularly to myocardial infarction, has not been defined. Therefore, we performed a study on the role of factor V Leiden in patients with myocardial infarction. The study was carried out in Bavarians of German origin, a relatively homogeneous population.

METHODS AND RESULTS

The study group consisted of 507 patients with documented myocardial infarction (77.5% (393/507) men, 22.5% (114/507) women), with a mean age of 56.1 (range 18-86) years. Strict criteria for patient selection and highly sensitive and specific functional tests for factor V Leiden were used. In addition, all patients with pathological test results were genotyped. The prevalence of factor V Leiden in patients with myocardial infarction was 8.7% (44/507), a significant increase in the prevalence of this mutation compared with the control group (3.7%, P =.0025). The odds ratio was 2.46 (95% CI 1.35-4.50).

CONCLUSIONS

A significantly increased prevalence of factor V Leiden in patients with documented myocardial infarction was seen. Patients with this mutation appear to have a predisposition for myocardial infarction.

Prothrombotic coagulation defects and cardiovascular risk factors in young women with acute myocardial infarction

We investigated the effect of prothrombotic coagulation defects in combination with smoking and other conventional risk factors on the risk of myocardial infarction in young women. In 217 women with a first myocardial infarction before the age of 50 years and 763 healthy control women from a population-based case-control study, factor V Leiden and prothrombin 20210A status were determined. Data on major cardiovascular risk factors and oral contraceptive use were combined with the presence or absence of these prothrombotic mutations, and compared between patients and controls. The overall odds ratio for myocardial infarction in the presence of a coagulation defect was 1.1 [95% confidence interval (CI) 0.6-1.9]. The combination of a prothrombotic mutation and current smoking increased the risk of myocardial infarction 12-fold (95% CI 5.7-27) compared with non-smokers without a coagulation defect. Among women who smoked cigarettes, factor V Leiden presence versus absence increased the risk of myocardial infarction by 2.0 (95% CI 0.9-4.6), and prothrombin 20210A presence versus absence had an odds ratio of 1.0 (95% CI 0.3-3.5). We conclude that factor V Leiden and prothrombin 20210A do not add substantially to the overall risk of myocardial infarction in young women. However, in women who smoke, the presence of factor V Leiden increased the risk of myocardial infarction twofold.

Combined carrier status of prothrombin 20210A and factor XIII-A Leu34 alleles as a strong risk factor for myocardial infarction: evidence of a gene-gene interaction

Studies associating the prothrombin 20210G>A (FII 20210A), factor V Leiden (FVL), and factor XIII Leu34 (FXIII-A Leu34) alleles with myocardial infarction (MI) have yielded conflicting results. Complicated gene-gene interactions, small sample sizes, and heterogeneous genetic and environmental backgrounds may contribute to opposing findings. Simultaneous analysis of multiple gene variants in a large sample size from a genetically isolated population may overcome these weaknesses. Genotyping was performed in 500 MI patients and 500 control subjects from the genetically isolated Newfoundland population to determine the prevalence of the FII 20210A, FVL, and FXIII-A Leu34 variants and their association with MI. Gene-gene interactions were also analyzed. The prevalence of the FII 20210A allele was higher in MI patients (3.2%) than in control subjects (1.0%; P =.015). The FII 20210A allele was also 5.6-fold higher in MI patients younger than 51 years than in age-matched control subjects (P =.04). FVL showed 3.9-fold higher prevalence in young patients than in patients older than 50 years (P =.004) and 2.7-fold higher than in age-matched control subjects (P =.007). Furthermore, the prevalence of combined carriers of the FXIII-A L34 and FII 20210A alleles was 12-fold higher in MI patients than in control subjects (P =.002) and with 92% penetrance. There was disequilibrium of the FXIII-A Leu34 allele to MI patients carrying the FII 20210A allele as a genetic background. Based on our data, we determined that (1) the FII 20210A allele is a risk factor for MI, possibly important for early onset; (2) FVL may predispose for early-onset MI; (3) the FXIII-A Leu34 allele predisposes for MI in males only; however, (4) interaction between the FII 20210A and FXIII-A Leu34 alleles forms a synergistic coeffect that strongly predisposes for MI, placing combined carriers at high risk for MI.

Factor V Leiden: The Copenhagen City Heart Study and 2 meta-analyses

Factor V Leiden (FVL) is associated with venous thrombosis; however, an association between FVL and arterial thrombosis remains controversial. We investigated FVL as a risk factor for myocardial infarction (MI), ischemic stroke (IS), or non-MI ischemic heart disease (non-MI-IHD). The design was 3 case-control studies and 3 prospective studies with 21 years' follow-up. The setting was the general population in Copenhagen, Denmark. The participants for The Copenhagen City Heart Study were 20- to 95-year-old participants without cardiovascular disease (control population, n = 7907) or participants diagnosed with MI (n = 469), IS (n = 231), or non-MI-IHD (n = 365). In addition, 3 independent patient populations from Copenhagen University Hospital with MI (n = 493), IS (n = 231), or non-MI-IHD (n = 448) were included. We measured FVL genotype; major cardiovascular risk factors; and MI, IS, and non-MI-IHD incidence and prevalence. Prevalences of FVL heterozygotes and homozygotes in control subjects from the general population were 7.7% and 0.2%. Odds ratios and relative risks of MI in FVL carriers (heterozygotes + homozygotes) versus noncarriers were 1.24 (95% confidence interval [CI], 0.91-1.69) and 0.83 (0.58-1.20) in case-control and prospective studies, respectively. Corresponding risks for IS were 0.92 (95% CI, 0.56-1.53) and 0.68 (0.45-1.04), and for non-MI-IHD 1.01 (95% CI, 0.71-1.44) and 0.97 (0.66-1.42). Findings from The Copenhagen City Heart Study suggest that FVL is not associated with MI, IS, or non-MI-IHD.

Interaction of hemostatic genetics with hormone therapy: new insights to explain arterial thrombosis in postmenopausal women

Genetic variants of key hemostatic mediators increasingly have been proposed as risk factors for atherothrombosis. The Hormone and Estrogen/Progestin Replacement Study group recently reported that the initiation of estrogen replacement in postmenopausal women with known coronary heart disease is associated with an early increase in cardiovascular events. A putative genetic susceptibility factor has been proposed a potential mediator of this increased event risk. This review outlines the recent literature to support the premise for this important proposal. Genetic profiling has great potential to improve the safety and efficacy of individualized pharmacotherapy in postmenopausal women and other at-risk populations for the prevention of cardiovascular disease.

Factor V(LEIDEN) and cardiopulmonary bypass: investigation of haemostatic parameters and the effect of aprotinin using an ex vivo model

It has been suggested that aprotinin results in significantly increased risk for perioperative thrombotic complications in patients with Factor V(LEIDEN) (F5L) due to its ability to competitively inhibit activated protein C (APC) function in vitro. No clinical studies have been performed to assess the effect of aprotinin on APC function of F5L in vivo. We developed an ex vivo model to mimic the effects of cardiopulmonary bypass with the exclusion of the patient in order to assess APC function. Blood from normal (n = 2) and F5L heterozygous donors (n = 2) was treated with aprotinin or placebo (saline). The blood was heparinized, added to the prime and circulated at 2 l/min through a modified cardiopulmonary bypass circuit. After 60 min of circulation, the heparin was neutralized with protamine sulfate. Blood samples, drawn at specific time points, were analysed for APC ratio. Results showed a decrease in APC ratio for both F5L and normal bloods with the addition of aprotinin (18% and 40%, respectively). APC ratios also decreased with the commencement of extracorporeal circulation for all bloods, resulting in an APC ratio of 1.35 in normal placebo-treated blood and 0.67 in F5L placebo-treated blood. The combined effect of aprotinin and extracorporeal circulation resulted in APC ratios of 0.90 for normal blood and 0.63 for F5L blood, corresponding to a severe dysfunction of APC intraoperatively (reference range 1.9-4.0). The data from this model predict an increased risk of perioperative thrombosis due to inhibition of APC function in cardiac surgical patients heterozygous for the F5L mutation. Aprotinin further compounds the severity of APC dysfunction, though the effect is more severe in normal blood. The ex vivo model employed was an effective tool for the investigation of the haemostatic effect of aprotinin. This model may be exploited for other applications such as the investigation of novel or emerging haemostatic agents prior to clinical trial.

Joint effect of G1691A factor V point mutation and factor VII Arg/Gln(353) gene polymorphism on the risk of premature coronary artery disease

The study sought an association between the G1691A factor V point mutation and factor VII Arg/Gln(353) gene polymorphism and premature coronary artery disease (CAD), and the interactive effect on CAD risk between the G1691A factor V point mutation and factor VII Arg/Gln(353) gene polymorphism as well as between tested polymorphisms and traditional risk factors. 167 patients with CAD younger than 55 years were compared with 132 healthy subjects. The frequency of factor V point mutation was 7.8 % among Slovene patients with premature CAD, and 4.5 % among controls. No association was found between either the factor V point mutation (AG genotype) or M1M1 genotype of factor VII Arg/Gln(353) gene polymorphism and the risk of CAD in Slovenia using univariate analysis (factor V point mutation: OR = 1.8, 95% CI = 0.7-4.9; p = 0.25; factor VII Arg/Gln(353) gene polymorphism: OR = 1, 95 % CI = 0.6-1.7; p = 0.9). However, a joint effect on the risk of CAD was found between factor V point mutation (AG genotype) and M1M1 genotype (OR = 3.6, 95 % CI = 1-12.9; p = 0.03). Additionally, an interactive effect on CAD risk was found between AG genotype and metabolic risk factors (OR = 3.8, 95% CI = 1.1-13.6; p = 0.03). In conclusion, we provide evidence for a joint effect on CAD risk between G1691A factor V point mutation and factor VII Arg/Gln(353) gene polymorphism as well as between factor V point mutation and metabolic risk factors.

DNA technology for the detection of common genetic variants that predispose to thrombophilia

With the identification of common single locus point mutations as risk factors for thrombophilia, many DNA testing methodologies have been described for detecting these variations. Traditionally, functional or immunological testing methods have been used to investigate quantitative anticoagulant deficiencies. However, with the emergence of the genetic variations, factor V Leiden, prothrombin 20210 and, to a lesser extent, the methylene tetrahydrofolate reductase (MTHFR677) and factor V HR2 haplotype, traditional testing methodologies have proved to be less useful and instead DNA technology is more commonly employed in diagnostics. This review considers many of the DNA techniques that have proved to be useful in the detection of common genetic variants that predispose to thrombophilia. Techniques involving gel analysis are used to detect the presence or absence of restriction sites, electrophoretic mobility shifts, as in single strand conformation polymorphism or denaturing gradient gel electrophoresis, and product formation in allele-specific amplification. Such techniques may be sensitive, but are unwielding and often need to be validated objectively. In order to overcome some of the limitations of gel analysis, especially when dealing with larger sample numbers, many alternative detection formats, such as closed tube systems, microplates and microarrays (minisequencing, real-time polymerase chain reaction, and oligonucleotide ligation assays) have been developed. In addition, many of the emerging technologies take advantage of colourimetric or fluorescence detection (including energy transfer) that allows qualitative and quantitative interpretation of results. With the large variety of DNA technologies available, the choice of methodology will depend on several factors including cost and the need for speed, simplicity and robustness.

Incidence of factor V Leiden in patients with acute myocardial infarction

The genetic defect of coagulation factor V known as factor V Leiden produces a resistance to degradation by activated protein C (APC) and increases the risk of venous thromboembolism. The data on arterial thrombosis associated with APC resistance are still not clearly defined. We conducted a study in patients presenting with acute myocardial infarction (MI) to assess whether factor V Leiden increases the risk of arterial thrombosis. We studied 109 patients who had a diagnosis of acute MI (69 males and 40 females, aged 25-91 years), and 112 controls. The study population was identified by characteristic ECG changes and elevation of serum CK-MB, whereas the control subjects were anonymous healthy blood donors with no known history of coronary artery disease. Blood samples from the patients and controls were analyzed for the factor V Leiden mutation by DNA analysis, using the polymerase chain reaction. Heterozygous factor V Leiden mutation was found in 9 of 109 (8%) MI patients and 5 of 112 (4%) control subjects (P =.42). In conclusion, this study shows no evidence of an association between factor V Leiden and acute MI.

Synergistic Effects of Prothrombotic Polymorphisms and Atherogenic Factors on the Risk of Myocardial Infarction in Young Males

Several recent studies evaluated a possible effect of the prothrombotic polymorphisms such as 5,10 methylenetetrahydrofolate reductase (MTHFR) nt 677C → T, factor V (F V) nt 1691G → A (F V Leiden), and factor II (F II) nt 20210 G → A on the risk of myocardial infarction. In the present study, we analyzed the effect of these prothrombotic polymorphisms, as well as apolipoprotein (Apo) E4, smoking, hypertension, diabetes mellitus, and hypercholesterolemia, on the risk of myocardial infarction in young males. We conducted a case-control study of 112 young males with first acute myocardial infarction (AMI) before the age of 52 and 187 healthy controls of similar age. The prevalences of heterozygotes for F V G1691A and F II G20210A were not significantly different between cases and controls (6.3% v 6.4% and 5.9% v 3.4% among cases and controls, respectively). In contrast, the prevalence of MTHFR 677T homozygosity and the allele frequency of Apo E4 were significantly higher among patients (24.1% v 10.7% and 9.4% v5.3% among cases and controls, respectively). Concomitant presence of hypertension, hypercholesterolemia, or diabetes and one or more of the four examined polymorphisms increased the risk by almost ninefold (odds ratio [OR] = 8.66; 95% confidence interval [CI], 3.49 to 21.5) and concomitant smoking by almost 18-fold (OR = 17.6; 95% CI, 6.30 to 48.9). When all atherogenic risk factors were analyzed simultaneously by a logistic model, the combination of prothrombotic and Apo E4 polymorphisms with current smoking increased the risk 25-fold (OR = 24.7; 95% CI, 7.17 to 84.9).The presented data suggest a synergistic effect between atherogenic and thrombogenic risk factors in the pathogenesis of AMI, as was recently found in a similar cohort of women.

Synergistic Effects of Prothrombotic Polymorphisms and Atherogenic Factors on the Risk of Myocardial Infarction in Young Males

Several recent studies evaluated a possible effect of the prothrombotic polymorphisms such as 5,10 methylenetetrahydrofolate reductase (MTHFR) nt 677C → T, factor V (F V) nt 1691G → A (F V Leiden), and factor II (F II) nt 20210 G → A on the risk of myocardial infarction. In the present study, we analyzed the effect of these prothrombotic polymorphisms, as well as apolipoprotein (Apo) E4, smoking, hypertension, diabetes mellitus, and hypercholesterolemia, on the risk of myocardial infarction in young males. We conducted a case-control study of 112 young males with first acute myocardial infarction (AMI) before the age of 52 and 187 healthy controls of similar age. The prevalences of heterozygotes for F V G1691A and F II G20210A were not significantly different between cases and controls (6.3% v 6.4% and 5.9% v 3.4% among cases and controls, respectively). In contrast, the prevalence of MTHFR 677T homozygosity and the allele frequency of Apo E4 were significantly higher among patients (24.1% v 10.7% and 9.4% v5.3% among cases and controls, respectively). Concomitant presence of hypertension, hypercholesterolemia, or diabetes and one or more of the four examined polymorphisms increased the risk by almost ninefold (odds ratio [OR] = 8.66; 95% confidence interval [CI], 3.49 to 21.5) and concomitant smoking by almost 18-fold (OR = 17.6; 95% CI, 6.30 to 48.9). When all atherogenic risk factors were analyzed simultaneously by a logistic model, the combination of prothrombotic and Apo E4 polymorphisms with current smoking increased the risk 25-fold (OR = 24.7; 95% CI, 7.17 to 84.9).The presented data suggest a synergistic effect between atherogenic and thrombogenic risk factors in the pathogenesis of AMI, as was recently found in a similar cohort of women.

Activated protein C resistance in patients with central retinal vein occlusion

AIM/BACKGROUND

A new defect in the anticoagulant system has recently been discovered--activated protein C resistance. The frequency of this disorder has been shown to be increased in young patients (< 50 years of age) with central retinal vein occlusion. This study was carried out to determine if there was any overrepresentation of activated protein C resistance in patients > 50 years of age with central retinal vein occlusion.

METHODS

Blood samples were obtained from 83 patients > 50 years of age and with a history of central retinal vein occlusion. The blood samples were analysed for activated protein C resistance with standard clinical laboratory methods.

RESULTS

In this material 11% of the patients were resistant to activated protein C. The normal incidence of activated protein C resistance in the same geographical area is 10-11%.

CONCLUSION

Activated protein C resistance does not seem to be a cause of central retinal vein occlusion in people older than 50 years.

Factor V Leiden (Resistance to Activated Protein C) Increases the Risk of Myocardial Infarction in Young Women

Factor V Leiden (factor V Arg506Gln), the genetic defect underlying resistance to activated protein C, is the most common risk factor for venous thrombosis. The relationship between this genetic abnormality and arterial disease is still unresolved. To assess whether factor V Leiden increases the risk of myocardial infarction (MI), we conducted a population-based case-control study among women 18 to 44 years of age in western Washington state. We included 84 women with first MI and 388 control women, ie, women residing in the same area in the same age range without MI (n = 388). The control women were contacted by random digit dialing. Data on risk factor status were collected via personal interview, and data on the factor V genotype via polymerase chain reaction techniques. The factor V Leiden mutation was found more often in women with MI (10%) than among controls (4%). The odds ratio for MI was 2.4 [95% confidence interval (CI) 1.0 to 5.9]. The risk was increased fourfold (CIgs 1.2 to 12.1) when adjusted for major cardiovascular risk factors. Among nonsmokers the factor V Leiden mutation had little effect (odds ratio 1.1, CI95 0.1 to 8.5), whereas it had a large effect among smokers (odds ratio 3.6, CI95 0.9 to 14.4), which, because smoking was itself a strong risk factor for MI, led to an odds ratio for smoking carriers of the mutation that was 32-fold increased compared with nonsmoking noncarriers. We conclude that factor V Leiden increases the risk of MI in young women. This effect seems to be confined largely to current smokers.

Mortality and Causes of Death in Families With the Factor V Leiden Mutation (Resistance to Activated Protein C)

To investigate whether resistance to activated protein C (APC resistance) because of a mutation in the factor V gene (factor V Leiden) leads to a decrease in life expectancy, we analyzed overall and cause-specific mortality in 171 parents whose offspring carried this mutation. Compared with the Dutch general population, and after adjustment for age, sex, and calendar period, we found no excess deaths in the parents (standardized mortality ratio [SMR], 1.0; 95% confidence interval [CI], 0.8 to 1.2). The cause-specific SMR for malignant neoplasms (1.0; 95% CI, 0.6 to 1.4), diseases of the circulatory system (1.0; 95% CI, 0.7 to 1.4), and cerebrovascular disease (1.0; 95% CI, 0.4 to 1.9) also did not differ from unity. The SMRs for diseases of the respiratory system (1.4; 95% CI, 0.6 to 2.6) and for ischemic heart diseases (1.1; 95% CI, 0.7 to 1.7) were slightly increased. Under the age of 45 years, there was a ninefold increase of dying from ischemic heart disease. Thromboembolic complications were mentioned only once (venous embolism or thrombosis) as an underlying (“primary”) cause of death (SMR, 2.3; 95% CI, 0.1 to 13.0) and three times (pulmonary embolisms) as a contributing (“secondary”) cause of death (SMR, 1.5; 95% CI, 0.3 to 4.4). We conclude that there is no major effect of APC resistance on life expectancy. Therefore, long-term anticoagulation in carriers of factor V Leiden, on the basis of the carrier state alone, is not indicated.

Activated protein C resistance due to a common factor V gene mutation is a major risk factor for venous thrombosis

Inherited resistance to activated protein C (APC) was recently discovered to be a cause of familial thrombophilia and is now known to be the most common genetic risk factor for venous thrombosis. It is caused by a single point mutation in the gene for factor V, which predicts substitution or arginine (R) at position 506 with a glutamine (Q). Accordingly, the activated form of mutated factor V (FVa:Q506) is more slowly degraded by activated protein C than normal FVa (FVa:R506) is, resulting in hypercoagulability and a lifelong 5- to 10-fold increased risk of venous thrombosis. Previously known inherited hypercoagulable states, i.e. deficiencies of the anticoagulant proteins antithrombin III, protein S, and protein C, are found fewer than 10-15% of thrombosis patients in western countries, whereas inherited APC resistance is present in 20-60% of such patients. The FV mutation is common in populations of Caucasian origin, with prevalences ranging from 1-15%, whereas it is not found in certain other ethnic groups such as Japanese and Chinese. The high prevalence of APC resistance, in combination with the availability of simple laboratory tests, will have a profound influence on the development of therapeutic and prophylactic regimens for thrombosis and will, it is hoped, result in a decreased incidence of thromboembolic events.

Clinical significance of the FV:Q506 mutation in unselected oncology patients

PURPOSE

A common germline mutation in the factor V gene (FV:Q506) has been associated with hypercoagulability in families with heritable predisposition to thrombosis. We examined the prevalence and clinical significance of the FV:Q506 mutation in cancer patients.

PATIENTS AND METHODS

We performed a retrospective cohort study by examining 353 consecutive, unselected patients in a general hematology/oncology clinic. We ascertained risk factors, obtained the clinical clotting history, and determined the heterozygous or homozygous presence of the FV:Q506 allele for each patient.

RESULTS

We detected a germline mutation in 5.4% (19 of 353) of patients, of whom 18 were heterozygous and 1 was homozygous for the FV:Q506 mutant allele. In 17 of 18 heterozygous patients, there was no history of venous thrombosis or catheter-associated thrombosis. These asymptomatic patients included 13 patients who had been diagnosed with cancer or leukemia for a mean of 66.2 months (median 69) and had received a variety of local and systemic treatments. In contrast, 1 of 18 heterozygous and 1 of 1 homozygous patients had developed deep vein thrombosis that was associated, respectively, with either recurrent thrombotic events or a strong family history for pulmonary embolus.

CONCLUSIONS

Routine screening for the FV:Q506 mutation in cancer patients without a personal or family history for venous thrombosis is not helpful in guiding management. In contrast, an episode of venous thrombosis in a patient with a mutant germline FV:Q506 allele was associated with recurrent thrombotic events. These findings suggest that patients heterozygous for the FV:Q506 allele may require an independent "susceptibility" element to manifest a venous hypercoagulable state. In addition, only 2 of 25 clinic patients with a venous clot carried the FV:Q506 allele suggesting this genetic defect plays a minor role in the hypercoagulable state of cancer.

Resistance to activated protein C: role in venous and arterial thrombosis

Activated protein C resistance is the most prevalent cause of thrombophilia: it is found in 20 to 30% of patients with a deep venous thrombosis history. Activated protein C resistance is due to an arginine 506 to glutamine mutation in factor V. This mutation prevents normal inactivation of activated factor V by activated protein C. The estimated increase in relative risk of venous thrombosis is 5- to 10-fold in heterozygotes, and 50- to 100-fold in homozygotes. Activated protein C resistance does not seem to play a role in arterial thrombosis and in the occurrence of myocardial infarction.

Familial thrombophilia: clinical and molecular analysis of Swedish families with inherited resistance to activated protein C or protein S deficiency

This report describes the characterization of Swedish families with inherited resistance to activated protein C (APC resistance) and/or protein S deficiency, two genetic disorders associated with functional impairment of the protein C anticoagulant pathway. The APC resistance phenotype was linked to the factor V gene locus in a kindred with independent inheritance of APC resistance and protein S deficiency. A point mutation changing Arg506 to a Gln (FV:Q506) in the factor V gene was the cause of APC resistance. In studies of 50 families with hereditary APC resistance, the FV:Q506 mutation was identified in 94% (47/50) of the families, and the thrombotic risk was found to be dependent on the factor V genotype. Moreover, 18 families with hereditary deficiency of free protein S were investigated. Type I protein S deficiency (low free and total protein S) and type III deficiency (low free but normal total protein S) coexisted in 78% (14/18) of the families, suggesting the two types to be phenotypic variants of the same genetic disorder. Deficiency of free protein S was caused by equimolar relationship between protein S and beta-chain containing isoforms of C4BP. Though protein S deficiency was a strong risk factor for thrombosis, the FV:Q506 mutation was identified as an additional genetic risk factor in 39% of the families. Thus, familial thrombophilia is a multiple gene disorder. The thrombophilic tendency associated with APC resistance or protein S deficiency was related to increased levels of prothrombin fragment 1 + 2, reflecting increased activation of the common coagulation pathway.

Ischemic stroke in the elderly. Role of the common factor V mutation causing resistance to activated protein C

BACKGROUND AND PURPOSE

A common missense mutation in coagulation factor V (Arg 506 Gln) creates phenotypic resistance to the anticoagulant effects of activated protein C and predisposes carriers to venous thrombosis. To assess a correlation between this common hypercoagulable state and ischemic cerebrovascular disease, we have compared the prevalence of this mutation in a group of stroke patients with that in several control patient groups.

METHODS

The presence of the factor V Arg 506 Gln mutation was determined by a direct polymerase chain reaction-based assay on peripheral blood leukocytes from 161 elderly patients with acute ischemic stroke, 116 elderly patients with stroke risk factors but without acute stroke, 54 healthy elderly control subjects, and 287 younger control individuals (197 blood donors and 90 neonates).

RESULTS

The prevalence of the heterozygous Arg 506 Gln factor V mutation was not significantly different in the elderly stroke patients (2.5%) compared with either of the age-matched control groups (2% to 4%). The prevalence of this mutation was significantly higher in each of two younger control groups (approximately 8%) than in the elderly stroke patients (2.5%).

CONCLUSIONS

The common factor V Arg 506 Gln mutation predisposing to venous thrombosis is not a significant genetic risk factor for ischemic stroke in the elderly.

Activated protein C resistance: from phenotype to genotype and clinical practice

The anticoagulant protein C system is an important regulator of the blood coagulation process. Its targets are the procoagulant cofactors factor Va and factor VIIIa, which are cleaved and inactivated by activated protein C, protein S and intact factor V working as cofactors. Genetic defects of protein C or protein S were, together with antithrombin III deficiency, the previously established major causes of familial venous thromboembolism. However, these abnormalities are found in less than 5-10% of patients with thrombosis. Inherited resistance to activated protein C was recently identified as a major risk factor for venous thromboembolism. The activated protein C-resistance phenotype is found in 20-60% of the patients with venous thrombosis, depending on selection criteria and on the prevalence of activated protein C-resistance in the population. The frequency of activated protein C-resistance is 2-10% in the normal populations studied so far. In more than 90% of cases, the molecular background for the activated protein C-resistance is a single point mutation in the factor V gene, which predicts substitution of an arginine at position 506 by a glutamine. Mutated factor V is activated by thrombin or factor Xa in the normal way, but impaired inactivation of mutated factor Va by activated protein C results in a life-long hypercoagulability. Owing to the high prevalence of activated protein C-resistance in the population, it occasionally occurs in patients with deficiency of protein S, protein C or antithrombin III. Individuals with combined defects suffer more severely from thrombosis, and often at a younger age, than those with single defects, suggesting thrombophilia to be a multigenetic disease.