Venous Thrombotic Risk in Family Members of Unselected Individuals with Factor V Leiden

In families with inherited thrombophilia the risk of venous thromboembolism is dependent on the clinical phenotype of the proband

The utility of laboratory investigation of relatives of individuals with inherited thrombophilia is uncertain. To assess the risk of venous thromboembolism (VTE) among the carriers, we investigated a family cohort of 1,720 relatives of probands with thrombophilia who were evaluated because of VTE (n=1,088), premature arterial thrombosis (n=113), obstetric complication (n=257), or universal screening before pregnancy or hormonal contraception or therapy (n=262); 968 relatives were carriers of thrombophilia. A first deep venous thrombosis (DVT) occurred in 44 carriers and 10 non-carriers during 37,688 and 29,548 observationyears from birth, respectively. The risk of DVT among the carriers compared with non-carriers was estimated as a hazard ratio (HR). If the proband had VTE and factor V Leiden (FVL) and/or prothrombin (PT)20210A, the HR for DVT was 2.77 (95%CI 1.21–4.82) in the carriers overall, and 5.54 (95%CI 3.20–187.00) in those homozygous or double heterozygous for FVL and PT20210A. If the proband had VTE and a deficiency of antithrombin (AT), protein C or S, the HR for DVT was 5.14 (95%CI 0.88–10.03) in the carriers overall, and 12.86 (95%CI 2.46–59.90) in those with AT deficiency. No increase in risk was found among the carriers who were relatives of the probands who were evaluated for reasons other than VTE. In conclusion, familial investigation for inherited thrombophilia seems justified for probands with previous VTE, but appears of doubtful utility for the relatives of probands without VTE. This should be taken with caution regarding families with deficiency of natural anticoagulants, given the low number of cases analysed.

Circulating microparticles in carriers of factor V Leiden with and without a history of venous thrombosis

Although factor V Leiden (FVL) is a major determinant of thrombotic risk, the reason why less than 10% of carriers eventually develop venous thromboembolic (VTE) events is unknown. Recent observations suggest that circulating levels of microparticles (MP) may contribute to the thrombogenic profile of FVL carriers. We measured the plasma level of annexin V-MP (AMP) platelet-MP (PMP), endothelial-MP (EMP), leukocyte-MP (LMP) and tissue factor-bearing MP (TF+MP), and the MP procoagulant activity (PPL) in 142 carriers of FVL (of these 30 homozygous and 49 with prior VTE), and in 142 age and gender-matched healthy individuals. The mean (± SD) level of AMP was 2,802 ± 853 MP/ μl in carriers and 1,682 ± 897 in controls (p<0.0001). A statistically significant difference between homozygous and heterozygous carriers of FVL was seen in the level of PMP, EMP and LMP, but not in that of the remaining parameters. When the analysis was confined to carriers with and without a VTE history, the mean level of AMP was 3,110 ± 791 MP/ μl in the former, and 2,615 ± 839 MP/μl in the latter (p<0.005). The mean level of all subtypes of circulating MP showed a similar pattern. The PPL clotting time was 39 ± 9 seconds (sec) in carriers, and 52 ± 15 sec in controls (p=0.003); and was 35 ± 8 sec in carriers with prior thrombosis, and 41 ± 10 sec in thrombosis-free carriers (p<0.005). Our study results suggest that circulating MP may contribute to the development of thrombosis in carriers of FVL mutation.

Genetic Risk Factors in Venous Thromboembolism

Genetic risk factors predispose to thrombophilia and play the most important etiopathogenic role in venous thromboembolism (VTE) in people younger than 50 years old. At least one inherited risk factor could be found in about half of the cases with a first episode of idiopathic VTE.Roughly, genetic risk factors are classified into two main categories: loss of function mutations (such as deficiencies of antithrombin, protein C, protein S) and gain of function mutations, (such as prothrombin mutation G20210A, factor V Leiden). A revolutionary contribution to the genetic background of VTE was brought by the achievements of the genome-wide association studies which analyze the association of a huge number of polymorphisms in large sample size.Hereditary thrombophilia testing should be done only in selected cases. The detection of hereditary thrombophilia has impact on the management of the anticoagulation in children with purpura fulminans, pregnant women at risk of VTE and may be useful in the assessment of the risk for recurrent thrombosis in patients presenting an episode of VTE at a young age (<40 years) and in cases with positive family history regarding thrombosis.

Guidance for the treatment and prevention of obstetric-associated venous thromboembolism

Venous thromboembolism (VTE), which may manifest as pulmonary embolism (PE) or deep vein thrombosis (DVT), is a serious and potentially fatal condition. Treatment and prevention of obstetric-related VTE is complicated by the need to consider fetal, as well as maternal, wellbeing when making management decisions. Although absolute VTE rates in this population are low, obstetric-associated VTE is an important cause of maternal morbidity and mortality. This manuscript, initiated by the Anticoagulation Forum, provides practical clinical guidance on the prevention and treatment of obstetric-associated VTE based on existing guidelines and consensus expert opinion based on available literature where guidelines are lacking.

Risk assessment of venous thrombosis in families with known hereditary thrombophilia: the MARseilles-NImes prediction model

BACKGROUND

Although predicting the risk of venous thrombosis (VT) in an individual from a family with inherited thrombophilia is of major importance, it is often not feasible.

OBJECTIVES

To develop a simple risk assessment model that improves prediction of the risk of VT for individuals of families with inherited thrombophilia.

PATIENTS/METHODS

1201 relatives from 430 families with inherited thrombophilia (deficiencies of antithrombin, protein C or protein S, and the factor V Leiden and F2 20210A mutations) were recruited at the referral center for thrombophilia in Marseilles, France, from 1986 to 2008. One hundred and twenty-two individuals had a personal history of VT. Sixteen preselected clinical and laboratory variables were used to derive the VT risk score.

RESULTS

The scores based on the 16 variables and on the five most strongly associated variables performed similarly (areas under receiver operating characteristic curves of 0.85 and 0.83, respectively). For the five-variable score, named the MARNI score, derived from family history score of VT, von Willebrand factor antigen levels, age, severity of thrombophilia, and FGG rs2066865, the risk of VT ranged from 0.2% for individuals with a score of 0 (n = 186) to > 70% for individuals with a score of ≥ 7 (n = 27). The model was validated with an internal bootstrap method.

CONCLUSIONS

With the use of a simple scoring system, assessment of the risk of VT in subjects from families with inherited thrombophilia can be greatly improved. External validation is now needed to replicate these findings.

Preventing thrombophilia-related complications of pregnancy: an update

Approximately half of all pregnancy-related venous thromboembolic events are associated with thrombophilia. Although the most compelling data for a link between thrombophilia and other adverse pregnancy outcomes derive from women with antiphospholipid antibodies, some studies also suggest an association between these pregnancy complications and hereditary thrombophilias. Management of thrombophilia often involves anticoagulant therapy; however, use of these agents during pregnancy is challenging. There is a paucity of high-quality studies and consequently, recommendations are based largely on extrapolation from data in nonpregnant women, in addition to observational studies and a few small randomized studies. This article will review the impact of the thrombophilias on pregnancy and its outcome, evidence for therapies aimed at the prevention of thrombophilia-related pregnancy complications, and the most recent recommendations contained in the 9th Edition of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

Testing for inherited thrombophilia and consequences for antithrombotic prophylaxis in patients with venous thromboembolism and their relatives. A review of the Guidelines from Scientific Societies and Working Groups

The clinical penetrance of venous thromboembolism (VTE) susceptibility genes is variable, being lower in heterozygous carriers of factor V Leiden and prothrombin 20210A (mild thrombophilia), and higher in the rare carriers of deficiencies of antithrombin, protein C or S, and those with multiple or homozygous abnormalities (high-risk thrombophilia). The absolute risk of VTE is low, and the utility of laboratory investigation for inherited thrombophilia in patients with VTE and their asymptomatic relatives has been largely debated, leading to the production of several Guidelines from Scientific Societies and Working Groups. The risk for VTE largely depends on the family history of VTE. Therefore, indiscriminate search for carriers is of no utility, and targeted screening is potentially more fruitful. In patients with VTE inherited thrombophilia is not scored as a determinant of recurrence, playing a minor role in the decision of prolonging anticoagulation; indeed, a few guidelines consider testing worthwhile to identify carriers of high-risk thrombophilia, particularly those with a family history of VTE. The identification of the asymptomatic carrier relatives of the probands with VTE and thrombophilia could reduce cases of provoked VTE, offering them primary antithrombotic prophylaxis during risk situations. In most guidelines, this is considered justified only for relatives of probands with a deficiency of natural anticoagulants or multiple abnormalities. Counselling the asymptomatic female relatives of individuals with VTE and/or thrombophilia before pregnancy or the prescription of hormonal treatments should be administered with consideration of the risk driven by the type of thrombophilia and the family history of VTE.

Pregnancy-associated venous thromboembolism: prevention and treatment

Pregnancy is associated with an increased risk of venous thromboembolism (VTE) and this condition remains an important cause of maternal morbidity and mortality. The use of anticoagulant therapy for treatment and prophylaxis of VTE during pregnancy is challenging because of the potential for fetal, as well as maternal, complications. Although evidence-based recommendations for the use of anticoagulants have been published, given the paucity of available data, guidelines are based largely upon observational studies and from data in nonpregnant patients. This article reviews the available literature and provides guidance for the management and prevention of VTE during pregnancy.

Factor V Leiden thrombophilia

Factor V Leiden is a genetic disorder characterized by a poor anticoagulant response to activated Protein C and an increased risk for venous thromboembolism. Deep venous thrombosis and pulmonary embolism are the most common manifestations, but thrombosis in unusual locations also occurs. The current evidence suggests that the mutation has at most a modest effect on recurrence risk after initial treatment of a first venous thromboembolism. Factor V Leiden is also associated with a 2- to 3-fold increased relative risk for pregnancy loss and possibly other obstetric complications, although the probability of a successful pregnancy outcome is high. The clinical expression of Factor V Leiden is influenced by the number of Factor V Leiden alleles, coexisting genetic and acquired thrombophilic disorders, and circumstantial risk factors. Diagnosis requires the activated Protein C resistance assay (a coagulation screening test) or DNA analysis of the F5 gene, which encodes the Factor V protein. The first acute thrombosis is treated according to standard guidelines. Decisions regarding the optimal duration of anticoagulation are based on an individualized assessment of the risks for venous thromboembolism recurrence and anticoagulant-related bleeding. In the absence of a history of thrombosis, long-term anticoagulation is not routinely recommended for asymptomatic Factor V Leiden heterozygotes, although prophylactic anticoagulation may be considered in high-risk clinical settings. In the absence of evidence that early diagnosis reduces morbidity or mortality, decisions regarding testing at-risk family members should be made on an individual basis.

Familial risk of venous thromboembolism: a nationwide cohort study

BACKGROUND

Venous thromboembolism has genetic determinants, but population-based data on familial risks are limited.

OBJECTIVES

To examine the familial risk of venous thromboembolism.

METHODS

We undertook a nationwide study of a cohort of patients with deep venous thrombosis or pulmonary embolism born after 1952. We used the Danish National Registry of Patients covering all Danish hospitals, for the years 1977 through 2009, to identify index cases of venous thromboembolism, and assessed the incidence among their siblings. We compared standardized incidence ratios (SIRs) of the observed and expected number of venous thromboembolism cases among siblings, using population-specific, gender-specific and age-specific incidence rates.

RESULTS

We identified 30,179 siblings of 19,599 cases of venous thromboembolism. The incidence among siblings was 2.2 cases per 1000 person-years, representing a relative risk of 3.08 (95% confidence interval [CI] 2.80-3.39) as compared with the general population. The risk was higher for both men (SIR 3.36, 95% CI 2.96-3.82) and women (SIR 2.81, 95% CI 2.45-3.23). The risk was similar among siblings of index cases with venous thrombosis and those of index cases with pulmonary embolism.

CONCLUSION

Venous thromboembolism has a strong familial component.

Predictors of thrombosis in relatives of patients with venous thromboembolism

PURPOSE OF REVIEW

Hereditary and acquired risk factors contribute to the development of venous thromboembolism (VTE). Relatives of patients who have a hereditary predisposition to thrombosis ('hereditary thrombophilia') will have a heightened risk of VTE if they share the same thrombophilic abnormality. However, if patients do not have a currently recognized thrombophilia it cannot be assumed that their relatives have a normal risk of thrombosis; the patient and their relatives may have a yet to be discovered hereditary abnormality.

RECENT FINDINGS

A recent study by our group suggests that the relatives of patients with unprovoked VTE at a young age (e.g. <45 years) have a substantially higher risk [odds ratio (OR) 3.3; 95% confidence interval (CI) 1.7-6.4] of developing VTE than the relatives of older patients with unprovoked VTE (e.g. >71 years). This effect occurred independently of whether patients had a currently recognized hereditary thrombophilia.

SUMMARY

Relatives of patients with unprovoked VTE have an increased risk of VTE. Testing for thrombophilia in the patients, and in the relatives of the patients who have a thrombophilia, allows the risk of thrombosis in the relatives to be estimated. Thrombosis at a young age appears to be an additional independent risk factor for a heightened risk of thrombosis in patients' relatives.

Unraveling the thrombophilia paradox: from hypercoagulability to the prothrombotic state

The thrombophilia paradox whereby thrombophilia testing identifies defects associated with an increased risk of a first venous thrombosis but not of a particularly high risk of recurrence is likely the result of limitations imposed by a limited dichotomous testing strategy compounded by test inaccuracy and imprecision. Consequently, the observed intermediate phenotype (defined by limited laboratory test results) is not fully concordant with the heritable genotype. The next generation of thrombophilia tests, which utilize either individual genomic analysis or global measurement of the composite plasma intermediate phenotype, may more accurately quantify the thrombophilic risk. In conjunction with clinical risk assessment a more quantitative measurement of hypercoagulability and definition of the prothrombotic state should facilitate transition of clinical management from a disease-focused to a more patient-focused strategy.

Genetics of venous thrombosis

Venous thrombosis (deep vein thrombosis, pulmonary embolism) is a common and serious disorder, with genetic and acquired risk factors. The genetic risk factors can be subdivided in to those that are strong, moderate and weak. Strong risk factors are deficiencies of antithrombin, protein C and protein S. Moderately strong are factor V Leiden, prothrombin 20210A, non-O blood group and fibrinogen 10034T. There are many weak genetic risk factors, including fibrinogen, factor XIII and factor XI variants. Even for moderately strong risk factors (relative risks 2-5), the majority of carriers will never develop thrombosis.

Preventing thrombophilia-related complications of pregnancy

Pregnancy is associated with an increased risk of venous thromboembolism (VTE) and approximately half of all pregnancy-related VTEs are associated with thrombophilia. Recent studies suggest that there is a link between thrombophilia and other adverse pregnancy outcomes, such as fetal loss, preeclampsia, placental abruption and intrauterine growth restriction. However, the associations reported are modest, and high quality data are limited. Although the most compelling data derive from pregnant women with antiphospholipid antibodies, the use of anticoagulants for the prevention of pregnancy complications other than VTE in women with heritable thrombophilias is becoming more frequent. In this article, we review the impact of the various thrombophilias on pregnancy and its outcome, the evidence for therapies aimed at prevention of thrombophilia-related pregnancy complications, and briefly discuss the role of screening for thrombophilia in pregnancy.

Fator V de Leiden na doença de Legg-Calvé-Perthes

Trobofilias hereditárias têm sido implicadas na patogênese da doenca de Legg-Calvé-Perthes. Uma investigação do fator de risco hereditário mais comum para hipercoagulabilidade - a mutação no gene do fator V (fator V de Leiden) - foi conduzida em 20 pacientes com Legg-Calvé-Perthes e 214 controles sadios. A prevalência do fator V de Leiden foi maior nos pacientes com Legg-Calvé-Perthes que no grupo controle (30 vs. 1,87%). A razão de chances (odds ratio) para o desenvolvimento de Legg-Calvé-Perthes foi de 22,5 (p<0,05; intervalo de confiança: 5,68- 89.07). Estes dados sugerem, o fator V de Leiden como fator de risco hereditário para hipercoagulabilidade associada ao desenvolvimento da doença de Legg-Calvé-Perthes.

Two cousins with neonatal stroke, PAI-1 4G variant and MTHFR A1298C mutation

The authors describe 2 female cousins with neonatal stroke. One was heterozygous for the plasminogen activator inhibitor-1 4G variant and compound heterozygous for the A1298C and C677T methylenetetrahydrofolate reductase mutations. Her cousin was homozygous for the plasminogen activator inhibitor-1 4G variant and heterozygous for the methylenetetrahydrofolate reductase A1298C and factor V Leiden mutations.

Inherited Thrombophilia: Key Points for Genetic Counseling

With the evolution of medical genetics to focus on highly prevalent, multifactorial conditions, it is inevitable that genetic counselors will be called upon to participate in the evaluation and counseling of individuals with inherited thrombophilia. The purpose of this review is to educate the genetic counselor on key issues related to risk assessment and genetic counseling for hereditary thrombophilia. The information contained in this document is derived from an extensive review of the literature, as well as the author's personal expertise. Upon completion of this review, the genetic counselor will be able to: a) describe inherited and acquired risk factors for thrombosis, b) collect and interpret personal and family histories to assess risk related to hereditary thrombophilia, c) discuss the potential advantages and disadvantages of thrombophilia testing, including psychosocial aspects and implications for medical management, and d) identify educational and support resources for patients and families.

The scientific basis for evaluation and management of thrombotic disorders

The hemostatic mechanisms at work in the body involve a complex series of interactions between platelets, the endothelium, and the coagulation cascade. Much has been learned regarding the molecular mechanisms governing these intricate processes. The hypercoagulable state involves a disruption of the normal homeostatic equilibrium. This state may be either inherent or acquired. The prevention of associated thromboembolic complications requires therapeutic anticoagulation. A broader understanding of the factors contributing to these prothrombotic tendencies and the subtleties involved in their management provides the surgeon with another weapon in the armamentarium to promote better and safer patient outcomes.

Can haematological tests predict cardiovascular risk? The 2005 Kettle Lecture*

The risk of venous or arterial thrombosis is routinely assessed by clinical variables (risk factors) supplemented by measurement of blood lipids and glucose for arterial thrombotic events. Haematological tests that might play a role in risk prediction include haemostatic variables, haematocrit and inflammatory markers (erythrocyte sedimentation rate, plasma viscosity, white cell count). Recent epidemiological studies of these phenotypes and related genotypes are reviewed. For the risk prediction of first venous thrombosis, screening for thrombophilias in 'high-risk' situations does not appear clinically effective or cost-effective; with the possible exception of women considering oral hormone replacement therapy. General screening after a first venous event to predict recurrence (or risk in asymptomatic relatives) does not appear effective; with the possible exception of d-dimer, which requires further study. For risk prediction of first arterial thrombosis, screening adds little to prediction by current clinical risk scores. Screening of persons after a first arterial event, or with atrial fibrillation (e.g. with D-dimer for stroke prediction), requires further study. In conclusion, haematological tests have very limited roles in the prediction of cardiovascular risk, and should only be used according to evidence-based guidelines. The need for management studies is highlighted.

Family history is a poor screen for prothrombotic genes in children with stroke

OBJECTIVE

To evaluate family history of early pathological thrombosis as a screen for genetic prothrombotic risk factors in children with stroke.

STUDY DESIGN

A 5-year retrospective review of standardized pediatric stroke clinic evaluations of children with arterial ischemic stroke (AIS) or sinovenous thrombosis (SVT). A family history of early pathological thrombosis was defined as stroke, heart attack, or deep venous thrombosis before 50 years of age or multiple miscarriages in the parents or grandparents of the patient. We evaluated the association between family history and the presence of the Factor V Leiden mutation (FVL) and/or Prothrombin G20210A mutation (PTG) in these children.

RESULTS

The study included 68 children. Thirteen (19.1%) had a positive family history of early pathological thrombosis, nine (13.2%) were heterozygous for FVL, and one (1.5%) was heterozygous for PTG. Family history was not associated with the presence of FVL (p = .36) or FVL combined with PTG (p = .40). For FVL, family history had a positive predictive value of 23.1% and a negative predictive value of 89.1%.

CONCLUSION

A family history of early thrombosis is not associated with the presence of FVL or PTG in children with stroke. We recommend that all children with stroke receive a prothrombotic workup regardless of family history.

Recurrence rate after a first venous thrombosis in patients with familial thrombophilia

OBJECTIVE

Few comprehensive data are available on the recurrence rate of venous thrombosis in carriers of thrombophilic defects from thrombophilic families. We prospectively determined the recurrence rate after a first venous thrombotic event in patients with familial thrombophilia attributable to factor V Leiden or deficiencies of protein C, S, or antithrombin.

METHODS AND RESULTS

Data were gathered during follow-up on the occurrence of risk situations, anticoagulation treatment, and events (eg, venous thrombosis, hemorrhage). Over a mean follow-up period of 5.6 years, 44 of the 180 patients with familial thrombophilia who did not use long-term anticoagulation experienced a recurrent venous thromboembolic event (5.0%/year; 95% CI 3.6 to 6.7) compared with 7 of the 124 patients on long-term anticoagulation (1.1%/year; 95% CI 0.4 to 2.2). Spontaneous events occurred less often in patients on long-term anticoagulation (57%) than in patients without long-term anticoagulation (75%). The highest recurrence rate was found among men with a deficiency in natural anticoagulants or multiple defects and women with antithrombin deficiency. Although long-term anticoagulation treatment decreased the incidence of recurrent events by 80%, it also resulted in a risk of major hemorrhage of 0.8% per year.

CONCLUSIONS

Extra care after a first event is required for men with a deficiency in natural anticoagulants or multiple defects and women with antithrombin deficiency.

Factor V Leiden and its effect on children with cardiac pathology

Factor V Leiden thrombophilia, formed by a genetic mutation, slows the body's anticoagulation response to clot formation. First described in 1994, factor V Leiden mutation has been identified as a contributing risk factor for venous thromboembolism. Although venous thromboembolism is considered rare in the pediatric population, Factor V Leiden has implications for certain at-risk pediatric patients.

Risk of a first venous thrombotic event in carriers of a familial thrombophilic defect. The European Prospective Cohort on Thrombophilia (EPCOT)

BACKGROUND

Reliable risk estimates for venous thrombosis in families with inherited thrombophilia are scarce but necessary for determining optimal screening and treatment policies.

OBJECTIVES

In the present analysis, we determined the risk of a first venous thrombotic event in carriers of a thrombophilic defect (i.e. antithrombin-, protein C- or protein S deficiency, or factor V Leiden).

PATIENTS AND METHODS

The asymptomatic carriers had been tested prior to this study in nine European thrombosis centers because of a symptomatic carrier in the family, and were followed prospectively for 5.7 years on average between March 1994 and January 2001. Annually, data were recorded on the occurrence of risk situations for venous thrombosis and events (e.g. venous thrombosis, death).

RESULTS

Twenty-six of the 575 asymptomatic carriers (4.5%) and seven of the 1118 controls (0.6%) experienced a first deep venous thrombosis or pulmonary embolism during follow-up. Of these events, 58% occurred spontaneously in the carriers compared with 43% in the controls. The incidence of first events was 0.8% per year (95% CI 0.5-1.2) in the carriers compared with 0.1% per year (95% CI 0.0-0.2) in the controls. The highest incidence was associated with antithrombin deficiency or combined defects, and the lowest incidence with factor V Leiden.

CONCLUSIONS

The incidence of venous events in asymptomatic individuals from thrombophilic families does not exceed the risk of bleeding associated with long-term anticoagulant treatment in the literature (1-3%).

The incidence of venous thromboembolism among Factor V Leiden carriers: a community-based cohort study

While Factor V (FV) Leiden is a risk factor for venous thromboembolism (VTE), the incidence of VTE among FV Leiden carriers is uncertain. The objective of the study was to estimate the overall age-specific and pregnancy-related VTE incidence and the relative risk among FV Leiden carriers. In a community-based sample of 3424 south-eastern Minnesota residents, 230 (6.7%) were genotyped as FV Leiden carriers; 220 carriers (mean age = 68 years) could be matched to a non-carrier on age, gender, ethnicity and length of medical history. We performed a retrospective cohort study of carriers and non-carriers by reviewing the complete medical records in the community for demographic and baseline characteristics, pregnancies and live births, and first lifetime VTE. Over 14 722 person-years, 24 (10.9%) carriers developed VTE [overall incidence = 163 (95% CI 104, 242) per 100,000 person-years]. VTE incidence rates for ages 15-29, 30-44, 45-59 and > or = 60 years were 0, 61, 244 and 764 per 100,000 person-years, respectively (cumulative VTE incidence at age 65 years = 6.3%). VTE incidence for carriers did not differ significantly from that for non-carriers except for those > or = 60 years old (relative risk = 3.6; 95% CI 2.0, 6.0). There were 311 live births among 130 women carriers; no VTE events occurred during pregnancy or postpartum [incidence = 0 (95% CI 0, 1186) per 100,000 women-years]. Most FV Leiden carriers do not develop VTE. Among all carriers, those > or = 60 years old are at the highest risk for VTE. The incidence of VTE among asymptomatic women carriers during pregnancy is low and insufficient to warrant prophylaxis.

Venous Thrombosis: The Role of Genes, Environment, and Behavior

Over the last decade we have witnessed an avalanche of newly identified risk factors for venous thrombosis. This has advanced our knowledge of its etiology, because more determinants have been described and because the underlying concepts have received a new and broader understanding.

Venous thrombosis is a common multicausal disease occurring as the result of interacting genetic, environmental and behavioral risk factors. Some of these have been known since medieval times, such as the increased risk of thrombosis during immobilization in pregnancy and after childbirth (although retained milk of the breast-feeding mother was seen as the primary cause for the latter). Pregnancy and puerperium still cause thrombosis, as do exogenous hormones in oral contraceptives and hormonal replacement therapy. Furthermore, the immobilization in the puerperium of the old days translates directly to situations of immobilization in current times, such as prolonged travel in airplanes or excessive electronic gaming.

While pedigrees with abundant thrombosis were observed in the early 1900s, the first cause of heritable thrombophilia (antithrombin deficiency) was discovered in 1965, with the subsequent identification of deficiencies of protein C and protein S in the early 1980s. These were uncommon and strong risk factors, whereas the more recently discovered genetic variants are common and weak, and cause disease only in the presence of other factors.

Venous thrombosis: the role of genes, environment, and behavior

Over the last decade we have witnessed an avalanche of newly identified risk factors for venous thrombosis. This has advanced our knowledge of its etiology, because more determinants have been described and because the underlying concepts have received a new and broader understanding. Venous thrombosis is a common multicausal disease occurring as the result of interacting genetic, environmental and behavioral risk factors. Some of these have been known since medieval times, such as the increased risk of thrombosis during immobilization in pregnancy and after childbirth (although retained milk of the breast-feeding mother was seen as the primary cause for the latter). Pregnancy and puerperium still cause thrombosis, as do exogenous hormones in oral contraceptives and hormonal replacement therapy. Furthermore, the immobilization in the puerperium of the old days translates directly to situations of immobilization in current times, such as prolonged travel in airplanes or excessive electronic gaming. While pedigrees with abundant thrombosis were observed in the early 1900s, the first cause of heritable thrombophilia (antithrombin deficiency) was discovered in 1965, with the subsequent identification of deficiencies of protein C and protein S in the early 1980s. These were uncommon and strong risk factors, whereas the more recently discovered genetic variants are common and weak, and cause disease only in the presence of other factors.

Familial thrombophilia and lifetime risk of venous thrombosis

BACKGROUND

We started a large multicenter prospective follow-up study to provide reliable risk estimates of venous thrombosis in families with various thrombophilic defects.

OBJECTIVES

This paper describes data collected at study entry on venous events experienced before study inclusion, i.e. the baseline data.

PATIENTS/METHODS

All individuals (probands, relatives) registered in nine European thrombosis centers with the factor (F)V Leiden mutation, a deficiency of antithrombin, protein C or protein S, or a combination of these defects, were enrolled between March 1994 and September 1997. As control individuals, partners, friends or acquaintances of the thrombophilic participants were included. Incidence and relative risk of objectively confirmed venous thrombotic events (VTEs) prior to entry were calculated for the relatives with thrombophilia and the controls.

RESULTS

Of the 846 relatives with thrombophilia (excluding probands), 139 (16%) had experienced a VTE with an incidence of 4.4 per 1000 person years. Of the controls, 15 of the 1212 (1%) controls had experienced a VTE with an incidence of 0.3 per 1000 person years. The risk of venous thrombosis associated with familial thrombophilia was 15.7 (95% CI 9.2-26.8) and remained similar after adjustment for regional and sex-effects (16.4; 95% CI 9.6-28.0). The highest incidence per 1000 person years was found in relatives with combined defects (8.4; 95% CI 5.6-12.2), and the lowest incidence was found in those with the FV Leiden mutation (1.5; 95% CI 0.8-2.6).

CONCLUSIONS

Considerable differences in the lifetime risk of VTE were observed among individuals with different thrombophilia defects.

Hormones and pregnancy: thromboembolic risks for women

During their lifetimes, women face several unique situations with an increased risk of venous thromboembolism (VTE). Doctors in a variety of specialties must advise women on the risks of oral contraceptives (OC), hormone replacement or pregnancy. Modern 'low dose' OC are associated with a three to sixfold increased relative risk of VTE. Hormone replacement and selective oestrogen receptor modulators confer a similar two to fourfold increase in thrombotic risk. However, because the baseline incidence of thrombosis is higher in older postmenopausal women, the absolute risk is higher than in younger OC users. The risk of venous thrombosis is six to 10-fold higher during pregnancy than in non-pregnant women of similar age. Thrombophilic disorders increase the thrombotic risk of OC, hormone replacement and pregnancy, especially in women with homozygous or combined defects. This review focuses on recent data estimating the thrombotic risk of hormonal therapies and pregnancy in women with and without other thrombotic risk factors.

Linkage analysis of factor VIII and von Willebrand factor loci as quantitative trait loci

Elevated factor (F)VIII levels contribute to venous thrombotic risk. FVIII levels are determined to a large extent by levels of von Willebrand factor (VWF), its carrier protein which protects FVIII against proteolysis. VWF levels are largely dependent on ABO blood group. Subjects with blood group non-O have higher VWF and FVIII levels than individuals with blood group O. Apart from ABO blood group no genetic determinants of high FVIII levels have been identified, whereas clustering of FVIII levels has been reported within families even after adjustment for ABO blood group and VWF levels. We investigated the FVIII and VWF loci as possible quantitative trait loci (QTL) influencing FVIII and VWF levels. Two sequence repeats in the FVIII gene and three repeats in the VWF gene were typed in 52 FV Leiden families. Multipoint sib-pair linkage analysis was performed with the MAPMAKER/SIBS program. FVIII levels adjusted for VWF levels and age, and VWF levels adjusted for ABO blood group and age, were used for this linkage analysis. No linkage of FVIII levels to the FVIII locus was found, whereas we found evidence that the VWF locus contains a QTL for VWF levels [maximum likelihood no dominance variance lod score = 0.70 (P = 0.04) and non-parametric Z-score = 1.92 (P = 0.03)]. About 20% of the total variation in VWF levels may be attributed to this VWF locus.

Role of the geneticist in testing and counseling for inherited thrombophilia

Within the past decade, the identification of two mutations that are relatively prevalent among the white population (the factor V Leiden and prothrombin G20210A gene mutations) has paved the way for a number of large cohort studies that have greatly advanced our understanding of the pathogenesis of venous thromboembolism (VTE). VTE is clearly a multigenic disorder, with well-characterized examples of gene-gene and gene-environment interactions underlying its pathogenesis. Increasing numbers of patients are being referred for testing, and many more diagnoses of inherited thrombophilia are being made. The purpose of this article is to discuss the practical applications of both diagnostic testing and genetic counseling for the major inherited thrombophilias: inherited resistance to activated protein C/factor V Leiden, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, and antithrombin deficiency. A description of each entity is included along with a discussion of the indications for testing, selection of the most appropriate screening test, and proper interpretation of test results. Informed consent for testing, screening of asymptomatic individuals in special circumstances (such as during pregnancy or before initiation of estrogen therapy), screening of family members, and posttest education are also addressed. This article emphasizes that these polymorphisms should be regarded as risk factors for thrombosis whose clinical expression generally depends on the coexistence of additional thrombophilic mutations or environmental conditions that provoke the development of VTE.

Clinical utility of factor V leiden (R506Q) testing for the diagnosis and management of thromboembolic disorders

OBJECTIVE

To review the current state of the art regarding the role of the clinical laboratory in diagnostic testing for the factor V Leiden (FVL) thrombophilic mutation (and other protein C resistance disorders), and to generate, through literature reviews and opinions of recognized thought-leaders, expert consensus recommendations on methodology and diagnostic, prognostic, and management issues pertaining to clinical FVL testing.

DATA SOURCES, EXTRACTION, AND SYNTHESIS

An initial thorough review of the medical literature and of current best clinical practices by a panel of 4 experts followed by a consensus conference review, editing, and ultimate approval by the majority of a panel of 28 additional coagulation laboratory experts.

CONCLUSIONS

Consensus recommendations were generated for topics of direct clinical relevance, including (1) defining those patients (and family members) who should (and should not) be tested for FVL; (2) defining the preferred FVL laboratory testing methods; and (3) defining the therapeutic, prophylactic, and management ramifications of FVL testing in affected individuals and their family members. As FVL is currently the most common recognized familial thrombophilia, it is hoped that these recommendations will assist laboratorians and clinicians caring for patients (and families) with this common mutation.

Risk of venous thromboembolism in carriers of factor V Leiden with a concomitant inherited thrombophilic defect: a retrospective analysis

Factor V Leiden is the most common genetic defect associated with venous thromboembolism. Its clinical expression is limited and shows a wide intrafamilial and interfamilial variation, which might be explained by the influence of other genetic risk factors. We retrospectively studied 226 patients with factor V Leiden and documented venous thromboembolism (probands) and 400 first-degree carrier relatives to assess the contribution of concomitant genetic risk factors to the occurrence of venous thromboembolism. The prothrombin G20210A mutation was found in 8.3%, homozygosity of factor V Leiden in 7.2%, and inherited deficiencies of antithrombin, protein C or protein S in 4.7% of symptomatic carriers (probands and relatives), as compared with 6.0, 3.4 and 0.9% of asymptomatic carriers, respectively. The total follow-up time in relatives was 11 049 years. Prevalences of venous thromboembolism were 10.8% in single heterozygous factor V Leiden carrier relatives, 16.0% in double-heterozygotes for factor V Leiden and the prothrombin mutation, 36.8% in homozygotes for factor V Leiden, and 40.0% in double-heterozygotes for factor V Leiden and an inherited deficiency of protein C or protein S. Annual incidences in these groups were 0.39, 0.57, 1.41, and 4.76%, respectively. Multivariate analysis showed a small, non-significant additional effect of the prothrombin mutation on the risk of venous thromboembolism in heterozygotes for factor V Leiden [adjusted hazard ratio, 1.3; 95% confidence interval (CI), 0.5-3.8]. This effect was more pronounced for homozygosity of factor V Leiden (adjusted hazard ratio, 3.9; 95% CI, 1.7-9.0) and inherited protein C or protein S deficiencies (adjusted hazard ratio, 17.5; 95% CI, 3.8-81.2). Our data provide evidence of clustering of the evaluated genetic thrombophilic defects in symptomatic factor V Leiden carriers and support the assumption that the clinical expression of factor V Leiden depends on clustering in a part of carriers.

Impact of the factor II: G20210A variant on the risk of venous thromboembolism in relatives from families with the factor V: R506Q mutation

OBJECTIVES

Factor V: R506Q mutation and the prothrombin G20210A variant (factor II: G20210A variant) are associated with an increased risk of venous thromboembolism (VTE). In cohorts of unrelated patients a cosegregation of both mutations has been shown to be associated with an increased risk of developing VTE. The aim of this study was to investigate the impact of the coinheritance of both mutations on the risk of VTE in relatives of symptomatic carriers of the factor V: R506Q mutation and the factor II: G20210A variant.

PATIENTS AND METHODS

Four families with 48 family members were investigated for the presence of the factor V: R506Q mutation and the factor II: G20210A mutation, and their clinical history was evaluated.

RESULTS

VTE was more frequent in family members with a combined defect (3/10; 30%) compared to those with a single mutation (1/16; 6%) or without a defect (1/12; 8%). The probability for VTE for 40-yr-old individuals with both mutations, a single mutation and no mutation was 56%, 12% and 20%, respectively.

CONCLUSIONS

These data suggest that the G to A transition at position 20210 of the prothrombin gene leads to an increase in the risk of VTE in carriers of the factor V: R506Q mutation. The determination of the factor II: G20210A variant in index patients carrying a factor V: R506Q mutation and, if present, in family members may help to identify individuals who are at high risk for VTE.

High factor VIII levels contribute to the thrombotic risk in families with factor V Leiden

Factor V Leiden (FVL)-carrying relatives of selected patients with venous thromboembolism (VTE) have much higher venous thrombotic risks than FVL-carrying relatives of unselected consecutive patients with VTE. To find an explanation for this, we explored other risk factors of VTE, in particular the presence of high factor VIII levels, in a retrospective follow-up study. We assessed levels of factor VIII, factor IX, fibrinogen, protein C, protein S, antithrombin, the presence of prothrombin 20210A, and the occurrence of VTE in 61 first-degree relatives of 12 selected thrombophilic families harbouring FVL, and 183 first-degree relatives of 47 unselected families of FVL carriers with a first VTE. In all families, FVL appeared to be an independent risk factor for VTE. Higher thrombosis incidence rates were found in carriers of both FVL and high factor VIII levels (> or = 150 IU/dl), while high levels of factor VIII appeared to be an independent thrombotic risk factor only in selected thrombophilic families. The fraction of individuals with more than one prothrombotic coagulation disorder was 10% higher in selected families. These results and the higher thrombotic risks we found in the thrombophilic families favour the hypothesis that other unknown co-existing genetic defects contribute to thrombophilia.

The risk of venous thromboembolism in family members with mutations in the genes of factor V or prothrombin or both

Factor V Leiden and the G20210A mutation in the prothrombin gene are the most frequent abnormalities associated with venous thromboembolism. It is unknown whether the risks due to the presence of either mutation are of the same magnitude. We compared the prevalence and incidence rate of venous thromboembolism in relatives with either mutation or both. The finding of different rates might influence the strategies for primary prevention of thrombosis in carriers of these mutations. The study population included 1076 relatives of probands with the prothrombin gene mutation, factor V Leiden or both who underwent screening for inherited thrombophilia and were found to be carriers of single mutations or double mutations or who were non-carriers. The prevalence of venous thromboembolism was 5.7% in relatives with the prothrombin gene mutation, 7.8% in those with factor V Leiden, 17.1% in those with both mutations and 2.5% in non-carriers. Annual incidences of thrombosis were 0.13% [95% confidence interval (CI) 0.06-0.24], 0.19% (0.13-0.25), 0.42% (0.15-0.83) and 0.066% (0.03-0.11), respectively, and the relative risk of thrombosis was two times higher in carriers of the prothrombin gene mutation, three times higher in those with factor V Leiden and six times higher in double carriers than in non-carriers. The incidence of venous thromboembolism in carriers of the prothrombin gene mutation is slightly lower than that observed in carriers of factor V Leiden, whereas in carriers of both mutations it is two or three times higher. These findings suggest that lifelong primary anticoagulant prophylaxis of venous thromboembolism is not needed in asymptomatic carriers of single or double mutations. Anticoagulant prophylaxis seems to be indicated only when transient risk factors for thrombosis coexist with mutations.

Factor V Leiden: the venous thrombotic risk in thrombophilic families

Factor V Leiden (FVL) leads to a sevenfold increased risk of venous thrombosis and is present in 50% of individuals from families referred because of unexplained familial thrombophilia. We assessed the association of FVL with venous thromboembolism (VTE) in 12 thrombophilic families of symptomatic probands with FVL in a retrospective follow-up study. We screened 182 first- and second-degree relatives of the 12 unrelated propositi for the FVL mutation and the occurrence of VTE. The incidence rate of VTE in carriers of FVL (0.56%/year) was about six times the incidence for the Dutch population (0.1%/year). The incidence rate in non-carriers also appeared to be higher (0.15% per year). At the age of 50 years, the probability of not being affected by VTE was reduced to 75% for carriers and to 93% for non-carriers (P = 0.009). Identification of carriers of FV Leiden may be worthwhile in young symptomatic individuals and their relatives with a strong positive family history of venous thromboembolism or a history of recurrent venous thrombosis who may be at risk (e.g. pregnancy, use of oral contraceptives). After adjustment for prothrombin G20210A (present in two families), even higher thrombotic incidence rates were found in carriers and non-carriers of FVL. This makes the presence of other unknown prothrombotic risk factors more probable in these families.