Association of idiopathic venous thromboembolism with single point-mutation at Arg506 of factor V

Testing for Factor V Leiden (FVL) and Prothrombin G20210A Genetic Variants

Laboratory testing for Factor V Leiden and Prothrombin G20210A genetic variants permits defining the increased relative risk for venous thromboembolism in selected patients. Laboratory DNA testing for these variants may be undertaken by a variety of methods, including fluorescence-based quantitative real-time PCR (qPCR). This is a rapid, simple, robust, and reliable method to identify genotypes of interest. This chapter describes the method that employs PCR amplification of the patient DNA region of interest and genotyping by allele-specific discrimination technology on a quantitative real-time PCR (qPCR) instrument.

Laboratory Testing for Activated Protein C Resistance (APCR): An Update

Activated protein C resistance (APCR) reflects a hemostatic state defined by a reduced ability of activated protein C (APC) to affect an anticoagulant response. This state of hemostatic imbalance is characterized by a heightened risk of venous thromboembolism. Protein C is an endogenous anticoagulant that is produced by the hepatocytes and undergoes proteolysis-mediated activation to APC. APC in turn degrades activated Factors V and VIII. APCR describes a state of resistance by activated Factors V and VIII to APC-mediated cleavage of these factors, thereby promoting amplified thrombin production and a potentially procoagulant state. This resistance of APC may be inherited or acquired. Mutations in Factor V are responsible for the most frequent form hereditary APCR. The predominant mutation, a G1691A missense mutation at Arginine 506, the so-called Factor V Leiden [FVL], causes a deletion of an APC-targeted cleavage site in Factor Va, thereby rendering it resistant to inactivation by APC. There are a variety of laboratory assays for APCR, but this chapter focuses on a procedure using a commercially available clotting assay that utilizes a snake venom and ACL TOP analyzers.

Arterial Thrombosis Associated with Factor V Leiden Mutation in a Child with Nephrotic Syndrome

Thromboembolism remains a common complication of nephrotic syndrome (NS) in adults and a less common complication in children. Venous thrombosis is well recognized, but arterial thrombosis occurs less frequently and is seen primarily in children. We report a case of arterial thrombosis associated with factor V Leiden (FVL) mutation in a young girl with NS. Screening for inherited thrombophilias such as FVL mutation may be beneficial for NS patients with thromboembolic vascular events not explained by conventional risk factors.

Education Case: Hereditary Thrombophilia With Double Heterozygous Factor V Leiden and Factor II c.*97G>A Mutations

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, see http://journals.sagepub.com/doi/10.1177/2374289517715040.¹.

Genetic mutations associated with susceptibility to perioperative complications in a longitudinal biorepository with integrated genomic and electronic health records

BACKGROUND

Existing genetic information can be leveraged to identify patients with susceptibilities to conditions that might impact their perioperative care, but clinicians generally have limited exposure and are not trained to contextualise this information. We identified patients with genetic susceptibilities to anaesthetic complications using a perioperative biorepository and characterised the concordance with existing diagnoses.

METHODS

Adult patients undergoing surgery within Michigan Medicine from 2012 to 2017 were consented for genotyping. Genotypes were integrated with the electronic health record (EHR). We retrospectively characterised frequencies of variants associated with butyrylcholinesterase deficiency, factor V Leiden, and malignant hyperthermia, three pharmacogenetic factors with perioperative implications. We calculated the percentage homozygous and heterozygous for each that had been diagnosed previously and searched for EHR findings consistent with a predisposition.

RESULTS

Analysis of genetic data revealed that 25 out of 40 769 (0.1%) patients were homozygous and 1918 (4.7%) were heterozygous for mutations associated with butyrylcholinesterase deficiency. Of the homozygous individuals, 14 (56%) carried a pre-existing diagnosis. For factor V Leiden, 29 (0.1%) were homozygous and 2153 (5.3%) heterozygous. Of the homozygous individuals, three (10%) were diagnosed by EHR-derived phenotype and six (21%) by clinician review. Malignant hyperthermia was assessed in a subset of patients. We detected two patients with associated mutations. Neither carried clinical diagnoses.

CONCLUSIONS

We identified patients with genetic susceptibility to perioperative complications using an open source script designed for clinician use. We validated this application in a retrospective analysis for three conditions with well-characterised inheritance, and showed that not all genetic susceptibilities were documented in the EHR.

Workflow for the Implementation of Precision Genomics in Healthcare

To enable the implementation of precise genomics in a local healthcare system, we devised a pipeline for filtering and reporting of relevant genetic information to healthy individuals based on exome or genome data. In our analytical pipeline, the first tier of filtering is variant-centric, and it is based on the selection of annotated pathogenic, protective, risk factor, and drug response variants, and their one-by-one detailed evaluation. This is followed by a second-tier gene-centric deconstruction and filtering of virtual gene lists associated with diseases, and VUS-centric filtering according to ACMG pathogenicity criteria and pre-defined deleteriousness criteria. By applying this filtering protocol, we were able to provide valuable insights regarding the carrier status, pharmacogenetic profile, actionable cardiovascular and cancer predispositions, and potentially pathogenic variants of unknown significance to our patients. Our experience demonstrates that genomic profiling can be implemented into routine healthcare and provide information of medical significance.

The genetics of venous thromboembolism: a systematic review of thrombophilia families

Genetic risk factors are important for the occurrence and prognosis of venous thromboembolism (VTE). The studies of thrombophilia families are important for dissecting the genetic background of the thrombotic disease. We conducted the systematic review of all published family-based studies on VTE genetics across all racial groups through PubMed and Embase prior to 13th April 2020. This systematic review of 287 families (including 225 Caucasian families, 52 East Asian families, and families of other ethnicities) revealed a total of 21 different genes; the five most reported mutated genes were F5 (88/287, 30.7%), SERPINC1 (67/287, 23.3%), PROC (65/287, 22.6%), F2 (40/287, 13.9%) and PROS1 (48/287, 16.7%). For Caucasian families, F5 mutations were most frequently reported at 37.8% (85/225), while PROS1 mutations were most frequently reported, at 40.4% (21/52), for East Asian families (Chinese, Japanese and Korean). Factor V Leiden was reported more frequently in Caucasians than in East Asians. Missense mutations were reported frequently in the SERPINC1, PROC and PROS1 genes. In conclusion, our study found the most likely mutated genes associated with VTE among different ethnic groups and provided indications for VTE genetic testing and research in the future.

Below-Knee Amputation Resulting from an Arterial Thrombosis from Tourniquet Use in a Patient with Undiagnosed Factor V Leiden: A Case Report

CASE

A 38-year-old woman presented with previously undiagnosed factor V Leiden (FVL), who suffered a complete superficial femoral arterial thrombosis after tourniquet use during the surgical repair of one of her bilateral tibial plafond fractures. This patient's injury eventually resulted in a below-knee amputation.

CONCLUSION

We recommend expanding hypercoagulable screening on patients with risk factors based on a detailed history and physical examination. We also recommend limiting or negating tourniquet use in patients with FVL or other hypercoagulable disorders.

Risk Factors in Central Retinal Vein Occlusion and Activated Protein C Resistance

Introduction

Central retinal vein occlusion (CRVO) tends to be a disease of older individuals, with some known major risk factors, and activated protein C resistance seems to be one of the causes in younger patients. In this study, we reviewed risk factors including activated protein C resistance in a series of patients with CRVO.

Methods

Twenty-four patients with a diagnosis of CRVO presenting either acutely or for a follow-up visit during the study period, were enrolled. Ages ranged between 31 and 83 years (mean 59.7). The risk factors, presence of ischemia, the results of biochemical serological and hematological tests, especially activated protein C resistance (APC-R), were analysed.

Results

In 17 patients (71%) one or more of the following risk factors existed: hypertension, diabetes, oral contraceptive usage, family history of thrombosis, and previous operation. In 40% of the eyes, there were ischemic changes. Serum triglycerides were high in 4 of 21 patients (19%) and cholesterol and urea were high in 10 of 21 patients (19%). APC-R was found in 6 out of 24 patients (25%).

Conclusions

Besides known predisposing factors like hypertension, diabetes, glaucoma and hyperlipidemia, APC-R seems to be a risk factor for CRVO at all ages.

Factor V Leiden paradox in a middle-aged Swedish population: A prospective study

Few prospective studies have examined the factor V paradox: factor V Leiden (FVL) is a stronger risk factor for deep venous thrombosis (DVT) than for pulmonary embolism (PE). The present study, to the best of our knowledge, is the first population-based study aimed to examine the relationship between FVL and incidence of venous thromboembolism (VTE), DVT and PE in a prospective cohort study of middle-aged Swedish individuals. FVL was determined in 4890 subjects (aged 46–68 years, 57% women) from the general population without previous VTE or cancer, who participated in the Malmö Diet and Cancer study between 1991 and 1994. Incident cases of VTE were identified from the Swedish patient register during a mean follow-up of 15.6 years. Of 4890 subjects with determination of FVL (10.2% carriers), 220 had VTE during follow-up (113 DVT, 78 PE, 29 both). Incidence of VTE was significantly higher in subjects with heterozygous and homozygous FVL: adjusted hazard ratios (HR) were 1.8 (95% CI 1.3–2.6, p=0.001) and 6.5 (2.1–21, p=0.001), respectively. The population attributable fraction was 8.7% for FVL. Adjusted HRs for DVT were 2.2 (1.4–3.3, p<0.001) for heterozygotes and 3.3 (0.5–24, p=0.233) for homozygotes. Adjusted HRs for PE were 1.2 (0.65–2.2, p=0.582) for heterozygotes and 8.7 (2.1–36, p=0.003) for homozygotes. The FVL paradox was confirmed for heterozygotes for FVL. However, homozygotes for FVL had a high risk for PE, suggesting that the FVL paradox is related to the carriership of one wild type and one mutated factor V allele.

Investigation of methylenetetrahydrofolate reductase C677T and factor V Leiden mutation as a genetic marker for retinal vein occlusion

PURPOSE:

Thromboembolic phenomenon is one of the causes of retinal vein occlusion (RVO) which is in fact a multifactorial disease. Therefore, we aimed to study methylenetetrahydrofolate reductase gene polymorphism (MTHFR C677T) and factor V Leiden as genetic risk factors of RVO.

MATERIALS AND METHODS:

A total of 50 (19 males and 31 females) cases of RVO were compared with 50 age- and sex-matched (21 males and 29 females) controls. Complete ocular examination was done for all samples. The diagnosis of RVO was made clinically; however, fundus fluorescein angiography and optical coherence tomography were performed when needed. Serum homocysteine levels were estimated by automatic chemiluminescence analyzer, whereas MTHFR C677T and factor V Leiden mutations were detected by polymerase chain reaction–restriction fragment length polymorphism method.

RESULTS:

The mean age of RVO cases and controls was 54.62 ± 13.92 years and 58.72 ± 11.20 years, respectively. 48.3% of cases and 51.7% of controls were diabetic. 65.3% of cases were hypertensive proving hypertension as a strong risk factor (P = 0.003) of RVO. Serum homocysteine was also found significantly high (P = 0.025) with mean values of 19.98 ± 9.03 μmol/L and 16.98 ± 8.29 μmol/L in cases and controls, respectively. The MTHFR genotype (CT) was found in 83.3% patients of central RVO group and 78.6% cases of branch RVO group that was significantly associated with high serum homocysteine levels. Factor V Leiden mutation was absent in all individuals.

CONCLUSION:

Hyperhomocysteinemia is an important risk factor for RVO, especially in patients with MTHFR C677T gene polymorphism.

Classic thrombophilic gene variants

Thrombophilia is defined as a condition predisposing to the development of venous thromboembolism (VTE) on the basis of a hypercoagu-lable state. Over the past decades, great advances in the pathogenesis of VTE have been made and nowadays it is well established that a thrombophilic state may be associated with acquired and/or inherited factors. The rare loss-of-function mutations of the genes encoding natural anticoagulant proteins (i. e. protein C, protein S and antithrombin) and the more common gain-of-function polymorphisms factor V Leiden and prothrombin G20210A are the main genetic determinants of thrombophilia. In addition, non-O blood group has been consistently demonstrated to be the most frequent inherited marker of an increased risk of VTE. The mechanism role of these inherited thrombophilia markers will be discussed in this narrative review.

Family history of venous thromboembolism as a risk factor and genetic research tool

Familial clustering of venous thromboembolism (VTE) was described as far back as 1905 by Briggs. Although Egeberg discovered inherited deficiency of antithrombin in 1965, it was not until Dahlback discovered resistance to activated protein C in 1993 that it became clear that genetic factors are common risk factors of VTE. Several genes have been linked to familial aggregation of VTE and genome-wide association studies have found several novel gene loci. Still, it has been estimated that much of the heritability for VTE remains to be discovered. Family history (FH) of VTE is therefore still important to determine whether a patient has an increased genetic risk of VTE. FH has the potential to represent the sum of effects and interactions between environmental and genetic factors. In this article the design, methodology, results, clinical and genetic implications of FH studies of VTE are reviewed. FH in first-degree relatives (siblings and/or parents) is associated with a 2–3 times increased familial relative risk (FRR). However, the FRR is dependent on age, number of affected relatives, and presentation of VTE (provoked/unprovoked). Especially high familial risks are observed in individuals with two or more affected siblings (FFR> 50). However, the familial risk for recurrent VTE is much lower or non-significant. Moreover, FH of VTE appears mainly to be important for venous diseases (i. e. VTE and varicose veins). The familial associations with other diseases are weaker. In conclusion, FH of VTE is an important research tool and a clinically potential useful risk factor for VTE.

Laboratory Testing for Activated Protein C Resistance (APCR)

Activated protein C resistance (APCR) describes a hemostatic disorder characterized by a poor anticoagulant response to activated protein C (APC). This results in an increased risk of venous thrombosis, including deep vein thrombosis and pulmonary embolism. Protein C is a natural anticoagulant that is synthesized in the liver and is activated to APC via proteolysis. APC then degrades Factors Va and VIIIa. APCR describes the reduced inability of APC to cleave Factors Va and VIIIa, which therefore promotes increased thrombin generation and potentially leads to a prothrombotic state. APCR may be hereditary or acquired. The most common hereditary defect is due to mutations in Factor V, predominantly the Factor V Leiden [FVL] mutation-a G1691A missense mutation at Arginine 506 that results in its replacement by a glutamine [R506Q] and the abolition of an APC inactivation cleavage site in Factor Va. Laboratory testing for APCR may be undertaken by a variety of methods, but this chapter describes an automated procedure using a commercial Russell Viper Venom-based clotting assay, and using CS-5100 and STA-R analyzers.

Inherited thrombophilia: a double-edged sword

Inherited thrombophilia is a blood coagulation disorder that increases the risk for venous thromboembolism (VTE). During the last decades, the practice of testing has evolved from testing selected populations, leading to high perceived risks, to broad testing for various conditions that included VTE, arterial thrombosis, and pregnancy complications. Because results of such tests usually do not guide treatment decisions, not testing patients with VTE for inherited thrombophilia is on the "Choosing Wisely" list endorsed by multiple specialty societies, including ASH. Inherited thrombophilia can be regarded a double-edged sword, as despite the rationale not to test, it is still being performed frequently. Another way of seeing inherited thrombophilia as a double-edged sword lies in its 2-sided association with reproduction, both in men and in women. Current areas of research are whether women with inherited thrombophilia and pregnancy complications benefit from anticoagulant therapy with regard to improving the chance of a successful pregnancy. Potential effects of inherited thrombophilia, most notably factor V Leiden, on improved embryo implantation in women and sperm counts in men are intriguing, but are currently poorly understood.

Pharmacogenomics and pharmacogenetics for the intensive care unit: a narrative review

PURPOSE

Knowledge of how alterations in pharmacogenomics and pharmacogenetics may affect drug therapy in the intensive care unit (ICU) has received little study. We review the clinically relevant application of pharmacogenetics and pharmacogenomics to drugs and conditions encountered in the ICU.

SOURCE

We selected relevant literature to illustrate the important concepts contained within.

PRINCIPAL FINDINGS

Two main approaches have been used to identify genetic abnormalities - the candidate gene approach and the genome-wide approach. Genetic variability in response to drugs may occur as a result of alterations of drug-metabolizing (cytochrome P [CYP]) enzymes, receptors, and transport proteins leading to enhancement or delay in the therapeutic response. Of relevance to the ICU, genetic variation in CYP-450 isoenzymes results in altered effects of midazolam, fentanyl, morphine, codeine, phenytoin, clopidogrel, warfarin, carvedilol, metoprolol, HMG-CoA reductase inhibitors, calcineurin inhibitors, non-steroidal anti-inflammatory agents, proton pump inhibitors, and ondansetron. Changes in cholinesterase enzyme function may affect the disposition of succinylcholine, benzylisoquinoline muscle relaxants, remifentanil, and hydralazine. Genetic variation in transport proteins leads to differences in the response to opioids and clopidogrel. Polymorphisms in drug receptors result in altered effects of β-blockers, catecholamines, antipsychotic agents, and opioids. Genetic variation also contributes to the diversity and incidence of diseases and conditions such as sepsis, malignant hyperthermia, drug-induced hypersensitivity reactions, cardiac channelopathies, thromboembolic disease, and congestive heart failure.

CONCLUSION

Application of pharmacogenetics and pharmacogenomics has seen improvements in drug therapy. Ongoing study and incorporation of these concepts into clinical decision making in the ICU has the potential to affect patient outcomes.

Coagulation disorders and their cutaneous presentations: Pathophysiology

Hypercoagulable states are inherited or acquired predispositions to venous or arterial thromboses that are best understood in the context of the coagulation cascade. Dermatologists can play a critical role in diagnosing and treating patients with hypercoagulable states because cutaneous symptoms may be a presenting manifestation, thereby reducing morbidity and mortality related to these conditions. This review focuses on the epidemiology and pathophysiology of hypercoagulable states, while the accompanying article iterates the basic clinical features, diagnostic testing, and management of patients who have these conditions.

Identification and functional characterization of a novel F5 mutation (Ala512Val, FVB onn ) associated with activated protein C resistance

Essentials Activated protein C (APC) resistance is a prevalent risk factor for venous thrombosis. A novel missense mutation (Ala512Val - FVBonn ) was characterized in vitro and in silico. FVBonn is a new cause of APC resistance and venous thrombosis. FVBonn expresses additionally enhanced procoagulant activity in the absence of APC.

SUMMARY

Background Activated protein C (APC) resistance is a prevalent risk factor for venous thrombosis. This phenotype is most commonly associated with the factor V Arg506Gln mutation (FV Leiden), which impairs the APC-mediated inactivation of both activated FV (FVa) and activated FVIII (FVIIIa). Objectives Here, we report the identification and characterization of a novel FV mutation (Ala512Val, FVBonn ) in six patients with APC resistance and venous thrombosis or recurrent abortions. Methods FVBonn was expressed in a recombinant system and compared with recombinant wild-type (WT) FV and FV Leiden in several functional assays. Results FVBonn conferred APC resistance to FV-depleted plasma, both in the activated partial thromboplastin time (APTT)-based test (APC sensitivity ratio [APCsr] of 1.98 for FVBonn versus 4.31 for WT FV and 1.59 for FV Leiden) and in the thrombin generation-based test (normalized APCsr of 5.41 for FVBonn versus 1.00 for WT FV and 8.99 for FV Leiden). The APC-mediated inactivation of FVaBonn was slower than that of WT FVa (mainly because of delayed cleavage at Arg506), but was greatly stimulated by protein S. The APC cofactor activity of FVBonn in FVIIIa inactivation was ~ 24% lower than that of WT FV. In line with these findings, an in silico analysis showed that the Ala512Val mutation is located in the same loop as the Arg506 APC cleavage site and might hamper its interaction with APC. Moreover, FVBonn was more procoagulant than WT FV and FV Leiden in the absence of APC, because of an increased activation rate and, possibly, an enhanced interaction with activated FX. Conclusions FVBonn induces hypercoagulability via a combination of increased activation/procoagulant activity, decreased susceptibility to APC-mediated inactivation, and slightly reduced APC cofactor activity.

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.

Venous Thromboembolism in Heterozygotes for Factor V Leiden—The Second-Hit Hypothesis: A Report of Two Patients and a Review of the English-Language Literature

Resistance to activated protein C (factor V Leiden, FV-R506Q) is the most prevalent inherited hypercoagulable state with a frequency of 4.5% in the American population, but 70% of heterozygotes do not experience venous thromboembolic disease. Heterozygosity for FV-R506Q will coexist in patients with deficiencies of protein S (26.1 %), protein C (14.9%), antithrombin III (15.1%), homocystinuria/ hyperhomocysteinemia (29.6%), pregnancy or postpartum (27.9%), oral contraceptives (27.5%), trauma and surgery (18.6%), and lupus anticoagulant and/or antiphospholipid antibodies (40%). The second-hit hypothesis proposes that heterozygotes for factor V Leiden mutation who do experience venous thrombosis will have a second hypercoagulable state either hereditary or acquired. Key Words: Thromboembolism—Factor V Leiden—Heterozygotes.

The Predictability of Factor V Leiden (FV:Q506) Gene Mutation via Clotting-Based Diagnosis of Activated Protein C Resistance

After the discovery of activated protein C resistance (APCR) due to factor V Leiden mutation and the causal relationship of the phenomenon with clinical thromboembolism, a wide variety of functional clotting-based assays were developed for testing of APCR in relation to the specific DNA-based analysis of FV:Q506 Leiden. The aim of this study is to assess a clotting-based APCR assay using procoagulant crotalidae snake venom with respect to the sensitivity, specificity, and predictability for the presence of the factor V Leiden mutation. APCR testing and factor V DNA analyses have been performed concurrently on 319 patient specimens. APCR values of the patients with homozygous factor V Leiden mutation (70.4±13.5 s) were significantly lower (p<0.001) in comparison to the subjects with the heterozygous mutation (87.6±13.4 s). The assay is highly sensitive (98.7%) and specific (91.9%) for the screening of factor V Leiden mutation. The sensitivity and specificity of the APCR testing reached to 100% below the cut-off value of 120 s among the patients with homozygous factor V Leiden mutation. Therefore, this method could help the desired effective optimal screening strategy for the laboratory search of hereditary thrombophilia focusing on the diagnosis of APCR due to FV:Q506.

Prevalence of Factor V Leiden Is Not Increased in Women with Recurrent Miscarriage

The purpose of this study was to determine if there is an increased prevalence of the thrombophilic genetic mutant factor V Leiden in patients with recurrent miscarriage. Functional assays were conducted for activated protein C resistance and genetic detection of factor V Leiden in 100 women with recurrent miscarriage compared with a control group. The prevalence of factor V Leiden in patients was 6/100 (6%) compared with 3/85 (3.5%) in controls. The difference was not statistically significant. Antithrombotic prophylaxis with heparin and/ or aspirin in a subsequent pregnancy in five of the six patients with factor V Leiden was associated with maintenance of pregnancy and delivery of a live, healthy, full-term infant in four. We have been unable to demonstrate a statistically significant increased prevalence of factor V Leiden in women with recurrent miscarriage. If antithrombotic prophylaxis in pregnancy can be shown by controlled therapeutic trial to prevent miscarriage in these patients, identification of this subgroup would be important. Key Words: Recurrent miscarriage—Factor V Leiden—Activated protein C resistance.

Pro- and anticoagulant properties of factor V in pathogenesis of thrombosis and bleeding disorders

Factor V (FV) serves an important role in the regulation of blood coagulation, having both pro- and anticoagulant properties. The circulating high molecular weight single-chain FV molecule undergoes a series of proteolytic cleavages during both activation of coagulation and during anticoagulant regulation of coagulation by activated protein C (APC). It is noteworthy that mutations in the factor V gene (F5) either cause thrombosis or bleeding. New insights into the importance and complexity of FV functions have been generated from elucidation of the pathogenic mechanisms of two familial mutations in the F5 gene. The first mutation was identified as a result of the discovery of APC resistance as the most common risk factor for venous thrombosis. The mutation (FV Leiden) predicts the Arg(506) Gln replacement, which impairs the normal regulation of FVa by APC, as the Arg506 site is an important APC cleavage site. In addition, elucidation of APC resistance resulted in the discovery of the anticoagulant APC cofactor activity of FV. The second FV mutation (FV(A2440G) ), identified in a family with an autosomal dominant bleeding disorder, has led to the discovery of an alternative splicing generating a previously unidentified FV isoform (FV-Short), which inhibits coagulation via an unexpected and intriguing mechanism involving the coagulation inhibitor TFPI-α. These are naturally occurring mutations in the F5 gene that have generated new knowledge on the role of FV in regulation of coagulation and the importance of genetic risk factors for thrombosis and bleeding.

Association of thrombogenic genes polymorphisms with hepatocellular carcinoma in HCV Egyptian patients

The rate of development of fibrosis varies among HCV patients and affected by many variables. We aimed to investigate the association between mutations in Factor V, prothrombin gene and thrombospondin 1 polymorphisms with hepatic fibrosis progression rate and development of HCC in patients infected with HCV and if they are potential markers for early prediction of disease progression. A total of 280 HCV-infected patients (70 with mild fibrosis, 70 with advanced fibrosis, 70 cirrhotic patients and 70 HCC patients) and 100 healthy controls were included. Factor V Leiden G1691A, prothrombin G20210A and thrombospondin 1 mutations were analyzed by restriction fragment length polymorphism. We observed that there were no significant differences between Factor V Leiden (G1691A) or TPS-1 (A2210G) polymorphisms in the four patient subgroups and control group. In HCC patients, the frequencies of GA genotype were significantly increased compared with control subject. HCV patients carrying GA genotype were more likely to develop hepatocellular carcinoma (OR=5.4, 95% CI=1.09-27.05; P=0.026).We concluded that the risk of HCC was increased 5-fold in subjects carrying GA genotype of prothrombin G20210A gene. However, there was no evidence for a significant association between thrombogenic genes polymorphisms and progression of fibrosis in HCV Egyptian patients.

Factor V Leiden

Factor V Leiden (FVLeiden ) is a common hereditary thrombophilia that causes activated protein C (APC) resistance. This review describes many of the most fascinating features of FVLeiden , including background features, mechanisms of hypercoagulability, the founder mutation concept, the "FVLeiden paradox," synergistic interaction with other thrombotic risk factors, the intertwined relationship between FVLeiden and APC resistance testing, and other, uncommon mutations implicated in causing APC resistance. In addition, there are several conditions where laboratory tests for APC resistance and FVLeiden are or can be discrepant, including lupus anticoagulants, anticoagulants such as direct thrombin inhibitors (dabigatran, argatroban, and bivalirudin) and rivaroxaban, as well as pseudohomozygous, pseudo-wildtype, liver transplant, and bone marrow transplant patients. The laboratory test error rate for FVLeiden is also presented.

Activated protein C resistance testing for factor V Leiden

Activated protein C resistance assays can detect factor V Leiden with high accuracy, depending on the method used. Factor Xa inhibitors such as rivaroxaban and direct thrombin inhibitors including dabigatran, argatroban, and bivalirudin can cause falsely normal results. Lupus anticoagulants can cause incorrect results in most current assays. Assays that include dilution into factor V-deficient plasma are needed to avoid interference from factor deficiencies or elevations, which can arise from a wide variety of conditions such as warfarin, liver dysfunction, or pregnancy. The pros and cons of the currently available assays are discussed.

Associations of coagulation factor V Leiden and prothrombin G20210A mutations with Budd-Chiari syndrome and portal vein thrombosis: a systematic review and meta-analysis

BACKGROUND & AIMS

We conducted a systematic review and meta-analysis to evaluate the associations of the coagulation factor V (encoded by F5) Leiden (FVL) or prothrombin (encoded by F2) G20210A mutation with Budd-Chiari syndrome or portal vein thrombosis (PVT).

METHODS

Relevant articles were identified in searches of the PubMed, EMBASE, Cochrane Library, and ScienceDirect databases. The prevalence of the FVL and prothrombin G20210A mutations were compared between patients with Budd-Chiari syndrome or PVT without cirrhosis and healthy individuals (controls) and between patients with cirrhosis, with and without PVT. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

RESULTS

We initially identified 869 articles, and included 27 in our final analysis. Compared with controls, patients with Budd-Chiari syndrome had a significantly higher prevalence of the FVL mutation (OR, 6.21; 95% CI, 3.93-9.79) and a similar prevalence of the prothrombin G20210A mutation (OR, 1.90; 95% CI, 0.69-5.23); patients with PVT without cirrhosis had a significantly higher prevalence of the FVL mutation (OR, 1.85; 95% CI, 1.09-3.13) or the prothrombin G20210A mutation (OR, 5.01; 95% CI, 3.03-8.30). Compared with patients with cirrhosis without PVT, patients with cirrhosis and PVT had a significantly higher prevalence of the FVL mutation (OR, 2.55; 95% CI, 1.29-5.07). We observed a trend toward a higher prevalence of the prothrombin G20210A mutation in patients with cirrhosis and PVT, but the difference was not statistically significant (OR, 2.93; 95% CI, 0.94-9.07).

CONCLUSIONS

Based on a meta-analysis, the FVL mutation is associated with an increased risk of Budd-Chiari syndrome, PVT without cirrhosis, and PVT in cirrhosis. The prothrombin G20210A mutation is associated with PVT, but not Budd-Chiari syndrome. Studies are needed to confirm these findings in different racial and ethnic groups.

Anticoagulant factor V: factors affecting the integration of novel scientific discoveries into the broader framework

Since its initial discovery in the 1940s, factor V has long been viewed as an important procoagulant protein in the coagulation cascade. However, in the later part of the 20th century, two different scientists proposed novel anticoagulant roles for factor V. Philip Majerus proposed the first anticoagulant function for factor V in 1983, yet ultimately it was not widely accepted by the broader scientific community. In contrast, Björn Dahlbäck proposed a different anticoagulant role for factor V in 1994. While this role was initially contested, it was ultimately accepted and integrated into the scientific framework. In this paper, I present a detailed historical account of these two anticoagulant discoveries and propose three key reasons why Dahlbäck's anticoagulant role for factor V was accepted whereas Majerus' proposed role was largely overlooked. Perhaps most importantly, Dahlbäck's proposed anticoagulant role was of great clinical interest because the discovery involved the study of an important subset of patients with thrombophilia. Soon after Dahlbäck's 1994 work, this patient population was shown to possess the factor V Leiden mutation. Also key in the ultimate acceptance of the second proposed anticoagulant role was the persistence of the scientist who made the discovery and the interest in and ability of others to replicate and reinforce this work. This analysis of two different yet similar discoveries sheds light on factors that play an important role in how new discoveries are incorporated into the existing scientific framework.

A genetic association study of D-dimer levels with 50K SNPs from a candidate gene chip in four ethnic groups

INTRODUCTION

D-dimer, a fibrin degradation product, is related to risk of cardiovascular disease and venous thromboembolism. Genetic determinants of D-dimer are not well characterized; notably, few data have been reported for African American (AA), Asian, and Hispanic populations.

MATERIALS AND METHODS

We conducted a large-scale candidate gene association study to identify variants in genes associated with D-dimer levels in multi-ethnic populations. Four cohorts, comprising 6,848 European Americans (EAs), 2,192 AAs, 670 Asians, and 1,286 Hispanics in the National Heart, Lung, and Blood Institute Candidate Gene Association Resource consortium, were assembled. Approximately 50,000 genotyped single nucleotide polymorphisms (SNPs) in 2,000 cardiovascular disease gene loci were analyzed by linear regression, adjusting for age, sex, study site, and principal components in each cohort and ethnic group. Results across studies were combined within each ethnic group by meta-analysis.

RESULTS

Twelve SNPs in coagulation factor V (F5) and 3 SNPs in the fibrinogen alpha chain (FGA) were significantly associated with D-dimer level in EAs with p<2.0×10(-6). The signal for the most associated SNP in F5 (rs6025, factor V Leiden) was replicated in Hispanics (p=0.023), while that for the top functional SNP in FGA (rs6050) was replicated in AAs (p=0.006). No additional SNPs were significantly associated with D-dimer.

CONCLUSIONS

Our study replicated previously reported associations of D-dimer with SNPs in F5 and FGA in EAs; we demonstrated replication of the association of D-dimer with FGA rs6050 in AAs and the factor V Leiden variant in Hispanics.

Factors that influence the bleeding phenotype in severe hemophilic patients

Hemophilia A and B are rare, X-linked bleeding disorders resulting from a partial or total deficiency of functionally active coagulation factor VIII or factor IX, respectively. Endogenous factor levels have traditionally been used to characterize the severity of the disorder, with severe hemophilia considered as circulating levels of factor less than 1% of normal. Identifying patients with severe hemophilia is essential to effective treatment, since these patients are at highest risk of spontaneous life or limb-threatening bleeding and disability resulting from repeated joint bleeding and are most likely to benefit from prophylaxis. However, there is variability in bleeding tendency, even among patients with severe hemophilia. This article will review potential modifiers of hemophilia-associated bleeding other than endogenous factor activity, which may influence bleeding tendencies and complications in hemophilic patients considered to have severe hemophilia. These potential modifiers include physiologic factors, such as elements of the hemostatic system; pathophysiologic factors, such as hemophilic arthropathy, associated inflammation, and angiogenesis; and others, such as seasonal variation, body weight, and physical activity.

Inherited Thrombophilia

Thrombophilia alters normal hemostasis, shifting the balance in favor of thrombus formation. Inherited conditions include factor V Leiden (FVL), prothrombin G20210A mutation, deficiencies in natural anticoagulants (antithrombin [AT], protein C, and protein S), hyperhomocysteinemia, and elevations in clotting factors (factors VIII and XI). Although FVL and prothrombin mutation are common disorders, deficiencies in the natural anticoagulants are rare. The risk of initial thrombosis conferred by inherited thrombophilia varies with the highest risk in those homozygous for either FVL or prothrombin mutation, or with AT deficiency. In the nonpregnant patient, the presence of a thrombophilia does not affect treatment of an acute event. Although vitamin B supplementation has been shown to decrease the levels of homocysteine, the treatment has failed to show a benefit in thrombus prevention and is therefore not recommended.

Factor V Leiden mutation is a risk factor for hepatic artery thrombosis in liver transplantation

BACKGROUND

Hepatic artery thrombosis (HAT) after orthotopic liver transplantation (OLT) is associated with significant morbidity and mortality. Factor V Leiden (FVL) mutation is the most common genetic defect that predisposes to thrombosis. The reconstruction of hepatic artery with arterial graft is a documented risk factor for HAT. However, the relationship among FVL mutation, arterial graft, and HAT remains to be determined.

METHODS

We randomly genotyped 485 patients who underwent OLT from April 2002 to January 2011 and studied the incidence of Hepatic artery thrombosis in the presence of FVL mutation.

RESULTS

Of 485 patients, 21 patients (4.3%) developed HAT (13 male, 8 female); 10 patients (4 male, 6 female) were heterozygous for the FVL mutation. The incidences of HAT in patients without versus with the FVL mutation were 3.8% and 30% (P = .007). Of patients with HAT, 8 hepatic arteries were reconstructed with infrarenal aortic conduits. All 3 patients (100%) with vs 5 (28%) without FVL who received arterial grafts developed HAT (P = .042).

CONCLUSION

Our study suggested that the FVL mutation may be a risk factor for HAT in liver transplantation; the risk is augmented in the presence of an arterial graft.

Prevalence of the Factor V E666D Mutation and Its Correlation With Activated Protein C Resistance in the Chinese Population

BACKGROUND

Factor V (FV) Leiden mutation-related activated protein C resistance (APCR) is one of the common inherited risk factors for venous thromboembolism (VTE) in caucasian population. Although APCR could be identified in some of the Chinese healthy people and patients with VTE, it was not related to FV Leiden mutation. In 2008, we have identified a novel FV mutation (FV E666D) in exon 13 in a hereditary APCR family. And we presumed that the novel mutation might be a genetic defect of APCR in the Chinese population. The aim of our study was to evaluate the prevalence of FV E666D mutation and its correlation with APCR in the Chinese population in a larger series.

METHODS

From June 2009 to January 2011, 163 consecutive patients who underwent thrombophilia tests in our hospital were recruited. The clinical data were retrospectively reviewed. Thrombophilia tests included APCR, anticoagulant proteins, and antiphospholipid antibodies. Factor V E666D mutation was detected.

RESULT

Of the 163 patients, 6 (3.7%) were identified as APCR positive, 2.9% for patients without thrombosis and 5.1% for patients with thrombosis or thrombosis history. Factor V E666D mutation was not detectable in all the 163 patients including 6 APCR-positive patients.

CONCLUSIONS

The prevalence of APCR either in the nonthrombotic patients or in the patients with thrombosis was lower than that reported in other Chinese studies. Our study couldn't provide illustration whether FV E666D mutation is correlated with APCR in the Chinese population.

Inherited and acquired thrombophilias

Thrombophilias represent an evolving story that continues to stir controversy for care providers and obstetrical patients. The predominant thrombophilic mutations include the factor V Leiden mutation, prothrombin gene mutation G20210A, methylene tetrahydrafolate reductase C667T, and deficiencies of the natural anticoagulants proteins C and S, and antithrombin. Prospective cohort studies have provided an accurate assessment of the risk of placenta-mediated complications posed by common inherited thrombophilic conditions. Acquired thrombophilic conditions consist of the antiphospholipid antibody syndrome (APAS) and hyperhomocysteinemia. Well-conducted, placebo-controlled, randomized trials have demonstrated no benefit of anticoagulation in women with recurrent pregnancy loss and inherited thrombophilia. The routine use of anticoagulation to prevent other placenta-mediated complications in the setting of inherited thrombophilia should be considered experimental until the results of adequate clinical trials are available. Heparin anticoagulation and antiplatelet therapies are the cornerstone of treatment of APAS in pregnancy.

Evidence-based approach to thrombophilia testing

Thrombophilia can be identified in about half of all patients presenting with VTE. Testing has increased tremendously for various indications, but whether the results of such tests help in the clinical management of patients has not been settled. I use evidence from observational studies to conclude that testing for hereditary thrombophilia generally does not alter the clinical management of patients with VTE, with occasional exceptions for women at fertile age. Because testing for thrombophilia only serves limited purpose this should not be performed on a routine basis.

Factor V Leiden and FII 20210 testing in thromboembolic disorders

Factor V Leiden and prothrombin (F2) c.20210G>A mutation detection are very important in order to define the increased relative risk for venous thromboembolism in selected patients. Use of DNA-based methods to detect both mutations has become widely available in clinical diagnostic laboratories, including fluorescence-based quantitative real-time PCR (qPCR). The latter is a rapid, simple, robust and reliable method to identify genotypes of interest. There are several chemistries used for qPCR; this article describes their principles and applicability for Factor V Leiden and prothrombin (F2) c.20210G>A mutation detection.