Hereditary Thrombophilia as a Model for Multigenic Disease

Recurrent mutations in a SERPINC1 hotspot associate with venous thrombosis without apparent antithrombin deficiency

Despite the essential anticoagulant function of antithrombin and the high risk of thrombosis associated with its deficiency, the prevalence of antithrombin deficiency among patients with venous thromboembolism (VTE) is very low. However, increasing evidence suggests that antithrombin deficiency may be underestimated. The analysis of SERPINC1, the gene encoding antithrombin, in 1,304 consecutive Chinese VTE patients and 1,334 healthy controls revealed a hotspot involving residues 294 and 295 that severely increases the risk of VTE. We detected the c.883G>A (p.Val295Met) (rs201381904) mutation in 11 patients and just one control (OR = 13.6; 95% CI: 1.7-107.1); c.881G>T (p.Arg294Leu) (rs587776397) in six patients but no controls; and c.880C>T (p.Arg294Cys) (rs747142328) in two patients but no controls. In addition, c.881G>A (p.Arg294His) (rs587776397) was identified in one control. These mutations were absent in a Caucasian cohort. Carriers of these mutations had normal antithrombin levels and anticoagulant activity, consistent with results obtained in a recombinant model. However, mutation carriers had a significantly increased endogenous thrombin potential. Our results suggest the existence in the Chinese population of a hotspot in SERPINC1 that significantly increases the risk of VTE by impairing the anticoagulant capacity of the hemostatic system. This effect is not revealed by current antigen or in vitro functional antithrombin assays.

The correlation analysis of tumor necrosis factor-alpha-308G/A polymorphism and venous thromboembolism risk: A meta-analysis

OBJECTIVE

Venous thromboembolism is a common complex disorder, being the resultant of gene-gene and gene-environment interactions. Tumor necrosis factor-alpha is a proinflammatory cytokine which has been implicated in venous thromboembolism risk. A promoter 308G/A polymorphism in the tumor necrosis factor-alpha gene has been suggested to modulate the risk for venous thromboembolism. However, the published findings remain inconsistent.

METHODS

In this study, we conducted a meta-analysis of all available data regarding this issue. Eligible studies were identified through search of Pubmed, EBSCO Medline, Web of Science, and China National Knowledge Infrastructure (CNKI, Chinese) databases up to June 2014. Pooled Odd ratios (ORs) with 95% confidence intervals were applied to estimating the strength of the genetic association in the random-effects model or fixed-effects model.

RESULTS

A total of 10 studies involving 1999 venous thromboembolism cases and 2166 controls were included in this meta-analysis to evaluate the association between tumor necrosis factor-alpha-308G/A polymorphism and venous thromboembolism risk. Overall, no significantly increased risk venous thromboembolism was observed in all comparison models when all studies were pooled into the meta-analysis. However, in stratified analyses by ethnicity, there was a pronounced association with venous thromboembolism risk among West Asians in three genetic models (A vs. G: OR = 1.82, 95%CI = 1.13-2.94; GA vs. GG: OR = 1.82, 95%CI = 1.08-3.06; AA/GA vs. GG: OR = 1.88, 95%CI = 1.12-3.16). When stratifying by source of controls, no significant result was detected in all genetic models.

CONCLUSION

This meta-analysis demonstrates that tumor necrosis factor-alpha 308G/A polymorphism may contribute to susceptibility to venous thromboembolism among West Asians. Studies are needed to ascertain these findings in larger samples and different racial groups.

Mild Antithrombin Deficiency and Risk of Recurrent Venous Thromboembolism

Background—

Antithrombin deficiency, defined by antithrombin levels of <70%, is a major thrombophilic condition associated with an increased risk of venous thromboembolism (VTE). No prospective data are available about the risk of recurrent VTE associated with mildly decreased antithrombin levels (70–80%).

Methods and Results—

Consecutive patients with a first VTE were stratified according to functional antithrombin levels (<70%, 70–80%, >80%) and were followed up for a mean of 8.70 years to assess the incidence of VTE recurrence. A total of 823 patients (mean age, 48.3 years; 41.9% male) were enrolled. Recurrent VTE occurred in 253 patients (3.53% per patient-year). With stratification for antithrombin levels, VTE recurrence occurred in 19 patients with antithrombin levels <70% (5.90% per patient-year), in 20 patients with antithrombin levels 70% to 80% (5.35% per patient-year), and in 214 patients with antithrombin levels >80% (3.31% per patient-year). After adjustment for major VTE risk factors and for anticoagulation duration, the risk of VTE recurrence was significantly higher in patients with antithrombin levels <70% (hazard ratio, 3.48; 95% confidence interval, 2.16–5.61) and antithrombin levels 70% to 80% (hazard ratio, 2.40; 95% confidence interval, 1.51–3.80) compared with patients with antithrombin levels >80%. When the population was stratified according to the presence or absence of major risk factors for the index event, the association remained significant only in patients with unprovoked VTE.

Conclusions—

The presence of mild antithrombin deficiency (70–80% antithrombin) in patients with unprovoked VTE is associated with a significantly increased risk of recurrence and should be taken into account when the duration of secondary prevention is determined.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01382550.

Genome-wide linkage scan in affected sibling pairs identifies novel susceptibility region for venous thromboembolism: Genetics In Familial Thrombosis study

BACKGROUND

Venous thromboembolism (VTE) is a multicausal disorder involving environmental and genetic risk factors. In many thrombophilic families the clustering of thrombotic events cannot be explained by known genetic risk factors, indicating that some remain to be discovered.

OBJECTIVES

We aimed to identify novel thrombosis susceptibility alleles in a large panel of small thrombophilic families: the Genetics In Familial Thrombosis (GIFT) study.

PATIENTS/METHODS

In the GIFT study, 201 families were recruited consisting of 438 siblings with an objectively confirmed VTE at a young age. Multipoint linkage analysis (402 SSR markers) and fine mapping were performed, followed by genotyping of tagging SNPs in positional candidate genes.

RESULTS

Established genetic risk factors such as factor V Leiden, ABO blood group non-O, prothrombin 20210A, fibrinogen gamma 10034T and deficiencies of antithrombin, protein C and protein S were more frequent in GIFT patients than in unselected VTE patients. Linkage supported the presence of novel thrombosis susceptibility loci on 7p21.3-22.2 (LOD score = 3.23) and Xq24-27.3 (LOD score = 1.95). Simulation analysis showed that the chr7 signal was genome-wide statistically significant (P = 0.022). Tagging SNPs (n = 157) in eight positional candidate genes (LOD drop 1.5 regions) were genotyped in GIFT patients and 332 healthy controls. Five chr7 SNPs associated with VTE. SNP THSD7A rs2074597 was responsible for part of the chr7 signal.

CONCLUSIONS

The GIFT panel is rich in established genetic risk factors for VTE, but genetic factors remain unidentified in many families. Genome-wide linkage failed to identify the previously established genetic risk factors for VTE, but identified a novel VTE susceptibility locus on chr7.

Factor V Leiden and thrombosis in patients with inflammatory bowel disease (IBD): a meta-analysis

BACKGROUND

Testing for genetic risks of Factor V Leiden ( FVL ) in inflammatory bowel disease (IBD) patients with thromboembolism (TE) is common, but the safety and utility of such testing need review.

AIM

The aim of the present study was to investigate whether the FVL polymorphisms would be one inherited prothrombotic risk factor that could significantly increase the risk of thrombosis in patients with IBD.

METHODS

We performed an electronic databases search to identify published studies correlating the FVL mutations with four populations including one IBD group with TE complications, one control IBD group without TE complications, one control non-IBD group with TE complications and another healthy control (HC) group. Statistical analysis was performed with Review Manager (RevMan) 5.0. Sub-analysis/sensitivity analysis was also performed.

RESULTS

We identified 112 titles and included 22 studies in this meta-analysis. The odds ratio (OR) of TE in IBD patients with FVL was higher as compared with IBD patients (OR: 4.00; 95%CI: 2.04, 7.87) and HC (OR: 3.19; 95%CI: 1.38, 7.36). There was a 1.25-fold (95%CI: 0.90-1.74) increase in incidence of FVL gene mutation in IBD patients compared with HC. The FVL mutations were not significantly different between IBD patients with thrombosis and non-IBD patients with thrombosis (OR: 0.79; 95%CI: 0.43, 1.47).

CONCLUSION

FVL plays a role in IBD-TE, but to no greater extent than it does in the general population with TE.

Venous valvular stasis-associated hypoxia and thrombosis: what is the link?

This review focuses on the role of the venous valves in the genesis of thrombus formation in venous thromboembolic disease (VTE). Clinical VTE and the evidence for the valvular origin of venous thrombosis are reviewed. Virchow's triad is then used as a framework for discussion to approach the question posed regarding the link between venous valvular stasis-associated hypoxia and thrombosis. Thus, the effects of blood flow stasis, hypercoagulability of blood, and the characteristics of the vessel wall within the venous valvular sinus are assessed in turn.

Advances in understanding pathogenic mechanisms of thrombophilic disorders

Venous thromboembolism is a major medical problem, annually affecting 1 in 1000 individuals. It is a typical multifactorial disease, involving both genetic and circumstantial risk factors that affect a delicate balance between procoagulant and anticoagulant forces. In the last 50 years, the molecular basis of blood coagulation and the anticoagulant systems that control it have been elucidated. This has laid the foundation for discoveries of both common and rare genetic traits that tip the natural balance in favor of coagulation, with a resulting lifelong increased risk of venous thrombosis. Multiple mutations in the genes for anticoagulant proteins such as antithrombin, protein C, and protein S have been identified and constitute important risk factors. Two single mutations in the genes for coagulation factor V (FV Leiden) and prothrombin (20210G>A), resulting from approximately 20,000-year-old mutations with subsequent founder effects, are common in the general population and constitute major genetic risk factors for thrombosis. In celebration of the 50-year anniversary of the American Society of Hematology, this invited review highlights discoveries that have contributed to our present understanding of the systems that control blood coagulation and the genetic factors that are involved in the pathogenesis of venous thrombosis.

Factors leading to decreased rates of deep vein thrombosis and pulmonary embolism after total knee arthroplasty

We evaluated a total of 473 knees (264 patients) to determine the prevalence of deep vein thrombosis and pulmonary embolism (PE) in those who were not given thromboprophylaxis after total knee arthroplasty (TKA). Deep vein thrombosis was diagnosed by roentgenographic venography, and PE was diagnosed by perfusion lung scanning. In patients with bilateral TKA, 47 (11%) of 418 venograms showed positive findings for thrombi, whereas in patients with unilateral TKA, 11 (20%) of 55 venograms showed positive findings for thrombi (P = .758). No patient had symptoms of PE, and findings for the perfusion lung scans were negative in all patients. We neither treat our patients for deep vein thrombosis and PE prophylactically nor therapeutically unless patient has a symptomatic PE.

The John Charnley Award: heritable thrombophilia and development of thromboembolic disease after total hip arthroplasty

We retrospectively assessed whether heritable thrombophilia-hypofibrinolysis was more common in patients developing venous thromboembolism after total hip replacement than among control patients who did not develop venous thromboembolism, as an approach to better identify causes of venous thromboembolism after total hip arthroplasty. Twenty patients with proximal deep venous thrombosis after THA and 23 patients with symptomatic pulmonary embolism were compared with 43 control patients who did not have postoperative venous thromboembolism. Five of 42 patients with venous thromboembolism (12%) and 0 of 43 control patients (0%) had antithrombin III deficiency (< 75%). Nine of 42 patients with venous thromboembolism (21%) and 2 of 43 control patients (4.7%) had protein C deficiency (< 70%). Ten of 43 patients with venous thromboembolism (9 heterozygous, 1 homozygous; 23%) and 1 of 43 control patients (heterozygous; 2%) had the prothrombin gene mutation. Patients who had venous thromboembolism after total hip arthroplasty were more likely than matched control patients to have heritable thrombophilia with antithrombin III or protein C deficiency, or homo-heterozygosity for the prothrombin gene mutation. Screening for these three tests of heritable thrombophilia before total hip arthroplasty should improve the identification of patients with a reduced risk of venous thromboembolism who may need only mild thromboprophylaxis, and of those patients with heritable thrombophilia in whom prophylaxis should be more aggressive.

LEVEL OF EVIDENCE

Prognostic study, Level II-1 (lesser-quality RCT). See the Guidelines for Authors for a complete description of levels of evidence.

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%).

Managing oral anticoagulant therapy in patients with mechanical heart valves undergoing elective surgery

The optimal perioperative anticoagulation management in patients on warfarin therapy is poorly defined because of the lack of randomized trials. Because guidelines are heterogeneous, we hypothesized that treatment strategies are not uniform in clinical practice. During the Annual Meeting of the Italian Federation of Anticoagulation Clinics, a questionnaire with four different clinical scenarios was distributed. Two scenarios described the cases of patients with a mechanical heart valve in the mitral position and additional risk factors for systemic embolism, one undergoing major surgery (case 1) and one undergoing minor surgery (case 3). Two scenarios described patients with an aortic mechanical heart valve, one undergoing major surgery (case 2) and one minor surgery (case 4). Different preoperative and postoperative management options were offered. Treatment options for all scenarios were the same. Of the 300 questionnaires distributed, 72 were returned (24%). Outpatient full-dose low molecular weight heparin (LMWH) was the most selected strategy in the preoperative phase. It was chosen by 90.3% of participants in case 3, 87.5% in case 1, 62.5% in case 2, and 52.8% in case 4. In the postoperative phase, full-dose LMWH remained the most selected option for cases 1 (75%) and 3 (70.8%), whereas low-dose LMWH was selected by the majority for cases 2 (50%) and 4 (61.1%). Even among expert clinicians, the management of perioperative anticoagulation is heterogeneous. In particular, the definition of risk categories and the optimal intensity of antithrombotic drugs remain to be assessed by well-designed prospective studies.

LMWH for Perioperative Anticoagulation in Patients on Chronic Warfarin Therapy

OBJECTIVE:

To review current data regarding low-molecular-weight heparin (LMWH) use for perioperative anticoagulation in patients receiving chronic warfarin therapy.

DATA SOURCES:

Data were obtained from the Sixth American College of Chest Physicians Consensus Conference on Antithrombotic Therapy guidelines and a MEDLINE search (1996-January 2003). Search terms included heparin, low-molecular-weight heparin, warfarin, perioperative care, and anticoagulants.

DATA SYNTHESIS:

Heparin is the most common agent used as bridge therapy for perioperative anticoagulation in patients on chronic warfarin therapy; LMWHs are also used. Studies that evaluated enoxaparin and/or dalteparin were reviewed.

CONCLUSIONS:

Although published studies demonstrate efficacy and safety of LMWHs, more data are needed to support their use as bridge therapy.

Genome scan of venous thrombosis in a pedigree with protein C deficiency

Kindred Vermont II has a high frequency of venous thrombosis, occurring primarily in pedigree members with type I protein C deficiency due to a 3363 inserted (Ins) C mutation in exon 6 of the protein C gene. However, only a subset of 3363 InsC carriers have suffered thrombotic episodes, suggesting that the increased risk of thrombosis results upon the co-occurrence of 3363 InsC with a second, unknown, thrombophilic mutation that segregates independently within the pedigree. To test this hypothesis and to localize the co-occurring gene, we performed a genome scan of venous thrombosis in Kindred Vermont II. Non-parametric linkage statistics identified three potential gene locations, on chromosomes 11q23 (nominal P < 0.0001), 18p11.2-q11.2 (P < 0.0007), and 10p12 (P < 0.0003), supporting the presence of at least one additional thrombophilic mutation in the pedigree. Identification of the unknown mutation(s) promises to reveal a new genetic risk factor for thrombophilia, contribute to our understanding of the blood clotting mechanism, and expand our knowledge of the diversity of oligogenic disease.

Familial segregation of venous thromboembolism

BACKGROUND

Venous thromboembolism (VTE) is postulated as a complex disease, but the heritability and mode of inheritance are uncertain.

OBJECTIVE

To determine if VTE (i) segregates in families; (ii) is attributable to inheritance, shared environment, or both; and (iii) the possible mode of inheritance.

PATIENTS AND METHODS

In a family-based study of relatives from 751 probands (60% female) with objectively diagnosed VTE (without cancer), we performed complex segregation analyses corrected for mode of ascertainment, considering age-specific, non-gender- and gender-specific liability classes under Mendelian and non-Mendelian assumptions. We tested 12 models categorized into four model sets: (i) sporadic (assumes no genetic effect); (ii) Mendelian inheritance of a major gene (including dominant, additive, recessive or codominant classes); (iii) mixed model (Mendelian inheritance including the same four classes plus the effect of polygenes); and (iv) non-Mendelian.

RESULTS

Among the 16 650 relatives, 753 (48% female) were affected with VTE, of whom 62% were first-degree relatives. The sporadic model was rejected in both non-gender- and gender-specific liability class analyses. Among the remaining gender-specific models, the unrestricted (non-Mendelian) inheritance model was favored with an estimated heritability of 0.52. Among the Mendelian models, the dominant mixed model was preferred, with an estimated heritability and major disease allele frequency of 0.62 and 0.25, respectively, suggesting an effect of several minor genes.

CONCLUSION

A multifactorial non-Mendelian inheritance model was favored as the cause for VTE, while a model postulating a purely environmental cause was rejected. VTE is probably a result of multigenic action as well as environmental exposures.

High prevalence of combined thrombophilic abnormalities in patients with inflammatory bowel disease

INTRODUCTION

A hypercoagulable state has been recognized in patients with inflammatory bowel disease.

OBJECTIVE

The aim of this study was to determine the frequency of single and combined thrombophilic abnormalities in patients from northern Portugal with Crohn's disease or ulcerative colitis, without a history of thrombosis. METHODS A cross-sectional study involving 116 patients (42 with ulcerative colitis, 74 with Crohn's disease), and 141 randomly chosen asymptomatic blood donors was carried out. Prothrombotic variables and genetic abnormalities were assessed.

RESULTS

The prevalence of single prothrombotic abnormalities (only one alteration) in inflammatory bowel disease patients was higher than in the reference population (26% and 18%, respectively; P < 0.02). The allelic frequency of genetic polymorphisms was higher in Crohn's disease and ulcerative colitis for MTHFR C677T, ACE Del and PAI-1 4G (P < 0.001) than in the reference population. The prevalence of combined thrombophilic abnormalities (at least two alterations) in both Crohn's disease and ulcerative colitis was also higher (22% and 21%, respectively) than in the reference population (9%; P < 0.01). These differences were not related to age or gender; however, in Crohn's disease the frequency of two or more abnormalities was related to disease activity (odds ratio 3.0 [1.3-6.7]).

CONCLUSION

Higher prevalences of single and combined thrombophilic defects were found in inflammatory bowel disease patients, factors that could be involved in the disease pathogenesis.

Evaluating chronic venous disease with a new venous severity scoring system

BACKGROUND

The Venous Clinical Severity Score (VCSS) has been proposed by the American Venous Forum as an objective means to clinically assess venous disease more completely than with the clinical CEAP classification. However, validation of the VCSS against an objective test is lacking. The purpose of this study was to test the VCSS against abnormalities found on venous ultrasound (US) scans.

METHODS

As part of a screening project in a large kindred population with protein C deficiency, VCSS and venous US scanning were performed in 210 patients (420 limbs). A single examiner scored the VCSS (0-3) clinically for pain, varicose veins, edema, skin pigmentation, inflammation, induration, ulcer duration and size, and compressive therapy. Another experienced examiner, blinded to the subject's medical history, performed a US examination of the deep and superficial venous system, with a hand-carried US system. The relationship between US and VCSS scores was analyzed by calculating an odds ratio (OR) and its 95% confidence interval (CI).

RESULTS

Of the 420 limbs screened, VCSS was 0 in 283 limbs, and VCSS was 1 or greater in the following categories: pain, 63 limbs; varicose veins, 70 limbs; edema, 51 limbs; skin pigmentation, 17 limbs; inflammation, 2 limbs; induration, 8 limbs; and compressive therapy, 9 limbs. The highest total score in any limb was 8. A clear association was seen with the VCSS and abnormalities found on US scans. When the score was dichotomized (0 = normal, 1 = any abnormality), it was a strong predictor of US scan abnormalities; limbs with VCSS greater than 0 had a 26-fold greater chance of US scan abnormalities than did limbs with VCSS = 0 (OR, 26.5; 95% CI, 11-64). With ultrasonography as the standard, sensitivity of VCSS compared with US scans was 89.3%, and specificity was 76.1%. Negative predictive value of VCSS = 0 was 97.9%, and positive predictive value for any positive score was 36.5%

CONCLUSIONS

The results of this study are based on a large kindred population with a higher risk for venous disease than found in the general population. Though the VCSS was devised to quantify the severity of chronic venous disease, this study found it a useful screening tool. The VCSS showed good association with abnormalities on US scans, and when VCSS = 0 there is a high likelihood that the patient does not have venous disease. This simple test may prove valuable in clinical practice.

A review of the technical, diagnostic, and epidemiologic considerations for protein S assays

OBJECTIVES

To review the state of the art relating to protein S deficiency as a risk factor for thrombosis and to make recommendations regarding the use of protein S measurements in the assessment of thrombotic risk in individual patients and families.

DATA SOURCES, EXTRACTION, AND SYNTHESIS

Selection criteria were developed for the inclusion of publications from 1985 to 2001 based on the relevant literature concerned with the systematic review of diagnostic tests. Minimal selection criteria were agreed on and the articles stratified into level 1 if they met these criteria and level 2 if they did not meet these criteria. The included articles were reviewed by the authors and abstracted onto predetermined data collection forms. These forms were then scored and recommendations based on level 1 studies. As described elsewhere, results of discussions at the College of American Pathologists Conference XXXVI on Diagnostic Issues in Thrombophilia were used to revise the manuscript into its final form.

CONCLUSIONS

Consensus was reached on 16 recommendations for the use of protein S assays in the assessment of thrombotic risk in individuals and families. Two themes run through the conclusions. First, protein S assays are the most technically problematic of the assays reviewed at this conference. Second, only 2 papers evaluating the diagnostic use of protein S assays met our level 1 inclusion criteria. These 2 problems point out the need for better standardized assays and rigorous studies of the diagnostic utility of these assays.

Laboratory issues in diagnosing abnormalities of protein C, thrombomodulin, and endothelial cell protein C receptor

OBJECTIVE

To review the current understanding of the pathophysiology of protein C deficiency and its role in congenital thrombophilia. Recommendations for diagnostic testing for protein C function and concentration, derived from the medical literature and consensus opinions of recognized experts in the field, are included, specifying whom, how, and when to test. The role of related proteins, such as thrombomodulin and endothelial protein C receptor, is also reviewed. Data Sources.-Review of the published medical literature.

DATA EXTRACTION AND SYNTHESIS

A summary of the medical literature and proposed testing recommendations were prepared and presented at the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. After discussion at the conference, consensus recommendations presented in this manuscript were accepted after a two-thirds majority vote by the participants.

CONCLUSIONS

Protein C deficiency is an uncommon genetic abnormality that may be a contributing cause of thrombophilia, often in conjunction with other genetic or acquired risk factors. When assay of protein C plasma levels is included in the laboratory evaluation of thrombophilia, a functional amidolytic protein C assay should be used for initial testing. The diagnosis of protein C deficiency should be established only after other acquired causes of protein C deficiency are excluded. A low protein C level should be confirmed with a subsequent assay on a new specimen. Antigenic protein C assays may be of benefit in subclassification of the type of protein C deficiency. The role of thrombomodulin and endothelial cell protein C receptor in thrombosis has yet to be clearly established, and diagnostic testing is not recommended at this time.

[Genetic risk factors of thrombosis]

Genetic risk factors became a frequent predisposing cause of venous thromboembolism (VTE) since the discovery of two mutations: factor V Leiden and G20210A mutation of prothrombin gene. One of these both mutations is associated with around 25% of VTE events. Interaction of genetic risk factors, such as interaction of FV Leiden or G20210A mutation of prothrombin with antithrombin, protein C or protein S deficiencies, as well as interaction with acquired risk factors, have demonstrated that venous thrombosis is a multifactorial disease. The search for thrombophilia must be done in VTE occurring before the age of 45, in case of recurrencies and in case of familial history of VTE.

Proteolysis of protein C in pooled normal plasma and purified protein C by activated protein C (APC)

Protein C is a vitamin-K dependent zymogen of the anti-coagulant serine protease activated protein C (APC). In this paper, we report four lines of evidence that APC can activate protein C in pooled normal plasma, and purified protein C. First, the addition of APC to protein C-deficient plasma supplemented with protein C produces a prolongation of the clotting time of plasma that is proportional to the amount of protein C. This behavior was observed with APC from the Chromogenix APC resistance kit (Dia Pharm, Franklin, OH, USA) and from APC derived from the thrombin activation of human protein C (Enzyme Research Laboratories, South Bend, IN, USA). Secondly, using immunoblotting after gel electrophoresis, the disappearance of epitopes for monoclonal antibodies that recognize protein C but not APC indicates a time course for the activation by APC of protein C in pooled normal plasma and protein C purified from plasma. Thirdly, the same time course for the disappearance of protein C specific epitope can be followed using ELISA. Finally, protein C can be activated by APC as indicated by the increase in APC specific synthetic substrate Tryp-Arg-Arg-p nitroaniline hydrolysis. Kinetic data indicate a value of 4.7+/-0.4 mM(-1) s(-1) for the activation of protein C by APC under physiological conditions and in the presence of calcium. These observations document that APC must function not only in the inactivation of activated factors V and VIII, but also in the activation of protein C. This additional action of APC may be important to consider more broadly because of APC in the treatment of sepsis.

Prothrombotic inherited abnormalities other than factor V Leiden mutation do not play a role in venous thrombosis in inflammatory bowel disease

OBJECTIVES

Because the incidence of thromboembolism is increased in patients with inflammatory bowel disease, we attempted to assess the role of prothrombotic inherited coagulation abnormalities in the development of thrombosis.

METHODS

Four populations were compared: 15 patients with inflammatory bowel disease and a previous venous thrombosis, 58 control patients with inflammatory bowel disease but without thrombosis, 110 patients without inflammatory bowel disease but with previous deep venous thrombosis, and 84 healthy subjects. Inherited and acquired risk factors of venous thrombosis, e.g., factor V Leiden and prothrombin 20210A mutations, C677T methylenetetrahydrofolate reductase polymorphism, a polymorphism located in exon 13 of factor V gene, inflammatory and hypercoagulability markers were studied in each population.

RESULTS

In the study, 14.3% of thrombotic patients with inflammatory bowel disease had factor V Leiden mutation versus 0% of control patients with inflammatory bowel disease (p = 0.04), 15.5% of thrombotic patients without inflammatory bowel disease (NS) and 3.6% of the healthy controls. A total of 14% of thrombotic patients with inflammatory bowel disease and 11.8% of thrombotic patients without inflammatory bowel disease carried prothrombin 20210A mutation, compared to 1.7% of control patients with inflammatory bowel disease; however, the difference was just below significance. Other inherited coagulation abnormalities were not statistically significantly different among the four populations.

CONCLUSIONS

Our study confirms that factor V Leiden mutation increases the risk for thrombotic events but is not more frequent in patients with inflammatory bowel disease. Our results do not support the role of other thrombotic risk factors.