Genetic determinants of activity and antigen levels of contact system factors.

Essentials Genetic variation may provide valuable insight into the role of the contact system in thrombosis. Explored associations of genetic variants with activity, antigen, and disease in RATIO study. Two novel loci were identified: KLKB1 rs4253243 for prekallikrein; KNG1 rs5029980 for HMWK levels. Contact system variants and haplotypes were not associated with myocardial infarction or stroke. SUMMARY: Background The complex, interdependent contact activation system has been implicated in thrombotic disease, although few genetic determinants of levels of proteins from this system are known. Objectives Our primary aim was to study the influence of common F11, F12, KLKB1, and KNG1 variants on factor (F) XI activity and FXI, FXII, prekallikrein (PK) and high-molecular-weight kininogen (HMWK) antigen levels, as well as the risk of myocardial infarction and ischemic stroke. Patients/methods We analyzed samples from all 630 healthy participants, 182 ischemic stroke patients and 216 myocardial infarction patients in the RATIO case-control study of women aged < 50 years. Forty-three tagging single nucleotide variants (SNVs) were genotyped to represent common genetic variation in the contact system genes. Antigen and activity levels were measured with sandwich-ELISA-based and one-stage clotting assays. We performed single variant, age-adjusted, linear regression analyses per trait and disease phenotype, assuming additive inheritance and determined conditionally independent associations. Haplotypes based on the lead SNV and all conditionally independent SNVs were tested for association with traits and disease. Results We identified two novel associations of KLKB1 SNV rs4253243 with PK antigen (ßconditional = -12.38; 95% CI, -20.07 to -4.69) and KNG1 SNV rs5029980 with HMWK antigen (ßconditional = 5.86; 95% CI, 2.40-9.32) and replicated previously reported associations in a single study. Further analyses probed whether the observed associations were indicative of linkage, pleiotropic effects or mediation. No individual SNVs or haplotypes were associated with the disease outcomes. Conclusion This study adds to current knowledge of how genetic variation influences contact system protein levels and clarifies interdependencies.

Prevalence of the metabolic syndrome and cardiovascular disease risk in chemotherapy-treated testicular germ cell tumour survivors.

BACKGROUND: Testicular cancer patients have an increased risk for cardiovascular disease (CVD), which might be related to the increased prevalence of the metabolic syndrome (MetS) in this group of patients. METHODS: We assessed the prevalence of MetS and calculated the 10-year CVD risk in a cohort of 255 testicular germ cell tumour survivors (median age, 38.7 years; interquartile range, 31-48) at a mean of 7.8 years after anti-cancer treatment, and compared these with data obtained from 360 healthy men. RESULTS: Survivors had an age-adjusted increased risk for MetS of 1.9 compared with that of healthy controls. The risk for MetS was highest in survivors treated with combination chemotherapy (CT) 2.3 (Adult Treatment Panel of the National Cholesterol Education Program classification) and 2.2 (International Diabetes Federation classification). The risk of MetS was especially increased in survivors with testosterone levels in the lowest quartile (OR, 2.5). Ten-year cardiovascular risk as assessed by the Framingham Risk Score (3.0%) and Systemic Coronary Risk Evaluation (1.7%) algorithms was low, independent of treatment, and was comparable to controls. CONCLUSION: Testicular germ cell tumour survivors have an increased prevalence of MetS, with hypogonadism and CT treatment being clear risk factors for the development of the syndrome. The increased prevalence of MetS was not associated with an increased 10-year cardiovascular risk.

Genetic variants associated with protein C levels.

BACKGROUND: Normal protein C (PC) plasma levels range widely in the general population. Factors influencing normal PC levels are thought to influence the risk of venous thrombosis. Little is known about the underlying genetic variants. OBJECTIVES: We performed a genome scan of normal PC levels to identify genes that regulate normal PC levels. PATIENTS/METHODS: We performed a variance components linkage analysis for normal PC levels in 275 individuals from a single, large family. We then sequenced candidate genes under the identified linkage peak in eight family members: four with high and four with low, but normal, PC levels. For variants showing a difference in carriers between those with high and low PC levels, we re-evaluated linkage in the 275 family members conditional on the measured genotype effect. Genotype-specific mean PC levels were determined using likelihood analysis. Findings were replicated in the Leiden Thrombophilia Study (LETS). RESULTS: We identified a quantitative trait locus at chromosome 5q14.1 affecting normal PC plasma level variability. Next-generation sequencing of 113 candidate genes under the linkage peak revealed four SNPs in BHMT2, ACOT12, SSBP2 and XRCC4, which significantly increased PC levels in our thrombophilic family, but not in LETS. CONCLUSIONS: We identified four genes at chromosome 5q14.1 that might influence normal PC levels. BHMT2 seems the most likely candidate to regulate PC levels via homocysteine, a competitive inhibitor to thrombin. Failure to replicate our findings in LETS might be due to differences between the studies in genetic background and linkage disequilibrium patterns.

Risk of venous thrombosis in patients with chronic kidney disease: identification of high-risk groups.

BACKGROUND: Although an association between venous thrombosis and chronic kidney disease has recently been established, it is unknown which patients with chronic kidney disease are most likely to benefit from thromboprophylaxis. OBJECTIVE: The aim of this study was to assess the association between venous thrombosis and chronic kidney disease in combination with arterial thrombosis, malignancy, surgery and thrombophilia to identify high-risk groups as a basis for personalized prevention. METHODS: This study included 2473 consecutive patients with first venous thrombosis and 2936 controls from a case-control study (the MEGA study). RESULTS: Moderately decreased kidney function (eGFR 30-60 mL min(-1) ) was associated with a 2.5-fold (95% CI, 1.9-3.4) increased risk and severely decreased kidney function (eGFR < 30 mL min(-1) ) was associated with a 5.5-fold (95% CI 1.8-16.7) increased risk of venous thrombosis, compared with those with normal kidney function (eGFR > 90 mL min(-1) ). The risk of venous thrombosis was additionally increased for moderately and severely reduced kidney function in combination with arterial thrombosis (odds ratio, 4.9; 95% CI, 2.2-10.9), malignancy (5.8; 95% CI, 2.8-12.1), surgery (14.0; 95%, CI 5.0-39.4), immobilization (17.1; 95% CI, 6.8-43.0) or thrombophilia (odds ratios, 4.3-9.5), with particularly high risks when three or more risk factors were present (odds ratio, 56.3; 95% CI, 7.6-419.3). CONCLUSION: Decreased kidney function is associated with an increased risk of venous thrombosis. The risk increased substantially in the presence of one or more other risk factors for thrombosis.

Risk of venous thrombosis in patients with major illnesses: results from the MEGA study.

BACKGROUND: The risk of venous thrombosis associated with major illnesses is not well known, and neither is the risk associated with the combined effect of immobilization and thrombophilia. The aim of this study was to assess the effect on the development of venous thrombosis of several major illnesses in combination with immobilization, body mass index, and thrombophilia, to identify high-risk groups that may provide a basis for personalized prevention. METHODS: This study included 4311 consecutive patients with a first episode of venous thrombosis, and 5768 controls from a case-control study (MEGA study). We calculated odds ratios (ORs) for venous thrombosis for patients with a self-reported history of major illnesses. RESULTS: Venous thrombosis risk was increased for all investigated major illnesses: liver disease, OR 1.7 (95% confidence interval [CI]1.0-2.9); kidney disease, OR 3.7 (95% CI 2.3-5.9); rheumatoid arthritis, OR 1.5 (95% CI 1.2-1.9); multiple sclerosis, OR 2.4 (95% CI 1.3-4.3); heart failure, OR 1.7 (95% CI 1.2-2.3); hemorrhagic stroke, OR 4.9 (95% CI 2.4-9.9); arterial thrombosis, OR 1.5 (95% CI 1.2-1.8); and the presence of any of the above major illnesses, OR 1.7 (95% CI 1.5-1.9). Combinations of major illnesses with immobilization and increased factor VIII (OR 79.9; 95% CI 33.2-192.2), increased FIX (OR 35.3; 95% CI 14.2-87.8), increased von Willebrand factor (OR 88.0; 95% CI 33.9-228.3), FV Leiden (OR 84.2; 95% CI 19.5-363.6), and blood group non-O (OR 53.1; 95% CI 30.9-91.4) were associated with increased venous thrombosis risks. CONCLUSIONS: All of the major illnesses reported here were associated with an increased risk of venous thrombosis. These risks were most pronounced at the time of immobilization or in the presence of thrombophilia.

Mortality and inherited thrombophilia: results from the European Prospective Cohort on Thrombophilia.

BACKGROUND: Data on the survival of individuals with hereditary thrombophilia are rare and only come from retrospective studies. OBJECTIVE: The aim of the present study was to assess mortality in individuals with known thrombophilia with and without a history of thrombosis in comparison to a control group. PATIENTS/METHODS: The European Prospective Cohort on Thrombophilia (EPCOT) study is a prospective, multi-center observational study performed to assess the risk of thrombosis in persons with inherited thrombophilia. In an extension of the present study, the vital status was assessed in 1240 individuals with thrombophilia (mean age 40.9 years, 59% women, 196 with antithrombin, 341 with protein C, 276 with protein S-deficiency, 330 with factor (F)V Leiden and 97 with combined defects, and 62% with a history of venous thrombosis [VT]) and 875 controls (mean age 42.5 years, 48% women, 7% with a history of VT). RESULTS: Seventy-two individuals with thrombophilia and 45 controls died during follow-up. The risk of death, adjusted for gender, thrombosis history and center, was not associated with thrombophilia (hazard ratio [HR] thrombophilia individuals vs. controls: 1.09, 95% confidence interval [CI] 0.66-1.78). When individuals with thrombophilia were evaluated separately, a history of thrombosis was not associated with mortality: the risk of death after adjustment for gender, anticoagulation and center was HR 0.79 (95% CI, 0.41-1.54). CONCLUSIONS: No increased risk of death in individuals with thrombophilia, not even in those with a history of thrombosis, was observed.

Genome scan of clot lysis time and its association with thrombosis in a protein C-deficient kindred.

BACKGROUND: Previously, we found increased clot-lysis time (CLT), as measured with a plasma-based assay, to increase the risk of venous thrombosis in two population-based case-control studies. The genes influencing CLT are as yet unknown. PATIENTS/METHODS: We tested CLT as risk factor for venous thrombosis in Kindred Vermont II (n = 346), a pedigree suffering from a high thrombosis risk, partially attributable to a type I protein C deficiency. Furthermore, we tested for quantitative trait loci (QTLs) for CLT, using variance component linkage analysis. RESULTS: Protein C-deficient family members had shorter CLTs than non-deficient members (median CLT 67 min vs. 75 min). One standard deviation increase in CLT increased the risk of venous thrombosis 2.4-fold in non-deficient family members. Protein C deficiency without elevated CLT increased the risk 6.9-fold. Combining both risk factors yielded a 27.8-fold increased risk. The heritability of CLT was 42-52%. We found suggestive evidence of linkage on chromosome 11 (62 cM), partly explained by the prothrombin 20210A mutation, and on chromosome 13 (52 cM). Thrombin-activatable fibrinolysis inhibitor genotypes did not explain the variation in CLT. CONCLUSION: Hypofibrinolysis appears to increase thrombosis risk in this family, especially in combination with protein C deficiency. Protein C deficiency is associated with short CLT. CLT is partly genetically regulated. Suggestive QTLs were found on chromosomes 11 and 13.

Chronic kidney disease stages 1-3 increase the risk of venous thrombosis.

BACKGROUND: End-stage renal disease has been associated with venous thrombosis (VT). However, the risk of VT in the early stages of chronic kidney disease (CKD) has not yet been investigated. The aim of this study was to investigate whether CKD patients with stage 1-3 disease are at increased risk of VT. METHODS: Eight thousand four hundred and ninety-five subjects were included in a prospective cohort study, in which renal function and albuminuria were assessed, starting in 1997-1998, and were followed for the occurrence of VT until 1 June 2007. CKD patients were staged according to the Kidney Disease Outcomes Quality Initiative guidelines, on the basis of 24-h urine albumin excretion and estimated glomerular filtration rates. Objectively verified symptomatic VT was considered to be the endpoint. RESULTS: Of the 8495 subjects, 243 had CKD stage 1, 856 CKD stage 2, and 491 CKD stage 3. During a median follow-up period of 9.2 years, 128 individuals developed VT. The hazard ratios (HRs) for CKD stages 1, 2 and 3 were, respectively, 2.2 [95% confidence interval (CI) 0.9-5.1], 1.9 (95% CI 1.1-3.1) and 1.6 (95% CI 0.9-2.8) relative to those without CKD after adjustment for age, sex, body mass index, hypertension, diabetes, malignancy, and high-sensitivity C-reactive protein. Subjects with CKD stage 3 and albuminuria (≥ 30 mg d(-1)) had an adjusted HR of 3.0, and subjects with CKD stage 3 without albuminuria had an adjusted HR of 1.0. CONCLUSIONS: CKD stages 1 and 2, and CKD stage 3 in the presence of albuminuria, are risk factors for VT. The risk of VT is more related to albuminuria than to impaired glomerular filtration rate.

Effect of APOE genotype on lipid levels in patients with coronary heart disease during a 3-week inpatient rehabilitation program.

It has been suggested that the apolipoprotein E (APOE) genotype modifies the effect of dietary and pharmacological interventions for lowering lipid levels. We wanted to determine whether APOE genotyping information would be useful in making lipid-lowering treatment decisions in clinical practice. We included 981 patients with coronary heart disease (CHD) enrolled in an inpatient 3-week standardized rehabilitation program. Of these, 555 (57%) patients received continued statin therapy and 232 (24%) patients received newly initiated statin therapy. Dietary intervention was part of the program only for 194 (20%) patients. Total cholesterol (TC) and low-density lipoprotein cholesterol (LDLC) levels decreased in all the groups of patients during rehabilitation. The decreases were less pronounced among the APOE E2 carriers. However, the observed variation among the groups with respect to reduction of lipid levels was accounted for mainly by the initial lipid levels (30-47%) and only marginally on the APOE genotype (1%) . We therefore found no evidence that APOE genotyping will be useful in guiding dietary or pharmacological lipid-lowering treatment decisions.

A genetic basis for the interrelation of coagulation factors.

BACKGROUND: Evidence found in the literature for a strong correlation between coagulation factors suggests that single genes might influence the plasma concentrations of multiple coagulation factors (i.e. pleiotropically acting genes). OBJECTIVE: To determine whether there is a genetic basis for the correlation among coagulation factors by assessing the heritability of interrelated coagulation factors. PATIENTS/METHODS: We performed principal components analysis, and subsequently variance components analysis, to estimate the heritability of principal components of coagulation factors in family members of a large French-Canadian kindred. RESULTS: Four clusters were identified by principal components analysis in 200 family members who did not carry the protein C 3363C mutation. Cluster 1 consisted of prothrombin, factor VII (FVII), FIX, FX and protein S; cluster 2 consisted of FV, FIX, protein C and tissue factor pathway inhibitor; cluster 3 consisted of FVIII and von Willebrand factor; and cluster 4 consisted of antithrombin, protein C and FVII. The heritability of the principal components estimated by variance components analysis was, respectively, 37%, 100%, 37%, and 37%. CONCLUSION: Our findings support the hypothesis that genes can influence plasma levels of interrelated coagulation factors.

How evidence-based are advertisements in journals regarding the subspecialty of rheumatology?

OBJECTIVES: In rheumatology, five different billion-dollar drugs have emerged in recent years, making this subspecialty the focus of extensive advertising campaigns. Considering this development and the fact that the scientific content of advertisements has been questioned, we initiated a study to determine how evidence-based advertisements are in four leading journals of rheumatology. METHODS: Advertisements were extracted from the journals Arthritis and Rheumatism, Rheumatology, Seminars in Arthritis and Rheumatism and the Journal of Rheumatology, and were evaluated using a standardized score form. RESULTS: In total, 353 advertisements were obtained, of which 84 were unique. Of the 300 references provided by these unique advertisements, 53 (18%) were considered 'supporting'. In addition, 87 (29%) of the 300 references referred to randomized controlled trials (RCTs), of which 49% supported the claim. The vast majority of RCTs (97%) were sponsored by the advertising company. In the 84 unique advertisements 288 claims were made, of which 190 provided one or more references. Of these 190 claims, 33 (17%) were judged 'well supported'. In total, only four (5%) of the 84 different advertisements were judged 'well supported' and 11 (13%) of the 84 were judged 'misleading' because they contained one or more misleading claims, i.e. claims with references to articles contradicting the claim. CONCLUSIONS: This study indicates that few advertisements in rheumatology journals are entirely evidence-based.

Attitudes toward genetic testing for thrombophilia in asymptomatic members of a large family with heritable protein C deficiency.

BACKGROUND: Little research has been performed regarding the psychological consequences of knowing that one is at an increased risk for venous thrombosis. OBJECTIVES: The aim of this study was to explore attitudes toward genetic testing for protein C deficiency. METHODS: Questionnaires about genetic testing attitudes, dispositional anxiety, risk perception, and thrombosis-related worry were completed by 168 asymptomatic members of a North-American kindred with a high incidence of heritable protein C deficiency conferring a high lifetime risk of venous thrombosis. A total of 76 subjects (45%) had not been tested for protein C deficiency before participating in our study whereas the other 92 subjects (55%) had been tested prior to filling in the questionnaire, of whom 34 people had protein C deficiency, while 58 did not. RESULTS: Family members with protein C deficiency perceived a higher risk of suffering venous thrombosis and scored higher on thrombosis-related worry than family members without protein C deficiency. Participants who had not been tested did not report excessive thrombosis-related worry. Participants with protein C deficiency reported a belief in the psychological and health benefits of testing, and felt that they experienced low psychological distress following the genetic test. High psychological distress following the test was related to dispositional anxiety and thrombosis-related worry. Participants without protein C deficiency were relieved after finding out that they did not have the deficiency. CONCLUSION: There seem to be few negative psychological consequences of knowing that one is at an increased risk for venous thrombosis, except in vulnerable individuals.

Thrombin generation profiles in deep venous thrombosis.

BACKGROUND: Reliable markers and methods to predict risk for thrombosis are essential to clinical management. OBJECTIVE: Using an integrated approach that defines an individual's comprehensive coagulation phenotype might prove valuable in identifying individuals at risk for experiencing a thrombotic event. METHODS: Using a numerical simulation model, we generated tissue factor (TF) initiated thrombin curves using coagulation factor levels from the Leiden Thrombophilia Study population and evaluated thrombotic risk, by sex, age, smoking, alcohol consumption, body mass index (BMI) and oral contraceptive (OC) use. We quantitated the initiation, propagation and termination phases of each individuals' comprehensive TF-initiated thrombin generation curve by the parameters: time to 10 nm of thrombin, maximum time, level and rate (MaxR) of thrombin generated and total thrombin. RESULTS: The greatest risk association was obtained using MaxR; with a 2.6-fold increased risk at MaxR exceeding the 90th percentile. The odds ratio (OR) for MaxR was 3.9 in men, 2.1 in women, and 2.9 in women on OCs. The association of risk with thrombin generation did not differ by age (OR:2.8 OR:2.5), BMI (OR:2.9 OR:2.3) or alcohol use. In both numerical simulations and empirical synthetic plasma, OC use created extreme shifts in thrombin generation in both control women and women with a prior thrombosis, with a larger shift in thrombin generation in control women. This suggests an interaction of OC use with underlying prothrombotic abnormalities. CONCLUSIONS: Thrombin generation based upon the individual's blood composition is associated with the risk for thrombosis and may be useful as a predictive marker for evaluating thrombosis on an individual basis.

Chronic venous abnormalities in symptomatic and asymptomatic protein C deficiency.

BACKGROUND: Thrombophilia is a frequent medical condition associated with symptomatic deep vein thrombosis (DVT). Unlike other clinical risk factors associated with DVT, such as surgery, thrombophilia has not been demonstrated to be associated with asymptomatic venous thrombotic events. Our aim was to search for asymptomatic sequelae of DVT in a protein C (PC)-deficient family. METHODS: We studied 228 individuals from a large kindred with PC deficiency and performed a systematic ultrasound examination. RESULTS: Among the 203 patients without a known history of venous thrombosis we found seven patients with abnormalities indicative of prior asymptomatic thrombosis: six (7.4%) in the PC-deficient group (n = 81) and only one (0.8%) in the non-deficient group (n = 122). The relative risk for these sequelae associated with PC deficiency was 9.0 (95% CI: 1.1-73.7). CONCLUSIONS: These data suggest that chronic venous abnormalities are frequently present and that thrombotic events in asymptomatic individuals with familial PC deficiency may be underestimated.

The plasma hemostatic proteome: thrombin generation in healthy individuals.

BACKGROUND AND OBJECTIVES: The range of plasma concentrations of hemostatic analytes in the population is wide. In this study these components of blood coagulation phenotype are integrated in an attempt to predict clinical risk. METHODS: We modeled tissue factor (TF)-induced thrombin generation in the control population (N = 473) from the Leiden Thrombophilia Study utilizing a numerical simulation model. Hypothetical thrombin generation curves were established by modeling pro- and anticoagulant factor levels for each individual. These curves were evaluated using parameters which describe the initiation, propagation and termination phases of thrombin generation, i.e. time to 10 nm thrombin (approximate clot time), total thrombin and the maximum rates and levels of thrombin generated. RESULTS AND CONCLUSIONS: The time to 10 nm thrombin varied over a 3-fold range (2.9-9.5 min), maximum levels varied over a approximately 4-fold range (200-800 nm), maximum rates varied approximately 4.8-fold (90-435 nm min(-1)) and total thrombin varied approximately 4.5-fold (39-177 microm s(-1)) within this control population. Thrombin generation curves, defined by the clotting factor concentrations, were distinguished by sex, age, alcohol consumption, body mass index (BMI) and oral contraceptive (OC) use (OC > sex > BMI > age). Our results show that the capacity for thrombin generation in response to a TF challenge may represent a method to identify an individual's propensity for developing thrombosis.