Frank W.G. Leebeek

Elevated levels of von Willebrand Factor in cirrhosis support platelet adhesion despite reduced functional capacity.

Cirrhosis of the liver is frequently accompanied by complex alterations in the hemostatic system, resulting in a bleeding tendency. Although many hemostatic changes in liver disease promote bleeding, compensatory mechanisms also are found, including high levels of the platelet adhesive protein von Willebrand Factor (VWF). However, conflicting reports on the functional properties of VWF in cirrhosis have appeared in literature. We have measured a panel of VWF parameters in plasma from patients with cirrhosis of varying severity and causes. Furthermore, we assessed the contribution of VWF to platelet adhesion, by measuring the ability of plasma from patients with cirrhosis to support adhesion of normal or patient platelets under flow conditions. VWF antigen levels were strongly increased in patients with cirrhosis. In contrast, the relative collagen binding activity, as well as the relative ristocetin cofactor activity, was significantly lower in patients as compared with controls, indicating loss of function. Accordingly, patients had a reduced fraction of high‐molecular‐weight VWF multimers. Both strongly elevated and reduced activity and antigen levels of the VWF cleaving protease ADAMTS13 were found in individual patients. Adhesion of either normal or patient platelets to a collagen surface was substantially increased when these platelets were resuspended in plasma of patients with cirrhosis, as compared with control plasma. In conclusion, highly elevated levels of VWF in patients with cirrhosis contribute to the induction of primary hemostasis despite reduced functional properties of the molecule. This phenomenon might compensate for defects in platelet number and function in patients with cirrhosis. (HEPATOLOGY 2006;44:53–61.)

Etiology, management, and outcome of the Budd-Chiari syndrome

BACKGROUND The Budd-Chiari syndrome (BCS) is hepatic venous outflow obstruction. What is known about the syndrome is based on small studies of prevalent cases. OBJECTIVE To characterize the causes and treatment of incident BCS. DESIGN Consecutive case series of patients with incident BCS, enrolled from October 2003 to October 2005 and followed until May 2006. SETTING Academic and nonacademic hospitals in France, Spain, Italy, Great Britain, Germany, Belgium, the Netherlands, Portugal, and Switzerland. PATIENTS Persons older than 16 years with definite hepatic outflow obstruction diagnosed by imaging. Persons with hepatic outflow obstruction due to heart failure, sinusoidal obstruction syndrome, cancer, or liver transplantation were excluded. MEASUREMENTS Signs and symptoms; laboratory and imaging findings; diagnosis; treatment; and overall, transplantation-free, and intervention-free survival. RESULTS 163 incident cases of BCS were identified. Median follow-up was 17 months (range, 0.1 to 31 months). Most patients (84%) had at least 1 thrombotic risk factor, and many (46%) had more than 1; the most common was myeloproliferative disorders (49% of 103 tested patients). Patients were mainly treated with anticoagulation (140 patients [86%]), transjugular intrahepatic portosystemic shunting (56 patients [34%]), or liver transplantation (20 patients [12%]), and 80 patients (49%) were managed noninvasively. Only 3 patients underwent surgical shunting. The survival rate was 87% (95% CI, 82% to 93%) at 1 year and 82% (CI, 75% to 88%) at 2 years. LIMITATION Treatment was not standardized across all centers, and data on important clinical variables were missing for some patients. CONCLUSION Most patients with BCS have at least 1 thrombotic risk factor, and many have more than 1; myeloproliferative disorders are most common. One- and 2-year survival rates are good with contemporary management, which includes noninvasive therapies (anticoagulation and diuretics) and invasive techniques. Transjugular intrahepatic portosystemic shunting seems to have replaced surgical shunting as the most common invasive therapeutic procedure. PRIMARY FUNDING SOURCE Fifth Framework Programme of the European Commission.

Evaluation of newer risk markers for coronary heart disease risk classification: a cohort study.

BACKGROUND Whether newer risk markers for coronary heart disease (CHD) improve CHD risk prediction remains unclear. OBJECTIVE To assess whether newer risk markers for CHD risk prediction and stratification improve Framingham risk score (FRS) predictions. DESIGN Prospective population-based study. SETTING The Rotterdam Study, Rotterdam, the Netherlands. PARTICIPANTS 5933 asymptomatic, community-dwelling participants (mean age, 69.1 years [SD, 8.5]). MEASUREMENTS Traditional CHD risk factors used in the FRS (age, sex, systolic blood pressure, treatment of hypertension, total and high-density lipoprotein cholesterol levels, smoking, and diabetes) and newer CHD risk factors (N-terminal fragment of prohormone B-type natriuretic peptide levels, von Willebrand factor antigen levels, fibrinogen levels, chronic kidney disease, leukocyte count, C-reactive protein levels, homocysteine levels, uric acid levels, coronary artery calcium [CAC] scores, carotid intima-media thickness, peripheral arterial disease, and pulse wave velocity). RESULTS Adding CAC scores to the FRS improved the accuracy of risk predictions (c-statistic increase, 0.05 [95% CI, 0.02 to 0.06]; net reclassification index, 19.3% overall [39.3% in those at intermediate risk, by FRS]). Levels of N-terminal fragment of prohormone B-type natriuretic peptide also improved risk predictions but to a lesser extent (c-statistic increase, 0.02 [CI, 0.01 to 0.04]; net reclassification index, 7.6% overall [33.0% in those at intermediate risk, by FRS]). Improvements in predictions with other newer markers were marginal. LIMITATION The findings may not be generalizable to younger or nonwhite populations. CONCLUSION Among 12 CHD risk markers, improvements in FRS predictions were most statistically and clinically significant with the addition of CAC scores. Further investigation is needed to assess whether risk refinements using CAC scores lead to a meaningful change in clinical outcome. Whether to use CAC score screening as a more routine test for risk prediction requires full consideration of the financial and clinical costs of performing versus not performing the test for both persons and health systems. PRIMARY FUNDING SOURCE Netherlands Organization for Health Research and Development (ZonMw).

Novel Associations of Multiple Genetic Loci With Plasma Levels of Factor VII, Factor VIII, and von Willebrand Factor The CHARGE (Cohorts for Heart and Aging Research in Genome Epidemiology) Consortium

A complex cascade of coagulation factors underlies hemostasis and prevents life-threatening blood loss from damaged blood vessels. The hemostatic factors VII and VIII, both produced in the liver, play central roles in the initiation and propagation, respectively, of fibrin formation. In the tissue-factor pathway, blood coagulation factor VII (FVII), once activated, serves as a catalyst for factor X (FX) activation, which converts prothrombin to thrombin. During propagation, activated factor VIII (FVIII) activates FX in the presence of activated factor IX. Von Willebrand factor (vWF), produced by endothelial cells and megakaryocytes, has multiple roles in hemostasis. Its primary role is to serve as an adhesion molecule that anchors platelets to exposed collagen after endothelial cell damage. The factor also acts as a carrier protein of FVIII, thereby prolonging the half-life of FVIII. Elevated circulating levels of FVIII and vWF are risk factors for venous thrombosis but the data supporting an association of FVII levels with arterial thrombosis are less consistent.1-5 Hemorrhagic complications are associated with deficiency in FVII and vWF (von Willebrand disease), as well as X-linked deficiency in FVIII (Hemophilia A).6-9 Plasma levels of these proteins are affected by environmental factors but they also are genetically influenced.10-13 Heritability estimates range from 0.53-0.63 for FVII, 0.40-0.61 for FVIII, and 0.31-0.75 for vWF.12, 13 To date, our understanding of genetic variation influencing plasma levels has been focused primarily on cis-acting variation in the genes encoding each protein product (F7, F8, and VWF, respectively). A large-scale genome-wide investigation of the genomic correlates of plasma levels has not been previously published. Using data from 23,608 adults, we investigated genome-wide associations between common genetic variation and plasma levels of FVII, FVIII, and vWF.Background— Plasma levels of coagulation factors VII (FVII), VIII (FVIII), and von Willebrand factor (vWF) influence risk of hemorrhage and thrombosis. We conducted genome-wide association studies to identify new loci associated with plasma levels. Methods and Results— The setting of the study included 5 community-based studies for discovery comprising 23 608 European-ancestry participants: Atherosclerosis Risk In Communities Study, Cardiovascular Health Study, British 1958 Birth Cohort, Framingham Heart Study, and Rotterdam Study. All subjects had genome-wide single-nucleotide polymorphism (SNP) scans and at least 1 phenotype measured: FVII activity/antigen, FVIII activity, and vWF antigen. Each study used its genotype data to impute to HapMap SNPs and independently conducted association analyses of hemostasis measures using an additive genetic model. Study findings were combined by meta-analysis. Replication was conducted in 7604 participants not in the discovery cohort. For FVII, 305 SNPs exceeded the genome-wide significance threshold of 5.0×10−8 and comprised 5 loci on 5 chromosomes: 2p23 (smallest P value 6.2×10−24), 4q25 (3.6×10−12), 11q12 (2.0×10−10), 13q34 (9.0×10−259), and 20q11.2 (5.7×10−37). Loci were within or near genes, including 4 new candidate genes and F7 (13q34). For vWF, 400 SNPs exceeded the threshold and marked 8 loci on 6 chromosomes: 6q24 (1.2×10−22), 8p21 (1.3×10−16), 9q34 (<5.0×10−324), 12p13 (1.7×10−32), 12q23 (7.3×10−10), 12q24.3 (3.8×10−11), 14q32 (2.3×10−10), and 19p13.2 (1.3×10−9). All loci were within genes, including 6 new candidate genes, as well as ABO (9q34) and VWF (12p13). For FVIII, 5 loci were identified and overlapped vWF findings. Nine of the 10 new findings were replicated. Conclusions— New genetic associations were discovered outside previously known biological pathways and may point to novel prevention and treatment targets of hemostasis disorders.

High von Willebrand Factor Levels Increase the Risk of First Ischemic Stroke Influence of ADAMTS13, Inflammation, and Genetic Variability

Background and Purpose— Elevated von Willebrand factor (vWF) concentrations are associated with an increased risk of ischemic heart disease. Several factors influence vWF antigen levels and activity, including blood group, genetic variability, acute-phase response, and proteolysis by A Disintegrin and Metalloprotease with ThromboSpondin motif (ADAMTS13), a determinant of proteolytic cleavage of vWF. We assessed how these factors affect the relation between vWF and the occurrence of stroke to understand the underlying mechanism. Methods— In a case-control study of 124 first-ever ischemic stroke patients and 125 age- and sex-matched controls, we studied vWF antigen (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCo), ADAMTS13 activity, the −1793C/G polymorphism in the vWF gene, and C-reactive protein. Results— vWF antigen and activity levels were significantly higher in cases than in controls. The relative risk of ischemic stroke was highest in individuals in the upper quartile of vWF:Ag (odds ratio, 3.2; 95% CI, 1.4 to 7.5) and vWF:RCo (odds ratio, 2.1; 95% CI, 0.9 to 4.8) compared with individuals in the lowest quartiles. In individuals with ADAMTS13 in the lowest quartile, the relative risk of stroke was 1.7 (95% CI, 0.7 to 3.9) compared with the highest quartile. C-reactive protein, ADAMTS13, and genetic variation did not affect the association between vWF and the relative risk of stroke, whereas blood group did affect the association. Conclusions— vWF antigen and activity are associated with the occurrence of acute ischemic stroke. This relation is unaffected by the severity of the acute-phase response or by genetic variation or degradation.

Myeloproliferative neoplasms in Budd-Chiari syndrome and portal vein thrombosis: a meta-analysis.

Myeloproliferative neoplasms (MPNs) are the most common cause of Budd-Chiari syndrome (BCS) and nonmalignant, noncirrhotic portal vein thrombosis (PVT). In this meta-analysis, we determined the prevalence of MPNs and their subtypes as well as JAK2V617F and its diagnostic role in these uncommon disorders. MEDLINE and EMBASE databases were searched. Prevalence of MPNs, JAK2V617F, and MPN subtypes were calculated using a random-effects model. A total of 1062 BCS and 855 PVT patients were included. In BCS, mean prevalence of MPNs and JAK2V617F was 40.9% (95% CI, 32.9%-49.5%) and 41.1% (95% CI, 32.3%-50.6%), respectively. In PVT, mean prevalence of MPNs and JAK2V617F was 31.5% (95% CI, 25.1%-38.8%) and 27.7% (95% CI, 20.8%-35.8%), respectively. JAK2V617F and MPNs were more frequent in BCS compared with PVT (P = .03 and P = .09, respectively). Polycythemia vera was more prevalent in BCS than in PVT (P = .001). JAK2V617F screening in splanchnic vein thrombosis (SVT) patients without typical hematologic MPN features identified MPN in 17.1% and 15.4% of screened BCS and PVT patients, respectively. These results demonstrate a high prevalence of MPNs and JAK2V617F in SVT patients and show differences in underlying etiology between these disorders. Furthermore, these results validate routine inclusion of JAK2V617F in the diagnostic workup of SVT patients.

Pharmacological Strategies to Decrease Transfusion Requirements in Patients Undergoing Surgery

Surgical procedures are inevitably associated with bleeding. The amount of blood loss may vary widely between different surgical procedures and depends on surgical as well as non-surgical factors. Whereas adequate surgical haemostasis may suffice in most patients, pro-haemostatic pharmacological agents may be of additional benefit in patients with (diffuse) surgical bleeding or in patients with a specific underlying haemostatic defect. In general, surgical haemostasis and pharmacological therapies can be complementary in controlling blood loss.The use of pharmacological therapies to reduce blood loss and blood transfusions in surgery has historically been restricted to a few drugs. Antifibrinolytic agents (aprotinin, tranexamic acid and aminocaproic acid) have the best evidence supporting their use, especially in cardiac surgery, liver transplantation and some orthopaedic surgical procedures. Meta-analyses of randomised, controlled trials in cardiac patients have suggested a slight benefit of aprotinin, compared with the other antifibrinolytics. Desmopressin is the treatment of choice in patients with mild haemophilia A and von Willebrand disease. It has also been shown to be effective in patients undergoing cardiac surgery who received aspirin up to the time of operation. However, overall evidence does not support a beneficial effect of desmopressin in patients without pre-existing coagulopathy undergoing elective surgical procedures. Topical agents, such as fibrin sealants have been successfully used in a variety of surgical procedures. However, only very few controlled clinical trials have been performed and scientific evidence supporting their use is still limited.Novel drugs, like recombinant factor VIIa (eptacog alfa), are currently under clinical investigation. Recombinant factor VIIa has been introduced for the treatment of haemophilia patients with inhibitors, either in surgical or non-surgical situations. Preliminary data indicate that it may also be effective in surgical patients without pre-existing coagulation abnormalities. More clinical trials are warranted before definitive conclusions can be drawn about the safety and the exact role of this new drug in surgical patients.Only adequately powered and properly designed randomised, clinical trials will allow us to define the most effective and the safest pharmacological therapies for reducing blood loss and transfusion requirements in surgical patients. Future trials should also consider cost-effectiveness because of considerable differences in the costs of the available pro-haemostatic pharmacological agents.

Factor VIII gene (F8) mutation and risk of inhibitor development in nonsevere hemophilia A

Neutralizing antibodies (inhibitors) toward factor VIII form a severe complication in nonsevere hemophilia A, profoundly aggravating the bleeding pattern. Identification of high-risk patients is hampered by lack of data that take exposure days to therapeutic factor VIII concentrates into account. In the INSIGHT study, we analyzed the association between F8 mutation and inhibitor development in patients with nonsevere hemophilia A (factor VIII 2-40 IU/dL). This analysis included 1112 nonsevere hemophilia A patients from 14 centers in Europe and Australia that had genotyped at least 70% of their patients. Inhibitor risk was calculated as Kaplan-Meier incidence with cumulative number of exposure days as the time variable. During 44 800 exposure days (median, 24 exposure days per patient; interquartile range [IQR], 7-90), 59 of the 1112 patients developed an inhibitor; cumulative incidence of 5.3% (95% confidence interval [CI], 4.0-6.6) after a median of 28 exposure days (IQR, 12-71). The inhibitor risk at 50 exposure days was 6.7% (95% CI, 4.5-8.9) and at 100 exposure days the risk further increased to 13.3% (95% CI, 9.6-17.0). Among a total of 214 different F8 missense mutations 19 were associated with inhibitor development. These results emphasize the importance of F8 genotyping in nonsevere hemophilia A.

High functional levels of thrombin-activatable fibrinolysis inhibitor are associated with an increased risk of first ischemic stroke

Summary.  Background and objective: Several studies have suggested that thrombin‐activatable fibrinolysis inhibitor (TAFI) levels are associated with the risk of arterial thrombosis, but results have been contradictory. We studied functional TAFI levels and TAFI gene polymorphisms in 124 patients with a recent ischemic stroke and 125 age‐ and sex‐matched controls to establish the role of TAFI in ischemic stroke. Methods and results: Functional TAFI levels, defined as TAFI‐related retardation (RT), the difference in clot lysis time (LT) in the absence or presence of a specific activated TAFI inhibitor (potato carboxypeptidase inhibitor [PCI]), were higher in patients than controls (19.5 ± 4.2 vs. 17.7 ± 3.7 min, P < 0.005). Clot LTs in the presence of PCI, which were independent of TAFI, were also increased in ischemic stroke patients. This indicates that in these patients fibrinolysis is impaired not only by high TAFI levels, but also by other mechanisms. Individuals with functional TAFI levels in the highest quartile had an increased risk of ischemic stroke compared with the lowest quartile [odds ratio (OR) 4.0, 95% confidence interval (CI): 1.6–9.8]. In an unselected group of 36 of the 125 stroke patients functional TAFI levels were also measured at 3 months, and were persistently high. This indicates that increased functional TAFI levels after stroke are not caused by an acute phase reaction. No difference was found between patients and controls with respect to TAFI genotype distribution. Conclusions: Increased functional TAFI levels, resulting in decreased fibrinolysis, are associated with an increased risk of ischemic stroke.

High von Willebrand Factor Levels Increase the Risk of Stroke The Rotterdam Study

Background and Purpose— Many studies have investigated the role of plasma von Willebrand factor level in coronary heart disease, but few have investigated its role in stroke. The aim of this study was to determine if von Willebrand factor levels are associated with the risk of stroke. Methods— The study was part of the Rotterdam Study, a large population-based cohort study among subjects aged ≥55 years. We included 6 250 participants who were free from stroke at baseline (1997 to 2001) and for whom blood samples were available. Follow-up for incident stroke was complete up to January 1, 2005. Data were analyzed with Cox proportional hazards models adjusted for age and sex and additionally with models adjusted for other potential confounders including ABO blood group. A subgroup analysis was performed in participants without atrial fibrillation. Effect modification by sex was tested on a multiplicative and on an additive scale. Results— During an average follow-up time of 5.0 years, 290 first-ever strokes occurred, of which 197 were classified as ischemic. The risk of stroke increased with increasing von Willebrand factor levels (age- and sex-adjusted hazard ratios per SD increase in von Willebrand factor level: 1.12 [95% CI, 1.01 to 1.25] for stroke, 1.13 [95% CI, 0.99 to 1.29] for ischemic stroke). Adjustments for additional confounders slightly attenuated the association. The association was also present in subjects without atrial fibrillation and did not differ between sexes. Conclusion— High von Willebrand factor levels are associated with stroke risk in the general population.