Dysfunction Of Von Willebrand Factor Research Articles

Characterization and Quantification of Von Willebrand Factor Proteoforms in Von Willebrand Disease Patients and Healthy Controls: Insights from the Win-Study

Background: Von Willebrand disease (VWD) is a commonly inherited bleeding disorder which is characterized by either low (type 1) or absent (type 3) levels of Von Willebrand factor (VWF) or by the occurrence of dysfunctional VWF proteoforms (type 2) in plasma. The complexity of diagnosing and managing VWD arises from limited understanding of the diverse VWF proteoforms present in both healthy individuals as well as in VWD patients. Objective: The aim of this study was to investigate the plasma proteome and to characterize VWF proteoforms in Von Willebrand disease (VWD) patients, that were enrolled in the Willebrand in the Netherlands (WiN) 1 study, compared with healthy controls. Method: We selected type 1, type 2A, type 2M, type 2N and type 3 patients from the WiN cohort for which extensive laboratory- and genotype data were available. Plasma from 64 VWD patients and ten healthy controls was analyzed using a combination of discovery- and targeted mass spectrometry-based approaches. Results: Both discovery-based as well as targeted quantitative proteomics analysis revealed significant variation in VWF levels across the selected VWD patient group, which was in line with reported clinical laboratory data. Elevated VWF-propeptide/VWF ratios were observed in plasma samples from a range of VWD patients, with notable increases observed in VWD type 2A, B, and M, indicating accelerated clearance of these VWF proteoforms. Discovery-based proteomics revealed a strong VWF-F8 relationship in all VWD subtypes and healthy controls, except for type 2N VWD. We were able to identify peptides corresponding with common polymorphisms ( e.g. p.Thr798Ala, p.Gln852Arg, p.Thr1381Ala), for which the observed peptide distribution was in line with the minor allele frequency reported by the Broad institute. In addition, we identified peptides corresponding with 16 pathogenic VWF variants (e.g. p.Arg1306Trp, p. Phe1293Leu, p.Cys1190Arg, p.Arg1374His or p.Tyr1584Cys) of which p.Cys1190Arg wild-type and variant peptide aligned with the zygosity at DNA level (Figure X). Based on spike-in with stable isotope-labeled peptides, the variant-to-wildtype ratios varied among VWD patients with distinct pathogenic variants, ranging from 0.5-2.5 in type 2M (p.Phe1293Leu) and type 1 patients (p.Tyr1584Cys), <1 in type 2A patients (p.Arg1374His), to >8 in type 2B patients (p.Arg1306Trp), suggesting distinct stoichiometry of VWF variants among these patients (Figure 2). Conclusion: Our study highlights the feasibility of VWF proteoform identification and quantification from plasma and suggest a potential role in unravelling their contribution to the biological variations and clinical diversity observed in VWD. 1 De Wee et al., Determinants of bleeding phenotype in adult patients with moderate or severe von Willebrand disease. Thromb Haemost. 2012 Oct;108(4):683-92.

Challenges in the management of women with type 2B von Willebrand disease during pregnancy and the postpartum period: evidence from literature and data from an international registry and physicians’ survey—communication from the Scientific and Standardization Committees of the International Society on Thrombosis and Haemostasis

BackgroundManagement of women with type 2B von Willebrand disease (VWD) during pregnancy is challenging because of dysfunctional von Willebrand factor (VWF) and the complexity resulting from discrepant VWF/factor VIII (VWF/FVIII) levels, impaired platelet-dependent VWF activity, progressive thrombocytopenia, and risks associated with the use of desmopressin. There is a lack of high-quality evidence to support clinical decision making. ObjectivesIn this study, we examined the current diagnostic and management approaches and outcomes in women with VWD during pregnancy. MethodsData were collected via 3 avenues: literature review, an international registry, and an international survey on physicians’ practices for the management of pregnancy in women with VWD. The registry and survey were supported by the International Society on Thrombosis and Haemostasis. ResultsData on clinical and laboratory features, management and bleeding complications, and pregnancy outcomes of a total of 55 pregnancies from 49 women across the globe (literature: 35, registry: 20) and data reported by 112 physicians were analyzed. We describe the largest dataset on pregnancies in women with type 2B VWD available to date. The data highlight the following key issues: a) bleeding complications remain a concern in these patients, b) the target safe VWF level and the ideal monitoring approach are unknown, c) there is a wide range of hemostatic management practices in the type and timing of treatment, and d) physicians have diverse views on the mode of delivery and use of neuraxial anesthesia. ConclusionWe conclude that an international consensus and guidance are critically required for better care and improved outcomes in this patient cohort.

Von Willebrand factor in diagnostics and treatment of cardiovascular disease: Recent advances and prospects.

Von Willebrand factor (VWF) is a large multimeric glycoprotein involved in hemostasis. It is essential for platelet adhesion to the subendothelium of the damaged endothelial layer at high shear rates. Such shear rates occur in small-diameter arteries, especially at stenotic sites. Moreover, VWF carries coagulation factor VIII and protects it from proteolysis in the bloodstream. Deficiency or dysfunction of VWF predisposes to bleeding. In contrast, an increase in the concentration of high molecular weight multimers (HMWM) of VWF is closely associated with arterial thrombotic events. Severe aortic stenosis (AS) or hypertrophic obstructive cardiomyopathy (HOCM) can deplete HMWM of VWF and lead to cryptogenic, gastrointestinal, subcutaneous, and mucosal bleeding. Considering that VWF facilitates primary hemostasis and a local inflammatory response at high shear rates, its dysfunction may contribute to the development of coronary artery disease (CAD) and its complications. However, current diagnostic methods do not allow for an in-depth analysis of this contribution. The development of novel diagnostic techniques, primarily microfluidic, is underway. Such methods can provide physiologically relevant assessments of VWF function at high shear rates; however, they have not been introduced into clinical practice. The development and use of agents targeting VWF interaction with the vessel wall and/or platelets may be reasonable in prevention of CAD and its complications, given the prominent role of VWF in arterial thrombosis.

Real-World Analysis of Healthcare Resource Utilization and Costs Among Patients Diagnosed with Von Willebrand Disease and Angiodysplasia

Background: Von Willebrand disease (VWD), an autosomal inherited bleeding disorder, is characterized by deficiency or dysfunction of von Willebrand factor (VWF). Patients with VWD may suffer from recurrent bleeding in the gastrointestinal (GI) tract associated with angiodysplasia (AGD). Recurrent hospitalizations due to bleeding are common in patients with VWD and AGD, causing significant financial burden and poor quality of life. There are limited data on the economic and clinical burden of patients with VWD and AGD. This study aims to understand the healthcare resource utilization (HCRU) and economic burden among patients with VWD related AGD from patient and payer perspectives. Objectives: To describe the sociodemographic & clinical characteristics, HCRU & all-cause costs (ACC), treatment and procedure patterns for patients with VWD of any type and AGD. Methods: This retrospective, observational cohort study used the IBM MarketScan® database (2011-2020), containing healthcare data from the United States (US). Selected patients had ≥1 medical claim for VWD or low VWF, ≥1 medical claim for AGD, and ≥3 GI-related bleed episodes within a year identified using International Classification of Diseases (ICD-9/10) codes. The index date was defined as the date of the first GI bleed-related medical claim before or within 30 days of the first AGD claim. Otherwise, it was defined as the date of the first AGD-related medical claim. Patients were excluded if they did not have 6 months pre- and 12 months post-index continuous enrollment and if they had ≥2 medical claims of hemophilia A (HA), hemophilia B, acquired HA, ulcerative colitis, Crohn's disease, acquired VWD, or other bleeding disorders atleast 30 days apart. HCRU and ACC were compared with a VWD (only) cohort (i.e., continuously enrolled VWD patients without AGD) and a general cohort (i.e., continuously enrolled patients without VWD or AGD) to improve the strength of the evidence via reducing the risk of bias and generating statistical inferences. For comparison of the cohorts, 1:4 exact matching was performed using age, gender, index year, and Charlson Comorbidity Index (CCI) score (relaxing age and index year by ± 5 years). Statistical comparisons were made using ANOVA tests for continuous and Chi-square tests for categorical variables. The ACC were inflated to 2021 US dollars using the annual medical care component of the consumer price index. In addition to the HCRU and ACC comparisons, clinical characteristics of the VWD and AGD cohort were reported along with 2 other cohorts that met 2 of the 3 inclusion criteria to allow for a more relevant description of diagnostics, procedures, and bleed rates. Results: After exact matching, 34 patients were selected from the VWD & AGD cohort with 136 patients each from VWD (only) and general population. Mean (SD) HCRU were significantly higher for the VWD & AGD cohort than the VWD (only) and general cohorts: {2.2 (2.2), 0.6 (1.3), and 0.3 (0.6)} inpatient visits, {17.6 (36.4), 3.4 (10.9), and 2.0 (7.1)} inpatient hospital days, {2.2 (2.6), 0.8 (2.1), and 0.7 (1.5)} emergency visits, and {28.8 (19.4), 18.8 (16.0), and 17.3 (19.6)} outpatient visits, respectively. Mean (SD) total ACC were significantly higher for the VWD & AGD cohort than the VWD (only) and general cohorts {$150,101 ($305,052), $48,249 ($97,689), and $31,029 ($45,512), respectively} (Table 1). Sociodemographic and clinical characteristics (e.g. diagnosis related procedures, bleed rates) of the VWD cohort along with the 2 cohorts that met 2 of 3 inclusion criteria are reported in Table 2. Conclusions: This study found that patients with VWD and AGD were predominantly female with high HCRU and clinical burden due to recurrent bleeding episodes. The data demonstrated a substantial economic burden, primarily driven by hospitalizations. The diagnostic journey for patients and HCRU is highly variable and may benefit from a more structured and empiric understanding of how VWD and AGD patients are diagnosed and treated. Additionally, costs and burden of VWD & AGD could be mitigated by greater outpatient management to prevent recurrent GI bleeds (i.e. VWF prophylaxis). More research is needed to better understand disease management and healthcare outcomes of patients with VWD and AGD. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Von Willebrand Disease-Specific Aspects in Women.

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, which results from a deficiency or dysfunction of von Willebrand factor (VWF). The major symptoms of patients affected by VWD include mucocutaneous and gastrointestinal bleeding, easy bruising, and prolonged provoked bleeding due to injury or surgery. Although women and men are equally likely to be affected by VWD, women continue to be disproportionately affected by the bleeding challenges. Women with VWD suffer from sex-specific symptoms, such as menorrhagia, and are at higher risk of reproductive problems and recurrent miscarriage. Furthermore, pregnant women with VWD are more likely at higher risk of suffering from primary and secondary peripartal hemorrhage and anemia and the need for transfusions. Despite being affected by gynecologic and obstetrical bleeding, women face multiple barriers in obtaining an accurate diagnosis. This constitutes a problem that needs to be addressed, and early appropriate medical care should be ensured. There are several effective treatment options for women with VWD that can significantly improve their quality of life, including desmopressin, VWF concentrates, hormonal therapy, and antifibrinolytic therapy. During pregnancy, the monitoring of VWF activity levels is essential. The peripartal management depends on the type of VWD and on the measured levels of VWF levels and activity prior to delivery.

How Do Laboratories Perform von Willebrand Disease Diagnostics and Classification of von Willebrand Disease Patients? Results from External Quality Data and an International Survey

Reduced or dysfunctional von Willebrand factor (VWF) may lead to von Willebrand disease (VWD), which is a common inherited bleeding disorder. VWD is classified into three major types: type 1 is a partial quantitative deficiency of VWF, type 3 is a complete quantitative deficiency of VWF, and type 2 consists of qualitative abnormalities of VWF. To arrive at a correct VWD diagnosis, multiple tests and a correct interpretation of these tests are needed. The aim of the present study was to gain insight into the approach of laboratories toward VWD diagnosis. Data from four samples of the external quality assessment (EQA) VWF surveys of the ECAT (External Quality Control for Assays and Tests) were evaluated. Furthermore, results were analyzed of a questionnaire that was sent to hemostasis laboratories about VWD diagnostic approaches. For most EQA samples, the majority of participants indicated the correct classification. However, 6 to 60% indicated another classification. For all samples, significant differences in VWF results were observed between the correct and incorrect classifications. The questionnaire demonstrated that the testing approach varied between the laboratories, especially for parameters that were essential for discrimination between VWD type 1 and healthy individuals, as well as the cutoff values used to discriminate VWD types 1 and 2. Diagnosis of VWD is heterogeneous in diagnostic approach, guidelines, and cutoff values within large ranges of VWF results between laboratories. Harmonization of approaches and increased accuracy of VWF measurements may help to establish a correct diagnosis.

How Do Laboratories Perform von Willebrand Disease Diagnostics and Classification of von Willebrand Disease Patients? Results from External Quality Data and an International Survey.

Reduced or dysfunctional von Willebrand factor (VWF) may lead to von Willebrand disease (VWD), which is a common inherited bleeding disorder. VWD is classified into three major types: type 1 is a partial quantitative deficiency of VWF, type 3 is a complete quantitative deficiency of VWF, and type 2 consists of qualitative abnormalities of VWF. To arrive at a correct VWD diagnosis, multiple tests and a correct interpretation of these tests are needed. The aim of the present study was to gain insight into the approach of laboratories toward VWD diagnosis. Data from four samples of the external quality assessment (EQA) VWF surveys of the ECAT (External Quality Control for Assays and Tests) were evaluated. Furthermore, results were analyzed of a questionnaire that was sent to hemostasis laboratories about VWD diagnostic approaches. For most EQA samples, the majority of participants indicated the correct classification. However, 6 to 60% indicated another classification. For all samples, significant differences in VWF results were observed between the correct and incorrect classifications. The questionnaire demonstrated that the testing approach varied between the laboratories, especially for parameters that were essential for discrimination between VWD type 1 and healthy individuals, as well as the cutoff values used to discriminate VWD types 1 and 2. Diagnosis of VWD is heterogeneous in diagnostic approach, guidelines, and cutoff values within large ranges of VWF results between laboratories. Harmonization of approaches and increased accuracy of VWF measurements may help to establish a correct diagnosis.

How Do Laboratories Perform von Willebrand Disease Diagnostics and Classification of von Willebrand Disease Patients? Results from External Quality Data and an International Survey.

Reduced or dysfunctional von Willebrand factor (VWF) may lead to von Willebrand disease (VWD), which is a common inherited bleeding disorder. VWD is classified into three major types: type 1 is a partial quantitative deficiency of VWF, type 3 is a complete quantitative deficiency of VWF, and type 2 consists of qualitative abnormalities of VWF. To arrive at a correct VWD diagnosis, multiple tests and a correct interpretation of these tests are needed. The aim of the present study was to gain insight into the approach of laboratories toward VWD diagnosis. Data from four samples of the external quality assessment (EQA) VWF surveys of the ECAT (External Quality Control for Assays and Tests) were evaluated. Furthermore, results were analyzed of a questionnaire that was sent to hemostasis laboratories about VWD diagnostic approaches. For most EQA samples, the majority of participants indicated the correct classification. However, 6 to 60% indicated another classification. For all samples, significant differences in VWF results were observed between the correct and incorrect classifications. The questionnaire demonstrated that the testing approach varied between the laboratories, especially for parameters that were essential for discrimination between VWD type 1 and healthy individuals, as well as the cutoff values used to discriminate VWD types 1 and 2. Diagnosis of VWD is heterogeneous in diagnostic approach, guidelines, and cutoff values within large ranges of VWF results between laboratories. Harmonization of approaches and increased accuracy of VWF measurements may help to establish a correct diagnosis.

Functional heterogeneity of the von Willebrand factor: pathogenetic significance and practical aspects of use in cardiology

This review focuses on the participation of von Willebrand factor (VWF), that considerably contributes to thrombogenesis in damaged blood vessels, in the pathogenesis of atherosclerosis-induced cardiovascular pathology. Excessive formation and dysfunction of VWF leads to intravascular thrombosis and facilitates the development of endothelial dysfunction, vascular inflammation, and, thereby, the initiation and progression of atherosclerosis. The review presents information based on the analysis of full-text publications from PubMed that address the role of VWF in the development of atherosclerosis and its complications as well as the potential for influencing this index.

Towards novel treatment options in von Willebrand disease.

Deficiency or dysfunction of von Willebrand factor (VWF) is associated with a bleeding disorder known as von Willebrand disease (VWD). The clinical manifestations of VWD are heterogeneous, and are in part dictated by the structural or functional defects of VWF. The tools to control bleeding in VWD are dominated by VWF concentrates, desmopressin and antifibrinolytic therapy. In view of these treatments being considered as effective, it is surprising that quality-of-life studies consistently demonstrate a significant mental and physical burden in VWD patients, particularly in women. Apparently, the current weaponry to support the management of VWD is insufficient to fully address the needs of the patients. It is important therefore to continue to search for innovative treatment options which could better serve the VWD patients. In this short review, two of such options are discussed in more detail: emicizumab to correct for the deficiency of factor VIII (FVIII), and the pegylated aptamer BT200 to increase endogenous levels of the VWF/FVIII complex.

A novel mouse model of type 2N VWD was developed by CRISPR/Cas9 gene editing and recapitulates human type 2N VWD

AbstractType 2N von Willebrand disease is caused by mutations in the factor VIII (FVIII) binding site of von Willebrand factor (VWF), resulting in dysfunctional VWF with defective binding capacity for FVIII. We developed a novel type 2N mouse model using CRISPR/Cas9 technology. In homozygous VWF2N/2N mice, plasma VWF levels were normal (1167 ± 257 mU/mL), but the VWF was completely incapable of binding FVIII, resulting in 53 ± 23 mU/mL of plasma FVIII levels that were similar to those in VWF-deficient (VWF−/−) mice. When wild-type human or mouse VWF was infused into VWF2N/2N mice, endogenous plasma FVIII was restored, peaking at 4 to 6 hours post-infusion, demonstrating that FVIII expressed in VWF2N mice is viable but short-lived unprotected in plasma due to dysfunctional 2N VWF. The whole blood clotting time and thrombin generation were impaired in VWF2N/2N but not in VWF−/− mice. Bleeding time and blood loss in VWF2N/2N mice were similar to wild-type mice in the lateral tail vein or ventral artery injury model. However, VWF2N/2N mice, but not VWF−/− mice, lost a significant amount of blood during the primary bleeding phase after a tail tip amputation injury model, indicating that alternative pathways can at least partially restore hemostasis when VWF is absent. In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in severe type 2N patients. This unique model can be used to investigate the biological properties of VWF/FVIII association in hemostasis and beyond.

Anticoagulation Use and Outcomes Among Patients with Atrial Fibrillation and Von Willebrand Disease

Intro: Von Willebrand disease (VWD) is a coagulopathy caused by deficiency or dysfunction of von Willebrand factor (VWF), resulting in prolonged and excessive bleeding. Patients are advised to avoid aspirin (ASA), P2Y12 inhibitors, or anticoagulation (AC) so as not to exacerbate this condition. However, typical treatment for atrial fibrillation (AF) includes anticoagulation, particularly if the risk of stroke by CHA 2DS 2-VASC score is 2+. Current recommendations suggest giving necessary antiplatelet (AP) or AC therapy over no treatment with assessment of bleeding risk throughout the course. However, this is a conditional recommendation based on low certainty in evidence, and there are no specific guidelines on treating AF in patients with VWD. This study aims to assess anticoagulation use, bleeding risk, and stroke risk in patients with VWF and AF.Methods: We conducted an IRB-approved analysis of coded data from institutional electronic medical records to select patients with diagnosis of VWD, low ristocetin cofactor level, or any abnormal VWF panel as well as patients with diagnosis of AF or atrial flutter. Three hundred and forty patients met criteria. Patients were manually screened for inclusion criteria and excluded for inaccurate diagnosis or insufficient data. Eighty-nine patients were included in the analysis. Primary endpoint was rate of major bleeding defined by ISTH criteria while on AC or AP. Categorical data were tested using the Fisher exact test at the nominal 0.05 two-sided significance level, and all person-time comparisons are made against the rate of bleeding on AC alone.Results: Most patients were female (64.0%; 57/89), and 28.1% (25/89) were deceased at the time of data collection. Date of diagnosis of AF ranged from 1980-2020. 42.7% (38/89) of patients were ever prescribed ASA, 43.8% (39/89) a P2Y12 inhibitor, 56.2% (50/89) AC, and 23.6% (21/89) had never been prescribed AP or AC. Of patients with a CHA 2DS 2-VASC of 2+, 57.5% (46/80) were ever prescribed AC. 32.0% (16/50) of patients ever prescribed AC and 25.6% (10/39) patients never prescribed AC had at least one major bleeding event (p=0.428). The rate of major bleeding on AC alone was 8.9 events per 100 person-years (32 events/359.2 years), 10.2 events per 100 person-years on AP alone (41 events/402.3 years) (p=0.572), and 1.06 events per 100 person-years (8 events/757.47 years) in patients never prescribed AC or AP (p=<0.0001). Notably, the rate of major bleeding on AC and AP together was 28.07 events per 100 person-years (23 events/81.94 years) (p=<0.0001) occurring in 7 patients, 6 of whom also had a diagnosis of acute coronary syndrome (ACS). Length of time to first major bleed is shown in Figure 1. 16.9% (15/89) of patients had thromboembolic strokes after diagnosis of AF, and 53.3% (8/15) of those strokes occurred when patients were not prescribed AC.Discussion: This retrospective observational study over 40 years characterizes AC and AP use in patients with VWD and AF. Only 57.5% of patients with CHA 2DS 2-VASC of 2+ received standard of care AC despite conditional recommendations to give necessary anticoagulation to patients with VWD. In parallel with the general population, AC use significantly increases the rate of major bleeding in patients with VWD, but there was no difference in bleeding rate between standard AC and AP monotherapy. However, major bleeding rates were notably elevated in patients prescribed concomitant AC and AP which most commonly occurred in the setting of ACS. This analysis is limited by its retrospective nature, the lack of granular details in the coded database, and incomplete data in older charts. Overall, these data do not support the use of AP monotherapy over standard AC to reduce bleeding rates for patients with VWD and AF. Additionally, AC and AP co-administration should be avoided due to high rates of major bleeding, but more studies are required to understand AP and AC strategies in patients with VWD, AF, and ACS. Although the rate of major bleeding is elevated with AC use in patients with VWD, there is no difference in lifetime prevalence of major bleeding events by AC vs no AC use. Finally, over half of thromboembolic strokes occurred when not prescribed AC. Shared decision-making around stroke and bleeding risk is advised in considering AC use for AF in patients with VWD. Prospective studies should further evaluate the risk of major bleeding and stroke in patients with VWD and AF on standard AC vs no AC. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

An international survey to inform priorities for new guidelines on von Willebrand disease.

von Willebrand disease (VWD) is an inherited bleeding disorder caused by a quantitative or qualitative dysfunction of von Willebrand factor. Clinicians, patients and other stakeholders have many questions about the diagnosis and management of the disease. To identify topics of highest importance to stakeholders that could be addressed by guidelines to be developed by the American Society of Hematology (ASH), the International Society on Thrombosis and Haemostasis (ISTH), the National Hemophilia Foundation (NHF) and the World Federation of Hemophilia (WFH). A survey to determine and prioritize topics to be addressed in the collaborative development of guidelines for VWD was distributed to international stakeholders including patients, caregivers and healthcare providers (HCPs). Representatives of the four organizations coordinated the distribution strategy. The survey focused on both diagnosis and management of VWD, soliciting 7-point Likert-scale responses and open-ended comments, in English, French and Spanish. We conducted descriptive analysis with comparison of results by stakeholder type, gender and countries' income classification for the rating questions and qualitative conventional content data analysis for the open-ended responses. A total of 601 participants responded to the survey (49% patients/caregivers and 51% healthcare providers). The highest priority topics identified were diagnostic criteria/classification, bleeding assessment tools and treatment options for women and surgical patients. In contrast, screening for anaemia and differentiating plasma-derived therapy versus recombinant therapies received lower ratings. This survey highlighted areas of importance to a diverse representation of stakeholders in the diagnosis and management of VWD, providing a framework for future guideline development and implementation.

ADAMTS13, an Anti-thrombotic Protein: Evidence Outside of Thrombotic Thrombocytopenic Purpura

von Willebrand factor (VWF) is a large multimeric plasma glycoprotein that plays a crucial role in hemostasis and thrombosis. VWF recruits platelets at sites of vascular injury by acting as a molecular bridge between circulating platelets and the site of injured or activated blood vessels. Biosynthesis of VWF is restricted to endothelial cells and megakaryocytes. Endothelial VWF is constitutively secreted into plasma and subendothelium, or is stored as "ultra-large" (UL)-VWF multimers in endothelial Weibel-Palade bodies. VWF produced in megakaryocytes is packaged as UL-VWF in the a-granules of platelets. VWF stored in endothelial and platelet storage organelles is secreted in a regulated process in response to stimulation by secretagogues. Absence or dysfunction of VWF results in bleeding symptoms, as observed in patients with von Willebrand disease. An abnormally high activity of VWF can lead to thrombotic events. Interestingly, the activity of VWF is determined by the size of its multimers and UL-VWF can spontaneously form platelet aggregates. An important regulator of VWF size is the metalloprotease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), which digests large thrombogenic VWF molecules into smaller, less reactive multimers via cleavage of the Y1605-M1606 bond in the VWF A2 domain. ADAMTS13 is mainly synthesized in the liver by hepatic stellate cells, but other sites of synthesis, including renal podocytes, tubular epithelial cell, platelets and endothelial cells, have also been described. ADAMTS13 is released as an active enzyme into the circulation with no physiological inhibitors. Reduced or absent ADAMTS13 activity causes the microangiopathic disorder thrombotic thrombocytopenic purpura (TTP), characterized by VWF and platelet-rich microthrombi that cause multiple organ failure and even death when left untreated. Besides its clear role in the pathophysiology of TTP, the anti-thrombotic and even anti-inflammatory properties of ADAMTS13 have also become apparent in various other thrombotic conditions. High VWF levels and low ADAMTS13 levels are associated with increased risk or even worse outcome of cardiovascular disease, including ischemic stroke and myocardial infarction. Preclinical studies in mouse models showed the beneficial effect of ADAMTS13 in both cerebral and myocardial ischemia/ reperfusion injury by decreasing both thrombosis and inflammation. In addition, ADAMTS13 was shown to also exert a direct thrombolytic effect on VWF-rich thrombi. In a mouse model of ischemic stroke, this thrombolytic activity resulted in efficient lysis of intracranial thrombi that were resistant to standard treatment with tissue plasminogen activator. Hence, ADAMTS13, as a therapeutic agent, could become an interesting avenue, not only to manage TTP, but also to treat other thrombotic complications. Disclosures De Meyer: Fonds voor Wetenschappelijk Onderzoek: Research Funding; KU Leuven: Employment, Research Funding; Ablynx: Consultancy, Research Funding; Cerenovus: Membership on an entity's Board of Directors or advisory committees; WhiteSwell: Consultancy.

A Murine Model of Type 2N VWD Was Developed By CRISPR/Cas9 Gene Editing and Recapitulates Human Type 2N VWD

Von Willebrand Disease (VWD) is caused by either an inherited deficiency of von Willebrand factor (VWF) protein or synthesis of a dysfunctional von Willebrand factor (VWF) that is referred to as a type 2 variant. One of the important functions of VWF is to serve as a carrier protein for FVIII - prolonging FVIII's plasma half-life from <2 hrs without VWF to 10-12 hrs with VWF. A variant form of VWF was identified in 1982 in which VWF did not bind FVIII resulting in FVIII's rapid clearance and a phenotype similar to moderate hemophilia and currently referred to as type 2N VWD. Type 2N VWD is caused by an autosomal recessive variant of VWF in which mutations in the D'D3 region of VWF cause decreased or absent binding of FVIII to VWF resulting in rapid FVIII clearance similar to that seen in the absence of VWF. These individuals may have a type 2N mutation on each of their VWF alleles or, more commonly, have 1 allele with a 2N mutation and their 2nd allele contains a null mutation (producing no VWF). In each of these scenarios, only functionally abnormal VWF is synthesized, resulting in reduced or absent FVIII binding, rapid FVIII clearance, and a marked reduction in plasma FVIII. While Lillicrap and coworkers have demonstrated 2N VWF expression by hydrodynamic transfection in a VWF-/- mouse, their approach represents a model of plasma 2N VWF dysfunction but does not recapitulate human 2N VWD where the abnormal VWF is not only in plasma, but also in endothelial cells and platelets.We selected 8 different human type 2N mutations, and mutated murine VWF at these positions and expressed the mutant VWF in HEK293T cells in vitro. Binding of each of the 2N mutants of mouse VWF to both murine and human FVIII was tested. The G785E 2N mutation had the most severe defect with negligible binding to both human (rhF8) and mouse FVIII (mF8) and was therefore chosen for further study. Using CRISPR/Cas9 gene editing, we generated two lines of VWF2N mice (termed VWF2N1/2N1 and VWF2N2/2N2) each with a 2N causative 2354G>A (G785E) mutation on the C57BL6 background. Plasma VWF levels were measured by ELISA and FVIII was measured by chromogenic assay. VWF binding to FVIII was determined by FVIII binding to monoclonal captured VWF or by VWF binding to monoclonal captured FVIII. For the remainder of this abstract, we will only discuss the VWF2N1/2N1 mice and refer to them as wt VWF+/+, heterozygous VWF2N/+ or homozygous VWF2N/2N mice. The plasma VWF in VWF+/+, VWD2N/+ or VWF2N/2N mice was 109±31, 100±27, and 115±29 U/dL. The plasma FVIII levels in homozygous VWF2N/2N mice were markedly reduced to 4.9±2.2 U/dL compared to either wt (84±21U/dL) or heterozygous (82±18U/dL) controls. VWF binding to rhF8 was reduced to <2% in VWF2N/2N mice and 57±9% in VWF2N/+ mice when compared to wt controls.To assess the clinical phenotype of VWF2N/2N mice, tail bleeding times were determined demonstrating prolongation to 3.1±0.4 hrs in VWF2N/2N mice in contrast to 2.4±0.4 in VWF2N/+ and 2.1±1.0 hrs in wt controls. ROTEM assessment of whole blood clotting time (wbCT) and whole blood thrombin generation assays (wbTGA) were performed. The wbCT was 10.7±1.1 min in VWF2N/2N mice compared to 8.3±0.5 min in VWF2N/+ heterozygotes. In wbTGA, the Lag Time and Peak Time in the VWF2N/2N group were 18.53±5.57 and 34.15±8.37 min, respectively, which were significantly longer than those obtained in the VWF2N/+ group (8.3±0.5 and 17.83±2.33 min, respectively). Peak Thrombin, Endogenous Thrombin Potential, and Thrombin Generation rate in the VWF2N/2N group were significantly lower than those obtained in the VWF2N/+ group.In human type 2N VWD, FVIII synthesis is normal but plasma levels are reduced because of increased FVIII clearance in the absence of VWF binding. Infusion of rhVWF (no FVIII) into the VWF2N/2N mice demonstrated rhVWF peaking by 30 minutes with a rescue of the endogenous mouse FVIII (44±1.7 U/dL) at 4-6 hrs post infusion. This demonstrates improved FVIII survival in the presence of normal VWF.In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in Type 2N patients. Plasma levels of VWF are normal in our VWF2N/2N mice. This VWF is incapable of binding FVIII at neutral pH, but is otherwise fully functional. This is a unique model of 2N VWD that can be used to investigate the biological properties of VWF/FVIII association. DisclosuresMontgomery:BCW: Patents & Royalties: GPIbM assay patent to the BloodCenter of Wisconsin.

Transcatheter aortic valve implantation leads to a restoration of von Willebrand factor (VWF) abnormalities in patients with severe aortic stenosis – Incidence and relevance of clinical and subclinical VWF dysfunction in patients undergoing transfemoral TAVI

BackgroundIn this study, we sought to analyze the incidence and relevance of von Willebrand factor (VWF) abnormalities in patients undergoing transcatheter aortic valve implantation (TAVI), especially on perioperative bleeding. Furthermore, we hypothesized that, similar to aortic valve surgery, TAVI results in a restoration of VWF abnormalities. Methods and resultsWe performed a prospective analysis of periinterventional VWF parameters in 74 patients (80±7years, female in 37.5%) undergoing transfemoral TAVI for severe symptomatic aortic valve stenosis. At baseline, VWF:Ag was 210±90IU/dl with a mean VWF activity of 166±106IU/dl; activity-to-antigen ratio was 0.85±0.45. Heyde's syndrome (severe aortic stenosis plus GI bleeding from angiodyplasia) was observed in 2/74 (2.7%). Whereas preprocedural loss of high-molecular-weight (HMW) VWF multimers was found in thirty-six patients (48.6%), none of the patients fulfilled criteria for possible acquired VW syndrome. After TAVI, an increase of both VWF:Ag and activity compared to baseline was observed (p<0.01). In patients with HMW multimer loss, post-interventional recovery of multimers occurred in all cases. In the two patients with Heyde's syndrome, a trend towards reduced VWF:Ag was seen, with loss of HMW multimers in one patient. Of interest, all patients suffering from periprocedural major bleeding (5/74; 6.8%) exhibited activity-to-antigen ratios <0.7, indicating subclinical VWF dysfunction. ConclusionWhereas clinically relevant VWF dysfunction is rare, loss of HMW VWF multimers is common in TAVI patients. Similar to surgery, TAVI leads to a restoration of this loss. Furthermore, VWF parameters may be useful parameter to evaluate risk of periprocedural bleeding.

Wish-Qol Study - Assessment of Health-Related Quality of Life (HRQoL) and Health-Economic Aspects in Patients with Von Willebrand Disease (VWD) in France: Results of the Women Cohort

Background: Von Willebrand disease (VWD) is the most common inherited bleeding disorder with a prevalence of 1% in the general population. VWD results from a deficiency in or a dysfunction of von Willebrand factor which is a protein that is necessary for normal platelet adhesion and protection of factor VIII from proteolysis in the circulation. Nevertheless, prevalence of the most symptomatic forms such as bleeds requiring replacement treatment and /or hospitalization is about 0.01%. Although VWD affects both genders, there is a higher proportion in females than in males.VWD seems to be more symptomatic in women because of their reproductive life. Women with VWD have an increased bleeding risk in numerous situations including anemia, menorrhagia, bleeding during pregnancy, postpartum hemorrhage and impairments in their quality of life (QoL).The prevalence of menorrhagia in women with VWD is 74-92%. According to the Francecoag Network, the referral-based prevalence of moderate-to-severe VWD patients is about 1,750 cases in France.Aim: Since the disease and its treatment can affect every-day life of patients and their families, a French HRQoL Study (WiSH-QoL) exploring this impact started 22 months ago.Methods: This non-interventional 5-year study evaluates patients HRQoL and costs of care in France. At least 350 patients will be followed for 24 months in minimum 30 centers. HRQoL is assessed with the generic SF-36 and the disease-specific VWD-QoL questionnaires. Bleeding severity was measured using the Tosetto Bleeding Score (BS).Results: Since October 2014, 245 patients have been included. We present here the first interim analysis with a focus on the female group. At the first interim analysis, data from 140 patients were documented: 91 adults with a median age of 40.0 years [18.3-78.0] and 49 children with a median age of 10.1 years [2.9-17.5]. VWD Types were already identified for 122 (87%) of these patients: 33 with VWD type 1 (27%) including 5 type 1 Vicenza; 76 type 2 (62%) and 13 type 3 (11%). The median Tosetto bleeding score reported for 124 patients (males and females) was +7 ranging from -1 to +28.From the 95 female patients, 70 were aged ≥18 years, 21 were adolescents between 8-17 years and 4 were girls below 4 years of age. Median age was 29.4 (range 4.3-78.0) years. A total of 25 women had type 1 VWD (31%), 49 had type 2 VWD (60%), and 7 had type 3 VWD (9%), for 14 patients VWD type is undetermined. The median Tosetto bleeding score of the female group was +8 ranging from -1 to +28.Out of 95 patients, 45 patients (47.4%) have received a concomitant treatment due to menorrhagia, such as iron therapy, oral contraceptive, levonorgestrel intrauterin system: 5/21 patients in the group between 8 and 17 years and 40/70 in the group ≥18 years. Out of the 60 women of childbearing potential defined as age between 15-50 years, 6 women were pregnant at time of inclusion. A total of 46 patients, aged 18 years or more have had obstetrical history prior to study inclusion. The mean number of childbirth was more than 2 i.e 2.39 range (1-8) per woman, 75% of these deliveries were natural delivery and 25% were caesarean section. Out of 108 deliveries, 28 (26%) were experienced with post-partum hemorrhages.Conclusions: With the results of the WiSH-QoL study, the first prospective study of von Willebrand disease conducted in France, especially the VWD-specific evaluation of HRQoL and treatment satisfaction a deeper insight will be gathered into the patients' daily life, their perception of well-being and their specific health care needs. With the additional domain 'pregnancy' included in the French version of the VWD-QoL questionnaire for female adult patients, it will possible to better understand how women may be affected by VWD during childbearing years. DisclosuresBorel-Derlon:LFB: Other: Reference expert and national coordinator for VWD; Octapharma: Research Funding; NovoNordisk: Other: Expert for scientific committee; Shire - Baxalta: Research Funding. Chatelanaz:LFB Biomedicaments: Employment. Doriat-Robin:LFB Biomedicaments: Employment. von Mackensen:SOBI: Research Funding; Shire: Research Funding.

Von Willebrand disease - the 'Dos' and 'Don'ts' in surgery.

Von Willebrand disease (VWD) is the most common genetic bleeding disorder. VWD is caused by a deficiency or dysfunction of von Willebrand factor (VWF), a plasma protein that mediates the initial adhesion of platelets at sites of vascular injury and binds and stabilises coagulation factor VIII (FVIII) in the blood. Prophylaxis of surgical bleeding in patients with VWD requires consideration of the individual situation, including the type of procedure and the bleeding rate, before decisions about treatment type, dose, duration and adjunctive therapy with antifibrinolytics or antithrombotic prophylaxis can be made. Although desmopressin (DDAVP)-stimulated release of endogenous VWD is an effective treatment strategy in many patients, plasma concentrates containing VWF are the preferred option for most patients undergoing surgical procedures. Recommendations for the management of surgery in patients with VWD are summarised, including the severity of VWD and the type of the surgical procedure.

Monitoring Therapy during Treatment of von Willebrand Disease.

von Willebrand factor (VWF) is an adhesive plasma protein that primarily acts to bridge platelets to sites of vascular injury and thus prevent bleeding. von Willebrand disease (VWD) is the most common inherited bleeding disorder and is caused by deficiency and/or defects of VWF, leading to low levels of plasma VWF or dysfunctional VWF. Factor VIII (FVIII) is also reduced in many patients with VWD, since VWF stabilizes and protects FVIII from degradation. Treatment of VWD primarily entails replacement of VWF, and sometimes FVIII, to protect against bleeding. This may entail use of VWF/FVIII concentrates, and/or desmopressin (1-deamino-8-d-arginine vasopressin) to release endogenous VWF in some patients. Adjunct therapies include antifibrinolytics and hormonal therapies in women. Optimal treatment of VWD entails measuring the effects of treatment, either as a trial before surgery or during therapeutic management. This is usually accomplished by performance of the same tests that are used to help diagnose VWD, although additional monitoring (clinically and/or by laboratory testing) may also be performed. The current review provides an overview of the treatment of VWD but is primarily focused on the monitoring of such therapy.

Vonicog alfa for the treatment of von Willebrand disease

ABSTRACTIntroduction: von Willebrand disease (VWD) is the most frequent inherited bleeding disorder. It is caused by the quantitative and/or qualitative abnormalities of von Willebrand factor (VWF), an adhesive protein crucial for platelet-subendothelium interaction and for factor VIII stabilization in plasma. Clinical manifestations are mainly represented by excessive mucocutaneous bleeding and prolonged oozing after surgical procedures. The aim of therapy in VWD is to correct the abnormal platelet adhesion-aggregation as a result of low or dysfunctional VWF and the abnormal intrinsic coagulation owing to low FVIII levels. Current therapeutic options are desmopressin, which releases endogenous VWF from endothelial cells, and exogenous VWF contained in plasma-derived VWF/FVIII concentrates.Areas covered: This paper focuses on the potential therapeutic benefits for VWD of the first recombinant VWF concentrate, vonicog alfa. Topics covered include clinical development, pharmacokinetic profile, safety and efficacy data from Phase 1 and 3 clinical studies of vonicog alpha in patients with clinically severe VWD.Expert opinion: Vonicog alfa may provide advantages in treatment of VWD because it is a recombinant high-purity VWF, with a high efficacy profile when co-administered with FVIII as well as alone. Due to its efficacy even without FVIII, vonicog alfa offers the possibility of a more targeted, personalized replacement therapy based on the needs of each individual patient.