Prevalence and characterization of anti-VWF antibodies in a population of patients with type 3 VWD.

von Willebrand disease (VWD) is an inherited bleeding disorder caused by quantitative or qualitative defects in the von Willebrand factor (VWF) protein. Type 3 VWD has a severe bleeding phenotype caused by the absence of VWF, in which treatment usually involves replacement therapy with VWF-containing products. The immune system can react to the VWF product and form anti-VWF antibodies to neutralize or clear the VWF, which can compromise efficacy of treatment or lead to anaphylaxis.

The common VWF variant p.Y1584C: detailed pathogenic examination of an enigmatic sequence change.

Background: As knowledge of the human genome has advanced, so too has the recognition that interpretation of the pathogenic nature of sequence variants can be challenging. The von Willebrand factor (VWF) gene exhibits a significant degree of sequence variability, and the first VWF variant associated with type 1 von Willebrand disease (VWD), c.4751 A>G, p.

Von Willebrand Factor (VWF) multiplex activity assay differentiation of type 1 von Willebrand Disease (VWD) and variant VWD.

Introduction: VWD diagnosis is challenging requiring multiple VWF activity tests using many individual assays. We have developed an ELISA-based VWF Multiplex Activity Assay (VWF-MAA) to address this concern; however, the ability of the VWF-MAA to discriminate between type 1 VWD, variant VWD, and normal subjects has not been evaluated.

Aim: To evaluate the VWF-MAA and its ability to differentiate between type 1 VWD, variant VWD and normal subjects in individuals undergoing an initial laboratory evaluation for bleeding.

Variability in International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee endorsed Bleeding Assessment Tool (ISTH-BAT) score with normal aging in healthy females: contributory factors and clinical significance.

Background: Bleeding assessment tools are key screening tests used in the evaluation of patients with suspected inherited bleeding disorders. The International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee endorsed Bleeding Assessment Tool (ISTH-BAT) has differing reference ranges for adult males (0-3), adult females (0-5), and children (0-2), reflecting differing bleeding symptoms and exposure to hemostatic challenges in these healthy population subgroups. Age is known to markedly impact bleeding score in individuals with von Willebrand disease.

Ristocetin dependent cofactor activity in von Willebrand disease diagnosis: Limitations of relying on a single measure.

Background: Von Willebrand disease (VWD) is a common inherited bleeding disorder, however the diagnosis can be complicated by a subjective bleeding history and issues with some current von Willebrand factor (VWF) laboratory assays.

Objectives: In the Zimmerman Program, we sought to determine how often a type 1 diagnosis was based on a single low VWF ristocetin cofactor (VWF:RCo) level resulting from the common genetic variant p.D1472H or an isolated assay issue, if that low value was corroborated by the VWF glycoprotein-IbM (VWF:GPIbM) assay, and if retesting confirmed original levels.

Longitudinal bleeding assessment in von Willebrand disease utilizing an interim bleeding score.

Background: Assessment of bleeding phenotype is critically important in the diagnosis of von Willebrand disease (VWD). Despite advances in bleeding assessment tools (BATs), standardized tools to evaluate bleeding following diagnosis (interim bleeding) are lacking.

Objectives: We assessed the clinical utility of an interim bleeding protocol in a multicenter, international study involving patients with VWD.

Molecular pathogenesis and heterogeneity in type 3 VWD families in U.S. Zimmerman program.

Background: Type 3 von Willebrand Disease (VWD) is a rare and severe form of VWD characterized by the absence of von Willebrand factor (VWF).

Objectives: As part of the Zimmerman Program, we sought to explore the molecular pathogenesis, correlate bleeding phenotype and severity, and determine the inheritance pattern found in type 3 VWD families.

Patients/methods: 62 index cases with a pre-existing diagnosis of type 3 VWD were analyzed.

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

Type 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.

von Willebrand factor levels in the diagnosis of von Willebrand disease: a systematic review and meta-analysis.

von Willebrand disease (VWD) is associated with significant morbidity as a result of excessive mucocutaneous bleeding. Early diagnosis and treatment are important to prevent and treat these symptoms. We systematically reviewed the accuracy of diagnostic tests using different cutoff values of von Willebrand factor antigen (VWF:Ag) and platelet-dependent von Willebrand factor (VWF) activity assays in the diagnosis of VWD.

Screening for von Willebrand disease does not impact posttonsillectomy bleeding in a low-risk population.

Background: Bleeding is an important complication in children following tonsillectomy. Screening with coagulation tests prior to procedure is common to assess bleeding risk in the perioperative period, although ASH/ASPHO Choosing Wisely guidelines recommend against routine PT/PTT testing. Our aim was to compare von Willebrand factor antigen (VWF:Ag) and activity levels among patients with postoperative bleeding following tonsillectomy to evaluate for potential risk for bleeding.

Thromboelastometry assessment of hemostatic properties in various murine models with coagulopathy and the effect of factor VIII therapeutics.

Background: Rotational thromboelastometry (ROTEM) has been commonly used to assess the viscoelastic properties of the blood clotting process in the clinic for patients with a hemostatic or prothrombotic disorder.

Objective: To evaluate the capability of ROTEM in assessing hemostatic properties in whole blood from various mouse models with genetic bleeding or clotting disease and the effect of factor VIII (FVIII) therapeutics in FVIII mice.

Methods: Mice with a genetic deficiency in either a coagulation factor or a platelet glycoprotein were used in this study.

ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease.

Background: von Willebrand disease (VWD) is the most common inherited bleeding disorder known in humans. Accurate and timely diagnosis presents numerous challenges.

Objective: These evidence-based guidelines of 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) are intended to support patients, clinicians, and other health care professionals in their decisions about VWD diagnosis.

von Willebrand factor antigen levels are associated with burden of rare nonsynonymous variants in the VWF gene.

Approximately 35% of patients with type 1 von Willebrand disease (VWD) do not have a known pathogenic variant in the von Willebrand factor (VWF) gene. We aimed to understand the impact of VWF coding variants on VWD risk and VWF antigen (VWF:Ag) levels, studying 527 patients with low VWF and VWD and 210 healthy controls. VWF sequencing was performed and VWF:Ag levels assayed.

Laboratory variability in the diagnosis of type 2 VWD variants.

Essentials Patients with von Willebrand disease were enrolled in our study. Type 2 VWD diagnoses were based on original test results. Repeat evaluation resulted in many patients receiving a different type 2 diagnosis.

von Willebrand factor variant D1472H has no effect in mice with humanized VWF-platelet interactions.

The von Willebrand factor ristocetin cofactor activity assay (VWF:RCo) is used for diagnosis of von Willebrand disease (VWD) because of its ability to evaluate VWF binding to platelets. VWF sequence variant p.D1472H is associated with lower VWF:RCo levels in the absence of associated bleeding symptoms, indicating the VWF:RCo may not be accurate for characterizing VWF function in individuals with this variant.

A rat model of severe VWD by elimination of the VWF gene using CRISPR/Cas9.

Background: Von Willebrand Disease (VWD) is the most common inherited bleeding disorder, caused by quantitative and qualitative changes in von Willebrand factor (VWF). The biology of VWD, studied in canine, porcine, and murine models, differ in species-specific biology of VWF and the amenability to experimental manipulations such as phlebotomy. The factor VIII (FVIII) levels in these models are higher than in humans with type 3 VWD, suggesting functional differences between FVIII and VWF.

von Willebrand factor binding to myosin assists in coagulation.

von Willebrand factor (VWF) binds to platelets and collagen as a means of facilitating coagulation at sites of injury. Recent evidence has shown that myosin can serve as a surface for thrombin generation and binds to activated factor V and factor X. We studied whether VWF can also bind myosin as a means of bringing factor VIII (FVIII) to sites of clot formation.

Low VWF levels in children and lack of association with bleeding in children undergoing tonsillectomy.

von Willebrand disease is a common bleeding disorder, but diagnosis can be difficult in young children who have not had bleeding challenges. We sought to evaluate the correlation between bleeding and von Willebrand factor (VWF) levels in children undergoing surgical challenge with tonsillectomy. Children ages 0 to 18 undergoing tonsillectomy without a personal or family history of bleeding were enrolled prospectively following informed consent and institutional review board approval.

The severe spontaneous bleeding phenotype in a novel hemophilia A rat model is rescued by platelet FVIII expression.

Previous studies have shown that platelet-specific factor VIII (FVIII) expression (2bF8) restores hemostasis and induces immune tolerance in hemophilia A (HA) mice even with preexisting inhibitors. Here we investigated for the first time whether platelet FVIII expression can prevent severe spontaneous bleeding in rat HA, a model mimicking the frequent spontaneous bleeding in patients with severe HA. A novel FVIII-/- rat model in a Dahl inbred background (Dahl-FVIII-/-) with nearly the entire rat FVIII gene inverted was created by using a CRISPR/Cas9 strategy.

How we approach: Training pediatric coagulationists.

Unique expertise is required for the care of children, adolescents, and young adults with bleeding and clotting disorders. A number of Hemophilia Treatment Centers have developed pediatric hemostasis and thrombosis fellowship programs to facilitate subspecialty training and recruitment and retention in this field. This manuscript reviews an approach to training pediatric coagulationists including a description of current programs, sample curriculum, funding sources, and expected outcomes.

The impact of GPIbα on platelet-targeted FVIII gene therapy in hemophilia A mice with pre-existing anti-FVIII immunity.

Essentials Platelet-specific FVIII gene therapy is effective in hemophilia A mice even with inhibitors. The impact of platelet adherence via VWF/GPIbα binding on platelet gene therapy was investigated. GPIbα does not significantly affect platelet gene therapy of hemophilia A with inhibitors.

Humanized GPIbα-von Willebrand factor interaction in the mouse.

The interaction of platelet glycoprotein Ibα (GPIbα) with von Willebrand factor (VWF) initiates hemostasis after vascular injury and also contributes to pathological thrombosis. GPIbα binding to the VWF A1 domain (VWFA1) is a target for antithrombotic intervention, but attempts to develop pharmacologic inhibitors have been hindered by the lack of animal models because of the species specificity of the interaction. To address this problem, we generated a knockin mouse with exon 28-encoding domains A1 and A2 replaced by the human homolog (VWF).

Von Willebrand disease in the United States: perspective from the Zimmerman program.

This article will discuss the diagnosis and management of von Willebrand disease (VWD) in the United States and results from the Zimmerman Program, a national study of VWD. An algorithm is presented to show how we currently approach diagnostic testing for VWD, including the potential replacement of the ristocetin cofactor assay with a new von Willebrand factor (VWF)-GPIb binding assay. Results from the Zimmerman Program type 1 cohort are presented, including the findings that genetic defects in the gene are most common with VWF levels <30 IU/dL, but bleeding symptoms were present across the entire cohort regardless of VWF level.