Type 2M/2A von Willebrand disease: a shared phenotype between type 2M and 2A.

ABSTRACT: Four variants have been continuously subjected to debate and received different von Willebrand disease (VWD) classifications: p.R1315L, p.R1315C, p.R1374H, and p.R1374C. We chose to comprehensively investigate these variants with full set of VWD tests, protein-modeling predictions and applying structural biology. Patients with p.R1315L, p.R1315C, p.R1374H, and p.R1374C were included. A group with type 2A and 2M was included to better understand similarities and differences. Patients were investigated for phenotypic assays and underlying disease mechanisms. We applied deep protein modeling predictions and structural biology to elucidate the causative effects of variants. Forty-three patients with these variants and 70 with 2A (n = 35) or 2M (n = 35) were studied. Patients with p.R1315L, p.R1374H, or p.R1374C showed a common phenotype between 2M and 2A using von Willebrand factor (VWF):GPIbR/VWF:Ag and VWF:CB/VWF:Ag ratios and VWF multimeric profile, whereas p.R1315C represented a type 2M phenotype. There was an overall reduced VWF synthesis or secretion in 2M and cases with p.R1315L, p.R1374H, and p.R1374C, but not in 2A. Reduced VWF survival was observed in most 2A (77%), 2M (80%), and all 40 cases with p.R1315L, p.R1374H, and p.R1374C. These were the only variants that fall at the interface between the A1-A2 domains. p.R1315L/C mutants induce more compactness and internal mobility, whereas p.R1374H/C display a more extended overall geometry. We propose a new classification of type 2M/2A for p.R1315L, p.R1374H, and p.R1374C because they share a common phenotype with 2M and 2A. Our structural analysis shows the unique location of these variants on the A1-A2 domains and their distinctive effect on VWF.

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. METHODS: A total of 177 plasma samples from the Zimmerman Program: Comparative Effectiveness in the Diagnosis of VWD were evaluated from 11 centres across the US and Canada. The VWF-MAA was compared to Versiti Blood Research Institute (VBRI) and Local Center (LC) assigned VWD diagnosis. RESULTS: Overall, 129/177 (72.9%) were correctly assigned as normal (non-VWD), type 1, or variant VWD compared to the VBRI assigned diagnosis. VWF-MAA assigned non-VWD accurately in 29/57 (50.9%) samples, and type 1 VWD accurately in 93/110 (84.6%) samples. Considering LC diagnosis where there was agreement with VWF-MAA and not VBRI diagnosis, type 1 VWD was accurate in 105/110 (95.5%) samples. Bland-Altman analysis demonstrated good correlation between laboratory methods. VWD, types 2A, 2B, 1C VWD were also assigned by the VWF-MAA. CONCLUSIONS: We demonstrate that the VWF-MAA has utility in differentiating type 1 VWD, variant VWD and normal subjects in individuals undergoing an initial laboratory evaluation for bleeding.

Periprocedural management of type 2N von Willebrand disease with efanesoctocog alfa.

Type 2 Normandy von Willebrand disease (type 2N VWD) is a rare qualitative defect in von Willebrand factor (VWF) that results in impaired factor VIII (FVIII) binding and consequently reduced FVIII levels. Current perioperative strategies require VWF concentrates to attain durable hemostatic FVIII levels. This case highlights the successful perioperative management of a 78-year-old female with type 2N VWD and coronary artery disease utilizing efanesoctocog alfa, a novel long-acting recombinant FVIII product approved for hemophilia A. By decoupling the FVIII-VWF interaction, efanesoctocog alfa achieves prolonged FVIII circulation independent of VWF. A single administration targeting 90% FVIII levels yielded sustained FVIII elevation without achieving supraphysiologic VWF levels, thus mitigating potential cardiovascular risks. This is the first report of efanesoctocog alfa use in type 2N VWD. Further clinical studies are necessary to corroborate its efficacy and safety for this indication.

Laboratory Testing for von Willebrand Factor: Factor VIII Binding for the Diagnosis or Exclusion of Type 2N von Willebrand Disease: An Update.

von Willebrand factor (VWF) is a large adhesive plasma protein that expresses several functional activities. One of these activities is to bind coagulation factor VIII (FVIII) and to protect it from degradation. Deficiency of, and/or defects in, VWF can give rise to a bleeding disorder called von Willebrand disease (VWD). The defect in VWF that affects its ability to bind to and protect FVIII is captured within type 2N VWD. In these patients, FVIII is produced normally; however, plasma FVIII quickly degrades as it is not bound to and protected by VWF. These patients phenotypically resemble those with hemophilia A, where instead, FVIII is produced in lower amount. Both hemophilia A and 2N VWD patients therefore present with reduced levels of plasma FVIII relative to VWF level. However, therapy differs, since patients with hemophilia A are given FVIII replacement products, or FVIII mimicking products; instead, patients with 2N VWD require VWF replacement therapy, since FVIII replacement will only be effective for a short term, given this replacement product will quickly degrade in the absence of functional VWF. Thus, 2N VWD needs to be differentiated from hemophilia A. This can be achieved by genetic testing or by use of a VWF:FVIII binding assay. The current chapter provides a protocol for the performance of a commercial VWF:FVIII binding assay.

von Willebrand factor neutralizing and non-neutralizing alloantibodies in 213 subjects with type 3 von Willebrand disease enrolled in 3WINTERS-IPS.

BACKGROUND: Type 3 von Willebrand disease (VWD) is the most severe form of this disease owing to the almost complete deficiency of von Willebrand factor (VWF). Replacement therapy with plasma-derived products containing VWF or recombinant VWF rarely cause the development of alloantibodies against VWF that may be accompanied by anaphylactic reactions. OBJECTIVE: The objective of this study was to assess the prevalence of anti-VWF alloantibodies in subjects with type 3 VWD enrolled in the 3WINTERS-IPS. METHODS: An indirect in-house enzyme-linked immunosorbent assay has been used to test all the alloantibodies against VWF. Neutralizing antibodies (inhibitors) have been tested with a Bethesda-based method by using a VWF collagen binding (VWF:CB) assay. Samples positive for anti-VWF antibodies were further tested with Bethesda-based methods by using the semiautomated gain-of-function glycoprotein-Ib binding (VWF:GPIbM) and a VWF antigen (VWF:Ag) enzyme-linked immunosorbent assay. RESULTS: In total, 18 of the 213 (8.4%) subjects tested positive for anti-VWF antibodies and 13 of 213 (6%) had VWF:CB inhibitors. These 13 were among the 18 with anti-VWF antibodies. Of the 5 without VWF:CB inhibitors, 3 had non-neutralizing antibodies, 1 only inhibitor against VWF:GPIbM, and one could not be tested further. Ten of the 13 subjects with VWF:CB inhibitors also had VWF:GPIbM inhibitors, 6 of whom also had VWF:Ag inhibitors. Subjects with inhibitors were homozygous for VWF null alleles (11/14), homozygous for a missense variant (1/14), or partially characterized (2/14). CONCLUSIONS: Anti-VWF antibodies were found in 8.4% of subjects with type 3 VWD, whereas neutralizing VWF inhibitors were found in 6%, mainly in subjects homozygous for VWF null alleles. Because inhibitors may be directed toward different VWF epitopes, their detection is dependent on the assay used.

A nanobody against the VWF A3 domain detects ADAMTS13-induced proteolysis in congenital and acquired VWD.

von Willebrand factor (VWF) is a multimeric protein, the size of which is regulated via ADAMTS13-mediated proteolysis within the A2 domain. We aimed to isolate nanobodies distinguishing between proteolyzed and non-proteolyzed VWF, leading to the identification of a nanobody (designated KB-VWF-D3.1) targeting the A3 domain, the epitope of which overlaps the collagen-binding site. Although KB-VWF-D3.1 binds with similar efficiency to dimeric and multimeric derivatives of VWF, binding to VWF was lost upon proteolysis by ADAMTS13, suggesting that proteolysis in the A2 domain modulates exposure of its epitope in the A3 domain. We therefore used KB-VWF-D3.1 to monitor VWF degradation in plasma samples. Spiking experiments showed that a loss of 10% intact VWF could be detected using this nanobody. By comparing plasma from volunteers to that from congenital von Willebrand disease (VWD) patients, intact-VWF levels were significantly reduced for all VWD types, and most severely in VWD type 2A-group 2, in which mutations promote ADAMTS13-mediated proteolysis. Unexpectedly, we also observed increased proteolysis in some patients with VWD type 1 and VWD type 2M. A significant correlation (r = 0.51, P < .0001) between the relative amount of high-molecular weight multimers and levels of intact VWF was observed. Reduced levels of intact VWF were further found in plasmas from patients with severe aortic stenosis and patients receiving mechanical circulatory support. KB-VWF-D3.1 is thus a nanobody that detects changes in the exposure of its epitope within the collagen-binding site of the A3 domain. In view of its unique characteristics, it has the potential to be used as a diagnostic tool to investigate whether a loss of larger multimers is due to ADAMTS13-mediated proteolysis.

Phenotypic and genetic characterizations of the Milan cohort of von Willebrand disease type 2.

von Willebrand disease (VWD) type 2 is caused by qualitative abnormalities of von Willebrand factor (VWF). This study aimed to determine the genotypic and phenotypic characterizations of a large VWD type 2 cohort from Milan. We included 321 patients (54% female) within 148 unrelated families from 1995 to 2021. Patients were fully characterized using laboratory phenotypic tests, and the genotypic diagnosis was confirmed by target genetic analysis using Sanger sequencing. Patients were diagnosed with type 2A (n = 98; 48 families), 2B (n = 85; 38 families), 2M (n = 112; 50 families), or 2N (n = 26; 12 families). Eighty-two unique VWF variants, including 8 novel variants, were found. The potential pathogenic effect of novel variants was assessed by in silico analysis. Most patients were heterozygous for a single variant (n = 259; 81%), whereas 37 cases (11%) had 2 variants (4 homozygous, 9 in trans, and 24 in cis). Twenty-five patients (8%) had ≥3 variants, mainly as a result of gene conversions. Among the 82 distinct variants identified, 5 different types, including missense (n = 64), gene conversion (n = 10), synonymous (n = 1), deletion (n = 4), and splice (n = 3), were observed. The results from this large cohort showed that VWD type 2 is invariably due to variants that do not prevent the synthesis of the protein, and a vast majority of patients (88%) had missense variants. Given the complexity of type 2 diagnosis and the necessity of performing several phenotypic tests, genetic analysis for patients suspected of having type 2 is beneficial to establish the correct diagnosis.

Von Willebrand disease type 2M: Correlation between genotype and phenotype.

BACKGROUND: An appropriate clinical diagnosis of von Willebrand disease (VWD) can be challenging because of a variable bleeding pattern and laboratory phenotype. Genotyping is a powerful diagnostic tool and may have an essential role in the diagnostic field of VWD. OBJECTIVES: To unravel the clinical and laboratory heterogeneity of genetically confirmed VWD type 2M patients and to investigate their relationship. METHODS: Patients with a confirmed VWD type 2M genetic variant in the A1 or A3 domain of von Willebrand factor (VWF) and normal or only slightly aberrant VWF multimers were selected from all subjects genotyped at the Radboud university medical center because of a high suspicion of VWD. Bleeding scores and laboratory results were analyzed. RESULTS: Fifty patients had a clinically relevant genetic variant in the A1 domain. Median bleeding score was 5. Compared with the nationwide Willebrand in the Netherlands study type 2 cohort, bleeding after surgery or delivery was reported more frequently and mucocutaneous bleedings less frequently. Median VWF activity/VWF antigen (VWF:Act/VWF:Ag) ratio was 0.32, whereas VWF collagen binding activity/VWF antigen (VWF:CB/VWF:Ag) ratio was 0.80. Variants in the A3 domain were only found in two patients with low to normal VWF:Act/VWF:Ag ratios (0.45, 1.03) and low VWF:CB/VWF:Ag ratios (0.45, 0.63). CONCLUSION: Genetically confirmed VWD type 2M patients have a relatively mild clinical phenotype, except for bleeding after surgery and delivery. Laboratory phenotype is variable and depends on the underlying genetic variant. Addition of genotyping to the current phenotypic characterization may improve diagnosis and classification of VWD.

Type 2B von Willebrand Disease: Early Manifestation as Neonatal Thrombocytopenia.

Here, we report about a preterm female newborn with a prolonged course of severe thrombocytopenia and hematomas. The family history was positive for von Willebrand disease type 2B (VWD 2B). Diagnosis of VWD 2B was identified analyzing von Willebrand factor (VWF) parameters (VWF:antigen, VWF:activity, VWF multimer analyses) and performing light transmission aggregometry (with half concentration of ristocetin). In addition, the diagnosis was confirmed by molecular genetic analysis: identification of a disease-causing missense mutation (Val1316Met) in the VWF gene associated with a severe course of VWD 2B, which had been previously reported. Treatment with a VWF-containing plasma concentrate was initiated. Because the combination of prematurity and very low platelet count is often associated with intracranial bleeding, at the beginning platelet concentrates were transfused. Fortunately, the patient did not develop serious bleeding episodes. Interestingly, the patient had a mutation in the VWF gene, which had been described to be associated with aggravation of thrombocytopenia especially in stressful situations. Therefore, we replaced venous blood withdrawals by capillary blood samplings when possible and, consequently, we observed an increase of the platelet count after this change in management. At the age of 2 months, the patient was discharged after stabilization of the platelet count without any bleeding signs and without a need of long-term medication.

Type 2N VWD: Conclusions from the Spanish PCM-EVW-ES project.

INTRODUCTION: Type 2N von Willebrand disease (VWD) is characterized by a decreased affinity of von Willebrand factor (VWF) for factor VIII (FVIII). Abnormal binding of FVIII to VWF (VWF:FVIIIB), results in low FVIII plasma levels, which can lead to a misdiagnosis of mild haemophilia A. Accurate diagnosis of type 2N VWD is essential for appropriate genetic counselling and therapy. This disease can be distinguished from haemophilia A by in vitro assays (measurement VWF:FVIIIB activity) and/or genetic analysis. AIM: To identify the current challenges in the diagnosis and treatment of this type of VWD and provide an in-depth description of the phenotypes and mutations identified. RESULTS: Twenty-eight patients had at least one type 2N mutation, and 13 of these had a type 2N mutation combined with other variations. Three type 2N mutations were detected: p.Arg816Trp, p.Arg854Gln, and p.Arg763Ser. Two of these are the most frequently described mutations worldwide. This mutational spectrum differs from the broad spectrum seen in neighbouring France, where at least eight distinct 2N mutations have been found. In the PCM-EVW-ES cohort, 11 asymptomatic type 2N carriers with borderline FVIII plasma levels would probably have been excluded if the evaluation had been based on clinical and laboratory data only. Likewise, three patients with a severe phenotype would have been classified as homozygous for a 2N mutation if only the phenotype study had been performed. CONCLUSION: The high detection yield and affordability of next-generation sequencing support the use of this technology as a first-line diagnostic tool in this setting.

Type 2B von Willebrand Disease in Pregnancy: A Systematic Literature Review.

Our objective was to review the maternal characteristics and obstetric complications in women with type 2B von Willebrand disease (VWD). A systematic literature search was conducted using PubMed, Scopus, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov. We included all publications that addressed type 2B VWD in pregnancy. Our primary and secondary outcomes were incidence of postpartum hemorrhage (PPH) and incidence of thrombocytopenia in pregnancy. Two reviewers independently identified eligible studies and abstracted data including maternal characteristics, hematologic characteristics, treatment, and delivery outcomes. Twenty studies met inclusion criteria. There were 27 women (32 pregnancies) with type 2B VWD. Primary PPH was reported in 9/20 women (45%) and secondary PPH was reported in 6/13 women (46%). Thrombocytopenia in pregnancy was present in 27/28 women (96%); 23/27 women (85%) had platelet count <100 × 109/L, mean 33.7 ± 22.7 × 109/L. Factor concentrate treatment was administered before delivery (n = 16) and postpartum (n = 18), some women received both. Seventeen deliveries required blood products postpartum with 13/17 (76%) platelet transfusions and 6/17 (35%) red blood cell transfusions. No maternal mortality was reported. Women with type 2B VWD have significant morbidity in pregnancy related to high incidence of severe thrombocytopenia and primary and secondary PPH.

2B or not 2B? A diagnosis of von Willebrand disease a lifetime of 86 years in the making.

Type 2B von Willebrand disease (2B VWD) is a rare, autosomal dominant bleeding disorder characterized by a hyperadhesive form of von Willebrand factor (VWF). 2B VWD expresses phenotypically as an enhanced ristocetin-induced platelet aggregation and usually also a discordance in VWF activity versus protein level, with loss of high molecular weight VWF and (mild) thrombocytopenia. While all cases of 2B VWD supposedly share these characteristics, there is significant heterogeneity in laboratory findings within this group of patients, which are largely dictated by the underlying genetic defect. We present a case of such a patient, expressing a clearly atypical VWF phenotype, but as still associated with enhanced ristocetin-induced platelet aggregation, thrombocytopenia, and a previously undescribed VWF variant (c.4130C>G; p.Ala1377Gly). The patient was misdiagnosed over his lifetime as idiotypic thrombocytopenia - a (mis)diagnosis that took a lifetime of 86 years to redress.

Von Willebrand disease type 2N: An update.

Quantitative or qualitative defects of von Willebrand factor (VWF) are responsible for the most common inherited bleeding disorder, von Willebrand disease (VWD). Type 2N VWD is an uncommon recessive disorder that results from gene mutations located in the region coding for the binding site of VWF for factor VIII (FVIII). This narrative review describes the pathophysiology, diagnostic procedures and treatment as well as the molecular biology of type 2N VWD. Although other VWF-dependent functions like binding to platelets and collagen are preserved, FVIII plasma levels are low due to the rapid clearance of this moiety in the absence or reduction of its binding to VWF. The diagnosis of type 2N should be considered in patients with low FVIII coagulant activity (FVIII:C) and disproportionally higher VWF antigen, especially when they present with an autosomal recessive pattern of inheritance. Because an accurate diagnosis is essential for genetic counseling and optimal treatment, type 2N must be distinguished from mild/moderate hemophilia A and its carrier state. This differential diagnosis can be obtained by using the laboratory assay of the FVIII binding capacity of VWF (VWF:FVIIIB) or analysis of the FVIII binding site on the VWF gene.

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. Some genetic variants were particularly likely to move type 2 subcategories. ABSTRACT: Introduction Type 2 von Willebrand disease (VWD) refers to patients with a qualitative defect in von Willebrand factor. Accurate diagnosis of type 2 VWD subtypes can be challenging. Aim of the study To compare the historical diagnosis of type 2 VWD with current laboratory testing. Methods Subjects were enrolled in the Zimmerman Program either because of a preexisting diagnosis of VWD (retrospective cohort) or from evaluation for bleeding symptoms or suspected VWD (prospective cohort). Original diagnosis was assigned by the local center and central diagnosis was based on central laboratory testing. Results Two hundred and seventeen index cases in the retrospective cohort and 35 subjects in the prospective cohort carried a local diagnosis of type 2 VWD (29% and 6% of enrolled index cases, respectively). In the retrospective cohort, the diagnosis was confirmed in 66% of cases with a preexisting diagnosis of 2A, 77% 2B, 54% 2M, and 72% 2N. In the prospective cohort, 31% were confirmed 2A, 60% 2B, 23% 2M, and 100% 2N. Several genetic variants were repeatedly implicated in subjects with changed diagnosis: p.M1304R, p.R1315C, p.R1374C, and p.R1374H. Conclusions Both the prospective and retrospective cohorts demonstrated consistent variation in subjects whose diagnosis changed between 2A, 2B, and 2M. The importance of accurately diagnosing type 2 VWD may be most significant in the 2B subtype given potential concerns with the use of desmopressin in type 2B VWD. Some genetic variants appear in multiple types of VWD, making specific diagnoses challenging.

Are Iranian patients with von Willebrand disease type 2N properly differentiated from hemophilia A and do they receive appropriate treatment?

: The defect function of the von Willebrand factor (VWF) in carrying factor VIII (FVIII) leads to von Willebrand disease type 2N (VWD 2N) which could be easily misdiagnosed as hemophilia A. Differentiating of VWD 2N from hemophilia A is crucial for patient treatment and genetic counseling. As a retrospective study, we aimed to evaluate the current diagnostic work-up of Iranian patients with mild/moderate deficiency of FVIII levels and the possibility of misdiagnosis of VWD 2N as hemophilia A. All patients who referred to the reference coagulation laboratory at the Iranian Blood Transfusion Organization in a 10-months period for bleeding diathesis work-up with the request of FVIII activity level were included. Clinical and laboratory phenotypes including International Society on Thrombosis and Hemostasis - Bleeding Assessment Tool, FVIII activity, VWF antigen, VWF ristocetin cofactor, and FVIII binding capacity of VWF were assessed on suspected cases for VWD 2N. In total, the results of 896 patients for investigation of VWD 2N were evaluated and five new patients were identified within unrelated families with abnormal VWF:FVIIIB levels. Four were heterozygous for VWD 2N and one homozygous whom all were misdiagnosed as hemophilia A and underwent inappropriate treatments. The median bleeding score of the VWD 2N population was nine (4-13). In Iran, probably a significant number of VWD 2N patients are misdiagnosed as hemophilia A due to insufficient test panel for subtyping of von Willebrand disease. This study also emphasized the need for inclusion of the VWF:FVIIIB in suspected hemophilia A to achieve an optimal treatment strategy.

Molecular and clinical profile of type 2 von Willebrand disease in Iran: a thirteen-year experience.

Type 2 von Willebrand disease (VWD) is the most common congenital bleeding disorder, with variable bleeding tendency and a complex laboratory phenotype. In the current study, we report the clinical and molecular profile of a large number of Iranian patients with type 2 VWD. All exons, intron-exon boundaries, and untranslated regions were sequenced by Sanger sequencing for direct mutation detection. All identified mutations were confirmed in family members and by relevant bioinformatics studies. A total of 136 patients with type 2 VWD were diagnosed, including 42 (30.9%), 32 (23.6%), 38 (27.9%), and 24 (17.6%) patients with type 2A, type 2B, type 2M, and type 2N, respectively. Epistaxis (49%), gum bleeding (30.2%), ecchymosis (23.2%), and menorrhagia (16.3%) were the most common clinical presentations, while miscarriage (2.3%) and umbilical cord bleeding (0.8%) were the rarest. Thirty mutations were identified within the VWF gene, nine (30%) being novel, with p.Arg1379Cys (n = 20), p.Val1316Met (n = 13), p.Arg1597Trp (n = 13), p.Arg1374Cys (n = 10), p.Ser1506Leu (n = 10), and p.Arg1308Cys (n = 9) the most common. Type 2 VWD is a hemorrhagic disorder with variable bleeding tendency and a heterogeneous molecular basis in patients in Iran.

Evaluation of clinical severity in patients with type 2N von Willebrand disease using microchip-based flow-chamber system.

Type 2N von Willebrand disease (VWD) is characterized by impaired factor VIII (FVIII) binding to von Willebrand factor (VWF). Type 2N VWD patients generally exhibit mild bleeding tendency, but some exhibit a more severe hemorrhagic pattern. An assay for assessing hemostatic potential and predict clinical severity could significantly improve clinical management in these patients. We examined the relationship between bleeding score (BS) and the potential for thrombus formation in whole blood from type 2N VWD patients with various BS using rotational thromboelastometry (ROTEM) and microchip flow-chamber system (T-TAS®). Collagen-coated PL-chips, or thromboplastin- and collagen-coated AR-chips, were utilized in the T-TAS to assess platelet thrombus formation at high shear flow, or fibrin-rich platelet thrombus formation at low shear flow, respectively. Neither ROTEM nor the T-TAS using PL-chips reflected the BS. The AR-chip parameters in the T-TAS, however, were highly sensitive to different BS levels among these patients, despite similar FVIII/VWF-related measurements including FVIII/VWF binding. Additionally, the results with AR-chip assay were restored to normal after infusions of FVIII/VWF concentrates in the most severe patients. The data indicate that T-TAS using AR-chips may be a useful assay for predicting clinical severity and assessing therapeutic efficiency in type 2N VWD patients.