Prophylaxis in severe forms of von Willebrand's disease: results from the von Willebrand Disease Prophylaxis Network (VWD PN)

Gastrointestinal bleeding in von Willebrand patients: special diagnostic and management considerations

INTRODUCTION

Severe and recurrent gastrointestinal (GI) bleeding caused by angiodysplasia is a significant problem in patients with von Willebrand disease (VWD) and in those with acquired von Willebrand syndrome (AVWS). At present, angiodysplasia-related GI bleeding is often refractory to standard treatment including replacement therapy with von Willebrand factor (VWF) concentrates and continues to remain a major challenge and cause of significant morbidity in patients despite advances in diagnostics and therapeutics.

AREAS COVERED

This paper reviews the available literature on GI bleeding in VWD patients, examines the molecular mechanisms implicated in angiodysplasia-related GI bleeding, and summarizes existing strategies in the management of bleeding GI angiodysplasia in patients with VWF abnormalities. Suggestions are made for further research directions.

EXPERT OPINION

Bleeding from angiodysplasia poses a significant challenge for individuals with abnormal VWF. Diagnosis remains a challenge and may require multiple radiologic and endoscopic investigations. Additionally, there is a need for enhanced understanding at a molecular level to identify effective therapies. Future studies of VWF replacement therapies using newer formulations as well as other adjunctive treatments to prevent and treat bleeding will hopefully improve care.

Pharmacokinetic-Pharmacodynamic Comparison of Recombinant and Plasma-Derived von Willebrand Factor in Patients with von Willebrand Disease Type 3

Background

Recombinant von Willebrand factor (rVWF, vonicog alfa, Vonvendi/Veyvondi, Takeda Pharmaceuticals USA, Lexington, MA) and several plasma-derived VWF/factor VIII (pdVWF/FVIII) concentrates are available for treating bleeding episodes in patients with von Willebrand disease (VWD).

Purpose

To develop population pharmacokinetic (PK)/pharmacodynamic (PD) models that describe VWF:ristocetin cofactor (VWF:RCo) activity and its relationship with FVIII activity (FVIII:C) over time following intravenous administration of either rVWF or a pdVWF/FVIII concentrate (VWF:RCo/FVIII:C 2.4:1) in patients with VWD; to use the final PK/PD models for an in silico comparison of rVWF and pdVWF/FVIII.

Methods

The population PK model for rVWF was based on data from four clinical studies in which rVWF was administered to adult patients with VWD type 1, 2 or 3 (phase 1: NCT00816660; phase 3: NCT01410227 and NCT02283268) or severe hemophilia A (phase 1: EudraCT 2011-004314-42). The PK and PK/PD models for pdVWF/FVIII were based on data from the phase 1 study (NCT00816660) in patients with type 3 VWD who received either rVWF plus recombinant FVIII (rFVIII, octocog alfa, ADVATE^®, Takeda Pharmaceuticals USA, Lexington, MA, USA) or pdVWF/FVIII.

Results

There was a marked difference in clearance following rVWF administration compared with pdVWF/FVIII in type 3 VWD, leading to a ~1.75 longer mean residence time (ie, persistence of VWF:RCo activity in the body) and half-life for rVWF versus pdVWF/FVIII. Simulations showed that following repeated administration of rVWF (50 IU/kg), a FVIII:C activity of >40 IU/dL can be maintained for the full 72 h dosing interval.

Conclusion

The slower elimination of VWF:RCo following rVWF administration results in a prolonged effect on FVIII turnover compared with pdVWF/FVIII administration.

Building the foundation for a community-generated national research blueprint for inherited bleeding disorders: research priorities for mucocutaneous bleeding disorders

BACKGROUND

Excessive or abnormal mucocutaneous bleeding (MCB) may impact all aspects of the physical and psychosocial wellbeing of those who live with it (PWMCB). The evidence base for the optimal diagnosis and management of disorders such as inherited platelet disorders, hereditary hemorrhagic telangiectasia (HHT), hypermobility spectrum disorders (HSD), Ehlers-Danlos syndromes (EDS), and von Willebrand disease (VWD) remains thin with enormous potential for targeted research.

RESEARCH DESIGN AND METHODS

National Hemophilia Foundation and American Thrombosis and Hemostasis Network initiated the development of a National Research Blueprint for Inherited Bleeding Disorders with extensive all-stakeholder consultations to identify the priorities of people with inherited bleeding disorders and those who care for them. They recruited multidisciplinary expert working groups (WG) to distill community-identified priorities into concrete research questions and score their feasibility, impact, and risk.

RESULTS

WG2 detailed 38 high priority research questions concerning the biology of MCB, VWD, inherited qualitative platelet function defects, HDS/EDS, HHT, bleeding disorder of unknown cause, novel therapeutics, and aging.

CONCLUSIONS

Improving our understanding of the basic biology of MCB, large cohort longitudinal natural history studies, collaboration, and creative approaches to novel therapeutics will be important in maximizing the benefit of future research for the entire MCB community.

Von Willebrand Disease Epidemiology, Burden of Illness and Management: A Systematic Review

Introduction

Although hereditary von Willebrand disease (VWD) is the most common bleeding disorder, its epidemiology is not well understood. A systematic review (PROSPERO CRD42020197674/CRD42021244374) on the epidemiology/burden of illness of VWD was conducted to better understand patients' unmet needs.

Methods

Observational studies (published January 1, 2010 to April 14, 2021) were identified in MEDLINE and Embase databases, using free-text keywords and thesaurus terms for VWD and outcomes of interest. Pragmatic web-based searches of the gray literature, including conference abstracts, were performed, and reference lists of retained publications were manually searched for additional sources. Case reports and clinical trials (phase 1-3) were excluded. Outcomes of interest were incidence, prevalence, mortality, patient characteristics, burden of illness, and therapeutic management/treatments currently used for VWD.

Results

Of the 3095 identified sources, 168 were included in this systematic review. Reported VWD prevalence (22 sources) ranged from 108.9 to 2200 per 100,000 in population-based studies and from 0.3 to 16.5 per 100,000 in referral-based studies. Reported times between first symptom onset and diagnosis (two sources; mean 669 days; median 3 years) highlighted gaps in timely VWD diagnosis. Bleeding events reported in 72-94% of the patients with VWD (all types; 27 sources) were mostly mucocutaneous including epistaxis, menorrhagia, and oral/gum bleeding. Poorer health-related quality of life (three sources) and greater health care resource utilization (three sources) were reported for patients with VWD than in general populations.

Conclusion

Available data suggest that patients with VWD experience high disease burden in terms of bleeding, poor quality of life, and health care resource utilization.

Efficacy and safety of von Willebrand factor concentrate almost devoid of factor VIII (Wilfactin®) in paediatric patients under 6 years of age with severe von Willebrand disease

BACKGROUND

Plasma-derived von Willebrand factor (VWF) (Wilfactin^®, LFB, France) was developed for prophylaxis and treatment of haemorrhages in both adults and adolescents with von Willebrand disease (VWD). Replacement therapy in paediatric patients is a key element of the clinical trial programme.

MATERIAL AND METHODS

Patients aged <6 years with severe VWD were enrolled in a multinational, open-label study to evaluate the in vivo recovery for Wilfactin^®, and its efficacy in preventing and treating bleeding episodes and during surgery. Overall haemostatic efficacy based on a 4-point scale was assessed by investigators. The treatment period ≥18 months investigated the long-term safety.

RESULTS

Nine patients, including 7 with type 3 VWD were exposed to treatment with Wilfactin^® for up to 4.2 years. Recovery of VWF in 7 patients (n=5 type 3, n=1 type 2, n=1 type 1) was 1.8±0.4 IU/dL per IU/kg. Of the 62 bleeds, 89% were controlled with one (73%) or two (16%) infusions of Wilfactin^®. The median dose per infusion was 54 IU/kg. A factor VIII dose was co-administered in 1.6% of bleeds. "Excellent"/"Good" haemostatic efficacy was achieved in 90.3% of episodes. Six patients underwent 11 minor surgical interventions. Treatment duration was 1 day (range: 1-6 days) with a dose administered 30-60 minutes before procedure of 56 IU/kg (range: 41-106 IU/kg). Haemostasis was rated as "Excellent" in all surgeries. During 4-year prophylactic treatment in one patient, breakthrough bleeds were reported in 2.2% of infusions. No VWF inhibitors, thromboembolic events or allergic/anaphylactic-type reactions were observed following a total exposure of 770 days.

DISCUSSION

The results show that Wilfactin^® provides a safe and effective treatment in patients <6 years of age with severe VWD.

Special considerations in GI bleeding in VWD patients

Gastrointestinal (GI) bleeding is an important cause of morbidity and mortality in von Willebrand disease (VWD). It has been noted that GI bleeding caused by angiodysplasia is overrepresented in VWD patients compared to other causes. The bleeding from angiodysplasia is notoriously difficult to treat; recurrences and rebleeds are common. A growing body of basic science evidence demonstrates that von Willebrand factor negatively regulates angiogenesis through multiple pathways. VWD is clinically highly associated with angiodysplasia. The predisposition to angiodysplasia likely accounts for many of the clinical difficulties related to managing GI bleeding in VWD patients. Diagnosis and treatment are challenging with the current tools available, and much further research is needed to further optimize care for these patients with regard to acute treatment, prophylaxis, and adjunctive therapies. In this review we provide an overview of the available literature on GI bleeding in VWD and explore the molecular underpinnings of angiodysplasia-related GI bleeding. Considerations for diagnostic effectiveness are discussed, as well as the natural history and recurrence of these lesions and which therapeutic options are available for acute and prophylactic management.

Effectiveness of long-term prophylaxis using pdFVIII/VWF concentrate in patients with inherited von Willebrand disease

Background

Patients with symptomatic von Willebrand disease (VWD) should be offered long‐term prophylaxis (LTP) to prevent recurrent bleedings. Our objective was to evaluate the effectiveness and safety of Voncento®, a plasma‐derived FVIII/VWF concentrate (ratio 1:2.4), administrated in LTP.

Methods

We included patients from the OPALE study (May 2016 to April 2021), a French multicenter observational study following patients with inherited VWD, who received a Voncento® LTP during the study period.

Results

Among the 130 OPALE‐study patients, 23 patients (12 women) received a LTP and were therefore included. The median (range) age was 16 (1–85) years; 16 patients were type 3, 1 was type 2A, 6 were type 2B. Before inclusion, 19 (83%) were under LTP and 4 (17%) received on‐demand (OD) treatment. The indications for initiating prophylaxis in the overall population were joint bleeding (43%), ear, nose, and throat (ENT) bleeding including epistaxis or oral bleeding (39%), and recurrent muscle hematoma (22%). The medians (ranges) dose of Voncento® per infusion, frequency, and weekly dose were 45 (33–109) IU/kg, 2 infusions per week, and 96 (44–222) IU/kg/week, respectively. The median (range) annualized bleeding rate (ABR) was 0.8, 0.7 (0–3.5), and 0 (0–2.3) for type 2A, 2B, 3 patients, respectively. There was no difference regarding to the dose, frequency of infusion, or in terms of ABR in 9/19 patients who replaced previous concentrates with Voncento®. During the study period, no adverse event was reported.

Conclusion

These results suggest that Voncento® is effective to prevent recurrent bleedings in patients symptomatic VWD.

Recent advances in therapeutic options for rare hemostatic disorders: selected poster extracts of recent research in hemophilia A, congenital hemophilia with inhibitors, von Willebrand disease, and thrombotic thrombocytopenic purpura presented at the 29th congress of the International Society on Thrombosis and Haemostasis (ISTH 2021, Jul 17-21; virtual congress)

Hemophilia, von Willebrand disease (VWD), and thrombotic thrombocytopenic purpura (TTP) are rare diseases affecting normal hemostasis. Although they differ in their pathogenesis and clinical manifestation, if left undiagnosed and untreated, all these conditions can result in severe long-term consequences and can be potentially life-threatening. This article summarizes a poster series funded by Takeda and presented virtually at the 29th annual congress of the International Society on Thrombosis and Haemostasis (ISTH) in 2021: Data from real-world evidence highlight the importance of joint health and personalized prophylaxis to prevent bleeding for patients with hemophilia, the need to further raise disease awareness in support of timely diagnosis and access to treatment in general practice settings for patients with VWD, and describe the clinical burden for patients with TTP and the importance to advance treatment options for these patients.

Recombinant von Willebrand factor prophylaxis in patients with severe von Willebrand disease: phase 3 study results

International guidelines conditionally recommend long-term prophylaxis in patients with von Willebrand disease (VWD) and severe/frequent bleeding. As recombinant von Willebrand factor (rVWF, vonicog alfa) may reduce the frequency of treated spontaneous bleeding events (BEs), we investigated the efficacy and safety of rVWF prophylaxis in adults with severe VWD. Patients with BEs requiring VWF therapy in the past year (on-demand VWF therapy [Prior On-Demand group] or plasma-derived VWF prophylaxis [pdVWF; Switch group]) were enrolled in a prospective, open-label, nonrandomized, phase 3 study. Planned duration of rVWF prophylaxis was 12 months; starting rVWF dose was 50±10 VWF:RCo IU/kg twice weekly (Prior On-Demand group) or based on prior pdVWF weekly dose/dosing frequency (Switch group). The primary endpoint was annualized bleeding rate of treated spontaneous BEs (sABR) during rVWF prophylaxis. Over the 12-month study period, treated sABR decreased by 91.5% on-study versus historical sABR in 13 patients in Prior On-Demand group, and by 45.0% in 10 patients in Switch group (model-based analysis ratio [95% CI]: 0.085 [0.021-0.346] and 0.550 [0.086-3.523], respectively). No treated spontaneous BEs were recorded in 84.6% (11/13) and 70.0% (7/10) of patients, respectively. The safety profile of rVWF was consistent with the previously established profile, with no new adverse drug reactions identified. Findings suggest that rVWF prophylaxis can reduce treated spontaneous BEs in patients previously receiving on-demand VWF therapy and maintains at least the same level of hemostatic control in patients who switch from prophylaxis with pdVWF to rVWF, with a favorable safety profile. Trial registration: www.clinicaltrials.gov (#NCT02973087) and www.clinicaltrialsregister.eu (#EudraCT 2016-001478-14).

Outcomes of long-term von Willebrand factor prophylaxis use in von Willebrand disease: A systematic literature review

BACKGROUND

Von Willebrand Disease (VWD) is a common inherited bleeding disorder. Patients with VWD suffering from severe bleeding may benefit from the use of secondary long-term prophylaxis.

AIM

Systematically summarize the evidence on the clinical outcomes of secondary long-term prophylaxis in patients with VWD and severe recurrent bleedings.

METHODS

We searched Medline and EMBASE through October 2019 for relevant randomized clinical trials (RCTs) and comparative observational studies (OS) assessing the effects of secondary long-term prophylaxis in patients with VWD. We used Cochrane Risk of Bias (RoB) tool and the RoB for Non-Randomized Studies of interventions (ROBINS-I) tool to assess the quality of the included studies. We conducted random-effects meta-analyses and assessed the certainty of the evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.

RESULTS

We included 12 studies. Evidence from one placebo controlled RCT suggested that VWD prophylaxis as compared to no prophylaxis reduced the rate of bleeding episodes (Rate ratio [RR], .24; 95% confidence interval [CI], .17-.35; low certainty evidence), and of epistaxis (RR, .38; 95%CI, .21-.67; moderate certainty evidence), and may increase serious adverse events RR 2.73 (95%CI .12-59.57; low certainty). Evidence from four before-and-after studies in which researchers reported comparative data suggested that VWD prophylaxis reduced the rate of bleeding (RR .34; 95%CI, .25-.46; very low certainty evidence).

CONCLUSION

VWD prophylaxis treatment seems to reduce the risk of spontaneous bleeding, epistaxis, and hospitalizations. More RCTs should be conducted to increase the certainty in these benefits.

Gastrointestinal Bleeding in Congenital Bleeding Disorders

Gastrointestinal bleeding (GIB) is serious, intractable, and potentially life-threatening condition. There is considerable heterogeneity in GIB phenotypes among congenital bleeding disorders (CBDs), making GIB difficult to manage. Although GIB is rarely encountered in CBDs, its severity in some patients makes the need for a comprehensive and precise assessment of underlying factors and management approaches imperative. Initial evaluation of GIB begins with assessment of hematological status; GIB should be ruled out in patients with chronic anemia, and in presentations that include hematemesis, hematochezia, or melena. High-risk patients with recurrent GIB require urgent interventions such as replacement therapy for treatment of coagulation factor deficiency (CFD). However, the best management strategy for CFD-related bleeding remains controversial. While several investigations have identified CBDs as potential risk factors for GIB, research has focused on assessing the risks for individual factor deficiencies and other CBDs. This review highlights recent findings on the prevalence, management strategies, and alternative therapies of GIB related to CFDs, and platelet disorders.

Prophylactic management of patients with von Willebrand disease

Von Willebrand disease, the most common inherited bleeding disorder that affects both males and females, is due to quantitative or qualitative defects of the multimeric glycoprotein von Willebrand factor, which cause mucous membrane bleeding but also soft tissue bleeding owing to the secondary deficiency of factor VIII. The aim of treatment is to correct this dual defect of hemostasis. In addition to the episodic management of bleeding episodes, therapy includes their short- or long-term prevention. Short-term prophylaxis is mainly warranted in order to provide effective hemostatic coverage to patients undergoing surgery or invasive procedures and to affected women at the time of delivery or during menstruations associated with excessive bleeding. The aim of long-term prophylaxis is to prevent bleeding in particular categories of patients at increased risk of frequent and spontaneous bleeding in the joints, nose, and gastrointestinal tract.

The Intriguing Relationships of von Willebrand Factor, ADAMTS13 and Cardiac Disease

von Willebrand factor (VWF) is an adhesive protein involved in primary hemostasis and facilitates platelet adhesion to sites of vascular injury, thereby promoting thrombus formation. VWF exists in plasma as multimers of increasing size, with the largest (high molecular weight; HMW) expressing the greatest functional activity. A deficiency of VWF is associated with a bleeding disorder called von Willebrand disease (VWD), whereas an excess of VWF, in particular the HMW forms, is associated with thrombosis. ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif-13), also known as VWF-cleaving protease, functions to moderate the activity of VWF by cleaving multimers of VWF and limiting the expression of the largest multimers of VWF. A deficiency of ADAMTS13 is therefore associated with an excess of (HMW forms of) VWF, and thus thrombosis. Indeed, any disturbance of the VWF/ADAMTS13 ratio or ‘axis’ may be associated with pathophysiological processes, including prothrombotic tendency. However, both thrombosis or bleeding may be associated with such disturbances, depending on the presenting events. This review evaluates the relationship of VWF and ADAMTS13 with cardiac disease, including cardiac failure, and associated pathophysiology.

Von Willebrand Disease: Current Status of Diagnosis and Management

Von Willebrand disease (VWD) is a common bleeding disorder, affecting male and female individuals equally, that often manifests in mucosal bleeding. VWD can be secondary to a quantitative (Type 1 and Type 3) or qualitative (Type 2) defects in Von Willebrand factor (VWF). Initial testing includes VWF antigen, as well as a platelet binding assay to differentiate between qualitative and quantitative defects. Further subtyping requires additional testing and is needed to ensure appropriate treatment. Desmopressin, antifibrinolytics, hormonal treatments for heavy menstrual bleeding, and VWF concentrates are commonly used in the treatment of VWD.

Addressing unmet needs in rare bleeding disorders: selected poster extracts of recent research in hemophilia A and von Willebrand disease presented at the 14th Annual Congress of the European Association for Haemophilia and Allied Disorders (EAHAD) (Feb 3-5, 2021; virtual congress)

Hemophilia A and von Willebrand disease (VWD) are inherited rare bleeding disorders affecting normal hemostasis. Patients with VWD, especially those with severe disease types, share some similarities to patients with hemophilia A in their burden of disease: they suffer from an increased risk of potentially severe and life-threatening bleeds and associated long-term consequences, such as impaired joint health and overall lower quality of life. However, the two bleeding disorders differ in their primary cause and affected patient population, and comprise a range of different bleeding phenotypes with varying unmet needs. Generating scientific evidence to advance health care for patients with rare bleeding disorders is challenging due to the low prevalence and heterogeneity of affected populations, including patient demographics and symptom severities. Innovative study designs are needed to adequately answer relevant scientific questions and address patients' unmet needs. In support of advancing clinical outcomes and treatment options for these patients, at the recent EAHAD 2021 annual congress, novel approaches and data from clinical and real-world observational studies, as well as systematic literature analyses, were presented. Herein, extracts from seven selected posters reporting research in hemophilia A and VWD funded by Takeda are discussed.

Economic Burden Associated with Major Surgery in Patients with von Willebrand Disease: A United States Retrospective Administrative Database Analysis

Purpose

To estimate the incremental economic burden of major surgeries in patients with von Willebrand disease (VWD).

Patients and Methods

This was a retrospective analysis of the IBM Health MarketScan^® database (2008–2018). Patients with at least two healthcare visits for VWD in the database who had undergone at least one major surgery unrelated to VWD (identified via International Classification of Diseases, Ninth and Tenth Revisions procedure codes) were included. Patients without VWD with major surgeries were selected from a 1% random database sample. All patients had ≥12 months of continuous healthcare plan enrollment before and following their first major surgery. Patients with VWD were matched (1:1) with patients without VWD using propensity score matching. Regression models compared healthcare resource utilization and costs between the matched cohorts over a 12-month period after patients’ index major surgery.

Results

After propensity score matching, 2972 pairs were selected. Musculoskeletal and digestive surgeries were the two most common major surgeries (patients with VWD, 39.6% and 25.0%; without VWD, 37.1% and 23.4%, respectively). Patients with VWD were significantly more likely (p<0.0001) to have an inpatient admission (odds ratio = 1.71; 95% confidence interval [CI] 1.52–1.92) or emergency room visit (odds ratio = 1.41; 95% CI 1.25–1.59) than patients without VWD. The numbers of inpatient admissions (incidence rate ratio [IRR] = 1.47; 95% CI 1.35–1.60), emergency room visits (IRR = 1.44; 95% CI 1.31–1.59), and outpatient visits (IRR = 1.16; 95% CI 1.11–1.21) per patient were also significantly greater for patients with VWD than for those without VWD (p<0.0001). Patients with VWD incurred significantly higher (p<0.0001) total healthcare costs (medical and pharmacy) per patient than patients without VWD ($50,733.89 versus $30,154.84, respectively).

Conclusion

Healthcare resource utilization and associated costs among patients undergoing major surgeries were significantly higher for those with VWD than for patients without VWD.

Perioperative Management of Orthopaedic Patients with Hematologic Disorders: A Critical Analysis Review

Perioperative management of orthopaedic patients with a hematologic disorder is a complex endeavor that requires a multidisciplinary team-based approach. A team composed of an experienced orthopaedic surgeon, an anesthesiologist, and a hematologist is necessary to achieve optimal outcomes. Patients with hemophilia and other complex hematologic disorders should be managed at, or in consultation with a hematologist at, a comprehensive hemophilia center. Bleeding disorders and inherited thrombophilia present unique challenges for the perioperative management of orthopaedic surgery. Comprehensive preoperative planning and familiarity with treatment guidelines can help to minimize these risks. Knowledge of the disease processes outlined in this article will provide orthopaedic surgeons with the requisite background knowledge that is needed to initiate safe and effective treatment strategies involving this high-risk patient population.

How I treat gastrointestinal bleeding in congenital and acquired von Willebrand disease

Gastrointestinal (GI) bleeding is distinctive of severe von Willebrand disease (VWD), generally arising in older patients; in most cases, blood transfusion and hospitalization are required. The presence of arteriovenous malformations is often described when endoscopic examinations are performed. Patients with congenital type 3, 2A, and 2B are those most frequently affected by this symptom, possibly due to the loss of high-molecular-weight multimers of von Willebrand factor (VWF). GI bleeding can also occur in patients affected by acquired von Willebrand syndrome. Endoscopic examination of the GI tract is necessary to exclude ulcers and polyps or cancer as possible causes of GI bleeding. In congenital VWD, prophylaxis with VWF/factor VIII concentrates is generally started after GI-bleeding events, but this therapy is not always successful. Iron supplementation must be prescribed to avoid chronic iron deficiency. Possible rescue therapies (high-dose statins, octreotide, thalidomide, lenalidomide, and tamoxifen) were described in a few case reports and series; however, surgery may be necessary in emergency situations or if medical treatment fails to stop bleeding. In this article, we present several clinical cases that highlight the clinical challenges of these patients and possible strategies for their long-term management.

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

BACKGROUND

von Willebrand disease (VWD) is a common inherited bleeding disorder. Significant variability exists in management options offered to patients.

OBJECTIVE

These evidence-based guidelines from 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 health care professionals in their decisions about management of VWD.

METHODS

ASH, ISTH, NHF, and WFH formed a multidisciplinary guideline panel. Three patient representatives were included. The panel was balanced to minimize potential bias from conflicts of interest. The University of Kansas Outcomes and Implementation Research Unit and the McMaster Grading of Recommendations Assessment, Development and Evaluation (GRADE) Centre supported the guideline development process, including performing and updating systematic evidence reviews (through November 2019). The panel prioritized clinical questions and outcomes according to their importance to clinicians and patients. The panel used the GRADE approach, including GRADE Evidence-to-Decision frameworks, to assess evidence and make recommendations, which were subject to public comment.

RESULTS

The panel agreed on 12 recommendations and outlined future research priorities.

CONCLUSIONS

These guidelines make key recommendations regarding prophylaxis for frequent recurrent bleeding, desmopressin trials to determine therapy, use of antiplatelet agents and anticoagulant therapy, target VWF and factor VIII activity levels for major surgery, strategies to reduce bleeding during minor surgery or invasive procedures, management options for heavy menstrual bleeding, management of VWD in the context of neuraxial anesthesia during labor and delivery, and management in the postpartum setting.

Translating the success of prophylaxis in haemophilia to von Willebrand disease

INTRODUCTION

There is limited awareness of von Willebrand disease (VWD), leading to challenges in both diagnosis and defining the optimal treatment approach for these patients. Patients with VWD are typically treated on-demand, with short-term prophylaxis used during surgery. In contrast, early initiation, and long-term use of prophylaxis is the standard of care in patients with severe haemophilia and can be successfully used to prevent joint bleeding and reduce chronic arthropathy.

AIM

To provide an understanding of the current evidence for the prophylactic treatment of patients with VWD and compare this to the management of patients with haemophilia.

METHODS

Review of published literature using a non-systematic search of PubMed and reference lists of sourced articles.

RESULTS

The successes seen with prophylaxis in haemophilia provide the rationale for long-term prophylaxis in patients with severe forms of VWD; preventing spontaneous, excessive and sometimes life-threatening bleeding, and reducing chronic joint disease. Currently, there are a few clinical trials assessing the long-term benefits of prophylaxis in VWD, and guidelines for the optimal prophylaxis treatment approach are lacking. Greater attempts to provide comprehensive, long-term care for patients with VWD are needed but still lacking within the community. This review highlights the success of prophylaxis in haemophilia and how this knowledge might be applied and translated to patients with VWD.

CONCLUSIONS

Lessons can be learned from the use of prophylaxis in haemophilia and prophylaxis should be considered the standard of care for a subgroup of patients with severe VWD.

Economic burden of major bleeding events in commercially insured patients with von Willebrand disease based on claims data from the United States

BACKGROUND: von Willebrand disease (VWD) can lead to serious, life-threatening bleeding events associated with substantial clinical and economic burden. OBJECTIVE: To estimate the prevalence, health care resource utilization (HCRU), and costs associated with major bleeding events in patients with VWD. METHODS: This was a retrospective analysis of the IBM MarketScan database (2008-2016). Selected patients had ≥ 2 VWD diagnoses, no diagnosis of acquired coagulation factor deficiency, and continuous health care plan enrollment for ≥ 12 months from eligibility start date. Prevalence was calculated as the proportion of eligible patients with ≥ 1 major bleeding event during the observation period (start to end of continuous eligibility). HCRU and costs in the 12-month continuous enrollment period following the first major bleeding event were compared with those from a comparable 12-month period for patients without major bleeding events. RESULTS: Of the 19,785 patients with VWD, 15% experienced ≥ 1 major bleeding event during a median follow-up of 4 years; 89% of these events were gastrointestinal bleeds. For the economic analysis, 773 patients with ≥ 1 major bleeding event and 4,285 patients without major bleeding events met the selection criteria. Controlling for baseline covariates, patients with major bleeding events had significantly (P < 0.0001) more inpatient admissions (incidence rate ratio [IRR] = 3.2; 95% CI = 2.78-3.77), longer inpatient stays (IRR = 3.9; 95% CI = 3.12-4.93), and more emergency department visits (IRR = 2.0; 95% CI = 1.77-2.27) and outpatient visits (IRR = 1.3; 95% CI = 1.19-1.34) than patients without major bleeding events. Annual health care costs were significantly higher (P < 0.01) for patients with major bleeding events than those without them (predicted mean cost differences: total = $20,890, pharmacy = $2,593, and medical = $18,293). CONCLUSIONS: Major bleeding events were associated with increased HCRU and costs, mostly inpatient costs. Therefore, optimizing therapy to prevent or reduce major bleeding events has the potential to reduce health care use and costs in patients with VWD. DISCLOSURES: This study was funded by Baxalta U.S. Inc., a Takeda company (Lexington, MA). The study sponsor was involved with the study design, analysis, and interpretation of data; writing of the manuscript; and the decision to publish the article. Lu, Wu, and Ewenstein are employees of Baxalta U.S. Inc., a Takeda company, and are Takeda stock owners. Farahbakhshian is an employee of Shire U.S. Inc., a Takeda company, and is a Takeda stock owner. Oladapo was an employee of Baxalta U.S. Inc., a Takeda company, at the time the analysis was completed and the manuscript developed, and is a Takeda stock owner.

New therapies for von Willebrand disease

The management of von Willebrand disease (VWD) is based upon the dual correction of the primary hemostasis defect, due to the inherited deficiency of von Willebrand factor (VWF), and of the secondary defect of factor VIII coagulant activity (FVIII:C), due to the loss of binding and stabilization by VWF of this intrinsic coagulation factor in flowing blood. The traditional therapeutic weapons (the synthetic derivative of the antidiuretic hormone desmopressin and plasma-derived VWF/FVIII concentrates) are able to transiently correct both the defects. With the goal of tackling the primary deficiency in the disease, that is, VWF, but at the same time exploiting the normal capacity of patients to produce FVIII, the novel approach of replacing only VWF was implemented in the last 10 years. Following the manufacturing of a concentrate fractionated from human plasma and of one obtained by recombinant DNA technology, clinical studies have shown that VWF-only products correct not only the primary VWF deficiency but also the secondary FVIII:C deficiency. The demonstrated efficacy of these products in various clinical situations and, ultimately, in such a hemostasis-challenging context as surgery testifies to the effectiveness and safety of this approach. It remains to be seen whether VWF-only products are efficacious and safe in still-unexplored situations, such as use in children; the long-term use for prophylaxis; and in recurrent gastrointestinal (GI) bleeding due to angiodysplasia, a major therapeutic problem in VWD.

New therapies for von Willebrand disease

The management of von Willebrand disease (VWD) is based upon the dual correction of the primary hemostasis defect, due to the inherited deficiency of von Willebrand factor (VWF), and of the secondary defect of factor VIII coagulant activity (FVIII:C), due to the loss of binding and stabilization by VWF of this intrinsic coagulation factor in flowing blood. The traditional therapeutic weapons (the synthetic derivative of the antidiuretic hormone desmopressin and plasma-derived VWF/FVIII concentrates) are able to transiently correct both the defects. With the goal of tackling the primary deficiency in the disease, that is, VWF, but at the same time exploiting the normal capacity of patients to produce FVIII, the novel approach of replacing only VWF was implemented in the last 10 years. Following the manufacturing of a concentrate fractionated from human plasma and of one obtained by recombinant DNA technology, clinical studies have shown that VWF-only products correct not only the primary VWF deficiency but also the secondary FVIII:C deficiency. The demonstrated efficacy of these products in various clinical situations and, ultimately, in such a hemostasis-challenging context as surgery testifies to the effectiveness and safety of this approach. It remains to be seen whether VWF-only products are efficacious and safe in still-unexplored situations, such as use in children; the long-term use for prophylaxis; and in recurrent gastrointestinal (GI) bleeding due to angiodysplasia, a major therapeutic problem in VWD.

Updated overview on von Willebrand disease: focus on the interest of genotyping

Introduction: Von Willebrand disease (VWD) is the most common inherited bleeding disorder, characterized by a quantitative or qualitative defect of von Willebrand factor (VWF), a multimeric glycoprotein crucial for primary hemostasis and coagulation. VWD pathophysiology is heterogeneous as it includes several types and subtypes which therapeutic management is different. The mainstays of VWD treatment are desmopressin and replacement therapy based on both plasma-derived concentrates and a recently developed recombinant VWF. VWD definitive diagnosis is achieved by a battery of phenotypic biologic assays and genotyping is currently performed mostly for research.Areas covered: This narrative review will firstly present a general overview on VWD epidemiology, pathophysiology, classification, clinics, phenotypic biologic diagnosis, and treatment. Secondly, a focus on VWD genotyping will be presented with specific emphasis on the evolution of its technical aspects, its applications for research dedicated to a better understanding of VWD pathophysiology and epidemiology and its interest in both a faster diagnosis and an optimal treatment of VWD.Expert opinion: Based on analysis of the literature, it can be concluded that the fast evolution of genetic techniques together with the development of innovating treatments may significantly change diagnostic flow charts for VWD and their use for specific and personalized treatment.

Platelets compensate for poor thrombin generation in type 3 von Willebrand disease

In type 3 von Willebrand disease (VWD3), the most severe form with absent von Willebrand factor (VWF), the bleeding phenotype is variable. Platelet contribution to the hemostatic defect in VWD3 calls upon further studies. We investigated the contribution of platelets to in vitro thrombin generation (TG) and platelet procoagulant activity in VWD3. TG was assessed by calibrated automated thrombogram (CAT) in platelet-poor (PPP) and -rich plasma (PRP) from 9 patients before and in 6 patients also 30 min after receiving their regular VWF therapy. Responsiveness of PPP to FVIII and protein S was also investigated. TG data were compared with routine laboratory variables, rotational thromboelastometry (ROTEM) and platelet expression of P-selectin and phosphatidylserine in flow cytometry. Compared with healthy controls, TG was markedly decreased in VWD3 PPP (peak thrombin was 16% of normal median), but not in PRP (77% of normal median) (p = 0.002). Six out of nine patients (67%) were high responders in their platelet P-selectin, and 5/9 (56%) in phosphatidylserine expression. Replacement therapy improved TG in PPP, while in PRP TG only modestly increased or was unaffected. In PPP, FVIII levels associated with TG and in vitro FVIII-supplemented TG inclined up to threefold. Conversely, a FVIII inhibitory antibody reduced plasma TG in all, but especially in patients with remnant FVIII levels. Inhibition of protein S improved plasma TG, particularly at low FVIII levels. ROTEM failed to detect VWD3.In VWD3, TG is reduced in PPP and regulated by FVIII and protein S, but TG is close to normal in PRP. VWD3 platelets seem to compensate for the FVIII-associated reduction in TG by their exposure of P-selectin and phosphatidylserine.

A phase III study comparing secondary long-term prophylaxis versus on-demand treatment with vWF/FVIII concentrates in severe inherited von Willebrand disease

BACKGROUND

There is a lack of prospective clinical trials specifically designed to evaluate the benefits of prophylaxis with vWF/FVIII concentrates in patients with inherited von Willebrand disease (vWD). The aim of the study was to compare efficacy of secondary long-term prophylaxis (PRO) with vWF/FVIII in the prevention of bleeding episodes in severe vWD patients to standard of care (on-demand treatment; ODT).

MATERIALS AND METHODS

In this 12-month, phase III, open-label study (PRO.WILL), vWD patients (aged ≥6 years) were randomised to PRO (n=9; 5 completed) or ODT (n=10; 7 completed) treatment with Fanhdi^®/Alphanate^® (Grifols) according to current licensing status for use in vWD. We assessed the proportion of patients who did not present any spontaneous bleeding episode, adverse events (AEs) or thrombotic events.

RESULTS

All patients on ODT had vWD type 2 or 3 vs 70% of patients on PRO. All ODT patients experienced bleeds vs 60% on PRO. PRO patients showed fewer bleeds (n=32 vs n=172 [112 in the same patient, mostly mucosal]; p<0.0001) and lower risk of bleeding (relative attributable risk estimate: -0.667; 95% CI: -2.374, -0.107; p<0.001). Most frequent bleeds in ODT and PRO groups were, respectively, epistaxis (n=52 vs n=15) and gastrointestinal (n=13 [9 in the same patient] vs n=1). While most bleeds lasted one day under ODT (31/32), only epistaxis did so in PRO group (14/15). No AEs due to study medication were observed.

DISCUSSION

Despite the small sample size and the heterogeneity of the study population, patients on vWF/FVIII prophylaxis showed a reduction in bleeding risk and rate compared to on-demand treatment.

Von Willebrand disease in the elderly: clinical perspectives

Von Willebrand disease (VWD) is an inherited bleeding disorder that affects up to 1% of the population. In most cases, VWD results from a mutation in the von Willebrand Factor (VWF) gene, which alters the amount and function of VWF, a key glycoprotein in both primary and secondary hemostasis. A comprehensive analysis of patients with VWD should include VWF activity, antigen levels, platelet function, and a careful bleeding history. Treatment options include antifibrinolytics, desmopressin, and VWF replacement therapy. VWF levels fluctuate due to age, stress, environmental exposures, and pharmacologic treatment. Treatment guidelines exist to treat and prevent bleeding for patients undergoing surgery and medical procedures, but often these must be reevaluated in the setting of age-related comorbidities including cardiovascular events, venous thrombosis, and malignancy. In addition, many age-related complications are associated with a secondary acquired von Willebrand syndrome (AVWS), including malignancies, hypothyroidism, cardiovascular diseases, and cardiac replacement devices. The current literature is limited by a lack of older patients in clinical trials. Larger studies are needed to determine if age-related comorbidities affect VWD patients at different frequencies than the general elderly population. There is also a significant need for registry-based studies to evaluate many age-related comorbidities in VWD patients.

von Willebrand factor regulation of blood vessel formation

Several important physiological processes, from permeability to inflammation to hemostasis, take place at the vessel wall and are regulated by endothelial cells (ECs). Thus, proteins that have been identified as regulators of one process are increasingly found to be involved in other vascular functions. Such is the case for von Willebrand factor (VWF), a large glycoprotein best known for its critical role in hemostasis. In vitro and in vivo studies have shown that lack of VWF causes enhanced vascularization, both constitutively and following ischemia. This evidence is supported by studies on blood outgrowth EC (BOEC) from patients with lack of VWF synthesis (type 3 von Willebrand disease [VWD]). The molecular pathways are likely to involve VWF binding partners, such as integrin αvβ3, and components of Weibel-Palade bodies, such as angiopoietin-2 and galectin-3, whose storage is regulated by VWF; these converge on the master regulator of angiogenesis and endothelial homeostasis, vascular endothelial growth factor signaling. Recent studies suggest that the roles of VWF may be tissue specific. The ability of VWF to regulate angiogenesis has clinical implications for a subset of VWD patients with severe, intractable gastrointestinal bleeding resulting from vascular malformations. In this article, we review the evidence showing that VWF is involved in blood vessel formation, discuss the role of VWF high-molecular-weight multimers in regulating angiogenesis, and review the value of studies on BOEC in developing a precision medicine approach to validate novel treatments for angiodysplasia in congenital VWD and acquired von Willebrand syndrome.

Advances in the diagnosis and treatment of Von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, yet diagnosis and management remain challenging. Development and use of bleeding assessment tools allows for improved stratification of which patients may require further assessment and which patients are most likely to require treatment of their VWD. New options for laboratory assessment of von Willebrand factor (VWF) activity include a new platelet-binding assay, the VWF:GPIbM, which is subject to less variability than the ristocetin cofactor activity assay, and collagen-binding assays that provide insight into a different function of VWF. Genetic testing may be helpful in some cases where a type 2 VWD variant is suspected but is usually not helpful in type 1 VWD. Finally, treatment options for VWD are reviewed, including the use of recombinant VWF. Despite these advances, still more work is required to improve diagnosis, treatment, and quality of life for affected patients.

Contemporary issues in the management of von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder. Bleeding scores in VWD, focused in particular on mucosal bleeding, can be very useful in the diagnosis and validation of different types of treatment. The results of an extended prospective study with a large amount of information on clinical phenotype and implications in treatment are reviewed in this article. Treatment of mucosal and joint bleeding in severe VWD remains difficult in some patients. Due to the lack of data on the use of prophylaxis in these patients it is difficult to establish optimal treatment regimens. An overview of the literature, with a focus on the ongoing PRO.WILL study, is provided here. Furthermore, understanding the changes in von Willebrand factor (VWF) levels during pregnancy is very important for establishing the optimal management strategy for pregnancy and delivery in women with VWD. A recently published prospective observational cohort study in women with and without VWD during the postpartum period provides important data that should allow the improvement of postpartum treatment protocols.

Advances in the diagnosis and treatment of Von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, yet diagnosis and management remain challenging. Development and use of bleeding assessment tools allows for improved stratification of which patients may require further assessment and which patients are most likely to require treatment of their VWD. New options for laboratory assessment of von Willebrand factor (VWF) activity include a new platelet-binding assay, the VWF:GPIbM, which is subject to less variability than the ristocetin cofactor activity assay, and collagen-binding assays that provide insight into a different function of VWF. Genetic testing may be helpful in some cases where a type 2 VWD variant is suspected but is usually not helpful in type 1 VWD. Finally, treatment options for VWD are reviewed, including the use of recombinant VWF. Despite these advances, still more work is required to improve diagnosis, treatment, and quality of life for affected patients.

Gastrointestinal angiodysplasia and bleeding in von Willebrand disease

Von Willebrand disease (VWD), the most common genetic bleeding disorder, is characterised by a quantitative or qualitative defect of von Willebrand factor (VWF). Patients with VWD suffer from mucocutaneous bleeding, of severity usually proportional to the degree of VWF defect. In particular, gastrointestinal bleeding associated with angiodysplasia is often a severe symptom of difficult management. This review focuses on the pathophysiology, diagnosis and treatment of VWD-associated gastrointestinal angiodysplasia and related bleeding.

Safety of a pasteurized plasma-derived Factor VIII and von Willebrand factor concentrate: analysis of 33 years of pharmacovigilance data

BACKGROUND

Haemate-P/Humate-P (Humate-P) is a pasteurized human plasma-derived concentrate containing both Factor VIII and von Willebrand factor for treatment of hemophilia A and von Willebrand disease (VWD).

STUDY DESIGN AND METHODS

We analyzed the safety of Humate-P based on more than 33 years of postmarketing pharmacovigilance data, representing an estimated exposure of approximately 25,000 patient-years. The analysis comprises reports of potential adverse drug reactions (ADRs) from all sources, reported as part of routine pharmacovigilance at CSL Behring. ADRs considered clinically relevant or potential risks of Humate-P were identified based on defined and standardized Medical Dictionary for Regulatory Activities queries. Recognizing the limitations of spontaneous reporting, we also reviewed the literature, including clinical trials with mandatory reporting.

RESULTS

From 1982 to 2015, a total of 670 postmarketing cases had been reported via pharmacovigilance, for an overall reporting rate of approximately one ADR per 3900 administered standard doses. Of these cases, 343 involved ADRs considered clinically relevant risks (33 thromboembolic complications, 97 inhibitor formation, 110 hypersensitivity or allergic reactions) or potential risks (103 suspected virus transmissions) for Humate-P. Most thromboembolic complications occurred in patients undergoing surgery or with other known risk factors. Inhibitor formation occurred mostly in patients with hemophilia A (24 cases were high titer). Most patients with hypersensitivity or allergic reactions had VWD. None of the reported suspected virus transmission cases were confirmed to be associated with Humate-P. Reported results of company-sponsored studies showed a low incidence of adverse events possibly or probably related to Humate-P.

CONCLUSIONS

More than 33 years of pharmacovigilance data continue to support the safety of Humate-P.

Long-term impact of joint bleeds in von Willebrand disease: a nested case-control study

Patients with severe von Willebrand disease (VWD) may develop arthropathy after joint bleeds. Information on its prevalence and severity is limited. We aimed to assess the occurrence and severity of arthropathy in VWD and its impact on daily life. VWD patients with and without verified joint bleeds were matched for age, sex and Factor VIII level or von Willebrand Factor activity in a nested case-control study within the Willebrand in the Netherlands study. Assessments included the Hemophilia Joint Health Score (0–124), Pettersson score (0–13 per joint X-ray), Hemophilia Activity List score (0–100), joint pain (Visual Analog Scale 0–10), and the Impact on Participation and Autonomy questionnaire (0–20). Arthropathy was defined as a Hemophilia Joint Health Score of 10 or higher, or a Pettersson score over 3 of at least one joint. We included 48 patients with verified joint bleeds (cases) and 48 controls: 60% males, mean age 46 years (range 18–80), median von Willebrand Factor activity 5 versus 8 IU/dL and Factor VIII 24 versus 36 IU/dL. Arthropathy occurred in 40% of the cases versus 10% of the controls (P<0.01). The cases reported more functional limitations compared to the controls (median Hemophilia Activity List score: 88 vs. 100, P<0.01). Arthropathy was related to joint pain and less social participation (Visual Analog Scale>3: 13 of 19 vs. 3 of 28, P<0.01, and median score on the participation questionnaire 6.1 vs. 0.9, P<0.01). In conclusion, arthropathy occurs in 40% of VWD patients after joint bleeds and is associated with pain, radiological abnormalities, functional limitations, and less social participation (Dutch trial register: NTR4548).

Current challenges in the diagnosis and management of patients with inherited von Willebrand's disease in Italy: an Expert Meeting Report on the diagnosis and surgical and secondary long-term prophylaxis

Recent advances in the care of von Willebrand's disease (vWD) have allowed the majority of patients to be managed adequately. Even in the more severe forms, it is now possible to control recurrent bleeding through secondary long-term prophylaxis with von Willebrand factor-containing concentrates. Moreover, in the setting of surgical prophylaxis, the combination of interdisciplinary management and close patient monitoring yields a positive outcome in nearly all cases, although safety concerns remain. In clinical practice, the effectiveness of therapy is hindered by the difficulties in making a rapid, yet accurate diagnosis, in identifying the subgroup of bleeders who may benefit most from a specific strategy, and in selecting the optimal product and regimen.Since specific guidelines for heavy bleeders requiring short- and long-term prophylaxis are still lacking, sharing the experience of experts dealing with vWD patients on a daily basis is crucial to fill gaps in information relating to patient management. To address this important issue, 13 Italian haematologists met in Milan on April, 2, 2016 and in Florence on July, 9, 2016. A 30-question survey constituted the input to discuss (i) optimisation of the diagnostic workflow for vWD, (ii) the characteristics of patients who may benefit from secondary long-term prophylaxis (in particular with the purified von Willebrand factor concentrate with a low content of factor VIII), (iii) the key elements to consider when selecting a concentrate and (iv) the pre-operative and post-operative management of vWD patients. A summary of the main points covered is provided in this report.

Angiodysplasia in von Willebrand Disease: Understanding the Clinical and Basic Science

Severe and intractable gastrointestinal bleeding caused by angiodysplasia is a debilitating problem for up to 20% of patients with von Willebrand disease (VWD). Currently, the lack of an optimal treatment for this recurrent problem presents an ongoing challenge for many physicians in their management of affected patients. Over the past few years, studies have pointed to a regulatory role for the hemostatic protein, von Willebrand factor (VWF), in angiogenesis, providing a novel target for the modulation of vessel development. This article will review the clinical implications and molecular pathology of angiodysplasia in VWD.

Diagnosis and Treatment of von Willebrand Disease and Rare Bleeding Disorders

Along with haemophilia A and B, von Willebrand disease (VWD) and rare bleeding disorders (RBDs) cover all inherited bleeding disorders of coagulation. Bleeding tendency, which can range from extremely severe to mild, is the common symptom. VWD, due to a deficiency and/or abnormality of von Willebrand factor (VWF), represents the most frequent bleeding disorder, mostly inherited as an autosomal dominant trait. The diagnosis may be difficult, based on a bleeding history and different diagnostic assays, which evaluate the pleiotropic functions of VWF. Different treatment options are available for optimal management of bleeding and their prevention, and long-term outcomes are generally good. RBDs are autosomal recessive disorders caused by a deficiency of any other clotting factor, apart from factor XII, and cover roughly 5% of all bleeding disorders. The prevalence of the severe forms can range from 1 case in 500,000 up to 1 in 2–3 million, according to the defect. Diagnosis is based on bleeding history, coagulation screening tests and specific factor assays. A crucial problem in RBDs diagnosis is represented by the non-linear relationship between clinical bleeding severity and residual clotting levels; genetic diagnosis may help in understanding the phenotype. Replacement therapies are differently available for patients with RBDs, allowing the successful treatment of the vast majority of bleeding symptoms.