Biological effect of desmopressin in eight patients with type 2N ('Normandy') von Willebrand disease. Collaborative Group

Type 2N von Willebrand disease: genotype drives different bleeding phenotypes and treatment needs

BACKGROUND

Type 2 Normandy von Willebrand disease (VWD2N) is usually perceived as a mild bleeding disorder that can be treated with desmopressin (DDAVP). However, VWD2N patients can be compound heterozygous or homozygous for different variants, with p.Arg854Gln (R854Q) being the most frequent causative one. There are limited data about the impact of 2N variants on VWD2N phenotype and DDAVP response.

OBJECTIVES

This study aims to describe the phenotype of VWD2N, including DDAVP response, according to genotype.

METHODS

VWD2N patients with a complete genotype/phenotype characterization by the French reference center for VWD, including MCMDM-1VWD bleeding score, were eligible to be included in the study. Results of the DDAVP trial were also collected.

RESULTS

A total of 123 VWD2N patients from the French registry were included in this study. Results were stratified according to the presence (R854QPos, n = 114) or absence (R854QNeg, n = 9) of at least 1 R854Q allele. Three R854QPos subgroups were further individualized: patients homozygous (R854QHmz, n = 55), compound heterozygous for R854Q and a null allele (R854Q/3, n = 48), or compound heterozygous for R854Q and another 2N variant (R854Q/2N, n = 11).

FVIII

C levels were significantly lower in R854QNeg and R854Q/3 patients compared with R854QHmz ones (P < .001 and P < .0001, respectively). R854QNeg patients were diagnosed earlier due to bleeding symptoms and had a higher bleeding score than R854QPos patients (P < .001). In DDAVP trial, FVIII:C survival was lower in VWD type 2N than in type 1 patients. R854QPos patients had a heterogeneous DDAVP response, which was best predicted by baseline FVIII:C level.

CONCLUSION

The heterogeneous genetic background of VWD2N drives different bleeding phenotypes and response patterns to DDAVP, underlining the clinical relevance of DDAVP trial to identify patients potentially eligible to alternative therapeutic options.

Current Understanding of Inherited Modifiers of FVIII Pharmacokinetic Variation

The inherited bleeding disorder hemophilia A involves the quantitative deficiency of the coagulation cofactor factor VIII (FVIII). Prophylactic treatment of severe hemophilia A patients with FVIII concentrates aims to reduce the frequency of spontaneous joint bleeding and requires personalized tailoring of dosing regimens to account for the substantial inter-individual variability of FVIII pharmacokinetics. The strong reproducibility of FVIII pharmacokinetic (PK) metrics between repeat analyses in the same individual suggests this trait is genetically regulated. While the influence of plasma von Willebrand factor antigen (VWF:Ag) levels, ABO blood group, and patient age on FVIII PK is well established, estimates suggest these factors account for less than 35% of the overall variability in FVIII PK. More recent studies have identified genetic determinants that modify FVIII clearance or half-life including VWF gene variants that impair VWF-FVIII binding resulting in the accelerated clearance of VWF-free FVIII. Additionally, variants in receptors that regulate the clearance of FVIII or the VWF-FVIII complex have been associated with FVIII PK. The characterization of genetic modifiers of FVIII PK will provide mechanistic insight into a subject of clinical significance and support the development of personalized treatment plans for patients with hemophilia A.

Desmopressin response depends on the presence and type of genetic variants in patients with type 1 and type 2 von Willebrand disease

All type 1 VWD patients without a VWF gene variant have a complete response to desmopressin.

In type 1 and type 2 VWD patients with a VWF gene variant, desmopressin response highly depends on the causative VWF gene variant.

Patients with type 1 and type 2 von Willebrand disease (VWD) can be treated with desmopressin. Although a previous study has shown that the location of the causative VWF gene variant is associated with desmopressin response in type 1 VWD, the association between variants in the VWF gene and desmopressin response is not yet fully understood. Our primary aim was to compare desmopressin response in type 1 VWD patients with and without a VWF gene variant. Secondly, we investigated whether desmopressin response depends on specific VWF gene variants in type 1 and type 2 VWD. We included 250 patients from the Willebrand in the Netherlands study: 72 type 1 without a VWF gene variant, 108 type 1 with a variant, 45 type 2A, 16 type 2M, and 9 type 2N patients. VWF gene was analyzed with ion semiconductor sequencing and Multiplex Ligation-dependent Probe Amplification. Complete response to desmopressin was observed in all type 1 VWD patients without a variant, 64.3% of type 1 patients with a variant, and 31.3% of type 2 patients (P < .001). Despite a large interindividual variability in desmopressin response, patients with the same variant had comparable desmopressin responses. For instance, in 6 type 1 patients with exon 4 to 5 deletion, mean VWF activity at 1 hour after desmopressin was 0.81 IU/mL, with a coefficient of variation of 22.9%. In conclusion, all type 1 VWD patients without a VWF gene variant respond to desmopressin. In type 1 and type 2 VWD patients with a VWF variant, desmopressin response highly depends on the VWF gene variants.

The lesson learned from the new c.2547-1G>T mutation combined with p.R854Q:when a type 2N mutation reveals a quantitative von Willebrand factor defect

Type 2N is a rare von Willebrand disease (VWD) variant involving an impairment in the FVIII carrier function of von Willebrand factor (VWF). It has a phenotype that mimics hemophilia A, and FVIII binding to VWF (VWF:FVIIIB) is tested to differentiate between the two disorders. Type 2N VWF defects may also be associated with quantitative VWF mutations (type 2N/type 1), further complicating the identification of cases. We report on a new quantitative VWF mutation (c.2547-1G>T) revealed by a p.R854Q type 2N mutation acting as homozygous despite being carried as a heterozygous defect. The proband had near-normal VWF levels (initially ruling out a defective VWF synthesis) and slightly reduced FVIII levels, while a VWF:FVIIIB test showed significantly reduced binding. Routine tests on type 2N homozygotes or heterozygotes combined with quantitative VWF defects in our cohort showed reduced FVIII levels in both groups, but it was only in the former that the FVIII/VWF:Ag ratio was always significantly reduced. The two tests are therefore not enough to identify all forms of type 2N VWD. While relatives of type 2N homozygotes usually have normal FVIII levels and FVIII/VWF:Ag ratios, relatives of type 2N/type 1 may have high FVIII/VWF:Ag ratios, but their VWF:FVIIIB and/or VWF:FVIIIB/VWF:Ag ratios are always low. Measuring FVIII and VWF levels may therefore suggest type 2N VWD in patients carrying type 2N mutations alone, but not in type 2N combined with quantitative VWF defects. The VWF:FVIIIB test should consequently always be included when exploring VWF function, whatever VWD patient’s phenotype.

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

A novel type 2N VWD mouse model was established in which VWF is incapable of binding FVIII but is otherwise fully functional.

VWF^2N/2N mice exhibited a severe bleeding phenotype after tail tip amputation but not in lateral tail vein or ventral artery injury models.

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

Population pharmacokinetics of the von Willebrand factor-factor VIII interaction in patients with von Willebrand disease

Recent studies have reported that patients with von Willebrand disease treated perioperatively with a von Willebrand factor (VWF)/factor VIII (FVIII) concentrate with a ratio of 2.4:1 (Humate P/Haemate P) often present with VWF and/or FVIII levels outside of prespecified target levels necessary to prevent bleeding. Pharmacokinetic (PK)-guided dosing may resolve this problem. As clinical guidelines increasingly recommend aiming for certain target levels of both VWF and FVIII, application of an integrated population PK model describing both VWF activity (VWF:Act) and FVIII levels may improve dosing and quality of care. In total, 695 VWF:Act and 894 FVIII level measurements from 118 patients (174 surgeries) who were treated perioperatively with the VWF/FVIII concentrate were used to develop this population PK model using nonlinear mixed-effects modeling. VWF:Act and FVIII levels were analyzed simultaneously using a turnover model. The protective effect of VWF:Act on FVIII clearance was described with an inhibitory maximum effect function. An average perioperative VWF:Act level of 1.23 IU/mL decreased FVIII clearance from 460 mL/h to 264 mL/h, and increased FVIII half-life from 6.6 to 11.4 hours. Clearly, in the presence of VWF, FVIII clearance decreased with a concomitant increase of FVIII half-life, clarifying the higher FVIII levels observed after repetitive dosing with this concentrate. VWF:Act and FVIII levels during perioperative treatment were described adequately by this newly developed integrated population PK model. Clinical application of this model may facilitate more accurate targeting of VWF:Act and FVIII levels during perioperative treatment with this specific VWF/FVIII concentrate (Humate P/Haemate P).

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.

Life in the shadow of a dominant partner: the FVIII-VWF association and its clinical implications for hemophilia A

A normal hemostatic response to vascular injury requires both factor VIII (FVIII) and von Willebrand factor (VWF). In plasma, VWF and FVIII normally circulate as a noncovalent complex, and each has a critical function in the maintenance of hemostasis. Furthermore, the interaction between VWF and FVIII plays a crucial role in FVIII function, immunogenicity, and clearance, with VWF essentially serving as a chaperone for FVIII. Several novel recombinant FVIII (rFVIII) therapies for hemophilia A have been in clinical development, which aim to increase the half-life of FVIII (∼12 hours) and reduce dosing frequency by utilizing bioengineering techniques including PEGylation, Fc fusion, and single-chain design. However, these approaches have achieved only moderate increases in half-life of 1.5- to 2-fold compared with marketed FVIII products. Clearance of PEGylated rFVIII, rFVIIIFc, and rVIII-SingleChain is still regulated to a large extent by interaction with VWF. Therefore, the half-life of VWF (∼15 hours) appears to be the limiting factor that has confounded attempts to extend the half-life of rFVIII. A greater understanding of the interaction between FVIII and VWF is required to drive novel bioengineering strategies for products that either prolong the survival of VWF or limit VWF-mediated clearance of FVIII.

Therapeutic consequences for misdiagnosis of type 2N von Willebrand disease

Patients presenting with a low FVIII:C and with normal VWF levels are usually presumed to have hemophilia (males) or be carriers for hemophilia (females). Some of these patients may instead have VWD:2N. Such patients if misdiagnosed are likely to suffer from insufficiently treated bleeds. We report 2 males and 1 female who presented with a low FVIII:C (1-21%) and minimally reduced/normal VWF and were assumed to have, or be a carrier for, hemophilia A. Eventually all were found to have VWD:2N. Prior to the correct diagnosis the males had been treated with rFVIII with poor responses and ultimately adverse clinical consequences.

Treatment of patients with von Willebrand disease

Von Willebrand disease (vWD) is the most common hereditary bleeding disorder. The aim of therapy is to correct the dual hemostatic defect, due to defective platelet adhesion-aggregation and abnormal coagulation due to Factor VIII (FVIII) deficiency. The choice of treatment depends on a number of factors, including the severity of the bleed, the procedure planned, the subtype and severity of the disease and the age and morbidity of the patient. Desmopressin (DDAVP) is the treatment of choice for type 1 vWD as it increases endogenous release of FVIII and von Willebrand factor (vWF) and is also used in some subtypes of type 2 vWD. In those patients in whom DDAVP is ineffective or contraindicated, levels can be restored by infusing vWF:FVIII concentrates. The role of antifibrinolytic treatment is an important adjunct to replacement therapy during minor or major surgery involving mucosal surfaces. The dosing and timing of vWF:FVIII concentrates is important depending on the nature of the surgical procedure. The role of secondary prophylaxis needs to be further defined.

Functional architecture of Weibel-Palade bodies

Weibel-Palade bodies (WPBs) are elongated secretory organelles specific to endothelial cells that contain von Willebrand factor (VWF) and a variety of other proteins that contribute to inflammation, angiogenesis, and tissue repair. The remarkable architecture of WPBs is because of the unique properties of their major constituent VWF. VWF is stored inside WPBs as tubules, but on its release, forms strikingly long strings that arrest bleeding by recruiting blood platelets to sites of vascular injury. In recent years considerable progress has been made regarding the molecular events that underlie the packaging of VWF multimers into tubules and the processes leading to the formation of elongated WPBs. Mechanisms directing the conversion of tightly packaged VWF tubules into VWF strings on the surface of endothelial cells are starting to be unraveled. Several modes of exocytosis have now been described for WPBs, emphasizing the plasticity of these organelles. WPB exocytosis plays a role in the pathophysiology and treatment of von Willebrand disease and may have impact on common hematologic and cardiovascular disorders. This review summarizes the major advances made on the biogenesis and exocytosis of WPBs and places these recent discoveries in the context of von Willebrand disease.

How I treat von Willebrand disease

Recent multicenter studies have clarified the molecular basis underlying the different von Willebrand disease (VWD) types, all of which are caused by the deficiency and/or abnormality of von Willebrand factor (VWF). These studies have suggested a unifying pathophysiologic concept. The diagnosis of VWD, remains difficult because its clinical and laboratory phenotype is very heterogeneous and may overlap with normal subjects. Stringent criteria are therefore required for a clinically useful diagnosis. In this paper, we delineate a practical approach to the diagnosis and treatment of VWD. Our approach is based on the critical importance of a standardized bleeding history that has been condensed into a final bleeding score and a few widely available laboratory tests, such as VWF ristocetin cofactor activity, VWF antigen and factor VIII. This approach would help identify those subjects who will probably benefit from a diagnosis of VWD. The next step involves performing a trial infusion with desmopressin in all patients who fail to exhibit an enhanced responsiveness to ristocetin. On the basis of these results and through a series of illustrative examples, the clinician will be able to select the best approach for the optimal management of VWD, according to the patient's characteristics and clinical circumstances.

Factor VIII and von Willebrand factor interaction: biological, clinical and therapeutic importance

The interaction of factor VIII (FVIII) with von Willebrand Factor (VWF) is of direct clinical significance in the diagnosis and treatment of patients with haemophilia A and von Willebrand disease (VWD). A normal haemostatic response to vascular injury requires both FVIII and VWF. It is well-established that in addition to its role in mediating platelet to platelet and platelet to matrix binding, VWF has a direct role in thrombin and fibrin generation by acting as a carrier molecule for the cofactor FVIII. Recent studies show that the interaction affects not only the biology of both FVIII and VWF, and the pathology of haemophilia and VWD, but also presents opportunities in the treatment of haemophilia. This review details the mechanisms and the molecular determinants of FVIII interaction with VWF, and the role of FVIII-VWF interaction in modulating FVIII interactions with other proteases, cell types and cellular receptors. The effect of defective interaction of FVIII with VWF as a result of mutations in either protein is discussed.

Optimizing treatment of von Willebrand disease by using phenotypic and molecular data

The wide clinical spectrum of von Willebrand disease (VWD), its complex pathophysiology and its classification into distinct quantitative (type 1 or type 3) and qualitative (type 2) types with further subtle distinctions have prevented most clinicians from establishing a straightforward approach to diagnosing and treating this inherited bleeding disorder. The results of studies involving large cohorts of patients with a wide range of bleeding manifestations and variable von Willebrand factor (VWF) reduction have recently become available. These data have allowed the proposal of minimal criteria for a clinically useful diagnosis and for differentiating patients with mild VWD from subjects with borderline or only slightly reduced VWF levels who will not benefit from a specific diagnosis. These criteria are based on measurement of VWF ristocetin cofactor (VWF:RCo), VWF antigen (VWF:Ag), factor VIII and a standardized bleeding score (BS). Demonstration of the inheritance of the disorder could help to classify patients for whom insufficient hemostatic challenges may produce a falsely reassuring BS (like in children). Using this approach, mild VWD appears to be mostly composed of type 1 cases. Complemented by the results of desmopressin trial infusion, these parameters form the basis for a clinically oriented classification of all forms of VWD and may be useful for selecting the best treatment according to the severity of the disease. Although few molecular data have revealed practical utility, there is no doubt that the clarification of the molecular pathophysiology of VWD has allowed the unification of this complex disorder into a simple conceptual framework. This framework underlies the proposed utilization of simple phenotypic markers for optimizing treatments in individual patients.

Intracellular cotrafficking of factor VIII and von Willebrand factor type 2N variants to storage organelles

Weibel-Palade bodies (WPBs) are the endothelial storage organelles that are formed upon von Willebrand factor (VWF) expression. Apart from VWF, WPBs contain a variety of hemostatic and inflammatory proteins. Some of these are thought to be targeted to WPBs by directly interacting with VWF in the secretory pathway. Previous studies have demonstrated that coexpression of factor VIII (FVIII) with VWF results in costorage of both proteins. However, whether cotrafficking is driven by intracellular FVIII-VWF assembly has remained unclear. We now have addressed this issue using recombinant VWF type 2N variants that are known to display reduced FVIII binding in the circulation. Binding studies using purified fluorescent FVIII and VWF type 2N variants revealed FVIII binding defects varying from moderate (Arg854Gln, Cys1060Arg) to severe (Arg763Gly, Thr791Met, Arg816Trp). Upon expression in HEK293 cells, all VWF variants induced formation of WPB-like organelles that were able to recruit P-selectin, as well as FVIII. WPBs containing FVIII did not display their typical elongated shape, suggesting that FVIII affects the organization of VWF tubules therein. The finding that VWF type 2N variants are still capable of cotargeting FVIII to storage granules implies that trafficking of WPB cargo proteins does not necessarily require high-affinity assembly with VWF.

The use of desmopressin in von Willebrand disease: the experience of the first 30 years (1977-2007)

The aim of the treatment for von Willebrand disease (VWD) is to correct the dual defect of haemostasis, i.e. the abnormal platelet adhesion as a result of reduced and/or dysfunctional von Willebrand factor (VWF) and the abnormal coagulation expressed by low levels of factor VIII (FVIII). Correction of both deficiencies can be achieved by administering the synthetic peptide desmopressin (DDAVP) or, in cases unresponsive to this agent, the plasma concentrates containing VWF and FVIII (VWF/FVIII). DDAVP is the treatment of choice for type 1 VWD because it can induce release of normal VWF from cellular compartments, but the drug can be clinically useful also in other VWD types, including acquired von Willebrand syndrome (AVWS). A test dose of DDAVP at the time of diagnosis is recommended to establish the individual patterns of biological response and to predict clinical efficacy during bleeding and surgery. DDAVP is not effective in VWD type 3 and in severe forms of VWD 1 and 2. It can induce transient thrombocytopenia in patients with VWD type 2B. The results of several retrospective studies on the use of DDAVP in VWD management have been reported by many authors in different countries for the last 30 years. However, despite the widespread use of DDAVP in the treatment of VWD, there are only a few prospective clinical trials in a large number of cases on DDAVP efficacy and safety aimed at determining benefits and limits of this therapeutic approach. An investigator-driven observational prospective study on clinical efficacy of DDAVP in 200 patients with VWD types 1 and 2 has been recently organized: the effectiveness and safety of DDAVP will be evaluated prospectively for 24 months during bleeding episodes and minor or major surgeries in the VWD patients who were exposed to an infusion trial at enrollment.

Von Willebrand disease

von Willebrand disease is a common inherited bleeding disorder and many cases are diagnosed in childhood. It has a negative impact on the quality of life of affected individuals; therefore, it is important that the condition be recognized and diagnosed. This article reviews the pathophysiology of the condition, the current classification scheme, and the available treatments, highlighting issues specific to the pediatric population.

Intravenous DDAVP and factor VIII-von Willebrand factor concentrate for the treatment and prophylaxis of bleedings in patients With von Willebrand disease type 1, 2 and 3

The current standard set of von Willebrand factor (VWF) parameters used to differentiate type 1 from type 2 VWD include bleeding times (BTs), factor VIII coagulant activity (FVIII:C), VWF antigen (VWF:Ag), VWF ristocetine cofactor activity (VWF:RCo), VWF collagen binding activity (VWF:CB), ristocetine induced platelet aggregation (RIPA), and analysis of VWF multimers in low and high resolution agarose gels and the response to DDAVP. The BTs and RIPA are normal in asymptomatic carriers of a mutant VWF allele, in dominant type 1, and in recessive type 2N VWD, and this category has a normal response of VWF parameters to DDAVP. The response of FVIII:C is compromised in type 2N VWD. The BTs and RIPA are usually normal in type Vicenza and mild type 2A VWD, and these two VWD variants show a transiently good response of BT and VWF parameters followed by short in vivo half life times of VWF parameters. The BTS are strongly prolonged and RIPA typically absent in recessive severe type 1 and 3 VWD, in dominant type 2A and in recessive type 2C (very likely also 2D) VWD and consequently associated with low or absent platelet VWF, and no or poor response of VWF parameters to DDAVP. The BTs are prolonged and RIPA increased in dominant type 2B VWD, that is featured by normal platelet VWF and a poor response of BT and functional VWF to DDAVP. The BTs are prolonged and RIPA decreased in dominant type 2A and 2U, that all have low VWF platelet, very low VWF:RCo values as compared to VWF:Ag, and a poor response of functional VWF to DDAVP. VWD type 2M is featured by the presence of all VWF multimers in a low resolution agarose gel, normal or slightly prolonged BT, decreased RIPA, a poor response of VWF:RCo and a good response of FVIII and VWF:CB to DDAVP and therefore clearly in between dominant type 1 and 2U. The existing recommendations for prophylaxis and treatment of bleedings in type 2 VWD patients with FVIII/VWF concentrates are mainly derived from pharmocokinetic studies in type 3 VWD patients. FVIII/VWF concentrates should be characterised by labelling with FVIII:C, VWF:RCo, VWF:CB and VWF multimeric pattern to determine their safety and efficacy in prospective management studies. As the bleeding tendency is moderate in type 2 and severe in type 3 VWD and the FVIII:C levels are near normal in type 2 and very low in type 3 VWD patients. Proper recommendations of FVIII/VWF concentrates using VWF:RCo unit dosing for the prophylaxis and treatment of bleeding episodes are proposed and has to be stratified for the severity of bleeding, the type of surgery either minor or major and for type 2 and type 3 VWD as well.

Treatment of urgent bleeding in von Willebrand disease

von Willebrand factor (VWF) is a complex plasma protein that promotes platelet adhesion to the subendothelial matrix of injured blood vessels and provides stability to factor VIII in the circulation. von Willebrand disease (VWD) is a haemorrhagic disorder of highly variable severity caused by qualitative and quantitative abnormalities of VWF. The approach to treating urgent bleeding in patients with VWD is dependent on an accurate diagnosis of the patient's type of VWD and knowledge of the expected responses to treatment modalities. These include administration of desmopressin (DDAVP), a vasopressin analogue that promotes the release of VWF and factor VIII (FVIII) from storage sites, and replacement therapy with a viral-inactivated concentrate containing normal VWF and FVIII. Monitoring of an individual's response in the non-bleeding state is required to determine the response to desmopressin that may be achieved and to determine the individual pharmacokinetics of infused VWF and FVIII. In this article, specific approaches to the choice of treatment modalities, calculation of dosages, monitoring of therapy, possible side effects and complications of the treatment of the various types of VWD will be discussed.

Classification and characterization of hereditary types 2A, 2B, 2C, 2D, 2E, 2M, 2N, and 2U (unclassifiable) von Willebrand disease

All variants of type 2 von Willebrand disease (VWD) patients, except 2N, show a defective von Willebrand factor (VWF) protein (on cross immunoelectrophoresis or multimeric analysis), decreased ratios for VWF:RCo/Ag and VWF:CB/Ag and prolonged bleeding time. The bleeding time is normal and FVIII:C levels are clearly lower than VWF:Ag in type 2N VWD. High resolution multimeric analysis of VWF in plasma demonstrates that proteolysis of VWF is increased in type 2A and 2B VWD with increased triplet structure of each visuable band (not present in types 2M and 2U), and that proteolysis of VWF is minimal in type 2C, 2D, and 2E variants that show aberrant multimeric structure of individual oligomers. VWD 2B differs from 2A by normal VWF in platelets, and increased ristocetine-induced platelet aggregation (RIPA). RIPA, which very likely reflects the VWF content of platelets, is normal in mild, decreased in moderate, and absent in severe type 2A VWD. RIPA is decreased or absent in 2M, 2U, 2C, and 2D, variable in 2E, and normal in 2N. VWD 2M is usually mild and characterized by decreased VWF:RCo and RIPA, a normal or near normal VWF multimeric pattern in a low resolution agarose gel. VWD 2A-like or unclassifiable (2U) is distinct from 2A and 2B and typically featured by low VWF:RCo and RIPA with the relative lack of high large VWF multimers. VWD type 2C is recessive and shows a characteristic multimeric pattern with a lack of high molecular weight multimers, the presence of one single-banded multimers instead of triplets caused by homozygosity or double hereozygosity for a mutation in the multimerization part of VWF gene. Autosomal dominant type 2D is rare and characterized by the lack of high molecular weight multimers and the presence of a characteristic intervening subband between individual oligimers due to mutation in the dimerization part of the VWF gene. In VWD type 2E, the large VWF multimers are missing and the pattern of the individual multimers shows only one clearly identifiable band, and there is no intervening band and no marked increase in the smallest oligomer. 2E appears to be less well defined, is usually autosomal dominant, and accounts for about one third of patients with 2A in a large cohort of VWD patients.

Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor

von Willebrand disease (VWD) is a bleeding disorder caused by inherited defects in the concentration, structure, or function of von Willebrand factor (VWF). VWD is classified into three primary categories. Type 1 includes partial quantitative deficiency, type 2 includes qualitative defects, and type 3 includes virtually complete deficiency of VWF. VWD type 2 is divided into four secondary categories. Type 2A includes variants with decreased platelet adhesion caused by selective deficiency of high-molecular-weight VWF multimers. Type 2B includes variants with increased affinity for platelet glycoprotein Ib. Type 2M includes variants with markedly defective platelet adhesion despite a relatively normal size distribution of VWF multimers. Type 2N includes variants with markedly decreased affinity for factor VIII. These six categories of VWD correlate with important clinical features and therapeutic requirements. Some VWF gene mutations, alone or in combination, have complex effects and give rise to mixed VWD phenotypes. Certain VWD types, especially type 1 and type 2A, encompass several pathophysiologic mechanisms that sometimes can be distinguished by appropriate laboratory studies. The clinical significance of this heterogeneity is under investigation, which may support further subdivision of VWD type 1 or type 2A in the future.

Von Willebrand's disease: clinical management

The aim of treatment of von Willebrand's disease (VWD) is to correct the dual defect of haemostasis, i.e. the abnormal platelet adhesion due to reduced and/or dysfunctional von Willebrand factor (VWF) and the abnormal coagulation expressed by low levels of factor VIII (FVIII). Desmopressin (DDAVP) is the treatment of choice for type 1 VWD because it can induce release of normal VWF from cellular compartments. Prospective studies on biological response versus clinical efficacy of DDAVP in VWD type 1 and 2 are in progress to further explore its benefits and limits as therapeutic option. In type 3 and in severe forms of type 1 and 2 VWD, DDAVP is not effective and for these patients plasma virally inactivated concentrates containing VWF and FVIII are the mainstay of treatment. Several intermediate- and high-purity VWF/FVIII concentrates are available and have been shown to be effective in clinical practice (bleeding and surgery). New VWF products almost devoid of FVIII are now under evaluation in clinical practice. Although thrombotic events are rare in VWD patients receiving repeated infusions of concentrates, there is some concern that sustained high FVIII levels may increase risk of postoperative venous thromboembolism. Dosage and timing of VWF/FVIII administrations should be planned to keep FVIII level between 50 and 150 U/dL. Appropriate dosage and timing in repeated infusions are also very important in patients exposed to secondary long term prophylaxis for recurrent bleedings.

Treatment of von Willebrand disease

The bleeding tendency in von Willebrand disease (VWD) is heterogeneous and some patients with the mildest form of the disease have no significant bleeding symptoms throughout their lives. In some cases, the most difficult task for a clinician is to decide whether any treatment is actually required. However, cases with moderate to severe factor VIII (FVIII) and von Willebrand factor (VWF) deficiency usually require treatment to stop or prevent bleeding. Increasing autologous FVIII/VWF by desmopressin administration or providing normal allogeneic VWF through the infusion of plasma-derived concentrates can correct FVIII and VWF deficiencies and normalize or shorten bleeding time (BT). FVIII levels are the best predictors of soft tissue or surgical bleeding, while BT normalization, reflecting the correction of platelet-dependent functions of VWF, is considered a reliable indicator of an effective treatment of mucosal bleeding. Recombinant concentrates of FVIII are not indicated (apart from cases with alloantibodies against exogenous VWF), since they are devoid of VWF and lack its stabilizing effect on circulating FVIII. A very-high-purity concentrate of VWF has recently been made available, but its advantages over conventional concentrates containing both FVIII and VWF moieties are not obvious. The best way to select the appropriate treatment is to perform a test infusion with desmopressin in any patient with clinically significant VWD, provided that he/she has no contraindication to the compound or belongs to subtype with an anticipated lack of response (for example, type 3 VWD with FVIII/VWF lower than 5%).

Management of von Willebrand disease: a guideline from the UK Haemophilia Centre Doctors' Organization

von Willebrand disease (VWD) is the commonest inherited bleeding disorder. The aim of therapy for VWD is to correct the two defects of haemostasis in this disorder, impaired primary haemostasis because of defective platelet adhesion and aggregation and impaired coagulation as a result of low levels of factor VIII. The objective of this guideline is to inform individuals making choices about the treatment and management of VWD including the use of therapeutic products. This is the second edition of this UK Haemophilia Centre Doctors' Organization (UKHCDO) guideline and supersedes the previous edition which was published in 1994.

Evaluation of an automated screening assay for von Willebrand disease type 2N

Evaluating the factor VIII (FVIII) binding activity of von Willebrand factor (VWF) is an important step in the diagnostic work-up of families affected by apparent mild haemophilia A. In von Willebrand's disease (VWD) type 2N (Normandy), mutations at the N-terminal end of the mature VWF subunit gene prevent the binding of FVIII. Individuals heterozygous for type 2N VWD are generally asymptomatic. Homozygotes and compound heterozygotes present with a clinical picture which mimics haemophilia A, with a markedly reduced FVIII : C activity and VWF within the normal range, but instead of exhibiting X-linked inheritance they show an autosomal recessive inheritance pattern. The distinction between haemophilia A and VWD type 2N has important implications for therapy and genetic counselling. We present a highly specific enzyme-linked immunosorbent assay screening method for the Normandy variant, which measures VWF : FVIII binding activity in parallel with VWF antigen, using monoclonal capture and detection antibodies. The assay is fully automated using a robotic microtitre plate processor, requiring minimal user intervention and providing the capacity to screen large numbers of patients.

Guidelines for the diagnosis and management of von Willebrand disease in Italy

von Willebrand disease (vWD) is a bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) defects of von Willebrand factor (vWF). The molecular basis of type 2 and 3 vWD are now known and those of type 1 vWD are being understood. Phenotypic diagnosis is based on the measurements of plasma and platelet vWF, of the ability of vWF to interact with platelet receptors and the analysis of the multimeric structure of vWF. Due to the heterogeneity of vWF defects and the variables that interfere with vWF levels, a correct diagnosis of types and subtypes may sometimes be difficult but is very important for therapy. The aim of treatment is to correct the dual defects of haemostasis, i.e. abnormal intrinsic coagulation expressed by low levels of factor VIII (FVIII) and abnormal platelet adhesion. Desmopressin is the treatment of choice in patients with type 1 vWD, who account for approximately 70% of cases, because it corrects FVIII-vWF levels and the prolonged bleeding time (BT) in the majority of these patients. In type 3 and in severe forms of type 1 and 2 vWD patients, desmopressin is not effective and it is necessary to resort to plasma concentrates containing FVIII and vWF. Treated with virucidal methods, these concentrates are effective and safe, but they cannot always correct BT defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of BT after plasma concentrate treatment is associated with continued bleeding.

Identification of von Willebrand disease type 2N (Normandy) in Australia: a cross-laboratory investigation using different methods

We report on a cross-laboratory study of type 2N von Willebrand disease (vWD). We tested 101 selected plasma samples for factor VIII and factor VIII binding activity of von Willebrand factor (vWF). Of these plasma samples, 31 were cotested by 2 specialist centers using different detection procedures for vWF-factor VIII binding: there was good agreement between results obtained by chromogenic assay and enzyme-linked immunosorbent assay. In total, 8 patients with type 2N vWD were identified. The 2-stage factor VIII assay detected a deficiency of factor VIII relative to vWF antigen in all 8 patients; the 1-stage factor VIII assay detected a relative deficiency in only 3 patients. Four patients were homozygous for the most common type 2N mutation (R854Q), 3 patients were presumed to be compound heterozygotes, and in 1 patient no type 2N mutations were identified. In this study of patients from 5 specialist centers in Australia, type 2N vWD was found in 5 families. The 2-stage factor VIII assay was more useful as a screening test than the 1-stage assay, and both vWF-factor VIII binding assays were equally effective.

Advances in the genetics and treatment of von Willebrand disease

von Willebrand disease (VWD) is a bleeding disorder caused by quantitative (type 1 and 3) or qualitative (type 2) defects of von Willebrand factor (VWF). The mechanisms of most inherited VWD types have been recently elucidated by genetic and molecular diagnosis, but the phenotypic tests based on measurements of plasma and platelet VWF, the ability of VWF to interact with its platelet receptor, and the analysis of the multimeric composition of VWF are always essential to identify patients with different VWD subtypes. The aim of treatment is to correct the dual defects of hemostasis, ie, abnormal coagulation expressed by low levels of factor VIII (FVIII) and abnormal platelet adhesion expressed by prolonged bleeding time (BT). Desmopressin is the treatment of choice in most patients with type 1 and type 2 VWD, who account for 60 to 70% of cases. In type 3 and in some severe forms of type 1 and type 2 VWD, desmopressin is not effective, and it is necessary to resort to plasma concentrates containing FVIII and VWF. Treated with virucidal methods, these concentrates are effective and currently safe, but they do not always correct the BT defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of the BT after concentrates is associated with continued bleeding.

Management of inherited von Willebrand disease

von Willebrand disease is a bleeding disorder caused by quantitative or qualitative defects of von Willebrand factor. The diagnosis is based on measurements of plasma and platelet von Willebrand factor, the ability of von Willebrand factor to interact with its platelet receptor and the analysis of the multimeric composition of von Willebrand factor. Owing to the heterogeneity of von Willebrand factor defects, a correct diagnosis of types and subtypes may be sometimes difficult but is very important for an appropriate therapy. The aim of treatment is to correct the dual defects of haemostasis, i.e. abnormal coagulation, expressed by a low level of factor VIII, and abnormal platelet adhesion, expressed by a prolonged bleeding time. Desmopressin is the treatment of choice in patients with type I von Willebrand disease, who account for approximately 70% of cases, because it corrects the factor VIII/von Willebrand factor level and the prolonged bleeding time in most of these patients. In type 3 and in the majority of type 2 von Willebrand disease patients, desmopressin is not effective and it is necessary to resort to plasma concentrates containing factor VIII and von Willebrand factor. Treated with virucidal methods, these concentrates are effective and currently safe, but they do not always correct the bleeding time defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when a poor correction of the bleeding time after concentrates is associated with continued bleeding. Studies are in progress, first to better characterize patients with type I von Willebrand disease and to determine their response to desmopressin, and second, to evaluate the pharmacokinetics of factor VIII following factor VIII/von Willebrand factor concentrates and to establish the indication for concentrates.

Type 2N von Willebrand disease: clinical manifestations, pathophysiology, laboratory diagnosis and molecular biology

Type 2N von Willebrand disease encompasses all patients with factor VIII deficiency caused by a markedly decreased affinity of von Willebrand factor for factor VIII. It is recessively inherited and clinically similar to mild haemophilia. The differential biological diagnosis is of major importance for providing the optimal treatment and relevant genetic counselling. This accurate diagnosis is based on an evaluation of the factor VIII-binding capacity of plasma von Willebrand factor. Furthermore, molecular biology techniques allow the identification of missense mutations in the von Willebrand factor gene. All of these induce the substitution of amino acid residues located in the N terminal part of the mature von Willebrand factor molecule, which contains the factor VIII binding site. Most of them induce a classical type 2N von Willebrand disease phenotype with factor VIII deficiency but a normal level and multimeric pattern of von Willebrand factor.

How I treat patients with von Willebrand disease

Von Willebrand disease (vWD) is a frequent inherited disorder of hemostasis that affects both sexes. Two abnormalities are characteristic of the disease, which is caused by a deficiency or a defect in the multimeric glycoprotein called von Willebrand factor: low platelet adhesion to injured blood vessels and defective intrinsic coagulation owing to low plasma levels of factor VIII. There are 2 main options available for the treatment of spontaneous bleeding episodes and for bleeding prophylaxis: desmopressin and transfusional therapy with plasma products. Desmopressin is the treatment of choice for most patients with type 1 vWD, who account for approximately 70% to 80% of cases. This nontransfusional hemostatic agent raises endogenous factor VIII and von Willebrand factor 3 to 5 times and thereby corrects both the intrinsic coagulation and the primary hemostasis defects. In patients with the more severe type 3 and in most patients with type 2 disease, desmopressin is ineffective or is contraindicated and it is usually necessary to resort to plasma concentrates containing both factor VIII and von Willebrand factor. Concentrates treated with virucidal methods should be preferred to cryoprecipitate because they are equally effective and are perceived as safer. (Blood. 2001;97:1915-1919)

Unexpected presentation of type 2N von Willebrand disease in pregnancy

The finding of low factor VIII levels in pregnancy immediately raises concern of haemophilia A carriage, especially with a history of bleeding in the maternal grandfather. However, the diagnosis of type 2N von Willebrand disease (2N vWD) should also be considered as illustrated here. This is also the first reported case of the management of 2N vWD in pregnancy.

Treatment of von Willebrand disease

von Willebrand disease is the most frequent of inherited bleeding disorders (1:100 affected individuals in the general population). The aim of treatment is to correct the dual defects of haemostasis, i.e., abnormal coagulation expressed by low levels of factor VIII and abnormal platelet adhesion expressed by a prolonged bleeding time. There are two main options available for the management of von Willebrand disease: desmopressin and transfusion therapy with blood products. Desmopressin is the treatment of choice in patients with type 1 von Willebrand disease, who account for approximately 80% of cases. This pharmacological compound raises endogenous factor VIII and von Willebrand factors and thereby corrects the intrinsic coagulation defect and the prolonged bleeding time in most type 1 patients. In type 3 and in the majority of type 2 patients desmopressin is not effective, and it is necessary to resort to plasma concentrates containing factor VIII and von Willebrand factor. Treated with virucidal methods, these concentrates are effective and currently safe, but the bleeding time defect is not always corrected by them. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of the bleeding time after concentrates is associated with continued bleeding.

von Willebrand disease and its management in oral and maxillofacial surgery

von Willebrand disease (vWD) is the most common of the hereditary disorders of coagulation. We describe the pathophysiology, diagnosis and the new simplified classification of the disorder and discuss the management of patients about to undergo dental procedures and maxillofacial surgery. Close collaboration between oral and maxillofacial surgeons and haematologists in the management of patients with vWD is essential.

Treatment of von Willebrand Disease

The general goal of therapy in von Willebrand disease is to correct the two defects that are related to the bleeding tendency of these patients, i.e., the abnormal primary hemostasis expressed by a prolonged bleeding time (BT) and the abnormal intrinsic coagulation due to low factor VIII (FVIII) levels. There are two main treatments in von Willebrand disease, i.e., desmopressin and transfusional therapy with blood products. Desmopressin is most effective in patients with type 1, who account for about 80 per cent of all patients. The remaining patients with type 2 and type 3 von Willebrand disease do not respond consistently to desmopressin and need the infusion of blood products containing FVIII and von Willebrand factor. Virally-inactivated concentrates that are currently on the market are preferable to fresh-frozen plasma and cryoprecipate, that still carry a small risk of transmitting blood-borne infections. In rare instance, particularly for hemorrhoages in mucosal tracts such as gastrointestinal bleeding, platelet concentrates are useful adjuncts to plasma concentrates when patients do not respond to the latters. The role of purified von Willebrand factor and of recombinant products is still unclear.