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

New treatment approaches to von Willebrand disease

von Willebrand disease (VWD) is the commonest inherited bleeding disorder and results from either a quantitative or qualitative deficiency in the plasma glycoprotein von Willebrand factor (VWF). Recent large cohort studies have significantly enhanced our understanding of the molecular mechanisms involved in the pathogenesis of VWD. In contrast, however, there have been relatively few advances in the therapeutic options available for the treatment of bleeding in patients with VWD. Established treatment options include tranexamic acid, 1-deamino-8-d-arginine vasopressin (DDAVP), and plasma-derived VWF concentrates. In addition, a recombinant VWF has also recently been developed. In this review, we focus on how recent insights into the clinical and molecular aspects underpinning VWD are already beginning to influence treatment in the clinic. For example, a number of different bleeding assessment tools (BATs) have been developed to objectively assess bleeding symptoms in patients with VWD. Interestingly, however, these BAT scores may also have an important role to play in predicting bleeding risk in VWD. Furthermore, recent studies have demonstrated that enhanced VWF clearance plays a critical role in the etiology of both type 1 and type 2 VWD. These findings have direct translational relevance with respect to the use of DDAVP in patients with VWD. As understanding of the mechanisms involved in VWD pathogenesis continues to advance, novel treatment options are likely to emerge. Critically, however, large adequately powered and stratified clinical trials will be required to address the outstanding questions that remain regarding VWD treatment optimization.

[Von Willebrand disease. Molecular biology and diagnosis]

BACKGROUND

Von Willebrand disease is the most common inherited disorder of the coagulation proteins in humans. There are three types: 1, 2A, 2B, 2N, 2M and 3. It is associated with mutations on chromosome 12 in the region p13.2, encoding the von Willebrand factor (VWF), which is synthesized in endothelial cells and megakaryocytes.

DISCUSSION

The VWF gene has been characterised using molecular biology techniques, which have acquired an important role in diagnosis von Willebrand disease, as well as in the investigation of alterations in other genes, which may be involved in regulating the synthesis, processing, and secretion of VWF. However, there are still no strategies to integrate the molecular biology diagnostic tests available. Analysis of VWF multimers is a methodology that meets the characteristics for diagnosis, but it is not easy to standardise. Considering that even in tertiary centres in our country, von Willebrand patients do not have a definitive diagnosis, it is necessary to implement these methodologies to study and improve diagnosis.

CONCLUSIONS

Von Willebrand disease is highly heterogeneous due to the molecular mechanisms that produce the various clinical and laboratory phenotypes. In Mexico there are few studies related to this disease; therefore it is essential to conduct a comprehensive study including clinical, basic, and special testing laboratory tests, in order to establish a correct diagnosis, develop new therapeutic approaches, and offer the appropriate medical care and genetic counselling.

Antigenic Peptides Capable of Inducing Specific Antibodies for Detection of the Major Alterations Found in Type 2B Von Willebrand Disease

Von Willebrand disease (VWD) is an inherited hemorrhagic disorder promoted by either quantitative or qualitative defects of the von Willebrand factor (VWF). The disease represents the most common human coagulopathy afflicting 1.3% of the population. Qualitative defects are subdivided into four subtypes and classified according to the molecular dysfunction of the VWF. The differential diagnosis of the VWD is a difficult task, relying on a panel of tests aimed to assess the plasma levels and function of the VWF. Here, we propose biochemical approaches for the identification of structural variants of the VWF. A bioinformatic analysis was conducted to design seven peptides among which three were representatives of specific amino acid sequences belonging to normal VWF and four encompassed sequences found in the most common VWD subtype 2B. These peptides were used to immunize mice, after which, peptide-specific immunoglobulins were purified. This resulted in four Ig preparations capable of detecting alterations in the subtype 2B VWD plus additional three antibody fractions targeting the normal VWF. The panel of antibodies could serve many applications among them (1) assessment of VWF: antigen interaction, (2) VWF multimer analysis, and (3) production of monoclonal antibodies against VWF for therapeutic purposes as in thrombotic thrombocytopenic purpura.

The molecular genetics of von Willebrand disease

Quantitative and/or qualitative deficiency of von Willebrand factor (vWF) is associated with the most common inherited bleeding disease von Willebrand disease (vWD). vWD is a complex disease with clinical and genetic heterogeneity. Incomplete penetrance and variable expression due to genetic and environmental factors contribute to its complexity. vWD also has a complex molecular pathogenesis. Some vWF gene mutations are associated with the affected vWF biosynthesis and multimerization, whereas others are associated with increased clearance and functional impairment. Moreover, in addition to a particular mutation, type O blood may result in the more severe phenotype. The present review aimed to provide a summary of the current literature on the molecular genetics of vWD.

Conflict of interest:None declared.

von Willebrand's disease: a report from a meeting in the Åland islands

von Willebrand's disease (VWD) is probably the most common bleeding disorder, with some studies indicating that up to 1% of the population may have the condition. Over recent years interest in VWD has fallen compared to that of haemophilia, partly the result of focus on blood-borne diseases such as HIV and hepatitis. Now the time has come to revisit VWD, and in view of this some 60 international physicians with clinical and scientific interest in VWD met over 4 days in 2010 in the Åland islands to discuss state-of-the-art issues in the disease. The Åland islands are where Erik von Willebrand had first observed a bleeding disorder in a number of members of a family from Föglö, and 2010 was also the 140th anniversary of his birth. This report summarizes the main papers presented at the symposium; topics ranged from genetics and biochemistry through to classification of VWD, pharmacokinetics and laboratory assays used in the diagnosis of the disease, inhibitors, treatment guidelines in different age groups including the elderly who often have comorbid conditions that present challenges, and prophylaxis. Other topics included managing surgeries in patients with VWD and the role of FVIII in VWF replacement, a controversial subject.

Inherited platelet disorders

OBJECTIVE

To present the latest information on inherited platelet disorders in domestic animals.

DATA SOURCES

Research articles and reviews spanning 40 years available on PubMed.

HUMAN DATA SYNTHESIS

Information regarding inherited platelet disorders in people is plentiful and often descriptions of human conditions have led to the identification of similar disorders in veterinary species. There are exceptions, however, in which specific inherited platelet disorders were first described in animals with subsequent identification in people.

VETERINARY DATA SYNTHESIS

Many inherited platelet disorders have been documented in animals at the functional and molecular level and that information is presented in this review.

CONCLUSIONS

Much progress has been made in the past 20 years in the characterization of inherited platelet disorders in animals at the functional, biochemical, and molecular level. The study of inherited platelet disorders has greatly enhanced the understanding of platelet physiology and has led in some instances to the development of platelet inhibitory medications. Characterization of inherited disorders at the molecular level greatly facilitates diagnosis and identification of affected and heterozygous animals thus avoiding propagation of the defect by breeders. When used with available functional and biochemical diagnostic tests, it significantly enhances the quality of care and case management.

Bleeding tendency and efficacy of anti-haemorrhagic treatments in patients with type 1 von Willebrand disease and increased von Willebrand factor clearance

Accelerated clearance of von Willebrand factor (VWF) has been recently identified as a major pathophysiologic mechanism inducing low VWF in some patients with von Willebrand disease (VWD). The frequency of bleeding and the best treatment of these patients have never been evaluated prospectively in large series of patients. It was the aim of the present study to prospectively evaluate clinical events of 60 heterozygous patients with VWD Vicenza (VWD-VI) carrying R1205H VWF mutation and 23 with C1130F mutation, both characterised by markedly increased VWF clearance. During 71 months of follow-up, 65% of patients with VWD-VI and 61% with C1130F required treatment. The rate of spontaneous bleeding requiring consultation/treatment was 7.5/100 patients-year in patients with C1130F mutation vs. 1.9/100 patients-year in those with R1205H (p=0.004). This difference persisted also by multivariate analysis adjusted for sex, age and blood group (hazard ratio [HR]=3.3 for C1130F, 95% confidence interval [CI] 1.16-9.27) and females were at greater risk of bleeding (HR=3, 95%CI 1.01-9.93) because of menorrhagia. Only 3/15 (20 %) women in fertile age with VWD-VI compared to 8/9 (89 %) with C1130F mutation required consultation/treatment for menorrhagia (iron supplementation, combined oral contraceptives, tranexamic acid). Almost all dental extractions, minor surgeries and deliveries occurring during follow-up were successfully managed with desmopressin. Major surgery required factor VIII/VWF concentrates, but a few cases benefited from desmopressin. In conclusion, similar to patients with type 1 VWD, also in patients with increased VWF clearance desmopressin maintains a major therapeutic role.