Classification of variant von Willebrand's disease subtypes by analysis of functional characteristics and multimeric composition of factor VIII/von Willebrand factor

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.

von Willebrand disease: clinical and laboratory lessons learned from the large von Willebrand disease studies

During the past 25 years, our knowledge concerning the pathogenesis, diagnostic strategies, and treatment of von Willebrand disease (VWD) has increased significantly. Following the immunological differentiation of factor VIII (FVIII) and von Willebrand factor (VWF) in the 1970s and the cloning of the FVIII and VWF genes in the mid-1980s, substantial progress has been made in our understanding of this, the most common inherited bleeding disorder. We now recognize that VWD represents a range of genetic diseases all with the clinical endpoint of increased mucocutaneous bleeding. The molecular pathology of Type 2 and 3 VWD is now comprehensively documented and involves rare sequence variants at the VWF locus. In contrast, the genetic causation of Type 1 disease remains incompletely defined and in many cases appears to involve genetic determinants in addition to or instead of VWF. The diagnostic triad of a personal history of excessive mucocutaneous bleeding, laboratory tests for VWF that are consistent with VWD, and a family history of the condition remain the keystone to VWD identification. In the laboratory, measurement of VWF antigen and function continue to be the most important diagnostic studies, and while our understanding of the molecular genetic pathology of VWD has advanced considerably in the past decade, genetic testing as a component of diagnosis is limited to certain distinct subtypes of the disorder. Treatment of VWD has been relatively unchanged for the past decade and continues to involve either stimulation of the release of intrinsic VWF with desmopressin or the infusion of VWF concentrates.

Effect of multimerization of human and recombinant von Willebrand factor on platelet aggregation, binding to collagen and binding of coagulation factor VIII

The smallest circulating von Willebrand factor (vWF) molecule is a dimer composed of two identical subunits containing binding sites for heparin, collagen, platelet glycoproteins and coagulation factor VIII (FVIII). Interdimeric disulfide linking leads to multimers composed of up to 40 dimers. vWF serves as a carrier of FVIII and is required for normal interactions of platelets with the subendothelium of the injured vessel wall. Von Willebrand factor was purified from human plasma cryoprecipitate and fermentation supernatant of recombinant CHO cells by anion exchange chromatography. Heparin affinity chromatography was used to isolate vWF polymers of different degree of multimerization. Analysis of collagen binding and platelet aggregation revealed that these activities increase with increasing degree of multimerization of vWF. Binding of FVIII to vWF was studied by real-time biospecific interaction analysis and surface plasmon technology. The binding data showed that the binding of FVIII is independent of vWF multimerization. Using recombinant FVIII and recombinant vWF, real-time biospecific interaction analysis resulted in a potential stoichiometry of 2 to 2.5 vWF-subunits per bound FVIII molecule. The kinetic analysis of the vWF-FVIII interaction resulted in a binding rate constant of about 3 x 10(6) M-1 s-1 and an equilibrium dissociation constant of about 0.4 x 10(-9) M.

Lack of correlation between factor VIII related antigen multimeric analysis pattern and parallel or non-parallel dose response curves in an ELISA factor VIII related antigen assay

Factor VIII related antigen has been measured and epitope distribution has been explored by testing the degree of parallelism between standard and test plasma dose response curves using an enzyme immunoassay. Normal plasma, plasma fractions, and plasma from patients with haemophilia and von Willebrand's disease have been tested. All showed parallelism except for plasma from patients with the variant type IIA von Willebrand's disease, of which 10 had parallel and five had non-parallel dose response curves when compared with that of normal plasma. In one family plasma from seven members showed parallelism but from four others did not. An unrelated patient was tested on three occasions, and although the samples were parallel to each other, no sample was parallel to the standard. No correlation was found between parallelism as shown by the enzyme immunoassay and differences in factor VIII related antigen multimeric pattern, including triplet configuration, seen in the type IIA patients.

Analysis of the complexity of the multimeric structure of factor VIII related antigen/von Willebrand protein using a modified electrophoretic technique

A method for multimeric analysis of factor VIII related antigen/von Willebrand protein is described. By modifying an existing method the technique has been simplified and optimised so that the different molecular forms of factor VIII related antigen and their triplet structure can be visualised. Clear differences can be seen between patterns in normals and type IIA von Willebrand's disease variants in that the latter lack high and intermediate multimers and also have a different configuration to the triplet pattern in the lower molecular weight multimers. Differences in triplet pattern can also be seen in different type IIA patients. The advantages and further application of this method for investigating the molecular defect in von Willebrand's disease are discussed.