The International Society on Thrombosis and Haematosis von Willebrand Disease Database: An Update

Abstract

The online locus-specific database for von Willebrand disease (VWFdb) acts as a repository for sequence variant data and associated resources for those with an interest in the disorder. It currently holds details of 561 mutations and 217 polymorphisms in the von Willebrand factor (VWF) gene. Lists can be queried and displayed by VWF region or disease type. A total of 42% of the mutations are located in the large exon 28, the most heavily studied VWF region, and mutations have been reported in all but 4 of the 51 protein-coding exons. Polymorphisms are reported in the 5' and 3' untranslated regions and in 33 exons and 35 introns. Additional resources include references linked to sequence variation entries, descriptors of each VWD type, genomic and cDNA sequences, nomenclature for VWF and its attributes, Human Genome Variation Society sequence variant nomenclature recommendations, multimer images, and related densitometry traces for type 2 VWD. Analysis of recessively inherited VWD indicates that whereas the majority (69%) of type 3 VWD patients are homozygous for their mutations, the majority (62%) of 2N patients are compound heterozygous. Comparison of missense substitutions reported as mutations with those reported as polymorphisms suggests that loss or gain of cysteine, tryptophan, methionine, or glutamate residues are more likely to result in a pathogenic effect than loss/gain of other VWF residues.

Solution structure of the major factor VIII binding region on von Willebrand factor

“…Type 2N mutations that involve a cysteine residue (C788R/Y, Y795C, and C804F in TIL9; C858S/F in E9) are associated with aberrant multimerization, poor secretion, and reduced FVIII binding, 45 indicating that correct disulfide-bond formation is critical to the folding and function of VWF (Figure 3). Of the type 2N mutations, 3 account for the majority of cases reported (T791M, R816W, and R854Q), 10 of which R854Q occurs with polymorphic frequency, 4 and all of which are in immediate proximity to the b1-to-b2 loop. However, the most accurate reporters of the FVIII binding site are those mutations that are associated with a more severe type 2N phenotype; that is, E787K, T791M, and R816W.…”

“…However, the most accurate reporters of the FVIII binding site are those mutations that are associated with a more severe type 2N phenotype; that is, E787K, T791M, and R816W. 10 Two of these mutations, T791M and R816W, together with T789P, M800V, R816Q, and H817Q, are clustered around a region of positive charge density on TIL9 ( Figure 6B-C). Two regions on the FVIII light chain have been implicated in binding VWF, that is, the N-terminal acidic a3 domain and the C-terminal C2 domain.…”

“…3 First, 72% of unique missense mutations that directly affect FVIII binding to VWF (type 2N VWD) are found in domains TIL9 and E9. 10 Importantly, the most severe type 2N phenotypes, characterized by the lowest circulating plasma FVIII levels, are due to mutations in TIL9 (Figure 1 and supplemental Figure 1 available on the Blood Web site). 4 Second, epitope-mapping studies of potent FVIII binding-blocking monoclonal antibodies (mAbs) mAb-418 (VWF epitope, residues 765-816) and mAb-32B12 (VWF epitope, residues 814-821) indicate that the putative FVIII binding site is localized to TIL9.…”

Role of calcium in regulating the intra- and extracellular cleavage of von Willebrand factor by the protease ADAMTS13

“…30,31 To test this hypothesis, a series of FRET constructs were expressed in which monomeric YFP (Venus) and CFP (Cerulean) flank the full VWF-A2 domain (Figure 3). Besides wildtype (VWF-A2 FRET) and Lock (Lock-FRET) proteins, 2 calciumbinding mutants R1597W-FRET and D1498M-FRET were also developed ( Figure 3A).…”

Laboratory hemostasis: milestones in Clinical Chemistry and Laboratory Medicine

“…Second line assays are typically those designed to provide further insights into abnormalities of screening tests, or used to monitor more accurately some antithrombotic therapies, and thereby include clotting factors assays [27] , ristocetin-induced platelet agglutination and VWF antigen tests [28] , anticardiolipin (aCL) IgG and IgM, anti-β (2) glycoprotein I (anti-β (2) GPI) antibodies IgG and IgM and phospholipid-dependent coagulation assays [29,30] , platelet function tests such as Platelet Function Analyzer-100 (PFA-100) and aggregometry [31,32] , assays for heparin-induced thrombocytopenia [33,34] , additional tests for thrombophilia screening including resistance to activated protein C, antithrombin, proteins C and S, and genetic polymorphisms/mutations (e.g., prothrombin G20210A and factor V Leiden) [35,36] along with ecarin clotting time, chromogenic anti-factor Xa and dilute Russell viper venom time (dRVVT) for monitoring novel anticoagulants [37,38] . Both first and second line tests might be available to most clinical laboratories, whereas third line tests -which are intended to troubleshoot the most challenging conditions and encompass analyses such as VWF collagen binding, VWF ristocetin cofactor assay, VWF-FVIII binding assay, multimer and molecular analysis for the precise classification of VWD [39,40] , coagulation factors inhibitors testing [41,42] , analyses of rare thrombophilic mutations [43] , rare platelet functional disorders [44] , pharmacogenetics testing [45,46] -are occasionally used and typically available in specialized laboratories. Quality in laboratory diagnostics is irrecusable, since spurious results obtained on unsuitable specimens may negatively bias the clinical decision-making and jeopardize patient safety.…”