2N (n ‫؍‬ 4 of 4), but in none of those with type 1 VWD. Genotype provided more information than phenotype in predicting individual responses to DDAVP only in patients with 2A and 2N VWD. This prospective study showed that the rate of biologic response to DDAVP is relatively low not only in type 2 but also in type 1 VWD when uniform and stringent criteria for patient selection and responsiveness are applied.

No abstract

von Willebrand disease (vWD) is a frequent and heterogeneous bleeding disorder which is characterized by quantitative and/or qualitative abnormalities of von Willebrand factor (vwF). vwF is a high molecular weight (HMw), multimeric glycoprotein, which carries factor VIII (FVIII) and mediates platelet adhesion and aggregation ar high shear rates (l,Z). The vwF gene, of 178 kb, contains 52 exons. A precursor protein, pre-pro-vWF, containing four types of repeating domains (A to D), is synthesized in endothelial cells and megakaryocytes (Fig. 1). Disulphide bridges involved in the dimerization and multim erization of vWF are located in the C-terminal part and D3 domain, respectively. vWF multimers are composed of mature vWF subunits of 270 kDa corresponding to the 2050 C-terminal aa of pre-pro-vWF. These subunits contain two remarkable disulphide loops of l g5 aa in Al and ,{3 domains, an important proteolytic site within ,{2 domain, between aa 842 and 843, and an RGD sequence in Cl domain. The functions of vWF are related to the presence along the 270 kDa subunit of a series of binding sites for FVIII, collagen, platelet glycoproteins (GP) GPIb and GPIIb/IIIa (Fig.1). The multimerization of vWF is also essential for its role in platelet adhesion and aggregation.

Summary.  Background: Candidate von Willebrand factor (VWF) mutations were identified in 70% of index cases in the European study ‘Molecular and Clinical Markers for the Diagnosis and Management of type 1 von Willebrand Disease’. The majority of these were missense mutations. Objectives: To assess whether 14 representative missense mutations are the cause of the phenotype observed in the patients and to examine their mode of pathogenicity. Methods: Transfection experiments were performed with full‐length wild‐type or mutant VWF cDNA for these 14 missense mutations. VWF antigen levels were measured, and VWF multimer analysis was performed on secreted and intracellular VWF. Results: For seven of the missense mutations (G160W, N166I, L2207P, C2257S, C2304Y, G2441C, and C2477Y), we found marked intracellular retention and impaired secretion of VWF, major loss of high molecular weight multimers in transfections of mutant constructs alone, and virtually normal multimers in cotransfections with wild‐type VWF, establishing the pathogenicity of these mutations. Four of the mutations (R2287W, R2464C, G2518S, and Q2520P) were established as being very probably causative, on the basis of a mild reduction in the secreted VWF or on characteristic faster‐running multimeric bands. For three candidate changes (G19R, P2063S, and R2313H), the transfection results were indistinguishable from wild‐type recombinant VWF and we could not prove these changes to be pathogenic. Other mechanisms not explored using this in vitro expression system may be responsible for pathogenicity. Conclusions: The pathogenic nature of 11 of 14 candidate missense mutations identified in patients with type 1 VWD was confirmed. Intracellular retention of mutant VWF is the predominant responsible mechanism.

We report the identification of von Willebrand factor (vWF) gene mutations within exon 28 occurring in three unrelated families with an infrequent form of type 2 von Willebrand disease (vWD). A C-->T transition and a G-->A transition, both at the codon for arginine 611 of the mature vWF subunit, were found. They result in either a cysteine or an histidine substitution, respectively. Patients were found to be heterozygous for these substitutions and the vWD was transmitted dominantly. These substitutions have been reproduced by in vitro mutagenesis of full-length cDNA of vWF and transiently expressed in Cos- 7 cells. The corresponding recombinant vWFs (rvWF) exhibited decreased expression and a significant decrease in the high molecular weight multimeric forms. In addition, ristocetin- and botrocetin-induced binding of mutated rvWFs to platelets were markedly decreased as compared with that for the wild-type rvWFs. Thus, the structural and functional characterization of both mutated rvWFs confirmed that the two nucleotide substitutions identified at position 611 of the mature subunit of vWF are real mutations. Although they are located in the A1 loop containing most of the type 2B mutations inducing increased affinity of vWF for platelet glycoprotein Ib, they are responsible for abnormal vWF with decreased platelet-dependent function.