Discrepant platelet and plasma von Willebrand factor in von Willebrand disease patients with p.Pro2808Leufs*24

Background A novel variant, p.Pro2808Leufs*24, in the von Willebrand factor (VWF) gene was previously identified in the Canadian von Willebrand disease (VWD) patient population. Clinical observations of type 3 VWD patients with this variant indicate a milder bleeding phenotype compared to other type 3 patients. Objective To assess the effect of the Pro2808Leufs*24 variant on the molecular pathogenesis of VWD and correlate with the phenotype observed in patients. Patients/Methods Phenotypic data from individuals in the Canadian type 3 VWD study was analysed. VWF expression in platelets and plasma was assessed via immunoblotting. Cellular expression of VWF in platelets and blood outgrowth endothelial cells (BOEC) was examined via immunofluorescence microscopy and biochemical analysis in a type 3 index case and family member with Pro2808Leufs*24. Results Twenty-six individuals withthe Pro2808Leufs*24 variant (16 type 3 VWD homozygous or compound heterozygous and 10 heterozygous family members). Bleeding scores were lower in type 3 patients with Pro2808Leufs*24 compared to type 3 patients with other variants, confirming a milder bleeding phenotype. Immunoblotting of platelet lysates detected VWF in in the platelets of type 3 patients with Pro2808Leufs*24. Examination of an index case detected VWF within platelets via immunofluorescence microscopy, and in vitro experiments showed that this VWF was released upon platelet activation. Patient BOECs showed decreased VWF synthesis and secretion, although some VWF-containing granules were observed. Conclusion Type 3 VWD patients with the Pro2808Leufs*24 have bioavailable platelet-derived VWF which may produce a milder bleeding phenotype than other type 3s . This article is protected by copyright. All rights reserved.