Characterization of large in-frame von Willebrand factor deletions highlights differing pathogenic mechanisms

• Published in: Blood advances Vol. 4; no. 13; pp. 2979 - 2990
• Main Authors: Cartwright, Ashley, Webster, Simon J., de Jong, Annika, Dirven, Richard J., Bloomer, Lisa D.S., AL-Buhairan, Ahlam M., Budde, Ulrich, Halldén, Christer, Habart, David, Goudemand, Jenny, Peake, Ian R., Eikenboom, Jeroen C.J., Goodeve, Anne C., Hampshire, Daniel J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 14.07.2020; American Society of Hematology
• Subjects: Biomedical Laboratory Science/Technology; Biomedicinsk laboratorievetenskap/teknologi; Medical and Health Sciences; Medical Biotechnology; Medicin och hälsovetenskap; Medicinsk bioteknologi; Thrombosis and Hemostasis
• ISSN: 2473-9529; 2473-9537; 2473-9537
• DOI: 10.1182/bloodadvances.2018027813

Copy number variation (CNV) is known to cause all von Willebrand disease (VWD) types, although the associated pathogenic mechanisms involved have not been extensively studied. Notably, in-frame CNV provides a unique opportunity to investigate how specific von Willebrand factor (VWF) domains influence the processing and packaging of the protein. Using multiplex ligation-dependent probe amplification, this study determined the extent to which CNV contributed to VWD in the Molecular and Clinical Markers for the Diagnosis and Management of Type 1 von Willebrand Disease cohort, highlighting in-frame deletions of exons 3, 4-5, 32-34, and 33-34. Heterozygous in vitro recombinant VWF expression demonstrated that, although deletion of exons 3, 32-34, and 33-34 all resulted in significant reductions in total VWF (P < .0001, P < .001, and P < .01, respectively), only deletion of exons 3 and 32-34 had a significant impact on VWF secretion (P < .0001). High-resolution microscopy of heterozygous and homozygous deletions confirmed these observations, indicating that deletion of exons 3 and 32-34 severely impaired pseudo-Weibel-Palade body (WPB) formation, whereas deletion of exons 33-34 did not, with this variant still exhibiting pseudo-WPB formation similar to wild-type VWF. In-frame deletions in VWD, therefore, contribute to pathogenesis via moderate or severe defects in VWF biosynthesis and secretion. •In-frame VWF deletions have differing impacts on VWF biosynthesis and secretion linked to pseudo-WPB formation and intracellular localization.•Characterization of in-frame deletions highlights new pathogenic mechanisms and an influence of the A3 domain in VWF packaging and processing. [Display omitted]