Identification and characterization of the elusive mutation causing the historical von Willebrand Disease type IIC Miami. (20th August 2016)

• Record Type: Journal Article
• Authors: Obser, T.; Ledford‐Kraemer, M.; Oyen, F.; Brehm, M. A.; Denis, C. V.; Marschalek, R.; Montgomery, R. R.; Sadler, J. E.; Schneppenheim, S.; Budde, U.; Schneppenheim, R.
• Is Part Of: Journal of thrombosis and haemostasis. Volume 14:Number 9(2016:Sep.)
• Page Start: 1725
• Page End: 1735
• Publication Date: 2016-08-20
• Subjects: ADAMTS‐13, mouse -- genetics -- physiopathology -- von Willebrand disease, type 2A -- von Willebrand factor; Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.13398
• Languages: English
• ISSNs: 1538-7933

Abstract

Abstract : Essentials Von Willebrand disease IIC Miami features high von Willebrand factor (VWF) with reduced function. We aimed to identify and characterize the elusive underlying mutation in the original family. An inframe duplication of VWF exons 9–10 was identified and characterized. The mutation causes a defect in VWF multimerization and decreased VWF clearance from the circulation. Summary: Background: A variant of von Willebrand disease (VWD) type 2A, phenotype IIC (VWD2AIIC), is characterized by recessive inheritance, low von Willebrand factor antigen (VWF:Ag), lack of VWF high‐molecular‐weight multimers, absence of VWF proteolytic fragments and mutations in the VWF propeptide. A family with dominantly inherited VWD2AIIC but markedly elevated VWF:Ag of > 2 U L −1 was described as VWD type IIC Miami (VWD2AIIC‐Miami) in 1993; however, the molecular defect remained elusive. Objectives: To identify the molecular mechanism underlying the phenotype of the original VWD2AIIC‐Miami. Patients and Methods: We studied the original family with VWD2AIIC‐Miami phenotypically and by genotyping. The identified mutation was recombinantly expressed and characterized by standard techniques, confocal imaging and in a mouse model, respectively. Results: By Multiplex ligation‐dependent probe amplification we identified an in‐frame duplication of VWF exons 9‐10 (c.998_1156dup; p.Glu333_385dup) in all patients. Recombinant mutant (rm)VWF only presented as a dimer. Co‐expressed with wild‐type VWF, the multimer pattern was indistinguishable from patients' plasma VWF. Immunofluorescence studies indicated retention of rmVWF in unusually large intracellular granules in the endoplasmic reticulum. ADAMTS‐13 proteolysis of rmVWF under denaturing conditions was normal; however, an aberrant proteolytic fragment was apparent. A decreased ratio of VWF propeptide to VWF:Ag and a 1‐desamino‐8‐d ‐arginine vasopressin (DDAVP) test in one patient indicated delayed VWF clearance, which was supported by clearance data after infusion of rmVWF into VWF −/− mice. Conclusion: The unique phenotype of VWD2 type IIC‐Miami results from dominant impairment of multimer assembly, an aberrant structure of mutant mature VWF and reduced clearance in vivo .