PB0283 - Enhanced cleavage of ADAMTS13 of the VWF G1609R variant causing severe bleeding symptoms in the pedigree with 2A von Willebrand disease

Sunday, June 23, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

Ziqi Zhang

postgraduate
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
Shanghai, Shanghai, China (People's Republic)

Co-Author(s)

QD

Qiulan Ding

Professor
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
Shanghai, Shanghai, China (People's Republic)
XW

Xuefeng Wang

Professor
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
Shanghai, Shanghai, China (People's Republic)
JD

Jing Dai

Professor
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China
Shanghai, Shanghai, China (People's Republic)
QL

Qian Liang

Doctor of Medicine
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
Shanghai, Shanghai, China (People's Republic)
Shijie Zhou, MA

postgraduate
ruijin hospital
Shanghai, Shanghai, China (People's Republic)

Background: Type 2A VWD is the most common form of all four type 2 VWD, resulting from the loss of intermediate- and high-molecular-weight VWF multimers. It can be divided into two groups, with group I are characterized by impaired intracellular secretion of HMWM, and group II increased susceptibility of VWF to proteolysis by the ADAMTS13 metalloproteinase.

Aims: To explore the basic mechanisms of the VWF G1609R variant causing a severe bleeding symptoms in one clinical pedigree.

Methods: The patient was subjected to standard procedure for the laboratory diagnosis of VWD as well as next generation sequencing (NGS) of the whole coding VWF. Recombinant full-length VWF protein was expressed in Att20 cells, while ELISA, collagen binding experiments, SDS-agarose gel electrophoresis, and microfluidics were conducted before and after their reaction with ADAMTS13. The VWF A2 domain fragment underwent thermal stability experiments and HPLC.

Results: The patients showed slightly low levels of VWF:Ag, VWF:Act, and VWF:Act/VWF:Ag < 0.7, with a lack of HMW VWF multimers and a partial loss of the intermediate-molecular-weight multimers. However, the level of VWF:CB had significantly dropped and VWF:CB/VWF:Ag < 0.1. (Figure 1)Once ADAMTS13 added, the collagen binding ability of rG1609R declined in comparison to rWT.Similar to the patient's plasma results, the addition of urea as a reactive denaturant caused a more noticeable decrease in VWF:CB and VWF multimers.(Figure 2) Moreover, the G1609R-A2 fragment displayed worse thermostability and was hydrolyzed by ADAMTS13 more quickly than WT-A2.

Conclusion(s): Based on the results,we categorized the G1609R variant in group II type 2A variants. G1609R variant of VWF is accelerated by ADAMTS13 cleavage, resulting in a decrease in VWF multimers and a significantly drop in VWF collagen binding.The significant decrease in VWF collagen binding is the main cause of severe bleeding symptoms in the pedigree.