Clinical and laboratory phenotype variability in type 2M von Willebrand disease

J Thromb Haemost. 2017 Aug;15(8):1559-1566. doi: 10.1111/jth.13742. Epub 2017 Jun 23.

Abstract

Essentials The pathophysiology of type 2M von Willebrand disease (VWD) is poorly understood. Sequence variations in type 2M VWD subjects were characterized. A high degree of clinical and laboratory variability exists within type 2M VWD variants. Some type 2M variants may share features of type 2A VWD.

Summary: Background von Willebrand factor (VWF) is a multimeric coagulation factor that tethers platelets to injured subendothelium. Type 2M von Willebrand disease (VWD) is characterized by a qualitative defect in VWF with preserved multimer distribution. Objectives Through the Zimmerman Program for the Molecular and Clinical Biology for VWD, five VWF sequence variations were studied in subjects diagnosed with type 2M VWD. Methods Bleeding phenotype was assessed using the ISTH bleeding assessment tool. Full-length VWF gene sequencing was performed for each subject. Each variant was placed into a recombinant VWF vector using site-directed mutagenesis and expressed in HEK293T cells as homozygous or heterozygous VWF. Variant expression, collagen binding and platelet GPIbα binding were studied through ELISA assays. Multimer analysis was performed by gel electrophoresis. Results Bleeding scores were elevated for all subjects except for the p.P1162L and p.R1374C variants. Although all had reduced VWF ristocetin cofactor activity/VWF antigen ratios on plasma testing, recombinant VWF did not show a classic type 2M phenotype for any of the five variants. Homozygous expression of variants p.D1283Y, p.R1349C, p.R1374C and p.I1453N was consistent with type 2A VWD, although all had normal expression as heterozygous recombinant VWF. Variant p.P1162L had normal VWF expression and function, consistent with the lack of bleeding symptoms. Conclusions Although originally classified as type 2M VWD, these homozygous recombinant VWF variants do not fulfill complete 2M VWD diagnostic criteria. A better classification schema and improved testing for putative type 2M variants is needed in order to effectively diagnose and treat affected patients.

Keywords: clinical laboratory techniques; hemorrhage; platelets; von Willebrand disease; von Willebrand factor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged, 80 and over
  • Blood Coagulation / genetics*
  • Case-Control Studies
  • Collagen / metabolism
  • Female
  • Genetic Predisposition to Disease
  • Genetic Variation*
  • HEK293 Cells
  • Hemorrhage / blood
  • Hemorrhage / diagnosis
  • Hemorrhage / genetics*
  • Heterozygote
  • Homozygote
  • Humans
  • Male
  • Middle Aged
  • Pedigree
  • Phenotype
  • Platelet Glycoprotein GPIb-IX Complex / metabolism
  • Protein Binding
  • Protein Multimerization
  • Severity of Illness Index
  • Transfection
  • United States
  • von Willebrand Disease, Type 2 / blood
  • von Willebrand Disease, Type 2 / diagnosis
  • von Willebrand Disease, Type 2 / genetics*
  • von Willebrand Factor / chemistry
  • von Willebrand Factor / genetics*
  • von Willebrand Factor / metabolism

Substances

  • Platelet Glycoprotein GPIb-IX Complex
  • adhesion receptor
  • von Willebrand Factor
  • Collagen