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Variability in platelet‐ and collagen‐binding defects in type 2M von Willebrand disease
Author(s) -
Larsen D. M.,
Haberichter S. L.,
Gill J. C.,
Shapiro A. D.,
Flood V. H.
Publication year - 2013
Publication title -
haemophilia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.213
H-Index - 92
eISSN - 1365-2516
pISSN - 1351-8216
DOI - 10.1111/hae.12117
Subject(s) - von willebrand disease , von willebrand factor , recombinant dna , platelet , platelet membrane glycoprotein , microbiology and biotechnology , mutation , medicine , antigen , immunology , gene , chemistry , biochemistry , biology
Summary Type 2M von Willebrand disease ( VWD ) includes qualitative defects in von W illebrand factor ( VWF ) function, with normal multimer distribution but a defect in VWF activity with respect to platelet or collagen binding. We characterized novel VWF gene mutations found in type 2M VWD subjects enrolled in the Zimmerman Program for the Molecular and Clinical Biology of VWD . Subjects were enrolled based on a pre‐existing diagnosis of type 2M VWD . Testing included full‐length gene sequencing, VWF antigen ( VWF :Ag), VWF ristocetin cofactor activity ( VWF : RCo ), VWF collagen binding and multimer distribution. Recombinant VWF variants were synthesized using site‐directed mutagenesis and expressed in HEK293T cells. Platelet binding was measured by flow cytometry with fixed platelets and ELISA with recombinant glycoprotein Ibα ( GPIbα ). Four novel VWF A1 domain mutations were found in individuals with type 2M VWD : S1358N, S1387I, S1394F and Q1402P. All subjects had a history of bleeding, VWF : RCo < 40 IU dL −1 , VWF : RCo / VWF : Ag ratios <0.6 and normal multimer distribution. No defect in expression, secretion, or multimerization was found for any of the mutations. All showed decreased binding to intact platelets, and decreased or absent binding to a mutant GPIbα construct with spontaneous VWF binding. 1387I had decreased binding to all collagen types tested. 1402P had reduced binding exclusively to type VI collagen. Type 2M VWD is a heterogeneous category comprised of both collagen‐ and platelet‐binding defects. Understanding the precise defect for each mutation may ultimately lead to better diagnosis and treatment.