Gain-of-function GPIb ELISA assay for VWF activity in the Zimmerman Program for the Molecular and Clinical Biology of VWD

von Willebrand disease (VWD) is a common bleeding disorder, but diagnosis is sometimes challenging because of issues with the current von Willebrand factor (VWF) assays, VWF antigen (VWF:Ag) and VWF ristocetin cofactor activity (VWF:RCo), used for diagnosis. We evaluated 113 healthy controls and 164 VWD subjects enrolled in the T.S. ZimmermanProgram for the Molecular and Clinical Biology of VWD for VWF: Ag, VWF: RCo, and a new enzyme-linked immunosorbent assay (ELISA)-based assay of VWF-glycoprotein Ib (GPIb) interactions using a gain-of-function GPIb construct (tGPIb alpha(235Y;239V)) as a receptor to bind its ligand VWF in an assay independent of ristocetin (VWF:IbCo ELISA). Healthy controls, type 1, 2A, 2M, and 2N subjects had VWF: RCo/VWF: Ag ratios similar to the ratio obtained with VWF: IbCo ELISA/VWF:Ag. Type 2B VWD subjects, however, had elevated VWF: IbCo ELISA/VWF: Ag ratios. Type 3 VWD subjects had undetectable (< 1.6 U/dL) VWF: IbCo ELISA values. As previously reported, VWF: RCo/VWF: Ag ratio was decreased with a common A1 domain polymorphism, D1472H, as was direct binding to ristocetin for a 1472H A1 loop construct. The VWF: IbCo ELISA, however, was not affected by D1472H. The VWF: IbCo ELISA may be useful in testing VWF binding to GPIb, discrimination of type 2 variants, and in the diagnosis of VWD as it avoids some of the pitfalls of VWF: RCo assays. (Blood. 2011; 117(6): e67-e74)