Analysis of Arg834Gln and Val902Glu type 2A von Willebrand disease mutations: studies with recombinant von Willebrand factor and correlation with patient characteristics

Abstract

Type 2A von Willebrand disease (vWD), the most common qualitative form of vWD, is characterized by a relative decrease in circulating intermediate and high molecular weight (HMW) multimers. We studied the biosynthesis of recombinant von Willebrand factor (vWF) containing each of two type 2A vWD mutations previously reported by us, Arg834Gln and Val902Glu. The structure of recombinant Arg834Gln vWF within transfected COS-7 cells and the secretion of HMW multimers were similar to wild type vWF. The normal transport and secretion of Arg834Gln vWF, categorizes it as a group II type 2A mutation. In contrast, the Val90- 2Glu mutation resulted in intracellular proteolysis of vWF with the generation of a 176-kD fragment and retention of vWF between the endoplasmic reticulum and the Golgi complex. Moreover, the 176-kD fragment was also increased in plasma from patients with the Val902Glu mutation. Significantly impaired secretion and intracellular proteolysis of Val902Glu vWF categorizes a new sub-group of type 2A mutations. The intracellular proteolysis of vWF Val902Glu explains the lack of response to 1-deamino 8-D-arginine vasopressin (DDAVP) in patients who carry the mutation.