Platelet membrane glycoprotein polymorphisms do not influence the clinical expressivity of von Willebrand disease type I

Abstract

Von Willebrand disease (VWD) is characterized by a significant variation in bleeding symptoms among patients with similar laboratory profiles and equivalent plasma levels of von Willebrand factor (VWF) activities. Considering the recent suggestion that platelet membrane glycoprotein polymorphisms (PltGPs) may play a role as modulators of thromboembolic or haemorrhagic diseases, we investigated the role of different PltGPs and GPVI content in the clinical expression of patients with VWD type 1. The diagnosis of VWD (n = 76) was based on laboratory findings (VWF:Ag, VWF:RCo, VWF:CB, FVIII:C, and multimer analysis), family and personal history of bleeding. All patients were interviewed using a standardized questionnaire, and classified into two categories: bleeders (unequivocal bleeding tendency, n = 53) and non bleeders (absence of bleeding symptoms, n = 23). PltGPs, HPA-1, 2 and 5 and C807T of GPla were determined by fluorophore-labelled hybridization probes on a LightCycler(TM). GPVI content was measured by western blotting.

VWF:Ag,VWF:RCo,VWF:CB and FVIII:C levels were not significantly different between symptomatic and asymptomatic patients. There were no differences in the genotype distribution and allele frequencies between bleeders and non bleeders for the platelet alloantigen systems HPA-1, 2, 5 and the GPla C807T polymorphism. The levels of platelet GPVI were similar in symptomatic and asymptomatic VWD patients (109.6 +/- 58.4 vs 114.1 +/- 52.5, respectively; p: 0.77). These results show that PltGPs HPA-1, 2 and 5 or the C807T dimorphism of GPla do not influence the clinical expressivity of VWD type I. The wide variation in GPVI content was not associated with the severity of bleeding in the patients. Other genetic factors that may contribute to the variable expressivity of VWD type I should be investigated.