Genetic polymorphism H131R of Fcgamma receptor type IIA (FcgammaRIIA) in a healthy Finnish population and in patients with or without platelet-associated IgG.

Abstract

Patients (n=113) with histories of thrombocytopenia and with different profiles for platelet-associated IgG (PA-IgG) were subdivided according to the genetic polymorphism H131R in the Fcgamma receptor type IIA (FcgammaRIIA). PA-IgG was measured by the direct platelet immunofluorescence test (PIFT), and GP IIbIIIa and/or GP Ib-specific PA-IgG was investigated by a modified version of the direct monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay. As a control, the distribution of FcgammaRIIA polymorphism H131R was determined among 93 healthy Finnish blood donors. The frequencies for H131 and R131 were 0.56 and 0.44 (CI: 0.37-0.51), respectively, which did not differ significantly from those in other Caucasian populations. The distribution of the genotypes HH131, HR131 and RR131 in the patients and controls did not differ significantly. In the HH131 group, the PA-IgG was higher than in the RR131 group (p=0.082). Female patients with the genotype RR131 seemed to be younger than those with HH131 (p=0.065). Among the female patients, a significantly greater number were under 40 yr old in the RR131 group than in the HH131 group (p=0.0060). Within the RR131 group, the female patients were far younger than the male patients (median 29 vs. 61 yr; p=0.0021). The results point to the heterogeneity of immune thrombocytopenia, which may partly explain the poor predictive value of PA-IgG studies.