Fcgamma receptor IIa and IIIa polymorphisms in childhood immune thrombocytopenic purpura.

Fcgamma receptor-mediated destruction of autoantibody-sensitized platelets is central to the immune pathophysiology of childhood immune thrombocytopenic purpura (ITP). Allelic variants exist among the random population for some Fcgamma receptors. The variants represent single nucleotide polymorphisms, leading to functional differences in the ability to bind immunoglobulin (Ig)G or IgG subclasses. The genotypic frequencies for two Fcgamma receptor single nucleotide polymorphisms, FcgammaRIIa-131 arginine (R) versus histidine (H) and FcgammaRIIIa-158 valine (V) versus phenylalanine (F) were examined in 98 children diagnosed with childhood ITP. The genotype frequencies were compared with those of 130 healthy control subjects. Chi-square analysis was used to determine whether the allelic frequencies of the high-affinity receptor variants were associated with childhood ITP. Both the FcgammaRIIa-131H and the FcgammaRIIIa-158V were significantly over-represented in children with ITP versus the control subjects (P-values 0.03). The same statistical difference was noted with the combined FcgammaRIIa-131H and FcgammaRIIIa-158V allelic gene frequencies. There was no statistical difference between children who later developed chronic ITP compared with children with acute ITP, suggesting that additional factors are responsible for the development of the chronic form of the disease. These observations underscore the importance of Fcgamma receptor-mediated cell clearance in childhood ITP.