The human FCGR2/3 locus contains highly homologous genes encoding the five major receptors for IgG (Fc-gamma receptors, FcγRs). In two prior GWAS on Kawasaki disease (KD), a SNP in FCGR2A (131H>R; rs1801274) was identified to be associated with disease susceptibility. However, the FCGR2/3 locus contains multiple single nucleotide polymorphisms (SNPs) and copy number variations (CNVs), which were not covered by the detection platforms used in the GWAS. In this study we therefore focused on further fine-mapping of this locus to investigate the association of the different genetic variations with KD susceptibility. A highly accurate and validated multiplex ligation-dependent probe amplification (MLPA) assay was used to analyze all functionally relevant SNPs and CNVs within this locus. In a genetic association study involving case-control and family-based testing with 1028 patients with KD, the previous finding of FCGR2A-131H as a susceptibility marker for KD was confirmed (OR 1.16; 95%CI 1.08-1.32, meta-P = 0.01). In addition, we found a novel significant association of the FCGR2C-ORF haplotype with susceptibility to KD (OR 1.34; 95% confidence interval 1.11-1.62, meta-P = 0.003). FCGR2C-ORF leads to the expression of an extra, functionally activating FcγR (i.e. FcγRIIc) on myeloid cell types and NK cells. Being absent in Asian individuals, the FCGR2C-ORF haplotype only contributed to KD susceptibility in European subjects, independent of the established association with FCGR2A-H131R. We did not find any significant association of CNV of the locus with susceptibility to KD.
Our data point to an important role of the activating FcγRs in KD pathology. We hypothesize that the identified functional SNPs might alter the balance between the activating and inhibitory FcγRs leading to unbalanced inflammation and KD.