Genetics of microscopic polyangiitis in the Japanese population.

The epidemiology of ANCA-associated vasculitis is substantially different between Caucasians and Japanese, which may be related to differences in genetic backgrounds. In this review, I discussed our findings on the genetics of microscopic polyangiitis (MPA) in Japanese. Analysis of HLA genes revealed a significant increase in the HLA-DRB1*09:01-DQB1*03:03 haplotype MPA. This is one of the most frequent haplotypes in Japanese, but is nearly absent in Caucasians, and has been shown to be associated with multiple autoimmune diseases. Analysis of KIR genes revealed significant decreases in the carrier frequency of an activating receptor KIR2DS3 in MPA. When KIRs were analyzed in combination with HLA ligands, the proportion of individuals carrying KIR3DL1 and HLA-Bw4 but not KIR3DS1, the most inhibitory of all KIR3DS1/3DL1/HLA-B combinations, was significantly increased in MPA. These results suggested that decreased activation of NK and/or T cells may cause a predisposition to MPA. LILRA2 is an activating receptor involved in granulocyte and macrophage activation. LILRA2 SNP rs2241524 G >A, which disrupts the intron 6 splice acceptor site, was significantly associated with MPA. The risk allele produces an LILRA2 isoform lacking three amino acids in the linker region. These findings, when confirmed by larger-scale studies, will shed light on the molecular mechanisms of MPA. (*English Translation of J Jpn Coll Angiol 2009; 49: 31-37.).