Kirino et al. reported that the missense coding ERAP1 SNP Arg725Gln (rs17482078) significantly affected BD risk in HLA-B*51 carriers in a Turkish population, suggesting a gene-gene interaction between ERAP1 rs17482078 and HLA-B*51 in BD12 like that found between ERAP1 variants and the disease-associated HLA alleles observed in psoriasis and ankylosing spondylitis (AS)13,14. The gene discussed is HLA-B; the disease is Behcet disease.