ERAP1 and Behcet disease: Intriguingly, the observed genetic epistasis in which homozygosity for ERAP1 p.Arg725Gln mutation strongly increases the OR for BD development in HLA-B51 + vs. HLA-B51- individuals, suggests a role for MHC-I, peptide, and T cell interactions in BD pathogenesis, thereby revealing a possible MHC-I-opathy (6).