ERAP1 and psoriasis: GWAS have suggested a role for both ERAP1 and ERAP2 in the onset of several immuno-mediated diseases (IMD), such as ankylosing spondylitis (AS), Behçet’s disease (BD), psoriasis (Ps), inflammatory bowel disease (IBD), juvenile idiopathic arthritis (JIA), birdshot chorioretinopathy (BSCR), type I diabetes mellitus (T1D) and multiple sclerosis (MS)21–29.