ERAP2 and Crohn disease: ERAP1 is reportedly associated with HLA‐B27− and HLA‐B40­positive AS,95 while ERAP2 is related to HLA‐B27+ and HLA‐B27− AS.97 ERAP1 is also involved in the development of juvenile idiopathic arthritis, psoriasis, and Behçet’s disease, while ERAP2 is related to Crohn’s disease and psoriasis, as well as birdshot chorioretinopathy,79,91 with unclear mechanisms.