Of all the genes located in the vicinity of the MHC on BTA23, C4A, ENSBTAG00000006864, and IER3 have been linked to abnormal intestinal morphology or physiology, whereas PKHD1, ENSBTAG00000013919, ENSBTAG00000038397, and SKIV2L are involved in bowel diseases (Crohn’s disease, ulcerative colitis, syndromic diarrhea, gastrointestinal ulcer, or tricho-hepato-enteric-syndrome). The gene discussed is IER3; the disease is ulcerative colitis.