The diseases that share the largest number of genomic regions include CD and UC (BSN/APEH/MST1, C11orf30/LRRC32, C1orf81/KIF21B, CARD9, DAB2/PTGER4, GOT1/NKX2-3, IL10, IL23R, NAIP1/CYCSP42, PUS10, RCL1/JAK2, TNFSF15, ZGPAT, ZPBP2/GSDMB), followed by T1D and RA (AFF3/LONAF2, C4orf52/RBPJ, CTLA4, DKFZp667F0711, IL2RA, KIAA1109, PTPN22, RPS2P14/RSBN1, SH2B3/ATXN2, UBASH3A, ZPBP2/GSDMB). The gene discussed is PTGER4; the disease is type 1 diabetes mellitus.