We previously identified TNFSF15 as the most significant susceptibility gene at non-HLA loci for both primary biliary cirrhosis (PBC) and Crohn's diseases (CD) in the Japanese population. The aim of this study is to identify further disease susceptibility genes shared by PBC and CD. We selected 15 and 33 genetic variants that were significantly associated with PBC and CD, respectively, based on previously reported genome-wide association studies of the Japanese population. Next, an association study was independently performed for these genetic variants in CD (1312 CD patients and 3331 healthy controls) and PBC (1279 PBC patients and 1015 healthy controls) cohorts. Two CD susceptibility genes, ICOSLG rs2838519 and IL12B rs6556412, were also nominally associated with susceptibility to PBC (P=3.85 × 10 -2 and P=8.40 × 10 -3, respectively). Three PBC susceptibility genes, CXCR5 rs6421571, STAT4 rs7574865 and NFKB1 rs230534, were nominally associated with susceptibility to CD (P=2.82 × 10 -2, P=3.88 × 10 -2 and P=2.04 × 10 -2, respectively). The effect of ICOSLG and CXCR5 variants were concordant but the effect of STAT4, NFKB1 and IL12B variants were discordant for PBC and CD. TNFSF15 and ICOSLG-CXCR5 might constitute a shared pathogenic pathway in the development of PBC and CD in the Japanese population, whereas IL12B-STAT4-NFKB1 might constitute an opposite pathogenic pathway, reflecting the different balance between Th1 and Th17 in the two diseases.
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