Integrative analysis of transcriptome-wide association study data and messenger RNA expression profiles identified candidate genes and pathways for inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a complex disease, resulting from abnormal immune response to intestinal tract microbiota in genetically susceptible individuals. Crohn's disease and ulcerative colitis (UC) are the two major types of IBD. Transcriptome-wide association study (TWAS) of IBD was first performed using a large-scale genome-wide association study summary data sets of IBD. The FUSION software was applied for TWAS, considering various tissues and cells. The genes identified by TWAS were then validated by the gene expression profiling data sets of IBD. The functional annotation and potential pathways of common differentially expressed genes were further subjected to gene ontology (GO) and pathway enrichment analysis. Integrative analysis of TWAS and messenger RNA (mRNA) expression data detected several tissues related common genes for UC, such as HLA-DRB1 (P = 0.024; mRNA expression ratio = 1.700) and TAP2 in colon (P = 0.047; mRNA expression ratio = 2.170). Further comparing the GO enrichment analysis results of TWAS and mRNA expression data, we identified 11 common GO terms for UC, such as plasma membrane (P value = 5.08 × 10 ) in intestinal tissues and immune response (P = 0.001) in peripheral blood. We also detected several common pathways for UC, including cell adhesion molecules (P = 0.003) in intestinal tissues, IBD (P = 0.049) in whole blood and phagosome (P = 0.0003) in peripheral blood. Our study results provide novel clues for understanding the genetic mechanism of IBD.