This study explored the causal and molecular overlap among Crohn’s disease (CD), celiac disease (CeD), and ankylosing spondylitis (AS). Bidirectional Mendelian randomization revealed significant causal associations between each disease pair. Transcriptomic analyses identified three consistently upregulated hub genes—P2RY8, ITGAL, and GPR65—across all conditions, which were validated in independent datasets and inflammatory cell models. Functional enrichment suggested these genes are involved in immune signaling and mucosal inflammation. Regulatory network and molecular docking analyses further highlighted Trichostatin A as a potential therapeutic agent. These findings reveal shared genetic and immune-related mechanisms, offering novel targets for cross-disease treatment strategies.