Fig. 1

Overview of this study. First, bidirectional MR was performed between PD and IBD, CD, UC. Second, a meta-analysis was conducted to integrate the causal effects between PD and IBD, CD, UC. We then performed PLACO and FUMA analyses to identify pleiotropic genes related to diseases. Moreover, drug target MR was conducted to estimate the causal effects of blood, brain, and intestinal druggable eQTLs on both PD and IBD to identify shared drug targets. Colocalization analyses verified the association between genes and disease, and gene function analysis illustrated the role of possible drug targets in biological processes. In the final step, we overlapped the results from the drug-target MR and FUMA to generate credible shared drug targets. MR, Mendelian randomization; PD, Parkinson’s disease; IBD, inflammatory bowel disease; CD, Crohn’s disease; UC, ulcerative disease; PLACO, pleiotropic analysis under composite null hypothesis; FUMA, functional mapping combining annotation of genetic associations; eQTL, expression quantitative trait locus