Lack of Causal Associations of Inflammatory Bowel Disease with Parkinson's Disease and Other Neurodegenerative Disorders

Background: Observational studies have indicated associations between inflammatory bowel disease (IBD) and neurodegenerative diseases, including Parkinson's disease (PD). Objective: To evaluate the causal associations of IBD with PD and other selected neurodegenerative disorders using updated data. Methods: Bidirectional two-sample Mendelian randomization studies using genome-wide association studies summary statistics of IBD and PD. Results: We found a lack of evidence for the causal association of IBD on PD (odds ratio [OR], 1.014; 95% confidence interval [CI], 0.967-1.063; P = 0.573). Reverse analysis also indicated no evidence of a causal effect for PD on IBD (OR, 0.978; 95% CI, 0.910-1.052; P = 0.549). The causality between IBD and Alzheimer's disease, amyotrophic lateral sclerosis, and multiple sclerosis was unfounded (all P > 0.05). Conclusions: The updated analyses provide no clear evidence for causal associations of IBD with PD or the other three neurodegenerative diseases. Potential confounders might contribute to the previously observed associations, and further investigations are warranted. (c) 2023 International Parkinson and Movement Disorder Society.