ObjectiveTo conduct a two-sample Mendelian randomization (MR) study to assess the bidirectional causal relationship between multiple sclerosis and inflammatory bowel disease. MethodsWe performed two-sample bidirectional MR analysis using publicly available genome-wide association study (GWAS) data. The primary analysis method used was the inverse variance weighted (IVW) method, with MR-Egger weighted median as a supplementary analysis. Sensitivity analyses were conducted. ResultsIVW, weighted median, and weighted mode all supported a causal relationship between multiple sclerosis and an increased risk of ulcerative colitis (OR=1.07, 95%CI 1.01 to 1.13, P=0.018), while no association was found between multiple sclerosis and Crohn's disease. Sensitivity analyses suggested that the study results were not affected by pleiotropy. ConclusionGenetic predisposition to multiple sclerosis is associated with an elevated risk of developing ulcerative colitis but not Crohn’s disease.
