Two-sample Mendelian randomization study reveals no causal relationship between inflammatory bowel disease and urological cancers

Abstract

Background: Relationships between inflammatory bowel disease (IBD) and urologic cancers have been identified in previous epidemiologic and observational studies, but causality remains uncertain. We tried to examine whether IBD was causally associated with urological cancers in this Mendelian randomization (MR) study. Methods: The causal relationship between IBD and its main subtypes and urological cancers were investigated using genome-wide association study (GWAS) data. To get a more reliable conclusion, all outcomes were then divided into training set and validation set. Eligible single-nucleotide polymorphisms (SNPs) were selected as instrumental variables (IVs) based on the assumptions of the MR analysis. The Inverse variance weighted (IVW) was applied as the main method with four others as complementary methods. Results: In this two-sample MR study, no genetic evidence for causal effect of IBD on urological cancers was found neither in the training set nor in the validation set using IVW method. Likewise, we did not observe any significant association of Crohn’s disease (CD) and ulcerative colitis (UC) on urological cancers. Results of other methods were in accordance with those of the IVW method. Conclusion: In this study, we confirmed that IBD was not a genetic causal risk factor for urological cancers in European population.