Association Between Inflammatory Bowel Disease and Atopic Dermatitis: A Two-Sample Mendelian Randomization Study

To The Editors, Inflammatory bowel disease (IBD) is a type of idiopathic inflammatory disease including Crohn's disease and ulcerative colitis. Atopic dermatitis (AD) is a common inflammatory skin disorder. Recent studies indicated that the incidence and prevalence of IBD and AD are strongly related,1 and a bidirectional relationship was found through a meta-analysis.2 Mendelian randomization (MR) is an excellent method that uses genetic variants as instrumental variables to assess causal relationships between chronic diseases. Here, we performed a 2-sample MR analysis for the association between IBD and AD. The raw data were collected from OpenGWAS database (https://gwas.mrcieu.ac.uk/). For IBD, we extracted the result of an analysis by Liu et al from 9 GWAS studies with 34,652 subjects to generate the instrumental variables (IVs; ieu-a-31).3 For AD, the data by Ishigaki et al from 28 GWAS studies with 212,036 subjects were used in the exposure datasheet...