Parental inflammatory bowel disease and autism in the offspring: Triangulating the evidence using four complementary study designs.

ABSTRACT Importance Evidence linking parental diagnoses of inflammatory bowel disease (IBD) with offspring autism is inconclusive. Objective To investigate associations between parental diagnoses of IBD and offspring autism and elucidate their underlying aetiology by conducting four complementary studies. Design, Setting and Participants (1) Nationwide population-based cohort study using Swedish registers to examine associations between parental IBD diagnoses and autism diagnoses in offspring, (2) Linkage disequilibrium (LD)-score regression to estimate the genetic correlation between the phenotypes. (3) Polygenic risk score (PRS) analyses in the Avon Longitudinal Study of Parents and Children (ALSPAC) to investigate associations between maternal genetic liability to IBD and autism factor mean score in offspring. (4) Two-sample Mendelian randomization (MR) to assess bidirectional causal links between genetic liability to IBD and autism. Results Observational analyses provided evidence of an association between parental IBD diagnoses and offspring autism diagnosis in mutually adjusted models (maternal: OR= 1.32; 95% CI: 1.25 to 1.40; p Conclusions and relevance Triangulating evidence from a nationwide register-based cohort study, genetic correlation, polygenic risk score analyses and MR, we found evidence of a potentially causal link between parental, particularly maternal, diagnoses and genetic liability to IBD and offspring autism. Perinatal immune system dysregulation, micronutrient malabsorption and anaemia may be implicated.