Environmental Factors Associated with Risk of Crohn’s Disease Development in the CCC-GEM Project

Background and aims To date, it is unclear how environmental factors influence Crohn’s Disease (CD) risk and how they interact with biological processes. This study investigates the association between environmental exposures and CD risk and evaluates their association with pre-disease biomarkers. Methods We studied 4,289 healthy first-degree relatives (FDRs) of CD patients from the Crohn's and Colitis Canada - Genetic, Environmental, Microbial (CCC-GEM) project. Regression models identified environmental factors associated with future CD onset and their association with pre-disease biological factors, including altered intestinal permeability measured by urinary fractional excretion of lactulose to mannitol ratio(LMR); gut inflammation via fecal calprotectin(FCP) levels; and fecal microbiome composition through 16S rRNA sequencing. Results Over a 5.62-year median follow-up, 86 FDRs developed CD. Living with a dog between ages 5-15 (HR=0.62; 95% CI=0.40-0.96; P = .034), and living with a large family size in the first year of life (HR=0.43; 95% CI=0.21-0.85; P = .016) were associated with decreased CD risk; whereas having a bird at the time of recruitment (HR=2.78; CI=1.36-5.68; P = .005) was associated with an increased CD risk. Furthermore, living with a dog was associated with reduced LMR, altered relative abundance of multiple bacterial genera, and increased Chao1 diversity; while bird owners had higher FCP levels. Large family during participants' first year of life was associated with altered microbiota composition without affecting FCP or LMR. Conclusion This study identifies environmental variables associated with CD risk. These variables were also associated with altered barrier function, subclinical inflammation, and gut microbiome composition shifts, suggesting potential roles in CD pathogenesis.