Molecular Genetic Architecture of Monogenic Pediatric IBD Differs from Complex Pediatric and Adult IBD

Inflammatory bowel disease (IBD) manifests as a complex disease resulting from gene–environment interactions or as a monogenic disease resulting from deleterious mutations. While monogenic IBD is predominantly pediatric, only one-quarter of complex IBD is pediatric. In this study, we were the first to systematically compare genetic architecture between monogenic and complex pediatric and adult IBD on genetic and molecular pathway levels. Genes reported as causal for monogenic pediatric IBD and related syndromes and as risk factors for pediatric and adult complex IBD were analyzed using CytoScape and ClueGO software tools to elucidate significantly enriched Gene Ontology (GO) terms. Despite the small overlap (seven genes) between monogenic IBD genes (85) and complex IBD loci (240), GO analysis revealed several enriched GO terms shared between subgroups (13.9%). Terms Th17 cell differentiation and Jak/STAT signaling were enriched in both monogenic and complex IBD subgroups. However, primary immunodeficiency and B-cell receptor signaling pathway were specifically enriched only for pediatric subgroups, confirming existing clinical observations and experimental evidence of primary immunodeficiency in pediatric IBD patients. In addition, comparative analysis identified patients below 6 years of age to significantly differ from complex pediatric and adult IBD and could be considered a separate entity.