Distribution of monogenic VEOIBD by age of diagnosis and monogenic aetiology identified. [A] Proportion of patients with monogenic VEOIBD by age at diagnosis. Monogenic VEOIBD was identified in 22.0% of patients with infantile-onset IBD compared with 4.6% of patients with IBD diagnosed at age 2 to <6 years. [B] Further stratification of infantile-onset disease group identified monogenic VEOIBD in 42.9% of patients diagnosed at <6 months, 41.7% diagnosed from 6 months to <12 months, and 4.5% diagnosed from 12 to <24 months. [C] Distribution of the 17 cases of monogenic VEOIBD identified in this cohort. IL10 signaling defects were most common, followed by chronic granulomatous disease, IPEX syndrome, and trichohepatoenteric syndrome. VEOIBD, very early onset inflammatory bowel disease.