Using WES in a selected cohort of VEO-IBD patients in whom no Mendelian disorders were clinically suspected, we identified five patients with rare, pathogenic mutations in four PID-associated genes (XIAP, CYBA, CYBB, and SH2D1A), one of which was a de novo mosaic variant (p.W380X in CYBB). The gene discussed is XIAP; the disease is inflammatory bowel disease.