It has been reported that genes responsible for primary immunodeficiency diseases (PID), including interleukin-10 (IL-10) or IL-10 receptor (IL-10R) deficiency, X-linked inhibitor of apoptosis (XIAP) deficiency, immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, Wiskott–Aldrich syndrome (WAS), chronic granulomatous disease (CGD), and common variable immunodeficiency, are involved in the molecular pathogenesis of pediatric IBD (5–7). The gene discussed is XIAP; the disease is inflammatory bowel disease.