However, there should be careful consideration of monogenic forms of inflammatory bowel disease (e.g., IL-10 signalling defects, immunodysregulation polyendocrinopathy enteropathy X-linked—IPEX [287]—syndrome, Wiskott–Aldrich syndrome or increasingly X-linked inhibitor of apoptosis—XIAP–deficiency] [240], which are IEI for which allo-HCT is appropriate. This evidence concerns the gene XIAP and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.