XIAP and immunodeficiency disease: Finally, some IEI, also classified as combined immunodeficiencies, can share with IPEX syndrome signs of enteropathy or widespread autoimmunity early in life, with or without Treg impairment, but with clear defects in other T- and B-cell subsets and additional manifestations strictly related to the consequent immunodeficiency (e.g., mutations in RAG1, RAG2, CD3G, NEMO, WASP, ARPC1B, XIAP, NLRC4, STAT5b, NFKBIA, and TTC7A) (52, 80).