This was true for 24 WAS patients with mutations in WASP, for 19 XLP patients with mutations in BIRC4/XIAP, for 18 patients with X-SCID due to mutations in IL2RG, and for 16 patients with a class switch recombination defect (HIGM syndrome) due to mutations in CD40L/CD154. The gene discussed is XIAP; the disease is T-B+ severe combined immunodeficiency due to gamma chain deficiency.