Support for this hypothesis comes from a patient who carried loss-of-function mutations in FAS, UNC13D, and XIAP. He was not included in this study because the genetic and clinical complexity of his picture fulfilled the diagnostic criteria of ALPS but also shared features of FHL and X-linked lymphoproliferative disease (Boggio E. et al, submitted). The gene discussed is XIAP; the disease is autoimmune lymphoproliferative syndrome.