XIAP and agammaglobulinemia: XLP1 (due to mutations of the SH2D1A gene) affects cytotoxic T and NK cell function. Affected males are at high risk for fulminant infectious mononucleosis, HLH, EBV-driven lymphoma, bone marrow aplasia, and hypogammaglobulinemia. XLP2 (with mutations of XIAP) is characterized by increased incidence of HLH and inflammatory disease (especially of the gut), but not of EBV-related lymphoma