X-linked lymphoproliferative syndrome (XLP) is typified by vulnerability to Epstein-Barr virus (EBV) infection, dysgammaglobulinemia, and lymphoma – mutations in SH2D1A and XIAP genes are implicated, affecting the immune cell functions including NK cell and T cell activities (158). The gene discussed is XIAP; the disease is X-linked lymphoproliferative disease.