Whereas SAP-deficiency and CD27-deficiency predispose specifically to Epstein–Barr virus (EBV) infection and EBV-induced lymphoproliferative disorders, OX40-deficiency is associated with Kaposi's sarcoma induced by Kaposi's sarcoma herpesvirus3, 7. The gene discussed is TNFRSF4; the disease is Kaposi's sarcoma.