Furthermore, X-linked lymphoproliferative syndrome (XLP), which is characterized by a high susceptibility to Epstein-Barr virus (EBV) infection, is caused by mutation of the gene encoding either signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) or X-linked inhibitor of apoptosis (XIAP). This evidence concerns the gene XIAP and X-linked lymphoproliferative syndrome.