SH2D1A and X-linked lymphoproliferative syndrome: Loss of function mutations of the SAP encoding gene SH2D1A causes X-linked lymphoproliferative disease type 1 (XLP-1), a primary immunodeficiency characterized by multiple defects in the T and NK cell compartments leading to EBV-triggered hemophagocytic lymphohistiocytosis (HLH), hypogammaglobulinemia, and predisposition to lymphomas (12).