SH2D1A and X-linked lymphoproliferative syndrome: Notably, 2B4 and NTBA dysfunction was described to be associated with a severe form of immunodeficiency, the X-linked lymphoproliferative syndrome type 1 (XLP-1), caused by mutations in SH2D1A, the gene encoding the signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) (148).