In the absence of SAP and EAT-2, there is loss of activating function through SLAM family receptors, most notably in humans with mutations in the SH2D1A (SAP) gene who develop X-linked lymphoproliferative disease (XLP), a condition characterized by the failure to clear persistent viral infections such as EBV, lymphoid hyperplasia, and lymphoma development [8], [12]. The gene discussed is SH2D1B; the disease is X-linked lymphoproliferative disease.