SH2D1A and SH2D1B are small, adaptor proteins with a single SH2-domain that play important signal transduction roles mediated by the signaling lymphocytic activation molecule (SLAM) family receptors. SH2D1A (also called SAP or SLAM-associated protein) is frequently mutated in patients with X-linked lymphoproliferative disease (Duncan’s disease), which is characterized by extreme susceptibility to Epstein-Barr virus; approximately 50 different SH2D1A mutations have been reported to date). The single SH2D1B gene in humans (also called EAT-2 or Ewing's sarcoma's/FLI1-activated transcript 2) is present as a pair of duplicated EAT-2A and EAT-2B genes with identical genomic organization in mouse and rat.