SH2D1A and X-linked lymphoproliferative syndrome: XLP1 is a rare and often fatal X-linked immunodeficiency disease caused by mutation of the SH2D1A gene, this gene encodes for a 128-amino acid protein (SAP), which is comprised of a 5-amino acid N-terminal sequence, a Src homology 2 (SH2) domain and a 25-amino acid C-terminal tail (6).