Examples include the autoimmune lymphoproliferative syndrome (ALPS), caused by a defective lymphocyte apoptosis mediated by the Fas/Fas ligand pathway [7], and deficiencies in ADA2 (DADA2), an enzyme involved in purine metabolism, both cases having impairment of marrow precursors and immune system function [8, 9]. The gene discussed is ADA2; the disease is autoimmune lymphoproliferative syndrome.