Initially, autosomal recessive CASPASE 8 mutations had been identified in patients presenting with features of autoimmune lymphoproliferative syndrome (ALPS) such as lymph node and spleen enlargement, FAS-mediated apoptosis defect, mild elevation of CD4- CD8- double negative T cells, and bacterial or/and viral infections. The gene discussed is FAS; the disease is autoimmune lymphoproliferative syndrome.