FAS and autoimmune lymphoproliferative syndrome: Autoimmune lymphoproliferative syndrome (ALPS) is a rare nonmalignant lymphoproliferative disorder associated with increased CD3+TCRαβ+CD4-CD8- double-negative T (DNT) cells and disorder of impaired lymphocyte apoptosis associated with defects in the FAS signaling cascade.17,18 The diagnostic criteria for ALPS were created by consensus in 1999 by investigators at the National Institutes of Health and revised in 2010 by a group of international investigators.