Impairment of central tolerance by inherited defects of thymic development leads to syndromes including the autoimmune lymphoproliferative syndromes (ALPS), caused by failure of the extrinsic activation-induced cell death pathways (mutations in FAS, FASLG, and FADD), and autoimmune polyglandular syndrome (APS) 1, caused by mutations in AIRE. Here, FASLG is linked to autoimmune lymphoproliferative syndrome.