Mono- or biallelic germline variants in FAS (locus 10q23.31, encodes CD95), FASL, (locus 1q24.3, encodes CD95L) and CASP10 (locus 2q33.1, encodes caspase 10), can cause different subtypes of ALPS. The gene discussed is FAS; the disease is autoimmune lymphoproliferative syndrome.