Currently, this expanding group of disorders includes prototypical autoimmune lymphoproliferative syndrome (ALPS, OMIM #601859), which is caused by defects in the FAS pathway of apoptosis (FAS, FASLG, and CASP10), and RAS-associated autoimmune leukoproliferative disorder (RALD), which is caused by somatic mutations in NRAS or KRAS. Most patients harbor pathogenic variants in the FAS gene inherited in an autosomal dominant fashion (272). Here, FAS is linked to autoimmune lymphoproliferative syndrome.