FAS and Immunodeficiency: Finally, the close association of autoimmunity and immunodeficiency is highlighted by two immunodeficiencies characterized by increased autoimmune phenomena: the autoimmune lymphoproliferative syndrome (ALPS) and the Kabuki syndrome (KS); the former is marked by organomegalies and by the presence of somatic or germline mutations of genes involved in apoptosis (i.e., FAS, FASL, CASP10, CASP 8, NRAS, or KRAS); KS is marked by malformations and intellectual disability, and is caused by mutations in the KDM6A or KMT2D genes, which are involved in tolerance and immune system maturation [29,30].