Deficiency of Treg cells caused by mutations of Foxp3 results in early onset autoimmune disease as demonstrated in Foxp3 mutant scurfy mice and humans with IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome (32, 33). The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.