Defects in the gene coding for the Treg-specific transcription factor forkhead box protein P3 (Foxp3) lead to an aggressive and fatal autoimmune disorder known as immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) in humans and a comparable systemic lymphoproliferative disease in scurfy mutant mice [42,43]. This evidence concerns the gene FOXP3 and polyendocrinopathy.