Nevertheless, Foxp3 expression is essential for the suppressive function of Treg cells, because loss-of-function foxp3 mutations result in strong hyper-lymphoproliferative disease and multi-organ autoimmunity in humans (IPEX syndrome, immune dysregulation, polyendocrinopathy, enteropathy, X-linked) [20], [21] and mice (scurfy mice) [22], [23]. Here, FOXP3 is linked to polyendocrinopathy.