This dependence is compellingly illustrated by the fact that loss of function of FOXP3 leads to the development of the fatal autoimmune lymphoproliferative disorder IPEX (immunodysregulation, polyendocrinopathy, and enteropathy, X-linked) syndrome [1,2]. The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.