X-chromosome encoded transcription factor FOXP3 is necessary for the development and function of Tregs and humans with mutation leading to loss of function in the FOXP3 gene develop a fatal lymphoproliferative autoimmune disorder, IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) [4,5]. The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.