Further proof for the significance of Foxp3 in Treg differentiation and function came from studies analyzing mutations associated with the nonfunctional expression of Foxp3 in humans, causing IPEX syndrome (immune dysregulation polyendocrinopathy and enteropathy), which requires bone marrow transplantation in early childhood [25]. Here, FOXP3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.