Treg cells critical role in hair regeneration is clinically illustrated in the IPEX (immune dysregulation, polyendocrinopathy, enteropathy X-linked) syndrome, a rare genetic disorder caused by a mutation in the human FOXP3 gene causing aberrant Treg cell development and systemic autoimmune dysfunction including alopecia universalis, a severe form of hair loss characterized by the loss of all hair52,120. This evidence concerns the gene FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.