FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome: The critical importance of FOXP3 is demonstrated by mutations in the FOXP3 gene, which result in severe Treg dysfunction and manifest as immune dysregulation, polyendocrinopathy, and enteropathy, X-linked syndrome (IPEX),2,3 a severe multiorgan autoimmune condition.