FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome: The IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome due to FOXP3 gene mutations is unequivocal evidence that deficiency or dysfunction of nTreg cells can be a primary cause of not only autoimmune diseases such as type 1 diabetes, but also inflammatory bowel disease and allergy in humans.