Within this group, those that course with autoimmunity are the result of defects in regulatory T cell development and/or function (8–10), whose hallmark disease is immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX), a disease caused by mutations in the FOXP3 gene (11–13). Here, FOXP3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.