Genetic deficiencies of the transcription factor Foxp3, the Treg master regulator, results in the fatal systemic autoimmune diseases, immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) in humans and Scurfy in mice (32–34). This evidence concerns the gene FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.