In mice on a non-autoimmune genetic background, constitutive genetic Foxp3 deficiency (6, 7) or acute Foxp3+ Treg cell ablation based on Foxp3-driven expression of a human diphtheria toxin receptor (DTR) (8–10) recapitulates many clinical features of the human IPEX syndrome, but the manifestation of β cell autoimmunity has not been reported. This evidence concerns the gene FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.