In mice, conditional deletion of Foxp3 in CD4+ T cells leads to fatally lymphoproliferative autoimmunity, which includes high IgE levels, enteropathy, type 1 diabetes and failure to thrive, while ectopic expression of Foxp3 can re-program conventional CD4+ T cells as anti-inflammatory Treg cells (75). The gene discussed is FOXP3; the disease is Failure to thrive.