Deficiency in Treg number or function leads to a group of disorders known as ‘Tregopathies’, the prototype condition being IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) caused by mutations in FOXP3 gene. The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.