FOXP3 and polyendocrinopathy: The importance of FOXP3 for efficient regulation of the immune system is best illustrated by the development of lethal lymphoproliferative disease in both mice and humans with genetic deficiencies in FOXP3, known respectively as scurfy and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome5, 6, 7.