Previously, much emphasis has been put on the importance of the FKH of Foxp3 since mutations that lead to immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome were identified within the FKH [14] and mutations disrupting FKH function caused dysregulation of key TReg functional genes [18]. Here, FOXP3 is linked to polyendocrinopathy.