However, FoxP3 holds a pivotal role to regulatory T cell function, as evidenced by the X-Linked syndrome of immune dysregulation, polyendocrinopathy, and enteropathy (IPEX) caused by a mutation in the FoxP3 gene leading to large amounts of polyclonal T-cell activation and tissue infiltration (21, 22). Here, FOXP3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.