FOXP3 and polyendocrinopathy: Furthermore, a FOXP3 splice site mutation causing exon 7 skipping and two different mutations in FOXP3 exon 7 have been identified in patients with immune dysregulation, polyendocrinopathy, enteropathy, and X-linked (IPEX) syndrome, a rare genetic disorder that causes severe autoimmune disease in children [132,134,135], suggesting that exon 7 has an important role in the suppressive function of FOXP3 [121].