Although the functional role of all FOXP3 isoforms is not yet fully understood, it is interesting that patients with frameshift mutations on FOXP3 resulting in exon 2 deletion but retaining expression of FOXP3Δ2, have milder forms of IPEX (25). Here, FOXP3 is linked to immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.