FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome: In FOXP3, loss of dimerization capacity as a result of an in-frame single amino acid deletion in the leucine zipper domain results in an immunological disorder known as IPEX syndrome (MIM 304790), with disease severity comparable to that resulting from loss of DNA-binding activity in FOXP3 [25, 26].