FOXP3 Forkhead Domain Mutation and Regulatory T Cells in the IPEX Syndrome

To the Editor: The immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, a rare disorder characterized by multiorgan autoimmunity, often results in death in infancy.1 The IPEX syndrome results from mutations in the forkhead box P3 (FOXP3) gene, which encodes a transcriptional repressor considered to be the master regulator of differentiation in CD4+ regulatory T (Treg) cells.2,3 Multiple FOXP3 mutations resulting in a range of clinical outcomes have been characterized.1–3 Since neither genetic sequencing nor protein expression correlates reliably with clinical manifestations in the IPEX syndrome,4 identification of the functional consequences of individual mutations is critical to . . .