FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome: In pediatric patients, severe immune dysregulation in IPEX syndrome (Immune dysregulation, polyendocrinopathy, enteropathy, X‐linked syndrome), caused primarily by mutations in the FOXP3 gene located on the X chromosome, leads to defective regulatory T cell function and widespread autoimmunity.