Single-gene IEIs generally refer to monogenic autoimmune disorders, such as immune dysregulation, polyendocrinopathy, and enteropathy with X-linked inheritance (or IPEX syndrome) caused by mutations in the forkhead box P3 (Foxp3), and APECED caused by mutations in the autoimmune regulatory transcription factor (AIRE) (71). The gene discussed is FOXP3; the disease is polyendocrinopathy.