In 2001, the mutation of a gene encoding the transcription factor Forkhead box P3 (Foxp3) was identified as the disease-causative event underlying IPEX (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked syndrome) syndrome in humans and the Scurfy phenotype in mice (8–10). The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.