CD4 and polyendocrinopathy: Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is caused by mutations in FOXP3 (Forkhead-Box-Protein P3), a transcription factor that is expressed in a subset of thymic CD4+ T-lymphocytes which are required to maintain tolerance, and prevent autoimmune diseases (5, 6).