Peripheral FOXP3 expression was normal (CD127−/CD4+/CD25+/FOXP3+—396 cells—63%) and a pathogenic mutation in FOXP3 gene (c.1150G>A; p.Ala384Thr), confirmed the diagnosis of IPEX syndrome. This evidence concerns the gene CD4 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.