The proportion of Tregs, evaluated by flow cytometry, may be highly variable: low or absent FOXP3-expressing cells can be considered as highly suspicious for IPEX syndrome; however, several FOXP3 mutations demonstrate deleterious effects on the protein function, without preventing protein expression (27, 33). The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.