In the case of rare diseases, such as X-linked autoimmunity–allergic dysregulation syndrome (XLAAD)/immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX), the patients lack CD25+ Tregs and could develop severe eczema, eosinophilia, elevated IgE, and food allergies, which indicated that Tregs were crucial for the development of allergic diseases [27]. The gene discussed is IGHE; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.