In vitro studies have described a high heterogeneity in the severity of functional impairments among Tregs from different IPEX patients [72]; moreover, a lack of correlation between the genotype and the phenotype has been reported, which reflects the complexity of FOXP3 interactions and the role of non-genetic factors in the clinical manifestations of the disease, such as environmental and epigenetic factors [73]. The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.