Therefore, it is extremely important to search for diagnostic markers that allow for the shortening of time for accurate diagnosis as well as a comprehensive analysis of genetic disorders contributing to the development and progression of many diseases classified as PID [161,162] One such molecule is the Foxp3 protein in which mutation causes the immunodysregulation polyendocrinopathy enteropathy X-linked syndrome (IPEX) classified as a monogenic disorder [163]. The gene discussed is FOXP3; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.