Overexpression of four factors (Oct4, Sox2, Klf4, Myc, or Oct4, Sox2, Nanog, Lin28) reprograms somatic cells to become induced pluripotent stem cells (iPSCs). Reprogramming accompanies genetic and epigenetic changes. We will investigate the molecular mechanism of somatic cell reprogramming. iPSCs provide an incredible resource for cell-based therapy, in vitro disease model and screening drugs. We apply the iPSCs to investigate one of the most prevalent female mental retardation disorders called Rett syndrome.