Back in 1999, the Methyl-CpG binding Protein 2 (MECP2) gene was discovered as the genetic cause of Rett syndrome (Amir et al., 1999); since then, hundreds of different mutations of the gene have been associated with RTT and less frequently with other forms of intellectual disabilities, such as autism, schizophrenia, mental retardation and Angelman-like syndrome (Chahrour and Zoghbi, 2007). Here, MECP2 is linked to Intellectual disability.