Mutations in the X-linked gene encoding Methyl-CPG-binding protein 2 (MECP2) cause the neurodevelopmental disorder Rett syndrome [1], and MECP2 mutations and duplications have been documented in several other neurodevelopmental and neuropsychiatric disorders, such as X-linked mental retardation syndrome, severe neonatal encephalopathy, Angelman's syndrome, and in some cases of idiopathic autism [2]–[4]. This evidence concerns the gene MECP2 and X-linked syndromic intellectual disability.