Rett syndrome (RTT) is an X-linked neurodevelopmental condition primarily caused by loss-of-function mutations of the X-linked methyl-CpG-binding protein 2 gene (MECP2).1 The estimated global prevalence of RTT is approximately five to ten cases per 100,000 females (males are rarely affected).2 The classic phenotype of RTT is characterized by seemingly normal pre- and perinatal development until approximately 6 to 18 months of age, at which point affected individuals experience a severe developmental regression. Here, MECP2 is linked to Rett syndrome.