The National Institute of Neurological Disorders and Stroke (NINDS), the National Institute of Child Health and Human Development (NICHD) and the National Institute of Mental Health (NIMH) have entered into a public-private partnership with the International Rett Syndrome Association (IRSA) and the Rett Syndrome Research Foundation (RSRF) to jointly sponsor this funding opportunity announcement with set-aside funds aimed at understanding and/or treating Rett Syndrome (RTT). This FOA invites investigator-initiated grant applications to conduct research relevant to the basic understanding, cure, prevention and improved treatments for RTT and its complications.