Rett syndrome (RTT) is a devastating disease that affects 1 in every 10,000 children born in the United States, primarily females. RTT patients undergo apparently normal development until 6-18 months of age, followed by impaired motor function, stagnation and then regression of developmental skills, hypotonia, seizures and a spectrum of autistic behaviors. Rett syndrome is a rare disease that shares certain pathways with major developmental disorders such as autism and schizophrenia, increasing the potential impact. There is no cure for Rett syndrome and the animal model does not entirely recapitulate the human disease. Thus, having the possibility to screen drugs directly in human neurons is a major milestone.