Autism spectrum disorders (ASD) are complex neurodevelopmental diseases. Using Rett syndrome (RTT) as an ASD prototype, we generated induced pluripotent stem cells (iPSCs). Neurons derived from RTT-iPSCs had fewer synapses and altered connectivity when compared to control neurons. In addition, we used drugs to rescue synaptic defects in RTT neurons, indicating that autistic neurons can be reverted. Our data provide evidence of a developmental window in an autistic syndrome, where potential therapies could be successfully employed. Moreover our model recapitulates early stages of a human neurodevelopmental disease and represents a promising cellular tool for drug screening, diagnosis and personalized treatment.