Autism spectrum disorders (ASDs) are thought to involve changes in synaptic plasticity, or the remodeling of neural connections during development. Synaptic plasticity is crucial for learning and memory as well as the development of brain structures. Mutations in genes associated with a particular modulator of synaptic plasticity, the NMDA neurotransmitter receptor, have been shown to contribute to mental retardation, fragile X syndrome, and tuberous sclerosis complex, all of which are conditions associated with ASDs. These genes might therefore contribute to ASD by disrupting a molecular pathway common to all of these disorders, and affecting synaptic plasticity. In this study, six genes involved in NMDA receptor-dependent synaptic plasticity will be examined in a study of Iranian families with ASD. The sequence of these genes will be examined in DNA from related individuals, both typical and with ASD, to determine whether sequence variations in any of these genes are associated with ASD. Determining whether genes involved in synaptic plasticity play a role in ASD may identify new gene variants conferring a risk of autism, as well as further our understanding of synaptic dysfunction in autism.