Autism spectrum disorders (ASD) now affect an astounding 1 in every 88 children in America (CDC Report, 2012). Individuals with ASD show symptoms that include deficits in communication and social interactions as well as repetitive behaviors. A number of genes associated with synapse formation and function are mutated in patients with ASD, suggesting autism is a disorder of the synapse. ASD is a debilitating lifelong medical condition for patients and their caregivers, so finding new ways to diagnose, treat and prevent ASD remains one of the biggest challenges in neuroscience. In unpublished studies, we made a revolutionary discovery that directly addresses this challenge. Specifically, we found that a single molecular mechanism-transcription elongation-can be directly linked to expression of a large number (>34) of synapse-associated ASD candidate genes. Elongation is the process where RNA polymerase II, in coordination with numerous elongation factors, traverses DNA to generate a gene transcript. This process has never been studied in the context of any brain disease. Here, we will test the novel hypothesis that deficits in transcription elongation can reduce expression of ASD candidate genes and impair synapse function. This hypothesis is strongly supported by clinical data from ASD patients and by our unpublished experiments with cultured cortical neurons. To test this hypothesis, we will determine the extent to which genes associated with the elongation machinery regulate a) expression of numerous ASD candidate genes, b) synapse function and c) ASD-like behaviors in mouse models. We noticed that at least 10 genes associated with transcription elongation are mutated in patients with ASD. We will determine the extent to which these 10 mutations impair transcription elongation and expression of known ASD genes in neurons. Lastly, we describe a novel approach that will allow us to identify chemicals commonly found in the environment that impair