Among the genetic mutations associated with a susceptibility to autism are those found in two families of genes, the neurexins and the neuroligins. Neurexins and neuroligins are protein components of the synapse, the specialized junction between neurons where communication between cells occurs. Neurexins are present in the presynaptic cell (the cell sending information), and neuroligins are present on the postsynaptic cell (the cell receiving information). Because neurexins and neuroligins recognize and bind each other very specifically, they are thought to be involved in the formation and maintenance of synapses, and to be involved in the specification of particular synaptic connections between particular cells of the brain. In this study, Dr. Comoletti and colleagues will study the molecular basis of the interaction between neurexins and neuroligins: by mutating various regions of each gene, they will determine which parts of the encoded proteins are important for these physical interactions to occur. This research will further our understanding of how neurexins and neuroligins function at the synapse, and may provide valuable information for the identification of drugs that could be used to target these proteins.