Autism spectrum disorders (ASD) can be conceived of as having multiple distinct genetic risk genes, one of which is SHANK3 on the end of chromosome 22. The loss of one form of SHANK3 causes a form of ASD known as Phelan McDermid Syndrome (PMS), which comprises 0.5-1% of all ASD cases. PMS is characterized by ASD, as well as global developmental delay, motor skills deficits, and delayed or absent speech. To date, no studies have comprehensively described the behavioral features of PMS and few have characterized ASD symptom domains in PMS according to best-practice guidelines. The aim for this project is to use a comprehensive assessment battery to characterize the behavioral, cognitive, language, sensory, and motor deficits in PMS. This work will also establish a patient population that can be followed over time using repeated longitudinal assessments to clarify the natural history of the disorder. We expect that the knowledge gained from completing this study will aid in understanding the range of deficits in PMS and establishing a neurobiological footprint of the disorder to identify important targets for intervention. If successful, this project will help to establish the foundation for future clinical trials in PMS and in other ASD-related disorders that share its signaling pathways.