A double-blind, randomized, placebo controlled, phase 2 human clinical trial of Insulin-Like Growth Factor-1 (IGF-1) in children with a genetic cause of autism (Phelan McDermid Syndrome) is currently underway at the Seaver Autism Center for Research and Treatment at Mount Sinai. That study builds on previous work in a mouse model system of Phelan McDermid Syndrome which showed that IGF-1 treatment reversed the effects of disrupted glutamate signaling associated with impaired learning and memory. This Treatment Grant will expand the current study to add a cohort of children with autism but without Phelan McDermid Syndrome. IGF-1 is a commercially available compound that is known to promote synaptic maturation and plasticity. It has already been shown to reverse behavioral and physiological deficits associated with Rett Syndrome in mouse models and preliminary results in children with Rett syndrome are promising. Results from this trial are expected to provide evidence that IGF-1 is safe, well tolerated, and efficacious in targeting core symptoms of autism in children without Phelan McDermid Syndrome because of the potential that the glutamate signaling pathway is relevant to diverse forms of autism.