IGF-1 is an FDA approved, commercially available compound that crosses the blood-brain barrier and has beneficial effects on synaptic development by promoting neuronal cell survival, synaptic maturation, and synaptic plasticity. IGF-1 is effective in reversing mouse and neuronal models of Rett syndrome and Phelan McDermid syndrome, both single gene causes of ASD and may therefore be effective in treating autism spectrum disorders (ASD) more broadly.