ABSTRACT Copy number variations (CNVs) are a major cause of neurodevelopmental disorders, but their biological investigation and pharmacological targeting pose many challenges. Deletions locus are among the most frequent causes of autism spectrum disorder and duplications at the 16p11.2 (ASD). However, alterations in the corresponding protein networks, especially at key cellular sites for pathogenesis, have not been investigated in this or other CNVs. We propose to use compartment-specific neuroproteomics, combined with bioinformatics, super-resolution microscopy, and drug repurposing, to understand and alter dendritic excitability phenotypes in 16p11.2 mouse and induced pluripotent stem cell (iPSC) models. Based on our extensive preliminary data, we hypothesize that altered expression of PRRT2, which likely regulates the trafficking of a subset of ion channels and receptors, drives and abnormal complement of ion channels and receptor on the plasma membrane, leading to abnormal excitability, excitatory/inhibitory (E/I) balance, and network properties in 16p11.2 models and patients. These phenotypes may be reversed by targeting ion channel function using FDA- approved anti-epileptic drugs or ERK signaling using repurposed cancer drugs. Our collaborative team, which includes experts in neurodevelopmental disorders (Penzes), neuroproteomics (Savas), molecular pharmacology (Barbolina), and ion channel physiology (George) will employ a powerful and multidisciplinary combination of highly innovative methodologies to pursue the following Specific Aims: (1) To chart the developmental regulation and determine molecular mechanisms underlying abnormal excitability in dup and del mice and human neurons. (2) To chart the developmental profile and determine the molecular mechanisms underlying the role of PRRT2 as a driver of excitability and seizure phenotypes. (3) Pharmacological reversal of 16p11.2 del and dup phenotypes. This proposal will be the first to demonstrate that cellular subcompartment-specific proteomics combined with super-resolution microscopy, informed by highly penetrant monogenic disease genes within a CNV, can identify novel disease mechanisms. Such phenotypes could be reversed globally by targeting network hubs using repurposed drugs, opening novel strategies for the treatment of neurodevelopmental disorders.