PROJECT SUMMARY Schizophrenia (Scz) is a common and debilitating neurodevelopmental disorder. However, the genetic architecture of Scz is highly complex, impeding research progress. Recently, the Scz Exome Meta-Analysis (SCHEMA) Consortium has identified genes with ultra-rare coding variants that each confer substantial risk for Scz. We hypothesize that the presence of these rare variants in human induced pluripotent stem cells (hiPSCs) will lead to neuronal phenotypes relevant to Scz. The PI, Dr. Pan Li, has extensive experience with gene editing and iPSCs, including development of an improved method for seamless introduction and removal of mutations into hiPSCs. She has previously focused on neurodegenerative disorders, but with this application proposes to change to study of Scz. This transition is facilitated by the location of her lab in the Division of Neurobiology, which has a long track record of research into major mental illnesses and of highly collaborative research using iPSCs (eg the HD iPSC Consortium). In Specific Aim 1, isogenic hiPSC lines with protein truncating variants associated with Scz will be genetically engineered by CRISPR-assisted homologous recombination to generate panels of iPSC lines, with each isogenic line bearing a different N-terminal protein truncating point mutation. Knockdown and overexpression rescue experiments will determine whether there is loss of protein expression and thus loss of gene function. In Specific Aim 2, the effect of mutations on gene and protein expression will be studied using RNA seq and quantitative proteomics. In Specific Aim 3, the effects of mutations on synaptic and electrophysiological phenotypes will be delineated. We hypothesize that understanding the cellular phenotypes and altered signaling pathways evoked by the SCHEMA mutations will clarify the cellular pathogenesis of subtypes of schizophrenia, and provide potential therapeutic targets.