PROJECT SUMMARY/ABSTRACT Induced pluripotent stem cells (iPSCs) and human cerebral organoids are poised to provide insight into how brain development changes in individuals with neurodevelopmental disorders. Though the molecular fidelity of cortical organoids have been assessed relative to the primary fetal brain reference datasets, it is unknown how well cortical organoid phenotypes predict inter-individual differences in postnatal longitudinal brain growth. Identifying what in vitro phenotypes are related to in vivo traits will be useful for interpreting experiments implementing organoids to understand mechanisms of neurodevelopment disorders. To test this relationship, it is necessary to derive a population of iPSC lines from well-characterized individuals. This proposal uses iPSC- derived cerebral organoids from participants in the Infant Brain Imaging Study (IBIS) to test the relationship between organoid neuroepithelial bud structure and gene expression phenotypes to in vivo brain development and cognitive behavioral measurements. Specifically, this proposal uses 17 iPSC lines generated from 5 participants without a family history of neuropsychiatric disorders, 9 participants who had a sibling with ASD, and 3 participants with ASD, each with at least 2 brain MRI scans at 6, 12 and/or 24 months of age. All participants have Mullens Scale of Early Learning, Vineland Adaptive Behavior and Autism Diagnostic Observation Scale score at 24 months of age. 3 clones of each iPSC line were generated. To identify inter- individual differences between iPSC donors and within iPSC clones from the same individual, we will assess single cell gene expression and organoid structure across the differentiation. Single cell RNA sequencing will be performed after neuroepithelial buds form (14 days post differentiation) and neuronal maturation (84 days post differentiation). Intact organoid immunolabeling will be completed at these time points and earlier in neurogenesis (56 days post differentiation). When completed, this project will identify the strengths and limitations of cerebral organoids as reproducible, predictive models of human cortical development. This proposal seeks to leverage the rigorous coursework, mentorships, networks and technical training available at the University of North Carolina at Chapel Hill and through IBIS collaborators. By completing this proposal, the applicant will have the appropriate technical training and communication skills to become an independent investigator with a strong professional network in the field of neurodevelopment.