Duplication Versus Deletion Through the Lens of 15q13.3: Clinical and Research Implications of Studying Copy Number Variants Associated with Neuropsychiatric Disorders in Induced Pluripotent Stem Cell-Derived Neurons.

Copy number variants (CNVs), involving duplication or deletion of susceptible intervals of the human genome, underlie a range of neurodevelopmental and neuropsychiatric disorders. As accessible in vivo animal models of these disorders often cannot be generated, induced pluripotent stem cell (iPSC) models derived from patients carrying these CNVs can reveal alterations of brain development and neuronal function that contribute to these disorders. CNVs involving deletion versus duplication of a particular genomic interval often result both in distinct clinical phenotypes and in differential phenotypic penetrance. This review initially focuses on CNVs at 15q13.3, which contribute to autism spectrum disorder, attention deficit/hyperactivity disorder, and schizophrenia. Like most CNVs, deletions at 15q13.3 usually cause severe clinical phenotypes, while duplications instead result in highly variable penetrance, with some carriers exhibiting no clinical phenotype. Here, we describe cellular and molecular phenotypes seen in iPSC-derived neuronal models of 15q13.3 duplication and deletion, which may contribute both to the differential clinical consequences and phenotypic penetrance. We then relate this work to many other CNVs involving both duplication and deletion, summarizing findings from iPSC studies and their relationship to clinical phenotype. Together, this work highlights how CNVs involving duplication versus deletion can differentially alter neural development and function to contribute to neuropsychiatric disorders. iPSC-derived neuronal models of these disorders can be used both to understand the underlying neurodevelopmental alterations and to develop pharmacological or molecular approaches for phenotypic rescue that may suggest leads for patient intervention. Top: Deletion versus duplication of the same genomic interval results in different clinical phenotypes and degrees of phenotypic penetrance. Example findings schematized. Bottom: iPSC-derived neurons from individuals with these CNVs involving deletion versus duplication likewise often differential phenotypes (increases or decreases) in the categories shown. Figure created with BioRender.com.