Cellular Basis for Genetic Susceptibility to Neurodevelopmental Disorders

Project Summary In contrast to syndromic CNVs such as the 17p11.2 deletion in Smith-Magenis syndrome, which mostly occur de novo and are highly penetrant, more recent studies have identified another class of CNVs that are frequently inherited and associated with variable expressivity. We previously identified a 520-kbp deletion on chromosome 16p12.1 that was associated with multiple neurodevelopmental outcomes, including intellectual disability/developmental delay (ID/DD), schizophrenia, autism, and epilepsy. This variant is inherited in >95% of cases from carrier parents manifesting neuropsychiatric features. We also found that affected children with the deletion were more likely to carry another large CNV or rare deleterious mutation elsewhere in the genome compared to carrier parents. Thus, while the 16p12.1 deletion confers significant risk for a range of disorders, the ultimate phenotypic trajectory is determined by variants in the genetic background. Functional assessment of the deletion would therefore provide a novel cellular paradigm for how the same variant confers susceptibility to distinct neurodevelopmental disorders. Here, we propose to study induced pluripotent stem cells (iPSCs) reprogrammed from peripheral blood mononuclear cells (PBMC) from three families with the 16p12.1 deletion, each including two or more affected children who manifest severe ID/DD or autism, carrier parents with neuropsychiatric features, and unaffected non-carrier parents. We will generate neural progenitor cells (NPCs) and differentiated cortical neurons from 12 individuals from three families, including affected children with either severe ID or autism, carrier parents with neuropsychiatric features, and non-carrier parents, and assess the impact of the deletion during different timepoints of neuronal development, including in neural progenitor cells (NPCs) and differentiated cortical neurons. In Aim 1, we will assess cellular properties of iPSC-derived NPCs, including cell proliferation, cell cycle, and apoptosis, and perform RNA sequencing of NPCs to identify gene expression changes and altered biological pathways. To assess the effect of the deletion independent of the genetic background, we will also generate a CRISPR/Cas-9 mediated deletion in an isogenic background and compare with controls. In Aim 2, we will differentiate the NPCs to cortical neurons, and perform a series of assays to measure changes in neuronal properties such as soma size, dendritic length and complexity, and synaptic development, as well as changes in action potential and firing properties. These results will be integrated with transcriptomic and available experimental data from Drosophila and X. laevis models for homologs of individual genes within the 16p12.1 region, in order to identify the mechanistic signatures associated with the 16p12.1 deletion. Overall, our proposal aims to establish human iPSC models for the 16p12.1 deletion as a cellular paradigm to understand risk for nosologically distinct disorders, and also provide a catalogue of associated neuronal phenotypes that can be compared with models of other CNVs and individual genes associated with neurodevelopmental disorders.