Project Summary Neuro-developmental disorders (NDD) are often caused by genetic mutations that lead to haploinsufficiency, or a loss-of-gene function. Mutations that cause haploinsufficiency of neurodevelopmental genes affect over 200,000 births each year, and commonly result in congenital malformations, intellectual disability, epilepsy and motor and behavioral impairments. While symptomatic treatments exist, for most conditions there are no treatments that directly correct the reduced levels of the haploinsufficient gene. Recent research by our group and others has revealed that many NDD-causing genes are normally under active repression by microRNAs, small, non-coding RNAs that function in gene silencing. This raises the possibility of removing this microRNA “brake” to increase gene expression and help restore normal function in NDD haploinsufficiency. We hypothesize that the expression of downregulated genes can be restored through steric-blocking antisense oligonucleotides (ASO) that specifically disrupt gene repression by microRNAs. Our preliminary data support this hypothesis and demonstrate that ASOs that prevent a particular microRNA from binding to STXBP1 (a common NDD-causing gene) robustly upregulate gene and protein expression. We propose a novel pipeline to systematically develop ASOs to treat genetic NDD. First, we will use bioinformatic and wet lab experimental approaches to identify and validate microRNAs that potently repress leading NDD-causing genes. Next, we will use a high-throughput microRNA reporter assays to screen ASOs that can relieve this microRNA-mediated gene repression. Third, we will take lead ASOs identified from the high-throughput screen and test them on neurons derived from patients with genetically-defined NDD to determine if they can rescue gene expression and function. Together, this work will establish pre-clinical efficacy for an ASO-based therapy targeting microRNAs to treat neurodevelopmental disorders arising from haploinsufficiency, and lay the groundwork for first-in-human applications.