Abstract: We previously confirmed that loss of the X-linked gene NEXMIF results in social behavior deficits and intellectual disability. Although only male NEXMIF patients were initially diagnosed, 72% of recent clinical cases are female individuals of NEXMIF haploinsufficiency demonstrating similar neurological features. To further study the role of NEXMIF, we generated a Nexmif knockout (KO) mouse model which displays neuronal deficits, impaired learning and memory, repetitive behaviors, and social and communication defects. In line with female cases, heterozygous (HET) female mice show behavioral impairments similar to the KO male mice. HET mouse brains contain a mosaic of neurons of both NEXMIF-expressing wild-type (WT) and NEXMIF-lacking (KO) neurons. Due to the process of X chromosome inactivation (XCI), null cells in HET mice retain a silenced copy of WT Nexmif on the inactive X. Inhibition of XCI-promoting factors (XCIFs) has been shown effective in reactivating X-linked target genes, such as Mecp2. However, the experimental approaches and the biological effect of X chromosome reactivation (XCR) in the context of Nexmif-associated deficits have yet to be investigated. We aim to explore the feasibility of Nexmif gene reactivation via XCIF inhibition induced by small molecules including shRNAs and chemical compounds, and also establish a CRISPR-based strategy to specifically reactivate the Nexmif gene. We will then determine the rescue effects following Nexmif gene dosage restoration on neuronal morphology and behavioral deficits in HET female mice.