Malan syndrome is a rare neurodevelopmental disorder characterised by macrocephaly, developmental delay, intellectual disability and seizures. Symptoms typically emerge in childhood and there are no treatments currently available. Causative de novo mutations have been identified in the Nuclear factor I X-type (NFIX) gene, particularly exons 1-3, that confer haploinsufficiency. NFIX encodes a transcription factor critically associated with proper neuromuscular development; although, exact mechanisms are not fully elucidated. We utilised molecular techniques including RT-PCR, qPCR, Sanger sequencing, Western blotting and RNA-sequencing to characterise the mutations in 5 patient-derived fibroblast lines and analysed differences in their transcriptomic profiles compared to unaffected individuals. Results identified several altered biological processes, metabolic pathways and downstream targets. Additionally, we identified complex splicing mutations beyond those originally genotyped. Our findings provide significant insight into the extensive roles of NFIX and potential avenues for therapeutic development. In fact, this data is currently informing the refinement of NFIX-targeting antisense oligonucleotides. We utilised the neuroblastoma cell line, SH-SY5Y, to screen 44 antisense oligonucleotides and evaluated their efficacy at both RNA and protein level by qPCR and Western blotting. Furthermore, we are developing patient-derived neuronal stem cell models of Malan syndrome, the first of knowledge. These disease-relevant models will be used to validate our top therapeutic candidates and serve as a platform to explore mechanisms of Malan syndrome throughout neural development, an area yet to be fully understood. Overall, this project provides significant insight into the mechanisms behind the causative gene of Malan syndrome, NFIX, and approaches for its therapeutic targeting.