HUMAN IPSC TECHNOLOGY TO INVESTIGATE POTENTIAL THERAPEUTIC TARGETS AND UNDERLYING MECHANISMS OF NON-SYNDROMIC XLID DUE TO NEXMIF GENE MUTATION

Loss-of-function mutations in NEXMIF gene (neurite extension migration factor) cause a rare dominant neurodevelopmental condition named X-linked Intellectual Disorder 98(XLID-98) associated with intellectual disability (ID), autism spectrum disorder (ASD) and epilepsy. As NEXMIF is located on the X chromosome, homozygous males with XLID-98 show severe ID/language impairment, delayed psychomotricity, while heterozygous females show milder ID/language impairment, but higher incidence of drug-resistant epilepsy. The exact molecular function of Nexmif is unknown, but studies in mice suggest its involvement in neuron development. We investigated the consequences of NEXMIF mutations in human neurons derived from induced pluripotent stem cells (iPSC) knockout (KO) for NEXMIF. We investigated the role of NEXMIF during early human neuronal differentiation and show that NEXMIF KO neurons undergo accelerated cell‑cycle exit and premature neuronal differentiation. Electrophysiological analyses revealed increased baseline excitability and enhanced sensitivity to the epileptogenic agent 4‑aminopyridine, consistent with the epileptic phenotype observed in individuals with XLID‑98. At the molecular level, NEXMIF KO neurons exhibited dysregulation of chloride transporters and GABAergic signaling, including increased expression of KCC2, VGAT and GAD65/67, suggesting a homeostatic adaptive response to neuronal hyperexcitability.
This study will provide insight into NEXMIF‑regulated cellular mechanisms and may also provide new insights into epilepsy therapies.