OBJECTIVE: To explore the clinical characteristics of a child with early-onset infantile epileptic encephalopathy type 8 associated with synonymous variant of ARHGEF9 gene. METHODS: Clinical data of the patient was summarized. The child and his parents were subjected to trio-whole exome sequencing. RESULTS: The child has presented with global developmental delay, epilepsy, impulsive behavior, hypersensitivity to sound, and mental retardation. He was found to harbor a de novo synonymous variant c.741C>T (p.Cys247Cys) of the ARHGEF9 gene. RNA splicing analysis confirmed that the variant has led to abnormal splicing of exon 5, resulting in a 55-bp deletion. CONCLUSION The clinical features of ARHGEF9 gene-related early-onset infantile epileptic encephalopathy type 8 includes mental and motor developmental delay, epilepsy, auditory allergy, and hyperactivity impulsivity. For synonymous variant, in vitro study and transcriptional experiment may be carried out to evaluate its functional and splicing effect. Above finding has enriched the phenotypic and genotypic spectrum of the ARHGEF9 gene.
Child ; Epilepsy/genetics* ; Exons ; Humans ; Infant ; Intellectual Disability/genetics* ; Male ; Rho Guanine Nucleotide Exchange Factors/genetics* ; Spasms, Infantile/genetics*

The radial migration of cortical pyramidal neurons (PNs) during corticogenesis is necessary for establishing a multilayered cerebral cortex. Neuronal migration defects are considered a critical etiology of neurodevelopmental disorders, including autism spectrum disorders (ASDs), schizophrenia, epilepsy, and intellectual disability (ID). TRIO is a high-risk candidate gene for ASDs and ID. However, its role in embryonic radial migration and the etiology of ASDs and ID are not fully understood. In this study, we found that the in vivo conditional knockout or in utero knockout of Trio in excitatory precursors in the neocortex caused aberrant polarity and halted the migration of late-born PNs. Further investigation of the underlying mechanism revealed that the interaction of the Trio N-terminal SH3 domain with Myosin X mediated the adherence of migrating neurons to radial glial fibers through regulating the membrane location of neuronal cadherin (N-cadherin). Also, independent or synergistic overexpression of RAC1 and RHOA showed different phenotypic recoveries of the abnormal neuronal migration by affecting the morphological transition and/or the glial fiber-dependent locomotion. Taken together, our findings clarify a novel mechanism of Trio in regulating N-cadherin cell surface expression via the interaction of Myosin X with its N-terminal SH3 domain. These results suggest the vital roles of the guanine nucleotide exchange factor 1 (GEF1) and GEF2 domains in regulating radial migration by activating their Rho GTPase effectors in both distinct and cooperative manners, which might be associated with the abnormal phenotypes in neurodevelopmental disorders.
Autism Spectrum Disorder/metabolism* ; Cell Movement/genetics* ; Humans ; Interneurons/metabolism* ; Neurodevelopmental Disorders/genetics* ; Neurons/metabolism* ; Rho Guanine Nucleotide Exchange Factors/genetics*