Autism spectrum disorder (ASD) pathophysiology often involves striatal dysfunction, yet the underlying mechanisms remain unclear. Mutations in Forkhead box G1 (FOXG1) cause FOXG1 syndrome, a condition sharing core ASD features. Here, loss of Foxg1 in the indirect pathway spiny projection neurons (iSPNs) in mice recapitulates ASD symptoms, including social, language, and fine movement deficits. Foxg1 deficiency causes dendritic simplification, spine reduction, and impairs excitatory synaptic transmission. Transcriptome reveals that FOXG1 drives gene networks to multidimensionally control synaptic functions from spine morphogenesis, synaptic maturation, ion transmembrane transport, glutamate receptor clustering, to neurotransmitter release and synaptic transmission. Importantly, FOXG1 directly activates the transcription of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits, and pharmacological potentiation of AMPAR activity normalizes synaptic function and rescues behavioral deficits. Our study provides a new perspective on the relationship between FOXG1 and ASD etiology in iSPNs and suggests the potential of AMPAR activation as a therapeutic intervention for ASD and FOXG1 Syndrome.

There is increasing interest in the utility of electrophysiological measures such as resting EEG and evoked potential (EPs) to serve as biomarkers to facilitate therapeutic development for rare genetic neurodevelopmental disorders (NDDs). Research on this topic thus far has been encouraging, but has also revealed the necessity for unique methods when acquiring EEG and EPs in children with genetic NDDs. Details of these methods are typically beyond the scope of research publications, yet are crucial to the quality and ultimately, usability of the data. In the current manuscript, we detail the methods that we have developed for acquiring EEG and EPs as part of multi-site studies with participants with Rett syndrome, CDKL5 deficiency disorder, MECP2 duplication syndrome, and FOXG1 syndrome. By making our methods accessible, we hope to support other groups interested in acquiring EEG and/or EPs as part of clinical trials or research studies with individuals with genetic NDDs, including groups without prior experience with EEG/EP acquisition. The paper is presented as step-by-step procedures followed by a discussion of issues that may arise during acquisition and ways to troubleshoot these issues. We then discuss considerations for choosing EEG equipment and study paradigms and briefly, considerations for data analysis.

Single allelic mutations in the FOXG1 gene lead to FOXG1 syndrome (FS). To understand the pathophysiology of FS, which vary depending on FOXG1 mutation types, patient-specific animal models are critical. Here, we report a patient-specific Q84Pfs heterozygous (Q84Pfs-Het) mouse model, which recapitulates various FS phenotypes across cellular, brain structural, and behavioral levels. Q84Pfs-Het cortex shows dysregulations of genes controlling cell proliferation, neuronal projection and migration, synaptic assembly, and synaptic vesicle transport. The Q84Pfs allele produces the N-terminal fragment of FOXG1 (Q84Pfs protein) in Q84Pfs-Het mouse brains, which forms intracellular speckles, interacts with FOXG1 full-length protein, and triggers the sequestration of FOXG1 to distinct subcellular domains. Q84Pfs protein promotes the radial glial cell identity and suppresses neuronal migration in the cortex. Our study uncovers the role of the FOXG1 fragment from FS-causing FOXG1 variants and identifies the genes involved in FS-like cellular and behavioral phenotypes, providing insights into the pathophysiology of FS. FOXG1 syndrome is characterized by moderate-to-profound developmental delay and intellectual disability, postnatal growth deficiency, congenital or postnatal microcephaly, hyperkinetic/dyskinetic movement disorder, hypotonia, neurobehavioral/psychiatric manifestations (motor stereotypies, impairment of social interaction, abnormal sleep patterns, unexplained episodes of crying, restlessness, and bruxism), feeding difficulties with poor weight gain, strabismus, seizures, spasticity, gastroesophageal reflux, and aspiration. Some individuals have cortical visual impairment, kyphosis, scoliosis, and/or abnormal breathing. Characteristic neuroimaging findings include corpus callosum anomalies (especially a marked, filiform thinning of the rostrum of the corpus callosum), a simplified gyral pattern, and hyperplasia of the fornices. The diagnosis of FOXG1 syndrome is established in a proband with clinical and/or characteristic neuroimaging findings and a heterozygous pathogenic variant in FOXG1 identified by molecular genetic testing. Treatment of manifestations: Developmental and educational support; consideration of anti-dyskinetic pharmacotherapy; treatment for seizures by an experienced neurologist; treatment of spasticity per orthopedist; physical medicine and rehabilitation, physical therapy, and occupational therapy to help avoid contractures and falls; anti-spasmodic pharmacotherapy; feeding therapy with gastrostomy tube placement as needed; standard treatment of gastroesophageal reflux; treatment for refractive errors and strabismus per ophthalmologist; standard treatments for scoliosis; social work and family support. Surveillance: At each visit, monitor developmental progress, educational needs, seizures, changes in tone, movement disorders, growth, nutritional status, and safety of oral intake; behavioral assessment for irritability and sleep issues; assess for evidence of gastroesophageal reflux, aspiration, and/or respiratory insufficiency; physical medicine, occupational therapy, physical therapy assessment for mobility and self-help skills; monitor for strabismus and need for low vision services per treating ophthalmologist; assess family needs. FOXG1 syndrome is an autosomal dominant disorder typically caused by a de novo pathogenic variant. Risk to future pregnancies is presumed to be low as the proband most likely has a de novo FOXG1 pathogenic variant. There is, however, a recurrence risk to sibs based on the possibility of parental germline mosaicism. Given this risk, prenatal and preimplantation genetic testing may be considered.

FOXG1 syndrome is a devastating neurodevelopmental disorder caused by haploinsufficiency of the transcription factor FOXG1, leading to intellectual disability, epilepsy, and white-matter deficits. Although FOXG1 is well known for its neuronal functions, its role in glial pathology remains poorly understood. Here, we show that reducing FOXG1 selectively in neurons impairs oligodendrocyte lineage progression and myelination, establishing a critical non-cell-autonomous role for neuronal FOXG1 in glial maturation. To restore FOXG1 in neurons, we developed AAV vectors expressing human FOXG1 under neuron-specific promoters. Neonatal administration of these vectors normalized oligodendrocyte precursor cell (OPC) accumulation, enhanced myelination, and corrected hippocampal structural abnormalities in Foxg1 conditional heterozygous mice. To test therapeutic robustness under stringent conditions, we used the patient-specific W300X heterozygous model, which combines FOXG1 loss-of-function with a toxic truncated protein and represents one of the most severe FOXG1 syndrome genotypes. Remarkably, neuron-restricted AAV-FOXG1 delivery produced substantial rescue even in this high-bar model, suppressing OPC overaccumulation, restoring myelination, and progressively improving dentate gyrus morphology, with benefits persisting into adulthood. Moreover, adolescent administration remained highly effective, rescuing myelination, axonal bundle thickness, and microglial activation. These findings identify neuronal FOXG1 as a master regulator of neuron-glia interactions and establish neuron-targeted AAV-FOXG1 as a potent and clinically translatable therapeutic strategy across diverse severities of FOXG1 syndrome.

FOXG1 syndrome is a severe genetic neurodevelopmental disorder characterized by intellectual and developmental disabilities (IDD), postnatal microcephaly, epilepsy, and movement disorder. With the advent of molecular therapies, establishing the natural history of FOXG1 syndrome is critical to enable clinical trial readiness. However, traditional study designs are challenging to implement for rare disorders without significant burden to participants. The study population included 101 children and adults with (likely) pathogenic variants in or involving FOXG1 (ages 0.4 - 34.8 years). Participant medical records underwent systematic annotation and harmonization of recorded clinical phenotypes, interventions, and outcomes through use of a patient-centric real-world data (RWD) platform. Retrospective medical record data were paired with prospective administration of validated measures of development and behavior, including the Vineland-3, the Aberrant Behavior Checklist, and the Children’s Sleep Habits Questionnaire. Descriptive and inferential statistics were employed to characterize longitudinal phenotypes and to explore genotype-phenotype correlations. Through systematic evaluation of 101 people with FOXG1 syndrome, we generated a robust dataset encompassing >40,000 annotated clinical terminology concepts that represent >770 cumulative patient data years. Core clinical phenotypes include IDD, gastrointestinal disorders, strabismus, epilepsy, movement disorders, and sleep problems. The FOXG1 syndrome behavioral phenotype is characterized by irritability, including aggressive behaviors, stereotypies, social withdrawal, and lethargy; in those with missense variants, features of autism spectrum disorders are also reported. Data derived from both medical records and validated measures confirm and expand upon previously described genotype-phenotype correlations, whereby truncating variants are associated with greater limitations across motor and communication domains, as well as increased frequency of core FOXG1 syndrome phenotypes. Further, individuals with truncating variants had higher scores on a composite measure of FOXG1 syndrome severity, which persists when modeled longitudinally. Employing the same composite measure, we demonstrate that FOXG1 syndrome is a static encephalopathy without evidence of neurodegeneration. By combining retrospective RWD with prospective survey administration in a large sample population, we establish the natural history of FOXG1 syndrome and highlight candidate clinical endpoints for use in clinical trials, including quantitative evaluations of communication and movement disorders. The online version contains supplementary material available at 10.1186/s11689-025-09653-1.