Re-expression of SynGAP protein in adulthood improves translatable measures of brain function and behavior

Sex-specific perturbations of neuronal development caused by mutations in the autism risk gene DDX3X

DDX3X is an X-linked RNA helicase that escapes X chromosome inactivation and is expressed at higher levels in female brains. Mutations in DDX3X are associated with intellectual disability (ID) and autism spectrum disorder (ASD) and are predominantly identified in females (DDX3X syndrome). Using cellular and mouse models, we show that Ddx3x mediates sexual dimorphisms in brain development at a molecular, cellular, and behavioral level. During cortical neuronal development, Ddx3x sustains a female-biased signature of enhanced ribosomal biogenesis and mRNA metabolism. Compared to male neurons, female neurons display larger nucleoli, higher expression of a set of ribosomal proteins, and a higher cytoplasm-to-nucleus ratio of ribosomal RNA. All these sex dimorphisms are obliterated by Ddx3x loss. Ddx3x regulates dendritic arborization complexity in a sex- and dose-dependent manner in both female and male neurons. Ddx3x modulates the development of dendritic spines but only in female neurons. Further, ablating Ddx3x conditionally in forebrain neurons is sufficient to yield sex-specific changes in developmental outcomes and motor function. Together, these findings pose Ddx3x as a mediator of sexual differentiation during neurodevelopment and open new avenues to understand sex differences in health and disease.

The MNK-SYNGAP1 axis in specific learning disorder: gene expression pattern and new perspectives

Specific learning disorder (SLD) is a neurodevelopmental disorder that significantly affects children's academic performance. This study aimed to investigate the expression levels of the MAP Kinase Interacting Serine/Threonine Kinase 1-2 (MNK1, MNK2), Synaptic Ras GTPase Activating Protein 1 (SYNGAP1) genes, and the long non-coding RNA Synaptic Ras GTPase Activating Protein 1-Anti Sense1 (SYNGAP1-AS1), which are believed to play a key role in neurodevelopmental pathways, in children with SLD. Understanding the role of these genes in synaptic plasticity and cognitive function may provide insights into the molecular mechanisms underlying SLD. This study included 38 children diagnosed with SLD and 35 healthy controls aged 6 to 16. RNA was isolated from blood samples, and gene expression levels were measured using quantitative polymerase chain reaction (qPCR). The statistical analysis was conducted to compare the expression levels between the SLD and control groups and within SLD subgroups based on severity and sex. MNK1 and SYNGAP1 expression levels were significantly upregulated in the SLD group compared to the control group (8.33-fold and 16.52-fold increase, respectively; p < 0.001). lncSYNGAP1-AS1 showed a 26.58-fold increase, while MNK2 was downregulated by 2.2-fold, although these changes were not statistically significant. No significant differences were observed between sexes or between the severity subgroups of SLD.

CONCLUSION

he upregulation of MNK1 and SYNGAP1 in children with SLD suggests their involvement in the neurodevelopmental pathways associated with cognitive processes such as learning and memory. These findings provide a foundation for future research into the molecular basis and potential therapeutic targets of SLD.

WHAT IS KNOWN

• SYNGAP1 is a key regulator of synaptic plasticity and learning, primarily functioning through Ras signaling inhibition. Its deficiency impairs long-term potentiation (LTP) and is associated with neurodevelopmental disorders (NDDs) such as autism spectrum disorder (ASD) and intellectual disability. • The MAPK/ERK pathway plays a crucial role in learning and memory, and its dysregulation has been linked to several neurological conditions. MNK1/2 interacts with SYNGAP1 in synaptic signaling.

WHAT IS NEW

• This study is the first to demonstrate significant upregulation of SYNGAP1 and MKNK1 in children with SLD. • Understanding the role of the MKNK-SYNGAP1 axis may guide the development of targeted therapies aimed at enhancing synaptic plasticity to improve learning and memory outcomes in children with SLD.

Mesoscale proximity labeling to study macro changes to chromatin occupancy

Proximity labeling traditionally identifies interactomes of a single protein or RNA, though this approach limits mechanistic understanding of biomolecules functioning within complex systems. Here, we demonstrate a strategy for deciphering ligand-induced changes to global biomolecular interactions by enabling proximity labelling at the mesoscale, across an entire cellular system. By inserting nanoscale proximity labelling catalysts throughout chromatin, this system, MesoMap, provided new insights into how HDAC inhibitors regulate gene expression. Furthermore, it revealed that the orphaned drug candidate, SR-1815, regulates disease-linked Syngap1 gene expression through direct inhibition of kinases implicated in both neurological disorders and cancer. Through precise mapping of global chromatin mobility, MesoMap promotes insights into how drug-like chemical probes induce transcriptional dynamics within healthy and disease-associated cellular states.

The Endo-GeneScreen Platform Identifies Drug-Like Probes that Regulate Endogenous Protein Levels within Physiological Contexts

Traditional phenotypic drug discovery platforms have suffered from poor scalability and a lack of mechanistic understanding of newly discovered phenotypic probes. To address this, we created Endo- GeneScreen (EGS), a high-throughput enabled screening platform that identifies bioactive small molecules capable of regulating endogenous protein expression encoded by any preselected target gene within a biologically appropriate context. As a proof-of-concept, EGS successfully identified drug candidates that up-regulate endogenous expression of neuronal Syngap1, a gene that causes a neurodevelopmental disorder when haploinsufficient. For example, SR-1815, a previously unknown and undescribed kinase inhibitor, alleviated major cellular consequences of Syngap1 loss-of-function by restoring normal SynGAP protein levels and dampening neuronal hyperactivity within haploinsufficient neurons. Moreover, we demonstrate that EGS assays accelerate preclinical development of identified drug candidates and facilitate mode-of-action deconvolution studies. Thus, EGS identifies first-in-class bioactive small molecule probes that promote biological discovery and precision therapeutic development.

Epigenetic modulation rescues neurodevelopmental deficits in Syngap1+/- mice

SYNGAP1 is a Ras GTPase-activating protein that plays a crucial role during brain development and in synaptic plasticity. Sporadic heterozygous mutations in SYNGAP1 affect social and emotional behaviour observed in intellectual disability (ID) and autism spectrum disorder (ASD). Although neurophysiological deficits have been extensively studied, the epigenetic landscape of SYNGAP1 mutation-mediated intellectual disability is unexplored. Here, we have found that the p300/CBP specific acetylation marks of histones are significantly repressed in the hippocampus of adolescent Syngap1+/- mice. Additionally, we observed decreased dendritic branching of newly born DCX+ neurons in these mice, suggesting altered adult hippocampal neurogenesis. To establish the causal relationship of Syngap1+/- phenotype and the altered histone acetylation signature we have treated 2-4 months old Syngap1+/- mice with glucose-derived carbon nanosphere (CSP) conjugated potent small molecule activator (TTK21) of p300/CBP lysine acetyltransferase (CSP-TTK21). The enhancement of the p300/CBP specific acetylation marks of histones by CSP-TTK21 restored synaptic functions, increased dendritic branching of DCX+ neurons, enables the capability to reorganise cortical circuits in response to change in the sensory stimuli, and improves behavioural measures in Syngap1+/- mice that are very closely comparable to wild type littermates. Further, hippocampal RNA-Seq analysis of these mice revealed that the expression of many critical genes such as Adcy1, Ntrk3, Egr1, and Foxj1 which are key regulators of synaptic plasticity and neurogenesis and are well associated with ID/ASD reversed upon CSP-TTK21 treatment. This study could be the first demonstration of the reversal of autistic behaviour and neural wiring upon the modulation of altered epigenetic modification(s).

Plural molecular and cellular mechanisms of pore domain KCNQ2 encephalopathy

KCNQ2 variants in children with neurodevelopmental impairment are difficult to assess due to their heterogeneity and unclear pathogenic mechanisms. We describe a child with neonatal-onset epilepsy, developmental impairment of intermediate severity, and KCNQ2 G256W heterozygosity. Analyzing prior KCNQ2 channel cryoelectron microscopy models revealed G256 as a node of an arch-shaped non-covalent bond network linking S5, the pore turret, and the ion path. Co-expression with G256W dominantly suppressed conduction by wild-type subunits in heterologous cells. Ezogabine partly reversed this suppression. Kcnq2G256W/+ mice have epilepsy leading to premature deaths. Hippocampal CA1 pyramidal cells from G256W/+ brain slices showed hyperexcitability. G256W/+ pyramidal cell KCNQ2 and KCNQ3 immunolabeling was significantly shifted from axon initial segments to neuronal somata. Despite normal mRNA levels, G256W/+ mouse KCNQ2 protein levels were reduced by about 50%. Our findings indicate that G256W pathogenicity results from multiplicative effects, including reductions in intrinsic conduction, subcellular targeting, and protein stability. These studies provide evidence for an unexpected and novel role for the KCNQ2 pore turret and introduce a valid animal model of KCNQ2 encephalopathy. Our results, spanning structure to behavior, may be broadly applicable because the majority of KCNQ2 encephalopathy patients share variants near the selectivity filter.

Roadmap to advance therapeutics for SYNGAP1-related disorder: a patient organization perspective from SynGAP Research Fund

SYNGAP1-related disorder (SRD) is a developmental and epileptic encephalopathy caused by a disruption of the SYNGAP1 gene. At the beginning of 2024, it is one of many rare monogenic brain disorders without disease-modifying treatments, but that is changing. This article chronicles the last 5 years, beginning when treatments for SRD were not publicly in development, to the start of 2024 when many SRD-specific treatments are advancing. We discuss the progress across many realms that have brought SRD to the forefront of drug development and highlight how Patient Advocacy Groups (PAGs) have had direct roles in accelerating the route to meaningful treatments for our children. We start with a summary of why SRD is an attractive pharmaceutical target. Second, we introduce the disease, the clinical features, and the number of patients. Next, we describe our PAG, our international partners and cite examples of the broad range of activities we believe are accelerating our pace toward treatments. We summarize the current SYNGAP1 pipeline and the status of each public project. Finally, we discuss two open questions that urgently need to be addressed in advance of clinical trials for SRD.

Developmental Syngap1 Haploinsufficiency in Medial Ganglionic Eminence-Derived Interneurons Impairs Auditory Cortex Activity, Social Behavior, and Extinction of Fear Memory

Mutations in SYNGAP1, a protein enriched at glutamatergic synapses, cause intellectual disability associated with epilepsy, autism spectrum disorder, and sensory dysfunctions. Several studies showed that Syngap1 regulates the time course of forebrain glutamatergic synapse maturation; however, the developmental role of Syngap1 in inhibitory GABAergic neurons is less clear. GABAergic neurons can be classified into different subtypes based on their morphology, connectivity, and physiological properties. Whether Syngap1 expression specifically in parvalbumin (PV)-expressing and somatostatin (SST)-expressing interneurons, which are derived from the medial ganglionic eminence (MGE), plays a role in the emergence of distinct brain functions remains largely unknown. We used genetic strategies to generate Syngap1 haploinsufficiency in (1) prenatal interneurons derived from the medial ganglionic eminence, (2) in postnatal PV cells, and (3) in prenatal SST interneurons. We further performed in vivo recordings and behavioral assays to test whether and how these different genetic manipulations alter brain function and behavior in mice of either sex. Mice with prenatal-onset Syngap1 haploinsufficiency restricted to Nkx2.1-expressing neurons show abnormal cortical oscillations and increased entrainment induced by 40 Hz auditory stimulation but lack stimulus-specific adaptation. This latter phenotype was reproduced in mice with Syngap1 haploinsufficiency restricted to PV, but not SST, interneurons. Prenatal-onset Syngap1 haploinsufficiency in Nkx2.1-expressing neurons led to impaired social behavior and inability to extinguish fear memories; however, neither postnatal PV- nor prenatal SST-specific mutant mice show these phenotypes. We speculate that Syngap1 haploinsufficiency in prenatal/perinatal PV interneurons may contribute to cortical activity and cognitive alterations associated with Syngap1 mutations.

Subjective sleep assessment in individuals with SYNGAP1-associated syndrome

STUDY OBJECTIVES

Sleep disturbances are common in neurodevelopmental disorders, affecting patients and caregivers' quality of life. SYNGAP1-associated syndrome, a rare neurodevelopmental disorder, is marked by intellectual disability, developmental delay, epilepsy, and sleep issues. However, research on sleep quality in these individuals is limited. This study aimed to evaluate genetic variants, epilepsy, and sleep patterns in SYNGAP1-associated syndrome patients and their caregivers.

METHODS

An online survey was applied to 11 caregivers of individuals diagnosed with SYNGAP1-associated syndrome. Specific clinical inquiries were included, addressing childbirth, previous surgeries, and medication use. Inquiries about epilepsy included type of epilepsy, type and frequency of seizures, antiseizure medications, and complementary nonpharmacological treatments. Children's Sleep Habits Questionnaire was applied to assess the patients' sleep profile. Pittsburgh Sleep Quality Index was used to evaluate the sleep quality of caregivers.

RESULTS

Genetic analysis showed heterozygous mutations in SYNGAP1, often leading to loss of function. Epilepsy was present in 82% of participants, with 77.8% having drug-resistant seizures. Using the Children's Sleep Habits Questionnaire, 81.8% of patients exhibited poor sleep habits, including bedtime resistance, anxiety, night awakenings, parasomnias, and daytime sleepiness. Caregivers also reported poor sleep quality according to the Pittsburgh Sleep Quality Index.

CONCLUSIONS

This study highlights the high prevalence of epilepsy and sleep problems in SYNGAP1-associated syndrome, impacting both patients and caregivers. Further research is crucial to understand the syndrome's effects on sleep disturbances, emphasizing the need for targeted interventions to improve sleep quality in individuals with rare genetic syndromes and their caregivers.

CITATION

Mosini A, Moysés-Oliveira M, Adami L, et al. Subjective sleep assessment in individuals with SYNGAP1-associated syndrome. J Clin Sleep Med. 2024;20(12):1879-1885.

Sex-specific perturbations of neuronal development caused by mutations in the autism risk gene DDX3X

DDX3X is an X-linked RNA helicases that escapes X chromosome inactivation and is expressed at higher levels in female brains. Mutations in DDX3X are associated with intellectual disability (ID) and autism spectrum disorder (ASD) and are predominantly identified in females. Using cellular and mouse models, we show that Ddx3x mediates sexual dimorphisms in brain development at a molecular, cellular, and behavioral level. During cortical neuronal development, Ddx3x sustains a female-biased signature of enhanced ribosomal biogenesis and mRNA translation. Female neurons display higher levels of ribosomal proteins and larger nucleoli, and these sex dimorphisms are obliterated by Ddx3x loss. Ddx3x regulates dendritic outgrowth in a sex- and dose-dependent manner in both female and male neurons, and dendritic spine development only in female neurons. Further, ablating Ddx3x conditionally in forebrain neurons is sufficient to yield sex-specific changes in developmental outcomes and motor function. Together, these findings pose Ddx3x as a mediator of sexual differentiation during neurodevelopment and open new avenues to understand sex differences in health and disease.

Hyperexcitability and translational phenotypes in a preclinical mouse model of SYNGAP1-related intellectual disability

Disruption of SYNGAP1 directly causes a genetically identifiable neurodevelopmental disorder (NDD) called SYNGAP1-related intellectual disability (SRID). Without functional SynGAP1 protein, individuals are developmentally delayed and have prominent features of intellectual disability (ID), motor impairments, and epilepsy. Over the past two decades, there have been numerous discoveries indicating the critical role of Syngap1. Several rodent models with a loss of Syngap1 have been engineered, identifying precise roles in neuronal structure and function, as well as key biochemical pathways key for synapse integrity. Homozygous loss of SYNGAP1/Syngap1 is lethal. Heterozygous mutations of Syngap1 result in a broad range of behavioral phenotypes. Our in vivo functional data, using the original mouse model from the Huganir laboratory, corroborated behaviors including robust hyperactivity and deficits in learning and memory in young adults. Furthermore, we described impairments in the domain of sleep, characterized using neurophysiological data that was collected with wireless, telemetric electroencephalography (EEG). Syngap1+/- mice exhibited elevated spiking events and spike trains, in addition to elevated power, most notably in the delta power frequency. For the first time, we illustrated that primary neurons from Syngap1+/- mice displayed: 1) increased network firing activity, 2) greater bursts, 3) and shorter inter-burst intervals between peaks, by utilizing high density microelectrode arrays (HD-MEA). Our work bridges in vitro electrophysiological neuronal activity and function with in vivo neurophysiological brain activity and function. These data elucidate quantitative, translational biomarkers in vivo and in vitro that can be utilized for the development and efficacy assessment of targeted treatments for SRID.

Key roles of C2/GAP domains in SYNGAP1-related pathophysiology

Mutations in SYNGAP1 are a common genetic cause of intellectual disability (ID) and a risk factor for autism. SYNGAP1 encodes a synaptic GTPase-activating protein (GAP) that has both signaling and scaffolding roles. Most pathogenic variants of SYNGAP1 are predicted to result in haploinsufficiency. However, some affected individuals carry missense mutations in its calcium/lipid binding (C2) and GAP domains, suggesting that many clinical features result from loss of functions carried out by these domains. To test this hypothesis, we targeted the exons encoding the C2 and GAP domains of SYNGAP. Rats heterozygous for this deletion exhibit reduced exploration and fear extinction, altered social investigation, and spontaneous seizures-key phenotypes shared with Syngap heterozygous null rats. Together, these findings indicate that the reduction of SYNGAP C2/GAP domain function is a main feature of SYNGAP haploinsufficiency. This rat model provides an important system for the study of ID, autism, and epilepsy.

Behavioural and neurodevelopmental characteristics of SYNGAP1

BACKGROUND

SYNGAP1 variants are associated with varying degrees of intellectual disability (ID), developmental delay (DD), epilepsy, autism, and behavioural difficulties. These features may also be observed in other monogenic conditions. There is a need to systematically compare the characteristics of SYNGAP1 with other monogenic causes of ID and DD to identify features unique to the SYNAGP1 phenotype. We aimed to contrast the neurodevelopmental and behavioural phenotype of children with SYNGAP1-related ID (SYNGAP1-ID) to children with other monogenic conditions and a matched degree of ID.

METHODS

Participants were identified from the IMAGINE-ID study, a UK-based, national cohort study of neuropsychiatric risk in children with ID of known genetic origin. Thirteen children with SYNGAP1 variants (age 4-16 years; 85% female) were matched (2:1) with 26 controls with other monogenic causes of ID for chronological and mental age, sex, socio-economic deprivation, adaptive behaviour, and physical health difficulties. Caregivers completed the Development and Wellbeing Assessment (DAWBA) and physical health questionnaires.

RESULTS

Our results demonstrate that seizures affected children with SYNGAP1-ID (84.6%) more frequently than the ID-comparison group (7.6%; p =  < 0.001). Fine-motor development was disproportionally impaired in SYNGAP1-ID, with 92.3% of children experiencing difficulties compared to 50% of ID-comparisons(p = 0.03). Gross motor and social development did not differ between the two groups. Children with SYNGAP1-ID were more likely to be non-verbal (61.5%) than ID-comparisons (23.1%; p = 0.01). Those children able to speak, spoke their first words at the same age as the ID-comparison group (mean = 3.25 years), yet achieved lower language competency (p = 0.04). Children with SYNGAP1-ID compared to the ID-comparison group were not more likely to meet criteria for autism (SYNGAP1-ID = 46.2%; ID-comparison = 30.7%; p = .35), attention-deficit hyperactivity disorder (15.4%;15.4%; p = 1), generalised anxiety (7.7%;15.4%; p = .49) or oppositional defiant disorder (7.7%;0%; p = .15).

CONCLUSION

For the first time, we demonstrate that SYNGAP1-ID is associated with fine motor and language difficulties beyond those experienced by children with other genetic causes of DD and ID. Targeted occupational and speech and language therapies should be incorporated early into SYNGAP1-ID management.

SYNGAP1-related developmental and epileptic encephalopathy: Genotypic and phenotypic characteristics and longitudinal insights

The clinical and genetic characteristics of SYNGAP1 mutations in Korean pediatric patients are not well understood. We retrospectively analyzed 13 individuals with SYNGAP1 mutations from a longitudinal aspect. Clinical data, genetic profiles, and electroencephalography (EEG) patterns were examined. Genotypic analyses included gene panels and whole-exome sequencing. All patients exhibited global developmental delay from early infancy, with motor development eventually reaching independent ambulation by 3 years of age. Language developmental delay varied significantly from nonverbal to simple sentences, which plateaued in all patients. Patients with the best language outcomes typically managed 2-3-word sentences, corresponding to a developmental age of 2-3 years. Epilepsy developed in 77% of patients, with onset consistently following developmental delays at a median age of 31 months. Longitudinal EEG data revealed a shift from occipital to frontal epileptiform discharges with age, suggesting a correlation with synaptic maturation. These findings suggest that the critical developmental plateau occurs between the ages of 2 and 5 years and is potentially influenced by epilepsy. By analyzing longitudinal data, our study contributes to a deeper understanding of SYNGAP1-related DEE, provides potential EEG biomarkers, and underlines the importance of early diagnosis and intervention to address this complex disorder.

Context-dependent hyperactivity in syngap1a and syngap1b zebrafish models of SYNGAP1-related disorder

Background and aims

SYNGAP1-related disorder (SYNGAP1-RD) is a prevalent genetic form of Autism Spectrum Disorder and Intellectual Disability (ASD/ID) and is caused by de novo or inherited mutations in one copy of the SYNGAP1 gene. In addition to ASD/ID, SYNGAP1 disorder is associated with comorbid symptoms including treatment-resistant-epilepsy, sleep disturbances, and gastrointestinal distress. Mechanistic links between these diverse symptoms and SYNGAP1 variants remain obscure, therefore, our goal was to generate a zebrafish model in which this range of symptoms can be studied.

Methods

We used CRISPR/Cas9 to introduce frameshift mutations in the syngap1a and syngap1b zebrafish duplicates (syngap1ab) and validated these stable models for Syngap1 loss-of-function. Because SYNGAP1 is extensively spliced, we mapped splice variants to the two zebrafish syngap1a and b genes and identified mammalian-like isoforms. We then quantified locomotory behaviors in zebrafish syngap1ab larvae under three conditions that normally evoke different arousal states in wild-type larvae: aversive, high-arousal acoustic, medium-arousal dark, and low-arousal light stimuli.

Results

We show that CRISPR/Cas9 indels in zebrafish syngap1a and syngap1b produced loss-of-function alleles at RNA and protein levels. Our analyses of zebrafish Syngap1 isoforms showed that, as in mammals, zebrafish Syngap1 N- and C-termini are extensively spliced. We identified a zebrafish syngap1 α1-like variant that maps exclusively to the syngap1b gene. Quantifying locomotor behaviors showed that syngap1ab mutant larvae are hyperactive compared to wild-type but to differing degrees depending on the stimulus. Hyperactivity was most pronounced in low arousal settings, and hyperactivity was proportional to the number of mutant syngap1 alleles.

Limitations

Syngap1 loss-of-function mutations produce relatively subtle phenotypes in zebrafish compared to mammals. For example, while mouse Syngap1 homozygotes die at birth, zebrafish syngap1ab-/- survive to adulthood and are fertile, thus some aspects of symptoms in people with SYNGAP1-Related Disorder are not likely to be reflected in zebrafish.

Conclusion

Our data support mutations in zebrafish syngap1ab as causal for hyperactivity associated with elevated arousal that is especially pronounced in low-arousal environments.

Hematopoietic stem cell gene therapy for the treatment of SYNGAP1-related non-specific intellectual disability

BACKGROUND

Synaptic Ras GTPase activating protein 1 (SYNGAP1)-related non-specific intellectual disability is a neurodevelopmental disorder caused by an insufficient level of SynGAP1 resulting in a dysfunction of neuronal synapses and presenting with a wide array of clinical phenotypes. Hematopoietic stem cell gene therapy has the potential to deliver therapeutic levels of functional SynGAP1 to affected neurons upon transduction of hematopoietic stem and progenitor cells with a lentiviral vector.

METHODS

As a novel approach toward the treatment of SYNGAP1, we have generated a lentiviral vector expressing a modified form of SynGAP1 for transduction of human CD34+ hematopoietic stem and progenitor cells. The gene-modified cells were then transplanted into adult immunodeficient SYNGAP1+/- heterozygous mice and evaluated for improvement of SYNGAP1-related clinical phenotypes. Expression of SynGAP1 was also evaluated in the brain tissue of transplanted mice.

RESULTS

In our proof-of-concept study, we have demonstrated significant improvement of SYNGAP1-related phenotypes including an improvement in motor abilities observed in mice transplanted with the vector transduced cells because they displayed decreased hyperactivity in an open field assay and an increased latency to fall in a rotarod assay. An increased level of SynGAP1 was also detected in the brains of these mice.

CONCLUSIONS

These early-stage results highlight the potential of this stem cell gene therapy approach as a treatment strategy for SYNGAP1.

Plural molecular and cellular mechanisms of pore domain KCNQ2 encephalopathy

KCNQ2 variants in children with neurodevelopmental impairment are difficult to assess due to their heterogeneity and unclear pathogenic mechanisms. We describe a child with neonatal-onset epilepsy, developmental impairment of intermediate severity, and KCNQ2 G256W heterozygosity. Analyzing prior KCNQ2 channel cryoelectron microscopy models revealed G256 as a node of an arch-shaped non-covalent bond network linking S5, the pore turret, and the ion path. Co-expression with G256W dominantly suppressed conduction by wild-type subunits in heterologous cells. Ezogabine partly reversed this suppression. G256W/+ mice have epilepsy leading to premature deaths. Hippocampal CA1 pyramidal cells from G256W/+ brain slices showed hyperexcitability. G256W/+ pyramidal cell KCNQ2 and KCNQ3 immunolabeling was significantly shifted from axon initial segments to neuronal somata. Despite normal mRNA levels, G256W/+ mouse KCNQ2 protein levels were reduced by about 50%. Our findings indicate that G256W pathogenicity results from multiplicative effects, including reductions in intrinsic conduction, subcellular targeting, and protein stability. These studies provide evidence for an unexpected and novel role for the KCNQ2 pore turret and introduce a valid animal model of KCNQ2 encephalopathy. Our results, spanning structure to behavior, may be broadly applicable because the majority of KCNQ2 encephalopathy patients share variants near the selectivity filter.

Hyperexcitability and translational phenotypes in a preclinical mouse model of SYNGAP1-Related Intellectual Disability

Disruption of SYNGAP1 directly causes a genetically identifiable neurodevelopmental disorder (NDD) called SYNGAP1-related intellectual disability (SRID). Without functional SynGAP1 protein, individuals are developmentally delayed and have prominent features of intellectual disability, motor impairments, and epilepsy. Over the past two decades, there have been numerous discoveries indicting the critical role of Syngap1. Several rodent models with a loss of Syngap1 have been engineered identifying precise roles in neuronal structure and function, as well as key biochemical pathways key for synapse integrity. Homozygous loss of SYNGAP1/Syngap1 is lethal. Heterozygous mutations of Syngap1 result in a broad range of behavioral phenotypes. Our in vivo functional data, using the original mouse model from the Huganir laboratory, corroborated behaviors including robust hyperactivity and deficits in learning and memory in young adults. Furthermore, we described impairments in the domain of sleep, characterized using neurophysiological data collected with wireless, telemetric electroencephalography (EEG). Syngap1+/- mice exhibited elevated spiking events and spike trains, in addition to elevated power, most notably in the delta power frequency. For the first time, we illustrated primary neurons from Syngap1+/- mice displayed increased network firing activity, greater bursts, and shorter inter-burst intervals between peaks by employing high density microelectrode arrays (HD-MEA). Our work bridges in-vitro electrophysiological neuronal activity and function with in vivo neurophysiological brain activity and function. These data elucidate quantitative, translational biomarkers in vivo and in vitro that can be utilized for the development and efficacy assessment of targeted treatments for SRID.

USP27X variants underlying X-linked intellectual disability disrupt protein function via distinct mechanisms

Neurodevelopmental disorders with intellectual disability (ND/ID) are a heterogeneous group of diseases driving lifelong deficits in cognition and behavior with no definitive cure. X-linked intellectual disability disorder 105 (XLID105, #300984; OMIM) is a ND/ID driven by hemizygous variants in the USP27X gene encoding a protein deubiquitylase with a role in cell proliferation and neural development. Currently, only four genetically diagnosed individuals from two unrelated families have been described with limited clinical data. Furthermore, the mechanisms underlying the disorder are unknown. Here, we report 10 new XLID105 individuals from nine families and determine the impact of gene variants on USP27X protein function. Using a combination of clinical genetics, bioinformatics, biochemical, and cell biology approaches, we determined that XLID105 variants alter USP27X protein biology via distinct mechanisms including changes in developmentally relevant protein-protein interactions and deubiquitylating activity. Our data better define the phenotypic spectrum of XLID105 and suggest that XLID105 is driven by USP27X functional disruption. Understanding the pathogenic mechanisms of XLID105 variants will provide molecular insight into USP27X biology and may create the potential for therapy development.

Non-synaptic function of the autism spectrum disorder-associated gene SYNGAP1 in cortical neurogenesis

Genes involved in synaptic function are enriched among those with autism spectrum disorder (ASD)-associated rare genetic variants. Dysregulated cortical neurogenesis has been implicated as a convergent mechanism in ASD pathophysiology, yet it remains unknown how 'synaptic' ASD risk genes contribute to these phenotypes, which arise before synaptogenesis. Here, we show that the synaptic Ras GTPase-activating (RASGAP) protein 1 (SYNGAP1, a top ASD risk gene) is expressed within the apical domain of human radial glia cells (hRGCs). In a human cortical organoid model of SYNGAP1 haploinsufficiency, we find dysregulated cytoskeletal dynamics that impair the scaffolding and division plane of hRGCs, resulting in disrupted lamination and accelerated maturation of cortical projection neurons. Additionally, we confirmed an imbalance in the ratio of progenitors to neurons in a mouse model of Syngap1 haploinsufficiency. Thus, SYNGAP1-related brain disorders may arise through non-synaptic mechanisms, highlighting the need to study genes associated with neurodevelopmental disorders (NDDs) in diverse human cell types and developmental stages.

Adult Phenotype of SYNGAP1-DEE

Background and Objectives

SYNGAP1 variants are associated with rare developmental and epileptic encephalopathies (DEEs). Although SYNGAP1-related childhood phenotypes are well characterized, the adult phenotype remains ill-defined. We sought to investigate phenotypes and outcomes in adults with SYNGAP1 variants and epilepsy.

Methods

Patients 18 years or older with DEE carrying likely pathogenic and pathogenic (LP/P) SYNGAP1 variants were recruited through physicians' practices and patient organization groups. We used standardized questionnaires to evaluate current seizures, medication use, sleep, gastrointestinal symptoms, pain response, gait, social communication disorder and adaptive skills of patients. We also assessed caregiver burden.

Results

Fourteen unrelated adult patients (median: 21 years, range: 18-65 years) with SYNGAP1-DEE were identified, 11 with novel and 3 with known LP/P SYNGAP1 de novo variants. One patient with a partial exon 3 deletion had greater daily living skills and social skills than others with single-nucleotide variants. Ten of 14 (71%) patients had drug-resistant seizures, treated with a median of 2 antiseizure medications. All patients (100%) had abnormal pain processing. Sleep disturbances, social communication disorders, and aggressive/self-injurious behaviors were each reported in 86% of patients. Only half of adults could walk with minimal or no assistance. Toileting was normal in 29%, and 71% had constipation. No adult patients could read or understand verbal material at a sixth-grade level or higher. Aggressive/self-injurious behaviors were leading cause of caregiver burden. The oldest patient was aged 65 years; although nonambulant, she had walked independently when younger.

Discussion

Seventy-one percent of patients with SYNGAP1-DEEs continue to have seizures when adults. Nonseizure comorbidities, especially aggression and self-injurious behaviors, are major management challenges in adults with SYNGAP1-DEE. Only 50% of adults can ambulate with minimal or no assistance. Almost all adult patients depend on caregivers for many activities of daily living. Prompt diagnostic genetic testing of adults with DEE can inform clinical care and guide outcomes of precision therapies.

Context-dependent hyperactivity in syngap1a and syngap1b zebrafish autism models

Background and Aims

SYNGAP1 disorder is a prevalent genetic form of Autism Spectrum Disorder and Intellectual Disability (ASD/ID) and is caused by de novo or inherited mutations in one copy of the SYNGAP1 gene. In addition to ASD/ID, SYNGAP1 disorder is associated with comorbid symptoms including treatment-resistant-epilepsy, sleep disturbances, and gastrointestinal distress. Mechanistic links between these diverse symptoms and SYNGAP1 variants remain obscure, therefore, our goal was to generate a zebrafish model in which this range of symptoms can be studied.

Methods

We used CRISPR/Cas9 to introduce frameshift mutations in the syngap1a and syngap1b zebrafish duplicates (syngap1ab) and validated these stable models for Syngap1 loss-of-function. Because SYNGAP1 is extensively spliced, we mapped splice variants to the two zebrafish syngap1a and b genes and identified mammalian-like isoforms. We then quantified locomotory behaviors in zebrafish syngap1ab larvae under three conditions that normally evoke different arousal states in wild type larvae: aversive, high-arousal acoustic, medium-arousal dark, and low-arousal light stimuli.

Results

We show that CRISPR/Cas9 indels in zebrafish syngap1a and syngap1b produced loss-of-function alleles at RNA and protein levels. Our analyses of zebrafish Syngap1 isoforms showed that, as in mammals, zebrafish Syngap1 N- and C-termini are extensively spliced. We identified a zebrafish syngap1 α1-like variant that maps exclusively to the syngap1b gene. Quantifying locomotor behaviors showed that syngap1ab larvae are hyperactive compared to wild type but to differing degrees depending on the stimulus. Hyperactivity was most pronounced in low arousal settings, with overall movement increasing with the number of mutant syngap1 alleles.

Conclusions

Our data support mutations in zebrafish syngap1ab as causal for hyperactivity associated with elevated arousal that is especially pronounced in low-arousal environments.

Hyperexcitability and translational phenotypes in a preclinical model of SYNGAP1 mutations

SYNGAP1 is a critical gene for neuronal development, synaptic structure, and function. Although rare, the disruption of SYNGAP1 directly causes a genetically identifiable neurodevelopmental disorder (NDD) called SYNGAP1 -related intellectual disability. Without functional SynGAP1 protein, patients present with intellectual disability, motor impairments, and epilepsy. Previous work using mouse models with a variety of germline and conditional mutations has helped delineate SynGAP1's critical roles in neuronal structure and function, as well as key biochemical signaling pathways essential to synapse integrity. Homozygous loss of SYNGAP1 is embryonically lethal. Heterozygous mutations of SynGAP1 result in a broad range of phenotypes including increased locomotor activity, impaired working spatial memory, impaired cued fear memory, and increased stereotypic behavior. Our in vivo functional data, using the original germline mutation mouse line from the Huganir laboratory, corroborated robust hyperactivity and learning and memory deficits. Here, we describe impairments in the translational biomarker domain of sleep, characterized using neurophysiological data collected with wireless telemetric electroencephalography (EEG). We discovered Syngap1+/- mice exhibited elevated spike trains in both number and duration, in addition to elevated power, most notably in the delta power band. Primary neurons from Syngap1+/- mice displayed increased network firing activity, greater spikes per burst, and shorter inter-burst intervals between peaks using high density micro-electrode arrays (HD-MEA). This work is translational, innovative, and highly significant as it outlines functional impairments in Syngap1 mutant mice. Simultaneously, the work utilized untethered, wireless neurophysiology that can discover potential biomarkers of Syngap1 RI-D, for clinical trials, as it has done with other NDDs. Our work is substantial forward progress toward translational work for SynGAP1R-ID as it bridges in-vitro electrophysiological neuronal activity and function with in vivo neurophysiological brain activity and function. These data elucidate multiple quantitative, translational biomarkers in vivo and in vitro for the development of treatments for SYNGAP1-related intellectual disability.

Exploiting moderate hypoxia to benefit patients with brain disease: Molecular mechanisms and translational research in progress

Hypoxia is increasingly recognized as an important physiological driving force. A specific transcriptional program, induced by a decrease in oxygen (O2) availability, for example, inspiratory hypoxia at high altitude, allows cells to adapt to lower O2 and limited energy metabolism. This transcriptional program is partly controlled by and partly independent of hypoxia-inducible factors. Remarkably, this same transcriptional program is stimulated in the brain by extensive motor-cognitive exercise, leading to a relative decrease in O2 supply, compared to the acutely augmented O2 requirement. We have coined the term "functional hypoxia" for this important demand-responsive, relative reduction in O2 availability. Functional hypoxia seems to be critical for enduring adaptation to higher physiological challenge that includes substantial "brain hardware upgrade," underlying advanced performance. Hypoxia-induced erythropoietin expression in the brain likely plays a decisive role in these processes, which can be imitated by recombinant human erythropoietin treatment. This article review presents hints of how inspiratory O2 manipulations can potentially contribute to enhanced brain function. It thereby provides the ground for exploiting moderate inspiratory plus functional hypoxia to treat individuals with brain disease. Finally, it sketches a planned multistep pilot study in healthy volunteers and first patients, about to start, aiming at improved performance upon motor-cognitive training under inspiratory hypoxia.

Reversal of an existing hearing loss by gene activation in Spns2 mutant mice

Hearing loss is highly heterogeneous, but one common form involves a failure to maintain the local ionic environment of the sensory hair cells reflected in a reduced endocochlear potential. We used a genetic approach to ask whether this type of pathology can be reversed, using the Spns2tm1a mouse mutant known to show this defect. By activating Spns2 gene transcription at different ages after the onset of hearing loss, we found that an existing auditory impairment can be reversed to give close to normal thresholds for an auditory brainstem response (ABR), at least at low to mid stimulus frequencies. Delaying the activation of Spns2 led to less effective recovery of ABR thresholds, suggesting that there is a critical period for intervention. Early activation of Spns2 not only led to improvement in auditory function but also to protection of sensory hair cells from secondary degeneration. The genetic approach we have used to establish that this type of hearing loss is in principle reversible could be extended to many other diseases using available mouse resources.

Hyperexcitability and translational phenotypes in a preclinical model of SYNGAP1 mutations

SYNGAP1 is a critical gene for neuronal development, synaptic structure, and function. Although rare, the disruption of SYNGAP1 directly causes a genetically identifiable neurodevelopmental disorder (NDD) called SYNGAP1-related intellectual disability. Without functional SynGAP1 protein, patients present with intellectual disability, motor impairments, and epilepsy. Previous work using mouse models with a variety of germline and conditional mutations has helped delineate SynGAP1's critical roles in neuronal structure and function, as well as key biochemical signaling pathways essential to synapse integrity. Homozygous loss of SYNGAP1 is embryonically lethal. Heterozygous mutations of SynGAP1 result in a broad range of phenotypes including increased locomotor activity, impaired working spatial memory, impaired cued fear memory, and increased stereotypic behavior. Our in vivo functional data, using the original germline mutation mouse line from the Huganir laboratory, corroborated robust hyperactivity and learning and memory deficits. Here, we describe impairments in the translational biomarker domain of sleep, characterized using neurophysiological data collected with wireless telemetric electroencephalography (EEG). We discovered Syngap1 +/- mice exhibited elevated spike trains in both number and duration, in addition to elevated power, most notably in the delta power band. Primary neurons from Syngap1 +/- mice displayed increased network firing activity, greater spikes per burst, and shorter inter-burst intervals between peaks using high density micro-electrode arrays (HD-MEA). This work is translational, innovative, and highly significant as it outlines functional impairments in Syngap1 mutant mice. Simultaneously, the work utilized untethered, wireless neurophysiology that can discover potential biomarkers of Syngap1R-ID, for clinical trials, as it has done with other NDDs. Our work is substantial forward progress toward translational work for SynGAP1R-ID as it bridges in-vitro electrophysiological neuronal activity and function with in vivo neurophysiological brain activity and function. These data elucidate multiple quantitative, translational biomarkers in vivo and in vitro for the development of treatments for SYNGAP1-related intellectual disability.

Upregulation of SYNGAP1 expression in mice and human neurons by redirecting alternative splicing

The Ras GTPase-activating protein SYNGAP1 plays a central role in synaptic plasticity, and de novo SYNGAP1 mutations are among the most frequent causes of autism and intellectual disability. How SYNGAP1 is regulated during development and how to treat SYNGAP1-associated haploinsufficiency remain challenging questions. Here, we characterize an alternative 3' splice site (A3SS) of SYNGAP1 that induces nonsense-mediated mRNA decay (A3SS-NMD) in mouse and human neural development. We demonstrate that PTBP1/2 directly bind to and promote SYNGAP1 A3SS inclusion. Genetic deletion of the Syngap1 A3SS in mice upregulates Syngap1 protein and alleviates the long-term potentiation and membrane excitability deficits caused by a Syngap1 knockout allele. We further report a splice-switching oligonucleotide (SSO) that converts SYNGAP1 unproductive isoform to the functional form in human iPSC-derived neurons. This study describes the regulation and function of SYNGAP1 A3SS-NMD, the genetic rescue of heterozygous Syngap1 knockout mice, and the development of an SSO to potentially alleviate SYNGAP1-associated haploinsufficiency.

Therapeutic validation and targeting of signalling networks that are dysregulated in intellectual disability

Intellectual disability (ID) represents a major burden on healthcare systems in the developed world. However, there is a disconnect between our knowledge of genes that are mutated in ID and our understanding of the underpinning molecular mechanisms that cause these disorders. We argue that elucidating the signalling and transcriptional networks that are dysregulated in patients will afford new therapeutic opportunities.

Proteomics and weighted gene correlated network analysis reveal glutamatergic synapse signaling in diazepam treatment of alcohol withdrawal

Background: Alcohol use disorder (AUD) is characterized by chronic excessive alcohol consumption, often alternating with periods of abstinence known as alcohol withdrawal syndrome (AWS). Diazepam is the preferred benzodiazepine for treatment of alcohol withdrawal syndrome under most circumstances, but the specific mechanism underlying the treatment needs further research. Methods: We constructed an animal model of two-bottle choices and chronic intermittent ethanol exposure. LC-MS/MS proteomic analysis based on the label-free and intensity-based quantification approach was used to detect the protein profile of the whole brain. Weighted gene correlated network analysis was applied for scale-free network topology analysis. We established a protein-protein interaction network based on the Search Tool for the Retrieval of Interacting Genes (STRING) database and Cytoscape software and identified hub proteins by CytoHubba and MCODE plugins of Cytoscape. The online tool Targetscan identified miRNA-mRNA pair interactions. Results: Seven hub proteins (Dlg3, Dlg4, Shank3, Grin2b, Camk2b, Camk2a and Syngap1) were implicated in alcohol withdrawal syndrome or diazepam treatment. In enrichment analysis, glutamatergic synapses were considered the most important pathway related to alcohol use disorder. Decreased glutamatergic synapses were observed in the late stage of withdrawal, as a protective mechanism that attenuated withdrawal-induced excitotoxicity. Diazepam treatment during withdrawal increased glutamatergic synapses, alleviating withdrawal-induced synapse inhibition. Conclusion: Glutamatergic synapses are considered the most important pathway related to alcohol use disorder that may be a potential molecular target for new interventional strategies.

Reversibility and therapeutic development for neurodevelopmental disorders, insights from genetic animal models

Neurodevelopmental Disorders (NDDs) encompass a broad spectrum of conditions resulting from atypical brain development. Over the past decades, we have had the fortune to witness enormous progress in diagnosis, etiology discovery, modeling, and mechanistic understanding of NDDs from both fundamental and clinical research. Here, we review recent neurobiological advances from experimental models of NDDs. We introduce several examples and highlight breakthroughs in reversal studies of phenotypes using genetically engineered models of NDDs. The in-depth understanding of brain pathophysiology underlying NDDs and evaluations of reversibility in animal models paves the foundation for discovering novel treatment options. We discuss how the expanding property of cutting-edge technologies, such as gene editing and AAV-mediated gene delivery, are leveraged in animal models for the therapeutic development of NDDs. We envision opportunities and challenges toward faithful modeling and fruitful clinical translation.

Activity-Induced Cortical Glutamatergic Neuron Nascent Proteins

Neuronal activity initiates signaling cascades that culminate in diverse outcomes including structural and functional neuronal plasticity, and metabolic changes. While studies have revealed activity-dependent neuronal cell type-specific transcriptional changes, unbiased quantitative analysis of cell-specific activity-induced dynamics in newly synthesized proteins (NSPs) synthesis in vivo has been complicated by cellular heterogeneity and a relatively low abundance of NSPs within the proteome in the brain. Here we combined targeted expression of mutant MetRS (methionine tRNA synthetase) in genetically defined cortical glutamatergic neurons with tight temporal control of treatment with the noncanonical amino acid, azidonorleucine, to biotinylate NSPs within a short period after pharmacologically induced seizure in male and female mice. By purifying peptides tagged with heavy or light biotin-alkynes and using direct tandem mass spectrometry detection of biotinylated peptides, we quantified activity-induced changes in cortical glutamatergic neuron NSPs. Seizure triggered significant changes in ∼300 NSPs, 33% of which were decreased by seizure. Proteins mediating excitatory and inhibitory synaptic plasticity, including SynGAP1, Pak3, GEPH1, Copine-6, and collybistin, and DNA and chromatin remodeling proteins, including Rad21, Smarca2, and Ddb1, are differentially synthesized in response to activity. Proteins likely to play homeostatic roles in response to activity, such as regulators of proteastasis, intracellular ion control, and cytoskeleton remodeling proteins, are activity induced. Conversely, seizure decreased newly synthetized NCAM, among others, suggesting that seizure induced degradation. Overall, we identified quantitative changes in the activity-induced nascent proteome from genetically defined cortical glutamatergic neurons as a strategy to discover downstream mediators of neuronal plasticity and generate hypotheses regarding their function.SIGNIFICANCE STATEMENT Activity-induced neuronal and synaptic plasticity are mediated by changes in the protein landscape, including changes in the activity-induced newly synthesized proteins; however, identifying neuronal cell type-specific nascent proteome dynamics in the intact brain has been technically challenging. We conducted an unbiased proteomic screen from which we identified significant activity-induced changes in ∼300 newly synthesized proteins in genetically defined cortical glutamatergic neurons within 20 h after pharmacologically induced seizure. Bioinformatic analysis of the dynamic nascent proteome indicates that the newly synthesized proteins play diverse roles in excitatory and inhibitory synaptic plasticity, chromatin remodeling, homeostatic mechanisms, and proteasomal and metabolic functions, extending our understanding of the diversity of plasticity mechanisms.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

Adult re-expression of IRSp53 rescues NMDA receptor function and social behavior in IRSp53-mutant mice

IRSp53 (or BAIAP2) is an abundant excitatory postsynaptic scaffolding/adaptor protein that is involved in actin regulation and has been implicated in autism spectrum disorders, schizophrenia, and attention-deficit/hyperactivity disorder. IRSp53 deletion in mice leads to enhanced NMDA receptor (NMDAR) function and social deficits that are responsive to NMDAR inhibition. However, it remains unclear whether IRSp53 re-expression in the adult IRSp53-mutant mouse brain after the completion of brain development could reverse these synaptic and behavioral dysfunctions. Here we employed a brain-blood barrier (BBB)-penetrant adeno-associated virus (AAV) known as PHP.eB to drive adult IRSp53 re-expression in IRSp53-mutant mice. The adult IRSp53 re-expression normalized social deficits without affecting hyperactivity or anxiety-like behavior. In addition, adult IRSp53 re-expression normalized NMDAR-mediated excitatory synaptic transmission in the medial prefrontal cortex. Our results suggest that adult IRSp53 re-expression can normalize synaptic and behavioral deficits in IRSp53-mutant mice and that BBB-penetrant adult gene re-expression has therapeutic potential.

Early and Late Corrections in Mouse Models of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social and repetitive symptoms. A key feature of ASD is early-life manifestations of symptoms, indicative of early pathophysiological mechanisms. In mouse models of ASD, increasing evidence indicates that there are early pathophysiological mechanisms that can be corrected early to prevent phenotypic defects in adults, overcoming the disadvantage of the short-lasting effects that characterize adult-initiated treatments. In addition, the results from gene restorations indicate that ASD-related phenotypes can be rescued in some cases even after the brain has fully matured. These results suggest that we need to consider both temporal and mechanistic aspects in studies of ASD models and carefully compare genetic and nongenetic corrections. Here, we summarize the early and late corrections in mouse models of ASD by genetic and pharmacological interventions and discuss how to better integrate these results to ensure efficient and long-lasting corrections for eventual clinical translation.

Rapid assessment of the temporal function and phenotypic reversibility of neurodevelopmental disorder risk genes in Caenorhabditis elegans

Recent studies have indicated that some phenotypes caused by decreased function of select neurodevelopmental disorder (NDD) risk genes can be reversed by restoring gene function in adulthood. However, few of the hundreds of risk genes have been assessed for adult phenotypic reversibility. We developed a strategy to rapidly assess the temporal requirements and phenotypic reversibility of NDD risk gene orthologs using a conditional protein degradation system and machine-vision phenotypic profiling in Caenorhabditis elegans. We measured how degrading and re-expressing orthologs of EBF3, BRN3A and DYNC1H1 at multiple periods throughout development affect 30 morphological, locomotor, sensory and learning phenotypes. We found that phenotypic reversibility was possible for each gene studied. However, the temporal requirements of gene function and degree of rescue varied by gene and phenotype. This work highlights the critical need to assess multiple windows of degradation and re-expression and a large number of phenotypes to understand the many roles a gene can have across the lifespan. This work also demonstrates the benefits of using a high-throughput model system to prioritize NDD risk genes for re-expression studies in other organisms.

Endogenous Syngap1 alpha splice forms promote cognitive function and seizure protection

Loss-of-function variants in SYNGAP1 cause a developmental encephalopathy defined by cognitive impairment, autistic features, and epilepsy. SYNGAP1 splicing leads to expression of distinct functional protein isoforms. Splicing imparts multiple cellular functions of SynGAP proteins through coding of distinct C-terminal motifs. However, it remains unknown how these different splice sequences function in vivo to regulate neuronal function and behavior. Reduced expression of SynGAP-α1/2 C-terminal splice variants in mice caused severe phenotypes, including reduced survival, impaired learning, and reduced seizure latency. In contrast, upregulation of α1/2 expression improved learning and increased seizure latency. Mice expressing α1-specific mutations, which disrupted SynGAP cellular functions without altering protein expression, promoted seizure, disrupted synapse plasticity, and impaired learning. These findings demonstrate that endogenous SynGAP isoforms with α1/2 spliced sequences promote cognitive function and impart seizure protection. Regulation of SynGAP-αexpression or function may be a viable therapeutic strategy to broadly improve cognitive function and mitigate seizure.

Pharmacological intervention in young adolescents rescues synaptic physiology and behavioural deficits in Syngap1+/- mice

Haploinsufficiency in SYNGAP1 is implicated in intellectual disability (ID) and autism spectrum disorder (ASD) and affects the maturation of dendritic spines. The abnormal spine development has been suggested to cause a disbalance of excitatory and inhibitory (E/I) neurotransmission at distinct developmental periods. In addition, E/I imbalances in Syngap1^+/- mice might be due to abnormalities in K⁺-Cl^- co-transporter function (NKCC1, KCC2), in a maner similar to the murine models of Fragile-X and Rett syndromes. To study whether an altered intracellular chloride ion concentration represents an underlying mechanism of modified function of GABAergic synapses in Dentate Gyrus Granule Cells of Syngap1^+/- recordings were performed at different developmental stages of the mice. We observed depolarised neurons at P14-15 as illustrated by decreased Cl^- reversal potential in Syngap1^+/- mice. The KCC2 expression was decreased compared to Wild-type (WT) mice at P14-15. The GSK-3β inhibitor, 6-bromoindirubin-3'-oxime (6BIO) that crosses the blood-brain barrier, was tested to restore the function of GABAergic synapses. We discovered that the intraperitoneal administration of 6BIO during the critical period or young adolescents [P30 to P80 (4-week to 10-week)] normalised an altered E/I balance, the deficits of synaptic plasticity, and behavioural performance like social novelty, anxiety, and memory of the Syngap1^+/- mice. In summary, altered GABAergic function in Syngap1^+/- mice is due to reduced KCC2 expression leading to an increase in the intracellular chloride concentration that can be counteracted by the 6BIO, which restored cognitive, emotional, and social symptoms by pharmacological intervention, particularly in adulthood.

CDKL5 deficiency disorder: a pathophysiology of neural maintenance

Critical periods are developmental time windows in which functional properties of the brain are particularly susceptible to the organism's experience. It was thought that therapeutic strategies for neurodevelopmental disorders (NDDs) required early life intervention for successful treatment, but previous studies in a mouse model of Rett syndrome indicated that this may not be the case, as some genetic disorders result from disruptions of neuromaintenance. In this issue of the JCI, Terzic et al. provide evidence that defective neuromaintenance also underlies CDKL5 deficiency disorder (CDD). The authors used genetic mouse models to examine the role of CDKL5 protein. Notably, when CDKL5 protein was restored in late adolescent Cdkl5-deficient animals, CDD behavioral defects were reversed. These results suggest that genetically or pharmacologically restoring CDKL5 may treat CDD after symptom onset.

Temporal manipulation of Cdkl5 reveals essential postdevelopmental functions and reversible CDKL5 deficiency disorder-related deficits

CDKL5 deficiency disorder (CDD) is an early onset, neurodevelopmental syndrome associated with pathogenic variants in the X-linked gene encoding cyclin-dependent kinase-like 5 (CDKL5). CDKL5 has been implicated in neuronal synapse maturation, yet its postdevelopmental necessity and the reversibility of CDD-associated impairments remain unknown. We temporally manipulated endogenous Cdkl5 expression in male mice and found that postdevelopmental loss of CDKL5 disrupts numerous behavioral domains, hippocampal circuit communication, and dendritic spine morphology, demonstrating an indispensable role for CDKL5 in the adult brain. Accordingly, restoration of Cdkl5 after the early stages of brain development using a conditional rescue mouse model ameliorated CDD-related behavioral impairments and aberrant NMDA receptor signaling. These findings highlight the requirement of CDKL5 beyond early development, underscore the potential for disease reversal in CDD, and suggest that a broad therapeutic time window exists for potential treatment of CDD-related deficits.

Sleep Abnormalities in the Synaptopathies-SYNGAP1-Related Intellectual Disability and Phelan-McDermid Syndrome

Neurodevelopmental disorders are frequently associated with sleep disturbances. One class of neurodevelopmental disorders, the genetic synaptopathies, is caused by mutations in genes encoding proteins found at the synapse. Mutations in these genes cause derangement of synapse development and function. We utilized a validated sleep instrument, Children's Sleep Habits Questionnaire (CSHQ) to examine the nature of sleep abnormalities occurring in individuals with two synaptopathies-Phelan-McDermid syndrome (PMD) (N = 47, male = 23, female = 24, age 1-46 years) and SYNGAP1-related intellectual disability (SYNGAP1-ID) (N = 64, male = 31, female = 33, age 1-64 years), when compared with unaffected siblings (N = 61, male = 25, female = 36, age 1-17 years). We found that both PMD and SYNGAP1-ID have significant sleep abnormalities with SYNGAP1-ID having greater severity of sleep disturbance than PMD. In addition, sleep disturbances were more severe for PMD in individuals 11 years and older compared with those less than 11 years old. Individuals with either disorder were more likely to use sleep aids than unaffected siblings. In conclusion, sleep disturbances are a significant phenotype in the synaptopathies PMD and SYNGAP1-ID. Improved sleep is a viable endpoint for future clinical trials for these neurodevelopmental disorders.

Syngap1 regulates experience-dependent cortical ensemble plasticity by promoting in vivo excitatory synapse strengthening

A significant proportion of autism risk genes regulate synapse function, including plasticity, which is believed to contribute to behavioral abnormalities. However, it remains unclear how impaired synapse plasticity contributes to network-level processes linked to adaptive behaviors, such as experience-dependent ensemble plasticity. We found that Syngap1, a major autism risk gene, promoted measures of experience-dependent excitatory synapse strengthening in the mouse cortex, including spike-timing-dependent glutamatergic synaptic potentiation and presynaptic bouton formation. Synaptic depression and bouton elimination were normal in Syngap1 mice. Within cortical networks, Syngap1 promoted experience-dependent increases in somatic neural activity in weakly active neurons. In contrast, plastic changes to highly active neurons from the same ensemble that paradoxically weaken with experience were unaffected. Thus, experience-dependent excitatory synapse strengthening mediated by Syngap1 shapes neuron-specific plasticity within cortical ensembles. We propose that other genes regulate neuron-specific weakening within ensembles, and together, these processes function to redistribute activity within cortical networks during experience.

Gene Editing and Modulation: the Holy Grail for the Genetic Epilepsies?

Epilepsy is a complex neurological disorder for which there are a large number of monogenic subtypes. Monogenic epilepsies are often severe and disabling, featuring drug-resistant seizures and significant developmental comorbidities. These disorders are potentially amenable to a precision medicine approach, of which genome editing using CRISPR/Cas represents the holy grail. Here we consider mutations in some of the most 'common' rare epilepsy genes and discuss the different CRISPR/Cas approaches that could be taken to cure these disorders. We consider scenarios where CRISPR-mediated gene modulation could serve as an effective therapeutic strategy and discuss whether a single gene corrective approach could hold therapeutic potential in the context of homeostatic compensation in the developing, highly dynamic brain. Despite an incomplete understanding of the mechanisms of the genetic epilepsies and current limitations of gene editing tools, CRISPR-mediated approaches have game-changing potential in the treatment of genetic epilepsy over the next decade.

Clinical Trial Design for Disease-Modifying Therapies for Genetic Epilepsies

Although trials with anti-seizure medications (ASMs) have not shown clear anti-epileptogenic or disease-modifying activity in humans to date, rapid advancements in genomic technology and emerging gene-mediated and gene replacement options offer hope for the successful development of disease-modifying therapies (DMTs) for genetic epilepsies. In fact, more than 26 potential DMTs are in various stages of preclinical and/or clinical development for genetic syndromes associated with epilepsy. The scope of disease-modification includes but is not limited to effects on the underlying pathophysiology, the condition's natural history, epilepsy severity, developmental achievement, function, behavior, sleep, and quality of life. While conventional regulatory clinical trials for epilepsy therapeutics have historically focused on seizure reduction, similarly designed trials may prove ill-equipped to identify these broader disease-modifying benefits. As we look forward to this pipeline of DMTs, focused consideration should be given to the challenges they pose to conventional clinical trial designs for epilepsy therapeutics. Just as DMTs promise to fundamentally alter how we approach the care of patients with genetic epilepsy syndromes, DMTs likewise challenge how we traditionally construct and measure the success of clinical trials. In the following, we briefly review the historical and preclinical frameworks for DMT development for genetic epilepsies and explore the many novel challenges posed for such trials, including the choice of suitable outcome measures, trial structure, timing and duration of treatment, feasible follow-up period, varying safety profile, and ethical concerns.

Candidate Genes for Eyelid Myoclonia with Absences, Review of the Literature

Eyelid myoclonia with absences (EMA), also known as Jeavons syndrome (JS) is a childhood onset epileptic syndrome with manifestations involving a clinical triad of absence seizures with eyelid myoclonia (EM), photosensitivity (PS), and seizures or electroencephalogram (EEG) paroxysms induced by eye closure. Although a genetic contribution to this syndrome is likely and some genetic alterations have been defined in several cases, the genes responsible for have not been identified. In this review, patients diagnosed with EMA (or EMA-like phenotype) with a genetic diagnosis are summarized. Based on this, four genes could be associated to this syndrome (SYNGAP1, KIA02022/NEXMIF, RORB, and CHD2). Moreover, although there is not enough evidence yet to consider them as candidate for EMA, three more genes present also different alterations in some patients with clinical diagnosis of the disease (SLC2A1, NAA10, and KCNB1). Therefore, a possible relationship of these genes with the disease is discussed in this review.

Modelling epilepsy in the mouse: challenges and solutions

In most mouse models of disease, the outward manifestation of a disorder can be measured easily, can be assessed with a trivial test such as hind limb clasping, or can even be observed simply by comparing the gross morphological characteristics of mutant and wild-type littermates. But what if we are trying to model a disorder with a phenotype that appears only sporadically and briefly, like epileptic seizures? The purpose of this Review is to highlight the challenges of modelling epilepsy, in which the most obvious manifestation of the disorder, seizures, occurs only intermittently, possibly very rarely and often at times when the mice are not under direct observation. Over time, researchers have developed a number of ways in which to overcome these challenges, each with their own advantages and disadvantages. In this Review, we describe the genetics of epilepsy and the ways in which genetically altered mouse models have been used. We also discuss the use of induced models in which seizures are brought about by artificial stimulation to the brain of wild-type animals, and conclude with the ways these different approaches could be used to develop a wider range of anti-seizure medications that could benefit larger patient populations.

Summary: This Review discusses the challenges of modelling epilepsy in mice, a condition in which the outward manifestation of the disorder appears only sporadically, and reviews possible solutions encompassing both genetic and induced models.

SynGAP is expressed in the murine suprachiasmatic nucleus and regulates circadian-gated locomotor activity and light-entrainment capacity

The suprachiasmatic nucleus (SCN) of the hypothalamus functions as the master circadian clock. The phasing of the SCN oscillator is locked to the daily solar cycle, and an intracellular signaling cassette from the small GTPase Ras to the p44/42 mitogen-activated protein kinase (ERK/MAPK) pathway is central to this entrainment process. Here, we analyzed the expression and function of SynGAP-a GTPase-activating protein that serves as a negative regulator of Ras signaling-within the murine SCN. Using a combination of immunohistochemical and Western blotting approaches, we show that SynGAP is broadly expressed throughout the SCN. In addition, temporal profiling assays revealed that SynGAP expression is regulated over the circadian cycle, with peak expression occurring during the circadian night. Further, time-of-day-gated expression of SynGAP was not observed in clock arrhythmic BMAL1 null mice, indicating that the daily oscillation in SynGAP is driven by the inherent circadian timing mechanism. We also show that SynGAP phosphorylation at serine 1138-an event that has been found to modulate its functional efficacy-is regulated by clock time and is responsive to photic input. Finally, circadian phenotypic analysis of Syngap1 heterozygous mice revealed enhanced locomotor activity, increased sensitivity to light-evoked clock entrainment, and elevated levels of light-evoked MAPK activity, which is consistent with the role of SynGAP as a negative regulator of MAPK signaling. These findings reveal that SynGAP functions as a modulator of SCN clock entrainment, an effect that may contribute to sleep and circadian abnormalities observed in patients with SYNGAP1 gene mutations.

pSynGAP1 disturbance-mediated hippocampal oscillation network impairment might contribute to long-term neurobehavioral abnormities in sepsis survivors

Although more patients survive sepsis and are increasingly discharged from the hospital, they often experience long-term cognitive and psychological impairment with significant socioeconomic impact. However, the pathophysiological mechanisms have not been fully elucidated. In the present study, we showed that LPS induced long-term neurobehavioral abnormities, as reflected by significantly decreased freezing time to context and sucrose preference. Using a high-throughput quantitative proteomic screen, we showed that phosphorylation of synaptic GTPase-activating protein 1 (pSynGAP1) was identified as the hub of synaptic plasticity and was significantly decreased following LPS exposure. This decreased pSynGAP was associated with significantly lower theta and gamma oscillations in the CA1 of the hippocampus. Notably, restoration of pSynGAP1 by roscovitine was able to reverse most of these abnormities. Taken together, our study suggested that pSynGAP1 disturbance-mediated hippocampal oscillation network impairment might play a critical role in long-term neurobehavioral abnormities of sepsis survivors.

Recent advances in gene therapy for neurodevelopmental disorders with epilepsy

Neurodevelopmental disorders can be caused by mutations in neuronal genes fundamental to brain development. These disorders have severe symptoms ranging from intellectually disability, social and cognitive impairments, and a subset are strongly linked with epilepsy. In this review, we focus on those neurodevelopmental disorders that are frequently characterized by the presence of epilepsy (NDD + E). We loosely group the genes linked to NDD + E with different neuronal functions: transcriptional regulation, intrinsic excitability and synaptic transmission. All these genes have in common a pivotal role in defining the brain architecture and function during early development, and when their function is altered, symptoms can present in the first stages of human life. The relationship with epilepsy is complex. In some NDD + E, epilepsy is a comorbidity and in others seizures appear to be the main cause of the pathology, suggesting that either structural changes (NDD) or neuronal communication (E) can lead to these disorders. Furthermore, grouping the genes that cause NDD + E, we review the uses and limitations of current models of the different disorders, and how different gene therapy strategies are being developed to treat them. We highlight where gene replacement may not be a treatment option, and where innovative therapeutic tools, such as CRISPR‐based gene editing, and new avenues of delivery are required. In general this group of genetically defined disorders, supported increasing knowledge of the mechanisms leading to neurological dysfunction serve as an excellent collection for illustrating the translational potential of gene therapy, including newly emerging tools.