Cell-Selective Adeno-Associated Virus-Mediated SCN1A Gene Regulation Therapy Rescues Mortality and Seizure Phenotypes in a Dravet Syndrome Mouse Model and Is Well Tolerated in Nonhuman Primates

Recent progress and challenges in gene therapy for pharmacoresistant focal epilepsy

Pharmacoresistant focal epilepsy represents a major unmet need. Recent years have seen several gene therapy strategies validated mainly in rodent models of temporal lobe epilepsy, and some of these have been de-risked for clinical trials. This review considers some of the challenges in progressing from experimental models to the clinic. Among these are identifying promising promoter-transgene combinations, establishing safe and efficacious doses, achieving optimal delivery, and extrapolating across different aetiologies.

Voltage-gated sodium channels in excitable cells as drug targets

Excitable cells - including neurons, muscle cells and cardiac myocytes - are unique in expressing high densities of voltage-gated sodium (NaV) channels. This molecular adaptation enables these cells to produce action potentials, and is essential to their function. With the advent of the molecular revolution, the concept of 'the' sodium channel has been supplanted by understanding that excitable cells in mammals can express any of nine different forms of sodium channels (NaV1.1-NaV1.9). Selective expression in particular types of cells, together with a key role in controlling action potential firing, makes some of these NaV subtypes especially attractive molecular targets for drug development. Although these different channel subtypes display a common overall structure, differences in their amino acid sequences have provided a basis for the development of subtype-specific drugs. This approach has resulted in exciting progress in the development of drugs for epilepsy, cardiac disorders and pain. In this Review, we discuss recent progress in the development of drugs that selectively target each of the sodium channel subtypes.

mTORopathies in Epilepsy and Neurodevelopmental Disorders: The Future of Therapeutics and the Role of Gene Editing

mTORopathies represent a group of neurodevelopmental disorders linked to dysregulated mTOR signaling, resulting in conditions such as tuberous sclerosis complex, focal cortical dysplasia, hemimegalencephaly, and Smith-Kingsmore Syndrome. These disorders often manifest with epilepsy, cognitive impairments, and, in some cases, structural brain anomalies. The mTOR pathway, a central regulator of cell growth and metabolism, plays a crucial role in brain development, where its hyperactivation leads to abnormal neuroplasticity, tumor formation, and heightened neuronal excitability. Current treatments primarily rely on mTOR inhibitors, such as rapamycin, which reduce seizure frequency and tumor size but fail to address underlying genetic causes. Advances in gene editing, particularly via CRISPR/Cas9, offer promising avenues for precision therapies targeting the genetic mutations driving mTORopathies. New delivery systems, including viral and non-viral vectors, aim to enhance the specificity and efficacy of these therapies, potentially transforming the management of these disorders. While gene editing holds curative potential, challenges remain concerning delivery, long-term safety, and ethical considerations. Continued research into mTOR mechanisms and innovative gene therapies may pave the way for transformative, personalized treatments for patients affected by these complex neurodevelopmental conditions.

State-of-the-art gene therapy in epilepsy

PURPOSE OF REVIEW

Gene therapy in epilepsy has undergone a rapid expansion in recent years. This has largely been driven by both advances in our understanding of epilepsy genetics and mechanisms, and also significant advances in gene therapy tools, in particular safe and effective viral vectors. Epilepsy remains an ideal target disease for gene therapy and this review highlights recent developments in this area.

RECENT FINDINGS

There have been continued advances in the development of antisense oligonucleotide therapies to knock down genes in the treatment of monogenic epilepsies with some now entering clinical trial. However, the greatest recent advances have been in vector gene therapy, which offers a more permanent solution by delivering therapeutic genes directly to the brain as a one-off therapy. In particular, there has been a growth in methods that target focal epilepsy. Such promising approaches close to or in clinical trial include expressing NPY and its Y2 receptor, knocking-down GluK5, a kainate receptor subunit, and the over-expression of Kv1.1, an endogenous potassium channel.In the future, it is likely that we will take advantage of approaches of regulating more precisely network excitability by using methods such as optogenetics, designer receptors exclusively activated by designer drugs (DREADDs), 'inhibitory' glutamate receptors activated by excessive glutamate spill-over, and activity-dependent promoters, which target gene expression to the 'hyperactive' neurons.

SUMMARY

Gene therapies offer a novel approach to the treatment of not just genetic epilepsies but any form of epilepsy and may in the future offer an alternative to drug and surgical therapies, allowing more precise, permanent and targeted treatment with fewer adverse effects.

Emerging Genetic Therapies in Epilepsy

Advances in next-generation sequencing have allowed for genetic characterization of many epilepsies that previously had no known cause. Although having a precise diagnosis has been very helpful for management, counseling, and prognosis, until recently true precision medicine approaches that could have disease-modifying effects have been lacking. This review will highlight how preclinical animal models of Dravet syndrome have allowed some novel gene therapy approaches to be studied and further developed such that they are now entering into the clinics.

Merritt-Putnam Symposium | Developmental and Epileptic Encephalopathies-Current Concepts and Novel Approaches

Developmental and epileptic encephalopathies (DEEs) are among the most severe and difficult to treat epilepsies. Two broad strategies for understanding the etiology and impacts of DEEs include genetic and complex adaptive systems approaches. This review, inspired by the 2024 Merritt-Putnam Symposium, describes current perspectives of DEE, identifies limitations of current views, and discusses potential novel ways forward. First, we discuss the rationale for a reevaluation of the role of seizures in the pathogenesis of cognitive and behavioral impairments in DEE. Second, we discuss newly emerging methods employing neural organoids to study brain development and DEE in vitro. Third, we present recent precision therapy approaches for the clinical treatment of DEE. Lastly, we discuss computational systems approaches to understanding the genetic landscape of DEE. The severe and multifaceted impacts of DEE and associated comorbidities underscore the necessity of novel interdisciplinary approaches to produce an improved understanding of etiology and more effective treatment strategies.

Interneuron-specific dual-AAV SCN1A gene replacement corrects epileptic phenotypes in mouse models of Dravet syndrome

Dravet syndrome (DS) is a severe developmental epileptic encephalopathy marked by treatment-resistant seizures, developmental delay, intellectual disability, motor deficits, and a 10 to 20% rate of premature death. Most patients with DS harbor loss-of-function mutations in one copy of SCN1A, which encodes the voltage-gated sodium channel (NaV)1.1 alpha subunit and has been associated with inhibitory neuron dysfunction. Here, we generated a split-intein form of SCN1A and used a dual-vector delivery approach to circumvent adeno-associated virus (AAV) packaging limitations. In addition, we applied previously developed enhancer technology to produce an interneuron-specific gene replacement therapy for DS, called DLX2.0-SCN1A. The split-intein SCN1A vectors produced full-length NaV1.1 protein, and functional sodium channels were recorded in HEK293 cells in vitro. Administration of dual DLX2.0-SCN1A AAVs to wild-type mice produced full-length, reconstituted human protein by Western blot and telencephalic interneuron-specific and dose-dependent NaV1.1 expression by immunohistochemistry. These vectors also conferred strong dose-dependent protection against postnatal mortality and seizures in Scn1afl/+;Meox2-Cre and Scn1a+/R613X DS mouse models. Injection of single or dual DLX2.0-SCN1A AAVs into wild-type mice did not result in increased mortality, weight loss, or gliosis as measured by immunohistochemistry. In contrast, expression of SCN1A in all neurons driven by the human SYNAPSIN I promoter caused an adverse effect marked by increased mortality in the preweaning period, before disease onset. These findings demonstrate proof of concept that interneuron-specific AAV-mediated SCN1A gene replacement can rescue DS phenotypes in mouse models and suggest that it could be a therapeutic approach for patients with DS.

Spotlight on mechanism of sudden unexpected death in epilepsy in Dravet syndrome

Dravet syndrome (DS) is a severe and catastrophic epilepsy with childhood onset. The incidence and prevalence of sudden unexpected death in epilepsy (SUDEP) are significantly higher in DS patients than in general epileptic populations. Although extensive research conducted, the underlying mechanisms of SUDEP occurring in DS patients remain unclear. This review focuses on the link between DS and SUDEP and analyzes the potential pathogenesis. We summarize the genetic basis of DS and SUDEP and elucidate the pathophysiological mechanisms of SUDEP in DS. Furthermore, given the drug-resistant nature of this disorder, the pharmacological approach has limited efficacy and often causes side effects, therefore, the non-pharmacological approaches and precise treatment can reduce the risk of SUDEP in this condition, open a new window to cure this disease, and provide a widened landscape of treatment options for patients.

International Precision Child Health Partnership (IPCHiP): an initiative to accelerate discovery and improve outcomes in rare pediatric disease

Advances in genomic technologies have revolutionized the diagnosis of rare genetic diseases, leading to the emergence of precision therapies. However, there remains significant effort ahead to ensure the promise of precision medicine translates to improved outcomes. Here, we discuss the challenges in advancing precision child health and highlight how international collaborations such as the International Precision Child Health Partnership, which embed research into clinical care, can maximize benefits for children globally.

Sudden Unexpected Death in Epilepsy: Central Respiratory Chemoreception

Sudden unexpected death in epilepsy (SUDEP) is a critical concern for individuals suffering from epilepsy, with respiratory dysfunction playing a significant role in its pathology. Fatal seizures are often characterized by central apnea and hypercapnia (elevated CO2 levels), indicating a failure in ventilatory control. Research has shown that both human epilepsy patients and animal models exhibit a reduced hypercapnic ventilatory response in the interictal (non-seizure) period, suggesting an impaired ability to regulate breathing in response to high CO2 levels. This review examines the role of central chemoreceptors-specifically the retrotrapezoid nucleus, raphe nuclei, nucleus tractus solitarius, locus coeruleus, and hypothalamus in this pathology. These structures are critical for sensing CO2 and maintaining respiratory homeostasis. Emerging evidence also implicates neuropeptidergic pathways within these chemoreceptive regions in SUDEP. Neuropeptides like galanin, pituitary adenylate cyclase-activating peptide (PACAP), orexin, somatostatin, and bombesin-like peptides may modulate chemosensitivity and respiratory function, potentially exacerbating respiratory failure during seizures. Understanding the mechanisms linking central chemoreception, respiratory control, and neuropeptidergic signaling is essential to developing targeted interventions to reduce the risk of SUDEP in epilepsy patients.

Antisense oligonucleotides modulate aberrant inclusion of poison exons in SCN1A-related Dravet syndrome

Dravet syndrome is a developmental and epileptic encephalopathy associated with pathogenic variants in SCN1A. Most disease-causing variants are located within coding regions, but recent work has shed light on the role of noncoding variants associated with a poison exon in intron 20 of SCN1A. Discovery of the SCN1A poison exon known as 20N has led to the first potential disease-modifying therapy for Dravet syndrome in the form of an antisense oligonucleotide. Here, we demonstrate the existence of 2 additional poison exons in introns 1 and 22 of SCN1A through targeted, deep-coverage long-read sequencing of SCN1A transcripts. We show that inclusion of these poison exons is developmentally regulated in the human brain, and that deep intronic variants associated with these poison exons lead to their aberrant inclusion in vitro in a minigene assay or in iPSC-derived neurons. Additionally, we show that splice-modulating antisense oligonucleotides can ameliorate aberrant inclusion of poison exons. Our findings highlight the role of deep intronic pathogenic variants in disease and provide additional therapeutic targets for precision medicine in Dravet syndrome and other SCN1A-related disorders.

Regulatory Elements for Gene Therapy of Epilepsy

The problem of drug resistance in epilepsy means that in many cases, a surgical treatment may be advised. But this is only possible if there is an epileptic focus, and resective brain surgery may have adverse side effects. One of the promising alternatives is gene therapy, which allows the targeted expression of therapeutic genes in different brain regions, and even in specific cell types. In this review, we provide detailed explanations of some key terms related to genetic engineering, and describe various regulatory elements that have already been used in the development of different approaches to treating epilepsy using viral vectors. We compare a few universal promoters for their strength and duration of transgene expression, and in our description of cell-specific promoters, we focus on elements driving expression in glutamatergic neurons, GABAergic neurons and astrocytes. We also explore enhancers and some other cis-regulatory elements currently used in viral vectors for gene therapy, and consider future perspectives of state-of-the-art technologies for designing new, stronger and more specific regulatory elements. Gene therapy has multiple advantages and should become more common in the future, but there is still a lot to study and invent in this field.

A comprehensive review of evolving treatment strategies for Dravet syndrome: Insights from randomized trials, meta-analyses, real-world evidence, and emerging therapeutic approaches

Dravet syndrome (DS) is a severe genetic developmental and epileptic encephalopathy, primarily caused by SCN1A gene mutations. Historically, treatments like clobazam and valproate have been used without evidence from randomized controlled trials (RCTs). However, the therapeutic landscape of DS has evolved with multiple RCTs demonstrating the efficacy and safety of three antiseizure medications (ASMs): stiripentol, cannabidiol (CBD), and fenfluramine. In the absence of direct comparisons between these therapies, several network meta-analyses have been conducted to compare the ASMs, while expert consensus has independently been developed to formulate treatment guidelines. While these three ASMs show promise in reducing seizures, increasing awareness of non-seizure outcomes-such as cognitive development and quality of life-has shifted the focus of evaluation. Some recent real-world studies of these ASMs have reported improvements in these non-seizure outcomes, alongside sustained efficacy and safety. However, natural history studies continue to underscore persistent deficits in these areas and highlight suboptimal long-term seizure control despite the use of these therapies. This review addresses these gaps by first discussing network meta-analyses and treatment guidelines, along with the practical limitations of these approaches. It then examines the long-term efficacy, safety, non-seizure effects, and cost-effectiveness from real-world studies of these ASMs. Finally, emerging research on novel therapeutic approaches, including genetic and serotonergic modulation, is explored. By evaluating these developments, this review aims to guide clinical decision-making and propose future directions for optimizing DS care.

Development of artificial transcription factors and their applications in cell reprograming, genetic screen, and disease treatment

Gene dysregulations are associated with many human diseases, such as cancers and hereditary diseases. Artificial transcription factors (ATFs) are synthetic molecular tools to regulate the expression of disease-associated genes, which is of great significance in basic biological research and biomedical applications. Recent advances in the engineering of ATFs for regulating endogenous gene expression provide an expanded set of tools for understanding and treating diseases. However, the potential immunogenicity, large size, inefficient delivery, and off-target effects persist as obstacles for ATFs to be developed into therapeutics. Moreover, the activation of an endogenous gene following ATF activity lacks durability. In this review, we first describe the functional components of ATFs, including DNA-binding domains, transcriptional effector domains, and control switches. We then highlight examples of applications of ATFs, including cell reprogramming and differentiation, pathogenic gene screening, and disease treatment. Finally, we analyze and summarize major challenges for the clinical translation of ATFs and propose potential strategies to improve these useful molecular tools.

Recent Advances in Pharmacologic Treatments of Drug-Resistant Epilepsy: Breakthrough in Sight

Epilepsy affects approximately 1% of the world population. Patients have recurrent seizures, increased physical and psychiatric comorbidities, and higher mortality rate than the general population. Over the last 40 years, research has resulted in 20 new antiseizure medications (ASMs) approved between 1990 and 2018. In spite of this, up to one-third of patients (~ 1 million patients in the USA) have drug-resistant epilepsy (DRE), with little change between 1982 and 2018, a period of intense new ASM development. A minority of patients with DRE may benefit from surgical treatment, but this specialized care remains challenging to scale. Therefore, the greatest hope for breakthroughs for patients with DRE is in pharmacologic therapies. Recently, several advances promise to change the outcomes for patients with DRE. Cenobamate, a drug with dual mechanisms of modulating sodium channel currents and GABA-A receptors, achieves 90-100% seizure reduction in 25-33% of patients with focal DRE, a response not observed with other ASMs. Fenfluramine, a serotonin-acting drug, dramatically reduces the frequency of convulsive seizures in Dravet syndrome, a devastating developmental epileptic encephalopathy with severe DRE. Both drugs reduce mortality. In addition, the possibility of DRE prevention was recently raised in patients with tuberous sclerosis complex, a relatively common genetic form of epilepsy. A paradigm shift is emerging in the treatment of epilepsy. Seizure freedom has become attainable in a significant proportion of patients with focal DRE, and dramatic seizure reduction has been achieved in a developmental encephalopathy. Coupled with a rich pipeline of new compounds under clinical development, the long sought-after breakthrough in the treatment of epilepsy may finally be in sight.

Therapeutic development approaches to treat haploinsufficiency diseases: restoring protein levels

Rare diseases affect one in ten people but only a small fraction of these diseases have an FDA-approved treatment. Haploinsufficiency, caused by a dominant loss-of-function mutation, is a unique rare disease group because patients have one normal allele of the affected gene. This makes rare haploinsufficiency diseases promising candidates for drug development by increasing expression of the normal gene allele, decreasing the target protein degradation and enhancing the target protein function. This review summarizes recent progresses and approaches used in the translational research of therapeutics to treat haploinsufficiency diseases including gene therapy, nucleotide-based therapeutics and small-molecule drug development. We hope that these drug development strategies will accelerate therapeutic development to treat haploinsufficiency diseases.

Pharmacotherapeutic strategies for drug-resistant epilepsy in children

Drug resistance is defined as the failure of adequate trials of two tolerated and appropriately chosen antiseizure medications to achieve sustained seizure freedom. In case of uncontrolled seizures, pseudo-drug-resistance (poor compliance, a worsening effect of an antiseizure medication, a diagnosis of psychogenic non-epileptic seizure) should be first ruled out in case of pediatric epilepsies. This paper discusses the process of choosing antiseizure medication and the concepts of rationale polytherapy and precision medicine. In drug-resistant epilepsy, when curative surgery is not feasible, the aim of the treatment is focused on the improvement of quality of life rather than on seizure count. In recent years, despite an increase in available antiseizure medications, the incidence of drug-resistant epilepsy has not changed. Precision medicine may offer in rare epilepsies a mechanism-driven treatment, but it is still unclear if this will end up in an improvement of efficacy in drug-resistant epilepsies. Gene therapy with antisense oligonucleotides or Adeno-associated Virus (AAV) is transitioning from the experimental side to the first human trial. It may modify the natural history of selected epileptic syndromes.

Metabolic aspects of genetic ion channel epilepsies

Nowadays, particularly in countries with high incomes, individual mutations in people affected by genetic epilepsies are identified, and genetic therapies are being developed. In addition, drugs are being screened to directly target specific mutations, and personalised medicine is possible. However, people with epilepsy do not yet benefit from these advances, and many types of epilepsies are medication-resistant, including Dravet syndrome. Thus, in the meantime, alternative and effective treatment options are needed. There is increasing evidence that metabolic deficits contribute to epileptic seizures and that such metabolic impairments may be amenable to treatment, with metabolic treatment options like the ketogenic diet being employed with some success. However, the brain metabolic alterations that occur in ion channel epilepsies are not well-understood, nor how these may differ from epilepsies that are of acquired and unknown origins. Here, we provide an overview of studies investigating metabolic alterations in epilepsies caused by mutations in the SCN1A and KCNA1 genes, which are currently the most studied ion channel epilepsies in animal models. The metabolic changes found in these models are likely to contribute to seizures. A metabolic basis of these ion channel epilepsies is supported by human and/or animal studies that show beneficial effects of the ketogenic diet, which may be mediated by the provision of auxiliary brain fuel in the form of ketone bodies. Other potentially more preferred dietary therapies including medium-chain triglycerides and triheptanoin have also been tested in a limited number of studies, but their efficacies remain to be clearly established. The extent to which brain metabolism is affected in people with Dravet syndrome, KCNA1 epilepsy and the models thereof still requires clarification. This requires more experiments that yield functional insight into metabolism.

Unraveling the genetic basis of epilepsy: Recent advances and implications for diagnosis and treatment

Epilepsy, affecting approximately 1% of the global population, manifests as recurring seizures and is heavily influenced by genetic factors. Recent advancements in genetic technologies have revolutionized our understanding of epilepsy's genetic landscape. Key studies, such as the discovery of mutations in ion channels (e.g., SCN1A and SCN2A), neurotransmitter receptors (e.g., GABRA1), and synaptic proteins (e.g., SYNGAP1, KCNQ2), have illuminated critical pathways underlying epilepsy susceptibility and pathogenesis. Genome-wide association studies (GWAS) have identified specific genetic variations linked to epilepsy risk, such as variants near SCN1A and PCDH7, enhancing diagnostic accuracy and enabling personalized treatment strategies. Moreover, epigenetic mechanisms, including DNA methylation (e.g., MBD5), histone modifications (e.g., HDACs), and non-coding RNAs (e.g., miR-134), play pivotal roles in altering gene expression and synaptic plasticity, contributing to epileptogenesis. These discoveries offer promising avenues for therapeutic interventions aimed at improving outcomes for epilepsy patients. Genetic testing has become essential in clinical practice, facilitating precise diagnosis and tailored management approaches based on individual genetic profiles. Furthermore, insights into epigenetic regulation suggest novel therapeutic targets for developing more effective epilepsy treatments. In summary, this review highlights significant progress in understanding the genetic and epigenetic foundations of epilepsy. By integrating findings from key studies and specifying genes involved in epigenetic modifications, we underscore the potential for advanced therapeutic strategies in this complex neurological disorder, emphasizing the importance of personalized medicine approaches in epilepsy management.

Adeno-Associated Viral Vectors in the Treatment of Epilepsy

Epilepsy is a brain disorder characterized by a persistent predisposition to epileptic seizures. With various etiologies of epilepsy, a significant proportion of patients develop pharmacoresistance to antiepileptic drugs, which necessitates the search for new therapeutic methods, in particular, using gene therapy. This review discusses the use of adeno-associated viral (AAV) vectors in gene therapy for epilepsy, emphasizing their advantages, such as high efficiency of neuronal tissue transduction and low immunogenicity/cytotoxicity. AAV vectors provide the possibility of personalized therapy due to the diversity of serotypes and genomic constructs, which allows for increasing the specificity and effectiveness of treatment. Promising orientations include the modulation of the expression of neuropeptides, ion channels, transcription, and neurotrophic factors, as well as the use of antisense oligonucleotides to regulate seizure activity, which can reduce the severity of epileptic disorders. This review summarizes the current advances in the use of AAV vectors for the treatment of epilepsy of various etiologies, demonstrating the significant potential of AAV vectors for the development of personalized and more effective approaches to reducing seizure activity and improving patient prognosis.

Recent advances and current status of gene therapy for epilepsy

BACKGROUND

Epilepsy is a common neurological disorder with complex pathogenic mechanisms, and refractory epilepsy often lacks effective treatments. Gene therapy is a promising therapeutic option, with various preclinical experiments achieving positive results, some of which have progressed to clinical studies.

DATA SOURCES

This narrative review was conducted by searching for papers published in PubMed/MEDLINE with the following single and/or combination keywords: epilepsy, children, neurodevelopmental disorders, genetics, gene therapy, vectors, transgenes, receptors, ion channels, micro RNAs (miRNAs), clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas)9 (CRISPR/Cas9), expression regulation, optogenetics, chemical genetics, mitochondrial epilepsy, challenges, ethics, and disease models.

RESULTS

Currently, gene therapy research in epilepsy primarily focuses on symptoms attenuation mediated by viral vectors such as adeno-associated virus and other types. Advances in gene therapy technologies, such as CRISPR/Cas9, have provided a new direction for epilepsy treatment. However, the clinical application still faces several challenges, including issues related to vectors, models, expression controllability, and ethical considerations.

CONCLUSIONS

Here, we summarize the relevant research and clinical advances in gene therapy for epilepsy and outline the challenges facing its clinical application. In addition to the shortcomings inherent in gene therapy components, the reconfiguration of excitatory and inhibitory properties in epilepsy treatment is a delicate process. On-demand, cell-autonomous treatments and multidisciplinary collaborations may be crucial in addressing these issues. Understanding gene therapy for epilepsy will help clinicians gain a clearer perception of the research progress and challenges, guiding the design of future clinical protocols and research decisions.

The expanding field of genetic developmental and epileptic encephalopathies: current understanding and future perspectives

Recent advances in genetic testing technologies have revolutionised the identification of genetic abnormalities in early onset developmental and epileptic encephalopathies (DEEs). In this Review, we provide an update on the expanding landscape of genetic factors contributing to DEEs, encompassing over 800 reported genes. We focus on the cellular and molecular mechanisms driving epileptogenesis, with an emphasis on emerging therapeutic strategies and effective treatment options. We explore noteworthy, novel genes linked to DEE phenotypes, such as gBRAT-1 and GNAO1, and gene families such as GRIN and HCN. Understanding the network-level effects of gene variants will pave the way for potential gene therapy applications. Given the diverse comorbidities associated with DEEs, a multidisciplinary team approach is essential. Despite ongoing efforts and improved genetic testing, DEEs lack a cure, and treatment complexities persist. This Review underscores the necessity for larger international prospective studies focusing on both seizure outcomes and developmental trajectories.

Medial septum parvalbumin-expressing inhibitory neurons are impaired in a mouse model of Dravet Syndrome

Dravet syndrome (DS) is a severe neurodevelopmental disorder caused by pathogenic variants in the SCN1A gene, which encodes the voltage-gated sodium channel Na v 1.1 α subunit. Experiments in animal models of DS - including the haploinsufficient Scn1a +/- mouse - have identified impaired excitability of interneurons in the hippocampus and neocortex; this is thought to underlie the treatment-resistant epilepsy that is a prominent feature of the DS phenotype. However, additional brain structures, such as the medial septum (MS), also express SCN1A . The medial septum is known to play an important role in cognitive function and thus may contribute to the intellectual impairment that also characterizes DS. In this study, we employed whole cell patch clamp recordings in acute brain slices to characterize the electrophysiological properties of MS neurons in Scn1a +/- mice versus age-matched wild-type littermate controls. We found no discernible genotype-related differences in MS cholinergic (ChAT) neurons, but significant dysfunction within MS parvalbumin-expressing (PV) inhibitory neurons in Scn1a +/- mice. We further identified heterogeneity of firing patterns among MS PV neurons, and additional genotype differences in the proportion of subtype representation. These results confirm that the MS is an additional locus of pathology in DS, that may contribute to co- morbidities such as cognitive impairment.

Progress report on new medications for seizures and epilepsy: A summary of the 17th Eilat Conference on New Antiepileptic Drugs and Devices (EILAT XVII). I. Drugs in preclinical and early clinical development

For >30 years, the Eilat Conference on New Antiepileptic Drugs and Devices has provided a forum for the discussion of advances in the development of new therapies for seizures and epilepsy. The EILAT XVII conference took place in Madrid, Spain, on May 5-8, 2024. Participants included basic scientists and clinical investigators from industry and academia, other health care professionals, and representatives from lay organizations. We summarize in this article information on treatments in preclinical and in early clinical development discussed at the conference. These include AMT-260, a gene therapy designed to downregulate the expression of Glu2K subunits of kainate receptors, in development for the treatment of drug-resistant seizures associated with mesial temporal sclerosis; BHV-7000, a selective activator of heteromeric Kv7.2/7.3 potassium channels, in development for the treatment of focal epilepsy; ETX101, a recombinant adeno-associated virus serotype 9 designed to increase NaV1.1 channel density in inhibitory γ-aminobutyric acidergic (GABAergic) neurons, in development for the treatment of SCN1A-positive Dravet syndrome; GAO-3-02, a compound structurally related to synaptamide, which exerts antiseizure activity at least in part through an action on cannabinoid type 2 receptors; LRP-661, a structural analogue of cannabidiol, in development for the treatment of seizures associated with Lennox-Gastaut syndrome, Dravet syndrome, and tuberous sclerosis complex; OV329, a selective inactivator of GABA aminotransferase, in development for the treatment of drug-resistant seizures; PRAX-628, a functionally selective potent sodium channel modulator with preference for the hyperexcitable state of sodium channels, in development for the treatment of focal seizures; RAP-219, a selective negative allosteric modulator of transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor regulatory protein γ-8, in development for the treatment of focal seizures; and rozanolixizumab, a humanized anti-neonatal Fc receptor monoclonal antibody, in development for the treatment of LGI1 autoimmune encephalitis. Treatments in more advanced development are summarized in Part II of this report.

Developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies, the most severe group of epilepsies, are characterized by seizures and frequent epileptiform activity associated with developmental slowing or regression. Onset typically occurs in infancy or childhood and includes many well-defined epilepsy syndromes. Patients have wide-ranging comorbidities including intellectual disability, psychiatric features, such as autism spectrum disorder and behavioural problems, movement and musculoskeletal disorders, gastrointestinal and sleep problems, together with an increased mortality rate. Problems change with age and patients require substantial support throughout life, placing a high psychosocial burden on parents, carers and the community. In many patients, the aetiology can be identified, and a genetic cause is found in >50% of patients using next-generation sequencing technologies. More than 900 genes have been identified as monogenic causes of developmental and epileptic encephalopathies and many cell components and processes have been implicated in their pathophysiology, including ion channels and transporters, synaptic proteins, cell signalling and metabolism and epigenetic regulation. Polygenic risk score analyses have shown that common variants also contribute to phenotypic variability. Holistic management, which encompasses antiseizure therapies and care for multimorbidities, is determined both by epilepsy syndrome and aetiology. Identification of the underlying aetiology enables the development of precision medicines to improve the long-term outcome of patients with these devastating diseases.

Dopamine Dilemma Overexcites the Hippocampus in Alzheimer's Disease

Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease Spoleti E, La Barbera L, Cauzzi E, De Paolis ML, Saba L, Marino R, Sciamanna G, Di Lazzaro V, Keller F, Nobili A, Krashia P. Mol Psychiatry . 2024;29(5):1265-1280. doi:10.1038/s41380-024-02408-9. Early and progressive dysfunctions of the dopaminergic system from the ventral tegmental area (VTA) have been described in Alzheimer's disease (AD). During the long pre-symptomatic phase, alterations in the function of parvalbumin interneurons (PV-INs) are also observed, resulting in cortical hyperexcitability represented by subclinical epilepsy and aberrant gamma oscillations. However, it is unknown whether the dopaminergic deficits contribute to brain hyperexcitability in AD. Here, using the Tg2576 mouse model of AD, we prove that reduced hippocampal dopaminergic innervation, due to VTA dopamine neuron degeneration, impairs PV-IN firing and gamma waves, weakens the inhibition of pyramidal neurons and induces hippocampal hyperexcitability via lower D2 receptor-mediated activation of the cAMP-response element binding protein (CREB) pathway. These alterations coincide with reduced PV-IN numbers and perineuronal net density. Importantly, L-DOPA and the selective D2 receptor agonist quinpirole rescue p-CREB levels and improve the PV-IN-mediated inhibition, thus reducing hyperexcitability. Moreover, similarly to quinpirole, sumanirole—another D2 receptor agonist and a known anticonvulsant—not only increases p-CREB levels in PV-INs but also restores gamma oscillations in Tg2576 mice. Conversely, blocking the dopaminergic transmission with sulpiride (a D2-like receptor antagonist) in wild-type mice reduces p-CREB levels in PV-INs, mimicking what occurs in Tg2576. Overall, these findings support the hypothesis that the VTA dopaminergic system integrity plays a key role in hippocampal PV-IN function and survival, disclosing a relevant contribution of the reduced dopaminergic tone to aberrant gamma waves, hippocampal hyperexcitability, and epileptiform activity in early AD.

Innovative drug discovery strategies in epilepsy: integrating next-generation syndrome-specific mouse models to address pharmacoresistance and epileptogenesis

INTRODUCTION

Although there are numerous treatment options already available for epilepsy, over 30% of patients remain resistant to these antiseizure medications (ASMs). Historically, ASM discovery has relied on the demonstration of efficacy through the use of 'traditional' acute in vivo seizure models (e.g. maximal electroshock, subcutaneous pentylenetetrazol, and kindling). However, advances in genetic sequencing technologies and remaining medical needs for people with treatment-resistant epilepsy or special patient populations have encouraged recent efforts to identify novel compounds in syndrome-specific models of epilepsy. Syndrome-specific models, including Scn1a variant models of Dravet syndrome and APP/PS1 mice associated with familial early-onset Alzheimer's disease, have already led to the discovery of two mechanistically novel treatments for developmental and epileptic encephalopathies (DEEs), namely cannabidiol and soticlestat, respectively.

AREAS COVERED

In this review, the authors discuss how it is likely that next-generation drug discovery efforts for epilepsy will more comprehensively integrate syndrome-specific epilepsy models into early drug discovery providing the reader with their expert perspectives.

EXPERT OPINION

The percentage of patients with pharmacoresistant epilepsy has remained unchanged despite over 30 marketed ASMs. Consequently, there is a high unmet need to reinvent and revise discovery strategies to more effectively address the remaining needs of patients with specific epilepsy syndromes, including drug-resistant epilepsy and DEEs.

ENVISIONing a critical period to preserve development: communication delays in SCN1A+ dravet syndrome

Severe Communication Delays are Independent of Seizure Burden and Persist Despite Contemporary Treatments in SCN1A+ Dravet Syndrome: Insights From the ENVISION Natural History Study Perry MS, Scheffer IE, Sullivan J, Brunklaus A, Boronat S, Wheless JW, Laux L, Patel AD, Roberts CM, Dlugos D, Holder D, Knupp KG, Lallas M, Phillips S, Segal E, Smeyers P, Lal D, Wirrell E, Zuberi S, Brünger T, Wojnaroski M, Maru B, O'Donnell P, Morton M, James E, Vila MC, Huang N, Gofshteyn JS, Rico S. Epilepsia . 2024 Feb;65(2):322–337. Epub 2023 Dec 22. PMID: 38049202. doi:10.1111/epi.17850 Objective: Dravet syndrome (DS) is a developmental and epileptic encephalopathy characterized by high seizure burden, treatment-resistant epilepsy, and developmental stagnation. Family members rate communication deficits among the most impactful disease manifestations. We evaluated seizure burden and language/communication development in children with DS. Methods: ENVISION was a prospective, observational study evaluating children with DS associated with SCN1A pathogenic variants (SCN1A+ DS) enrolled at age ≤5 years. Seizure burden and antiseizure medications were assessed every 3 months and communication and language every 6 months with the Bayley Scales of Infant and Toddler Development 3rd edition and the parent-reported Vineland Adaptive Behavior Scales 3rd edition. We report data from the first year of observation, including analyses stratified by age at Baseline: 0:6-2:0 years:months (Y:M; youngest), 2:1-3:6 Y:M (middle), and 3:7-5:0 Y:M (oldest). Results: Between December 2020 and March 2023, 58 children with DS enrolled at 16 sites internationally. Median follow-up was 17.5 months (range = 0.0-24.0), with 54 of 58 (93.1%) followed for at least 6 months and 51 of 58 (87.9%) for 12 months. Monthly countable seizure frequency (MCSF) increased with age (median [minimum-maximum] = 1.0 in the youngest [1.0-70.0] and middle [1.0-242.0] age groups and 4.5 [0.0-2647.0] in the oldest age group), and remained high, despite use of currently approved antiseizure medications. Language/communication delays were observed early, and developmental stagnation occurred after age 2 years with both instruments. In predictive modeling, chronologic age was the only significant covariate of seizure frequency (effect size = .52, P  = .024). MCSF, number of antiseizure medications, age at first seizure, and convulsive status epilepticus were not predictors of language/communication raw scores. Significance: In infants and young children with SCN1A+ DS, language/communication delay and stagnation were independent of seizure burden. Our findings emphasize that the optimal therapeutic window to prevent language/communication delay is before 3 years of age.

Intraparenchymal delivery of adeno-associated virus vectors for the gene therapy of neurological diseases

INTRODUCTION

In gene therapy with adeno-associated virus (AAV) vectors for diseases of the central nervous system, the vectors can be administered into blood vessels, cerebrospinal fluid space, or the brain parenchyma. When gene transfer to a large area of the brain is required, the first two methods are used, but for diseases in which local gene transfer is expected to be effective, vectors are administered directly into the brain parenchyma.

AREAS COVERED

Strategies for intraparenchymal vector delivery in gene therapy for Parkinson's disease, aromatic l-amino acid decarboxylase (AADC) deficiency, and epilepsy are reviewed.

EXPERT OPINION

Stereotactic intraparenchymal injection of AAV vectors allows precise gene delivery to the target site. Although more surgically invasive than intravascular or intrathecal administration, intraparenchymal vector delivery has the advantage of a lower vector dose, and preexisting neutralizing antibodies have little effect on the transduction efficacy. This approach improves motor function in AADC deficiency and led to regulatory approval of an AAV vector for the disease in the EU. Although further validation through clinical studies is needed, direct infusion of viral vectors into the brain parenchyma is expected to be a novel treatment for Parkinson's disease and drug-resistant epilepsy.

Adeno-associated virus vector delivery to the brain: Technology advancements and clinical applications

Adeno-associated virus (AAV) vectors have emerged as a promising tool in the development of gene therapies for various neurological diseases, including Alzheimer's disease and Parkinson's disease. However, the blood-brain barrier (BBB) poses a significant challenge to successfully delivering AAV vectors to the brain. Strategies that can overcome the BBB to improve the AAV delivery efficiency to the brain are essential to successful brain-targeted gene therapy. This review provides an overview of existing strategies employed for AAV delivery to the brain, including direct intraparenchymal injection, intra-cerebral spinal fluid injection, intranasal delivery, and intravenous injection of BBB-permeable AAVs. Focused ultrasound has emerged as a promising technology for the noninvasive and spatially targeted delivery of AAV administered by intravenous injection. This review also summarizes each strategy's current preclinical and clinical applications in treating neurological diseases. Moreover, this review includes a detailed discussion of the recent advances in the emerging focused ultrasound-mediated AAV delivery. Understanding the state-of-the-art of these gene delivery approaches is critical for future technology development to fulfill the great promise of AAV in neurological disease treatment.

Advancements in Dravet Syndrome Therapeutics: A Comprehensive Look at Present and Future Treatment Horizons: A Focused Review

Dravet syndrome (DS) is a developmental epileptic encephalopathy, characterized by fever-triggered focal or hemiclonic seizures at onset with various associated comorbidities like intellectual disability, gait abnormalities, and behavioral issues. It typically advances to drug-refractory epilepsy with multiple seizure semiology. In this review, we give a focused narrative on the treatment aspects of DS. We searched the PubMed database for articles on DS. More than 500 articles were reviewed, of which 55 relevant articles are included in this review. ClinicalTrials.gov database was also accessed for data on ongoing trials. Majority are caused by mutations in the SCN1A gene. Valproate and clobazam are the most commonly used traditional antiseizure medications. Stiripentol, fenfluramine, and cannabidiol are recently approved drugs with promising results. Ketogenic diet and vagus nerve stimulation are commonly tried nonpharmacologic modalities that have shown significant responses. Antisense oligonucleotides and viral vector-mediated gene transfer therapies are on the horizon. This review outlines the current existing treatment rationale, evidence for newly approved drugs, and the future scope of gene therapy in DS.

Neurosurgical gene therapy for central nervous system diseases

Viral vector mediated gene therapies for neurodegenerative and neurodevelopmental conditions that require neurosurgical administration continue to expand. We systematically reviewed the National Institutes of Health (NIH) ClinicalTrials.gov database to identify all clinical trials studying in-vivo viral vector mediated gene therapies targeted to the CNS for neurodegenerative and neurodevelopmental diseases. We isolated studies which delivered therapies using neurosurgical approaches: intracisternal, intraventricular, and/or intraparenchymal. Clinical trials primarily registered in international countries were included if they were referenced by an NIH registered clinical trial. We performed a scoping review to identify the preclinical studies that supported each human clinical trial. Key preclinical and clinical data were aggregated to characterize vector capsid design, delivery methods, gene expression profile, and clinical benefit. A total of 64 clinical trials were identified in active, completed, terminated, and long-term follow-up stages. A range of CNS conditions across pediatric and adult populations are being studied with CNS targeted viral vector gene therapy, including Alzheimer's disease, Parkinson's disease, AADC deficiency, sphingolipidoses, mucopolysaccharidoses, neuronal ceroid lipofuscinoses, spinal muscular atrophy, adrenoleukodystrophy, Canavan disease, frontotemporal dementia, Huntington's disease, Rett syndrome, Dravet syndrome, mesial temporal lobe epilepsy, and glutaric acidemia. Adeno-associated viral vectors (AAVs) were utilized by the majority of tested therapies, with vector serotypes, regulatory elements, delivery methods, and vector monitoring varying based on the disease being studied. Intraparenchymal delivery has evolved significantly, with MRI-guided convection-enhanced delivery established as a gold standard method for pioneering novel gene targets.

Brainwide silencing of prion protein by AAV-mediated delivery of an engineered compact epigenetic editor

Prion disease is caused by misfolding of the prion protein (PrP) into pathogenic self-propagating conformations, leading to rapid-onset dementia and death. However, elimination of endogenous PrP halts prion disease progression. In this study, we describe Coupled Histone tail for Autoinhibition Release of Methyltransferase (CHARM), a compact, enzyme-free epigenetic editor capable of silencing transcription through programmable DNA methylation. Using a histone H3 tail-Dnmt3l fusion, CHARM recruits and activates endogenous DNA methyltransferases, thereby reducing transgene size and cytotoxicity. When delivered to the mouse brain by systemic injection of adeno-associated virus (AAV), Prnp-targeted CHARM ablates PrP expression across the brain. Furthermore, we have temporally limited editor expression by implementing a kinetically tuned self-silencing approach. CHARM potentially represents a broadly applicable strategy to suppress pathogenic proteins, including those implicated in other neurodegenerative diseases.

Enhancing the action of serotonin by three different mechanisms prevents spontaneous seizure-induced mortality in Dravet mice

OBJECTIVE

Sudden unexpected death in epilepsy (SUDEP) is an underestimated complication of epilepsy. Previous studies have demonstrated that enhancement of serotonergic neurotransmission suppresses seizure-induced sudden death in evoked seizure models. However, it is unclear whether elevated serotonin (5-HT) function will prevent spontaneous seizure-induced mortality (SSIM), which is characteristic of human SUDEP. We examined the effects of 5-HT-enhancing agents that act by three different pharmacological mechanisms on SSIM in Dravet mice, which exhibit a high incidence of SUDEP, modeling human Dravet syndrome.

METHODS

Dravet mice of both sexes were evaluated for spontaneous seizure characterization and changes in SSIM incidence induced by agents that enhance 5-HT-mediated neurotransmission. Fluoxetine (a selective 5-HT reuptake inhibitor), fenfluramine (a 5-HT releaser and agonist), SR 57227 (a specific 5-HT3 receptor agonist), or saline (vehicle) was intraperitoneally administered over an 8-day period in Dravet mice, and the effect of these treatments on SSIM was examined.

RESULTS

Spontaneous seizures in Dravet mice generally progressed from wild running to tonic seizures with or without SSIM. Fluoxetine at 30 mg/kg, but not at 20 or 5 mg/kg, significantly reduced SSIM compared with the vehicle control. Fenfluramine at 1-10 mg/kg, but not .2 mg/kg, fully protected Dravet mice from SSIM, with all mice surviving. Compared with the vehicle control, SR 57227 at 20 mg/kg, but not at 10 or 5 mg/kg, significantly lowered SSIM. The effect of these drugs on SSIM was independent of sex.

SIGNIFICANCE

Our data demonstrate that elevating serotonergic function by fluoxetine, fenfluramine, or SR 57227 significantly reduces or eliminates SSIM in Dravet mice in a sex-independent manner. These findings suggest that deficits in serotonergic neurotransmission likely play an important role in the pathogenesis of SSIM, and fluoxetine and fenfluramine, which are US Food and Drug Administration-approved medications, may potentially prevent SUDEP in at-risk patients.

SCN1A Channels a Wide Range of Epileptic Phenotypes: Report of Novel and Known Variants with Variable Presentations

SCN1A, the gene encoding for the Nav1.1 channel, exhibits dominant interneuron-specific expression, whereby variants disrupting the channel's function affect the initiation and propagation of action potentials and neuronal excitability causing various types of epilepsy. Dravet syndrome (DS), the first described clinical presentation of SCN1A channelopathy, is characterized by severe myoclonic epilepsy in infancy (SMEI). Variants' characteristics and other genetic or epigenetic factors lead to extreme clinical heterogeneity, ranging from non-epileptic conditions to developmental and epileptic encephalopathy (DEE). This current study reports on findings from 343 patients referred by physicians in hospitals and tertiary care centers in Greece between 2017 and 2023. Positive family history for specific neurologic disorders was disclosed in 89 cases and the one common clinical feature was the onset of seizures, at a mean age of 17 months (range from birth to 15 years old). Most patients were specifically referred for SCN1A investigation (Sanger Sequencing and MLPA) and only five for next generation sequencing. Twenty-six SCN1A variants were detected, including nine novel causative variants (c.4567A>Τ, c.5564C>A, c.2176+2T>C, c.3646G>C, c.4331C>A, c.1130_1131delGAinsAC, c.1574_1580delCTGAGGA, c.4620A>G and c.5462A>C), and are herein presented, along with subsequent genotype-phenotype associations. The identification of novel variants complements SCN1A databases extending our expertise on genetic counseling and patient and family management including gene-based personalized interventions.

Temporal manipulation of the Scn1a gene reveals its essential role in adult brain function

Dravet syndrome is a severe epileptic encephalopathy, characterized by drug-resistant epilepsy, severe cognitive and behavioural deficits, with increased risk of sudden unexpected death (SUDEP). It is caused by haploinsufficiency of SCN1A gene encoding for the α-subunit of the voltage-gated sodium channel Nav1.1. Therapeutic approaches aiming to upregulate the healthy copy of SCN1A gene to restore its normal expression levels are being developed. However, whether Scn1a gene function is required only during a specific developmental time-window or, alternatively, if its physiological expression is necessary in adulthood is untested up to now. We induced Scn1a gene haploinsufficiency at two ages spanning postnatal brain development (P30 and P60) and compared the phenotypes of those mice to Scn1a perinatally induced mice (P2), recapitulating all deficits of Dravet mice. Induction of heterozygous Nav1.1 mutation at P30 and P60 elicited susceptibility to the development of both spontaneous and hyperthermia-induced seizures and SUDEP rates comparable to P2-induced mice, with symptom onset accompanied by the characteristic GABAergic interneuron dysfunction. Finally, delayed Scn1a haploinsufficiency induction provoked hyperactivity, anxiety and social attitude impairment at levels comparable to age matched P2-induced mice, while it was associated with a better cognitive performance, with P60-induced mice behaving like the control group. Our data show that maintenance of physiological levels of Nav1.1 during brain development is not sufficient to prevent Dravet symptoms and that long-lasting restoration of Scn1a gene expression would be required to grant optimal clinical benefit in patients with Dravet syndrome.

Established and emerging GABAA receptor pharmacotherapy for epilepsy

Drugs that modulate the GABAA receptor are widely used in clinical practice for both the long-term management of epilepsy and emergency seizure control. In addition to older medications that have well-defined roles for the treatment of epilepsy, recent discoveries into the structure and function of the GABAA receptor have led to the development of newer compounds designed to maximise therapeutic benefit whilst minimising adverse effects, and whose position within the epilepsy pharmacologic armamentarium is still emerging. Drugs that modulate the GABAA receptor will remain a cornerstone of epilepsy management for the foreseeable future and, in this article, we provide an overview of the mechanisms and clinical efficacy of both established and emerging pharmacotherapies.

Viral Vector-Based Gene Therapy for Epilepsy: What Does the Future Hold?

In recent years, many pre-clinical studies have tested gene therapy approaches as possible treatments for epilepsy, following the idea that they may provide an alternative to conventional pharmacological and surgical options. Multiple gene therapy approaches have been developed, including those based on anti-sense oligonucleotides, RNA interference, and viral vectors. In this opinion article, we focus on translational issues related to viral vector-mediated gene therapy for epilepsy. Research has advanced dramatically in addressing issues like viral vector optimization, target identification, strategies of gene expression, editing or regulation, and safety. Some of these pre-clinically validated potential gene therapies are now being tested in clinical trials, in patients with genetic or focal forms of drug-resistant epilepsy. Here, we discuss the ongoing translational research and the advancements that are needed and expected in the near future. We then describe the clinical trials in the pipeline and the further challenges that will need to be addressed at the clinical and economic levels. Our optimistic view is that all these issues and challenges can be overcome, and that gene therapy approaches for epilepsy will soon become a clinical reality.

Epilepsies

Recent advances in genetic diagnosis have revealed the underlying etiology of many epilepsies and have identified pathogenic, causative variants in numerous ion and ligand-gated channel genes. This chapter describes the clinical presentations of epilepsy associated with different channelopathies including classic electroclinical syndromes and emerging gene-specific phenotypes. Also discussed are the archetypal epilepsy channelopathy, SCN1A-Dravet syndrome, considering the expanding phenotype. Clinical presentations where a channelopathy is suspected, such as sleep-related hypermotor epilepsy and epilepsy in association with movement disorders, are reviewed. Channelopathies pose an intriguing problem for the development of gene therapies. Design of targeted therapies requires physiologic insights into the often multifaceted impact of a pathogenic variant, coupled with an understanding of the phenotypic spectrum of a gene. As gene-specific novel therapies come online for the channelopathies, it is essential that clinicians are able to recognize epilepsy phenotypes likely to be due to channelopathy and institute early genetic testing in both children and adults. These findings are likely to have immediate management implications and to inform prognostic and reproductive counseling.

Clinical and Genetic Features of Dravet Syndrome: A Prime Example of the Role of Precision Medicine in Genetic Epilepsy

Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy, is a rare and drug-resistant form of developmental and epileptic encephalopathies, which is both debilitating and challenging to manage, typically arising during the first year of life, with seizures often triggered by fever, infections, or vaccinations. It is characterized by frequent and prolonged seizures, developmental delays, and various other neurological and behavioral impairments. Most cases result from pathogenic mutations in the sodium voltage-gated channel alpha subunit 1 (SCN1A) gene, which encodes a critical voltage-gated sodium channel subunit involved in neuronal excitability. Precision medicine offers significant potential for improving DS diagnosis and treatment. Early genetic testing enables timely and accurate diagnosis. Advances in our understanding of DS's underlying genetic mechanisms and neurobiology have enabled the development of targeted therapies, such as gene therapy, offering more effective and less invasive treatment options for patients with DS. Targeted and gene therapies provide hope for more effective and personalized treatments. However, research into novel approaches remains in its early stages, and their clinical application remains to be seen. This review addresses the current understanding of clinical DS features, genetic involvement in DS development, and outcomes of novel DS therapies.

AAV-mediated interneuron-specific gene replacement for Dravet syndrome

Dravet syndrome (DS) is a devastating developmental epileptic encephalopathy marked by treatment-resistant seizures, developmental delay, intellectual disability, motor deficits, and a 10-20% rate of premature death. Most DS patients harbor loss-of-function mutations in one copy of SCN1A , which has been associated with inhibitory neuron dysfunction. Here we developed an interneuron-targeting AAV human SCN1A gene replacement therapy using cell class-specific enhancers. We generated a split-intein fusion form of SCN1A to circumvent AAV packaging limitations and deliver SCN1A via a dual vector approach using cell class-specific enhancers. These constructs produced full-length Na V 1.1 protein and functional sodium channels in HEK293 cells and in brain cells in vivo . After packaging these vectors into enhancer-AAVs and administering to mice, immunohistochemical analyses showed telencephalic GABAergic interneuron-specific and dose-dependent transgene biodistribution. These vectors conferred strong dose-dependent protection against postnatal mortality and seizures in two DS mouse models carrying independent loss-of-function alleles of Scn1a, at two independent research sites, supporting the robustness of this approach. No mortality or toxicity was observed in wild-type mice injected with single vectors expressing either the N-terminal or C-terminal halves of SCN1A , or the dual vector system targeting interneurons. In contrast, nonselective neuronal targeting of SCN1A conferred less rescue against mortality and presented substantial preweaning lethality. These findings demonstrate proof-of-concept that interneuron-specific AAV-mediated SCN1A gene replacement is sufficient for significant rescue in DS mouse models and suggest it could be an effective therapeutic approach for patients with DS.

Adeno-associated virus-mediated gene therapy for rare pediatric neurogenetic diseases: Current status and outlook

Rare pediatric neurogenetic diseases always have early onset, no specific therapy, high mortality, and pose a severe risk to the health and survival of children. Adeno-associated virus (AAV)-mediated gene therapy, a type of disease-modifying therapy, provides a new option for the treatment of rare pediatric neurogenetic diseases and represents a significant advancement in the field. Currently, the US Food and Drug Administration (FDA) and the European Medicines Association (EMA) have approved AAV-mediated gene therapy medications for treating spinal muscular atrophy, aromatic L-amino acid decarboxylase deficiency, and Duchenne muscular dystrophy. Numerous preclinical and clinical trial research findings from recent years indicate that AAV-mediated gene therapy has a promising future in treating genetic disorders. The quick approval process for rare diseases medications may bring hope for the treatment of children with rare neurogenetic diseases. AAV-mediated gene therapy is an emerging technology with certain risks and challenges. It is necessary to establish a standardized regulatory system and a sound long-term follow-up system to evaluate the efficacy and safety of gene therapy.

Preferential expression of SCN1A in GABAergic neurons improves survival and epileptic phenotype in a mouse model of Dravet syndrome

The SCN1A gene encodes the alpha subunit of a voltage-gated sodium channel (Nav1.1), which is essential for the function of inhibitory neurons in the brain. Mutations in this gene cause severe encephalopathies such as Dravet syndrome (DS). Upregulation of SCN1A expression by different approaches has demonstrated promising therapeutic effects in preclinical models of DS. Limiting the effect to inhibitory neurons may contribute to the restoration of brain homeostasis, increasing the safety and efficacy of the treatment. In this work, we have evaluated different approaches to obtain preferential expression of the full SCN1A cDNA (6 Kb) in GABAergic neurons, using high-capacity adenoviral vectors (HC-AdV). In order to favour infection of these cells, we considered ErbB4 as a surface target. Incorporation of the EGF-like domain from neuregulin 1 alpha (NRG1α) in the fiber of adenovirus capsid allowed preferential infection in cells lines expressing ErbB4. However, it had no impact on the infectivity of the vector in primary cultures or in vivo. For transcriptional control of transgene expression, we developed a regulatory sequence (DP3V) based on the Distal-less homolog enhancer (Dlx), the vesicular GABA transporter (VGAT) promoter, and a portion of the SCN1A gene. The hybrid DP3V promoter allowed preferential expression of transgenes in GABAergic neurons both in vitro and in vivo. A new HC-AdV expressing SCN1A under the control of this promoter showed improved survival and amelioration of the epileptic phenotype in a DS mouse model. These results increase the repertoire of gene therapy vectors for the treatment of DS and indicate a new avenue for the refinement of gene supplementation in this disease. KEY MESSAGES: Adenoviral vectors can deliver the SCN1A cDNA and are amenable for targeting. An adenoviral vector displaying an ErbB4 ligand in the capsid does not target GABAergic neurons. A hybrid promoter allows preferential expression of transgenes in GABAergic neurons. Preferential expression of SCN1A in GABAergic cells is therapeutic in a Dravet syndrome model.

Dravet syndrome: A systematic literature review of the illness burden

We performed a systematic literature review and narrative synthesis according to a pre-registered protocol (Prospero: CRD42022376561) to identify the evidence associated with the burden of illness in Dravet syndrome (DS), a developmental and epileptic encephalopathy characterized by drug-resistant epilepsy with neurocognitive and neurobehavioral impairment. We searched MEDLINE, Embase, and APA PsychInfo, Cochrane's database of systematic reviews, and Epistemonikos from inception to June 2022. Non-interventional studies reporting on epidemiology (incidence, prevalence, and mortality), patient and caregiver health-related quality of life (HRQoL), direct and indirect costs and healthcare resource utilization were eligible. Two reviewers independently carried out the screening. Pre-specified data were extracted and a narrative synthesis was conducted. Overall, 49 studies met the inclusion criteria. The incidence varied from 1:15 400-1:40 900, and the prevalence varied from 1.5 per 100 000 to 6.5 per 100 000. Mortality was reported in 3.7%-20.8% of DS patients, most commonly due to sudden unexpected death in epilepsy and status epilepticus. Patient HRQoL, assessed by caregivers, was lower than in non-DS epilepsy patients; mean scores (0 [worst] to 100/1 [best]) were 62.1 for the Kiddy KINDL/Kid-KINDL, 46.5-54.7 for the PedsQL and 0.42 for the EQ-5D-5L. Caregivers, especially mothers, were severely affected, with impacts on their time, energy, sleep, career, and finances, while siblings were also affected. Symptoms of depression were reported in 47%-70% of caregivers. Mean total direct costs were high across all studies, ranging from $11 048 to $77 914 per patient per year (PPPY), with inpatient admissions being a key cost driver across most studies. Mean costs related to lost productivity were only reported in three publications, ranging from approximately $19 000 to $20 000 PPPY ($17 596 for mothers vs $1564 for fathers). High seizure burden was associated with higher resource utilization, costs and poorer HRQoL. The burden of DS on patients, caregivers, the healthcare system, and society is profound, reflecting the severe nature of the syndrome. Future studies will be able to assess the impact that newly approved therapies have on reducing the burden of DS.

AAV-based in vivo gene therapy for neurological disorders

Recent advancements in gene supplementation therapy are expanding the options for the treatment of neurological disorders. Among the available delivery vehicles, adeno-associated virus (AAV) is often the favoured vector. However, the results have been variable, with some trials dramatically altering the course of disease whereas others have shown negligible efficacy or even unforeseen toxicity. Unlike traditional drug development with small molecules, therapeutic profiles of AAV gene therapies are dependent on both the AAV capsid and the therapeutic transgene. In this rapidly evolving field, numerous clinical trials of gene supplementation for neurological disorders are ongoing. Knowledge is growing about factors that impact the translation of preclinical studies to humans, including the administration route, timing of treatment, immune responses and limitations of available model systems. The field is also developing potential solutions to mitigate adverse effects, including AAV capsid engineering and designs to regulate transgene expression. At the same time, preclinical research is addressing new frontiers of gene supplementation for neurological disorders, with a focus on mitochondrial and neurodevelopmental disorders. In this Review, we describe the current state of AAV-mediated neurological gene supplementation therapy, including critical factors for optimizing the safety and efficacy of treatments, as well as unmet needs in this field.

Widespread genomic influences on phenotype in Dravet syndrome, a 'monogenic' condition

Dravet syndrome is an archetypal rare severe epilepsy, considered 'monogenic', typically caused by loss-of-function SCN1A variants. Despite a recognizable core phenotype, its marked phenotypic heterogeneity is incompletely explained by differences in the causal SCN1A variant or clinical factors. In 34 adults with SCN1A-related Dravet syndrome, we show additional genomic variation beyond SCN1A contributes to phenotype and its diversity, with an excess of rare variants in epilepsy-related genes as a set and examples of blended phenotypes, including one individual with an ultra-rare DEPDC5 variant and focal cortical dysplasia. The polygenic risk score for intelligence was lower, and for longevity, higher, in Dravet syndrome than in epilepsy controls. The causal, major-effect, SCN1A variant may need to act against a broadly compromised genomic background to generate the full Dravet syndrome phenotype, whilst genomic resilience may help to ameliorate the risk of premature mortality in adult Dravet syndrome survivors.

The ice age - A review on formulation of Adeno-associated virus therapeutics

Gene therapies offer promising therapeutic alternatives for many disorders that currently lack efficient treatment options. Due to their chemical nature and physico-chemical properties, delivery of polynucleic acids into target cells and subcellular compartments remains a significant challenge. Adeno-associated viruses (AAV) have gained a lot of interest for the efficient delivery of therapeutic single-stranded DNA (ssDNA) genomes over the past decades. More than a hundred products have been tested in clinical settings and three products have received market authorization by the US FDA in recent years. A lot of effort is being made to generate potent recombinant AAV (rAAV) vectors that show favorable safety and immunogenicity profiles for either local or systemic administration. Manufacturing processes are gradually being optimized to deliver a consistently high product quality and to serve potential market needs beyond rare indications. In contrast to protein therapeutics, most rAAV products are still supplied as frozen liquids within rather simple formulation buffers to enable sufficient product shelf life, significantly hampering global distribution and access. In this review, we aim to outline the hurdles of rAAV drug product development and discuss critical formulation and composition aspects of rAAV products under clinical evaluation. Further, we highlight recent development efforts in order to achieve stable liquid or lyophilized products. This review therefore provides a comprehensive overview on current state-of-the-art rAAV formulations and can further serve as a map for rational formulation development activities in the future.

New GABA-Targeting Therapies for the Treatment of Seizures and Epilepsy: II. Treatments in Clinical Development

The inhibitory neurotransmitter γ-aminobutyric acid (GABA) plays an important role in the modulation of neuronal excitability, and a disruption of GABAergic transmission contributes to the pathogenesis of some seizure disorders. Although many currently available antiseizure medications do act at least in part by potentiating GABAergic transmission, there is an opportunity for further research aimed at developing more innovative GABA-targeting therapies. The present article summarises available evidence on a number of such treatments in clinical development. These can be broadly divided into three groups. The first group consists of positive allosteric modulators of GABAA receptors and includes Staccato® alprazolam (an already marketed benzodiazepine being repurposed in epilepsy as a potential rescue inhalation treatment for prolonged and repetitive seizures), the α2/3/5 subtype-selective agents darigabat and ENX-101, and the orally active neurosteroids ETX155 and LPCN 2101. A second group comprises two drugs already marketed for non-neurological indications, which could be repurposed as treatments for seizure disorders. These include bumetanide, a diuretic agent that has undergone clinical trials in phenobarbital-resistant neonatal seizures and for which the rationale for further development in this indication is under debate, and ivermectin, an antiparasitic drug currently investigated in a randomised double-blind trial in focal epilepsy. The last group comprises a series of highly innovative therapies, namely GABAergic interneurons (NRTX-001) delivered via stereotactic cerebral implantation as a treatment for mesial temporal lobe epilepsy, an antisense oligonucleotide (STK-001) aimed at upregulating NaV1.1 currents and restoring the function of GABAergic interneurons, currently tested in a trial in patients with Dravet syndrome, and an adenoviral vector-based gene therapy (ETX-101) scheduled for investigation in Dravet syndrome. Another agent, a subcutaneously administered neuroactive peptide (NRP2945) that reportedly upregulates the expression of GABAA receptor α and β subunits is being investigated, with Lennox-Gastaut syndrome and other epilepsies as proposed indications. The diversity of the current pipeline underscores a strong interest in the GABA system as a target for new treatment development in epilepsy. To date, limited clinical data are available for these investigational treatments and further studies are required to assess their potential value in addressing unmet needs in epilepsy management.

A hyperthermic seizure unleashes a surge of spreading depolarizations in Scn1a-deficient mice

Spreading depolarization (SD) is a massive wave of cellular depolarization that slowly migrates across the brain gray matter. Cortical SD is frequently generated following brain injury, while less is understood about its potential contribution to genetic disorders of hyperexcitability, such as SCN1A-deficient epilepsy, in which febrile seizure often contributes to disease initiation. Here we report that spontaneous SD waves are predominant EEG abnormalities in the Scn1a-deficient mouse (Scn1a+/R1407X) and undergo sustained intensification following a single hyperthermic seizure. Chronic DC-band EEG recording detected spontaneous SDs, seizures, and seizure-SD complexes in Scn1a+/R1407X mice but not WT littermates. The SD events were infrequent, while a single hyperthermia-induced seizure robustly increased SD frequency over 4-fold during the initial postictal week. This prolonged neurological aftermath could be suppressed by memantine administration. Video, electromyogram, and EEG spectral analysis revealed distinct neurobehavioral patterns; individual seizures were associated with increased motor activities, while SDs were generally associated with immobility. We also identified a stereotypic SD prodrome, detectable over a minute before the onset of the DC potential shift, characterized by increased motor activity and bilateral EEG frequency changes. Our study suggests that cortical SD is a pathological manifestation in SCN1A-deficient epileptic encephalopathy.

Core Features Differentiate Dravet Syndrome from Febrile Seizures

An 11-month-old girl with febrile seizures and first unprovoked seizures was evaluated in the hospital. Relevant history included developmental delay and strong family history of febrile seizures and migraines. A routine electroencephalogram was performed and was abnormal due to the presence of a slowed posterior dominant rhythm, generalized spike-wave discharges, and multifocal sharp waves. The findings were concerning for a developmental and epileptic encephalopathy. Given the concern for a developmental and epileptic encephalopathy, a next generation sequence epilepsy gene panel was ordered which identified a pathogenic variant in SCN1A. The clinical history, electroencephalogram, and pathogenic variant were compatible with a diagnosis of Dravet syndrome. This Grand Rounds manuscript highlights the thought process, evaluation, differential diagnosis, treatment, and prognosis in Dravet syndrome.