The first mouse model of SCN1A GoF epilepsy with heterozygous Cre-dependent expression of the recurrent patient variant Scn1a-p.R1636Q is developed, the first study of SCN1A GoF epilepsy in a preclinical model in vivo and further investigation in the Scn1aflox(R1636Q)mouse will yield new mechanistic insights into disease mechanisms to drive advances in the treatment of SCN1A GoF epilepsy.
Abstract
The gene most commonly implicated in epilepsy, SCN1A, encodes the neuronal voltage-gated sodium channel subunit NaV1.1. SCN1A variants that reduce sodium current (“loss of function” variants) cause Dravet syndrome, a neurodevelopmental disorder defined by treatment-resistant temperature-sensitive epilepsy with onset at/around 5 months of age, developmental delay/intellectual disability, and features of or formal diagnosis autism. However, an emerging group of variants cause “gain of function” (GoF) effects on NaV1.1 and result in a distinct presentation with earlier onset than Dravet syndrome and prominent movement disorder but without temperature sensitivity. We developed the first mouse model of SCN1A GoF epilepsy with heterozygous Cre-dependent expression of the recurrent patient variant Scn1a-p.R1636Q. Global expression of this variant causes premature mortality in 100% (64/64) of mutant mice between postnatal day 12-18 due to spontaneous, convulsive seizures. Activation of the mutant allele in parvalbumin interneurons (Dlx5/6-Cre or PV-Cre), but not excitatory neurons (Slc17a7-Cre) or other interneuron subtypes (VIP-Cre or Sst-Cre), recapitulates the premature mortality and epilepsy phenotypes. Treatment of Scn1a-p.R1636Q mutant mice with the sodium channel blocker GS967 markedly prolongs lifespan. This work is the first study of SCN1A GoF epilepsy in a preclinical model in vivo. Further investigation in the Scn1aflox(R1636Q)mouse will yield new mechanistic insights into disease mechanisms to drive advances in the treatment of SCN1A GoF epilepsy.
Dravet syndrome is an epileptic encephalopathy most often caused by loss-of-function mutations in the SCN1A gene, leading to haploinsufficiency of the voltage-gated sodium channel NaV1.1. Seizures begin during infancy and wane throughout childhood, but behavioral symptoms, including intellectual disability, motor impairments, and autistic features, remain through adulthood. Seizures primarily stem from inhibitory neuron hypo-excitability in the cortex, hippocampus, and thalamus, but circuit abnormalities underlying persistent behavioral symptoms are poorly understood. Prior work showed synapse dysfunction in thalamocortical neurons in four-week-old DS mice, but elucidating the timing and progression of these alterations is necessary to understand the disease stages that synapse dysfunction may contribute to circuit and behavioral phenotypes. We investigated synapse function in the ventral posterolateral (VPL) and ventral posteromedial (VPM) thalamus prior to seizure onset (P13-P17), after the period of highest seizure burden (P28-P32), and in adulthood (P58-P63). VPL and VPM synaptic activity showed excitatory input to the VPL was reduced after seizure onset and this reduction persisted through adulthood, while VPM excitatory input was unaffected. We further showed a selective reduction in the function and number of excitatory sensory synapses in the VPL, with no change to cortical synapses. VPL and VPM neurons both showed inhibitory synapse dysfunction at four weeks, which persisted in adult DS mice only in VPL neurons. These results revealed persistent input- and cell-type-specific alterations to thalamic synapses that develop after seizure onset and are maintained into adulthood, suggesting synaptic deficits could contribute to ongoing somatosensory thalamocortical circuit dysfunction and behavioral deficits in DS.
Mona Safari, R. Desai, Harbal Rai et al.· Journal of Neurophysiology· 0 citations
Epilepsy is one of the most common neurological disorders, affecting more than 50 million people worldwide. Among the genetic etiologies of epilepsy, variants in genes coding for ion channels are vastly represented and characterized. Notably, loss-of-function (LoF) mutations in voltage-gated sodium channels (NaV) genes can result in a wide range of phenotypes including West syndrome, autism spectrum disorder, or Dravet Syndrome. Although the implication of NaV subtypes in epileptic syndromes and the relationship between seizures and inflammation have been extensively described, subtype-specific neuronal responses to inflammation in the context of NaV loss-of-function remain poorly understood. In this study, we investigated the consequences of subtype-specific downregulation of NaV expression in primary mouse cortical neurons. Using shRNA-mediated silencing of Scn1a, Scn2a, or Scn8a, we generated neuronal cultures with reduced expression of NaV1.1, NaV1.2, or NaV1.6 and evaluated neuronal survival, inflammatory gene expression, and global transcriptomic responses under basal conditions and following an inflammatory challenge. Subtype-specific NaV downregulations did not produce a uniform phenotype. Rather, minor differences under basal conditions led to important discrepancies following exposure to an inflammatory stimulus. Notably, NaV1.1 reduction was associated with synaptic transcriptional changes, whereas NaV1.6 downregulation led to a substantial inflammatory signaling remodeling. Our observations suggest that the consequences of NaV dysfunction are not only determined by their role in neuronal excitability but also depend on subtype-specific responses to inflammatory cues. They notably shed light on the relevance of inflammatory events in the onset and progression of epileptic syndromes related to NaV loss-of-function mutations.
Daniela Jacobsohn, David Guenoun, Nathalie Hertrich et al.· bioRxiv· 0 citations
In two patients with SCN2A epileptic encephalopathy, treatment with personalized allele-selective antisense oligonucleotides led to a decrease in seizure frequency with a positive safety profile, and a pathway from n = 1 to n of more patients with SCN2A-RD and other monogenic disorders is provided.
Olivia Kim-Mcmanus, L. Mignon, J. Douville et al.· Nature Medicine· 2 citations
GNB1 encephalopathy (GNB1-E) is a rare neurodevelopmental disorder associated with motor dysfunction, epilepsy and learning disability caused by mutations in the gene encoding the G protein subunit Gβ1. Previous work has shown that altered Gβ1 can disrupt activation of G-protein-coupled inwardly rectifying potassium (GIRK) channels, dysregulate neuronal excitability and cause seizures. However, the relevant upstream regulators of Gβ1 and the consequences of GIRK dysfunction for neuronal synaptic, cellular and circuit function have not been characterized. Here we report that mice of both sexes carrying the deleterious p.I80T mutation in Gnb1 present features consistent with GNB1-E, including developmental delay, decreased locomotion and increased anxiety. Using histology, whole-cell patch-clamp electrophysiology and pharmacology in ex vivo brain slices, we find that hippocampal neurons in heterozygous Gnb1I80T/+ mice exhibit simplified dendritic morphologies, decreased synaptic inhibition mediated by metabotropic GABAB receptors and increased dendritic excitability. These phenotypes result in longer duration dendritic calcium spikes in response to synaptic afferent stimulation, an effect that is reversed by a specific activator of GIRK channels, ML297. Given the known roles of dendritic calcium spikes in driving burst firing and inducing synaptic plasticity, these findings suggest that targeting dendritic excitability has therapeutic potential to address both the seizure susceptibility and learning deficits associated with GNB1-E. Significance Statement GNB1 encephalopathy (GNB1-E) is a rare neurodevelopmental disorder associated with motor dysfunction, epilepsy and learning disability for which there are currently no mechanism-based treatments. Here we show that a pathogenic variant of the G protein subunit Gβ1 impairs activation of neuronal G-protein-coupled inwardly rectifying potassium (GIRK) channels by inhibitory synaptic GABAB receptors. This leads to increased dendritic excitability and longer duration dendritic calcium spikes in mouse hippocampal neurons in response to stimulation of synaptic inputs. We find that this phenotype is reversed by a drug that activates GIRK channels, opening pathways to develop therapies for GNB1-E that specifically target dendritic excitability.
Sam Gritz, Anshul Voleti, Matthew S. Scarnati et al.· bioRxiv· 0 citations
Prime editing of a pathogenic Scn1a allele ameliorates seizure phenotypes in a GEFS(+) mouse model Kissling L, Pietrafesa F, Ranucci M, Bock D, Mathis N, Kulcsar PI, Ioannidi E, Schmidheini L, Talas A, Villiger E, Wildner H, Zhao X, Kompotis K, Zeilhofer HU, Schwank G. Sci Transl Med. 2026;18(849):eadz2557. Generalized epilepsy with febrile seizures plus (GEFS+) is an inherited epileptic disorder predominantly linked to autosomal-dominant, loss-of-function mutations in the sodium voltage-gated channel α subunit 1 (SCN1A) gene, which encodes the α subunit of the neuronal voltage-gated sodium ion channel type 1 (NaV1.1). Reduced NaV1.1 function in γ-aminobutyric acid (GABA)-ergic interneurons impairs inhibitory signaling and leads to neuronal hyperexcitability. Clinically, GEFS+ is characterized by a spectrum of seizure types, often beginning with febrile seizures in early childhood and progressing to generalized tonic-clonic seizures later in life. Here, we used prime editing to correct the pathogenic SCN1A-K1270 T mutation in the Scn1aKT/+ mouse model of GEFS+. Adeno-associated viral (AAV) vectors were used to deliver an intein-split prime editor under the control of a neuron-specific promoter into the cerebral ventricles of neonatal mice. This enabled efficient in vivo editing, achieving 34.7 ± 14.5% correction of the mutant allele in cortical bulk DNA, 81.2 ± 5.9% correction of mRNA, and improved multiple disease-relevant phenotypes. Survival increased from 80% in control-treated animals to 100% in treated mice, cortical inhibitory neuron transmission was improved (frequencies of inhibitory postsynaptic currents were increased from 0.32 to 1.32 hertz), and the frequency of induced febrile seizures decreased from 78.6% to 13.3%, approaching the frequency seen in wild-type mice (8%). These findings suggest the therapeutic potential of prime editing for the treatment of patients with SCN1A-associated GEFS+. In vivo adenine base editing ameliorates Dravet syndrome phenotypes in a mouse model Nelson AT, Hill SF, Simon M, Clatot J, Sakai HA, Xie J, Sousa AA, An M, Gao G, Lutz CM, Goldberg EM, Liu DR. Sci Transl Med. 2026;18(849):eadx5999. Dravet syndrome (DS) is a severe neurodevelopmental disorder characterized by drug-resistant epilepsy, temperature-sensitive seizures, cognitive impairment, and a high incidence of sudden unexpected death in epilepsy (SUDEP). DS is caused by loss-of-function variants in SCN1A, which encodes the α subunit of the voltage-gated sodium channel (Nav1.1). Current approved treatments manage symptoms of DS but do not correct the root cause of the disease. Here, we describe the use of an adenine base editor (ABE) to directly correct SCN1AR613X, a recurrent variant found in patients with DS. We identified ABE strategies to efficiently correct R613X in engineered homozygous SCN1AR613X human embryonic kidney 293 T and mouse Neuro-2a cells (72 and 92% correction efficiencies, respectively). We then used a dual-adeno-associated virus serotype 9 (AAV9) approach to deliver an optimized ABE system to Scn1aR613X/+ mice, which recapitulate several key DS pathologies. AAV9-ABE treatment of Scn1aR613X/+ neonates resulted in efficient DNA and mRNA editing (59 and 97%, respectively, in bulk neocortices), restoring parvalbumin-expressing inhibitory neuron excitability and sodium current to wild-type levels. This ameliorated both spontaneous and temperature-induced seizures and led to a 3.3-fold improvement in 45-day survival over vehicle-treated mice (ABE treated, 90%; and vehicle treated, 27%). Last, ABE treatment in 12-day-old mice resulted in a 3.0-fold improvement in 60-day survival over vehicle-treated mice (ABE treated, 82%; and vehicle treated, 27%). In conclusion, these data validate a strategy to correct SCN1A variants with ABE and highlight the potential of precision genome editing treatments for the treatment of DS and possibly other neurodevelopmental disorders.
Samantha A Dow, Tracy A. Bedrosian· Epilepsy Currents· 0 citations
Summary Mice with Scn1a haploinsufficiency replicate symptoms of Dravet syndrome (DS), a rare childhood disease characterized by febrile seizures at an early age. As adults, patients with DS suffer from epilepsy, motor dysfunction, psychological disorders, and cognitive disabilities. Patients with DS carry loss-of-function variants in the SCN1A gene, which encodes the voltage-gated sodium channel subunit NaV1.1. As shown in mice, this subunit is mainly expressed in GABAergic cells, especially parvalbumin-expressing interneurons (PV-INs). Consistent with this, interneuron-driven network activities, such as sharp wave ripple oscillations (SPW-R), are altered in Scn1a-deficient mice. By studying network and PV-IN activity during SPW-R in hippocampal slices from Scn1a+/− mice, we identified age-dependent impairments in ripple oscillation frequencies and in rhythmic action potential (AP) firing in PV-INs, accompanied by alterations in somatic and axonal AP waveforms. This age-dependent increase in hippocampal cellular and network abnormalities may contribute to the persisting cognitive deficits associated with Scn1a haploinsufficiency.
Raquel Lascorz, Fabian C. Roth· iScience· 0 citations