[Correlation between clinical phenotypes and genotypes among 46 children with SCN1A-related developmental epileptic encephalopathy].

OBJECTIVE: To explore the correlation between clinical phenotypes and genotypes among 46 children with SCN1A-related developmental epileptic encephalopathy (DEE). METHODS: Clinical data of 46 children with DEE and SCN1A variants identified at the Guangzhou Women and Children's Medical Center between January 2018 and June 2022 were collected. The children were grouped based on their age of onset, clinical manifestations, neurodevelopmental status, and results of genetic testing. The correlation between SCN1A genotypes and clinical phenotypes was analyzed. RESULTS: Among the 46 patients, 2 children (4.35%) had developed the symptoms before 3 months of age, 42 (91.30%) were between 3 to 9 months, and 2 cases (4.35%) were after 10 months. Two cases (4.35%) presented with epilepsy of infancy with migrating focal seizures (EIMFS), while 44 (95.7%) had presented with Dravet syndrome (DS), including 28 cases (63.6%) with focal onset (DS-F), 13 cases (29.5%) with myoclonic type (DS-M), 1 case (2.27%) with generalized type (DS-G), and 2 cases (4.55%) with status epilepticus type (DS-SE). Both of the two EIMFS children had severe developmental delay, and among the DS patients, 7 cases had normal development, while the remaining had developmental delay. A total of 44 variants were identified through genetic sequencing, which included 16 missense variants and 28 truncating variants. All EIMFS children had carried the c.677C>T (p.Thr226Met) missense variant. In the DS group, there was a significant difference in the age of onset between the missense variants group and the truncating variants group (P < 0.05). Missense variants were more common in D1 (7/15, 46.7%) and pore regions (8/15, 53.3%), while truncating variants were more common in D1 (12/28, 42.9%). Children with variants outside the pore region were more likely to develop myoclonic seizures. CONCLUSION: The clinical phenotypes of DEE are diverse. There is a difference in the age of onset between individuals with truncating and missense variants in the SCN1A gene. Missense variants outside the pore region are associated with a higher incidence of myoclonic seizures.

[Analysis of three Chinese pedigrees affected with Genetic epilepsy with febrile seizures plus due to variants of SCN1A gene].

OBJECTIVE: To analyze the clinical and genetic characteristics of three Chinese pedigrees affected with Genetic epilepsy with febrile seizures plus (GEFS+). METHODS: Three GEFS+ probands and their pedigree members presented at the Children's Hospital of Zhengzhou University from January 2020 to December 2021 were selected as the study subjects. Clinical data of the pedigrees were collected. Whole exome sequencing was carried out for the probands, and Sanger sequencing was used to verify the candidate variants. RESULTS: Proband 1 was a 3-year-and-2-month-old male with febrile seizure plus. His father, two aunts, grandmother, aunt grandmother, uncle grandfather, and paternal great-grandmother also had onset of febrile seizures at 1 ~ 2 years of age with remission before 6 years old. Proband 2 was a 1-year-and-4-month-old male with complex febrile seizure. His mother, maternal uncle, and maternal grandmother also had febrile seizures before 5 ~ 6 years of age. Proband 3 was a 3-year-and-11-month-old male with febrile seizure plus. His father and grandfather also had febrile seizures plus with remission at 7 ~ 8 years of age. Genetic testing revealed that proband 1 had harbored a paternally derived heterozygous SCN1A: c.1613T>C variant, proband 2 had harbored a maternally derived heterozygous SCN1A: c.2804A>G variant, and proband 3 had harbored a paternally derived heterozygous SCN1A: c.1271T>C variant. All of the three variants were predicted as likely pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (PM1+PM2_Supporting+PP1+PP3+PP4). CONCLUSION: The c.1613T>C, c.2804A>G and c.1271T>C variants probably underlay the pathogenesis of GEFS+ in these pedigrees.

Brainstem depolarization-induced lethal apnea associated with gain-of-function SCN1AL263V is prevented by sodium channel blockade.

Apneic events are frightening but largely benign events that often occur in infants. Here, we report apparent life-threatening apneic events in an infant with the homozygous SCN1AL263V missense mutation, which causes familial hemiplegic migraine type 3 in heterozygous family members, in the absence of epilepsy. Observations consistent with the events in the infant were made in an Scn1aL263V knock-in mouse model, in which apnea was preceded by a large brainstem DC-shift, indicative of profound brainstem depolarization. The L263V mutation caused gain of NaV1.1 function effects in transfected HEK293 cells. Sodium channel blockade mitigated the gain-of-function characteristics, rescued lethal apnea in Scn1aL263V mice, and decreased the frequency of severe apneic events in the patient. Hence, this study shows that SCN1AL263V can cause life-threatening apneic events, which in a mouse model were caused by profound brainstem depolarization. In addition to being potentially relevant to sudden infant death syndrome pathophysiology, these data indicate that sodium channel blockers may be considered therapeutic for apneic events in patients with these and other gain-of-function SCN1A mutations.

Functional Characteristics of the Nav1.1 p.Arg1596Cys Mutation Associated with Varying Severity of Epilepsy Phenotypes.

Mutations of the SCN1A gene, which encodes the voltage-dependent Na+ channel's α subunit, are associated with diverse epileptic syndromes ranging in severity, even intra-family, from febrile seizures to epileptic encephalopathy. The underlying cause of this variability is unknown, suggesting the involvement of additional factors. The aim of our study was to describe the properties of mutated channels and investigate genetic causes for clinical syndromes' variability in the family of five SCN1A gene p.Arg1596Cys mutation carriers. The analysis of additional genetic factors influencing SCN1A-associated phenotypes was conducted through exome sequencing (WES). To assess the impact of mutations, we used patch clamp analysis of mutated channels expressed in HEK cells and in vivo neural excitability studies (NESs). In cells expressing the mutant channel, sodium currents were reduced. NESs indicated increased excitability of peripheral motor neurons in mutation carriers. WES showed the absence of non-SCA1 pathogenic variants that could be causative of disease in the family. Variants of uncertain significance in three genes, as potential modifiers of the most severe phenotype, were identified. The p.Arg1596Cys substitution inhibits channel function, affecting steady-state inactivation kinetics. Its clinical manifestations involve not only epileptic symptoms but also increased excitability of peripheral motor fibers. The role of Nav1.1 in excitatory neurons cannot be ruled out as a significant factor of the clinical phenotype.

Unraveling Dravet Syndrome: Exploring the complex effects of sodium channel mutations on neuronal networks.

Dravet Syndrome (DS) is a severe developmental epileptic encephalopathy with frequent intractable seizures accompanied by cognitive impairment, often caused by pathogenic variants in SCN1A encoding sodium channel NaV1.1. Recent research utilizing in vitro patient-derived neuronal networks and accompanying in silico models uncovered that not just sodium-but also potassium-and synaptic currents were impaired in DS networks. Here, we explore the implications of these findings for three questions that remain elusive in DS: How do sodium channel impairments result in epilepsy? How can identical variants lead to varying phenotypes? What mechanisms underlie the developmental delay in DS patients? We speculate that impaired potassium currents might be a secondary effect to NaV1.1 mutations and could result in hyperexcitable neurons and epileptic networks. Moreover, we reason that homeostatic plasticity is actively engaged in DS networks, possibly affecting the phenotype and impairing learning and development when driven to extremes.

Switching from zonisamide to perampanel improved the frequency of seizures caused by hyperthermia in Dravet syndrome: a case report.

BACKGROUND: Dravet syndrome is a severe epilepsy disorder characterized by drug-resistant seizures and cognitive dysfunction, often caused by SCN1A gene mutations. It leads to neurodevelopmental delays and motor, behavioral, and cognitive impairments, with a high mortality rate. Treatment options include sodium valproate, clobazam, and newer agents such as cannabidiol and fenfluramine. Zonisamide, which is used in some cases, can cause hyperthermia and oligohydrosis. Herein, we present a case of a patient with Dravet syndrome whose seizures were controlled by treating infections and switching from zonisamide to perampanel. CASE PRESENTATION: A 24-year-old Japanese man with Dravet syndrome presented to our department with aspiration pneumonia. The patient had been treated with valproate, sodium bromide, and zonisamide for a long time. His seizures were triggered by hyperthermia. The patient was experiencing a sustained pattern of hyperthermia caused by infection, zonisamide, and persistent convulsions, which caused a vicious cycle of further seizures. In this case, the control of infection and switching from zonisamide to perampanel improved seizure frequency. CONCLUSION: Dravet syndrome usually begins with generalized clonic seizures in its infancy because of fever and progresses to various seizure types, often triggered by fever or seizure-induced heat due to mutations in the SCN1A gene that increases neuronal excitability. Seizures usually diminish with age, but the heat sensitivity remains. In this case, seizures were increased by repeated infections, and hyperthermia was induced by zonisamide, resulting in status epilepticus. Perampanel, an aminomethylphosphonic acid receptor antagonist, decreased seizures but caused psychiatric symptoms. It was effective in suppressing seizures of Dravet syndrome in this patient.

Identification of novel and de novo variant in the SCN1A gene confirms Dravet syndrome in Moroccan child: a case report.

Dravet syndrome is a severe form of epilepsy characterised by recurrent seizures and cognitive impairment. It is mainly caused by variant in the SCN1A gene in 90% of cases, which codes for the α subunit of the voltage-gated sodium channel. In this study, we present one suspected case of Dravet syndrome in Moroccan child that underwent exome analysis and were confirmed by Sanger sequencing. The variant was identified in the SCN1A gene, and is a new variant that has never been described in the literature. The variant was found de nova in our case, indicating that it was not inherited from the parents. The variant, SCN1A c.965-2A>G p.(?), is located at the splice site and results in an unknown modification of the protein. This variant is considered pathogenic on the basis of previous studies. These results contribute to our knowledge of the SCN1A gene mutations associated with Dravet syndrome and underline the importance of genetic analysis in the diagnosis and confirmation of this disorder. Further studies are needed to better understand the functional consequences of this variant and its implications for therapeutic strategies in Dravet syndrome.

Impact of variant subtype on electro-clinical phenotype of Dravet syndrome- a South Indian cohort study.

OBJECTIVE: We aimed to compare the electroclinical correlates of truncating and missense variants of SCN1A variants in children with Dravet syndrome (DS) and to determine phenotypic features in relation to variants identified and seizure outcomes. METHODS: A single center prospective study was carried out on a South Indian cohort. Patients below 18 years of age who met the clinical criteria for DS who had undergone genetic testing and completed a minimum of one year follow up were included. We compared the differences in clinical profile, seizure outcome, developmental characteristics and anti-seizure medication (ASM) responsiveness profiles between patients with missense and truncating variants. RESULTS: Out of a total of 3967 children with drug-resistant epilepsy during the period 2015-2021, 49 patients who fulfilled the inclusion criteria were studied. Thirty-seven had positive genetic tests, out of which 29 were SCN1A variants and 9 were other novel variants. The proportion of missense (14; 48.3%) and truncating SCN1A variants (15; 51.7%) was similar. A significant trend for developing multiple seizure types was noted among children with truncating variants (p = 0.035) and seizure freedom was more likely among children with missense variants (p = 0.042). All patients with truncating variants had ASM resistant epilepsy (p = 0.020). Developmental outcomes did not differ between the variant subtypes. CONCLUSION: Our results show that children harbouring missense variants demonstrated a significantly lower propensity for multiple seizure subtypes and a higher proportion with seizure freedom. However developmental implications appear to be independent of variant subtype.

Inherited SCN1A missense mutation in a Dravet Syndrome family: Neuropathological correlation, family screening and implications for adult carriers.

INTRODUCTION: Neuropathological findings in Dravet Syndrome (DS) are scarce, especially in adult patients, and often do not have a genetic confirmation. Additionally, the missense SCN1A pathogenic variant found has only been described as de novo mutation in previous literature. METHODS: We describe the clinical and genetic findings of a family (including three sisters and his father), using Sanger sequencing in the three sisters and in postmortem brain tissue in the father. The present study also shows the neuropathological findings of the father. RESULTS: Despite the presence of long term drug resistant epilepsy, starting with febrile seizures between 6 and 12 months of age, and intellectual disability (ID), the three sisters were diagnosed with DS in adulthood, identifying a missense SCN1A pathogenic variant in exon 20, previously described as de novo -p.Gly1332Glu (c .3995 G>A). The oldest sister had the most severe phenotype, with severe ID and wheel chair dependency, passing away at 52. The other two sisters had a moderate phenotype, being at the present seizure free, but with significant comorbidities, such as crouch gait and parkinsonism. Several relatives from the paternal path (including the father) presented epilepsy, but without ID. The father was diagnosed with Alzheimer´s Disease (AD) at 60, and because he donated his brain, the same variant was confirmed in postmortem study. Neither the MRI nor the histopathology showed specific morphological changes for DS, consistent with previous studies. CONCLUSIONS: This work supports the need to review the clinical and genetic spectra of DS in adults with epilepsy and unknown ID. The clinical consequences of this syndrome seem to have a functional rather than a structural basis, supported by the absence of specific neuropathological findings.

Severe communication delays are independent of seizure burden and persist despite contemporary treatments in SCN1A+ Dravet syndrome: Insights from the ENVISION natural history study.

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 = .0-24.0), 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 [.0-2647.0] 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.

Prediction of molecular phenotypes for novel SCN1A variants from a Turkish genetic epilepsy syndromes cohort and report of two new patients with recessive Dravet syndrome.

Dravet syndrome and genetic epilepsy with febrile seizures plus (GEFS+) are both epilepsy syndromes that can be attributed to deleterious mutations occurring in SCN1A, the gene encoding the pore-forming α-subunit of the NaV 1.1 voltage-gated sodium channel predominantly expressed in the central nervous system. In this research endeavor, our goal is to expand our prior cohort of Turkish patients affected by SCN1A-positive genetic epilepsy disorders. This will be accomplished by incorporating two recently discovered and infrequent index cases who possess a novel biallelic (homozygous) SCN1A missense variant, namely E158G, associated with Dravet syndrome. Furthermore, our intention is to use computational techniques to predict the molecular phenotypes of each distinct SCN1A variant that has been detected to date within our center. The correlation between genotype and phenotype in Dravet syndrome/GEFS+ is intricate and necessitates meticulous clinical investigation as well as advanced scientific exploration. Broadened mechanistic and structural insights into NaV 1.1 dysfunction offer significant promise in facilitating the development of targeted and effective therapies, which will ultimately enhance clinical outcomes in the treatment of epilepsy.

Non-pharmacological therapeutic needs in people with Dravet syndrome.

Dravet syndrome (DS) is a genetic rare disease, which is usually caused by a mutation in the SCN1A gene. DS is characterised by a drug-resistant epilepsy and by cognitive and behavioural disturbances. Thus, DS patients require both pharmacological and non-pharmacological treatments. However, there is a paucity of studies on non-pharmacological therapies and their potential benefits. The main aim of this study was to describe the non-pharmacological therapy modalities received by DS patients and their socio-economic impact on the family. Thus, we designed an online survey addressed to caregivers of DS patients. Our results indicated that up to 91.9% of the surveyed patients required non-pharmacological therapies, which were mainly directed to treat cognitive, sensory and motor impairments. In many cases, the economic costs of these therapies were borne entirely by the families. Nevertheless, patients required a deployment of resources not only at a health care level, but also at an educational level.

Fenfluramine increases survival and reduces markers of neurodegeneration in a mouse model of Dravet syndrome.

OBJECTIVE: In patients with Dravet syndrome (DS), fenfluramine reduced convulsive seizure frequency and provided clinical benefit in nonseizure endpoints (e.g., executive function, survival). In zebrafish mutant scn1 DS models, chronic fenfluramine treatment preserved neuronal cytoarchitecture prior to seizure onset and prevented gliosis; here, we extend these findings to a mammalian model of DS (Scn1a+/- mice) by evaluating the effects of fenfluramine on neuroinflammation (degenerated myelin, activated microglia) and survival. METHODS: Scn1a+/- DS mice were treated subcutaneously once daily with fenfluramine (15 mg/kg) or vehicle from postnatal day (PND) 7 until 35-37. Sagittal brain sections were processed for immunohistochemistry using antibodies to degraded myelin basic protein (D-MBP) for degenerated myelin, or CD11b for activated (inflammatory) microglia; sections were scored semi-quantitatively. Apoptotic nuclei were quantified by TUNEL assay. Statistical significance was evaluated by 1-way ANOVA with post-hoc Dunnett's test (D-MBP, CD11b, and TUNEL) or Logrank Mantel-Cox (survival). RESULTS: Quantitation of D-MBP immunostaining per 0.1 mm2 unit area of the parietal cortex and hippocampus CA3 yielded significantly higher spheroidal and punctate myelin debris counts in vehicle-treated DS mice than in wild-type mice. Fenfluramine treatment in DS mice significantly reduced these counts. Activated CD11b + microglia were more abundant in DS mouse corpus callosum and hippocampus than in wild-type controls. Fenfluramine treatment of DS mice resulted in significantly fewer activated CD11b + microglia than vehicle-treated DS mice in these brain regions. TUNEL staining in corpus callosum was increased in DS mice relative to wild-type controls. Fenfluramine treatment in DS mice lowered TUNEL staining relative to vehicle-treated DS mice. By PND 35-37, 55% of control DS mice had died, compared with 24% of DS mice receiving fenfluramine treatment (P = 0.0291). SIGNIFICANCE: This is the first report of anti-neuroinflammation and pro-survival after fenfluramine treatment in a mammalian DS model. These results corroborate prior data in humans and animal models and suggest important pharmacological activities for fenfluramine beyond seizure reduction. PLAIN LANGUAGE SUMMARY: Dravet syndrome is a severe epilepsy disorder that impairs learning and causes premature death. Clinical studies in patients with Dravet syndrome show that fenfluramine reduces convulsive seizures. Additional studies suggest that fenfluramine may have benefits beyond seizures, including promoting survival and improving control over emotions and behavior. Our study is the first to use a Dravet mouse model to investigate nonseizure outcomes of fenfluramine. Results showed that fenfluramine treatment of Dravet mice reduced neuroinflammation significantly more than saline treatment. Fenfluramine-treated Dravet mice also lived longer than saline-treated mice. These results support clinical observations that fenfluramine may have benefits beyond seizures.

Anticonvulsant effect of equilibrative nucleoside transporters 1 inhibitor in a mouse model of Dravet syndrome.

There are limited therapeutic options for patients with Dravet syndrome (DS). The equilibrative nucleoside transporters 1 (ENT1) mediate both the influx and efflux of adenosine across the cell membrane exerted beneficial effects in the treatment of epilepsy. This study aimed to evaluate the anticonvulsant effect of the ENT1 inhibitor in an animal model of DS (Scn1aE1099X/+ mice). J7 (5 mg/kg) treatment was efficacious in elevating seizure threshold in Scn1aE1099X/+ mice after hyperthermia exposure. Moreover, the J7 treatment significantly reduced the frequency of spontaneous excitatory post-synaptic currents (sEPSCs, ~35% reduction) without affecting the amplitude in dentate gyrus (DG) granule cells. Pretreatment with the adenosine A1 receptor (A1R) antagonist, DPCPX, abolished the J7 effects on sEPSCs. These observations suggest that the J7 shows an anticonvulsant effect in hyperthermia-induced seizures in Scn1aE1099X/+ mice. This effect possibly acts on presynaptic A1R-mediated signaling modulation in granule cells.

Cerebral hemiatrophy and hemiparesis following hemiclonic status epilepticus in Dravet syndrome.

Dravet syndrome is currently considered as an developmental and epileptic encephalopathy and, recently, mandatory, alert, and exclusionary criteria have been proposed. Here, we describe three patients with Dravet syndrome with the typical early presentation including febrile and afebrile alternating hemiclonic seizures due to loss-of-function SCN1A variants. Subsequently, they developed episodes of febrile focal status epilepticus (SE) associated with hemiparesis and cerebral hemiatrophy with posterior focal seizures, as a consequence of Dravet syndrome. This sequence of events has been previously published in patients with Dravet syndrome and does not contradict the recent classification by the International League Against Epilepsy (ILAE). The ILAE guidance identifies "Focal neurological findings" as alert criteria and "MRI showing a causal focal lesion" as exclusionary criteria for making an initial diagnosis of Dravet syndrome at presentation. Our three patients would correspond to a severe phenotype, similar to the well-known presentation of generalized atrophy following prolonged status epilepticus. Common genetic findings in cases of diffuse and unilateral brain involvement may help explain these clinical presentations. Further genotype-phenotype studies may provide additional insights into this electroclinical behavior.

Epileptogenic focal lesions in Dravet syndrome: A warning to investigators.

OBJECTIVE: Most patients with Dravet syndrome (DS) have unremarkable neuroimaging studies. However, a small number of patients exhibit focal abnormalities that may modify the epilepsy phenotype. We report a case series of DS patients carrying SCN1A variants concurrent with additional focal brain lesions, aiming to provide details regarding their clinical course, electrographic findings, and imaging features. METHODS: We reviewed the electronic medical records of patients with developmental and epileptic encephalopathies in our center, from January 2000 to December 2022, identifying 90 patients with DS resulting from SCN1A variants. Of these, patients displaying focal brain lesions were eligible. RESULTS: Five patients (4 males and 1 female), with median age of 26 years, were included. All exhibited clinical and electroencephalographic features consistent with the DS spectrum. Sequencing analysis of the SCN1A gene identified pathogenic variants. Magnetic resonance imaging (MRI) revealed focal cortical dysplasia (FCD) in two patients, while the remaining three had cystic lesions. Three patients had previously undergone resective epilepsy surgery in other centers, with no improvement in seizure frequency. Neuropathology studies revealed the presence of FCD type IIA, intracranial teratomas, and dysembryoplastic neuroepithelial tumor (DNET). SIGNIFICANCE: When an individual with an established diagnosis of genetic epilepsy and a focal lesion on MRI is undergoing preoperative evaluation, it is crucial to conduct a comprehensive analysis to understand the relevance of the focal finding for the patient's phenotype and thus anticipate potential surgical outcomes. In instances where epilepsy in DS patients is influenced by a specific focal structural lesion, resective surgery should be carefully considered after precise pharmacological treatment, acknowledging the persistent influence of an SCN1A variant on expected outcomes.

Transcranial static magnetic stimulation reduces seizures in a mouse model of Dravet syndrome.

Dravet syndrome is a rare form of severe genetic epilepsy characterized by recurrent and long-lasting seizures. It appears around the first year of life, with a quick evolution toward an increase in the frequency of the seizures, accompanied by a delay in motor and cognitive development, and does not respond well to antiepileptic medication. Most patients carry a mutation in the gene SCN1A encoding the α subunit of the voltage-gated sodium channel Nav1.1, resulting in hyperexcitability of neural circuits and seizure onset. In this work, we applied transcranial static magnetic stimulation (tSMS), a non-invasive, safe, easy-to-use and affordable neuromodulatory tool that reduces neural excitability in a mouse model of Dravet syndrome. We demonstrate that tSMS dramatically reduced the number of crises. Furthermore, crises recorded in the presence of the tSMS were shorter and less intense than in the sham condition. Since tSMS has demonstrated its efficacy at reducing cortical excitability in humans without showing unwanted side effects, in an attempt to anticipate a possible use of tSMS for Dravet Syndrome patients, we performed a numerical simulation in which the magnetic field generated by the magnet was modeled to estimate the magnetic field intensity reached in the cerebral cortex, which could help to design stimulation strategies in these patients. Our results provide a proof of concept for nonpharmacological treatment of Dravet syndrome, which opens the door to the design of new protocols for treatment.

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.

Persistent Nav1.1 and Nav1.6 currents drive spinal locomotor functions through nonlinear dynamics.

Persistent sodium current (INaP) in the spinal locomotor network promotes two distinct nonlinear firing patterns: a self-sustained spiking triggered by a brief excitation in bistable motoneurons and bursting oscillations in interneurons of the central pattern generator (CPG). Here, we identify the NaV channels responsible for INaP and their role in motor behaviors. We report the axonal Nav1.6 as the main molecular player for INaP in lumbar motoneurons. The inhibition of Nav1.6, but not of Nav1.1, in motoneurons impairs INaP, bistability, postural tone, and locomotor performance. In interneurons of the rhythmogenic CPG region, both Nav1.6 and Nav1.1 equally mediate INaP. Inhibition of both channels is required to abolish oscillatory bursting activities and the locomotor rhythm. Overall, Nav1.6 plays a significant role both in posture and locomotion by governing INaP-dependent bistability in motoneurons and working in tandem with Nav1.1 to provide INaP-dependent rhythmogenic properties of the CPG.