Neuronal Voltage-gated Sodium Channel Research Articles

Non-dravet syndrome epilepsy in 4 polish patients with SCN1A de novo mutations

Background: The spectrum of neurological disorders associated with mutations in SCN1A, which encodes the type 1 subunit of the neuronal voltage-gated sodium channel, is broad and can manifest as both epileptic (a heterogeneous group of epileptic syndromes) and non-epileptic conditions. Dravet syndrome (DRVT) and Genetic Epilepsy with Febrile Seizures plus (GEFS+) are the most frequent. However, there exist less common phenotypes with varying severity of clinical course that authors would like to highlight.

Inflammation provokes gating changes in the neuronal voltage-gated sodium channel, Nav1.6.

We recently showed that inflammation causes arrhythmogenic properties in cardiac voltage gated sodium channels (Nav). Here, we hypothesize that inflammation, via Nav, is a common trigger for other pathologies including neurological disorders. Based on our previous work, we further postulated that cannabidiol (CBD), the primary non-psychoactive constituent of Cannabis sativa, may protect against inflammation-induced neuropathy through its direct effects on neurological Nav1.6. To test these ideas, we used whole-cell patch clamp of human embryonic kidney (HEK 293) cells transiently transfected with SCN8A cDNA encoding neurological Nav1.6 α-subunit and incubated the cells under control conditions or in a cocktail of inflammatory mediators for 24 hours. Incubation in inflammatory mediators right-shifted the voltage dependence of both activation and steady-state fast inactivation, and increased late sodium current. Perfusion of CBD (IC50; 5 µM) during recording rescued all the gating changes in Nav1.6 provoked by incubation with inflammatory mediators. These findings suggest that inflammation, by affecting Nav, is a potential pathogenic trigger for neurological pathologies. Moreover, CBD, through its direct effects on Nav, could potentially mitigate the dysfunction induced by inflammation.

Epilepsy-Induced High Affinity Blockade of the Cardiac Sodium Current INa by Lamotrigine; A Potential for Acquired Arrythmias.

Lamotrigine is widely prescribed to treat bipolar neurological disorder and epilepsy. It exerts its antiepileptic action by blocking voltage-gated sodium channels in neurons. Recently, the US Food and Drug Administration issued a warning on the use of Lamotrigine after observations of conduction anomalies and Brugada syndrome patterns on the electrocardiograms of epileptic patients treated with the drug. Brugada syndrome and conduction disturbance are both associated with alterations of the cardiac sodium current (INa) kinetics and amplitude. In this study, we used the patch clamp technique on cardiomyocytes from epileptic rats to test the hypothesis that Lamotrigine also blocks INa in the heart. We found that Lamotrigine inhibited 60% of INa peak amplitude and reduced cardiac excitability in epileptic rats but had little effect in sham animals. Moreover, Lamotrigine inhibited 67% of INaL and, more importantly, prolonged the action potential refractory period in epileptic animals. Our results suggest that enhanced affinity of Lamotrigine for INa may in part explain the clinical phenotypes observed in epileptic patients.

Voltage-gated sodium channel scn8a is required for innervation and regeneration of amputated adult zebrafish fins

Teleost fishes and urodele amphibians can regenerate amputated appendages, whereas this ability is restricted to digit tips in adult mammals. One key component of appendage regeneration is reinnervation of the wound area. However, how innervation is regulated in injured appendages of adult vertebrates has seen limited research attention. From a forward genetics screen for temperature-sensitive defects in zebrafish fin regeneration, we identified a mutation that disrupted regeneration while also inducing paralysis at the restrictive temperature. Genetic mapping and complementation tests identify a mutation in the major neuronal voltage-gated sodium channel (VGSC) gene scn8ab. Conditional disruption of scn8ab impairs early regenerative events, including blastema formation, but does not affect morphogenesis of established regenerates. Whereas scn8ab mutations reduced neural activity as expected, they also disrupted axon regrowth and patterning in fin regenerates, resulting in hypoinnervation. Our findings indicate that the activity of VGSCs plays a proregenerative role by promoting innervation of appendage stumps.

Effect of subacute poisoning with lambdacyhalothrin on vascular endothelial growth factor 2 receptor in mice kidneys

BackgroundPyrethroids are used for insect control. They act on voltage-gated sodium channels in neurons. Lambdacyhalothrin (LCH) is a type II pyrethroid producing choreoatetosis and salivation in rodents. Vascular endothelial growth factor (VEGF) expression in the kidney is high in the glomerular podocytes and kidney tubules. VEGF receptor 2 (VEFGR2) is the main mediator in angiogenesis and it regulates blood vessel permeability. Lack of VEGF in podocytes impairs filtration. The nuclear factor κB (NFκB) is widely known as an important mediator of inflammation.The aim of the study was to check if subacute oral intoxication with 0.1LD50 of LCH affects kidney size, function and VEGFR2 and NFκB in mice kidneys.MethodsA total of 32 Albino Swiss mice was used: females controls, males controls, females receiving 2 mg/kg LCH, males receiving 2 mg/kg LCH orally for 7 days. On day 8 animals were sacrificed, blood and kidneys were obtained. Kidney mass was determined, creatinine concentration was measured in blood sera, VEGFR2 and NFκB in kidney homogenate supernatant with ELISA kit.ResultsThere was no statistically significant differences in kidney mass, creatinine concentration in blood sera nor NFκB but mean VEGFR2 concentration in the kidneys of females exposed to LCH was 128.01 ng/ml and showed statistically significant difference in comparison with control females. There was no statistically significant difference between VEGFR2 concentration in the kidneys of males exposed to LCH and control males.ConclusionThe VEGFR2 increases in the course of LCH intoxication in females probably due to the protective effect of oestrogens.

Clinical exome sequencing identifies a novel variant in SCN1A gene in a Moroccan patient with Dravet syndrome

Dravet syndrome (DS) is a rare genetic epilepsy syndrome inherited by an autosomal dominant manner. It’s characterized by occurrence of protracted febrile seizures (FS) followed by development of multiple seizure types and psychomotor retardation. Early DS diagnosis in a child with FS facilitate institution of appropriate treatment. In clinical practice, Exome-Sequencing (ES) become a powerful approach for molecular diagnosis in genetic epilepsies.
 A 3-year-old Moroccan girl, born to non-consanguineous parents, was diagnosed with DS. The FS (10-15min) began in the first year of life (10months) followed by fever (40°C) and sleep problems. MRI, EEG and psychomotor development were normal. Positive family history of FS was reported in the father. The focal myoclonic seizures developed during the second-year were prolonged, repeated and resistant to treatments. ES has shown a novel heterozygous missense variant [c.4265A>T (p. Tyr1422Phe)] in exon 21 of SCN1A gene that encodes the type-1-subunit of neuronal voltage-gated sodium channel which regulate neuronal excitability. This variant has been predicted to be probably damaging by in-silico analysis. Genetic counselling is recommended for all families with SCN1A mutation. More analyses are needed to identify the phenotypic features of this novel variant in order to establish an effective care management.
 Keywords: Dravet syndrome, Exome sequencing, SCN1A, Moroccan patient.

Biophysical characterization of SCN1A and SCN2A variants related to epilepsy

Epilepsy is a common pediatric neurological disorder characterized by recurrent unprovoked seizures. SCN1A and SCN2A encode two neuronal voltage-gated sodium channels, namely NaV1.1 and NaV1.2 respectively, both of them highly expressed throughout the central nervous system (CNS). NaV1.1 localized within the axon initial segment (AIS) plays a critical role in the initiation and propagation of action potentials, predominantly in γ-aminobutyric acid (GABA)ergic neurons of the hippocampus. NaV1.2 is expressed in excitatory neurons with a steady increase and redistribution from AIS to distal axons.

The L1624Q Variant in SCN1A Causes Familial Epilepsy Through a Mixed Gain and Loss of Channel Function.

Variants of the SCN1A gene encoding the neuronal voltage-gated sodium channel NaV1.1 cause over 85% of all cases of Dravet syndrome, a severe and often pharmacoresistent epileptic encephalopathy with mostly infantile onset. But with the increased availability of genetic testing for patients with epilepsy, variants in SCN1A have now also been described in a range of other epilepsy phenotypes. The vast majority of these epilepsy-associated variants are de novo, and most are either nonsense variants that truncate the channel or missense variants that are presumed to cause loss of channel function. However, biophysical analysis has revealed a significant subset of missense mutations that result in increased excitability, further complicating approaches to precision pharmacotherapy for patients with SCN1A variants and epilepsy. We describe clinical and biophysical data of a familial SCN1A variant encoding the NaV1.1 L1624Q mutant. This substitution is located on the extracellular linker between S3 and S4 of Domain IV of NaV1.1 and is a rare case of a familial SCN1A variant causing an autosomal dominant frontal lobe epilepsy. We expressed wild-type (WT) and L1642Q channels in CHO cells. Using patch-clamp to characterize channel properties at several temperatures, we show that the L1624Q variant increases persistent current, accelerates fast inactivation onset and decreases current density. While SCN1A-associated epilepsy is typically considered a loss-of-function disease, our results put L1624Q into a growing set of mixed gain and loss-of-function variants in SCN1A responsible for epilepsy.

Variant Intronic Enhancer Controls SCN10A-short Expression and Heart Conduction.

Genetic variants in SCN10A, encoding the neuronal voltage-gated sodium channel NaV1.8, are strongly associated with atrial fibrillation, Brugada syndrome, cardiac conduction velocities, and heart rate. The cardiac function of SCN10A has not been resolved, however, and diverging mechanisms have been proposed. Here, we investigated the cardiac expression of SCN10A and the function of a variant-sensitive intronic enhancer previously linked to the regulation of SCN5A, encoding the major essential cardiac sodium channel NaV1.5. The expression of SCN10A was investigated in mouse and human hearts. With the use of CRISPR/Cas9 genome editing, the mouse intronic enhancer was disrupted, and mutant mice were characterized by transcriptomic and electrophysiological analyses. The association of genetic variants at SCN5A-SCN10A enhancer regions and gene expression were evaluated by genome-wide association studies single-nucleotide polymorphism mapping and expression quantitative trait loci analysis. We found that cardiomyocytes of the atria, sinoatrial node, and ventricular conduction system express a short transcript comprising the last 7 exons of the gene (Scn10a-short). Transcription occurs from an intronic enhancer-promoter complex, whereas full-length Scn10a transcript was undetectable in the human and mouse heart. Expression quantitative trait loci analysis revealed that the genetic variants in linkage disequilibrium with genetic variant rs6801957 in the intronic enhancer associate with SCN10A transcript levels in the heart. Genetic modification of the enhancer in the mouse genome led to reduced cardiac Scn10a-short expression in atria and ventricles, reduced cardiac sodium current in atrial cardiomyocytes, atrial conduction slowing and arrhythmia, whereas the expression of Scn5a, the presumed enhancer target gene, remained unaffected. In patch-clamp transfection experiments, expression of Scn10a-short-encoded NaV1.8-short increased NaV1.5-mediated sodium current. We propose that noncoding genetic variation modulates transcriptional regulation of Scn10a-short in cardiomyocytes that impacts NaV1.5-mediated sodium current and heart rhythm. Genetic variants in and around SCN10A modulate enhancer function and expression of a cardiac-specific SCN10A-short transcript. We propose that noncoding genetic variation modulates transcriptional regulation of a functional C-terminal portion of NaV1.8 in cardiomyocytes that impacts on NaV1.5 function, cardiac conduction velocities, and arrhythmia susceptibility.

NaV1.2 EFL domain allosterically enhances Ca2+ binding to sites I and II of WT and pathogenic calmodulin mutants bound to the channel CTD

Neuronal voltage-gated sodium channel NaV1.2 C-terminal domain (CTD) binds calmodulin (CaM) constitutively at its IQ motif. A solution structure (6BUT) and other NMR evidence showed that the CaM N domain (CaMN) is structurally independent of the C-domain (CaMC) whether CaM is bound to the NaV1.2IQp (1,901-1,927) or NaV1.2CTD (1,777-1,937) with or without calcium. However, in the CaM+ NaV1.2CTD complex, the Ca2+ affinity of CaMN was more favorable than in free CaM, while Ca2+ affinity for CaMC was weaker than in the CaM+ NaV1.2IQp complex. The CTD EF-like (EFL) domain allosterically widened the energetic gap between CaM domains. Cardiomyopathy-associated CaM mutants (N53I(N54I), D95V(D96V), A102V(A103V), E104A(E105A), D129G(D130G), and F141L(F142L)) all bound the NaV1.2 IQ motif favorably under resting (apo) conditions and bound calcium normally at CaMN sites. However, only N53I and A102V bound calcium at CaMC sites at [Ca2+]< 100μM. Thus, they are expected to respond like wild-type CaM to Ca2+ spikes in excitable cells.

Generation of iPSC lines from two patients affected by febrile seizure due to inherited missense mutation in SCN1A gene.

Here, we described the generation of human induced pluripotent stem cell lines (hiPSCs) from fibroblasts isolated by punch biopsies of two siblings carrying inherited mutation (c.434T>C) in the SCN1A gene, encoding for the neuronal voltage gated sodium channel NaV1.1. The mutation leads to the substitution of a highly conserved methionine with a threonine (M145T) in the protein sequence, leading to infant febrile seizures (FS). The older brother, affected by complex FS, also developed temporal lobe epilepsy (TLE) during adolescence.

Effects of saxitoxins exposure on oligodendrocyte development in mouse neonates

Saxitoxins (STXs) are neurotoxins produced by cyanobacteria and dinoflagellates, and they are primarily known to block voltage-gated sodium channels in neurons. The present study aimed to obtain further information regarding the effects of these toxins on neurodevelopment by investigating the responses of murine subventricular zone (SVZ) neural progenitors to STXs. An in vitro neonatal mouse SVZ explant model was exposed to different concentrations of toxic cyanobacterial extracts to evaluate the migration and differentiation of SVZ-derived progenitor cells. To test the ability of STX to cross the placental barrier, pregnant mice received a single intraperitoneal injection of STXs (7.5 μg/kg body weight) on gestational day fifteen. Immunocytochemistry was performed to detect proliferating and differentiating progenitors, including oligodendrocyte progenitor cells (OPCs). It was found that specific proliferation of OPCs was significantly increased, but there was no corresponding increase in the number of differentiated oligodendrocytes, which may indicate a negative effect on the maturation process of these cells. Additionally, the data showed that STXs crossed the placental barrier. Thus, STXs can be considered a potential risk to fetal neurodevelopment.

Partial Blockade of Human Voltage-Dependent Sodium Channels by the Marine Toxins Azaspiracids.

Azaspiracid toxins were first identified at the end of the last century in Irish mussels, and during the last two decades considerable cytotoxic and neurotoxic effects caused by these toxins have been described. Azaspiracids are synthesized by dinoflagellates and accumulate in several species of filter-feeding bivalve mollusks, thereby incorporating into the food chain and causing human intoxications. Among the cellular effects of azaspiracids, inhibition of spikes in neurons and hyperpolarization of the neuronal membrane potential have been reported; however, the underlying processes leading to these effects were never elucidated. In this regard, initial studies reported no activity of the toxin in neuronal voltage-gated sodium channels, and a recent work described no effect of azaspiracid-1 on the inactivation kinetics of voltage-gated sodium channels; however, the relationship between the known alterations of the cytoskeleton caused by these toxins and their effects on ion channels has never been evaluated. In this work, the cytotoxic effect of azaspiracids was evaluated in human cells as well as their activity on voltage-gated sodium channels and in cell morphology in order to unravel the cellular targets involved in the mechanism of action of this group of marine toxins. The data reported here demonstrate, for the first time, that both azaspiracid-1 and azaspiracid-2 caused a rapid concentration-dependent inhibition of the amplitude of voltage-gated sodium currents without affecting their inactivation kinetics, an effect that was increased after long-term treatment of the cells with the toxin. Simultaneously, long-term exposure of the cells to azaspiracids caused a profound alteration of the cell cytoskeleton and decreased the metabolic activity of human cells. Altogether, the data presented here indicate that the partial blockade of voltage-gated sodium channels by these toxins is not related with their effect on the actin cytoskeleton. However, since azaspiracids are common toxins in European waters, their effect on voltage-gated sodium channels, first reported here, should be considered to avoid synergistic toxicity with other marine toxins that are known potent blockers of sodium channels such as the saxitoxins and tetrodotoxins, but further studies are needed in order to elucidate how these compounds alter ion homeostasis.

Super-Resolution Imaging Using a Novel High-Fidelity Antibody Reveals Close Association of the Neuronal Sodium Channel NaV1.6 with Ryanodine Receptors in Cardiac Muscle.

The voltage-gated sodium channel [pore-forming subunit of the neuronal voltage-gated sodium channel (NaV1.6)] has recently been found in cardiac myocytes. Emerging studies indicate a role for NaV1.6 in ionic homeostasis as well as arrhythmogenesis. Little is known about the spatial organization of these channels in cardiac muscle, mainly due to the lack of high-fidelity antibodies. Therefore, we developed and rigorously validated a novel rabbit polyclonal NaV1.6 antibody and undertook super-resolution microscopy studies of NaV1.6 localization in cardiac muscle. We developed and validated a novel rabbit polyclonal antibody against a C-terminal epitope on the neuronal sodium channel 1.6 (NaV1.6). Raw sera showed high affinity in immuno-fluorescence studies, which was improved with affinity purification. The antibody was rigorously validated for specificity via multiple approaches. Lastly, we used this antibody in proximity ligation assay (PLA) and super-resolution STochastic Optical Reconstruction Microscopy (STORM) studies, which revealed enrichment of NaV1.6 in close proximity to ryanodine receptor (RyR2), a key calcium (Ca2+) cycling protein, in cardiac myocytes. In summary, our novel NaV1.6 antibody demonstrates high degrees of specificity and fidelity in multiple preparations. It enabled multimodal microscopic studies and revealed that over half of the NaV1.6 channels in cardiac myocytes are located within 100 nm of ryanodine receptor Ca2+ release channels.

Carvacrol inhibits the neuronal voltage-gated sodium channels Nav1.2, Nav1.6, Nav1.3, Nav1.7, and Nav1.8 expressed in Xenopus oocytes with different potencies

Carvacrol is the predominant monoterpene in essential oils from many aromatic plants. Several animal studies showing analgesic effects of carvacrol indicate potential of carvacrol as a new medication for patients with refractory pain. Voltage-gated sodium channels (Nav) are thought to have crucial roles in the development of inflammatory and neuropathic pain, but there is limited information about whether the analgesic mechanism of carvacrol involves Nav. We used whole-cell, two-electrode, voltage-clamp techniques to examine the effects of carvacrol on sodium currents in Xenopus oocytes expressing α subunits of Nav1.2, Nav1.3, Nav1.6, Nav1.7, and Nav1.8. Carvacrol dose-dependently suppressed sodium currents at a holding potential that induced half-maximal current. The half-maximal inhibitory concentration values for Nav1.2, Nav1.3, Nav1.6, Nav1.7, and Nav1.8 were 233, 526, 215, 367, and 824 μmol/L, respectively, indicating that carvacrol had more potent inhibitory effects towards Nav1.2 and Nav1.6 than Nav1.3, Nav1.7, and Nav1.8. Gating analysis showed a depolarizing shift of the activation curve and a hyperpolarizing shift of the inactivation curve in all five α subunits following carvacrol treatment. Furthermore, carvacrol exhibits a use-dependent block for all five α Nav subunits. These findings provide a better understanding of the mechanisms associated with the analgesic effect of carvacrol.

Mutation spectrum of the SCN1A gene in a Hungarian population with epilepsy

PurposeThe vast majority of mutations responsible for epilepsy syndromes such as genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS) occur in the gene encoding the type 1 alpha subunit of neuronal voltage-gated sodium channel (SCN1A). Methods63 individuals presenting with either DS or GEFS + syndrome phenotype were screened for SCN1A gene mutation using Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA). ResultsOur research study identified 15 novel pathogen mutations in the SCN1A gene of which 12 appeared to be missense mutations with addition of two frameshift-deletions and one in-frame deletion. The distribution of clinical phenotypes in patients carrying SCN1A mutations was as follows: twelve patients had classical DS, three patients had GEFS + syndrome and two relatives of DS patients were suffering from febrile seizures. ConclusionsOur study highlights the phenotypic and genotypic heterogeneities of DS and GEFS + with the important aim of gaining a deeper understanding of SCN1A-related disorders. This study also represents the first genetic analysis of the SCN1A gene in a Hungarian cohort with the DS and GEFS + syndrome phenotype.

Voltage gated sodium channels and epilepsy

Epilepsy is the fourth most common neurological disorder and affects people of all ages. Medication for epilepsy is often life-long and has a major impact on the quality of life - mostly being related to substantial adverse effects. Therefore, over 30% of people with epilepsy do not achieve sufficient seizure control whilst effective medication being available.&amp;nbsp; Ion channels are often primary targets of anticonvulsant drugs. They can either act as blockers for voltage gated sodium and calcium channels or as activators for potassium or chloride channels. Additionally, modulators of ligand gated ion channels (GABA or Glutamate receptors) are frequently used to treat epilepsy.&amp;nbsp; Employing a panel of functional electrophysiological assays using fluorescence based methods and patch-clamping on a broad range of voltage and ligand gated ion channels, we were able to successfully screen for drugs with a beneficial action profile. In successful leads we found drugs that selectively interacted with TTX sensitive, neuronal voltage gated sodium channels. Activation and fast inactivation were unchanged, while an increased affinity in the slow inactivated state was observed. This profile is in contrast to traditional anticonvulsant drugs which show their major effects on the fast inactivated state of voltage gated sodium channels. One drug showed substantial shifts of the voltage dependence of the slow inactivation only for NaV1.2 and 1.6. This favours this drug for treating patients with diseases with compromised NaV1.1 function in interneurons, such as&amp;nbsp;Alzheimer's disease.

Interaction of NaV1.2 IQ Motif with Disease-Causing Mutants of Calmodulin

Calmodulin (CaM) binds constitutively to an IQ motif (residues 1901-1927, NaV1.2IQp) in the cytosolic C-terminal tail of the a-subunit of the neuronal voltage-gated sodium channel NaV1.2. Solution structures of CaM C-domain (CaMC) bound to NaV1.2IQp showed calcium binding reverses the orientation of (Ca2+)2-CaMC (2M5E.pdb) relative to apo CaMC (2KXW.pdb). Our structure of full-length apo human CaM bound to human NaV1.2IQp showed that only CaMc interacts with NaV1.2IQp. Thermodynamic and NMR analysis of the CaM-NaV1.2IQp complex showed no evidence for CaMN-NaV1.2IQp interactions, and indicated nearly identical affinity for calcium binding to the 4 EF-hand sites of CaM. Residues in NaV1.2IQp had different chemical environments when bound to apo and (Ca2+)4-CaM, consistent with the calcium-trigged change observed in the (Ca2+)2-CaMC-NaV1.2IQp interface (2M5E.pdb). Apo human CaM carrying cardiomyopathy-causing mutations [N53I(N54I), D95V(D96V), A102V(A103V), E104A(E105A), D129G(D130G), and F141L(F142L)] all bound tightly to NaV1.2IQp. However, mutations in CaMC inhibited Ca2+-mediated conformational changes of CaM bound to NaV1.2IQp. This suggests that high cytosolic Ca2+ levels would not be sufficient to trigger reversal of the orientation of these CaMC mutants. The effects of other recently described disease-causing CaM mutations are being investigated. NIH R01 GM57001 (MAS), NIH T32 NS045549 (RM), UI CCOM FUTURE in Biomedicine (AMK)

Dravet Syndrome: A Developmental and Epileptic Encephalopathy.

Selective Nav1.1 Activation Rescues Dravet Syndrome Mice From Seizures and Premature Death Richards KL, Milligan CJ, Richardson RJ, Jancovski N, Grunnet M, Jacobson LH, Undheim EAB, Mobli M, Chow CY, Herzig V, Csoti A, Panyi G, Reid CA, King GF, Petrou S. PNAS. 2018;115:E8077-E8085. doi:10.1073/pnas.1804764115Dravet syndrome is a catastrophic, pharmaco-resistant epileptic encephalopathy. Disease onset occurs in the first year of life, followed by developmental delay with cognitive and behavioral dysfunction and substantially elevated risk of premature death. The majority of affected individuals harbor a loss-of-function mutation in one allele ofSCN1A, which encodes the voltage-gated sodium channel Nav1.1. Brain Nav1.1 is primarily localized to fast-spiking inhibitory interneurons; thus, the mechanism of epileptogenesis in Dravet syndrome is hypothesized to be reduced inhibitory neurotransmission leading to brain hyperexcitability. We show that selective activation of Nav1.1 by venom peptide Hm1a restores the function of inhibitory interneurons from Dravet syndrome mice without affecting the firing of excitatory neurons. Intracerebroventricular infusion of Hm1a rescues Dravet syndrome mice from seizures and premature death. This precision medicine approach, which specifically targets the molecular deficit in Dravet syndrome, presents an opportunity for treatment of this intractable epilepsy. A Transient Developmental Window of Fast-Spiking Interneuron Dysfunction in a Mouse Model of Dravet Syndrome Favero M, Sotuyo NP, Lopez E, Kearney JA, Goldberg EM. J Neurosci. 2018;38:7912-7927. doi:10.1523/JNEUROSCI.0193-18.2018Dravet syndrome is a severe childhood-onset epilepsy largely due to heterozygous loss-of-function mutation of the gene SCN1A, which encodes the type 1 neuronal voltage-gated sodium (Na+) channel α subunit Nav1.1. Prior studies in mouse models of Dravet syndrome (Scn1a+/− mice) indicate that, in cerebral cortex, Nav1.1 is predominantly expressed in GABAergic interneurons, in particular in parvalbumin-positive fast-spiking basket cell interneurons (PVINs). This has led to a model of Dravet syndrome pathogenesis in which Nav1.1 mutation leads to preferential dysfunction of interneurons, decreased synaptic inhibition, hyperexcitability, and epilepsy. However, such studies have been implemented at early developmental time points. Here, we performed electrophysiological recordings in acute brain slices prepared from male and female Scn1a+/−mice as well as age-matched wild-type littermate controls and found that, later in development, the excitability of PVINs had normalized. Analysis of action potential waveforms indirectly suggests a reorganization of axonal Na+ channels in PVINs from Scn1a+/− mice, a finding supported by immunohistochemical data showing elongation of the axon initial segment. Our results imply that transient impairment of action potential generation by PVINs may contribute to the initial appearance of epilepsy, but is not the mechanism of ongoing, chronic epilepsy in Dravet syndrome. Significance Statement: Dravet syndrome is characterized by normal early development, temperature-sensitive seizures in infancy, progression to treatment-resistant epilepsy, developmental delay, autism, and sudden unexplained death due to mutation in SCN1A encoding the Na+ channel subunit Nav1.1. Prior work has revealed a preferential impact of Nav1.1 loss on the function of GABAergic inhibitory interneurons. However, such data derive exclusively from recordings of neurons in young Scn1a+/− mice. Here, we show that impaired action potential generation observed in parvalbumin-positive fast-spiking interneurons (PVINs) in Scn1a+/− mice during early development has normalized by postnatal day 35. This work suggests that a transient impairment of PVINs contributes to epilepsy onset, but is not the mechanism of ongoing, chronic epilepsy in Dravet syndrome.

The possible effect of SCN1A and SCN2A genetic variants on carbamazepine response among Khyber Pakhtunkhwa epileptic patients, Pakistan.

PurposeSCN1A (3184 A>G) and SCN2A (56G>A) gene encodes α subunit of the neuronal voltage-gated sodium channel, which is a target for carbamazepine (CBZ). Recent studies have demonstrated that polymorphism of SCN1A (3184 A>G) and SCN2A (56G>A) was associated with use of CBZ. However, it has not been determined whether the polymorphism affects CBZ or other antiepileptic drug responsiveness. The aim of the study was to establish whether the SCN1A (3184 A>G) and SCN2A (56G>A) polymorphisms of the SCN1A and SCN2A genes affect responsiveness to CBZ.MethodsSCN1A (3184 A>G) and SCN2A (56G>A) gene polymorphisms were genotyped in 93 Khyber Pakhtunkhwa epileptic patients treated with CBZ. The association between CBZ responsiveness and the polymorphism was estimated by adjusting for clinical factors affecting the outcome of therapy. The number of seizure episodes was documented at baseline, and the therapy of each of the 93 patients was followed up. The plasma level of CBZ was determined using reverse-phase high-performance liquid chromatography. SCN1A and SCN2A genes were genotyped using RFLP. Data were analyzed using Graph Pad Prism 6.ResultsMean age of the patients was 18.6±9.3 at the 3rd month and 18.7±9.5 at the 6th month. The baseline dose of CBZ was 468±19.8 mg/d and titrated at the rate of 48±1.4 and 4.0±0.2 mg/d. The difference in plasma level of CBZ was significant (P=0.004) between 3rd and 6th month among different genotypes of SCN1A gene in nonresponder and responder patients. At the 3rd month of the therapy, the poor responders were more likely (P=0.003 and P=0.01) to have variants (3184AG and 3184GG) of SCN1A gene. Similarly, poor responsders were more likely (P=0.0007 and P=0.001) to have variant genotypes (56GA, 56AA) of SCN2A gene at the 3rd month of the therapy.ConclusionThis study demonstrated a significant association between the SCN1A (3184 AG and GG) and SCN2A (56GA and AA) genotype with CBZ-nonresponsive epilepsy.