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Aberrant Sodium Channel Currents and Hyperexcitability of Medial Entorhinal Cortex Neurons in a Mouse Model of SCN8A Encephalopathy. J Neurosci 2017; 37:7643-7655. [PMID: 28676574 DOI: 10.1523/jneurosci.2709-16.2017] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 06/06/2017] [Accepted: 06/27/2017] [Indexed: 02/02/2023] Open
Abstract
SCN8A encephalopathy, or early infantile epileptic encephalopathy 13 (EIEE13), is caused predominantly by de novo gain-of-function mutations in the voltage-gated Na channel Nav1.6. Affected individuals suffer from refractory seizures, developmental delay, cognitive disability, and elevated risk of sudden unexpected death in epilepsy (SUDEP). A knock-in mouse model carrying the patient mutation p.Asn1768Asp (N1768D) reproduces many features of the disorder, including spontaneous seizures and SUDEP. We used the mouse model to examine the effects of the mutation on layer II stellate neurons of the medial entorhinal cortex (mEC), which transmit excitatory input to the hippocampus. Heterozygous (Scn8aD/+), homozygous (Scn8aD/D)), and WT (Scn8a+/+) littermates were compared at 3 weeks of age, the time of seizure onset for homozygous mice. Heterozygotes remain seizure free for another month. mEC layer II neurons of heterozygous and homozygous mice were hyperexcitable and generated long-lasting depolarizing potentials with bursts of action potentials after synaptic stimulation. Recording of Na currents revealed proexcitatory increases in persistent and resurgent currents and rightward shifts in inactivation parameters, leading to significant increases in the magnitude of window currents. The proexcitatory changes were more pronounced in homozygous mice than in heterozygotes, consistent with the earlier age of seizure onset in homozygotes. These studies demonstrate that the N1768D mutation increases the excitability of mEC layer II neurons by increasing persistent and resurgent Na currents and disrupting channel inactivation. The aberrant activities of mEC layer II neurons would provide excessive excitatory input to the hippocampus and contribute to hyperexcitability of hippocampal neurons in this model of SCN8A encephalopathy.SIGNIFICANCE STATEMENTSCN8A encephalopathy is a devastating neurological disorder that results from de novo mutations in the Na channel Nav1.6. In addition to seizures, patients suffer from cognitive and developmental delays and are at high risk for sudden unexpected death in epilepsy (SUDEP). A mouse knock-in model expressing the patient mutation N1768D reproduces several pathological phenotypes, including spontaneous seizures and sudden death. We demonstrate that medial entorhinal cortex (mEC) neurons from the mouse model exhibit proexcitatory alterations in Na channel activity, some of which were not seen in hippocampal or cortical neurons, and resulting in neuronal hyperexcitability. Because mEC neurons regulate the activity of the hippocampus, which plays an important role in seizure onset, we propose that these profound changes in mEC neuron excitability associated with the gain-of-function mutation of Nav1.6 may increase excitatory drive into the hippocampus, culminating in seizure activity and SUDEP.
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Ion Channel Genes and Epilepsy: Functional Alteration, Pathogenic Potential, and Mechanism of Epilepsy. Neurosci Bull 2017; 33:455-477. [PMID: 28488083 DOI: 10.1007/s12264-017-0134-1] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 02/20/2017] [Indexed: 01/29/2023] Open
Abstract
Ion channels are crucial in the generation and modulation of excitability in the nervous system and have been implicated in human epilepsy. Forty-one epilepsy-associated ion channel genes and their mutations are systematically reviewed. In this paper, we analyzed the genotypes, functional alterations (funotypes), and phenotypes of these mutations. Eleven genes featured loss-of-function mutations and six had gain-of-function mutations. Nine genes displayed diversified funotypes, among which a distinct funotype-phenotype correlation was found in SCN1A. These data suggest that the funotype is an essential consideration in evaluating the pathogenicity of mutations and a distinct funotype or funotype-phenotype correlation helps to define the pathogenic potential of a gene.
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Lamar T, Vanoye CG, Calhoun J, Wong JC, Dutton SBB, Jorge BS, Velinov M, Escayg A, Kearney JA. SCN3A deficiency associated with increased seizure susceptibility. Neurobiol Dis 2017; 102:38-48. [PMID: 28235671 DOI: 10.1016/j.nbd.2017.02.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 01/24/2017] [Accepted: 02/20/2017] [Indexed: 11/25/2022] Open
Abstract
Mutations in voltage-gated sodium channels expressed highly in the brain (SCN1A, SCN2A, SCN3A, and SCN8A) are responsible for an increasing number of epilepsy syndromes. In particular, mutations in the SCN3A gene, encoding the pore-forming Nav1.3 α subunit, have been identified in patients with focal epilepsy. Biophysical characterization of epilepsy-associated SCN3A variants suggests that both gain- and loss-of-function SCN3A mutations may lead to increased seizure susceptibility. In this report, we identified a novel SCN3A variant (L247P) by whole exome sequencing of a child with focal epilepsy, developmental delay, and autonomic nervous system dysfunction. Voltage clamp analysis showed no detectable sodium current in a heterologous expression system expressing the SCN3A-L247P variant. Furthermore, cell surface biotinylation demonstrated a reduction in the amount of SCN3A-L247P at the cell surface, suggesting the SCN3A-L247P variant is a trafficking-deficient mutant. To further explore the possible clinical consequences of reduced SCN3A activity, we investigated the effect of a hypomorphic Scn3a allele (Scn3aHyp) on seizure susceptibility and behavior using a gene trap mouse line. Heterozygous Scn3a mutant mice (Scn3a+/Hyp) did not exhibit spontaneous seizures nor were they susceptible to hyperthermia-induced seizures. However, they displayed increased susceptibility to electroconvulsive (6Hz) and chemiconvulsive (flurothyl and kainic acid) induced seizures. Scn3a+/Hyp mice also exhibited deficits in locomotor activity and motor learning. Taken together, these results provide evidence that loss-of-function of SCN3A caused by reduced protein expression or deficient trafficking to the plasma membrane may contribute to increased seizure susceptibility.
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Affiliation(s)
- Tyra Lamar
- Department of Human Genetics, Emory University, Atlanta, GA, USA
| | - Carlos G Vanoye
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Jeffrey Calhoun
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Jennifer C Wong
- Department of Human Genetics, Emory University, Atlanta, GA, USA
| | | | - Benjamin S Jorge
- Neuroscience Program, Vanderbilt University, Nashville, TN 37232, USA
| | - Milen Velinov
- New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA; Albert Einstein College of Medicine, Bronx, NY, USA
| | - Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, GA, USA.
| | - Jennifer A Kearney
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
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54
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Neuronal hyperexcitability in a mouse model of SCN8A epileptic encephalopathy. Proc Natl Acad Sci U S A 2017; 114:2383-2388. [PMID: 28193882 DOI: 10.1073/pnas.1616821114] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Patients with early infantile epileptic encephalopathy (EIEE) experience severe seizures and cognitive impairment and are at increased risk for sudden unexpected death in epilepsy (SUDEP). EIEE13 [Online Mendelian Inheritance in Man (OMIM) # 614558] is caused by de novo missense mutations in the voltage-gated sodium channel gene SCN8A Here, we investigated the neuronal phenotype of a mouse model expressing the gain-of-function SCN8A patient mutation, p.Asn1768Asp (Nav1.6-N1768D). Our results revealed regional and neuronal subtype specificity in the effects of the N1768D mutation. Acutely dissociated hippocampal neurons from Scn8aN1768D/+ mice showed increases in persistent sodium current (INa) density in CA1 pyramidal but not bipolar neurons. In CA3, INa,P was increased in both bipolar and pyramidal neurons. Measurement of action potential (AP) firing in Scn8aN1768D/+ pyramidal neurons in brain slices revealed early afterdepolarization (EAD)-like AP waveforms in CA1 but not in CA3 hippocampal or layer II/III neocortical neurons. The maximum spike frequency evoked by depolarizing current injections in Scn8aN1768D/+ CA1, but not CA3 or neocortical, pyramidal cells was significantly reduced compared with WT. Spontaneous firing was observed in subsets of neurons in CA1 and CA3, but not in the neocortex. The EAD-like waveforms of Scn8aN1768D/+ CA1 hippocampal neurons were blocked by tetrodotoxin, riluzole, and SN-6, implicating elevated persistent INa and reverse mode Na/Ca exchange in the mechanism of hyperexcitability. Our results demonstrate that Scn8a plays a vital role in neuronal excitability and provide insight into the mechanism and future treatment of epileptogenesis in EIEE13.
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55
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Structure-based assessment of disease-related mutations in human voltage-gated sodium channels. Protein Cell 2017; 8:401-438. [PMID: 28150151 PMCID: PMC5445024 DOI: 10.1007/s13238-017-0372-z] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 01/09/2017] [Indexed: 12/15/2022] Open
Abstract
Voltage-gated sodium (Nav) channels are essential for the rapid upstroke of action potentials and the propagation of electrical signals in nerves and muscles. Defects of Nav channels are associated with a variety of channelopathies. More than 1000 disease-related mutations have been identified in Nav channels, with Nav1.1 and Nav1.5 each harboring more than 400 mutations. Nav channels represent major targets for a wide array of neurotoxins and drugs. Atomic structures of Nav channels are required to understand their function and disease mechanisms. The recently determined atomic structure of the rabbit voltage-gated calcium (Cav) channel Cav1.1 provides a template for homology-based structural modeling of the evolutionarily related Nav channels. In this Resource article, we summarized all the reported disease-related mutations in human Nav channels, generated a homologous model of human Nav1.7, and structurally mapped disease-associated mutations. Before the determination of structures of human Nav channels, the analysis presented here serves as the base framework for mechanistic investigation of Nav channelopathies and for potential structure-based drug discovery.
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56
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Butler KM, da Silva C, Shafir Y, Weisfeld-Adams JD, Alexander JJ, Hegde M, Escayg A. De novo and inherited SCN8A epilepsy mutations detected by gene panel analysis. Epilepsy Res 2017; 129:17-25. [PMID: 27875746 PMCID: PMC5321682 DOI: 10.1016/j.eplepsyres.2016.11.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 10/31/2016] [Accepted: 11/05/2016] [Indexed: 12/19/2022]
Abstract
OBJECTIVES To determine the incidence of pathogenic SCN8A variants in a cohort of epilepsy patients referred for clinical genetic testing. We also investigated the contribution of SCN8A to autism spectrum disorder, intellectual disability, and neuromuscular disorders in individuals referred for clinical genetic testing at the same testing laboratory. METHODS Sequence data from 275 epilepsy panels screened by Emory Genetics Laboratory were reviewed for variants in SCN8A. Two additional cases with variants in SCN8A were ascertained from other testing laboratories. Parental samples were tested for variant segregation and clinical histories were examined. SCN8A variants detected from gene panel analyses for autism spectrum disorder, intellectual disability, and neuromuscular disorders were also examined. RESULTS Five variants in SCN8A were identified in five individuals with epilepsy. Three variants were de novo, one was inherited from an affected parent, and one was inherited from an unaffected parent. Four of the individuals have epilepsy and developmental delay/intellectual disability. The remaining individual has a milder epilepsy presentation without cognitive impairment. We also identified an amino acid substitution at an evolutionarily conserved SCN8A residue in a patient who was screened on the autism spectrum disorder panel. Additionally, we examined the distribution of pathogenic SCN8A variants across the Nav1.6 channel and identified four distinct clusters of variants. These clusters are primarily located in regions of the channel that are important for the kinetics of channel inactivation. CONCLUSIONS Variants in SCN8A may be responsible for a spectrum of epilepsies as well as other neurodevelopmental disorders without seizures. The predominant pathogenic mechanism appears to involve disruption of channel inactivation, leading to gain-of-function effects.
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Affiliation(s)
- Kameryn M Butler
- Department of Human Genetics, Emory University, Atlanta, GA 30322, United States
| | - Cristina da Silva
- Department of Human Genetics, Emory University, Atlanta, GA 30322, United States; EGL Genetic Diagnostics, Decatur, GA 30033, United States
| | - Yuval Shafir
- The Herman and Walter Samuelson Children's Hospital at Sinai, Division of Pediatric Neurology, Baltimore, MD 21209, United States
| | - James D Weisfeld-Adams
- Division of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, United States
| | - John J Alexander
- Department of Human Genetics, Emory University, Atlanta, GA 30322, United States; EGL Genetic Diagnostics, Decatur, GA 30033, United States
| | - Madhuri Hegde
- Department of Human Genetics, Emory University, Atlanta, GA 30322, United States
| | - Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, GA 30322, United States.
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57
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Reif PS, Tsai MH, Helbig I, Rosenow F, Klein KM. Precision medicine in genetic epilepsies: break of dawn? Expert Rev Neurother 2016; 17:381-392. [DOI: 10.1080/14737175.2017.1253476] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Philipp Sebastian Reif
- Epilepsy Center Frankfurt Rhine-Main, Department of Neurology, Center of Neurology and Neurosurgery, University Hospital, Goethe-University Frankfurt, Frankfurt, Germany
| | - Meng-Han Tsai
- Division of Brain Function & Epilepsy, Department of Neurology, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung, Taiwan
| | - Ingo Helbig
- Division of Neurology, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA
- Department of Neuropediatrics, Christian-Albrechts-University of Kiel and University Medical Center Schleswig-Holstein, Kiel, Germany
- Departments of Brain and Cognitive Sciences, Physiology and Cell Biology, Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Felix Rosenow
- Epilepsy Center Frankfurt Rhine-Main, Department of Neurology, Center of Neurology and Neurosurgery, University Hospital, Goethe-University Frankfurt, Frankfurt, Germany
- Epilepsy Center Hessen, Department of Neurology, University Hospitals Giessen & Marburg, and Philipps-University Marburg, Marburg, Germany
| | - Karl Martin Klein
- Epilepsy Center Frankfurt Rhine-Main, Department of Neurology, Center of Neurology and Neurosurgery, University Hospital, Goethe-University Frankfurt, Frankfurt, Germany
- Epilepsy Center Hessen, Department of Neurology, University Hospitals Giessen & Marburg, and Philipps-University Marburg, Marburg, Germany
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58
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Sprissler RS, Wagnon JL, Bunton-Stasyshyn RK, Meisler MH, Hammer MF. Altered gene expression profile in a mouse model of SCN8A encephalopathy. Exp Neurol 2016; 288:134-141. [PMID: 27836728 DOI: 10.1016/j.expneurol.2016.11.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 10/06/2016] [Accepted: 11/03/2016] [Indexed: 02/07/2023]
Abstract
SCN8A encephalopathy is a severe, early-onset epilepsy disorder resulting from de novo gain-of-function mutations in the voltage-gated sodium channel Nav1.6. To identify the effects of this disorder on mRNA expression, RNA-seq was performed on brain tissue from a knock-in mouse expressing the patient mutation p.Asn1768Asp (N1768D). RNA was isolated from forebrain, cerebellum, and brainstem both before and after seizure onset, and from age-matched wildtype littermates. Altered transcript profiles were observed only in forebrain and only after seizures. The abundance of 50 transcripts increased more than 3-fold and 15 transcripts decreased more than 3-fold after seizures. The elevated transcripts included two anti-convulsant neuropeptides and more than a dozen genes involved in reactive astrocytosis and response to neuronal damage. There was no change in the level of transcripts encoding other voltage-gated sodium, potassium or calcium channels. Reactive astrocytosis was observed in the hippocampus of mutant mice after seizures. There is considerable overlap between the genes affected in this genetic model of epilepsy and those altered by chemically induced seizures, traumatic brain injury, ischemia, and inflammation. The data support the view that gain-of-function mutations of SCN8A lead to pathogenic alterations in brain function contributing to encephalopathy.
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Affiliation(s)
- Ryan S Sprissler
- ARL Division of Biotechnology, University of Arizona, Tucson, AZ 85721, USA
| | - Jacy L Wagnon
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
| | | | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA; Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA.
| | - Michael F Hammer
- ARL Division of Biotechnology, University of Arizona, Tucson, AZ 85721, USA; Department of Neurology, University of Arizona, Tucson, AZ 85721, USA.
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59
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Cardiac arrhythmia in a mouse model of sodium channel SCN8A epileptic encephalopathy. Proc Natl Acad Sci U S A 2016; 113:12838-12843. [PMID: 27791149 DOI: 10.1073/pnas.1612746113] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Patients with early infantile epileptic encephalopathy (EIEE) are at increased risk for sudden unexpected death in epilepsy (SUDEP). De novo mutations of the sodium channel gene SCN8A, encoding the sodium channel Nav1.6, result in EIEE13 (OMIM 614558), which has a 10% risk of SUDEP. Here, we investigated the cardiac phenotype of a mouse model expressing the gain of function EIEE13 patient mutation p.Asn1768Asp in Scn8a (Nav1.6-N1768D). We tested Scn8aN1768D/+ mice for alterations in cardiac excitability. We observed prolongation of the early stages of action potential (AP) repolarization in mutant myocytes vs. controls. Scn8aN1768D/+ myocytes were hyperexcitable, with a lowered threshold for AP firing, increased incidence of delayed afterdepolarizations, increased calcium transient duration, increased incidence of diastolic calcium release, and ectopic contractility. Calcium transient duration and diastolic calcium release in the mutant myocytes were tetrodotoxin-sensitive. A selective inhibitor of reverse mode Na/Ca exchange blocked the increased incidence of diastolic calcium release in mutant cells. Scn8aN1768D/+ mice exhibited bradycardia compared with controls. This difference in heart rate dissipated after administration of norepinephrine, and there were no differences in heart rate in denervated ex vivo hearts, implicating parasympathetic hyperexcitability in the Scn8aN1768D/+ animals. When challenged with norepinephrine and caffeine to simulate a catecholaminergic surge, Scn8aN1768D/+ mice showed ventricular arrhythmias. Two of three mutant mice under continuous ECG telemetry recording experienced death, with severe bradycardia preceding asystole. Thus, in addition to central neuron hyperexcitability, Scn8aN1768D/+ mice have cardiac myoycte and parasympathetic neuron hyperexcitability. Simultaneous dysfunction in these systems may contribute to SUDEP associated with mutations of Scn8a.
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60
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Tanaka BS, Zhao P, Dib-Hajj FB, Morisset V, Tate S, Waxman SG, Dib-Hajj SD. A gain-of-function mutation in Nav1.6 in a case of trigeminal neuralgia. Mol Med 2016; 22:338-348. [PMID: 27496104 DOI: 10.2119/molmed.2016.00131] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 07/18/2016] [Indexed: 01/29/2023] Open
Abstract
Idiopathic trigeminal neuralgia (TN) is a debilitating pain disorder characterized by episodic unilateral facial pain along the territory of branches of the trigeminal nerve. Human painful disorders, but not TN, have been linked to gain-of-function mutations in peripheral voltage-gated sodium channels (NaV1.7, NaV1.8 and NaV1.9). Gain-of-function mutations in NaV1.6, which is expressed in myelinated and unmyelinated CNS and peripheral nervous system neurons and supports neuronal high-frequency firing, have been linked to epilepsy but not to pain. Here, we describe an individual who presented with evoked and spontaneous paroxysmal unilateral facial pain, and carried a diagnosis of TN. Magnetic resonance imaging showed unilateral neurovascular compression, consistent with pain in areas innervated by the second branch of the trigeminal nerve. Genetic analysis as part of a phase 2 clinical study in patients with TN conducted by Convergence Pharmaceuticals Ltd revealed a previously undescribed de novo missense mutation in NaV1.6 (c.A406G; p.Met136Val). Whole-cell voltage-clamp recordings show that the Met136Val mutation significantly increases peak current density (1.5-fold) and resurgent current (1.6-fold) without altering gating properties. Current-clamp studies in trigeminal ganglion (TRG) neurons showed that Met136Val increased the fraction of high-firing neurons, lowered the current threshold and increased the frequency of evoked action potentials in response to graded stimuli. Our results demonstrate a novel NaV1.6 mutation in TN, and show that this mutation potentiates transient and resurgent sodium currents and leads to increased excitability in TRG neurons. We suggest that this gain-of-function NaV1.6 mutation may exacerbate the pathophysiology of vascular compression and contribute to TN.
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Affiliation(s)
- Brian S Tanaka
- Department of Neurology.,Center for Neuroscience & Regeneration Research, Yale University School of Medicine, New Haven, CT 06510.,Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT 06516
| | - Peng Zhao
- Department of Neurology.,Center for Neuroscience & Regeneration Research, Yale University School of Medicine, New Haven, CT 06510.,Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT 06516
| | - Fadia B Dib-Hajj
- Department of Neurology.,Center for Neuroscience & Regeneration Research, Yale University School of Medicine, New Haven, CT 06510.,Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT 06516
| | - Valerie Morisset
- Convergence Pharmaceuticals Ltd, a Biogen company, Cambridge, United Kingdom
| | - Simon Tate
- Convergence Pharmaceuticals Ltd, a Biogen company, Cambridge, United Kingdom
| | - Stephen G Waxman
- Department of Neurology.,Center for Neuroscience & Regeneration Research, Yale University School of Medicine, New Haven, CT 06510.,Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT 06516
| | - Sulayman D Dib-Hajj
- Department of Neurology.,Center for Neuroscience & Regeneration Research, Yale University School of Medicine, New Haven, CT 06510.,Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, CT 06516
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61
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Ghovanloo MR, Aimar K, Ghadiry-Tavi R, Yu A, Ruben PC. Physiology and Pathophysiology of Sodium Channel Inactivation. CURRENT TOPICS IN MEMBRANES 2016; 78:479-509. [PMID: 27586293 DOI: 10.1016/bs.ctm.2016.04.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Voltage-gated sodium channels are present in different tissues within the human body, predominantly nerve, muscle, and heart. The sodium channel is composed of four similar domains, each containing six transmembrane segments. Each domain can be functionally organized into a voltage-sensing region and a pore region. The sodium channel may exist in resting, activated, fast inactivated, or slow inactivated states. Upon depolarization, when the channel opens, the fast inactivation gate is in its open state. Within the time frame of milliseconds, this gate closes and blocks the channel pore from conducting any more sodium ions. Repetitive or continuous stimulations of sodium channels result in a rate-dependent decrease of sodium current. This process may continue until the channel fully shuts down. This collapse is known as slow inactivation. This chapter reviews what is known to date regarding, sodium channel inactivation with a focus on various mutations within each NaV subtype and with clinical implications.
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Affiliation(s)
- M-R Ghovanloo
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - K Aimar
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - R Ghadiry-Tavi
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - A Yu
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - P C Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
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62
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Barker BS, Ottolini M, Wagnon JL, Hollander RM, Meisler MH, Patel MK. The SCN8A encephalopathy mutation p.Ile1327Val displays elevated sensitivity to the anticonvulsant phenytoin. Epilepsia 2016; 57:1458-66. [PMID: 27375106 DOI: 10.1111/epi.13461] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/10/2016] [Indexed: 12/16/2022]
Abstract
OBJECTIVE SCN8A encephalopathy (early infantile epileptic encephalopathy; EIEE13) is caused by gain-of-function mutations resulting in hyperactivity of the voltage-gated sodium channel Nav 1.6. The channel is concentrated at the axon initial segment (AIS) and is involved in establishing neuronal excitability. Clinical features of SCN8A encephalopathy include seizure onset between 0 and 18 months of age, intellectual disability, and developmental delay. Seizures are often refractory to treatment with standard antiepileptic drugs, and sudden unexpected death in epilepsy (SUDEP) has been reported in approximately 10% of patients. In a recent study, high doses of phenytoin were effective in four patients with SCN8A encephalopathy. In view of this observation, we have investigated the relationship between the functional effect of the SCN8A mutation p.Ile1327Val and its response to phenytoin. METHODS The mutation was introduced into the Scn8a cDNA by site-directed mutagenesis. Channel activity was characterized in transfected ND7/23 cells. The effects of phenytoin (100 μm) on mutant and wild-type (WT) channels were compared. RESULTS Channel activation parameters were shifted in a hyperpolarizing direction in the mutant channel, whereas inactivation parameters were shifted in a depolarizing direction, increasing Na channel window current. Macroscopic current decay was slowed in I1327V channels, indicating an impairment in the transition from open state to inactivated state. Channel deactivation was also delayed, allowing more channels to remain in the open state. Phenytoin (100 μm) resulted in hyperpolarized activation and inactivation curves as well as greater tonic block and use-dependent block of I1327V mutant channels relative to WT. SIGNIFICANCE SCN8A - I1327V is a gain-of-function mutation with altered features that are predicted to increase neuronal excitability and seizure susceptibility. Phenytoin is an effective inhibitor of the mutant channel and may be of use in treating patients with gain-of-function mutations of SCN8A.
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Affiliation(s)
- Bryan S Barker
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, Virginia, U.S.A.,Neuroscience Graduate Program, University of Virginia Health System, Charlottesville, Virginia, U.S.A
| | - Matteo Ottolini
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, Virginia, U.S.A
| | - Jacy L Wagnon
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - Rachel M Hollander
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - Manoj K Patel
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, Virginia, U.S.A.,Neuroscience Graduate Program, University of Virginia Health System, Charlottesville, Virginia, U.S.A
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63
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Meisler MH, Helman G, Hammer MF, Fureman BE, Gaillard WD, Goldin AL, Hirose S, Ishii A, Kroner BL, Lossin C, Mefford HC, Parent JM, Patel M, Schreiber J, Stewart R, Whittemore V, Wilcox K, Wagnon JL, Pearl PL, Vanderver A, Scheffer IE. SCN8A encephalopathy: Research progress and prospects. Epilepsia 2016; 57:1027-35. [PMID: 27270488 PMCID: PMC5495462 DOI: 10.1111/epi.13422] [Citation(s) in RCA: 102] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/26/2016] [Indexed: 01/15/2023]
Abstract
On April 21, 2015, the first SCN8A Encephalopathy Research Group convened in Washington, DC, to assess current research into clinical and pathogenic features of the disorder and prepare an agenda for future research collaborations. The group comprised clinical and basic scientists and representatives of patient advocacy groups. SCN8A encephalopathy is a rare disorder caused by de novo missense mutations of the sodium channel gene SCN8A, which encodes the neuronal sodium channel Nav 1.6. Since the initial description in 2012, approximately 140 affected individuals have been reported in publications or by SCN8A family groups. As a result, an understanding of the severe impact of SCN8A mutations is beginning to emerge. Defining a genetic epilepsy syndrome goes beyond identification of molecular etiology. Topics discussed at this meeting included (1) comparison between mutations of SCN8A and the SCN1A mutations in Dravet syndrome, (2) biophysical properties of the Nav 1.6 channel, (3) electrophysiologic effects of patient mutations on channel properties, (4) cell and animal models of SCN8A encephalopathy, (5) drug screening strategies, (6) the phenotypic spectrum of SCN8A encephalopathy, and (7) efforts to develop a bioregistry. A panel discussion of gaps in bioregistry, biobanking, and clinical outcomes data was followed by a planning session for improved integration of clinical and basic science research. Although SCN8A encephalopathy was identified only recently, there has been rapid progress in functional analysis and phenotypic classification. The focus is now shifting from identification of the underlying molecular cause to the development of strategies for drug screening and prioritized patient care.
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Affiliation(s)
- Miriam H. Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - Guy Helman
- Department of Neurology, Children’s National Health System, Washington, District of Columbia, U.S.A
- Center for Genetic Medicine Research, Children’s National Health System, Washington, District of Columbia, U.S.A
| | - Michael F. Hammer
- ARL Division of Biotechnology, University of Arizona, Tucson, Arizona, U.S.A
| | - Brandy E. Fureman
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A
| | - William D. Gaillard
- Department of Neurology, Children’s National Health System, Washington, District of Columbia, U.S.A
- Center for Neuroscience Research, Children’s National Health System, Washington, District of Columbia, U.S.A
| | - Alan L. Goldin
- Microbiology & Molecular Genetics and Anatomy & Neurobiology, University of California, Irvine, California, U.S.A
| | - Shinichi Hirose
- Department of Pediatrics, Fukuoka University School of Medicine, Fukuoka, Japan
| | - Atsushi Ishii
- Department of Pediatrics, Fukuoka University School of Medicine, Fukuoka, Japan
| | - Barbara L. Kroner
- Biostatistics and Epidemiology, RTI International, Rockville, Maryland, U.S.A
| | - Christoph Lossin
- Department of Neurology, School of Medicine, University of California Davis, Sacramento, California, U.S.A
| | - Heather C. Mefford
- Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, U.S.A
| | - Jack M. Parent
- Department of Neurology, University of Michigan Medical Center and VA Ann Arbor Healthcare System, Ann Arbor, Michigan, U.S.A
| | - Manoj Patel
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, Virginia, U.S.A
| | - John Schreiber
- Department of Neurology, Children’s National Health System, Washington, District of Columbia, U.S.A
| | - Randall Stewart
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A
| | - Vicky Whittemore
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A
| | - Karen Wilcox
- Anticonvulsant Drug Development Program, Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah, U.S.A
| | - Jacy L Wagnon
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, U.S.A
| | - Phillip L. Pearl
- Department of Neurology, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts, U.S.A
| | - Adeline Vanderver
- Department of Neurology, Children’s National Health System, Washington, District of Columbia, U.S.A
- Center for Genetic Medicine Research, Children’s National Health System, Washington, District of Columbia, U.S.A
- Department of Integrated Systems Biology and Pediatrics, George Washington University, Washington, District of Columbia, U.S.A
| | - Ingrid E. Scheffer
- Department of Neurology, Royal Children’s Hospital, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia
- Department of Medicine, Epilepsy Research Centre, University of Melbourne, Austin Health, Melbourne, Victoria, Australia
- Florey Institute of Neurosciences and Mental Health, Melbourne, Victoria, Australia
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Patel RR, Barbosa C, Brustovetsky T, Brustovetsky N, Cummins TR. Aberrant epilepsy-associated mutant Nav1.6 sodium channel activity can be targeted with cannabidiol. Brain 2016; 139:2164-81. [PMID: 27267376 DOI: 10.1093/brain/aww129] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 04/15/2016] [Indexed: 11/12/2022] Open
Abstract
Mutations in brain isoforms of voltage-gated sodium channels have been identified in patients with distinct epileptic phenotypes. Clinically, these patients often do not respond well to classic anti-epileptics and many remain refractory to treatment. Exogenous as well as endogenous cannabinoids have been shown to target voltage-gated sodium channels and cannabidiol has recently received attention for its potential efficacy in the treatment of childhood epilepsies. In this study, we further investigated the ability of cannabinoids to modulate sodium currents from wild-type and epilepsy-associated mutant voltage-gated sodium channels. We first determined the biophysical consequences of epilepsy-associated missense mutations in both Nav1.1 (arginine 1648 to histidine and asparagine 1788 to lysine) and Nav1.6 (asparagine 1768 to aspartic acid and leucine 1331 to valine) by obtaining whole-cell patch clamp recordings in human embryonic kidney 293T cells with 200 μM Navβ4 peptide in the pipette solution to induce resurgent sodium currents. Resurgent sodium current is an atypical near threshold current predicted to increase neuronal excitability and has been implicated in multiple disorders of excitability. We found that both mutations in Nav1.6 dramatically increased resurgent currents while mutations in Nav1.1 did not. We then examined the effects of anandamide and cannabidiol on peak transient and resurgent currents from wild-type and mutant channels. Interestingly, we found that cannabidiol can preferentially target resurgent sodium currents over peak transient currents generated by wild-type Nav1.6 as well as the aberrant resurgent and persistent current generated by Nav1.6 mutant channels. To further validate our findings, we examined the effects of cannabidiol on endogenous sodium currents from striatal neurons, and similarly we found an inhibition of resurgent and persistent current by cannabidiol. Moreover, current clamp recordings show that cannabidiol reduces overall action potential firing of striatal neurons. These findings suggest that cannabidiol could be exerting its anticonvulsant effects, at least in part, through its actions on voltage-gated sodium channels, and resurgent current may be a promising therapeutic target for the treatment of epilepsy syndromes.
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Affiliation(s)
- Reesha R Patel
- 1 Program in Medical Neuroscience, Neuroscience Research Building, 320 West 15th St, Indianapolis, IN, 46202, USA 2 Paul and Carole Stark Neurosciences Research Institute, 320 West 15th St, Indianapolis, IN, 46202, USA
| | - Cindy Barbosa
- 3 Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN, 46202, USA
| | - Tatiana Brustovetsky
- 3 Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN, 46202, USA
| | - Nickolay Brustovetsky
- 1 Program in Medical Neuroscience, Neuroscience Research Building, 320 West 15th St, Indianapolis, IN, 46202, USA 2 Paul and Carole Stark Neurosciences Research Institute, 320 West 15th St, Indianapolis, IN, 46202, USA 3 Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN, 46202, USA
| | - Theodore R Cummins
- 1 Program in Medical Neuroscience, Neuroscience Research Building, 320 West 15th St, Indianapolis, IN, 46202, USA 2 Paul and Carole Stark Neurosciences Research Institute, 320 West 15th St, Indianapolis, IN, 46202, USA 3 Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN, 46202, USA
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Abstract
Voltage-gated sodium channels (VGSCs) are fundamentally important for the generation and coordinated transmission of action potentials throughout the nervous system. It is, therefore, unsurprising that they have been shown to play a central role in the genesis and alleviation of epilepsy. Genetic studies on patients with epilepsy have identified more than 700 mutations among the genes that encode for VGSCs attesting to their role in pathogenesis. Further, many common antiepileptic drugs act on VGSCs to suppress seizure activity. Here, we present an account of the role of VGSCs in epilepsy, both through their pathogenic dysfunction and as targets for pharmacotherapy.
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Siekierska A, Isrie M, Liu Y, Scheldeman C, Vanthillo N, Lagae L, de Witte PAM, Van Esch H, Goldfarb M, Buyse GM. Gain-of-function FHF1 mutation causes early-onset epileptic encephalopathy with cerebellar atrophy. Neurology 2016; 86:2162-70. [PMID: 27164707 DOI: 10.1212/wnl.0000000000002752] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/12/2016] [Indexed: 01/30/2023] Open
Abstract
OBJECTIVE Voltage-gated sodium channel (Nav)-encoding genes are among early-onset epileptic encephalopathies (EOEE) targets, suggesting that other genes encoding Nav-binding proteins, such as fibroblast growth factor homologous factors (FHFs), may also play roles in these disorders. METHODS To identify additional genes for EOEE, we performed whole-exome sequencing in a family quintet with 2 siblings with a lethal disease characterized by EOEE and cerebellar atrophy. The pathogenic nature and functional consequences of the identified sequence alteration were determined by electrophysiologic studies in vitro and in vivo. RESULTS A de novo heterozygous missense mutation was identified in the FHF1 gene (FHF1AR114H, FHF1BR52H) in the 2 affected siblings. The mutant FHF1 proteins had a strong gain-of-function phenotype in transfected Neuro2A cells, enhancing the depolarizing shifts in Nav1.6 voltage-dependent fast inactivation, predicting increased neuronal excitability. Surprisingly, the gain-of-function effect is predicted to result from weaker interaction of mutant FHF1 with the Nav cytoplasmic tail. Transgenic overexpression of mutant FHF1B in zebrafish larvae enhanced epileptiform discharges, demonstrating the epileptic potential of this FHF1 mutation in the affected children. CONCLUSIONS Our data demonstrate that gain-of-function FHF mutations can cause neurologic disorder, and expand the repertoire of genetic causes (FHF1) and mechanisms (altered Nav gating) underlying EOEE and cerebellar atrophy.
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Affiliation(s)
- Aleksandra Siekierska
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Mala Isrie
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Yue Liu
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Chloë Scheldeman
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Niels Vanthillo
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Lieven Lagae
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Peter A M de Witte
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Hilde Van Esch
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Mitchell Goldfarb
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY
| | - Gunnar M Buyse
- From the Laboratory for Molecular Biodiscovery, Department of Pharmaceutical and Pharmacological Sciences (A.S., C.S., N.V., P.A.M.d.W.), and Laboratory for the Genetics of Cognition (M.I.), University of Leuven; Center for Human Genetics (M.I., H.V.E.) and Child Neurology (L.L., G.M.B.), University Hospitals Leuven; Department of Biological Sciences (Y.L., M.G.), Hunter College of City University, New York; and Graduate Program in Biology/Neuroscience at City University (Y.L.), New York, NY.
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Jones JM, Dionne L, Dell'Orco J, Parent R, Krueger JN, Cheng X, Dib-Hajj SD, Bunton-Stasyshyn RK, Sharkey LM, Dowling JJ, Murphy GG, Shakkottai VG, Shrager P, Meisler MH. Single amino acid deletion in transmembrane segment D4S6 of sodium channel Scn8a (Nav1.6) in a mouse mutant with a chronic movement disorder. Neurobiol Dis 2016; 89:36-45. [PMID: 26807988 PMCID: PMC4991781 DOI: 10.1016/j.nbd.2016.01.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 01/06/2016] [Accepted: 01/20/2016] [Indexed: 02/08/2023] Open
Abstract
Mutations of the neuronal sodium channel gene SCN8A are associated with lethal movement disorders in the mouse and with human epileptic encephalopathy. We describe a spontaneous mouse mutation, Scn8a(9J), that is associated with a chronic movement disorder with early onset tremor and adult onset dystonia. Scn8a(9J) homozygotes have a shortened lifespan, with only 50% of mutants surviving beyond 6 months of age. The 3 bp in-frame deletion removes 1 of the 3 adjacent isoleucine residues in transmembrane segment DIVS6 of Nav1.6 (p.Ile1750del). The altered helical orientation of the transmembrane segment displaces pore-lining amino acids with important roles in channel activation and inactivation. The predicted impact on channel activity was confirmed by analysis of cerebellar Purkinje neurons from mutant mice, which lack spontaneous and induced repetitive firing. In a heterologous expression system, the activity of the mutant channel was below the threshold for detection. Observations of decreased nerve conduction velocity and impaired behavior in an open field are also consistent with reduced activity of Nav1.6. The Nav1.6Δ1750 protein is only partially glycosylated. The abundance of mutant Nav1.6 is reduced at nodes of Ranvier and is not detectable at the axon initial segment. Despite a severe reduction in channel activity, the lifespan and motor function of Scn8a(9J/9J) mice are significantly better than null mutants lacking channel protein. The clinical phenotype of this severe hypomorphic mutant expands the spectrum of Scn8a disease to include a recessively inherited, chronic and progressive movement disorder.
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Affiliation(s)
- Julie M Jones
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, United States
| | - Louise Dionne
- The Jackson Laboratory, Bar Harbor, ME 04609, United States
| | - James Dell'Orco
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Rachel Parent
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Jamie N Krueger
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States
| | - Xiaoyang Cheng
- Department of Neurology and Centre for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06516, United States.
| | - Sulayman D Dib-Hajj
- Department of Neurology and Centre for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06516, United States
| | | | - Lisa M Sharkey
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - James J Dowling
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Geoffrey G Murphy
- Department of Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, United States; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Vikram G Shakkottai
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, United States
| | - Peter Shrager
- Department of Neurobiology & Anatomy, University of Rochester Medical Center, Rochester, NY 14642, United States
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, United States.
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Boerma RS, Braun KP, van den Broek MPH, van de Broek MPH, van Berkestijn FMC, Swinkels ME, Hagebeuk EO, Lindhout D, van Kempen M, Boon M, Nicolai J, de Kovel CG, Brilstra EH, Koeleman BPC. Remarkable Phenytoin Sensitivity in 4 Children with SCN8A-related Epilepsy: A Molecular Neuropharmacological Approach. Neurotherapeutics 2016; 13:192-7. [PMID: 26252990 PMCID: PMC4720675 DOI: 10.1007/s13311-015-0372-8] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Mutations in SCN8A are associated with epilepsy and intellectual disability. SCN8A encodes for sodium channel Nav1.6, which is located in the brain. Gain-of-function missense mutations in SCN8A are thought to lead to increased firing of excitatory neurons containing Nav1.6, and therefore to lead to increased seizure susceptibility. We hypothesized that sodium channel blockers could have a beneficial effect in patients with SCN8A-related epilepsy by blocking the overactive Nav1.6 and thereby counteracting the effect of the mutation. Herein, we describe 4 patients with a missense SCN8A mutation and epilepsy who all show a remarkably good response on high doses of phenytoin and loss of seizure control when phenytoin medication was reduced, while side effects were relatively mild. In 2 patients, repeated withdrawal of phenytoin led to the reoccurrence of seizures. Based on the findings in these patients and the underlying molecular mechanism we consider treatment with (high-dose) phenytoin as a possible treatment option in patients with difficult-to-control seizures due to an SCN8A mutation.
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Affiliation(s)
- Ragna S Boerma
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Kees P Braun
- Department of Pediatric Neurology, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | | | | | - Marielle E Swinkels
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Eveline O Hagebeuk
- Department of Neurology, University Medical Centre Groningen, Groningen, The Netherlands
| | - Dick Lindhout
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Marjan van Kempen
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Maartje Boon
- Department of Pediatric Neurology, Stichting Epilepsie Instellingen Nederland, Zwolle, The Netherlands
| | - Joost Nicolai
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands
- Epilepsy Center Kempenhaeghe, Heeze, The Netherlands
| | - Carolien G de Kovel
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Eva H Brilstra
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bobby P C Koeleman
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
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Myers C, Mefford H. Genetic investigations of the epileptic encephalopathies. PROGRESS IN BRAIN RESEARCH 2016; 226:35-60. [DOI: 10.1016/bs.pbr.2016.04.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Møller RS, Johannesen KM. Precision Medicine: SCN8A Encephalopathy Treated with Sodium Channel Blockers. Neurotherapeutics 2016; 13:190-1. [PMID: 26553437 PMCID: PMC4720666 DOI: 10.1007/s13311-015-0403-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Affiliation(s)
- Rikke S Møller
- The Danish Epilepsy Centre Filadelfia, Dianalund, Denmark.
- Institute for Regional Health Research, University of Southern Denmark, Odense, Denmark.
| | - Katrine M Johannesen
- The Danish Epilepsy Centre Filadelfia, Dianalund, Denmark
- Institute for Regional Health Research, University of Southern Denmark, Odense, Denmark
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Wagnon JL, Barker BS, Hounshell JA, Haaxma CA, Shealy A, Moss T, Parikh S, Messer RD, Patel MK, Meisler MH. Pathogenic mechanism of recurrent mutations of SCN8A in epileptic encephalopathy. Ann Clin Transl Neurol 2015; 3:114-23. [PMID: 26900580 PMCID: PMC4748308 DOI: 10.1002/acn3.276] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 11/20/2015] [Indexed: 12/03/2022] Open
Abstract
Objective The early infantile epileptic encephalopathy type 13 (EIEE13, OMIM #614558) results from de novo missense mutations of SCN8A encoding the voltage‐gated sodium channel Nav1.6. More than 20% of patients have recurrent mutations in residues Arg1617 or Arg1872. Our goal was to determine the functional effects of these mutations on channel properties. Methods Clinical exome sequencing was carried out on patients with early‐onset seizures, developmental delay, and cognitive impairment. Two mutations identified here, p.Arg1872Leu and p.Arg1872Gln, and two previously identified mutations, p.Arg1872Trp and p.Arg1617Gln, were introduced into Nav1.6 cDNA, and effects on electrophysiological properties were characterized in transfected ND7/23 cells. Interactions with FGF14, G‐protein subunit Gβγ, and sodium channel subunit β1 were assessed by coimmunoprecipitation. Results We identified two patients with the novel mutation p.Arg1872Leu and one patient with the recurrent mutation p.Arg1872Gln. The three mutations of Arg1872 and the mutation of Arg1617 all impaired the sodium channel transition from open state to inactivated state, resulting in channel hyperactivity. Other observed abnormalities contributing to elevated channel activity were increased persistent current, increased peak current density, hyperpolarizing shift in voltage dependence of activation, and depolarizing shift in steady‐state inactivation. Protein interactions were not affected. Interpretation Recurrent mutations at Arg1617 and Arg1872 lead to elevated Nav1.6 channel activity by impairing channel inactivation. Channel hyperactivity is the major pathogenic mechanism for gain‐of‐function mutations of SCN8A. EIEE13 differs mechanistically from Dravet syndrome, which is caused by loss‐of‐function mutations of SCN1A. This distinction has important consequences for selection of antiepileptic drugs and the development of gene‐ and mutation‐specific treatments.
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Affiliation(s)
- Jacy L Wagnon
- Department of Human Genetics University of Michigan Ann Arbor Michigan
| | - Bryan S Barker
- Department of Anesthesiology and Neuroscience Graduate Program University of Virginia Health System Charlottesville Virginia
| | - James A Hounshell
- Department of Anesthesiology and Neuroscience Graduate Program University of Virginia Health System Charlottesville Virginia
| | - Charlotte A Haaxma
- Department of Pediatric Neurology Radboud University Nijmegen The Netherlands
| | - Amy Shealy
- Cleveland Clinic Genomic Medicine Institute Cleveland Ohio
| | - Timothy Moss
- Cleveland Clinic Genomic Medicine Institute Cleveland Ohio
| | - Sumit Parikh
- Department of Pediatric Neurology Cleveland Clinic Cleveland Ohio
| | - Ricka D Messer
- Department of Pediatric Neurology Johns Hopkins Medical Institute Baltimore Maryland
| | - Manoj K Patel
- Department of Anesthesiology and Neuroscience Graduate Program University of Virginia Health System Charlottesville Virginia
| | - Miriam H Meisler
- Department of Human Genetics University of Michigan Ann Arbor Michigan
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Makinson CD, Dutt K, Lin F, Papale LA, Shankar A, Barela AJ, Liu R, Goldin AL, Escayg A. An Scn1a epilepsy mutation in Scn8a alters seizure susceptibility and behavior. Exp Neurol 2015; 275 Pt 1:46-58. [PMID: 26410685 DOI: 10.1016/j.expneurol.2015.09.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Revised: 09/03/2015] [Accepted: 09/12/2015] [Indexed: 11/26/2022]
Abstract
Understanding the role of SCN8A in epilepsy and behavior is critical in light of recently identified human SCN8A epilepsy mutations. We have previously demonstrated that Scn8a(med) and Scn8a(med-jo) mice carrying mutations in the Scn8a gene display increased resistance to flurothyl and kainic acid-induced seizures; however, they also exhibit spontaneous absence seizures. To further investigate the relationship between altered SCN8A function and epilepsy, we introduced the SCN1A-R1648H mutation, identified in a family with generalized epilepsy with febrile seizures plus (GEFS+), into the corresponding position (R1627H) of the mouse Scn8a gene. Heterozygous R1627H mice exhibited increased resistance to some forms of pharmacologically and electrically induced seizures and the mutant Scn8a allele ameliorated the phenotype of Scn1a-R1648H mutants. Hippocampal slices from heterozygous R1627H mice displayed decreased bursting behavior compared to wild-type littermates. Paradoxically, at the homozygous level, R1627H mice did not display increased seizure resistance and were susceptible to audiogenic seizures. We furthermore observed increased hippocampal pyramidal cell excitability in heterozygous and homozygous Scn8a-R1627H mutants, and decreased interneuron excitability in heterozygous Scn8a-R1627H mutants. These results expand the phenotypes associated with disruption of the Scn8a gene and demonstrate that an Scn8a mutation can both confer seizure protection and increase seizure susceptibility.
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Affiliation(s)
| | - Karoni Dutt
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
| | - Frank Lin
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332, USA
| | - Ligia A Papale
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA
| | - Anupama Shankar
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA
| | - Arthur J Barela
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA
| | - Robert Liu
- Department of Biology, Emory University, Atlanta, GA 30022, USA
| | - Alan L Goldin
- Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, CA 92697, USA.
| | - Andrew Escayg
- Department of Human Genetics, Emory University, Atlanta, GA 30022, USA.
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Abstract
Epilepsy is a group of disorders characterized by recurrent seizures, and is one of the most common neurological conditions. The genetic basis of epilepsy is clear from epidemiological studies and from rare gene discoveries in large families. The three major classes of epilepsy disorders are genetic generalized, focal and encephalopathic epilepsies, with several specific disorders within each class. Advances in genomic technologies that facilitate genome-wide discovery of both common and rare variants have led to a rapid increase in our understanding of epilepsy genetics. Copy number variant and genome-wide association studies have contributed to our understanding of the complex genetic architecture of generalized epilepsy, while genetic insights into the focal epilepsies and epileptic encephalopathies have come primarily from exome sequencing. It is increasingly clear that epilepsy is genetically heterogeneous, and novel gene discoveries have moved the field beyond the known contribution of ion channels to implicate chromatin remodeling, transcriptional regulation and regulation of the mammalian target of rapamycin (mTOR) protein in the etiology of epilepsy. Such discoveries pave the way for new therapeutics, some of which are already being studied. In this review, we discuss the rapid pace of gene discovery in epilepsy, as facilitated by genomic technologies, and highlight several novel genes and potential therapies.
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Affiliation(s)
- Candace T Myers
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA, 98195, USA
| | - Heather C Mefford
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA, 98195, USA.
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Takahashi S, Yamamoto S, Okayama A, Araki A, Saitsu H, Matsumoto N, Azuma H. Electroclinical features of epileptic encephalopathy caused by SCN8A mutation. Pediatr Int 2015; 57:758-62. [PMID: 25951352 DOI: 10.1111/ped.12622] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 12/09/2014] [Accepted: 12/10/2014] [Indexed: 02/02/2023]
Abstract
Voltage-gated sodium channel Nav 1.6, encoded by the gene SCN8A, plays a crucial role in controlling neuronal excitability. SCN8A mutations that cause increased channel activity are associated with seizures. We describe a patient with epileptic encephalopathy caused by de novo SCN8A mutation (c.5614C>T, p.Arg1872Trp). Seizures began 10 days after birth at which time brain magnetic resonance imaging (MRI) and electroencephalography (EEG) were normal. Seizure recurrence increased with age, leading to the development of frequent status epilepticus from 1 year of age. Seizure type included generalized tonic seizures and focal motor seizures. EEG first showed focal epileptic activity at the age of 4 months, and thereafter showed multifocal spikes. Serial MRI demonstrated brain atrophy, which appeared to progress with seizure aggravation. Clinical features that may give a clue to the diagnosis include normal EEG despite frequent seizures in early infancy and an increase in epileptic activity that occurs with aging.
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Affiliation(s)
- Satoru Takahashi
- Department of Pediatrics, Asahikawa Medical University, Asahikawa, Japan
| | - Shiho Yamamoto
- Department of Pediatrics, Asahikawa Medical University, Asahikawa, Japan
| | - Akie Okayama
- Department of Pediatrics, Asahikawa Medical University, Asahikawa, Japan
| | - Akiko Araki
- Department of Pediatrics, Asahikawa Medical University, Asahikawa, Japan
| | - Hirotomo Saitsu
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Naomichi Matsumoto
- Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
| | - Hiroshi Azuma
- Department of Pediatrics, Asahikawa Medical University, Asahikawa, Japan
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75
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Miceli F, Soldovieri MV, Ambrosino P, De Maria M, Manocchio L, Medoro A, Taglialatela M. Molecular pathophysiology and pharmacology of the voltage-sensing module of neuronal ion channels. Front Cell Neurosci 2015; 9:259. [PMID: 26236192 PMCID: PMC4502356 DOI: 10.3389/fncel.2015.00259] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Accepted: 06/22/2015] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated ion channels (VGICs) are membrane proteins that switch from a closed to open state in response to changes in membrane potential, thus enabling ion fluxes across the cell membranes. The mechanism that regulate the structural rearrangements occurring in VGICs in response to changes in membrane potential still remains one of the most challenging topic of modern biophysics. Na+, Ca2+ and K+ voltage-gated channels are structurally formed by the assembly of four similar domains, each comprising six transmembrane segments. Each domain can be divided into two main regions: the Pore Module (PM) and the Voltage-Sensing Module (VSM). The PM (helices S5 and S6 and intervening linker) is responsible for gate opening and ion selectivity; by contrast, the VSM, comprising the first four transmembrane helices (S1–S4), undergoes the first conformational changes in response to membrane voltage variations. In particular, the S4 segment of each domain, which contains several positively charged residues interspersed with hydrophobic amino acids, is located within the membrane electric field and plays an essential role in voltage sensing. In neurons, specific gating properties of each channel subtype underlie a variety of biological events, ranging from the generation and propagation of electrical impulses, to the secretion of neurotransmitters and to the regulation of gene expression. Given the important functional role played by the VSM in neuronal VGICs, it is not surprising that various VSM mutations affecting the gating process of these channels are responsible for human diseases, and that compounds acting on the VSM have emerged as important investigational tools with great therapeutic potential. In the present review we will briefly describe the most recent discoveries concerning how the VSM exerts its function, how genetically inherited diseases caused by mutations occurring in the VSM affects gating in VGICs, and how several classes of drugs and toxins selectively target the VSM.
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Affiliation(s)
- Francesco Miceli
- Department of Neuroscience, University of Naples Federico II Naples, Italy
| | | | - Paolo Ambrosino
- Department of Medicine and Health Sciences, University of Molise Campobasso, Italy
| | - Michela De Maria
- Department of Medicine and Health Sciences, University of Molise Campobasso, Italy
| | - Laura Manocchio
- Department of Medicine and Health Sciences, University of Molise Campobasso, Italy
| | - Alessandro Medoro
- Department of Medicine and Health Sciences, University of Molise Campobasso, Italy
| | - Maurizio Taglialatela
- Department of Neuroscience, University of Naples Federico II Naples, Italy ; Department of Medicine and Health Sciences, University of Molise Campobasso, Italy
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Berghuis B, de Kovel CGF, van Iterson L, Lamberts RJ, Sander JW, Lindhout D, Koeleman BPC. Complex SCN8A DNA-abnormalities in an individual with therapy resistant absence epilepsy. Epilepsy Res 2015. [PMID: 26220391 DOI: 10.1016/j.eplepsyres.2015.06.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
BACKGROUND De novo SCN8A missense mutations have been identified as a rare dominant cause of epileptic encephalopathy. We described a person with epileptic encephalopathy associated with a mosaic deletion of the SCN8A gene. METHODS Array comparative genome hybridization was used to identify chromosomal abnormalities. Next Generation Sequencing was used to screen for variants in known and candidate epilepsy genes. A single nucleotide polymorphism array was used to test whether the SCN8A variants were in cis or in trans. RESULTS We identified a de novo mosaic deletion of exons 2-14 of SCN8A, and a rare maternally inherited missense variant on the other allele in a woman presenting with absence seizures, challenging behavior, intellectual disability and QRS-fragmentation on the ECG. We also found a variant in SCN5A. CONCLUSIONS The combination of a rare missense variant with a de novo mosaic deletion of a large part of the SCN8A gene suggests that other possible mechanisms for SCN8A mutations may cause epilepsy; loss of function, genetic modifiers and cellular interference may play a role. This case expands the phenotype associated with SCN8A mutations, with absence epilepsy and regression in language and memory skills.
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Affiliation(s)
- Bianca Berghuis
- Stichting Epilepsie Instellingen Nederland SEIN, Zwolle, The Netherlands.
| | - Carolien G F de Kovel
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Loretta van Iterson
- Stichting Epilepsie Instellingen Nederland SEIN, Zwolle, The Netherlands; De Waterlelie School, Expertisecentrum voor Onderwijs en Epilepsie, Cruquius, The Netherlands
| | - Robert J Lamberts
- Stichting Epilepsie Instellingen Nederland SEIN, Zwolle, The Netherlands
| | - Josemir W Sander
- Stichting Epilepsie Instellingen Nederland SEIN, Zwolle, The Netherlands; NIHR UCL Hospitals Biomedical Research Centre, UCL Institute of Neurology, Queen Square, London WC1N 3BG, United Kingdom; Epilepsy Society, Chalfont St Peter SL9 0RJ, United Kingdom
| | - Dick Lindhout
- Stichting Epilepsie Instellingen Nederland SEIN, Zwolle, The Netherlands; Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bobby P C Koeleman
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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77
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Wagnon JL, Meisler MH. Recurrent and Non-Recurrent Mutations of SCN8A in Epileptic Encephalopathy. Front Neurol 2015; 6:104. [PMID: 26029160 PMCID: PMC4432670 DOI: 10.3389/fneur.2015.00104] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 04/27/2015] [Indexed: 01/03/2023] Open
Abstract
Mutations of the voltage-gated sodium channel SCN8A have been identified in approximately 1% of nearly 1,500 children with early-infantile epileptic encephalopathies (EIEE) who have been tested by DNA sequencing. EIEE caused by mutation of SCN8A is designated EIEE13 (OMIM #614558). Affected children have seizure onset before 18 months of age as well as developmental and cognitive disabilities, movement disorders, and a high incidence of sudden death (SUDEP). EIEE13 is caused by de novo missense mutations of evolutionarily conserved residues in the Nav1.6 channel protein. One-third of the mutations are recurrent, and many occur at CpG dinucleotides. In this review, we discuss the effect of pathogenic mutations on the structure of the channel protein, the rate of recurrent mutation, and changes in channel function underlying this devastating disorder.
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Affiliation(s)
- Jacy L Wagnon
- Department of Human Genetics, University of Michigan , Ann Arbor, MI , USA
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan , Ann Arbor, MI , USA
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78
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Galanopoulou AS, Moshé SL. Pathogenesis and new candidate treatments for infantile spasms and early life epileptic encephalopathies: A view from preclinical studies. Neurobiol Dis 2015; 79:135-49. [PMID: 25968935 DOI: 10.1016/j.nbd.2015.04.015] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Revised: 04/23/2015] [Accepted: 04/30/2015] [Indexed: 12/26/2022] Open
Abstract
Early onset and infantile epileptic encephalopathies (EIEEs) are usually associated with medically intractable or difficult to treat epileptic seizures and prominent cognitive, neurodevelopmental and behavioral consequences. EIEEs have numerous etiologies that contribute to the inter- and intra-syndromic phenotypic variability. Etiologies include structural and metabolic or genetic etiologies although a significant percentage is of unknown cause. The need to better understand their pathogenic mechanisms and identify better therapies has driven the development of animal models of EIEEs. Several rodent models of infantile spasms have emerged that recapitulate various aspects of the disease. The acute models manifest epileptic spasms after induction and include the NMDA rat model, the NMDA model with prior prenatal betamethasone or perinatal stress exposure, and the γ-butyrolactone induced spasms in a mouse model of Down syndrome. The chronic models include the tetrodotoxin rat model, the aristaless related homeobox X-linked (Arx) mouse models and the multiple-hit rat model of infantile spasms. We will discuss the main features and findings from these models on target mechanisms and emerging therapies. Genetic models have also provided interesting data on the pathogenesis of Dravet syndrome and proposed new therapies for testing. The genetic associations of many of the EIEEs have also been tested in rodent models as to their pathogenicity. Finally, several models have tested the impact of subclinical epileptiform discharges on brain function. The impact of these advances in animal modeling for therapy development will be discussed.
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Affiliation(s)
- Aristea S Galanopoulou
- Saul R. Korey Department of Neurology, Dominick P. Purpura Department of Neuroscience, Laboratory of Developmental Epilepsy, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA.
| | - Solomon L Moshé
- Saul R. Korey Department of Neurology, Dominick P. Purpura Department of Neuroscience, Laboratory of Developmental Epilepsy, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA; Department of Pediatrics, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA.
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79
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Blanchard MG, Willemsen MH, Walker JB, Dib-Hajj SD, Waxman SG, Jongmans MCJ, Kleefstra T, van de Warrenburg BP, Praamstra P, Nicolai J, Yntema HG, Bindels RJM, Meisler MH, Kamsteeg EJ. De novo gain-of-function and loss-of-function mutations of SCN8A in patients with intellectual disabilities and epilepsy. J Med Genet 2015; 52:330-7. [PMID: 25725044 PMCID: PMC4413743 DOI: 10.1136/jmedgenet-2014-102813] [Citation(s) in RCA: 101] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Accepted: 02/05/2015] [Indexed: 12/19/2022]
Abstract
BACKGROUND Mutations of SCN8A encoding the neuronal voltage-gated sodium channel NaV1.6 are associated with early-infantile epileptic encephalopathy type 13 (EIEE13) and intellectual disability. Using clinical exome sequencing, we have detected three novel de novo SCN8A mutations in patients with intellectual disabilities, and variable clinical features including seizures in two patients. To determine the causality of these SCN8A mutations in the disease of those three patients, we aimed to study the (dys)function of the mutant sodium channels. METHODS The functional consequences of the three SCN8A mutations were assessed using electrophysiological analyses in transfected cells. Genotype-phenotype correlations of these and other cases were related to the functional analyses. RESULTS The first mutant displayed a 10 mV hyperpolarising shift in voltage dependence of activation (gain of function), the second did not form functional channels (loss of function), while the third mutation was functionally indistinguishable from the wildtype channel. CONCLUSIONS Comparison of the clinical features of these patients with those in the literature suggests that gain-of-function mutations are associated with severe EIEE, while heterozygous loss-of-function mutations cause intellectual disability with or without seizures. These data demonstrate that functional analysis of missense mutations detected by clinical exome sequencing, both inherited and de novo, is valuable for clinical interpretation in the age of massive parallel sequencing.
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Affiliation(s)
- Maxime G Blanchard
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Marjolein H Willemsen
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Jaclyn B Walker
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, USA
| | - Sulayman D Dib-Hajj
- The Center for Neuroscience & Regeneration Research, Yale School of Medicine, New Haven, Connecticut, USA The Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, Connecticut, USA
| | - Stephen G Waxman
- The Center for Neuroscience & Regeneration Research, Yale School of Medicine, New Haven, Connecticut, USA The Rehabilitation Research Center, VA Connecticut Healthcare System, West Haven, Connecticut, USA
| | - Marjolijn C J Jongmans
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Tjitske Kleefstra
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Bart P van de Warrenburg
- Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Peter Praamstra
- Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Joost Nicolai
- Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands Epilepsy Center Kempenhaeghe, Heeze, The Netherlands
| | - Helger G Yntema
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
| | - René J M Bindels
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, USA
| | - Erik-Jan Kamsteeg
- Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands
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80
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Kong W, Zhang Y, Gao Y, Liu X, Gao K, Xie H, Wang J, Wu Y, Zhang Y, Wu X, Jiang Y. SCN8Amutations in Chinese children with early onset epilepsy and intellectual disability. Epilepsia 2015; 56:431-8. [PMID: 25785782 DOI: 10.1111/epi.12925] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/23/2014] [Indexed: 12/19/2022]
Affiliation(s)
- Weijing Kong
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Yujia Zhang
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Yang Gao
- Department of Neurosurgery; The Second Hospital of Dalian Medical University; Dalian China
| | - Xiaoyan Liu
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Kai Gao
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Han Xie
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Jingmin Wang
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Ye Wu
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Yuehua Zhang
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Xiru Wu
- Department of Pediatrics; Peking University First Hospital; Beijing China
| | - Yuwu Jiang
- Department of Pediatrics; Peking University First Hospital; Beijing China
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81
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Larsen J, Carvill GL, Gardella E, Kluger G, Schmiedel G, Barisic N, Depienne C, Brilstra E, Mang Y, Nielsen JEK, Kirkpatrick M, Goudie D, Goldman R, Jähn JA, Jepsen B, Gill D, Döcker M, Biskup S, McMahon JM, Koeleman B, Harris M, Braun K, de Kovel CGF, Marini C, Specchio N, Djémié T, Weckhuysen S, Tommerup N, Troncoso M, Troncoso L, Bevot A, Wolff M, Hjalgrim H, Guerrini R, Scheffer IE, Mefford HC, Møller RS. The phenotypic spectrum of SCN8A encephalopathy. Neurology 2015; 84:480-9. [PMID: 25568300 DOI: 10.1212/wnl.0000000000001211] [Citation(s) in RCA: 213] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE SCN8A encodes the sodium channel voltage-gated α8-subunit (Nav1.6). SCN8A mutations have recently been associated with epilepsy and neurodevelopmental disorders. We aimed to delineate the phenotype associated with SCN8A mutations. METHODS We used high-throughput sequence analysis of the SCN8A gene in 683 patients with a range of epileptic encephalopathies. In addition, we ascertained cases with SCN8A mutations from other centers. A detailed clinical history was obtained together with a review of EEG and imaging data. RESULTS Seventeen patients with de novo heterozygous mutations of SCN8A were studied. Seizure onset occurred at a mean age of 5 months (range: 1 day to 18 months); in general, seizures were not triggered by fever. Fifteen of 17 patients had multiple seizure types including focal, tonic, clonic, myoclonic and absence seizures, and epileptic spasms; seizures were refractory to antiepileptic therapy. Development was normal in 12 patients and slowed after seizure onset, often with regression; 5 patients had delayed development from birth. All patients developed intellectual disability, ranging from mild to severe. Motor manifestations were prominent including hypotonia, dystonia, hyperreflexia, and ataxia. EEG findings comprised moderate to severe background slowing with focal or multifocal epileptiform discharges. CONCLUSION SCN8A encephalopathy presents in infancy with multiple seizure types including focal seizures and spasms in some cases. Outcome is often poor and includes hypotonia and movement disorders. The majority of mutations arise de novo, although we observed a single case of somatic mosaicism in an unaffected parent.
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82
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Wagnon JL, Korn MJ, Parent R, Tarpey TA, Jones JM, Hammer MF, Murphy GG, Parent JM, Meisler MH. Convulsive seizures and SUDEP in a mouse model of SCN8A epileptic encephalopathy. Hum Mol Genet 2014; 24:506-15. [PMID: 25227913 PMCID: PMC4275076 DOI: 10.1093/hmg/ddu470] [Citation(s) in RCA: 109] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
De novo mutations of the voltage-gated sodium channel gene SCN8A have recently been recognized as a cause of epileptic encephalopathy, which is characterized by refractory seizures with developmental delay and cognitive disability. We previously described the heterozygous SCN8A missense mutation p.Asn1768Asp in a child with epileptic encephalopathy that included seizures, ataxia, and sudden unexpected death in epilepsy (SUDEP). The mutation results in increased persistent sodium current and hyperactivity of transfected neurons. We have characterized a knock-in mouse model expressing this dominant gain-of-function mutation to investigate the pathology of the altered channel in vivo. The mutant channel protein is stable in vivo. Heterozygous Scn8aN1768D/+ mice exhibit seizures and SUDEP, confirming the causality of the de novo mutation in the proband. Using video/EEG analysis, we detect ictal discharges that coincide with convulsive seizures and myoclonic jerks. Prior to seizure onset, heterozygous mutants are not defective in motor learning or fear conditioning, but do exhibit mild impairment of motor coordination and social discrimination. Homozygous mutant mice exhibit earlier seizure onset than heterozygotes and more rapid progression to death. Analysis of the intermediate phenotype of functionally hemizygous Scn8aN1768D/− mice indicates that severity is increased by a double dose of mutant protein and reduced by the presence of wild-type protein. Scn8aN1768D mutant mice provide a model of epileptic encephalopathy that will be valuable for studying the in vivo effects of hyperactive Nav1.6 and the response to therapeutic interventions.
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Affiliation(s)
| | | | - Rachel Parent
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, USA
| | - Taylor A Tarpey
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, USA
| | | | - Michael F Hammer
- Arizona Research Laboratories, Division of Biotechnology, University of Arizona, Tucson, AZ, USA
| | - Geoffrey G Murphy
- Molecular and Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109, USA Molecular and Integrative Physiology, University of Michigan Medical Center, Ann Arbor, MI 48109, USA and
| | - Jack M Parent
- Department of Neurology VA Ann Arbor Healthcare System, Ann Arbor, MI, USA
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83
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Li T, Tian C, Scalmani P, Frassoni C, Mantegazza M, Wang Y, Yang M, Wu S, Shu Y. Action potential initiation in neocortical inhibitory interneurons. PLoS Biol 2014; 12:e1001944. [PMID: 25203314 PMCID: PMC4159120 DOI: 10.1371/journal.pbio.1001944] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Accepted: 07/31/2014] [Indexed: 01/22/2023] Open
Abstract
Sodium channels add variety to inhibitory interneurons Different populations of inhibitory interneurons in the cerebral cortex express distinct subtypes of sodium channels, resulting in diverse action potential thresholds and network excitability. Action potential (AP) generation in inhibitory interneurons is critical for cortical excitation-inhibition balance and information processing. However, it remains unclear what determines AP initiation in different interneurons. We focused on two predominant interneuron types in neocortex: parvalbumin (PV)- and somatostatin (SST)-expressing neurons. Patch-clamp recording from mouse prefrontal cortical slices showed that axonal but not somatic Na+ channels exhibit different voltage-dependent properties. The minimal activation voltage of axonal channels in SST was substantially higher (∼7 mV) than in PV cells, consistent with differences in AP thresholds. A more mixed distribution of high- and low-threshold channel subtypes at the axon initial segment (AIS) of SST cells may lead to these differences. Surprisingly, NaV1.2 was found accumulated at AIS of SST but not PV cells; reducing NaV1.2-mediated currents in interneurons promoted recurrent network activity. Together, our results reveal the molecular identity of axonal Na+ channels in interneurons and their contribution to AP generation and regulation of network activity. Inhibitory interneurons in the cerebral cortex are diverse in many respects. Here, we examine whether this diversity extends to the composition of ion channels along the axon, which might determine the neurons' excitability. We performed patch-clamp recordings from cortical interneuron axons in brain slices obtained from two transgenic mouse lines. In each mouse line, distinct populations of inhibitory interneurons—those that express parvalbumin (PV) or those that express somatostatin (SST)—were labeled with green fluorescent protein to allow visualization. We show that action potentials initiate at the axon initial segment (a specialized region of the axon closest to the cell body) in both cell types, but SST neurons have a higher action potential threshold than PV neurons because their sodium channels require a greater degree of depolarization to be fully activated. At the molecular level, we found that the population of sodium channels in SST neurons requires a larger depolarization because it has a more mixed composition of high- and low-threshold sodium channel subtypes. In summary, this study reveals diversity in the molecular identity and voltage dependence of sodium channels that are responsible for initiating action potentials in different populations of interneurons. In addition, the presence of a particular subtype of sodium channel—NaV1.2—in inhibitory interneurons might explain why loss-of-function mutations in this channel result in epilepsy.
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Affiliation(s)
- Tun Li
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and University of Chinese Academy of Sciences, Shanghai, China
| | - Cuiping Tian
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and University of Chinese Academy of Sciences, Shanghai, China
| | - Paolo Scalmani
- U.O. of Neurophysiopathology and Diagnostic Epileptology, Foundation Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS) Neurological Institute Carlo Besta, Milano, Italy
| | - Carolina Frassoni
- U.O. of Clinical Epileptology and Experimental Neurophysiology, Foundation Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS) Neurological Institute Carlo Besta, Milano, Italy
| | - Massimo Mantegazza
- Institute of Molecular and Cellular Pharmacology (IPMC), Laboratory of Excellence Ion Channel Science and Therapeutics (LabEx ICST), CNRS UMR7275 and University of Nice-Sophia Antipolis, Valbonne, France
| | - Yonghong Wang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and University of Chinese Academy of Sciences, Shanghai, China
| | - Mingpo Yang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, and University of Chinese Academy of Sciences, Shanghai, China
| | - Si Wu
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, School of Brain and Cognitive Sciences, Beijing Normal University, Beijing, China
- Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, Beijing, China
| | - Yousheng Shu
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, School of Brain and Cognitive Sciences, Beijing Normal University, Beijing, China
- Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, Beijing, China
- * E-mail:
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de Kovel CGF, Meisler MH, Brilstra EH, van Berkestijn FMC, van 't Slot R, van Lieshout S, Nijman IJ, O'Brien JE, Hammer MF, Estacion M, Waxman SG, Dib-Hajj SD, Koeleman BPC. Characterization of a de novo SCN8A mutation in a patient with epileptic encephalopathy. Epilepsy Res 2014; 108:1511-8. [PMID: 25239001 DOI: 10.1016/j.eplepsyres.2014.08.020] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 05/19/2014] [Accepted: 08/26/2014] [Indexed: 10/24/2022]
Abstract
OBJECTIVE Recently, de novo SCN8A missense mutations have been identified as a rare dominant cause of epileptic encephalopathies (EIEE13). Functional studies on the first described case demonstrated gain-of-function effects of the mutation. We describe a novel de novo mutation of SCN8A in a patient with epileptic encephalopathy, and functional characterization of the mutant protein. DESIGN Whole exome sequencing was used to discover the variant. We generated a mutant cDNA, transfected HEK293 cells, and performed Western blotting to assess protein stability. To study channel functional properties, patch-clamp experiments were carried out in transfected neuronal ND7/23 cells. RESULTS The proband exhibited seizure onset at 6 months of age, diffuse brain atrophy, and more profound developmental impairment than the original case. The mutation p.Arg233Gly in the voltage sensing transmembrane segment D1S4 was present in the proband and absent in both parents. This mutation results in a temperature-sensitive reduction in protein expression as well as reduced sodium current amplitude and density and a relative increased response to a slow ramp stimulus, though this did not result in an absolute increased current at physiological temperatures. CONCLUSION The new de novo SCN8A mutation is clearly deleterious, resulting in an unstable protein with reduced channel activity. This differs from the gain-of-function attributes of the first SCN8A mutation in epileptic encephalopathy, pointing to heterogeneity of mechanisms. Since Nav1.6 is expressed in both excitatory and inhibitory neurons, a differential effect of a loss-of-function of Nav1.6 Arg223Gly on inhibitory interneurons may underlie the epilepsy phenotype in this patient.
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Affiliation(s)
- Carolien G F de Kovel
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.
| | - Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-5618, USA; Department of Neurology, University of Michigan, Ann Arbor, MI 48109-5618, USA
| | - Eva H Brilstra
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Ruben van 't Slot
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Stef van Lieshout
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Isaac J Nijman
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Janelle E O'Brien
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-5618, USA
| | - Michael F Hammer
- Arizona Research Laboratories, Division of Biotechnology, University of Arizona, Tucson, AZ 85721, USA
| | - Mark Estacion
- Department of Neurology, Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA; Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Stephen G Waxman
- Department of Neurology, Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA; Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Sulayman D Dib-Hajj
- Department of Neurology, Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06510, USA; Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT 06516, USA
| | - Bobby P C Koeleman
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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