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Lin ZJ, He JW, Zhu SY, Xue LH, Zheng JF, Zheng LQ, Huang BX, Chen GZ, Lin PX. Gene-gene interaction network analysis indicates CNTN2 is a candidate gene for idiopathic generalized epilepsy. Neurogenetics 2024; 25:131-139. [PMID: 38460076 DOI: 10.1007/s10048-024-00748-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Accepted: 01/19/2024] [Indexed: 03/11/2024]
Abstract
Twin and family studies have established the genetic contribution to idiopathic generalized epilepsy (IGE). The genetic architecture of IGE is generally complex and heterogeneous, and the majority of the genetic burden in IGE remains unsolved. We hypothesize that gene-gene interactions contribute to the complex inheritance of IGE. CNTN2 (OMIM* 615,400) variants have been identified in cases with familial adult myoclonic epilepsy and other epilepsies. To explore the gene-gene interaction network in IGE, we took the CNTN2 gene as an example and investigated its co-occurrent genetic variants in IGE cases. We performed whole-exome sequencing in 114 unrelated IGE cases and 296 healthy controls. Variants were qualified with sequencing quality, minor allele frequency, in silico prediction, genetic phenotype, and recurrent case numbers. The STRING_TOP25 gene interaction network analysis was introduced with the bait gene CNTN2 (denoted as A). The gene-gene interaction pair mode was presumed to be A + c, A + d, A + e, with a leading gene A, or A + B + f, A + B + g, A + B + h, with a double-gene A + B, or other combinations. We compared the number of gene interaction pairs between the case and control groups. We identified three pairs in the case group, CNTN2 + PTPN18, CNTN2 + CNTN1 + ANK2 + ANK3 + SNTG2, and CNTN2 + PTPRZ1, while we did not discover any pairs in the control group. The number of gene interaction pairs in the case group was much more than in the control group (p = 0.021). Taking together the genetic bioinformatics, reported epilepsy cases, and statistical evidence in the study, we supposed CNTN2 as a candidate pathogenic gene for IGE. The gene interaction network analysis might help screen candidate genes for IGE or other complex genetic disorders.
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Affiliation(s)
- Zhi-Jian Lin
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Jun-Wei He
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Sheng-Yin Zhu
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Li-Hong Xue
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Jian-Feng Zheng
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Li-Qin Zheng
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Bi-Xia Huang
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Guo-Zhang Chen
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China
| | - Peng-Xing Lin
- Department of Neurology, School of Clinical Medicine, the Affiliated Hospital of Putian UniversityFujian Medical UniversityBrain Science Institute of Putian University, 999 Dongzhen East Road, Licheng District, Putian, 351100, China.
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Chi W, Kiskinis E. Integrative analysis of epilepsy-associated genes reveals expression-phenotype correlations. Sci Rep 2024; 14:3587. [PMID: 38351047 PMCID: PMC10864290 DOI: 10.1038/s41598-024-53494-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 02/01/2024] [Indexed: 02/16/2024] Open
Abstract
Epilepsy is a highly prevalent neurological disorder characterized by recurrent seizures. Patients exhibit broad genetic, molecular, and clinical diversity involving mild to severe comorbidities. The factors that contribute to this phenotypic diversity remain unclear. Here we used publicly available datasets to systematically interrogate the expression pattern of 230 epilepsy-associated genes across human tissues, developmental stages, and central nervous system (CNS) cellular subtypes. We grouped genes based on their curated phenotypes into 3 broad classes: core epilepsy genes (CEG), where seizures are the dominant phenotype, developmental and epileptic encephalopathy genes (DEEG) that are associated with developmental and epileptic encephalopathy, and seizure-related genes (SRG), which are characterized by the presence of seizures and gross brain malformations. We find that compared to the other two groups of genes, DEEGs are highly expressed within the adult CNS, exhibit the highest and most dynamic expression in various brain regions across development, and are significantly enriched in GABAergic neurons. Our analysis provides an overview of the expression pattern of epilepsy-associated genes with spatiotemporal resolution and establishes a broad expression-phenotype correlation in epilepsy.
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Affiliation(s)
- Wanhao Chi
- The Ken & Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA.
| | - Evangelos Kiskinis
- The Ken & Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA.
- Simpson Querrey Institute, Northwestern University, Chicago, IL, 60611, USA.
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA.
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Bouzroud W, Tazzite A, Boussakri I, Gazzaz B, Dehbi H. A novel SCN8A variant of unknown significance in pediatric epilepsy: a case report. J Int Med Res 2023; 51:3000605231187931. [PMID: 37498161 PMCID: PMC10387795 DOI: 10.1177/03000605231187931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2023] Open
Abstract
Variants in SCN8A are associated with several diseases, including developmental and epileptic encephalopathy, intermediate epilepsy or mild-to-moderate developmental and epileptic encephalopathy, self-limited familial infantile epilepsy, neurodevelopmental delays with generalized epilepsy, neurodevelopmental disorder without epilepsy, hypotonia, and movement disorders. Herein, we report an 8-year-old Moroccan boy with intermediate epilepsy of unknown origin, intellectual disability, autism spectrum disorder, and hyperactivity. The patient presented a normal 46, XY karyotype and a normal comparative genomic hybridization profile. Whole-exome sequencing was performed, and heterozygous variants were identified in KCNK4 and SCN8A. The SCN8A variant [c.4499C > T (p.Pro1500Leu)] was also detected in the healthy mother and was classified as a variant of uncertain clinical significance. This variant occurs in a highly conserved domain, which may affect the function of the encoded protein. More studies are needed to confirm the pathogenicity of this novel variant to establish the effective care, management, and genetic counselling of affected individuals.
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Affiliation(s)
- Wafaa Bouzroud
- Medical Genetics Laboratory, Ibn Rochd University Hospital, Casablanca, Morocco
| | - Amal Tazzite
- Laboratory of Cellular and Molecular Pathology, Faculty of Medicine and Pharmacy, Hassan II University of Casablanca, Casablanca, Morocco
| | - Ikhlass Boussakri
- Laboratory of Cellular and Molecular Pathology, Faculty of Medicine and Pharmacy, Hassan II University of Casablanca, Casablanca, Morocco
| | - Bouchaïb Gazzaz
- Laboratory of Cellular and Molecular Pathology, Faculty of Medicine and Pharmacy, Hassan II University of Casablanca, Casablanca, Morocco
- Genetics Analysis Institute, Royal Gendarmerie, Rabat, Morocco
| | - Hind Dehbi
- Medical Genetics Laboratory, Ibn Rochd University Hospital, Casablanca, Morocco
- Laboratory of Cellular and Molecular Pathology, Faculty of Medicine and Pharmacy, Hassan II University of Casablanca, Casablanca, Morocco
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Chi W, Kiskinis E. Integrative Analysis of Epilepsy-Associated Genes Reveals Expression-Phenotype Correlations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.09.544142. [PMID: 37333355 PMCID: PMC10274872 DOI: 10.1101/2023.06.09.544142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Epilepsy is a highly prevalent neurological disorder characterized by recurrent seizures. Patients exhibit broad genetic, molecular, and clinical diversity involving mild to severe comorbidities. The factors that contribute to this phenotypic diversity remain unclear. We used publicly available datasets to systematically interrogate the expression pattern of 247 epilepsy-associated genes across human tissues, developmental stages, and central nervous system (CNS) cellular subtypes. We grouped genes based on their curated phenotypes into 3 broad classes: core epilepsy genes (CEG), where seizures are the core syndrome, developmental and epileptic encephalopathy genes (DEEG) that are associated with developmental delay, and seizure-related genes (SRG), which are characterized by developmental delay and gross brain malformations. We find that DEEGs are highly expressed within the CNS, while SRGs are most abundant in non-CNS tissues. DEEGs and CEGs exhibit highly dynamic expression in various brain regions across development, spiking during the prenatal to infancy transition. Lastly, the abundance of CEGs and SRGs is comparable within cellular subtypes in the brain, while the average expression level of DEEGs is significantly higher in GABAergic neurons and non-neuronal cells. Our analysis provides an overview of the expression pattern of epilepsy-associated genes with spatiotemporal resolution and establishes a broad expression-phenotype correlation in epilepsy.
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Affiliation(s)
- Wanhao Chi
- The Ken & Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Evangelos Kiskinis
- The Ken & Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
- Simpson Querrey Institute, Northwestern University, Chicago, IL 60611, USA
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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Echevarria-Cooper DM, Hawkins NA, Kearney JA. Strain-dependent effects on neurobehavioral and seizure phenotypes in Scn2aK1422E mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543929. [PMID: 37333275 PMCID: PMC10274703 DOI: 10.1101/2023.06.06.543929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Pathogenic variants in SCN2A are associated with a range of neurodevelopmental disorders (NDD). Despite being largely monogenic, SCN2A-related NDD show considerable phenotypic variation and complex genotype-phenotype correlations. Genetic modifiers can contribute to variability in disease phenotypes associated with rare driver mutations. Accordingly, different genetic backgrounds across inbred rodent strains have been shown to influence disease-related phenotypes, including those associated with SCN2A-related NDD. Recently, we developed a mouse model of the variant SCN2A-p.K1422E that was maintained as an isogenic line on the C57BL/6J (B6) strain. Our initial characterization of NDD phenotypes in heterozygous Scn2aK1422E mice revealed alterations in anxiety-related behavior and seizure susceptibility. To determine if background strain affects phenotype severity in the Scn2aK1422E mouse model, phenotypes of mice on B6 and [DBA/2J×B6]F1 hybrid (F1D2) strains were compared. Convergent evidence from neurobehavioral assays demonstrated lower anxiety-like behavior in Scn2aK1422E mice compared to wild-type and further suggested that this effect is more pronounced on the B6 background compared to the F1D2 background. Although there were no strain-dependent differences in occurrence of rare spontaneous seizures, response to the chemoconvulsant kainic acid revealed differences in seizure generalization and lethality risk, with variation based on strain and sex. Continued examination of strain-dependent effects in the Scn2aK1422E mouse model could reveal genetic backgrounds with unique susceptibility profiles that would be relevant for future studies on specific traits and enable the identification of highly penetrant phenotypes and modifier genes that could provide clues about the primary pathogenic mechanism of the K1422E variant.
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Affiliation(s)
- Dennis M. Echevarria-Cooper
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
- Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Chicago, IL 60611, USA
| | - Nicole A. Hawkins
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Jennifer A. Kearney
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
- Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Chicago, IL 60611, USA
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Hill SF, Ziobro JM, Jafar‐Nejad P, Rigo F, Meisler MH. Genetic interaction between Scn8a and potassium channel genes Kcna1 and Kcnq2. Epilepsia 2022; 63:e125-e131. [PMID: 35892317 PMCID: PMC9804156 DOI: 10.1111/epi.17374] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 07/24/2022] [Accepted: 07/25/2022] [Indexed: 01/07/2023]
Abstract
Voltage-gated sodium and potassium channels regulate the initiation and termination of neuronal action potentials. Gain-of-function mutations of sodium channel Scn8a and loss-of-function mutations of potassium channels Kcna1 and Kcnq2 increase neuronal activity and lead to seizure disorders. We tested the hypothesis that reducing the expression of Scn8a would compensate for loss-of-function mutations of Kcna1 or Kcnq2. Scn8a expression was reduced by the administration of an antisense oligonucleotide (ASO). This treatment lengthened the survival of the Kcn1a and Kcnq2 mutants, and reduced the seizure frequency in the Kcnq2 mutant mice. These observations suggest that reduction of SCN8A may be therapeutic for genetic epilepsies resulting from mutations in these potassium channel genes.
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Affiliation(s)
- Sophie F. Hill
- Neuroscience Graduate ProgramUniversity of MichiganAnn ArborMichiganUSA,Department of Human GeneticsUniversity of MichiganAnn ArborMichiganUSA
| | - Julie M. Ziobro
- Department of PediatricsUniversity of MichiganAnn ArborMichiganUSA
| | | | - Frank Rigo
- Ionis PharmaceuticalsCarlsbadCaliforniaUSA
| | - Miriam H. Meisler
- Neuroscience Graduate ProgramUniversity of MichiganAnn ArborMichiganUSA,Department of Human GeneticsUniversity of MichiganAnn ArborMichiganUSA,Department of NeurologyUniversity of MichiganAnn ArborMichiganUSA
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Xu C, Zhang Y, Gozal D, Carney P. Channelopathy of Dravet Syndrome and Potential Neuroprotective Effects of Cannabidiol. J Cent Nerv Syst Dis 2021; 13:11795735211048045. [PMID: 34992485 PMCID: PMC8724990 DOI: 10.1177/11795735211048045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Dravet syndrome (DS) is a channelopathy, neurodevelopmental, epileptic encephalopathy characterized by seizures, developmental delay, and cognitive impairment that includes susceptibility to thermally induced seizures, spontaneous seizures, ataxia, circadian rhythm and sleep disorders, autistic-like behaviors, and premature death. More than 80% of DS cases are linked to mutations in genes which encode voltage-gated sodium channel subunits, SCN1A and SCN1B, which encode the Nav1.1α subunit and Nav1.1β1 subunit, respectively. There are other gene mutations encoding potassium, calcium, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels related to DS. One-third of patients have pharmacoresistance epilepsy. DS is unresponsive to standard therapy. Cannabidiol (CBD), a non-psychoactive phytocannabinoid present in Cannabis, has been introduced for treating DS because of its anticonvulsant properties in animal models and humans, especially in pharmacoresistant patients. However, the etiological channelopathiological mechanism of DS and action mechanism of CBD on the channels are unclear. In this review, we summarize evidence of the direct and indirect action mechanism of sodium, potassium, calcium, and HCN channels in DS, especially sodium subunits. Some channels' loss-of-function or gain-of-function in inhibitory or excitatory neurons determine the balance of excitatory and inhibitory are associated with DS. A great variety of mechanisms of CBD anticonvulsant effects are focused on modulating these channels, especially sodium, calcium, and potassium channels, which will shed light on ionic channelopathy of DS and the precise molecular treatment of DS in the future.
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Affiliation(s)
- Changqing Xu
- Department of Child Health and the Child Health Research Institute, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Yumin Zhang
- Department of Anatomy, Physiology and Genetics; Department of Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - David Gozal
- Department of Child Health and the Child Health Research Institute, School of Medicine, University of Missouri, Columbia, MO, USA
| | - Paul Carney
- Departments of Child Health and Neurology, School of Medicine, University of Missouri, Columbia, MO, USA
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Abstract
Pathogenic variants in epilepsy genes result in a spectrum of clinical severity. One source of phenotypic heterogeneity is modifier genes that affect expressivity of a primary pathogenic variant. Mouse epilepsy models also display varying degrees of clinical severity on different genetic backgrounds. Mice with heterozygous deletion of Scn1a (Scn1a+/−) model Dravet syndrome, a severe epilepsy most often caused by SCN1A haploinsufficiency. Scn1a+/− mice recapitulate features of Dravet syndrome, including spontaneous seizures, sudden death, and cognitive/behavioral deficits. Scn1a+/− mice maintained on the 129S6/SvEvTac (129) strain have normal lifespan and no spontaneous seizures. In contrast, admixture with C57BL/6J (B6) results in epilepsy and premature lethality. We previously mapped Dravet Survival Modifier loci (Dsm1-Dsm5) responsible for strain-dependent differences in survival. Gabra2, encoding the GABAA α2 subunit, was nominated as a candidate modifier at Dsm1. Direct measurement of GABAA receptors found lower abundance of α2-containing receptors in hippocampal synapses of B6 mice relative to 129. We also identified a B6-specific single nucleotide deletion within Gabra2 that lowers mRNA and protein by nearly 50%. Repair of this deletion reestablished normal levels of Gabra2 expression. In this study, we used B6 mice with a repaired Gabra2 allele to evaluate Gabra2 as a genetic modifier of severity in Scn1a+/− mice. Gabra2 repair restored transcript and protein expression, increased abundance of α2-containing GABAA receptors in hippocampal synapses, and rescued epilepsy phenotypes of Scn1a+/− mice. These findings validate Gabra2 as a genetic modifier of Dravet syndrome, and support enhancing function of α2-containing GABAA receptors as treatment strategy for Dravet syndrome.
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Kruth KA, Grisolano TM, Ahern CA, Williams AJ. SCN2A channelopathies in the autism spectrum of neuropsychiatric disorders: a role for pluripotent stem cells? Mol Autism 2020; 11:23. [PMID: 32264956 PMCID: PMC7140374 DOI: 10.1186/s13229-020-00330-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/25/2020] [Indexed: 12/12/2022] Open
Abstract
Efforts to identify the causes of autism spectrum disorders have highlighted the importance of both genetics and environment, but the lack of human models for many of these disorders limits researchers’ attempts to understand the mechanisms of disease and to develop new treatments. Induced pluripotent stem cells offer the opportunity to study specific genetic and environmental risk factors, but the heterogeneity of donor genetics may obscure important findings. Diseases associated with unusually high rates of autism, such as SCN2A syndromes, provide an opportunity to study specific mutations with high effect sizes in a human genetic context and may reveal biological insights applicable to more common forms of autism. Loss-of-function mutations in the SCN2A gene, which encodes the voltage-gated sodium channel NaV1.2, are associated with autism rates up to 50%. Here, we review the findings from experimental models of SCN2A syndromes, including mouse and human cell studies, highlighting the potential role for patient-derived induced pluripotent stem cell technology to identify the molecular and cellular substrates of autism.
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Affiliation(s)
- Karina A Kruth
- Department of Psychiatry, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2326 PBDB, Iowa City, IA, 52242, USA
| | - Tierney M Grisolano
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2312 PBDB, Iowa City, IA, 52242, USA
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2312 PBDB, Iowa City, IA, 52242, USA
| | - Aislinn J Williams
- Department of Psychiatry, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2326 PBDB, Iowa City, IA, 52242, USA.
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Milh M, Roubertoux P, Biba N, Chavany J, Spiga Ghata A, Fulachier C, Collins SC, Wagner C, Roux JC, Yalcin B, Félix MS, Molinari F, Lenck-Santini PP, Villard L. A knock-in mouse model for KCNQ2-related epileptic encephalopathy displays spontaneous generalized seizures and cognitive impairment. Epilepsia 2020; 61:868-878. [PMID: 32239694 PMCID: PMC7317210 DOI: 10.1111/epi.16494] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 03/09/2020] [Accepted: 03/09/2020] [Indexed: 01/06/2023]
Abstract
Objective Early onset epileptic encephalopathy with suppression‐burst is one of the most severe epilepsy phenotypes in human patients. A significant proportion of cases have a genetic origin, and the most frequently mutated gene is KCNQ2, encoding Kv7.2, a voltage‐dependent potassium channel subunit, leading to so‐called KCNQ2‐related epileptic encephalopathy (KCNQ2‐REE). To study the pathophysiology of KCNQ2‐REE in detail and to provide a relevant preclinical model, we generated and described a knock‐in mouse model carrying the recurrent p.(Thr274Met) variant. Methods We introduced the p.(Thr274Met) variant by homologous recombination in embryonic stem cells, injected into C57Bl/6N blastocysts and implanted in pseudopregnant mice. Mice were then bred with 129Sv Cre‐deleter to generate heterozygous mice carrying the p.(Thr274Met), and animals were maintained on the 129Sv genetic background. We studied the development of this new model and performed in vivo electroencephalographic (EEG) recordings, neuroanatomical studies at different time points, and multiple behavioral tests. Results The Kcnq2Thr274Met/+ mice are viable and display generalized spontaneous seizures first observed between postnatal day 20 (P20) and P30. In vivo EEG recordings show that the paroxysmal events observed macroscopically are epileptic seizures. The brain of the Kcnq2Thr274Met/+ animals does not display major structural defects, similar to humans, and their body weight is normal. Kcnq2Thr274Met/+ mice have a reduced life span, with a peak of unexpected death occurring for 25% of the animals by 3 months of age. Epileptic seizures were generally not observed when animals grew older. Behavioral characterization reveals important deficits in spatial learning and memory in adults but no gross abnormality during early neurosensory development. Significance Taken together, our results indicate that we have generated a relevant model to study the pathophysiology of KCNQ2‐related epileptic encephalopathy and perform preclinical research for that devastating and currently intractable disease.
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Affiliation(s)
- Mathieu Milh
- Aix Marseille Univ, Inserm, MMG, Marseille, France.,Department of Pediatric Neurology, La Timone Children's Hospital, Marseille, France
| | | | - Najoua Biba
- Aix-Marseille University, Inmed, Inserm, U1249, Marseille, France
| | - Julie Chavany
- Aix Marseille Univ, Inserm, MMG, Marseille, France.,Department of Pediatric Neurology, La Timone Children's Hospital, Marseille, France
| | | | | | | | | | | | | | | | - Florence Molinari
- Aix Marseille Univ, Inserm, MMG, Marseille, France.,Aix-Marseille University, Inmed, Inserm, U1249, Marseille, France
| | | | - Laurent Villard
- Aix Marseille Univ, Inserm, MMG, Marseille, France.,Department of Medical Genetics, La Timone Children's Hospital, Marseille, France
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Balestrini S, Sisodiya SM. Personalized treatment in the epilepsies: challenges and opportunities. EXPERT REVIEW OF PRECISION MEDICINE AND DRUG DEVELOPMENT 2018. [DOI: 10.1080/23808993.2018.1486189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Simona Balestrini
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, and Epilepsy Society, Chalfont-St-Peter, Bucks, United Kingdom
| | - Sanjay M Sisodiya
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, and Epilepsy Society, Chalfont-St-Peter, Bucks, United Kingdom
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Abstract
Epilepsy, characterized by spontaneous recurrent seizures (SRS), is a serious and common neurological disorder afflicting an estimated 1% of the population worldwide. Animal experiments, especially those utilizing small laboratory rodents, remain essential to understanding the fundamental mechanisms underlying epilepsy and to prevent, diagnose, and treat this disease. While much attention has been focused on epileptogenesis in animal models of epilepsy, there is little discussion on SRS, the hallmark of epilepsy. This is in part due to the technical difficulties of rigorous SRS detection. In this review, we comprehensively summarize both genetic and acquired models of SRS and discuss the methodology used to monitor and detect SRS in mice and rats.
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Affiliation(s)
- Bin Gu
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC 27599, USA.
| | - Katherine A Dalton
- Psychology & Neuroscience Program, University of North Carolina, Chapel Hill, NC 27599, USA
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13
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Modulation of Abnormal Sodium Channel Currents in Heart and Brain: Hope for SUDEP Prevention and Seizure Reduction. Epilepsy Curr 2017; 17:306-310. [PMID: 29225548 DOI: 10.5698/1535-7597.17.5.306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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Rare variants of small effect size in neuronal excitability genes influence clinical outcome in Japanese cases of SCN1A truncation-positive Dravet syndrome. PLoS One 2017; 12:e0180485. [PMID: 28686619 PMCID: PMC5501540 DOI: 10.1371/journal.pone.0180485] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 06/15/2017] [Indexed: 12/18/2022] Open
Abstract
Dravet syndrome (DS) is a rare, devastating form of childhood epilepsy that is often associated with mutations in the voltage-gated sodium channel gene, SCN1A. There is considerable variability in expressivity within families, as well as among individuals carrying the same primary mutation, suggesting that clinical outcome is modulated by variants at other genes. To identify modifier gene variants that contribute to clinical outcome, we sequenced the exomes of 22 individuals at both ends of a phenotype distribution (i.e., mild and severe cognitive condition). We controlled for variation associated with different mutation types by limiting inclusion to individuals with a de novo truncation mutation resulting in SCN1A haploinsufficiency. We performed tests aimed at identifying 1) single common variants that are enriched in either phenotypic group, 2) sets of common or rare variants aggregated in and around genes associated with clinical outcome, and 3) rare variants in 237 candidate genes associated with neuronal excitability. While our power to identify enrichment of a common variant in either phenotypic group is limited as a result of the rarity of mild phenotypes in individuals with SCN1A truncation variants, our top candidates did not map to functional regions of genes, or in genes that are known to be associated with neurological pathways. In contrast, we found a statistically-significant excess of rare variants predicted to be damaging and of small effect size in genes associated with neuronal excitability in severely affected individuals. A KCNQ2 variant previously associated with benign neonatal seizures is present in 3 of 12 individuals in the severe category. To compare our results with the healthy population, we performed a similar analysis on whole exome sequencing data from 70 Japanese individuals in the 1000 genomes project. Interestingly, the frequency of rare damaging variants in the same set of neuronal excitability genes in healthy individuals is nearly as high as in severely affected individuals. Rather than a single common gene/variant modifying clinical outcome in SCN1A-related epilepsies, our results point to the cumulative effect of rare variants with little to no measurable phenotypic effect (i.e., typical genetic background) unless present in combination with a disease-causing truncation mutation in SCN1A.
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Noebels J. Precision physiology and rescue of brain ion channel disorders. J Gen Physiol 2017; 149:533-546. [PMID: 28428202 PMCID: PMC5412535 DOI: 10.1085/jgp.201711759] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 03/24/2017] [Indexed: 11/20/2022] Open
Abstract
Ion channel genes, originally implicated in inherited excitability disorders of muscle and heart, have captured a major role in the molecular diagnosis of central nervous system disease. Their arrival is heralded by neurologists confounded by a broad phenotypic spectrum of early-onset epilepsy, autism, and cognitive impairment with few effective treatments. As detection of rare structural variants in channel subunit proteins becomes routine, it is apparent that primary sequence alone cannot reliably predict clinical severity or pinpoint a therapeutic solution. Future gains in the clinical utility of variants as biomarkers integral to clinical decision making and drug discovery depend on our ability to unravel complex developmental relationships bridging single ion channel structure and human physiology.
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Affiliation(s)
- Jeffrey Noebels
- Department of Neurology, Baylor College of Medicine, Houston, TX 77030 .,Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030
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Abstract
This review attempts to give a concise and up-to-date overview on the role of potassium channels in epilepsies. Their role can be defined from a genetic perspective, focusing on variants and de novo mutations identified in genetic studies or animal models with targeted, specific mutations in genes coding for a member of the large potassium channel family. In these genetic studies, a demonstrated functional link to hyperexcitability often remains elusive. However, their role can also be defined from a functional perspective, based on dynamic, aggravating, or adaptive transcriptional and posttranslational alterations. In these cases, it often remains elusive whether the alteration is causal or merely incidental. With ∼80 potassium channel types, of which ∼10% are known to be associated with epilepsies (in humans) or a seizure phenotype (in animals), if genetically mutated, a comprehensive review is a challenging endeavor. This goal may seem all the more ambitious once the data on posttranslational alterations, found both in human tissue from epilepsy patients and in chronic or acute animal models, are included. We therefore summarize the literature, and expand only on key findings, particularly regarding functional alterations found in patient brain tissue and chronic animal models.
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Affiliation(s)
- Rüdiger Köhling
- Oscar Langendorff Institute of Physiology, University of Rostock, Rostock 18057, Germany
| | - Jakob Wolfart
- Oscar Langendorff Institute of Physiology, University of Rostock, Rostock 18057, Germany
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17
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Abstract
As the genetic etiologies of an expanding number of epilepsy syndromes are revealed, the complexity of the phenotype genotype correlation increases. As our review will show, multiple gene mutations cause different epilepsy syndromes, making identification of the specific mutation increasingly more important for prognostication and often more directed treatment. Examples of that include the need to avoid specific drugs in Dravet syndrome and the ongoing investigations of the potential use of new directed therapies such as retigabine in KCNQ2-related epilepsies, quinidine in KCNT1-related epilepsies, and memantine in GRIN2A-related epilepsies.
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Affiliation(s)
- Abeer J Hani
- Division of Pediatric Neurology, Department of Pediatrics, Duke Children's Hospital and Health Center, Suite T0913J, 2301 Erwin Road, Durham, NC 27710, USA
| | - Husam M Mikati
- Center of Human Genome Variation, LSRC, Duke University School of Medicine, 201 Trent Drive, Durham, NC 27710, USA
| | - Mohamad A Mikati
- Division of Pediatric Neurology, Department of Pediatrics, Duke Children's Hospital and Health Center, Suite T0913J, 2301 Erwin Road, Durham, NC 27710, USA.
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Subaran RL, Conte JM, Stewart WCL, Greenberg DA. Pathogenic EFHC1 mutations are tolerated in healthy individuals dependent on reported ancestry. Epilepsia 2014; 56:188-94. [PMID: 25489633 PMCID: PMC4354299 DOI: 10.1111/epi.12864] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/08/2014] [Indexed: 11/28/2022]
Abstract
OBJECTIVE Screening for specific coding mutations in the EFHC1 gene has been proposed as a means of assessing susceptibility to juvenile myoclonic epilepsy (JME). To clarify the role of these mutations, especially those reported to be highly penetrant, we sought to measure the frequency of exonic EFHC1 mutations across multiple population samples. METHODS To find and test variants of large effect, we sequenced all EFHC1 exons in 23 JME and 23 non-JME idiopathic generalized epilepsy (IGE) Hispanic patients, and 60 matched controls. We also genotyped specific EFHC1 variants in IGE cases and controls from multiple ethnic backgrounds, including 17 African American IGE patients, with 24 matched controls, and 92 Caucasian JME patients with 103 matched controls. These variants are reported to be pathogenic, but are also found among unphenotyped individuals in public databases. All subjects were from the New York City metro area and all controls were required to have no family history of seizures. RESULTS We found the reportedly pathogenic EFHC1 P77T-R221H (rs149055334-rs79761183) JME haplotype in one Hispanic control and in two African American controls. Public databases also show that the EFHC1 P77T-R221H JME haplotype is present in unphenotyped West African ancestry populations, and we show that it can be found at appreciable frequency in healthy individuals with no family history of epilepsy. We also found a novel splice-site mutation in a single Hispanic JME patient, the effect of which is unknown. SIGNIFICANCE Our findings raise questions about the effect of reportedly pathogenic EFHC1 mutations on JME. One intriguing possibility is that some EFHC1 mutations may be pathogenic only when introduced into specific genetic backgrounds. By focusing on data from multiple populations, including the understudied Hispanic and Black/African American populations, our study highlights that for complex traits like JME, the body of evidence necessary to infer causality is high.
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Affiliation(s)
- Ryan L Subaran
- Nationwide Children's Hospital Research Institute, The Ohio State University, Columbus, Ohio, U.S.A
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19
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Harrer JU, Üçeyler N, Doppler K, Fischer TZ, Dib-Hajj SD, Waxman SG, Sommer C. Neuropathic pain in two-generation twins carrying the sodium channel Nav1.7 functional variant R1150W. Pain 2014; 155:2199-203. [DOI: 10.1016/j.pain.2014.08.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Revised: 06/04/2014] [Accepted: 08/05/2014] [Indexed: 10/24/2022]
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Mutations in SCN10A are responsible for a large fraction of cases of Brugada syndrome. J Am Coll Cardiol 2014; 64:66-79. [PMID: 24998131 DOI: 10.1016/j.jacc.2014.04.032] [Citation(s) in RCA: 165] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Revised: 03/23/2014] [Accepted: 04/23/2014] [Indexed: 12/19/2022]
Abstract
BACKGROUND BrS is an inherited sudden cardiac death syndrome. Less than 35% of BrS probands have genetically identified pathogenic variants. Recent evidence has implicated SCN10A, a neuronal sodium channel gene encoding Nav1.8, in the electrical function of the heart. OBJECTIVES The purpose of this study was to test the hypothesis that SCN10A variants contribute to the development of Brugada syndrome (BrS). METHODS Clinical analysis and direct sequencing of BrS susceptibility genes were performed for 150 probands and family members as well as >200 healthy controls. Expression and coimmunoprecipitation studies were performed to functionally characterize the putative pathogenic mutations. RESULTS We identified 17 SCN10A mutations in 25 probands (20 male and 5 female); 23 of the 25 probands (92.0%) displayed overlapping phenotypes. SCN10A mutations were found in 16.7% of BrS probands, approaching our yield for SCN5A mutations (20.1%). Patients with BrS who had SCN10A mutations were more symptomatic and displayed significantly longer PR and QRS intervals compared with SCN10A-negative BrS probands. The majority of mutations localized to the transmembrane-spanning regions. Heterologous coexpression of wild-type (WT) SCN10A with WT-SCN5A in HEK cells caused a near doubling of sodium channel current compared with WT-SCN5A alone. In contrast, coexpression of SCN10A mutants (R14L and R1268Q) with WT-SCN5A caused a 79.4% and 84.4% reduction in sodium channel current, respectively. The coimmunoprecipitation studies provided evidence for the coassociation of Nav1.8 and Nav1.5 in the plasma membrane. CONCLUSIONS Our study identified SCN10A as a major susceptibility gene for BrS, thus greatly enhancing our ability to genotype and risk stratify probands and family members.
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Subaran RL, Greenberg DA. The Genetics of Common Epilepsy Disorders: Lessons Learned from the Channelopathy Era. CURRENT GENETIC MEDICINE REPORTS 2014. [DOI: 10.1007/s40142-014-0040-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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22
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Ream MA, Mikati MA. Clinical utility of genetic testing in pediatric drug-resistant epilepsy: a pilot study. Epilepsy Behav 2014; 37:241-8. [PMID: 25108116 DOI: 10.1016/j.yebeh.2014.06.018] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Revised: 06/09/2014] [Accepted: 06/11/2014] [Indexed: 12/23/2022]
Abstract
RATIONALE The utility of genetic testing in pediatric drug-resistant epilepsy (PDRE), its yield in "real life" clinical practice, and the practical implications of such testing are yet to be determined. GOAL To start to address the above gaps in our knowledge as they apply to a patient population seen in a tertiary care center. METHODS We retrospectively reviewed our experience with the use of clinically available genetic tests in the diagnosis and management of PDRE in one clinic over one year. Genetic testing included, depending on clinical judgment, one or more of the following: karyotype, chromosomal microarray, single gene sequencing, gene sequencing panels, and/or whole exome sequencing (WES). RESULTS We were more likely to perform genetic testing in patients with developmental delay, epileptic encephalopathy, and generalized epilepsy. In our unique population, the yield of specific genetic diagnosis was relatively high: karyotype 14.3%, microarray 16.7%, targeted single gene sequencing 15.4%, gene panels 46.2%, and WES 16.7%. Overall yield of diagnosis from at least one of the above tests was 34.5%. Disease-causing mutations that were not clinically suspected based on the patients' phenotypes and representing novel phenotypes were found in 6.9% (2/29), with an additional 17.2% (5/29) demonstrating pharmacologic variants. Three patients were incidentally found to be carriers of recessive neurologic diseases (10.3%). Variants of unknown significance (VUSs) were identified in 34.5% (10/29). CONCLUSIONS We conclude that genetic testing had at least some utility in our patient population of PDRE, that future similar larger studies in various populations are warranted, and that clinics offering such tests must be prepared to address the complicated questions raised by the results of such testing.
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Affiliation(s)
- Margie A Ream
- Duke University Medical Center, Department of Pediatrics, Division of Pediatric Neurology, USA
| | - Mohamad A Mikati
- Duke University Medical Center, Department of Pediatrics, Division of Pediatric Neurology, USA.
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Ferraro TN. The relationship between genes affecting the development of epilepsy and approaches to epilepsy therapy. Expert Rev Neurother 2014; 14:329-52. [DOI: 10.1586/14737175.2014.888651] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Deng H, Xiu X, Song Z. The molecular biology of genetic-based epilepsies. Mol Neurobiol 2013; 49:352-67. [PMID: 23934645 DOI: 10.1007/s12035-013-8523-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2013] [Accepted: 07/24/2013] [Indexed: 01/02/2023]
Abstract
Epilepsy is one of the most common neurological disorders characterized by abnormal electrical activity in the central nervous system. The clinical features of this disorder are recurrent seizures, difference in age onset, type, and frequency, leading to motor, sensory, cognitive, psychic, or autonomic disturbances. Since the discovery of the first monogenic gene mutation in 1995, it is proposed that genetic factor plays an important role in the mechanism of epilepsy. Genes discovered in idiopathic epilepsies encode for ion channel or neurotransmitter receptor proteins, whereas syndromes with epilepsy as a main feature are caused by genes that are involved in functions such as cortical development, mitochondrial function, and cell metabolism. The identification of these monogenic epilepsy-causing genes provides new insight into the pathogenesis of epilepsies. Although most of the identified gene mutations present a monogenic inheritance, most of idiopathic epilepsies are complex genetic diseases exhibiting a polygenic or oligogenic inheritance. This article reviews recent genetic and molecular progresses in exploring the pathogenesis of epilepsy, with special emphasis on monogenic epilepsy-causing genes, including voltage-gated channels (Na(+), K(+), Ca(2+), Cl(-), and HCN), ligand-gated channels (nicotinic acetylcholine and GABAA receptors), non-ion channel genes as well as the mitochondrial DNA genes. These progresses have improved our understanding of the complex neurological disorder.
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Affiliation(s)
- Hao Deng
- Center for Experimental Medicine, the Third Xiangya Hospital, Central South University, Tongzipo Road 138, Changsha, Hunan, 410013, People's Republic of China,
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25
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Rogawski MA. The intrinsic severity hypothesis of pharmacoresistance to antiepileptic drugs. Epilepsia 2013; 54 Suppl 2:33-40. [PMID: 23646969 DOI: 10.1111/epi.12182] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Pharmacoresistance to antiepileptic drugs (AEDs) is a barrier to seizure freedom for many persons with epilepsy. For nearly two decades, pharmacoresistance has been framed in terms of factors affecting the access of AEDs to their molecular targets in the brain or the actions of the drugs on these targets. Shortcomings in this prevailing view led to the formulation of the intrinsic severity hypothesis of pharmacoresistance to AEDs, which is based on the recognition that there are neurobiologic factors that confer phenotypic variation among individuals with etiologically similar forms of epilepsy and postulates that more severe epilepsy is more difficult to treat with AEDs. In recent years, progress has been made identifying potential genetic mechanisms of variation in epilepsy severity, including subclinical mutations in ion channels that increase or reduce epilepsy severity in mice. Efforts are underway to identify clinically important genetic modifiers. If it can be demonstrated that such severity factors play a role in pharmacoresistance, treatments could be devised to reverse severity mechanisms. By overcoming pharmacoresistance, this new approach to epilepsy therapy may allow drug refractory patients to achieve seizure freedom without side effects.
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Affiliation(s)
- Michael A Rogawski
- Department of Neurology, School of Medicine and Center for Neuroscience, University of California, Davis, Sacramento, California 95817, USA.
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26
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Kato M, Yamagata T, Kubota M, Arai H, Yamashita S, Nakagawa T, FujII T, Sugai K, Imai K, Uster T, Chitayat D, Weiss S, Kashii H, Kusano R, Matsumoto A, Nakamura K, Oyazato Y, Maeno M, Nishiyama K, Kodera H, Nakashima M, Tsurusaki Y, Miyake N, Saito K, Hayasaka K, Matsumoto N, Saitsu H. Clinical spectrum of early onset epileptic encephalopathies caused byKCNQ2mutation. Epilepsia 2013; 54:1282-7. [DOI: 10.1111/epi.12200] [Citation(s) in RCA: 158] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/18/2013] [Indexed: 11/29/2022]
Affiliation(s)
- Mitsuhiro Kato
- Department of Pediatrics; Yamagata University Faculty of Medicine; Yamagata Japan
| | | | - Masaya Kubota
- Division of Neurology; National Center for Child Health and Development; Tokyo Japan
| | - Hiroshi Arai
- Department of Pediatric Neurology; Morinomiya Hospital; Osaka Japan
| | - Sumimasa Yamashita
- Division of Child Neurology; Kanagawa Children's Medical Center; Yokohama Japan
| | - Taku Nakagawa
- Department of Pediatrics; Kobe University Graduate School of Medicine; Kobe Japan
| | - Takanari FujII
- Department of Pediatrics; Showa University Faculty of Medicine; Tokyo Japan
| | - Kenji Sugai
- Department of Child Neurology; National Center Hospital; National Center of Neurology and Psychiatry; Tokyo Japan
| | - Kaoru Imai
- Department of Pediatrics; Tokyo Women's Medical University; Tokyo Japan
| | - Tami Uster
- Department of Obstetrics and Gynecology; The Prenatal Diagnosis and Medical Genetics Program; Mount Sinai Hospital; University of Toronto; Toronto Ontario Canada
| | - David Chitayat
- Department of Obstetrics and Gynecology; The Prenatal Diagnosis and Medical Genetics Program; Mount Sinai Hospital; University of Toronto; Toronto Ontario Canada
- Division of Clinical and Metabolic Genetics; Department of Pediatrics; The Hospital for Sick Children; University of Toronto; Toronto Ontario Canada
| | - Shelly Weiss
- Division of Neurology; Department of Pediatrics; The Hospital for Sick Children; University of Toronto; Toronto Ontario Canada
| | - Hirofumi Kashii
- Division of Neurology; National Center for Child Health and Development; Tokyo Japan
| | - Ryosuke Kusano
- Department of Pediatrics; Jichi Medical University; Tochigi Japan
| | - Ayumi Matsumoto
- Department of Pediatrics; Jichi Medical University; Tochigi Japan
| | - Kazuyuki Nakamura
- Department of Pediatrics; Yamagata University Faculty of Medicine; Yamagata Japan
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Yoshinobu Oyazato
- Department of Pediatrics; Kobe University Graduate School of Medicine; Kobe Japan
| | - Mari Maeno
- Department of Pediatrics; Kobe University Graduate School of Medicine; Kobe Japan
| | - Kiyomi Nishiyama
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Hirofumi Kodera
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Mitsuko Nakashima
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Yoshinori Tsurusaki
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Noriko Miyake
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Kayoko Saito
- Institute of Medical Genetics; Tokyo Women's Medical University; Tokyo Japan
| | - Kiyoshi Hayasaka
- Department of Pediatrics; Yamagata University Faculty of Medicine; Yamagata Japan
| | - Naomichi Matsumoto
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
| | - Hirotomo Saitsu
- Department of Human Genetics; Yokohama City University Graduate School of Medicine; Yokohama Japan
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Touma M, Joshi M, Connolly MC, Grant PE, Hansen AR, Khwaja O, Berry GT, Kinney HC, Poduri A, Agrawal PB. Whole genome sequencing identifies SCN2A mutation in monozygotic twins with Ohtahara syndrome and unique neuropathologic findings. Epilepsia 2013; 54:e81-5. [PMID: 23550958 DOI: 10.1111/epi.12137] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/29/2013] [Indexed: 11/27/2022]
Abstract
Mutations in SCN2A gene cause a variety of epilepsy syndromes. We report a novel SCN2A-associated epilepsy phenotype in monozygotic twins with tonic seizures soon after birth and a suppression-burst electroencephalography (EEG) pattern. We reviewed the medical records, EEG tracings, magnetic resonance imaging (MRI), and neuropathologic findings, and performed whole genome sequencing (WGS) on Twin B's DNA and Sanger sequencing (SS) on candidate gene mutations. Extensive neurometabolic evaluation and early neuroimaging studies were normal. Twin A died of an iatrogenic cause at 2 weeks of life. His neuropathologic examination was remarkable for dentate-olivary dysplasia and granule cell dispersion of the dentate gyrus. Twin B became seizure free at 8 months and was off antiepileptic drugs by 2 years. His brain MRI, normal at 2 months, revealed evolving brainstem and basal ganglia abnormalities at 8 and 15 months that resolved by 20 months. At 2.5 years, Twin B demonstrated significant developmental delay. Twin B's WGS revealed a heterozygous variant c.788C>T predicted to cause p.Ala263Val change in SCN2A and confirmed to be de novo in both twins by SS. In conclusion, we have identified a de novo SCN2A mutation as the etiology for Ohtahara syndrome in monozygotic twins associated with a unique dentate-olivary dysplasia in the deceased twin.
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Affiliation(s)
- Marlin Touma
- Division of Newborn Medicine, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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28
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Using C. elegans to Decipher the Cellular and Molecular Mechanisms Underlying Neurodevelopmental Disorders. Mol Neurobiol 2013; 48:465-89. [DOI: 10.1007/s12035-013-8434-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2012] [Accepted: 02/26/2013] [Indexed: 10/27/2022]
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Ohmori I, Ouchida M, Kobayashi K, Jitsumori Y, Mori A, Michiue H, Nishiki T, Ohtsuka Y, Matsui H. CACNA1A variants may modify the epileptic phenotype of Dravet syndrome. Neurobiol Dis 2013; 50:209-17. [DOI: 10.1016/j.nbd.2012.10.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Revised: 10/04/2012] [Accepted: 10/19/2012] [Indexed: 10/27/2022] Open
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Lerche H, Shah M, Beck H, Noebels J, Johnston D, Vincent A. Ion channels in genetic and acquired forms of epilepsy. J Physiol 2012; 591:753-64. [PMID: 23090947 DOI: 10.1113/jphysiol.2012.240606] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Genetic mutations causing dysfunction of both voltage- and ligand-gated ion channels make a major contribution to the cause of many different types of familial epilepsy. Key mechanisms comprise defective Na(+) channels of inhibitory neurons, or GABA(A) receptors affecting pre- or postsynaptic GABAergic inhibition, or a dysfunction of different types of channels at axon initial segments. Many of these ion channel mutations have been modelled in mice, which has largely contributed to the understanding of where and how the ion channel defects lead to neuronal hyperexcitability. Animal models of febrile seizures or mesial temporal epilepsy have shown that dendritic K(+) channels, hyperpolarization-activated cation channels and T-type Ca(2+) channels play important roles in the generation of seizures. For the latter, it has been shown that suppression of their function by pharmacological mechanisms or in knock-out mice can antagonize epileptogenesis. Defects of ion channel function are also associated with forms of acquired epilepsy. Autoantibodies directed against ion channels or associated proteins, such as K(+) channels, LGI1 or NMDA receptors, have been identified in epileptic disorders that can largely be included under the term limbic encephalitis which includes limbic seizures, status epilepticus and psychiatric symptoms. We conclude that ion channels and associated proteins are important players in different types of genetic and acquired epilepsies. Nevertheless, the molecular bases for most common forms of epilepsy are not yet clear, and evidence to be discussed indicates just how much more we need to understand about the complex mechanisms that underlie epileptogenesis.
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Affiliation(s)
- Holger Lerche
- Department of Neurology and Epileptology, Hertie Institute of Clinical Brain Research, University of Tübingen, Tübingen, Germany
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31
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Need AC, Shashi V, Hitomi Y, Schoch K, Shianna KV, McDonald MT, Meisler MH, Goldstein DB. Clinical application of exome sequencing in undiagnosed genetic conditions. J Med Genet 2012; 49:353-61. [PMID: 22581936 PMCID: PMC3375064 DOI: 10.1136/jmedgenet-2012-100819] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Background There is considerable interest in the use of next-generation sequencing to help diagnose unidentified genetic conditions, but it is difficult to predict the success rate in a clinical setting that includes patients with a broad range of phenotypic presentations. Methods The authors present a pilot programme of whole-exome sequencing on 12 patients with unexplained and apparent genetic conditions, along with their unaffected parents. Unlike many previous studies, the authors did not seek patients with similar phenotypes, but rather enrolled any undiagnosed proband with an apparent genetic condition when predetermined criteria were met. Results This undertaking resulted in a likely genetic diagnosis in 6 of the 12 probands, including the identification of apparently causal mutations in four genes known to cause Mendelian disease (TCF4, EFTUD2, SCN2A and SMAD4) and one gene related to known Mendelian disease genes (NGLY1). Of particular interest is that at the time of this study, EFTUD2 was not yet known as a Mendelian disease gene but was nominated as a likely cause based on the observation of de novo mutations in two unrelated probands. In a seventh case with multiple disparate clinical features, the authors were able to identify homozygous mutations in EFEMP1 as a likely cause for macular degeneration (though likely not for other features). Conclusions This study provides evidence that next-generation sequencing can have high success rates in a clinical setting, but also highlights key challenges. It further suggests that the presentation of known Mendelian conditions may be considerably broader than currently recognised.
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Affiliation(s)
- Anna C Need
- Center for Human Genome Variation, Duke University School of Medicine, Box 91009, Durham, NC 27708, USA.
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Weckhuysen S, Mandelstam S, Suls A, Audenaert D, Deconinck T, Claes LRF, Deprez L, Smets K, Hristova D, Yordanova I, Jordanova A, Ceulemans B, Jansen A, Hasaerts D, Roelens F, Lagae L, Yendle S, Stanley T, Heron SE, Mulley JC, Berkovic SF, Scheffer IE, de Jonghe P. KCNQ2 encephalopathy: emerging phenotype of a neonatal epileptic encephalopathy. Ann Neurol 2012; 71:15-25. [PMID: 22275249 DOI: 10.1002/ana.22644] [Citation(s) in RCA: 350] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVE KCNQ2 and KCNQ3 mutations are known to be responsible for benign familial neonatal seizures (BFNS). A few reports on patients with a KCNQ2 mutation with a more severe outcome exist, but a definite relationship has not been established. In this study we investigated whether KCNQ2/3 mutations are a frequent cause of epileptic encephalopathies with an early onset and whether a recognizable phenotype exists. METHODS We analyzed 80 patients with unexplained neonatal or early-infantile seizures and associated psychomotor retardation for KCNQ2 and KCNQ3 mutations. Clinical and imaging data were reviewed in detail. RESULTS We found 7 different heterozygous KCNQ2 mutations in 8 patients (8/80; 10%); 6 mutations arose de novo. One parent with a milder phenotype was mosaic for the mutation. No KCNQ3 mutations were found. The 8 patients had onset of intractable seizures in the first week of life with a prominent tonic component. Seizures generally resolved by age 3 years but the children had profound, or less frequently severe, intellectual disability with motor impairment. Electroencephalography (EEG) at onset showed a burst-suppression pattern or multifocal epileptiform activity. Early magnetic resonance imaging (MRI) of the brain showed characteristic hyperintensities in the basal ganglia and thalamus that later resolved. INTERPRETATION KCNQ2 mutations are found in a substantial proportion of patients with a neonatal epileptic encephalopathy with a potentially recognizable electroclinical and radiological phenotype. This suggests that KCNQ2 screening should be included in the diagnostic workup of refractory neonatal seizures of unknown origin.
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Affiliation(s)
- Sarah Weckhuysen
- Neurogenetics Group, VIB-Department of Molecular Genetics, University of Antwerp, Antwerp, Belgium
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Experimental models of seizures and epilepsies. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2012; 105:57-82. [PMID: 22137429 DOI: 10.1016/b978-0-12-394596-9.00003-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Epilepsy is one of the most common neurological conditions that affect people of all ages. Epilepsy is characterized by occurrence of spontaneous recurrent seizures. Currently available drugs are ineffective in controlling seizures in approximately one-third of patients with epilepsy. Moreover, these drugs are associated with adverse effects, and none of them are effective in preventing development of epilepsy following an insult or injury. To develop an effective therapeutic strategy that can interfere with the process of development of epilepsy (epileptogenesis), it is crucial to study the changes that occur in the brain after an injury and before epilepsy develops. It is not possible to determine these changes in human tissue for obvious ethical reasons. Over the years, experimental models of epilepsies have contributed immensely in improving our understanding of mechanism of epileptogenesis as well as of seizure generation. There are many models that replicate at least some of the characteristics of human epilepsy. Each model has its advantages and disadvantages, and the investigator should be aware of this before selecting a specific model for his/her studies. Availability of a good animal model is a key to the development of an effective treatment. Unfortunately, there are many epilepsy syndromes, specifically pediatric, which still lack a valid animal model. It is vital that more research is done to develop animal models for such syndromes.
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Margineanu DG. Systems biology impact on antiepileptic drug discovery. Epilepsy Res 2011; 98:104-15. [PMID: 22055355 DOI: 10.1016/j.eplepsyres.2011.10.006] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Revised: 09/21/2011] [Accepted: 10/06/2011] [Indexed: 01/22/2023]
Abstract
Systems biology (SB), a recent trend in bioscience research to consider the complex interactions in biological systems from a holistic perspective, sees the disease as a disturbed network of interactions, rather than alteration of single molecular component(s). SB-relying network pharmacology replaces the prevailing focus on specific drug-receptor interaction and the corollary of rational drug design of "magic bullets", by the search for multi-target drugs that would act on biological networks as "magic shotguns". Epilepsy being a multi-factorial, polygenic and dynamic pathology, SB approach appears particularly fit and promising for antiepileptic drug (AED) discovery. In fact, long before the advent of SB, AED discovery already involved some SB-like elements. A reported SB project aimed to find out new drug targets in epilepsy relies on a relational database that integrates clinical information, recordings from deep electrodes and 3D-brain imagery with histology and molecular biology data on modified expression of specific genes in the brain regions displaying spontaneous epileptic activity. Since hitting a single target does not treat complex diseases, a proper pharmacological promiscuity might impart on an AED the merit of being multi-potent. However, multi-target drug discovery entails the complicated task of optimizing multiple activities of compounds, while having to balance drug-like properties and to control unwanted effects. Specific design tools for this new approach in drug discovery barely emerge, but computational methods making reliable in silico predictions of poly-pharmacology did appear, and their progress might be quite rapid. The current move away from reductionism into network pharmacology allows expecting that a proper integration of the intrinsic complexity of epileptic pathology in AED discovery might result in literally anti-epileptic drugs.
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Affiliation(s)
- Doru Georg Margineanu
- Department of Neurosciences, Faculty of Medicine and Pharmacy, University of Mons, Ave. Champ de Mars 6, B-7000 Mons, Belgium.
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Voltage-gated potassium channel KCNV2 (Kv8.2) contributes to epilepsy susceptibility. Proc Natl Acad Sci U S A 2011; 108:5443-8. [PMID: 21402906 DOI: 10.1073/pnas.1017539108] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Mutations in voltage-gated ion channels are responsible for several types of epilepsy. Genetic epilepsies often exhibit variable severity in individuals with the same mutation, which may be due to variation in genetic modifiers. The Scn2a(Q54) transgenic mouse model has a sodium channel mutation and exhibits epilepsy with strain-dependent severity. We previously mapped modifier loci that influence Scn2a(Q54) phenotype severity and identified Kcnv2, encoding the voltage-gated potassium channel subunit Kv8.2, as a candidate modifier. In this study, we demonstrate a threefold increase in hippocampal Kcnv2 expression associated with more severe epilepsy. In vivo exacerbation of the phenotype by Kcnv2 transgenes supports its identification as an epilepsy modifier. The contribution of KCNV2 to human epilepsy susceptibility is supported by identification of two nonsynonymous variants in epilepsy patients that alter function of Kv2.1/Kv8.2 heterotetrameric potassium channels. Our results demonstrate that altered potassium subunit function influences epilepsy susceptibility and implicate Kcnv2 as an epilepsy gene.
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Genetic modifiers of neurological disease. Curr Opin Genet Dev 2011; 21:349-53. [PMID: 21251811 DOI: 10.1016/j.gde.2010.12.007] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Accepted: 12/21/2010] [Indexed: 11/20/2022]
Abstract
Genetic modifiers make an important contribution to neurological disease phenotypes. Significant progress has been made by studying genetic modifiers in model organisms. The ability to study complex genetic interactions in model systems contributes to our understanding of the genetic factors that influence neurological disease. This will lead to the development of novel therapeutic strategies and personalized treatment based on genetic risk.
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Hawkins NA, Martin MS, Frankel WN, Kearney JA, Escayg A. Neuronal voltage-gated ion channels are genetic modifiers of generalized epilepsy with febrile seizures plus. Neurobiol Dis 2010; 41:655-60. [PMID: 21156207 DOI: 10.1016/j.nbd.2010.11.016] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 10/22/2010] [Accepted: 11/30/2010] [Indexed: 11/16/2022] Open
Abstract
Mutations in the neuronal voltage-gated sodium channel genes SCN1A and SCN2A are associated with inherited epilepsies, including genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (severe myoclonic epilepsy of infancy). The clinical presentation and severity of these epilepsies vary widely, even in people with the same mutation, suggesting the action of environmental or genetic modifiers. To gain support for the hypothesis that genetic modifiers can influence clinical presentation in patients with SCN1A-derived GEFS+, we used mouse models to study the effect of combining the human GEFS+ mutation SCN1A-R1648H with SCN2A, KCNQ2, and SCN8A mutations. Knock-in mice heterozygous for the R1648H mutation (Scn1a(RH/+)) have decreased thresholds to induced seizures and infrequent spontaneous seizures, whereas homozygotes display spontaneous seizures and premature lethality. Scn2a(Q54) transgenic mice have a mutation in Scn2a that results in spontaneous, adult-onset partial motor seizures, and mice carrying the Kcnq2-V182M mutation exhibit increased susceptibility to induced seizures, and rare spontaneous seizures as adults. Combining the Scn1a-R1648H allele with either Scn2a(Q54) or Kcnq2(V182M/+) results in early-onset, generalized tonic-clonic seizures and juvenile lethality in double heterozygous mice. In contrast, Scn8a mutants exhibit increased resistance to induced seizures. Combining the Scn1a-R1648H and Scn8a-med-jo alleles restores normal thresholds to flurothyl-induced seizures in Scn1a(RH/+) heterozygotes and improved survival of Scn1a(RH/RH) homozygotes. Our results demonstrate that variants in Scn2a, Kcnq2, and Scn8a can dramatically influence the phenotype of mice carrying the Scn1a-R1648H mutation and suggest that ion channel variants may contribute to the clinical variation seen in patients with monogenic epilepsy.
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Affiliation(s)
- Nicole A Hawkins
- Neuroscience Graduate Program, Vanderbilt University Medical Center, Nashville, TN 37232, USA
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Mantegazza M, Rusconi R, Scalmani P, Avanzini G, Franceschetti S. Epileptogenic ion channel mutations: from bedside to bench and, hopefully, back again. Epilepsy Res 2010; 92:1-29. [PMID: 20828990 DOI: 10.1016/j.eplepsyres.2010.08.003] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Revised: 07/30/2010] [Accepted: 08/08/2010] [Indexed: 01/21/2023]
Abstract
Mutations of genes coding for ion channels cause several genetically determined human epileptic syndromes. The identification of a gene variant linked to a particular disease gives important information, but it is usually necessary to perform functional studies in order to completely disclose the pathogenic mechanisms. The functional consequences of epileptogenic mutations have been studied both in vitro and in vivo with several experimental systems, studies that have provided significant knowledge on the pathogenic mechanisms that leads to inherited human epilepsies, and possibly also on the pathogenic mechanisms of non-genetic human epilepsies due to "acquired channelopathies". However, several open issues remain and difficulties in the interpretation of the experimental data have arisen that limit translational applications. We will highlight the value and the limits of different approaches to the study of epileptogenic channelopathies, focussing on the importance of the experimental systems in the assessment of the functional effects of the mutations and on the possible applications of the obtained results to the clinical practice.
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Affiliation(s)
- Massimo Mantegazza
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS UMR6097 and University of Nice-Sophia Antipolis, 660 route des Lucioles, 06560 Valbonne, France.
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Abstract
Sodium currents are essential for the initiation and propagation of neuronal firing. Alterations of sodium currents can lead to abnormal neuronal activity, such as occurs in epilepsy. The transient voltage-gated sodium current mediates the upstroke of the action potential. A small fraction of sodium current, termed the persistent sodium current (I(NaP)), fails to inactivate significantly, even with prolonged depolarization. I(NaP) is activated in the subthreshold voltage range and is capable of amplifying a neuron's response to synaptic input and enhancing its repetitive firing capability. A burgeoning literature is documenting mutations in sodium channels that underlie human disease, including epilepsy. Some of these mutations lead to altered neuronal excitability by increasing I(NaP). This review focuses on the pathophysiological effects of I(NaP) in epilepsy.
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Affiliation(s)
- Carl E Stafstrom
- Section of Pediatric Neurology, Department of Neurology, University of Wisconsin Madison, Wisconsin, USA.
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Meisler MH, O'Brien JE, Sharkey LM. Sodium channel gene family: epilepsy mutations, gene interactions and modifier effects. J Physiol 2010; 588:1841-8. [PMID: 20351042 DOI: 10.1113/jphysiol.2010.188482] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The human sodium channel family includes seven neuronal channels that are essential for the initiation and propagation of action potentials in the CNS and PNS. In view of their critical role in neuronal firing and their strong sequence conservation during evolution, it is not surprising that mutations in the sodium channel genes are responsible for a growing spectrum of channelopathies. Nearly 700 mutations of the SCN1A gene have been identified in patients with Dravet's syndrome (severe myoclonic epilepsy of infancy), making this the most commonly mutated gene in human epilepsy. A small number of mutations have been found in SCN2A, SCN3A and SCN9A, and studies in the mouse suggest that SCN8A may also contribute to seizure disorders. Interactions between genetic variants of SCN2A and KCNQ2 in the mouse and variants of SCN1A and SCN9A in patients provide models of potential genetic modifier effects in the more common human polygenic epilepsies. New methods for generating induced pluripotent stem cells and neurons from patients will facilitate functional analysis of amino acid substitutions in channel proteins. Whole genome sequencing and exome sequencing in patients with epilepsy will soon make it possible to detect multiple variants and their interactions in the genomes of patients with seizure disorders.
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Affiliation(s)
- Miriam H Meisler
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109-5618, USA.
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Abstract
Epileptogenesis is defined as the process of developing epilepsy-a disorder characterized by recurrent seizures-following an initial insult. Seizure incidence during the human lifespan is at its highest in infancy and childhood. Animal models of epilepsy and human tissue studies suggest that epileptogenesis involves a cascade of molecular, cellular and neuronal network alterations. Within minutes to days following the initial insult, there are acute early changes in neuronal networks, which include rapid alterations to ion channel kinetics as a result of membrane depolarization, post-translational modifications to existing functional proteins, and activation of immediate early genes. Subacute changes occur over hours to weeks, and include transcriptional events, neuronal death and activation of inflammatory cascades. The chronic changes that follow over weeks to months include anatomical changes, such as neurogenesis, mossy fiber sprouting, network reorganization, and gliosis. These epileptogenic processes are developmentally regulated and might contribute to differences in epileptogenesis between adult and developing brains. Here we review the factors responsible for enhanced seizure susceptibility in the developing brain, and consider age-specific mechanisms of epileptogenesis. An understanding of these factors could yield potential therapeutic targets for the prevention of epileptogenesis and also provide biomarkers for identifying patients at risk of developing epilepsy or for monitoring disease progression.
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Chioza BA, Aicardi J, Aschauer H, Brouwer O, Callenbach P, Covanis A, Dooley JM, Dulac O, Durner M, Eeg-Olofsson O, Feucht M, Friis ML, Guerrini R, Kjeldsen MJ, Nabbout R, Nashef L, Sander T, Sirén A, Wirrell E, McKeigue P, Robinson R, Gardiner RM, Everett KV. Genome wide high density SNP-based linkage analysis of childhood absence epilepsy identifies a susceptibility locus on chromosome 3p23-p14. Epilepsy Res 2009; 87:247-55. [PMID: 19837565 PMCID: PMC2791882 DOI: 10.1016/j.eplepsyres.2009.09.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Revised: 09/14/2009] [Accepted: 09/18/2009] [Indexed: 12/03/2022]
Abstract
Childhood absence epilepsy (CAE) is an idiopathic generalised epilepsy (IGE) characterised by typical absence seizures manifested by transitory loss of awareness with 2.5-4 Hz spike-wave complexes on ictal EEG. A genetic component to the aetiology is well recognised but the mechanism of inheritance and the genes involved are yet to be fully established. A genome wide single nucleotide polymorphism (SNP)-based high density linkage scan was carried out using 41 nuclear pedigrees with at least two affected members. Multipoint parametric and non-parametric linkage analyses were performed using MERLIN 1.1.1 and a susceptibility locus was identified on chromosome 3p23-p14 (Z(mean)=3.9, p<0.0001; HLOD=3.3, alpha=0.7). The linked region harbours the functional candidate genes TRAK1 and CACNA2D2. Fine-mapping using a tagSNP approach demonstrated disease association with variants in TRAK1.
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Affiliation(s)
- Barry A. Chioza
- Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK
| | | | - Harald Aschauer
- Department of General Psychiatry, Medical University Vienna, Austria
| | - Oebele Brouwer
- Department of Neurology, University Medical Centre Groningen, University of Groningen, The Netherlands
| | - Petra Callenbach
- Department of Neurology, University Medical Centre Groningen, University of Groningen, The Netherlands
| | | | | | - Olivier Dulac
- Neuropaediatrics Department, Hôpital Necker Enfant Malades, France
| | - Martina Durner
- Division of Statistical Genetics, Columbia University, USA
| | - Orvar Eeg-Olofsson
- Department of Women's and Children's Health/Neuropaediatrics, Uppsala University, Sweden
| | - Martha Feucht
- Department of Paediatrics, Medical University Vienna, Austria
| | | | - Renzo Guerrini
- Division of Child Neurology and Psychiatry, University of Pisa, and IRCCS Fondazione Stella Maris, Italy
| | | | - Rima Nabbout
- Neuropaediatrics Department, Hôpital Necker Enfant Malades, France
| | | | - Thomas Sander
- Cologne Center for Genomics, University of Cologne, Cologne, Germany
- Epilepsy Genetics Group, Department of Neurology, Charité University Medicine, Humboldt University of Berlin, Germany
| | - Auli Sirén
- Department of Paediatrics, Tampere University Hospital, Finland
| | - Elaine Wirrell
- Division of Child and Adolescent Neurology, Mayo Clinic, USA
| | - Paul McKeigue
- Public Health Sciences Section, Division of Community Health Sciences, The University of Edinburgh Medical School, UK
| | | | - R. Mark Gardiner
- Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK
| | - Kate V. Everett
- Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK
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Frankel WN, Yang Y, Mahaffey CL, Beyer BJ, O'Brien TP. Szt2, a novel gene for seizure threshold in mice. GENES BRAIN AND BEHAVIOR 2009; 8:568-76. [PMID: 19624305 DOI: 10.1111/j.1601-183x.2009.00509.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In a chemical mutagenesis screen we identified Szt2 (seizure threshold 2) as a gene that confers low seizure threshold to mice and may also enhance epileptogenesis. The semidominant phenotype was mapped to Chromosome 4 and narrowed further to a critical interval of approximately 650 kb. A novel large (> 10 kb) transcript in the critical interval was found to have fourfold increased steady-state expression at the RNA level in Szt2 homozygous mutant brain. The corresponding 72 exon gene encodes a 378-kD protein with no significant or suggestive sequence similarities to any other protein. The mutant allele of Szt2 contains a splice donor mutation after exon 32, predicting transcriptional read-through, translational frameshift and premature stop. A second Szt2 allele, containing a gene-trap mutation in exon 21, also conferred a low seizure threshold and increased RNA expression, but unlike the original allele, some gene-trap homozygotes died embryonically. Szt2 is transcribed in many tissues, with the highest expression in brain, and it is also expressed during embryonic development. Szt2 is highly conserved in evolution, with a clear, single orthologue found in all land vertebrates and in many invertebrates. Interestingly, in mammals the Szt2 gene resides in a highly conserved head-to-head configuration with Med8 (which encodes a Mediator complex subunit), separated by only 91 nt. While the biological function of Szt2 remains unknown, its high conservation, unique structure and effect on seizure threshold suggest that it serves an important role in the central nervous system.
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Affiliation(s)
- W N Frankel
- The Jackson Laboratory, Bar Harbor, Maine, USA.
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Bergren SK, Rutter ED, Kearney JA. Fine mapping of an epilepsy modifier gene on mouse Chromosome 19. Mamm Genome 2009; 20:359-66. [PMID: 19513789 DOI: 10.1007/s00335-009-9193-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Accepted: 05/08/2009] [Indexed: 11/25/2022]
Abstract
Mutations in voltage-gated sodium channels are associated with several types of human epilepsy. Variable expressivity and penetrance are common features of inherited epilepsy caused by sodium channel mutations, suggesting that genetic modifiers may influence clinical severity. The mouse model Scn2a(Q54) has an epilepsy phenotype due to a mutation in Scn2a that results in elevated persistent sodium current. Phenotype severity in Scn2a(Q54) mice is dependent on the genetic background. Congenic C57BL/6J.Q54 mice have delayed onset and low seizure frequency compared to (C57BL/6J x SJL/J)F1.Q54 mice. Previously, we identified two modifier loci that influence the Scn2a(Q54) epilepsy phenotype: Moe1 (modifier of epilepsy 1) on Chromosome 11 and Moe2 on Chromosome 19. We have constructed interval-specific congenic strains to further refine the position of Moe2 on Chromosome 19 to a 5-Mb region. Sequencing and expression analyses of genes in the critical interval suggested two potential modifier candidates: (1) voltage-gated potassium channel subunit subfamily V, member 2 (Kcnv2), and (2) SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a, member 2 (Smarca2). Based on its biological role in regulating membrane excitability and the association between ion channel variants and seizures, Kcnv2 is a strong functional candidate for Moe2. Modifier genes affecting the epilepsy phenotype of Scn2a(Q54) mice may contribute to variable expressivity and penetrance in human epilepsy patients with sodium channel mutations.
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Affiliation(s)
- Sarah K Bergren
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
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Han C, Dib-Hajj SD, Lin Z, Li Y, Eastman EM, Tyrrell L, Cao X, Yang Y, Waxman SG. Early- and late-onset inherited erythromelalgia: genotype-phenotype correlation. ACTA ACUST UNITED AC 2009; 132:1711-22. [PMID: 19369487 DOI: 10.1093/brain/awp078] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Inherited erythromelalgia (IEM), an autosomal dominant disorder characterized by severe burning pain in response to mild warmth, has been shown to be caused by gain-of-function mutations of sodium channel Na(v)1.7 which is preferentially expressed within dorsal root ganglion (DRG) and sympathetic ganglion neurons. Almost all physiologically characterized cases of IEM have been associated with onset in early childhood. Here, we report the voltage-clamp and current-clamp analysis of a new Na(v)1.7 mutation, Q10R, in a patient with clinical onset of erythromelalgia in the second decade. We show that the mutation in this patient hyperpolarizes activation by only -5.3 mV, a smaller shift than seen with early-onset erythromelalgia mutations, but similar to that of I136V, another mutation that is linked to delayed-onset IEM. Using current-clamp, we show that the expression of Q10R induces hyperexcitability in DRG neurons, but produces an increase in excitability that is smaller than the change produced by I848T, an early-onset erythromelalgia mutation. Our analysis suggests a genotype-phenotype relationship at three levels (clinical, cellular and molecular/ion channel), with mutations that produce smaller effects on sodium channel activation being associated with a smaller degree of DRG neuron excitability and later onset of clinical signs.
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Affiliation(s)
- Chongyang Han
- Department of Neurology, LCI 707, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8018, USA
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Mechanisms of human inherited epilepsies. Prog Neurobiol 2009; 87:41-57. [DOI: 10.1016/j.pneurobio.2008.09.016] [Citation(s) in RCA: 155] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 08/25/2008] [Accepted: 09/29/2008] [Indexed: 12/19/2022]
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Acevedo-Arozena A, Wells S, Potter P, Kelly M, Cox RD, Brown SDM. ENU mutagenesis, a way forward to understand gene function. Annu Rev Genomics Hum Genet 2008; 9:49-69. [PMID: 18949851 DOI: 10.1146/annurev.genom.9.081307.164224] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Arguably, the main challenge for contemporary genetics is to understand the function of every gene in a mammalian genome. The mouse has emerged as a model for this task because its genome can be manipulated in a number of ways to study gene function or mimic disease states. Two complementary genetic approaches can be used to generate mouse models. A reverse genetics or gene-driven approach (gene to phenotype) starts from a known gene and manipulates the genome to create genetically modified mice, such as knockouts. Alternatively, a forward genetics or phenotype-driven approach (phenotype to gene) involves screening mice for mutant phenotypes without previous knowledge of the genetic basis of the mutation. N-ethyl-N-nitrosourea (ENU) mutagenesis has been widely used for both approaches to generate mouse mutants. Here we review progress in ENU mutagenesis screening, with an emphasis on creating mouse models for human disorders.
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Catterall WA, Dib-Hajj S, Meisler MH, Pietrobon D. Inherited neuronal ion channelopathies: new windows on complex neurological diseases. J Neurosci 2008; 28:11768-77. [PMID: 19005038 PMCID: PMC3177942 DOI: 10.1523/jneurosci.3901-08.2008] [Citation(s) in RCA: 165] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 09/18/2008] [Accepted: 10/10/2008] [Indexed: 12/19/2022] Open
Abstract
Studies of genetic forms of epilepsy, chronic pain, and migraine caused by mutations in ion channels have given crucial insights into molecular mechanisms, pathogenesis, and therapeutic approaches to complex neurological disorders. Gain-of-function missense mutations in the brain type-I sodium channel Na(V)1.1 are a primary cause of generalized epilepsy with febrile seizures plus. Loss-of-function mutations in Na(V)1.1 channels cause severe myoclonic epilepsy of infancy, an intractable childhood epilepsy. Studies of a mouse model show that this disease is caused by selective loss of sodium current and excitability of GABAergic inhibitory interneurons, which leads to hyperexcitability, epilepsy, and ataxia. Mutations in the peripheral sodium channel Na(V)1.7 cause familial pain syndromes. Gain-of-function mutations cause erythromelalgia and paroxysmal extreme pain disorder as a result of hyperexcitability of sensory neurons, whereas loss-of-function mutations cause congenital indifference to pain because of attenuation of action potential firing. These experiments have defined correlations between genotype and phenotype in chronic pain diseases and focused attention on Na(V)1.7 as a therapeutic target. Familial hemiplegic migraine is caused by mutations in the calcium channel, Ca(V)2.1, which conducts P/Q-type calcium currents that initiate neurotransmitter release. These mutations increase activation at negative membrane potentials and increase evoked neurotransmitter release at cortical glutamatergic synapses. Studies of a mouse genetic model show that these gain-of-function effects lead to cortical spreading depression, aura, and potentially migraine. Overall, these experiments indicate that imbalance in the activity of excitatory and inhibitory neurons is an important underlying cause of these diseases.
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Affiliation(s)
- William A Catterall
- Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280, USA.
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Holland KD. SCN1A variant in a Scandinavian GEFS+ family: a wolf in sheep's clothing? Acta Neurol Scand 2008; 118:344-5; author reply 346. [PMID: 18616623 DOI: 10.1111/j.1600-0404.2008.01060.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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50
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Evaluation of SCN8A as a candidate gene for autosomal dominant essential tremor. Parkinsonism Relat Disord 2008; 15:321-3. [PMID: 18718804 DOI: 10.1016/j.parkreldis.2008.06.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Revised: 05/22/2008] [Accepted: 06/14/2008] [Indexed: 11/23/2022]
Abstract
OBJECTIVES Essential tremor (ET) is a common inherited movement disorder whose causes remain unknown. The presence of spontaneous tremor in murine mutants may provide clues into the pathogenesis of ET. SCN8A encodes the neuronal voltage gated sodium channel Na(v)1.6 that is widely expressed in the central nervous system. Several mutations of Scn8a in the mouse result in congenital postural tremor of the extremities and head. METHODS We screened SCN8A as a candidate gene in a cohort of 95 Caucasian patients with ET and a positive family history, including 48 patients with early onset in the first two decades of life. Early and adult onset ET subgroups did not differ in disease severity, but early onset patients had longer disease duration. Observed sequence variants were also screened in an ethnically matched control group. RESULTS We did not detect SCN8A mutations affecting amino acid sequence or splice sites in our cohort of ET patients. CONCLUSIONS Although mutations of Scn8a cause congenital tremor in mice, mutations in the sequence of the exons and splice sites of human SCN8A do not appear to be a common cause of autosomal dominant essential tremor in Caucasian patients.
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