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Uchino K, Kawano H, Tanaka Y, Adaniya Y, Asahara A, Deshimaru M, Kubota K, Watanabe T, Katsurabayashi S, Iwasaki K, Hirose S. Inhibitory synaptic transmission is impaired at higher extracellular Ca 2+ concentrations in Scn1a +/- mouse model of Dravet syndrome. Sci Rep 2021; 11:10634. [PMID: 34017040 PMCID: PMC8137694 DOI: 10.1038/s41598-021-90224-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 05/07/2021] [Indexed: 12/17/2022] Open
Abstract
Dravet syndrome (DS) is an intractable form of childhood epilepsy that occurs in infancy. More than 80% of all patients have a heterozygous abnormality in the SCN1A gene, which encodes a subunit of Na+ channels in the brain. However, the detailed pathogenesis of DS remains unclear. This study investigated the synaptic pathogenesis of this disease in terms of excitatory/inhibitory balance using a mouse model of DS. We show that excitatory postsynaptic currents were similar between Scn1a knock-in neurons (Scn1a+/- neurons) and wild-type neurons, but inhibitory postsynaptic currents were significantly lower in Scn1a+/- neurons. Moreover, both the vesicular release probability and the number of inhibitory synapses were significantly lower in Scn1a+/- neurons compared with wild-type neurons. There was no proportional increase in inhibitory postsynaptic current amplitude in response to increased extracellular Ca2+ concentrations. Our study revealed that the number of inhibitory synapses is significantly reduced in Scn1a+/- neurons, while the sensitivity of inhibitory synapses to extracellular Ca2+ concentrations is markedly increased. These data suggest that Ca2+ tethering in inhibitory nerve terminals may be disturbed following the synaptic burst, likely leading to epileptic symptoms.
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Affiliation(s)
- Kouya Uchino
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Hiroyuki Kawano
- Research Institute for the Molecular Pathogeneses of Epilepsy, Fukuoka University, Fukuoka, Japan
| | - Yasuyoshi Tanaka
- Research Institute for the Molecular Pathogeneses of Epilepsy, Fukuoka University, Fukuoka, Japan
| | - Yuna Adaniya
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Ai Asahara
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Masanobu Deshimaru
- Research Institute for the Molecular Pathogeneses of Epilepsy, Fukuoka University, Fukuoka, Japan
| | - Kaori Kubota
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Takuya Watanabe
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Shutaro Katsurabayashi
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan.
- Research Institute for the Molecular Pathogeneses of Epilepsy, Fukuoka University, Fukuoka, Japan.
| | - Katsunori Iwasaki
- Department of Neuropharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, 814-0180, Japan
| | - Shinichi Hirose
- Research Institute for the Molecular Pathogeneses of Epilepsy, Fukuoka University, Fukuoka, Japan
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan
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Hirose S, Tanaka Y, Shibata M, Kimura Y, Ishikawa M, Higurashi N, Yamamoto T, Ichise E, Chiyonobu T, Ishii A. Application of induced pluripotent stem cells in epilepsy. Mol Cell Neurosci 2020; 108:103535. [DOI: 10.1016/j.mcn.2020.103535] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 07/10/2020] [Accepted: 07/31/2020] [Indexed: 02/06/2023] Open
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Surguchov A, Surgucheva I, Sharma M, Sharma R, Singh V. Pore-Forming Proteins as Mediators of Novel Epigenetic Mechanism of Epilepsy. Front Neurol 2017; 8:3. [PMID: 28149289 PMCID: PMC5241277 DOI: 10.3389/fneur.2017.00003] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Accepted: 01/04/2017] [Indexed: 01/07/2023] Open
Abstract
Epilepsy is a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures. In the last two decades, numerous gene defects underlying different forms of epilepsy have been identified with most of these genes encoding ion channel proteins. Despite these developments, the etiology of majority of non-familial epilepsies has no known associated genetic mutations and cannot be explained by defects in identified ion channels alone. We hypothesize that de novo formation of ion channels by naturally unfolded proteins (NUPs) increases neuronal excitability. Altered ionic homeostasis may initiate/contribute to cellular cascades related to epileptogenesis in susceptible individuals. Here, we consider two small proteins, namely, α-synuclein and stefin B, as prototypical candidates to illustrate the underlying mechanism(s). Previous work points to an association between epilepsy and α-synuclein or stefin B, but the mechanism(s) underlying such association remains elusive. We review the evidence to link the structure-function of these proteins with disease processes. Epigenetic mechanisms unrelated to altered DNA sequence(s) that may affect epileptogenesis include transcriptional or posttranscriptional regulation. Such epigenetic mechanisms or their combination(s) enhance the levels of these proteins and as a result the ability to form annular structures, which upon incorporation into membrane form novel ion channels and disturb intracellular ion homeostasis. Alternative epigenetic mechanisms may change amyloidogenic proteins by posttranslational modifications, thereby increasing their propensity to form channels. Further research elucidating the details about the formation of ion channels through these mechanisms and their role in epileptogenesis may define new molecular targets and guide the development of new drug targets.
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Affiliation(s)
- Andrei Surguchov
- Department of Neurology, Kansas University Medical Center, Kansas City, KS, USA
| | - Irina Surgucheva
- Department of Neurology, Kansas University Medical Center, Kansas City, KS, USA
| | - Mukut Sharma
- Kansas City Veterans Administration Medical Center, Kansas City, MO, USA
- Midwest Biomedical Research Foundation, Kansas City, MO, USA
| | - Ram Sharma
- Kansas City Veterans Administration Medical Center, Kansas City, MO, USA
| | - Vikas Singh
- Department of Neurology, Kansas University Medical Center, Kansas City, KS, USA
- Kansas City Veterans Administration Medical Center, Kansas City, MO, USA
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Abstract
The γ-aminobutyric acid receptor type A (GABAA receptor) is a ligand-gated chloride channel that mediates major inhibitory functions in the central nervous system. GABAA receptors function mainly as pentamers containing α, β, and either γ or δ subunits. A number of antiepileptic drugs have agonistic effects on GABAA receptors. Hence, dysfunctions of GABAA receptors have been postulated to play important roles in the etiology of epilepsy. In fact, mutations or genetic variations of the genes encoding the α1, α6, β2, β3, γ2, or δ subunits (GABRA1, GABRA6, GABRB2, GABRB3, GABRG2, and GABRD, respectively) have been associated with human epilepsy, both with and without febrile seizures. Epilepsy resulting from mutations is commonly one of following, genetic (idiopathic) generalized epilepsy (e.g., juvenile myoclonic epilepsy), childhood absence epilepsy, genetic epilepsy with febrile seizures, or Dravet syndrome. Recently, mutations of GABRA1, GABRB2, and GABRB3 were associated with infantile spasms and Lennox-Gastaut syndrome. These mutations compromise hyperpolarization through GABAA receptors, which is believed to cause seizures. Interestingly, most of the insufficiencies are not caused by receptor gating abnormalities, but by complex mechanisms, including endoplasmic reticulum (ER)-associated degradation, nonsense-mediated mRNA decay, intracellular trafficking defects, and ER stress. Thus, GABAA receptor subunit mutations are now thought to participate in the pathomechanisms of epilepsy, and an improved understanding of these mutations should facilitate our understanding of epilepsy and the development of new therapies.
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Computational models of epilepsy. Seizure 2012; 21:748-59. [DOI: 10.1016/j.seizure.2012.08.012] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2012] [Revised: 08/29/2012] [Accepted: 08/29/2012] [Indexed: 11/23/2022] Open
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Ishii A, Miyajima T, Kurahashi H, Wang JW, Yasumoto S, Kaneko S, Hirose S. KCNQ2 abnormality in BECTS: benign childhood epilepsy with centrotemporal spikes following benign neonatal seizures resulting from a mutation of KCNQ2. Epilepsy Res 2012; 102:122-5. [PMID: 22884718 DOI: 10.1016/j.eplepsyres.2012.07.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 07/08/2012] [Indexed: 11/19/2022]
Abstract
The molecular pathogenesis of benign childhood epilepsy with centrotemporal spikes (BECTS) remains unclear whereas mutations of the KCNQ2 and KCNQ3 genes have been identified as causes of benign familial neonatal convulsions. We report here a girl with benign neonatal convulsions followed by BECTS, for whom a mutation of KCNQ2 was identified. This case may provide the clue to the understanding of the molecular pathogenesis of BECTS.
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Affiliation(s)
- Atsushi Ishii
- Department of Pediatrics, Fukuoka University, Fukuoka, Japan
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Affiliation(s)
- Manuel Castro-Gago
- Servicio de Neuropediatría, Hospital Clínico Universitario, Facultad de Medicina, Universidad de Santiago de Compostela Santiago de Compostela, Spain
| | - Laura Pérez-Gay
- Servicio de Neuropediatría, Hospital Clínico Universitario, Facultad de Medicina, Universidad de Santiago de Compostela Santiago de Compostela, Spain
| | - Jesús Eirís-Puñal
- Servicio de Neuropediatría, Hospital Clínico Universitario, Facultad de Medicina, Universidad de Santiago de Compostela Santiago de Compostela, Spain
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Ishii A, Zhang B, Kaneko S, Hirose S. Positive association between benign familial infantile convulsions and LGI4. Brain Dev 2010; 32:538-43. [PMID: 19815358 DOI: 10.1016/j.braindev.2009.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Revised: 09/04/2009] [Accepted: 09/07/2009] [Indexed: 11/25/2022]
Abstract
PURPOSE LGI4 is located in 19q13.11, where the locus of benign familial infantile convulsions (BFIC) has been mapped. LGI4 belongs to a family of proteins with the epilepsy-associated repeat (EAR) domain and is associated with various epilepsies. We investigated whether LGI4 is a candidate gene for BFIC. METHODS Fifteen patients with BFIC were examined for mutations and/or polymorphisms of LGI4 by using a direct sequencing method. RESULTS Several frequent polymorphisms were identified. The genotype frequency distribution of c.1722G/A polymorphism was significantly different between patients with BFIC and control subjects (p<0.05). Logistic regression analysis showed that the G allele of c.1722G/A polymorphism had significant recessive effects on the increased relative risk for BFIC (p<0.05). There was no association between c.1722G/A polymorphism and benign familial neonatal convulsion, an epilepsy phenotype similar to BFIC but genetically distinguished from BFIC. DISCUSSION The positive genotypic association between BFIC and c.1722G/A polymorphism suggests that LGI4 might contribute to the susceptibility to BFIC.
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Affiliation(s)
- Atsushi Ishii
- Department of Pediatrics, School of Medicine, Fukuoka University, Jonanku, Fukuoka, Japan
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9
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Ishii A, Fukuma G, Uehara A, Miyajima T, Makita Y, Hamachi A, Yasukochi M, Inoue T, Yasumoto S, Okada M, Kaneko S, Mitsudome A, Hirose S. A de novo KCNQ2 mutation detected in non-familial benign neonatal convulsions. Brain Dev 2009; 31:27-33. [PMID: 18640800 DOI: 10.1016/j.braindev.2008.05.010] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Revised: 05/12/2008] [Accepted: 05/23/2008] [Indexed: 11/17/2022]
Abstract
BACKGROUND The underlying genetic abnormalities of rare familial idiopathic epilepsy have been identified, such as mutation in KCNQ2, a K(+) channel gene. Yet, few genetic abnormalities have been reported for commoner epilepsy, i.e., sporadic idiopathic epilepsy, which share a phenotype similar to those of familial epilepsy. OBJECTIVE To search for the genetic cause of seizures in a girl with the diagnosis of non-familial benign neonatal convulsions, and define the consequence of the genetic abnormality identified. METHODS Genetic abnormality was explored within candidate genes for benign familial neonatal and infantile convulsions, such as KCNQ2, 3, 5, KCNE2, SCN1A and SCN2A. The electrophysiological properties of the channels harboring the identified mutation were examined. Western blotting and immunostaining were employed to characterize the expression and intracellular localization of the mutant channel molecules. RESULTS A novel heterozygous mutation (c.910-2delTTC or TTT, Phe304del) of KCNQ2 was identified in the patient. The mutation was de novo verified by parentage analysis. The mutation was associated with impaired functions of KCNQ K(+) channel. The mutant channels were expressed on the cell surface. CONCLUSION The mutant Phe304del of KCNQ2 leads to null function of the KCNQ K(+) channel but the mutation does not alter proper channel sorting onto the cell membrane. Our findings indicate that the genes responsible for rare inherited forms of idiopathic epilepsy could be also involved in sporadic forms of idiopathic epilepsy and expand our notion of the involvement of molecular mechanisms in the more common forms of idiopathic epilepsy.
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Affiliation(s)
- Atsushi Ishii
- Department of Pediatrics, School of Medicine, Fukuoka University, 45-1, 7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
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Curatolo P, Moavero R, Castro AL, Cerminara C. Pharmacotherapy of idiopathic generalized epilepsies. Expert Opin Pharmacother 2008; 10:5-17. [DOI: 10.1517/14656560802618647] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Neal J, Apse K, Sahin M, Walsh CA, Sheen VL. Deletion of chromosome 1p36 is associated with periventricular nodular heterotopia. Am J Med Genet A 2007; 140:1692-5. [PMID: 16835933 DOI: 10.1002/ajmg.a.31334] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Jason Neal
- Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115, USA
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12
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Hirose S. A new paradigm of channelopathy in epilepsy syndromes: Intracellular trafficking abnormality of channel molecules. Epilepsy Res 2006; 70 Suppl 1:S206-17. [PMID: 16860540 DOI: 10.1016/j.eplepsyres.2005.12.007] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2005] [Revised: 12/01/2005] [Accepted: 12/01/2005] [Indexed: 10/24/2022]
Abstract
Mutations in genes encoding ion channels in brain neurons have been identified in various epilepsy syndromes. In neuronal networks, "gain-of-function" of channels in excitatory neurotransmission could lead to hyper-excitation while "loss-of-function" in inhibitory transmission impairs neuronal inhibitory system, both of which can result in epilepsy. A working hypothesis to view epilepsy as a disorder of channel or "channelopathy" seems rational to explore the pathogenesis of epilepsy. However, the imbalance resulting from channel dysfunction is not sufficient to delineate the pathogenesis of all epilepsy syndromes of which the underlying channel abnormalities have been verified. Mutations identified in epilepsy, mainly in genes encoding subunits of GABA(A) receptors, undermine intracellular trafficking, thus leading to retention of channel molecules in the endoplasmic reticulum (ER). This process may cause ER stress followed by apoptosis, which is a known pathomechanism of certain neurodegenerative disorders. Thus, the pathomechanism of "channel trafficking abnormality" may provide a new paradigm to channelopathy to unsolved questions underlying epilepsy, such as differences between generalized epilepsy with febrile seizures plus and severe myoclonic epilepsy in infancy, which share the causative genetic abnormalities in the same genes and hence are so far considered to be within the spectrum of one disease entity or allelic variants.
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Affiliation(s)
- Shinichi Hirose
- Department of Pediatrics, Fukuoka University, 45-1,7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
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Urak L, Feucht M, Fathi N, Hornik K, Fuchs K. A GABRB3 promoter haplotype associated with childhood absence epilepsy impairs transcriptional activity. Hum Mol Genet 2006; 15:2533-41. [PMID: 16835263 DOI: 10.1093/hmg/ddl174] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Childhood absence epilepsy (CAE) is considered to exhibit a complex non-Mendelian pattern of inheritance. So far, only few CAE susceptibility genes have been identified. In a previous study of our group, an association between the GABA(A) receptor beta3 subunit (GABRB3) gene and CAE was shown. To further investigate this association, we screened 45 CAE patients of the first study for mutations in the 10 exons, the exon-intron boundaries and the regulatory sequences of GABRB3. Although we found no functionally relevant mutation, we did identify 13 single nucleotide polymorphisms (SNPs) in the GABRB3 gene region from the exon 1a promoter to the beginning of intron 3. Using these SNPs we defined four haplotypes for the respective GABRB3 gene region. A transmission disequilibrium test in the same 45 CAE patients and their parents indicated a significant association of this region and CAE (P=0.007075). Reporter gene assays in NT2 cells using exon 1a promoter constructs indicated that the disease-associated haplotype 2 promoter causes a significantly lower transcriptional activity than the haplotype 1 promoter that is over-represented in the controls. In silico analysis suggested that an exchange from T (haplotype 1) to C (haplotype 2) within this promoter impairs binding of the neuron-specific transcriptional activator N-Oct-3. Electrophoretic mobility shift assays demonstrated that the respective polymorphism reduces the nuclear protein binding affinity, thus explaining the results of the reporter gene assays. Reduced expression of the GABRB3 gene could therefore be one potential cause for the development of CAE, pathogenetically relevant in our patient group.
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Affiliation(s)
- Lydia Urak
- Division of Biochemistry and Molecular Biology, Center for Brain Research, Medical University of Vienna, Spitalgasse 4, 1090 Vienna, Austria
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Coppola G, Veggiotti P, Del Giudice EM, Bellini G, Longaretti F, Taglialatela M, Pascotto A. Mutational scanning of potassium, sodium and chloride ion channels in malignant migrating partial seizures in infancy. Brain Dev 2006; 28:76-9. [PMID: 16168594 DOI: 10.1016/j.braindev.2005.05.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 04/24/2005] [Accepted: 05/02/2005] [Indexed: 10/25/2022]
Abstract
The mutational analysis of potassium (KCNQ2, KCNQ3), sodium (SCN1A, SCN2A), and chloride (CLCN2) ion channels was performed in three children with typical features of the recently described syndrome of migrating partial seizures in infancy. Mutational analysis was performed by PCR and automatic sequencing. The coding regions, including the exon-intron boundaries, were amplified in the patients using appropriate primers sets. No mutations associated to migrating partial seizures have been found. Mutational screening of CLCN2 gene, revealed a homozygous mutation G2003C (exon 17), leading to a Ser/Thr substitution at the codon 668, in two of the three patients. The same variation has been found in 38 out of 100 control alleles. The identification of the genetic basis of this new epileptic encephalopathy requires further studies that might be enforced by familial cases.
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Affiliation(s)
- Giangennaro Coppola
- Department of Pediatrics, Clinic of Child and Adolescent Neuropsychiatry, Second University of Naples, Naples, Italy.
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Kurosawa K, Kawame H, Okamoto N, Ochiai Y, Akatsuka A, Kobayashi M, Shimohira M, Mizuno S, Wada K, Fukushima Y, Kawawaki H, Yamamoto T, Masuno M, Imaizumi K, Kuroki Y. Epilepsy and neurological findings in 11 individuals with 1p36 deletion syndrome. Brain Dev 2005; 27:378-82. [PMID: 16023556 DOI: 10.1016/j.braindev.2005.02.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2003] [Revised: 02/10/2005] [Accepted: 02/10/2005] [Indexed: 12/08/2022]
Abstract
The 1p36 deletion syndrome is a newly delineated multiple congenital anomalies/mental retardation syndrome characterized by mental retardation, growth delay, epilepsy, congenital heart defects, characteristic facial appearance, and precocious puberty. We analyzed 11 patients by fluorescence in situ hybridization (FISH) using commercially available bacterial artificial chromosome and P1-derived artificial chromosome genomic clones to define the chromosomal deletion responsible for the 1p36 deletion syndrome. Cytogenetic investigation revealed two cases with a terminal deletion of 1p36. Nine patients had an apparently normal karyotype with standard G-bands by trypsin using Giemsa (GTG), but FISH screening with the highly polymorphic genetic marker D1Z2, which is mapped to 1p36.3 and contains an unusual reiterated 40-bp variable number tandem repeat, revealed a submicroscopic deletion. All patients had severe to profound mental retardation. Based on the University of California Santa Cruz Genome Browser, we constructed a deletion map and analyzed the relationship between neurological findings and chromosomal deletions for the 11 cases. Six cases had intractable epilepsy and three had no seizures. The common deletion interval was about 1 million base pairs (Mbp) located between RP11-82D16 and RP4-785P20 (Rho guanine exchange factor (GEF) 16). The severity of clinical symptoms correlates with the size of the deletion. This is demonstrated by the 3 patients with at least 8Mbp deletions that display profound mental retardation and congenital heart defects. Although haploinsufficiency of the potassium channel beta-subunit (KCNAB2) is thought to be responsible for intractable seizures in the 1p36 deletion syndrome, this was not the case for 3 of the 11 patients in this study. Further investigation of the 1p36 region is necessary to allow identification of genes responsible for the 1p36 deletion syndrome.
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Affiliation(s)
- Kenji Kurosawa
- Division of Medical Genetics, Clinical Research Institute, Kanagawa Children's Medical Center, Yokohama, Kanagawa 232-8555, Japan.
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Pineda-Trujillo N, Carrizosa J, Cornejo W, Arias W, Franco C, Cabrera D, Bedoya G, Ruíz-Linares A. A novel SCN1A mutation associated with severe GEFS+ in a large South American pedigree. Seizure 2005; 14:123-8. [PMID: 15694566 DOI: 10.1016/j.seizure.2004.12.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Generalized epilepsy with febrile seizures plus (GEFS+) is an inherited epileptic syndrome with a marked clinical and genetic heterogeneity. Here we report the molecular characterization of a large pedigree with a severe clinical form of GEFS+. Genetic linkage analysis implied the involvement of the FEB3 in the disease phenotype of this family (parametric two-point lod-score of 2.2). Sequencing of the SCN1A gene revealed a novel aspartic acid for glycine substitution at position 1742 of this sodium channel subunit. The amino-acid replacement lies in the pore-forming region of domain IV of SCN1A. Our observations are consistent with the genotype-phenotype correlation studies suggesting that mutations in the pore-forming loop of SCN1A can lead to a clinically more severe epileptic syndrome.
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Affiliation(s)
- N Pineda-Trujillo
- Grupo de Genetica Molecular, Facultad de Medicina, Universidad de Antioquia, Medellin-Colombia; The Galton Laboratory, University College London, UK
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Faisal AA, White JA, Laughlin SB. Ion-Channel Noise Places Limits on the Miniaturization of the Brain’s Wiring. Curr Biol 2005; 15:1143-9. [PMID: 15964281 DOI: 10.1016/j.cub.2005.05.056] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2005] [Revised: 05/09/2005] [Accepted: 05/10/2005] [Indexed: 11/20/2022]
Abstract
The action potential (AP) is transmitted by the concerted action of voltage-gated ion channels. Thermodynamic fluctuations in channel proteins produce probabilistic gating behavior, causing channel noise. Miniaturizing signaling systems increases susceptibility to noise, and with many cortical, cerebellar, and peripheral axons <0.5 mum diameter [1, 2 and 3], channel noise could be significant [4 and 5]. Using biophysical theory and stochastic simulations, we investigated channel-noise limits in unmyelinated axons. Axons of diameter below 0.1 microm become inoperable because single, spontaneously opening Na channels generate spontaneous AP at rates that disrupt communication. This limiting diameter is relatively insensitive to variations in biophysical parameters (e.g., channel properties and density, membrane conductance and leak) and will apply to most spiking axons. We demonstrate that the essential molecular machinery can, in theory, fit into 0.06 microm diameter axons. However, a comprehensive survey of anatomical data shows a lower limit for AP-conducting axons of 0.08-0.1 microm diameter. Thus, molecular fluctuations constrain the wiring density of brains. Fluctuations have implications for epilepsy and neuropathic pain because changes in channel kinetics or axonal properties can change the rate at which channel noise generates spontaneous activity.
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Affiliation(s)
- A Aldo Faisal
- Department of Zoology, University of Cambridge, Downing Street, CB2 3EJ Cambridge, United Kingdom.
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18
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Abstract
PURPOSE To search for clues to molecular genetics of common idiopathic epilepsy syndromes. Genetic defects have been identified recently in certain inherited epilepsy syndromes in which the phenotypes are similar to those of common idiopathic epilepsies. METHODS Mutations identified as the causes of inherited idiopathic epilepsies were reviewed. RESULTS Mutations of the genes encoding two subunits of the neuronal nicotinic acetylcholine receptor were found in autosomal dominant nocturnal frontal lobe epilepsy. Mutations of two K(+)-channel genes were identified in benign familial neonatal convulsions. Mutations of the genes encoding several subunits of the voltage-gated Na(+)-channel and gamma-aminobutyric acid (GABA)(A) receptor also were identified as the underlying causes of various epilepsy syndromes, such as autosomal dominant epilepsy with febrile seizures plus, benign familial neonatal infantile seizures, and autosomal dominant juvenile myoclonic epilepsy. Mutations within the same gene may result in different epilepsy phenotypes. Thus, the Na(+) channel, GABA(A) receptor, and their auxiliaries may be involved in the pathogenesis of various types of epilepsy. Some forms of juvenile myoclonic epilepsy, idiopathic generalized epilepsy, and absence epilepsy may result from mutations of Ca(2+) channels. Mutations of the Cl(-) channel have been recently found to be associated with a certain type of epilepsy. The recent discovery that mutations of LGI1, a gene encoding a nonchannel molecule, are associated with autosomal partial epilepsy with auditory features may provide a new insight into our understanding of the genetics of idiopathic epilepsy. CONCLUSIONS These findings suggest the involvement of brain channelopathies in the pathogenesis of certain types of idiopathic epilepsy.
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Affiliation(s)
- Shinichi Hirose
- Department of Pediatrics, School of Medicine, Fukuoka University, Fukuoka, Japan.
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Abstract
Idiopathic generalized epilepsy (IGE) syndromes are diseases that are characterized by absence, myoclonic, and/or primary generalized tonic-clonic seizures in the absence of structural brain abnormalities. Although it was long hypothesized that IGE had a genetic basis, only recently have causative genes been identified. Here we review mutations in the GABA(A) receptor alpha1, gamma2, and delta subunits that have been associated with different IGE syndromes. These mutations affect GABA(A) receptor gating, expression, and/or trafficking of the receptor to the cell surface, all pathophysiological mechanisms that result in neuronal disinhibition and thus predispose affected patients to seizures.
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Affiliation(s)
- Robert L Macdonald
- Department of Neurology, Vanderbilt University, 6140 Medical Research Building III, 465 21st Ave Nashville, TN 37232-8552, USA.
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Wakamoto H, Hayashi M, Nagao H, Morimoto T, Kida K. Clinical investigation of genetic contributions to childhood-onset epilepsies and epileptic syndromes. Brain Dev 2004; 26:184-9. [PMID: 15030907 DOI: 10.1016/s0387-7604(03)00124-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2003] [Revised: 06/16/2003] [Accepted: 06/18/2003] [Indexed: 11/22/2022]
Abstract
Although there have been major advances in the understanding of the molecular bases of certain inherited epilepsy syndromes, clinical studies are still needed to verify the possible genetic contributions to common epilepsies. We examined the proportions of positive family histories of epilepsy (within second-degree relatives) and consanguinity (within first-degree relatives) in 311 probands with childhood-onset epilepsy, and found that they had high family history rates of epilepsy (19.3%) and consanguinity (6.1%). A positive family history of epilepsy was found more in probands with generalized epilepsy than in ones with localization-related epilepsy, and more in probands with idiopathic/cryptogenic epilepsy than in ones with symptomatic epilepsy. However, on analysis after the symptomatic epilepsies had been divided into two categories, probands with pre- or perinatal symptomatic generalized epilepsy and ones with postnatal symptomatic localization-related epilepsy showed high positive family history rates, similar to ones with idiopathic/cryptogenic epilepsy. On the other hand, a positive family history of consanguinity was noted more in probands with generalized epilepsy than in ones with localization-related epilepsy, but there was no significant difference between probands with idiopathic/cryptogenic epilepsy and ones with symptomatic epilepsy. These findings suggest that in addition to the hereditary effect on idiopathic/cryptogenic epilepsy, a genetic susceptibility may contribute to the development of pre- or perinatal symptomatic generalized epilepsy, and to that of postnatal symptomatic localization-related epilepsy. Furthermore, a genetic predisposition seems to have an influence through consanguinity on the etiologies of both idiopathic/cryptogenic and symptomatic generalized epilepsies.
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Affiliation(s)
- Hiroyuki Wakamoto
- Department of Pediatrics, Ehime Prefecture Niihama Hospital, 3-1-1 Hongo, Niihama City, Ehime 792-0042, Japan
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Fukuma G, Oguni H, Shirasaka Y, Watanabe K, Miyajima T, Yasumoto S, Ohfu M, Inoue T, Watanachai A, Kira R, Matsuo M, Muranaka H, Sofue F, Zhang B, Kaneko S, Mitsudome A, Hirose S. Mutations of Neuronal Voltage-gated Na+ Channel alpha1 Subunit Gene SCN1A in Core Severe Myoclonic Epilepsy in Infancy (SMEI) and in Borderline SMEI (SMEB). Epilepsia 2004; 45:140-8. [PMID: 14738421 DOI: 10.1111/j.0013-9580.2004.15103.x] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PURPOSE Severe myoclonic epilepsy in infancy (SMEI) is a distinct epilepsy syndrome. Patients with borderline SMEI (SMEB) are a subgroup with clinical features similar to those of core SMEI but are not necessarily consistent with the accepted diagnostic criteria for core SMEI. The aim of this study was to delineate the genetic correlation between core SMEI and SMEB and to estimate the frequency of mutations in both phenotypes. METHODS We examined 96 healthy volunteers and 58 unrelated individuals whose clinical features were consistent with either core SMEI (n = 31) or SMEB (n = 27). We screened for genetic abnormalities within exons and their flanking introns of the genes encoding major subunits of the Na+ channels (SCN1A, SCN2A, SCN1B, and SCN2B) by using a direct sequencing method. RESULTS In both core SMEI and SMEB, various mutations of SCN1A including nonsense and missense mutations were identified, whereas no mutations of SCN2A, SCN1B, and SCN2B were found within the regions examined. All mutations were heterozygous and not found in 192 control chromosomes. Mutations were identified in 26 (44.8%) of the 58 individuals and were more frequent (p < 0.05) in core SMEI (19 of 31) than in SMEB (seven of 27), as assessed by the continuity-adjusted chi2 test. Mutations resulting in a molecular truncation were found only in core SMEI. Among the mutations, two missense mutations were found in both core SMEI and SMEB. CONCLUSIONS Our findings confirm that SMEB is part of the SMEI spectrum and may expand the recognition of SMEI and suggest other responsible or modifying genes.
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Affiliation(s)
- Goryu Fukuma
- Department of Pediatrics, Fukuoka University, Japan
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23
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Duffy S, Nguyen PV, Baker GB. Phenylethylidenehydrazine, a novel GABA-transaminase inhibitor, reduces epileptiform activity in rat hippocampal slices. Neuroscience 2004; 126:423-32. [PMID: 15207360 DOI: 10.1016/j.neuroscience.2004.03.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/09/2004] [Indexed: 11/28/2022]
Abstract
Phenylethylidenehydrazine (PEH), an analog of the monoamine oxidase inhibitor, beta-phenylethylhydrazine (phenelzine), inhibits the gamma-aminobutyric acid (GABA) catabolic enzyme GABA-transaminase and increases brain levels of GABA. GABA is the predominant fast inhibitory transmitter counteracting glutamatergic excitation, and increased neural GABA could influence a wide range of synaptic and circuit properties under both physiologic and pathophysiologic conditions. To examine the scope of these effects, we applied PEH (or vehicle) to rat hippocampal slices and measured basal glutamatergic transmission, synaptic plasticity, and epileptiform activity using extracellular field and whole cell patch clamp recordings. In vitro pre-treatment with PEH (100 microM) increased the GABA content of hippocampal slices by approximately 60% over vehicle-treated controls, but it had no effect on basal field excitatory postsynaptic potentials, tonic GABA currents, paired-pulse facilitation, or long-term potentiation. In contrast, pre-incubation with PEH caused a dose- and time-dependent reduction in epileptiform burst frequency induced by superfusion with Mg2+-free or high-K+ artificial cerebrospinal fluid. Thus, the inhibitory effects of PEH are state-dependent: hyper-excitation during epileptiform bursting was reduced, whereas synaptic transmission and plasticity were unaffected.
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Affiliation(s)
- S Duffy
- Department of Physiology, University of Alberta, Edmonton, Canada
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24
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Bolander FF. Molecular Bases of Endocrinopathies. Mol Endocrinol 2004. [DOI: 10.1016/b978-012111232-5/50017-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Abstract
Febrile seizures (FS) may represent the most common seizure disorder in childhood and are known to be associated with putative genetic predispositions. Nevertheless, molecular genetic approaches toward understanding FS have been just initiated this decade. Recently, several genetic loci for FS have been mapped thereby assuring the genetic heterogeneity of FS. However, the exact molecular mechanisms of FS are yet to be elucidated. Genetic defects have been recently identified in autosomal dominant epilepsy with FS plus or generalized epilepsy with FS plus. The underlying mutations were found in genes encoding several Na+ channel subunits and the gamma2 subunit of gamma amino-butyric acid (GABA)A receptors in the brain. Furthermore, both channels are also associated with severe myoclonic epilepsy in infancy, where the seizure attacks often begin with prolonged FS and are precipitated by fever even afterwards. Na+ channels are associated with other temperature-sensitive disorders, and GABA(A) receptors are known to play an important role in the pathogenesis of FS. These lines of evidence suggest the involvement of various Na+ channels, GABA(A) receptors and additional auxiliary proteins in the pathogenesis of frequent FS and even in simple FS. This hypothesis may facilitate our understanding of the genetic background of FS.
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Affiliation(s)
- Shinichi Hirose
- Department of Pediatrics, School of Medicine, Fukuoka University, 45-1, 7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
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26
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Abstract
Mental retardation (MR) and epilepsy are both heterogeneous syndromes based on dysfunction in the brain and they are often closely associated. Hence, there should be some overlap in the underlying pathomechanisms, particularly when both syndromes result from genetic abnormalities, either polygenic or monogenic. Some 50 monogenic causes of MR have been found in genes localized on the X-chromosome and are responsible for X-linked MR. In contrast, monogenic causes of about 30 epilepsy syndromes are transmitted as an autosomal trait. Early this year, an X-chromosome-linked, Aristaless-related, homeobox gene, ARX, was found to be associated with both X-linked MR and epilepsy. The epilepsy phenotypes included West syndrome and other epilepsy phenotypes, indicating the genetic basis of the X-linked West syndrome. Another report implied that the ARX molecule plays a crucial role in cognitive function. These findings provide solid evidence for the relationship between MR and epilepsy at a molecular level, opening a new avenue for understanding the pathogeneses of MR associated with epilepsy.
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Affiliation(s)
- Shinichi Hirose
- Department of Pediatrics, School of Medicine, Fukuoka University, 45-1, 7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
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Ito M, Nagafuji H, Okazawa H, Yamakawa K, Sugawara T, Mazaki-Miyazaki E, Hirose S, Fukuma G, Mitsudome A, Wada K, Kaneko S. Autosomal dominant epilepsy with febrile seizures plus with missense mutations of the (Na+)-channel alpha 1 subunit gene, SCN1A. Epilepsy Res 2002; 48:15-23. [PMID: 11823106 DOI: 10.1016/s0920-1211(01)00313-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Evidence that febrile seizures have a strong genetic predisposition has been well documented. In families of probands with multiple febrile convulsions, an autosomal dominant inheritance with reduced penetrance is suspected. Four candidate loci for febrile seizures have been suggested to date; FEB1 on 8q13-q21, FEB2 on 19p, FEB3 on 2q23-q24, and FEB4 on 5q14-15. A missense mutation was identified in the voltage-gated sodium (Na(+))-channel beta 1 subunit gene, SCN1B at chromosome 19p13.1 in generalized epilepsy with the febrile seizures plus type 1 (GEFS+1) family. Several missense mutations of the (Na(+))-channel alpha 1 subunit (Nav1.1) gene, SCN1A were also identified in GEFS+2 families at chromosome 2q23-q24.3. The aim of this report is precisely to describe the phenotypes of Japanese patients with novel SCN1A mutations and to reevaluate the entity of GEFS+. Four family members over three generations and one isolated (phenotypically sporadic) case with SCN1A mutations were clinically investigated. The common seizure type in these patients was febrile and afebrile generalized tonic-clonic seizures (FS+). In addition to FS+, partial epilepsy phenotypes were suspected in all affected family members and electroencephalographically confirmed in three patients of two families. GEFS+ is genetically and clinically heterogeneous, and associated with generalized epilepsy and partial epilepsy as well. The spectrum of GEFS+ should be expanded to include partial epilepsies and better to be termed autosomal dominant epilepsy with febrile seizures plus (ADEFS+).
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Affiliation(s)
- M Ito
- Department of Pediatrics, Shiga Medical Center for Children, 5-7-30 Moriyama, Moriyama 524-0022, Japan.
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