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Abstract
Hyperekplexia is a rare disorder caused by autosomal dominant or recessive modes of inheritance and characterized by episodes of exaggerated startle. Five causative genes have been identified to date. The syndrome has been recognized for decades and due to its rarity, the literature contains mostly descriptive reports, many early studies lacking molecular genetic diagnoses. A spectrum of clinical severity exists. Severe cases can lead to neonatal cardiac arrest and death during an episode, an outcome prevented by early diagnosis and clinical vigilance. Large treatment studies are not feasible, so therapeutic measures continue to be empiric. A marked response to clonazepam is often reported but refractory cases exist. Herein we report the clinical course and treatment response of a severely affected infant homozygous for an SLC6A5 nonsense mutation and review the literature summarizing the history and genetic understanding of the disease as well as the described comorbidities and treatment options.
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2
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Chan KK, Cherk SWW, Lee HHC, Poon WT, Chan AYW. Hyperekplexia: a Chinese adolescent with 2 novel mutations of the GLRA1 gene. J Child Neurol 2014; 29:111-3. [PMID: 23143726 DOI: 10.1177/0883073812465338] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Hyperekplexia is a rare neurologic disorder, characterized by excessive startle response to unexpected stimuli. There are 3 cardinal features: generalized stiffness immediately after birth that normalizes during the first year of life; excessive startle reflex to unexpected (particularly auditory) stimuli; and a short period of generalized stiffness following the startle response while patient cannot elicit voluntary movements. Awareness of this condition will avoid misdiagnosis of disorders like epilepsy. Clonazepam is an effective medical treatment. We report a patient whose frequent falls triggered by sudden noise or tactile stimuli was initially misdiagnosed as epilepsy. The clinical diagnosis was subsequently revised to hyperekplexia and confirmed by mutation analysis of the GLRA1 gene, which showed c.497G>C (p.Cys166Ser) and c.526delG (p.Asp176Metfs*16). Both of them are novel mutations. His response to clonazepam is dramatic and has been able to engage in sports and social activities.
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3
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Hussain S, Prasad M, Rittey C, Desurkar A. A Startling Case of Neonatal Hyperekplexia Responsive to Levetiracetam: A New Alternative in Management? J Child Neurol 2013; 28:1513-1516. [PMID: 23034981 DOI: 10.1177/0883073812460094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The authors report a case of hyperekplexia presenting in the neonatal period resistant to clonazepam that responded subsequently to levetiracetam. Hyperekplexia is often misdiagnosed as epilepsy and can be difficult to manage with a particular concern over neonatal apnea and an increased risk of sudden infant death syndrome. The mainstay of therapy to date has been with clonazepam. The authors describe the salient features of their case, clinical diagnosis, and issues pertaining to management. The authors believe this is the first reported case of the use of levetiracetam for effectively treating hyperekplexia within the neonatal and infant period.
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Affiliation(s)
- Shanawaz Hussain
- 1Department of Pediatric Neurology, Sheffield Children's Hospital, Sheffield, UK
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4
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Dreissen YE, Bakker MJ, Koelman JH, Tijssen MA. Exaggerated startle reactions. Clin Neurophysiol 2012; 123:34-44. [DOI: 10.1016/j.clinph.2011.09.022] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2011] [Revised: 08/31/2011] [Accepted: 09/03/2011] [Indexed: 11/15/2022]
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5
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McAbee GN, Santilli AM, Stone J, Schnur RE. Ectodermal, skeletal, and genitourinary abnormalities with neonatal hyperekplexia. Pediatr Neurol 2011; 44:381-4. [PMID: 21481749 DOI: 10.1016/j.pediatrneurol.2010.12.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 12/01/2010] [Accepted: 12/27/2010] [Indexed: 10/18/2022]
Abstract
A new syndrome of the major form of hyperekplexia with neonatal onset is described. An infant manifested multisystem involvement with ectodermal anomalies, including lymphedema and double eyelashes (lymphedema-distichiasis syndrome), genitourinary anomalies, and skeletal dysplasia. Despite extensive genetic evaluation, no cytogenetic or molecular etiologies were identified. The literature was reviewed to assess other unusual neurologic and nonneurologic features that have been reported in association with neonatal-onset hyperekplexia-that is, hyperekplexia-plus syndromes.
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Affiliation(s)
- Gary N McAbee
- Division of Neurology, Department of Pediatrics, Robert Wood Johnson School of Medicine, and Children's Regional Hospital and Cooper University Hospital, Camden, New Jersey, USA.
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6
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Fine architecture and mutation mapping of human brain inhibitory system ligand gated ion channels by high-throughput homology modeling. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2011; 80:117-52. [PMID: 21109219 DOI: 10.1016/b978-0-12-381264-3.00004-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The common architecture of the brain inhibitory system ligand-gated ion-channels was examined at the level of each of the subunits and in their assembled pentameric arrangements. Structural modeling of the GABAA receptor, GlyR1, and the serotonin receptor, 5HTR3A, was carried out on a multi-homolog basis employing a high-throughput homology modeling pipeline. The locations of all the known mutations of each of the subunits of the receptor subfamily were mapped upon their computed structures and structural relationships between patterns of mutations in different subunits were identified, resulting in the zoning of mutations to four specific regions of the common subunit structure. These classifications may be of value in discerning probable molecular mechanisms and functional manifestations of emerging mutations and polymorphisms, providing the foundation for a family-specific predictive algorithm that may allow researchers to focus experimental effort on the most probable molecular indicators of compromised receptor function and disease mechanism.
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Nechay A, Stephenson JBP. Bath-induced paroxysmal disorders in infancy. Eur J Paediatr Neurol 2009; 13:203-8. [PMID: 18571948 DOI: 10.1016/j.ejpn.2008.04.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Revised: 04/17/2008] [Accepted: 04/18/2008] [Indexed: 11/28/2022]
Abstract
We reviewed those paroxysmal disorders of infancy and of the newborn in which the normal process of bathing may be an important trigger. We focused on infant bathing in normal temperature water (37 degrees C, range 36-38 degrees C) rather than in hot water that is above body temperature. Four principal diagnostic categories emerged: bathing epilepsy, alternating hemiplegia of childhood, hyperekplexia and paroxysmal extreme pain disorder. Bathing or water immersion epilepsy was the best studied and is arguably distinct from hot water epilepsy. The paroxysmal episodes previously attributed to aquagenic urticaria may have been examples of bathing epilepsy with a genetic component. Despite suggestions in the literature to the contrary, no convincing reports of bath-induced infantile syncope have been found. The underlying mechanisms of bath-induced paroxysmal disorders in infancy remain poorly understood, but all have autonomic manifestations and some if not all may be channelopathies.
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Affiliation(s)
- Alla Nechay
- Neurology Department, Paediatric Hospital, Kiev, Ukraine.
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8
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Peter A, Hansen ML, Merkl A, Voigtländer S, Bajbouj M, Danker-Hopfe H. REM sleep behavior disorder and excessive startle reaction to visual stimuli in a patient with pontine lesions. Sleep Med 2007; 9:697-700. [PMID: 18060836 DOI: 10.1016/j.sleep.2007.10.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 10/09/2007] [Indexed: 10/22/2022]
Affiliation(s)
- Anita Peter
- Charité Berlin, Interdisciplinary Sleep Lab of the Clinic and University Ambulance of Psychiatry and Psychotherapy, Eschenallee 3, 14050 Berlin, Germany.
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Eulenburg V, Becker K, Gomeza J, Schmitt B, Becker CM, Betz H. Mutations within the human GLYT2 (SLC6A5) gene associated with hyperekplexia. Biochem Biophys Res Commun 2006; 348:400-5. [PMID: 16884688 DOI: 10.1016/j.bbrc.2006.07.080] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Accepted: 07/07/2006] [Indexed: 11/28/2022]
Abstract
Hereditary hyperekplexia is a neuromotor disorder characterized by exaggerated startle reflexes and muscle stiffness in the neonate. The disease has been associated with mutations in the glycine receptor subunit genes GLRA1 and GLRB. Here, we describe mutations within the neuronal glycine transporter 2 gene (GLYT2, or SLC6A5, ) of hyperekplexia patients, whose symptoms cannot be attributed to glycine receptor mutations. One of the GLYT2 mutations identified causes truncation of the transporter protein and a complete loss of transport function. Our results are consistent with GLYT2 being a disease gene in human hyperekplexia.
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Affiliation(s)
- Volker Eulenburg
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60529 Frankfurt, Germany
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10
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Abstract
Startle syndromes consist of three heterogeneous groups of disorders with abnormal responses to startling events. The first is hyperekplexia, which can be split up into the "major" or "minor" form. The major form of hyperekplexia is characterised by excessive startle reflexes, startle-induced falls, and continuous stiffness in the neonatal period. This form has a genetic basis: mutations in the alpha1 subunit of the glycine receptor gene, GLRA1, or related genes. The minor form, which is restricted to excessive startle reflexes with no stiffness, has no known genetic cause or underlying pathophysiological substrate. The second group of startle syndromes are neuropsychiatric, in which excessive startling and various additional behavioural features occur. The third group are disorders in which startling stimuli can induce responses other than startle reflexes, such as startle-induced epilepsy. Diagnosis of startle syndromes depends on clinical history, electromyographic studies, and genetic screening. Further study of these disorders may enable improved discrimination between the different groups.
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Affiliation(s)
- Mirte J Bakker
- Department of Neurology, Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
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11
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Rees MI, Harvey K, Pearce BR, Chung SK, Duguid IC, Thomas P, Beatty S, Graham GE, Armstrong L, Shiang R, Abbott KJ, Zuberi SM, Stephenson JBP, Owen MJ, Tijssen MAJ, van den Maagdenberg AMJM, Smart TG, Supplisson S, Harvey RJ. Mutations in the gene encoding GlyT2 (SLC6A5) define a presynaptic component of human startle disease. Nat Genet 2006; 38:801-6. [PMID: 16751771 PMCID: PMC3204411 DOI: 10.1038/ng1814] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Accepted: 05/05/2006] [Indexed: 11/08/2022]
Abstract
Hyperekplexia is a human neurological disorder characterized by an excessive startle response and is typically caused by missense and nonsense mutations in the gene encoding the inhibitory glycine receptor (GlyR) alpha1 subunit (GLRA1). Genetic heterogeneity has been confirmed in rare sporadic cases, with mutations affecting other postsynaptic glycinergic proteins including the GlyR beta subunit (GLRB), gephyrin (GPHN) and RhoGEF collybistin (ARHGEF9). However, many individuals diagnosed with sporadic hyperekplexia do not carry mutations in these genes. Here we show that missense, nonsense and frameshift mutations in SLC6A5 (ref. 8), encoding the presynaptic glycine transporter 2 (GlyT2), also cause hyperekplexia. Individuals with mutations in SLC6A5 present with hypertonia, an exaggerated startle response to tactile or acoustic stimuli, and life-threatening neonatal apnea episodes. SLC6A5 mutations result in defective subcellular GlyT2 localization, decreased glycine uptake or both, with selected mutations affecting predicted glycine and Na+ binding sites.
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Affiliation(s)
- Mark I Rees
- School of Medicine, University of Wales Swansea, Singleton Park, West Glamorgan SA2 8PP, UK.
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12
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Betz H, Gomeza J, Armsen W, Scholze P, Eulenburg V. Glycine transporters: essential regulators of synaptic transmission. Biochem Soc Trans 2006; 34:55-8. [PMID: 16417482 DOI: 10.1042/bst0340055] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Glycine is a major inhibitory neurotransmitter in the mammalian CNS (central nervous system). Glycinergic neurotransmission is terminated by the uptake of glycine into glycinergic nerve terminals and neighbouring glial cells. This uptake process is mediated by specific Na+/Cl−-dependent GlyTs (glycine transporters), GlyT1 and GlyT2. GlyT1, in addition, is thought to regulate the concentration of glycine at excitatory synapses containing NMDARs (N-methyl-D-aspartate receptors), which require glycine as a co-agonist. We have analysed the physiological roles and regulation of GlyT1 and GlyT2 by generating transporter-deficient mice and searching for interacting proteins. Our genetic results indicate that at glycinergic synapses, the glial transporter GlyT1 catalyses the removal of glycine from the synaptic cleft, whereas GlyT2 is required for the re-uptake of glycine into nerve terminals, thereby allowing for neurotransmitter reloading of synaptic vesicles. Both GlyT1 and GlyT2 are essential for CNS function, as revealed by the lethal phenotypes of the respective knockout mice. Mice expressing only a single GlyT1 allele are phenotypically normal but may have enhanced NMDAR function. GlyT2 is highly enriched at glycinergic nerve terminals, and Ca2+-triggered exocytosis and internalization are thought to regulate GlyT2 numbers in the pre-synaptic plasma membrane. We have identified different interacting proteins that may play a role in GlyT2 trafficking and/or pre-synaptic localization.
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Affiliation(s)
- H Betz
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt, Germany.
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13
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Abstract
Glycine has multiple neurotransmitter functions in the central nervous system (CNS). In the spinal cord and brainstem of vertebrates, it serves as a major inhibitory neurotransmitter. In addition, it participates in excitatory neurotransmission by modulating the activity of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The extracellular concentrations of glycine are regulated by Na+/Cl(-)-dependent glycine transporters (GlyTs), which are expressed in neurons and adjacent glial cells. Considerable progress has been made recently towards elucidating the in vivo roles of GlyTs in the CNS. The generation and analysis of animals carrying targeted disruptions of GlyT genes (GlyT knockout mice) have allowed investigators to examine the different contributions of individual GlyT subtypes to synaptic transmission. In addition, they have provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors have been shown to modulate neurotransmission and might constitute promising therapeutic tools for the treatment of psychiatric and neurological disorders such as schizophrenia and pain. Therefore, pharmacological and genetic studies indicate that GlyTs are key regulators of both glycinergic inhibitory and glutamatergic excitatory neurotransmission. This chapter describes our present understanding of the functions of GlyTs and their involvement in the fine-tuning of neuronal communication.
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Affiliation(s)
- J Gomeza
- Department of Pharmacology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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14
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Eulenburg V, Armsen W, Betz H, Gomeza J. Glycine transporters: essential regulators of neurotransmission. Trends Biochem Sci 2005; 30:325-33. [PMID: 15950877 DOI: 10.1016/j.tibs.2005.04.004] [Citation(s) in RCA: 247] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Revised: 03/18/2005] [Accepted: 04/13/2005] [Indexed: 01/22/2023]
Abstract
Glycine has important neurotransmitter functions at inhibitory and excitatory synapses in the vertebrate central nervous system. The effective synaptic concentrations of glycine are regulated by glycine transporters (GlyTs), which mediate its reuptake into nerve terminals and adjacent glial cells. GlyTs are members of the Na(+)/Cl(-)-dependent transporter family, whose activities and subcellular distributions are regulated by phosphorylation and interactions with other proteins. The analysis of GlyT knockout mice has revealed distinct functions of individual GlyT subtypes in synaptic transmission and provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors could be of therapeutic value in cognitive disorders, schizophrenia and pain.
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Affiliation(s)
- Volker Eulenburg
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt, Germany
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15
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Harvey K, Duguid IC, Alldred MJ, Beatty SE, Ward H, Keep NH, Lingenfelter SE, Pearce BR, Lundgren J, Owen MJ, Smart TG, Lüscher B, Rees MI, Harvey RJ. The GDP-GTP exchange factor collybistin: an essential determinant of neuronal gephyrin clustering. J Neurosci 2004; 24:5816-26. [PMID: 15215304 PMCID: PMC6729214 DOI: 10.1523/jneurosci.1184-04.2004] [Citation(s) in RCA: 195] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Glycine receptors (GlyRs) and specific subtypes of GABA(A) receptors are clustered at synapses by the multidomain protein gephyrin, which in turn is translocated to the cell membrane by the GDP-GTP exchange factor collybistin. We report the characterization of several new variants of collybistin, which are created by alternative splicing of exons encoding an N-terminal src homology 3 (SH3) domain and three alternate C termini (CB1, CB2, and CB3). The presence of the SH3 domain negatively regulates the ability of collybistin to translocate gephyrin to submembrane microaggregates in transfected mammalian cells. Because the majority of native collybistin isoforms appear to harbor the SH3 domain, this suggests that collybistin activity may be regulated by protein-protein interactions at the SH3 domain. We localized the binding sites for collybistin and the GlyR beta subunit to the C-terminal MoeA homology domain of gephyrin and show that multimerization of this domain is required for collybistin-gephyrin and GlyR-gephyrin interactions. We also demonstrate that gephyrin clustering in recombinant systems and cultured neurons requires both collybistin-gephyrin interactions and an intact collybistin pleckstrin homology domain. The vital importance of collybistin for inhibitory synaptogenesis is underlined by the discovery of a mutation (G55A) in exon 2 of the human collybistin gene (ARHGEF9) in a patient with clinical symptoms of both hyperekplexia and epilepsy. The clinical manifestation of this collybistin missense mutation may result, at least in part, from mislocalization of gephyrin and a major GABA(A) receptor subtype.
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Affiliation(s)
- Kirsten Harvey
- Department of Pharmacology, The School of Pharmacy, London WC1N 1AX, United Kingdom.
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16
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Lerman-Sagie T, Watemberg N, Vinkler C, Fishhof J, Leshinsky-Silver E, Lev D. Familial hyperekplexia and refractory status epilepticus: a new autosomal recessive syndrome. J Child Neurol 2004; 19:522-5. [PMID: 15526957 DOI: 10.1177/08830738040190070801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Hyperekplexia is a rare disorder characterized by an exaggerated startle response to noise and handling and by neonatal hypertonia. It is predominantly an autosomal dominant disease; however, atypical cases with additional variable manifestations have been reported. We report a hitherto undescribed association of hyperekplexia and refractory status epilepticus in two siblings. Both children were born after an uneventful pregnancy to healthy unrelated Ashkenazi Jews. Both had increased startle and tone from birth and later became hypotonic. A metabolic evaluation, including a muscle biopsy, was normal. At the age of 18 months and 12 months, respectively, they developed status epilepticus refractory to all treatment that culminated in death. An autopsy in the girl did not reveal any brain pathology. The unusual association of hyperekplexia and refractory status epilepticus in both children suggests that this is a new autosomal recessive syndrome, possibly a channelopathy affecting both the brain and the spinal cord.
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Affiliation(s)
- Tally Lerman-Sagie
- Metabolic-Neuro-Genetic Clinic, Wolfson Medical Center, Holon, Israel 58100.
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17
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Ramanathan S, Woodroffe A, Flodman PL, Mays LZ, Hanouni M, Modahl CB, Steinberg-Epstein R, Bocian ME, Spence MA, Smith M. A case of autism with an interstitial deletion on 4q leading to hemizygosity for genes encoding for glutamine and glycine neurotransmitter receptor sub-units (AMPA 2, GLRA3, GLRB) and neuropeptide receptors NPY1R, NPY5R. BMC MEDICAL GENETICS 2004; 5:10. [PMID: 15090072 PMCID: PMC411038 DOI: 10.1186/1471-2350-5-10] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Accepted: 04/16/2004] [Indexed: 12/03/2022]
Abstract
Background Autism is a pervasive developmental disorder characterized by a triad of deficits: qualitative impairments in social interactions, communication deficits, and repetitive and stereotyped patterns of behavior. Although autism is etiologically heterogeneous, family and twin studies have established a definite genetic basis. The inheritance of idiopathic autism is presumed to be complex, with many genes involved; environmental factors are also possibly contributory. The analysis of chromosome abnormalities associated with autism contributes greatly to the identification of autism candidate genes. Case presentation We describe a child with autistic disorder and an interstitial deletion on chromosome 4q. This child first presented at 12 months of age with developmental delay and minor dysmorphic features. At 4 years of age a diagnosis of Pervasive Developmental Disorder was made. At 11 years of age he met diagnostic criteria for autism. Cytogenetic studies revealed a chromosome 4q deletion. The karyotype was 46, XY del 4 (q31.3-q33). Here we report the clinical phenotype of the child and the molecular characterization of the deletion using molecular cytogenetic techniques and analysis of polymorphic markers. These studies revealed a 19 megabase deletion spanning 4q32 to 4q34. Analysis of existing polymorphic markers and new markers developed in this study revealed that the deletion arose on a paternally derived chromosome. To date 33 genes of known or inferred function are deleted as a consequence of the deletion. Among these are the AMPA 2 gene that encodes the glutamate receptor GluR2 sub-unit, GLRA3 and GLRB genes that encode glycine receptor subunits and neuropeptide Y receptor genes NPY1R and NPY5R. Conclusions The deletion in this autistic subject serves to highlight specific autism candidate genes. He is hemizygous for AMPA 2, GLRA3, GLRB, NPY1R and NPY5R. GluR2 is the major determinant of AMPA receptor structure. Glutamate receptors maintain structural and functional plasticity of synapses. Neuropeptide Y and its receptors NPY1R and NPY5R play a role in hippocampal learning and memory. Glycine receptors are expressed in very early cortical development. Molecular cytogenetic studies and DNA sequence analysis in other patients with autism will be necessary to confirm that these genes are involved in autism.
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Affiliation(s)
| | - Abigail Woodroffe
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - Pamela L Flodman
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - Lee Z Mays
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - Mona Hanouni
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - Charlotte B Modahl
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | | | - Maureen E Bocian
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - M Anne Spence
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
| | - Moyra Smith
- Department of Pediatrics, University of California, Irvine; Irvine, CA, USA
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Gomeza J, Ohno K, Hülsmann S, Armsen W, Eulenburg V, Richter DW, Laube B, Betz H. Deletion of the mouse glycine transporter 2 results in a hyperekplexia phenotype and postnatal lethality. Neuron 2004; 40:797-806. [PMID: 14622583 DOI: 10.1016/s0896-6273(03)00673-1] [Citation(s) in RCA: 232] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The glycine transporter subtype 2 (GlyT2) is localized in the axon terminals of glycinergic neurons. Mice deficient in GlyT2 are normal at birth but during the second postnatal week develop a lethal neuromotor deficiency that resembles severe forms of human hyperekplexia (hereditary startle disease) and is characterized by spasticity, tremor, and an inability to right. Histological and immunological analyses failed to reveal anatomical or biochemical abnormalities, but the amplitudes of glycinergic miniature inhibitory currents (mIPSCs) were strikingly reduced in hypoglossal motoneurons and dissociated spinal neurons from GlyT2-deficient mice. Thus, postnatal GlyT2 function is crucial for efficient transmitter loading of synaptic vesicles in glycinergic nerve terminals, and the GlyT2 gene constitutes a candidate disease gene in human hyperekplexia patients.
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MESH Headings
- Amino Acid Transport Systems, Neutral/deficiency
- Amino Acid Transport Systems, Neutral/genetics
- Animals
- Animals, Newborn
- Brain Stem/growth & development
- Brain Stem/metabolism
- Brain Stem/physiopathology
- Disease Models, Animal
- Fetus
- Gene Deletion
- Genes, Lethal/genetics
- Glycine/metabolism
- Glycine Plasma Membrane Transport Proteins
- Heredodegenerative Disorders, Nervous System/genetics
- Heredodegenerative Disorders, Nervous System/metabolism
- Heredodegenerative Disorders, Nervous System/physiopathology
- Hypoglossal Nerve/metabolism
- Hypoglossal Nerve/physiopathology
- Mice
- Mice, Knockout
- Motor Neurons/metabolism
- Neural Inhibition/genetics
- Organ Culture Techniques
- Phenotype
- Presynaptic Terminals/metabolism
- Reflex, Startle/genetics
- Synaptic Transmission/genetics
- Synaptic Vesicles/metabolism
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Affiliation(s)
- Jesús Gomeza
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt, Germany
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19
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Affiliation(s)
- Peter Brown
- Sobell Department of Neurophysiology, Institute of Neurology, London, United Kingdom.
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20
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Chapter 30 Hyperekplexia. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s1567-4231(09)70178-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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21
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Tijssen MAJ, Vergouwe MN, van Dijk JG, Rees M, Frants RR, Brown P. Major and minor form of hereditary hyperekplexia. Mov Disord 2002; 17:826-30. [PMID: 12210885 DOI: 10.1002/mds.10168] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Hyperekplexia is a hereditary neurological disorder characterized by excessive startle responses. Within the disorder two clinical forms can be distinguished. The major form is characterized by continuous generalized stiffness in the first year of life and an exaggerated startle reflex, accompanied by temporary generalized stiffness and falls, whereas in the minor form only excessive startle and hypnic jerks have been described. Mutations in the gene encoding the alpha-1 subunit of the glycine receptor (GLRA1) are responsible for the major form of hyperekplexia but no mutation was detected in patients with the minor form in the large Dutch pedigree originally described by Suhren and colleagues. Here we describe the genetic analysis of the GLRA1 gene of two English families in which both forms of hyperekplexia were present. Mutation analysis revealed no genetic defect in the GLRA1 gene in patients carrying either the minor or major forms. This is further evidence that the minor form of hyperekplexia is seldom due to a genetic defect in the GLRA1 gene.
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Affiliation(s)
- Marina A J Tijssen
- Department of Neurology, Amsterdam Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
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22
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Abstract
Hyperekplexia (startle disease) is a rare non-epileptic disorder characterised by an exaggerated persistent startle reaction to unexpected auditory, somatosensory and visual stimuli, generalised muscular rigidity, and nocturnal myoclonus. The genetic basis is a mutation usually of the arginine residue 271 leading to neuronal hyperexcitability by impairing glycinergic inhibition. Hyperekplexia is usually familial, most often autosomal dominant with complete penetrance and variable expression. It can present in fetal life as abnormal intrauterine movements, or later at any time from the neonatal period to adulthood. Early manifestations include abnormal responses to unexpected auditory, visual, and somatosensory stimuli such as sustained tonic spasm, exaggerated startle response, and fetal posture with clenched fists and anxious stare. The tonic spasms may mimic generalised tonic seizures, leading to apnoea and death. Consistent generalised flexor spasm in response to tapping of the nasal bridge (without habituation) is the clinical hallmark of hyperekplexia. Electroencephalography may show fast spikes initially during the tonic spasms, followed by slowing of background activity with eventual flattening corresponding to the phase of apnoea bradycardia and cyanosis. Electromyography shows a characteristic almost permanent muscular activity with periods of electrical quietness. Nerve conduction velocity is normal. No specific computed tomography findings have been reported yet. Clonazepam, a gamma aminobutyric acid (GABA) receptor agonist, is the treatment of choice for hypertonia and apnoeic episodes. It, however, may not influence the degree of stiffness significantly. A simple manoeuvre like forced flexion of the head and legs towards the trunk is known to be life saving when prolonged stiffness impedes respiration.
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Affiliation(s)
- V Praveen
- Department of Neonatology, Kirwan Hospital for Women, Townsville, QLD 4817, Australia
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David-Watine B. The human gephyrin (GPHN) gene: structure, chromosome localization and expression in non-neuronal cells. Gene 2001; 271:239-45. [PMID: 11418245 DOI: 10.1016/s0378-1119(01)00511-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Gephyrin was first described as a peripheral membrane protein of 93 kDa anchoring the glycine receptor (GlyR) to subsynaptic microtubules and cytoskeleton. Analysis of knock-out mice demonstrated that gephyrin has additional functions in GABA(A) receptor localization at the synapse and in the biosynthetic pathway of the molybdenum cofactor (Moco). Here we describe a human non-neuronal gephyrin cDNA and the exon/intron organization of the human gephyrin gene. We found the coding region to consist of 27 exons and to span approximately 800 kb on the long arm of chromosome 14. This structure is almost identical to that of the mouse gephyrin gene except that sequences corresponding to three exons described in rat and mouse could not be identified in human. Mutations of the GlyR subunits and of gephyrin lead to severe neuromotor phenotypes in human and mouse. Hyperekplexia involves most frequently a mutation in the GlyR alpha1 subunit in humans. However, inactivation of the Moco biosynthesis pathway results in very similar symptomatology. The recent characterization of a deletion of two exons of the gephyrin gene in a patient with symptoms typical of Moco deficiency confirmed that the involvement of gephyrin in these pathologies cannot be excluded. The precise localization of the gephyrin gene allowed us to exclude it from being a candidate for the autosomal dominant spastic paraplegia, the locus of which maps to 14q between markers D14S259 and D14S1018. A description of its structure and exon boundaries should lay the groundwork for further analysis of its expression in humans.
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Affiliation(s)
- B David-Watine
- Laboratoire de Biologie Cellulaire et Moléculaire du Neurone, INSERM U-261, Institut Pasteur, 25, rue du Dr Roux, 75724 Paris Cedex 15, France.
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24
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Affiliation(s)
- M A Koning-Tijssen
- Department of Neurology, Academic Medical Center, University of Amsterdam, The Netherlands
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25
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Vergouwe MN, Tijssen MA, Peters AC, Wielaard R, Frants RR. Hyperekplexia phenotype due to compound heterozygosity for GLRA1 gene mutations. Ann Neurol 1999; 46:634-8. [PMID: 10514101 DOI: 10.1002/1531-8249(199910)46:4<634::aid-ana12>3.0.co;2-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Hyperekplexia (MIM 149400), or startle disease, is a neurological disorder characterized by generalized stiffness during the neonatal period, excessive startle reflexes, and generalized stiffness related to the startle response. Linkage analysis mapped a major gene for this disorder to chromosome 5q33-35. Subsequently, mutations in the GLRA1 gene, encoding the alpha1 subunit of the glycine receptor, were found in hyperekplexia families with an autosomal dominant or recessive inheritance pattern. In the present study, we describe the genetic analysis of the GLRA1 gene of a family consisting of 2 children with hyperekplexia, 2 nonaffected children, and their healthy nonconsanguineous parents. Although the pedigree suggested the presence of a recessive mutation, haplotype construction showed that the 2 affected children shared the same haplotype combination in which the maternal haplotype differed from the paternal haplotype, suggesting the presence of compound heterozygosity. Mutation analysis revealed different missense mutations on the two haplotypes, changing an arginine to a histidine at amino acid positions 252 and 392, respectively. It is interesting that the hyperekplexia phenotype was only seen in individuals compound heterozygous for the two mutations, whereas family members carrying either one of the two mutations had no clinical signs.
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Affiliation(s)
- M N Vergouwe
- Department of Human Genetics, Medical Genetics Center South-West Netherlands, Leiden
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26
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Abstract
Inborn errors of neurotransmitter receptors are recently described gene mutations that directly affect receptor function. Currently three conditions are known to be caused by this mechanism: hyperekplexia; two forms of congenital inherited myasthenic syndromes; and autosomal dominant nocturnal frontal lobe epilepsy. Here, neurotransmitters, their receptors and known inborn errors of receptor function are reviewed.
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Affiliation(s)
- R Surtees
- Institute of Child Health (UCLMS), London, UK
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Betz H, Kuhse J, Schmieden V, Laube B, Kirsch J, Harvey RJ. Structure and functions of inhibitory and excitatory glycine receptors. Ann N Y Acad Sci 1999; 868:667-76. [PMID: 10414351 DOI: 10.1111/j.1749-6632.1999.tb11343.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The strychnine-sensitive glycine receptor (GlyR) is a pentameric chloride channel protein that exists in several developmentally and regionally regulated isoforms in the CNS. These result from the differential expression of four genes encoding different variants (alpha 1-alpha 4) of the ligand-binding subunit of the GlyR. Their assembly with the structural beta subunit is governed by "assembly cassettes" within the extracellular domains of these proteins and creates chloride channels of distinct conductance properties. GlyR gating is potentiated by Zn2+, a metal ion co-released with different neurotransmitters. Site-directed mutagenesis has unraveled major determinants of agonist binding and Zn2+ potentiation. During development, glycine receptors mediate excitation that results in Ca2+ influx and neurotransmitter release. Ca2+ influx triggered by the activation of embryonic GlyRs is required for the synaptic localization of the GlyR and its anchoring protein gepyhrin. In the adult, mutations in GlyR-subunit genes result in motor disorders. The spastic and spasmodic phenotypes in mouse as well as human hereditary startle disease will be discussed.
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Affiliation(s)
- H Betz
- Max-Planck-Institut für Hirnforschung, Abteilung Neurochemie, Frankfurt am Main, Germany.
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