A child with hyperekplexia and epileptic myoclonus

Hyperekplexia is a rare neurogenetic disorder characterized by startle. Accurate diagnosis of this notorious mimicker of epilepsy is important to prevent life‐threatening apnoea. We report a novel case of concomitant GLRA1‐related hyperkeplexia and myoclonic epilepsy. A toddler with daily paroxysms of head drops and falls presented with epileptic myoclonus on EEG, however, whole‐exome sequencing revealed hyperekplexia‐related GLRA1 mutation. The boy eventually developed spells induced by noise and surprise. All his spells remitted upon treatment with clonazepam. Paediatricians and paediatric neurologists should be aware of this possible mixed presentation in order to appropriately tailor medication regimens and treatment goals. [Published with video sequence on www.epilepticdisorders.com ].     

Nomenclature of Genetically Determined Myoclonus Syndromes: Recommendations of the International Parkinson and Movement Disorder Society Task Force

Genetically determined myoclonus disorders are a result of a large number of genes. They have wide clinical variation and no systematic nomenclature. With next‐generation sequencing, genetic diagnostics require stringent criteria to associate genes and phenotype. To improve (future) classification and recognition of genetically determined movement disorders, the Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders (2012) advocates and renews the naming system of locus symbols. Here, we propose a nomenclature for myoclonus syndromes and related disorders with myoclonic jerks (hyperekplexia and myoclonic epileptic encephalopathies) to guide clinicians in their diagnostic approach to patients with these disorders. Sixty‐seven genes were included in the nomenclature. They were divided into 3 subgroups: prominent myoclonus syndromes, 35 genes; prominent myoclonus syndromes combined with another prominent movement disorder, 9 genes; disorders that present usually with other phenotypes but can manifest as a prominent myoclonus syndrome, 23 genes. An additional movement disorder is seen in nearly all myoclonus syndromes: ataxia (n = 41), ataxia and dystonia (n = 6), and dystonia (n = 5). However, no additional movement disorders were seen in related disorders. Cognitive decline and epilepsy are present in the vast majority. The anatomical origin of myoclonus is known in 64% of genetic disorders: cortical (n = 34), noncortical areas (n = 8), and both (n = 1). Cortical myoclonus is commonly seen in association with ataxia, and noncortical myoclonus is often seen with myoclonus‐dystonia. This new nomenclature of myoclonus will guide diagnostic testing and phenotype classification. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.     

Visually evoked startle response in a patient with epilepsy: a case report and review of the literature

Both symptomatic and genetic, cases with hyperekplexia or startle seizures induced by acoustic stimuli, are previously reported. By contrast, startle response induced by visual stimuli is rare. While visual stimuli are more commonly associated with startle seizures, here we present an 11-year-old girl with epilepsy, motor-mental retardation, and spastic tetraparesis, who had repetitive startle responses by photic stimulation during the electroencephalogram recording, without any spike-and-wave discharges associated with the startles. We report this unique case with startle responses induced both by acoustic and photic stimuli and review the literature related to this exceptionally rare combination of symptoms.     

Identification of a de novo Lys304Gln mutation in the glycine receptor α‐1 subunit gene in a Korean infant with hyperekplexia

Startle disease or hyperekplexia (STHE; MIM 149400) is a rare disorder that is characterized by marked muscular hypertonia in infancy and an exaggerated startle response to unexpected acoustic or tactile stimuli. Mutations in the gene encoding the α‐1 subunit of the inhibitory glycine receptor (GLRA1) were reported as causes of STHE. Recently, we encountered a Korean male infant with generalized stiffness that was observed from the first 3 days of life. The abnormal startle response was evident from the fourth week of life, and he showed marked improvement in the startle response and muscle hypertonia after being administered phenobarbital and clonazepam. Direct sequencing analysis of the infant and his parents revealed a de novo variation (c.910A>C) in the GLRA1 gene, resulting in a novel Lys304Gln missense mutation. © 2007 Movement Disorder Society     

Building new function into glycine receptors: a structural model for the activation of the glycine-gated chloride channel

1. The glycine receptor chloride channel mediates inhibitory neurotransmission and is a member of the ligand-gated ion channel superfamily, which includes the nicotinic acetylcholine receptor channel. 2. Activation of these channels involves a movement of the pore-lining second membrane-spanning domain with respect to the remainder of the protein. 3. The present review considers the evidence that the loops that connect this domain with the rest of the protein act as crucial components of the channel activation mechanism.     

Transient neuromotor phenotype in transgenic spastic mice expressing low levels of glycine receptor beta-subunit: an animal model of startle disease

Startle disease or hereditary hyperekplexia has been shown to result from mutations in the alpha1-subunit gene of the inhibitory glycine receptor (GlyR). In hyperekplexia patients, neuromotor symptoms generally become apparent at birth, improve with age, and often disappear in adulthood. Loss-of-function mutations of GlyR alpha or beta-subunits in mice show rather severe neuromotor phenotypes. Here, we generated mutant mice with a transient neuromotor deficiency by introducing a GlyR beta transgene into the spastic mouse (spa/spa), a recessive mutant carrying a transposon insertion within the GlyR beta-subunit gene. In spa/spa TG456 mice, one of three strains generated with this construct, which expressed very low levels of GlyR beta transgene-dependent mRNA and protein, the spastic phenotype was found to depend upon the transgene copy number. Notably, mice carrying two copies of the transgene showed an age-dependent sensitivity to tremor induction, which peaked at approximately 3-4 weeks postnatally. This closely resembles the development of symptoms in human hyperekplexia patients, where motor coordination significantly improves after adolescence. The spa/spa TG456 line thus may serve as an animal model of human startle disease.     

过度惊吓反应症临床及遗传学特征（附６例报告）

目的　分析6例过度惊吓反应症患儿的临床及遗传学特征。 方法　对2011年6月至2018年5月于北京大学第一医院诊断的6例过度惊吓反应症患儿的临床表现、诊治过程、脑电图（EEG）及神经影像学、遗传学结果等进行分析。 结果　6例中男5例、女1例。6例均为新生儿早期起病，均可因不经意的听觉或触觉刺激诱发过度惊跳反应和全身僵硬症状，3例曾出现短暂窒息发作，1例曾惊吓后摔倒致外伤。6例点鼻反射均阳性，4例合并疝。EEG示1例正常，5例为不典型放电或一过性异常。4例曾行头颅磁共振检查未见明显异常。经遗传学分析，6例中3例携带GLRA1基因杂合突变，2例携带GLRB基因复合杂合突变，1例经全外显子测序未发现基因突变。6例给予氯硝西泮治疗， 1例全身僵硬及过度惊吓反应均基本消失， 5例全身僵硬症状消失、偶有惊跳反应。6例智力发育均正常，2例存在宽基底步态状行走姿势。1例有相同症状而窒息死亡的明确家族史。 结论　过度惊吓反应症具有典型临床表现，点鼻反射阳性，可行基因诊断确诊。该病对氯硝西泮有良好的治疗反应。早期经临床诊断及基因确诊，及时、恰当治疗，对于改善预后至关重要。     

Magnetic resonance spectroscopy of cerebral cortex is normal in hereditary hyperekplexia due to mutations in the GLRA1 gene.

Excessive startling and stiffness in hereditary hyperekplexia has been attributed to lack of inhibition at either the cortical or brainstem level. Six patients with hereditary hyperekplexia (HH) and a confirmed mutation in the gene encoding the alpha(1) subunit of the glycine receptor (GLRA1) underwent single voxel (1)H magnetic resonance spectroscopy (MRS) of the brainstem and an area of frontal cortex and white matter using a method that allows absolute quantification of metabolites. The results of MRS were within normal limits, although there was a tendency for the neuronal marker N-acetyl aspartate to be reduced in the brainstem of patients compared with that in controls. Thus, we found no evidence to support a deficit in the cerebral cortex in patients with hereditary hyperekplexia due to mutations in the GLRA1 gene.     

过度惊吓反应症临床及遗传学特征（附６例报告）

目的　分析6例过度惊吓反应症患儿的临床及遗传学特征。 方法　对2011年6月至2018年5月于北京大学第一医院诊断的6例过度惊吓反应症患儿的临床表现、诊治过程、脑电图（EEG）及神经影像学、遗传学结果等进行分析。 结果　6例中男5例、女1例。6例均为新生儿早期起病,均可因不经意的听觉或触觉刺激诱发过度惊跳反应和全身僵硬症状,3例曾出现短暂窒息发作,1例曾惊吓后摔倒致外伤。6例点鼻反射均阳性,4例合并疝。EEG示1例正常,5例为不典型放电或一过性异常。4例曾行头颅磁共振检查未见明显异常。经遗传学分析,6例中3例携带GLRA1基因杂合突变,2例携带GLRB基因复合杂合突变,1例经全外显子测序未发现基因突变。6例给予氯硝西泮治疗, 1例全身僵硬及过度惊吓反应均基本消失, 5例全身僵硬症状消失、偶有惊跳反应。6例智力发育均正常,2例存在宽基底步态状行走姿势。1例有相同症状而窒息死亡的明确家族史。 结论　过度惊吓反应症具有典型临床表现,点鼻反射阳性,可行基因诊断确诊。该病对氯硝西泮有良好的治疗反应。早期经临床诊断及基因确诊,及时、恰当治疗,对于改善预后至关重要。