Article

A Longer Polyalanine Expansion Mutation in the ARX Gene Causes Early Infantile Epileptic Encephalopathy with Suppression-Burst Pattern (Ohtahara Syndrome)

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Abstract

Early infantile epileptic encephalopathy with suppression-burst pattern (EIEE) is one of the most severe and earliest forms of epilepsy, often evolving into West syndrome; however, the pathogenesis of EIEE remains unclear. ARX is a crucial gene for the development of interneurons in the fetal brain, and a polyalanine expansion mutation of ARX causes mental retardation and seizures, including those of West syndrome, in males. We screened the ARX mutation and found a hemizygous, de novo, 33-bp duplication in exon 2, 298_330dupGCGGCA(GCG)9, in two of three unrelated male patients with EIEE. This mutation is thought to expand the original 16 alanine residues to 27 alanine residues (A110_A111insAAAAAAAAAAA) in the first polyalanine tract of the ARX protein. Although EIEE is mainly associated with brain malformations, ARX is the first gene found to be responsible for idiopathic EIEE. Our observation that EIEE had a longer expansion of the polyalanine tract than is seen in West syndrome is consistent with the findings of earlier onset and more-severe phenotypes in EIEE than in West syndrome.

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... This group of disorders is genetically heterogenous. In individuals with EIEE, mutations have been identified in several genes including sodium channel, neuronal type a1 subunit (SCN1A) (Marini et al., 2009), syntaxin binding protein 1 (STXBP1) (Saitsu et al., 2008), Aristaless related homeobox (ARX) (Kato et al., 2007), cyclindependent kinase-like 5 (CDKL5) (Nemos et al., 2009), solute carrier family 25 member 22 (SLC25A22) (Molinari et al., 2009), and others (Tavyev Asher and Scaglia, 2012). Recently, mutations in KCNQ2 as a cause of EIEE have received attention (Kato et al., 2007). ...
... In individuals with EIEE, mutations have been identified in several genes including sodium channel, neuronal type a1 subunit (SCN1A) (Marini et al., 2009), syntaxin binding protein 1 (STXBP1) (Saitsu et al., 2008), Aristaless related homeobox (ARX) (Kato et al., 2007), cyclindependent kinase-like 5 (CDKL5) (Nemos et al., 2009), solute carrier family 25 member 22 (SLC25A22) (Molinari et al., 2009), and others (Tavyev Asher and Scaglia, 2012). Recently, mutations in KCNQ2 as a cause of EIEE have received attention (Kato et al., 2007). In many cases of EIEE genetic cause remains unknown. ...
... This group of disorders is genetically heterogenous. In individuals with EIEE, mutations have been identified in several genes including sodium channel, neuronal type a1 subunit (SCN1A) (Marini et al., 2009), syntaxin binding protein 1 (STXBP1) (Saitsu et al., 2008), Aristaless related homeobox (ARX) (Kato et al., 2007), cyclindependent kinase-like 5 (CDKL5) (Nemos et al., 2009), solute carrier family 25 member 22 (SLC25A22) (Molinari et al., 2009), and others (Tavyev Asher and Scaglia, 2012). Recently, mutations in KCNQ2 as a cause of EIEE have received attention (Kato et al., 2007). ...
... In individuals with EIEE, mutations have been identified in several genes including sodium channel, neuronal type a1 subunit (SCN1A) (Marini et al., 2009), syntaxin binding protein 1 (STXBP1) (Saitsu et al., 2008), Aristaless related homeobox (ARX) (Kato et al., 2007), cyclindependent kinase-like 5 (CDKL5) (Nemos et al., 2009), solute carrier family 25 member 22 (SLC25A22) (Molinari et al., 2009), and others (Tavyev Asher and Scaglia, 2012). Recently, mutations in KCNQ2 as a cause of EIEE have received attention (Kato et al., 2007). In many cases of EIEE genetic cause remains unknown. ...
... Rare, monogenetic, neurodevelopmental disorders in which seizures constitute a major co-morbidity include Rett syndrome (Glaze, 2005;Tarquinio et al., 2017), Cyclin-Dependent Kinase-Like 5 (CDKL5) deficiency disorder (Fehr et al., 2016), Fragile-X syndrome (Kidd et al., 2014), and different forms of both Dravet syndrome (Archer et al., 2006;Berry-Kravis, 2002;Evans et al., 2005) and Ohtahara syndrome (Beal et al., 2012). Patients with any of these rare conditions often do not display a single or even common types of seizures, however, but rather can display a multitude of different seizure types that include focal, multi-focal, or generalized seizures (Crino et al., 2002;Glaze et al., 1998;Kato et al., 2007;Musumeci et al., 1999). In many cases, individual patients can display multiple different seizure types. ...
... OS can originate from different genetic causes, as several single gene mutations have been identified as sufficient to be causal in different patients. While the search for additional genetic causes continues, mutations occurring within the autosomal syntaxin-binding protein 1 gene (STXBP1), the X-linked aristaless related homeobox (ARX) gene, the autosomal a2 subunit of the voltagegated sodium channel (SCN2A), and the autosomal voltage-gated potassium channel subfamily Q member 2 (KCNQ2) genes are now recognized individual causes for OS (Eks ßiog˘lu et al., 2011;Kato et al., 2007;Nakamura et al., 2013;Otsuka et al., 2010;Saitsu et al., 2012aSaitsu et al., ,b, 2010. ...
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Genetic neurodevelopmental disorders that often include epilepsy as part of their phenotype are a heterogeneous and clinically challenging spectrum of disorders in children. Although seizures often contribute significantly to morbidity in these affected populations, the mechanisms of epileptogenesis in these conditions remain poorly understood. Different model systems have been developed to aid unraveling these mechanisms, which include a number of specific mutant mouse lines which genocopy specific general types of mutations present in patients. These mouse models have not only allowed assessments of behavioral and electrographic seizure phenotypes to be ascertained, but also have allowed effects on the neurodevelopmental alterations and cognitive impairments associated with these disorders to be examined. In addition, these models play a role in advancing our understanding of these epileptic processes and developing preclinical therapeutics. The concordance of seizure phenotypes - in a select group of rare, genetic, neurodevelopmental disorders and epileptic encephalopathies - found between human patients and their model counterparts will be summarized. This review aims to assess whether models of Rett syndrome, CDKL5 deficiency disorder, Fragile-X syndrome, Dravet syndrome, and Ohtahara syndrome phenocopy the seizures seen in human patients.
... Although originally not considered to have a genetic connection, several genes have since been associated. Ohtahara syndrome can be associated with mutations in ARX (aristaless related homeobox) (Kato et al., 2007), CDKL5 (cyclin-dependent kinase-like 5), SLC25A22 (solute carrier family 25 (mitochondrial carrier: glutamate), member 22), STXBP1 (Syntaxin binding protein 1) (Saitsu et al., 2012), SPTAN1 (spectrin, alpha, non-erythrocytic 1), KCNQ2 (potassium voltage-gated channel, KQT-like subfamily, member 2), ARHGEF9 (Cdc42 guanine nucleotide exchange factor (GEF) 9), PCDH19 (protocadherin 19), PNKP (polynucleotide kinase 3'-phosphatase), SCN2A (sodium channel, voltage-gated, type II, alpha subunit), PLCB1 (phospholipase C, beta 1 (phosphoinositide-specific)), SCN8A (sodium channel, voltage gated, type VIII, alpha subunit) (OMIM 308350, 300203, 609302, 602926, 182810, 602235, 300429). ...
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Genetic findings in several epilepsy syndromes provide insights into the pathophysiology of specific subtypes of epilepsy and into mechanisms of epileptogenesis, because the genes encoding ion channels, and proteins associated to the vesical synaptic cycle, or involved in energy metabolism, influence neuronal excitability. The following aspects of genetic epilepsies will be discussed: new proposed “organization of the epilepsies”, genetic and other etiologies, electroclinical syndromes and their genetics and genetic testing in the epilepsies. The updated review is based on OMIM™ (Online Mendelian Inheritance in Man). Because of the vast genetic and phenotypic heterogeneity, bridging genotype and phenotype remains a major challenge in epilepsy genetics. The so-called “idiopathic” epilepsies are genetically determined. The new ILAE proposal on the “organization” of the epilepsies takes into account the genetic advances. However, despite proposed changes in the nomenclature, the concept of the electroclinical syndrome, i.e. seizure types, age-dependent onset, electroencephalographic criteria, and concomitant symptoms, such as movement disorders or developmental delay, remain important criteria to group the epilepsies. Although also the differentiation “generalized” versus “focal” is nowadays discussed critically, for practical reasons these categories remain valid. Similarly the categories “benign” syndromes of early childhood, epileptic encephalopathies, and fever-associated syndromes, have their utility. The large number of genetic defects in the epilepsies complicates their analysis. However, it is anticipated that novel genetic methods, that are able to analyze all known genes at a reasonable price, will help identify novel diagnostic and therapeutic avenues, including prognostic and genetic counseling. Today it is already possible to include into genetic testing genes responsible for the side effects of AEDs. In addition, for some epilepsy phenotypes it has became possible to predict the most efficacious antiepileptic drugs for patients based on their genetic makeup. Thus, the development of individualized medicine is expected to greatly improve the management of epilepsy patients.
... Prior to his death, his DQ indicated severe ID, which firmly associated ARX gene variants and severe ID/DD 35 . The linkage between ARX gene variants and SUDEP was previously considered as a potential cause of SUDEP 36 , but further studies are needed to emphasize this hypothesis, which firmly associated ARX gene variants and severe ID 35 , variants in this gene have been associated with X-linked severe ID, lissencephaly with abnormal genitalia [36][37][38][39][40][41] . Previous case control studies have suggested that epilepsy onset, AED polytherapy and poor seizure control are major risk factors for SUDEP 42 . ...
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Through next-generation sequencing in 68 Han Chinese patients with unexplained EIEEs we were able to detect pathogenic variants and likely pathogenic variants in 15% and 4% of the cases, respectively. Six of these variants are novel. A total detection rate of 19% of variants adds weight to the known efficacy of next-generation sequencing in detecting variants in patients with unexplained EIEE. Moderate to severe ID were presented in eleven patients of the thirteen variants-carrying patients which augments the recognized relation between EIEE and moderate to severe ID, especially in patients with seizures onset within the first year of life. We advise that further attention should be paid to EIEEs patients with ARX gene variants, especially those who are on AED poly therapy and with poor seizure control, as we lost one patient with a variant in ARX gene due to SUDEP.
... [4]); CDKL5, a gene important to neuronal signaling (Rett-like EEs [5]); and multiple GABA receptor subunits (6).In an exciting recent study, Shen and colleagues identify a number of pathological missense mutations in the γ2 subunit of the GABA A receptor that appear to contribute to early onset EE (A106T, I107T, P282S, R323Q, R323W, and F343L). Interestingly, these mutations all come from patients with otherwise unclassified EEs (although a subset were eventually diagnosed with Lennox-Gastaut syndrome) who have epilepsy phenotypes diverse in their seizure semiology, EEG signatures, and antiepileptic drug responsiveness. ...
... An expansion of seven alanine residues in the first polyalanine tract causes West syndrome that is more severe than that caused by the second polyalanine tract expansion mutation [38,40,41]: for example, Guerrini et al. [41] described an infantile epileptic-dyskinetic encephalopathy, with recurrent life-threatening status dystonicus associated with mutation in the first polyalanine tract. An expansion of eleven alanine residues in the first polyalanine tract was associated with Early Infantile Epileptic Encephalopathy with Suppression-Burst Pattern (Ohtahara Syndrome) [42]. Correlation between the length of the repeat and the severity of the clinical phenotype has emerged. ...
Article
Background: Epileptic encephalopathies represent the most severe epilepsies, with onset in infancy and childhood and seizures continuing in adulthood in most cases. New genetic causes are being identified at a rapid rate. Treatment is challenging and the overall outcome remains poor. Available targeted treatments, based on the precision medicine approach, are currently few. Objective: To provide an overview of the treatment of epileptic encephalopathies with known genetic determinants, including established treatment, anecdotal reports of specific treatment, and potential tailored precision medicine strategies. Method: Genes known to be associated to epileptic encephalopathy were selected. Genes where the association was uncertain or with no reports of details on treatment, were not included. Although some of the genes included are associated with multiple epilepsy phenotypes or other organ involvement, we have mainly focused on the epileptic encephalopathies and their antiepileptic treatments. Results: Most epileptic encephalopathies show genotypic and phenotypic heterogeneity. The treatment of seizures is difficult in most cases. The available evidence may provide some guidance for treatment: for example, ACTH seems to be effective in controlling infantile spams in a number of genetic epileptic encephalopathies. There are potentially effective tailored precision medicine strategies available for some of the encephalopathies, and therapies with currently unexplained effectiveness in others. Conclusions: Understanding the effect of the mutation is crucial for targeted treatment. There is a broad range of disease mechanisms underlying epileptic encephalopathies, and this makes the application of targeted treatments challenging. However, there is evidence that tailored treatment could significantly improve epilepsy treatment and prognosis.
... EIEE/OS belongs to a group of genetically and clinically distinct epileptic encephalopathies. Approximately 75% of EIEE may progress to West syndrome, a diagnosis with an adverse prognosis including the arrest of psychomotor development and abnormal EEG pattern negatively affecting brain functions [42]. Wolff et al. defined two groups of patients with distinct seizure onset (before or after three months of age). ...
Article
Early infantile epileptic encephalopathy/Ohtahara syndrome represents a group of genetically heterogeneous disorders affecting normal brain development and functioning. In this work, we present a case of two unrelated children diagnosed with early infantile epileptic encephalopathy and associated multiple congenital abnormalities. To obtain genetic diagnosis, these children were examined through multi-step diagnostic algorithm including G-banded karyotype analysis and whole-genomic screening using array-based comparative genomic hybridization (array-CGH) with negative results. Additionally, these children and their unaffected parents were enrolled for our pilot study of targeted nextgeneration sequencing technology (NGS) using commercial panel ClearSeq Inherited DiseaseXT (Agilent Technologies) and consequent validation by Sanger sequencing. Our analysis detected two distinct de novo pathogenic sequence variants in the SCN2A gene, resulting in p.Met1545Val and p.Ala263Val changes on the SCN2A protein level and explaining their pathological phenotypes. In conclusion, our findings indicate that NGS can become the optimal approach to the genetics diagnostics of disorders of central nervous system (CNS) which can lead to the discovery of new candidate genes.
... Aufgrund der geringen Fallzahl sind nur wenige Untersuchungen vorhanden. Gut dokumentiert sind Fälle mit Mutationen im ARX-Gen [3], im STXBP1-Gen [4] oder im KCNQ2-Gen [5]. ...
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Early Infantile Epileptic Encephalopathy (EIEE) is a rare but devastating neurological condition. The management and therapeutic approach towards affected children is challenging. In this article we review the three originally described entities of early onset epileptic encephalopathies as Ohtahara-Syndrom, early myoclonic encephalopathy and malignant migrating partial seizures of infancy and present an updated view of this condition. Derived from the International League Against Epilepsy (ILAE) recommendations a multidimensional classification approach is introduced. The diagnostic strategy from the perspective of the clinician is outlined. The multidimensional classification approach is further used to describe the treatment strategies. The article concludes with the genetics of EIEE, the prognosis and finally discusses future developments. In summary this article gives an overview to the clinician who is acutely confronted with a patient with EIEE and has to develop a diagnostic and treatment plan.
... The EIEE is usually described as a part of the same epileptic, age-dependent continuum of West syndrome (WS) and Lennox-Gastaut syndrome (LGS) [3]. The major causes of EIEE include structural brain abnormalities, with genetic mutations frequently in STXBP1, KCNQ2, ARX, and CDKL5, among several others, also having a massive role in the syndrome [4][5][6]. This rare disease has a poor prognosis. ...
Article
Introduction: Early infantile epileptic encephalopathy syndrome (EIEE), also known as Ohtahara syndrome, is an age-dependent epileptic encephalopathy syndrome defined by clinical features and electroencephalographic findings. Epileptic disorders with refractory seizures beginning in the neonatal period and/or early infancy have a potential risk of premature mortality, including sudden death. We aimed to identify the causes of death in EIEE and conducted a literature survey of fatal outcomes. Methods: We performed a literature search in MEDLINE, EMBASE, and Web of Science for data from inception until September 2017. The terms "death sudden," "unexplained death," "SUDEP," "lethal," and "fatal" and the medical subject heading terms "epileptic encephalopathy," "mortality," "death," "sudden infant death syndrome," and "human" were used in the search strategy. The EIEE case report studies reporting mortality were included. Results: The search yielded 1360 articles. After screening for titles and abstracts and removing duplicate entries, full texts of 15 articles were reviewed. After reading full texts, 11 articles met the inclusion criteria (9 articles in English and 2 in Japanese, dated from 1976 to 2015). The review comprised 38 unique cases of EIEE, 17 of which had death as an outcome. In all cases, the suppression-burst pattern on electroencephalographies (EEGs) was common. Most cases (55%) involved male infants. The mean (standard deviation [SD]) age at onset of seizure was 19.6 ± 33 days. The mean (SD) age at death was 12.9 ± 14.1 months. Most infants (58.8%) survived less than one year. The cause of death was described only in eight (47%) patients; the cause was pneumonia/respiratory illness or sudden unexpected death in epilepsy (SUDEP). Discussion: The results show EIEE as a severe disease associated with a premature mortality, evidenced by a very young age at death. Increasing interest in the detection of new molecular bases of EIEE is leading us to a better understanding of this severe disease, but well-reported data are lacking to clarify EIEE-related causes of death.
... region and provides instructions for producing a protein transcription factor, which is essential for the development of cerebral interneurons. A hemizygous 33bp duplication in exon 2 was firstly described in two unrelated patients with Ohtahara syndrome [20]. The infant had early onset of brief tonic seizures beginning during the first weeks of life followed by a transition from EIEE to West syndrome and severe developmental delay. ...
Article
The weight of monogenic abnormalities in the possible causes of epilepsy has grown significantly in recent years, due to the emergence of next-generation sequencing (NGS)techniques. Especially notable in early neonatal and infantile epilepsies, which seem to be explained by monogenic abnormalities. This short review focuses on the major genes associated with very early-onset epilepsies, where NGS techniques are most cost-effective: early infantile epileptic encephalopathy, early myoclonic encephalopathy, and other neonatal epilepsies. The discovery of the genetic mutation often follows several weeks or months of management, and rarely modifies it. However, clinical studies can sometimes better define medical treatment. The genetic causes of these epilepsies are very numerous and the pathophysiological knowledge very minimal. The big challenge for the coming years is to develop more targeted treatments based on research on animal models.
... dark CDS) and HSPA1B (51.5% dark CDS) also encode two primary 70-kilodalton (kDa) heat-shock proteins. Heat-shock proteins have been implicated in ALS [31,32] early infantile epileptic encephalopathy 1 (EIEE1) [47] and Partington syndrome [48]. Similarly, TBX1, which harbors mutations that cause the same phenotype as 22q11.2 ...
Article
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Background The human genome contains “dark” gene regions that cannot be adequately assembled or aligned using standard short-read sequencing technologies, preventing researchers from identifying mutations within these gene regions that may be relevant to human disease. Here, we identify regions with few mappable reads that we call dark by depth, and others that have ambiguous alignment, called camouflaged. We assess how well long-read or linked-read technologies resolve these regions. Results Based on standard whole-genome Illumina sequencing data, we identify 36,794 dark regions in 6054 gene bodies from pathways important to human health, development, and reproduction. Of these gene bodies, 8.7% are completely dark and 35.2% are ≥ 5% dark. We identify dark regions that are present in protein-coding exons across 748 genes. Linked-read or long-read sequencing technologies from 10x Genomics, PacBio, and Oxford Nanopore Technologies reduce dark protein-coding regions to approximately 50.5%, 35.6%, and 9.6%, respectively. We present an algorithm to resolve most camouflaged regions and apply it to the Alzheimer’s Disease Sequencing Project. We rescue a rare ten-nucleotide frameshift deletion in CR1, a top Alzheimer’s disease gene, found in disease cases but not in controls. Conclusions While we could not formally assess the association of the CR1 frameshift mutation with Alzheimer’s disease due to insufficient sample-size, we believe it merits investigating in a larger cohort. There remain thousands of potentially important genomic regions overlooked by short-read sequencing that are largely resolved by long-read technologies. Electronic supplementary material The online version of this article (10.1186/s13059-019-1707-2) contains supplementary material, which is available to authorized users.
... Severe early-onset epilepsy [111] ARHGEF9 Early infantile epileptic encephalopathy/epilepsy in X-linked mental retardation [112] ARX Lennox-Gastaut syndrome/Ohtahara syndrome/West syndrome [113][114][115] ...
Article
Genetic epidemiology studies have shown that most epilepsies involve some genetic cause. In addition, twin studies have helped strengthen the hypothesis that in most patients with epilepsy, a complex inheritance is involved. More recently, with the development of high-density single-nucleotide polymorphism (SNP) microarrays and next-generation sequencing (NGS) technologies, the discovery of genes related to the epilepsies has accelerated tremendously. Especially, the use of whole exome sequencing (WES) has had a considerable impact on the identification of rare genetic variants with large effect sizes, including inherited or de novo mutations in severe forms of childhood epilepsies. The identification of pathogenic variants in patients with these childhood epilepsies provides many benefits for patients and families, such as the confirmation of the genetic nature of the diseases. This process will allow for better genetic counseling, more accurate therapy decisions, and a significant positive emotional impact. However, to study the genetic component of the more common forms of epilepsy, the use of high-density SNP arrays in genome-wide association studies (GWAS) seems to be the strategy of choice. As such, researchers can identify loci containing genetic variants associated with the common forms of epilepsy. The knowledge generated over the past two decades about the effects of the mutations that cause the monogenic epilepsy is tremendous; however, the scientific community is just starting to apply this information in order to generate better target treatments.
... 16,17 Various mutations in ARX (MIM: 300382; HGNC: 18060) cause a diverse range of neurodevelopmental disorders ranging from structural CNS malformations and genitourinary abnormalities associated with premature truncation mutations (MIM: 300004 and 300215) to infantile spasms and epileptic encephalopathies associated with polyalanine repeats (MIM: 308350, 309510, and 300419) to isolated intellectual disability associated with missense mutations or ARX duplications (MIM: 300419). 16,[18][19][20][21][22][23][24] Although the exact pathogenic nature of these ARX mutations remains to be fully elucidated, the types of mutations and CNVs suggest that haploinsufficient, gain-of-function, and dominant-negative mechanisms exist for ARX-related disorders. 18 Prior studies have shown that Ebf3 haploinsufficiency in mice results in abnormal GABAergic interneuron migration and projection, 32 indicating that EBF3 is a critical regulator of inhibitory GABAergic neuronal development. ...
Article
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Early B cell factor 3 (EBF3) is a member of the highly evolutionarily conserved Collier/Olf/EBF (COE) family of transcription factors. Prior studies on invertebrate and vertebrate animals have shown that EBF3 homologs are essential for survival and that loss-of-function mutations are associated with a range of nervous system developmental defects, including perturbation of neuronal development and migration. Interestingly, aristaless-related homeobox (ARX), a homeobox-containing transcription factor critical for the regulation of nervous system development, transcriptionally represses EBF3 expression. However, human neurodevelopmental disorders related to EBF3 have not been reported. Here, we describe three individuals who are affected by global developmental delay, intellectual disability, and expressive speech disorder and carry de novo variants in EBF3. Associated features seen in these individuals include congenital hypotonia, structural CNS malformations, ataxia, and genitourinary abnormalities. The de novo variants affect a single conserved residue in a zinc finger motif crucial for DNA binding and are deleterious in a fly model. Our findings indicate that mutations in EBF3 cause a genetic neurodevelopmental syndrome and suggest that loss of EBF3 function might mediate a subset of neurologic phenotypes shared by ARX-related disorders, including intellectual disability, abnormal genitalia, and structural CNS malformations.
... The intercritical EEG findings show high voltage bursts of slow waves mixed with multifocal spikes, with phases of flat suppression [59][60][61] (Fig. 2). Mutations in several genes have been implicated, including ARX, STXBP1, KCNQ2, SLC25A22, and CDKL5 [62][63][64][65]. Structural cerebral anomalies are often detected by brain MRI, including cerebral asymmetry, hemimegalencephaly, lissencephaly and focal-cortical dysplasia [61,65,66]. ...
Article
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Background: At the onset, differentiation between abnormal non-epileptic movements, and epileptic seizures presenting in early life is difficult as is clinical diagnosis and prognostic evaluation of the various seizure disorders presenting at this age. Seizures starting in the first year of life including the neonatal period might have a favorable course, such as in infants presenting with benign familial neonatal epilepsy, febrile seizures simplex or acute symptomatic seizures. However, in some cases, the onset of seizures at birth or in the first months of life have a dramatic evolution with severe cerebral impairment. Seizure disorders starting in early life include the "epileptic encephalopathies", a group of conditions characterized by drug resistant seizures, delayed developmental skills, and intellective disability. This group of disorders includes early infantile epileptic encephalopathy also known as Ohtahara syndrome, early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, infantile spasms syndrome (also known as West syndrome), severe myoclonic epilepsy in infancy (also known as Dravet syndrome) and, myoclonic encephalopathies in non-progressive disorder. Here we report on seizures manifesting in the first year of life including the neonatal period. Conditions with a benign course, and those with severe evolution are presented. At this early age, clinical identification of seizures, distinction of each of these disorders, type of treatment and prognosis is particularly challenging. The aim of this report is to present the clinical manifestations of each of these disorders and provide an updated review of the conditions associated with seizures in the first year of life.
... Recent studies demonstrated that CDKL5 regulates axon outgrowth, dendritic morphogenesis and synapse formation [24]. The first identified EIEE-causing gene was ARX, encoding the transcription factor Aristaless-Related Homeobox [25]. Expansions in the first and second poly-alanine tracts in ARX cause a spectrum of disorders, from EIEE to non-syndromic mental retardation [26]. ...
Article
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Developmental and epileptic encephalopathies (DEEs) are the spectrum of severe epilepsies characterized by early-onset, refractory seizures occurring in the context of developmental regression or plateauing. Early infantile epileptic encephalopathy (EIEE) is one of the earliest forms of DEE, manifesting as frequent epileptic spasms and characteristic electroencephalogram findings in early infancy. In recent years, next-generation sequencing approaches have identified a number of monogenic determinants underlying DEE. In the case of EIEE, 85 genes have been registered in Online Mendelian Inheritance in Man as causative genes. Model organisms are indispensable tools for understanding the in vivo roles of the newly identified causative genes. In this review, we first present an overview of epilepsy and its genetic etiology, especially focusing on EIEE and then briefly summarize epilepsy research using animal and patient-derived induced pluripotent stem cell (iPSC) models. The Drosophila model, which is characterized by easy gene manipulation, a short generation time, low cost and fewer ethical restrictions when designing experiments, is optimal for understanding the genetics of DEE. We therefore highlight studies with Drosophila models for EIEE and discuss the future development of their practical use.
... Of these, syntaxin-binding protein 1 (STXBP1), which regulates the release of synaptic vesicles and the secretion of neurotransmitters, is the major contributor and explains~30% of cases [38,44]. Pathogenic variants in other genes include the voltage-gated potassium channel gene (KCNQ2) (~20%) [38,45]; SCN2A, a gene encoding the voltage gated sodium channel Na v 1.2 (~10%) [38,46] aristaless-related homeobox (ARX), a regulator of the proliferation and differentiation of neuronal progenitors [47]; solute carrier family 25 member 22 (SLC25A22), which encodes a mitochondrial glutamate transporter [48]; and potassium-activated channel subfamily T member 1 (KCNT1), which is widely expressed in the nervous system [49,50] (See Table 1 for additional genes). ...
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The high pace of gene discovery has resulted in thrilling advances in the field of epilepsy genetics. Clinical testing with comprehensive gene panels, exomes, or genomes are now increasingly available and have led to a significant higher diagnostic yield in early-onset epilepsies and enabled precision medicine approaches. These have been instrumental in providing insights into the pathophysiology of both early-onset benign and self-limited syndromes and devastating developmental and epileptic encephalopathies (DEEs). Genetic heterogeneity is seen in many epilepsy syndromes such as West syndrome and epilepsy of infancy with migrating focal seizures (EIMFS), indicating that two or more genetic loci produce the same or similar phenotypes. At the same time, some genes such as SCN2A can be associated with a wide range of epilepsy syndromes ranging from self-limited familial neonatal epilepsy at the mild end to Ohtahara syndrome, EIFMS, West syndrome, Lennox–Gastaut syndrome, or unclassifiable DEEs at the severe end of the spectrum. The aim of this study was to review the clinical and genetic heterogeneity associated with epilepsy syndromes starting in the first year of life including: Self-limited familial neonatal, neonatal-infantile or infantile epilepsies, genetic epilepsy with febrile seizures plus spectrum, myoclonic epilepsy in infancy, Ohtahara syndrome, early myoclonic encephalopathy, West syndrome, Dravet syndrome, EIMFS, and unclassifiable DEEs. We also elaborate on the advantages and pitfalls of genetic testing in such conditions. Finally, we describe how a genetic diagnosis can potentially enable precision therapy in monogenic epilepsies and emphasize that early genetic testing is a cornerstone for such therapeutic strategies.
... A common mutation consists of an in-frame 24bp duplication (Szczaluba et al., 2006), whilst longer mutations, 27bp, and 33bp have also be reported (Demos et al., 2009;Reish et al., 2009). The longest known mutation exhibits the addition of eleven alanine residues, resulting in Ohtahara syndrome (Kato et al., 2007). Other intellectual disability, seizures related disorders have also been observed (Turner et al., 2002). ...
Article
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Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.
... In doing this, ARX controls numerous functions such as neuronal stem-cell proliferation, migration and differentiation, axonal guidance, and synaptic activity [2][3][4][5][6][7]. As ARX is located in Xp21.3, loss-of-function (LoF) and partial-LoF mutations contribute to a nearly continuous series of X-chromosome-linked neurodevelopmental disorders (NDDs) ranging from lissencephaly with abnormal genitalia (XLAG; MIM 300215), developmental and epileptic encephalopathy type 1 (DEE1; MIM 308350), X-linked intellectual disability (XLID; 300419), ID with hand dystonia (Partington syndrome; MIM 309510), and autism [8][9][10][11][12]. Of note, many target genes of this pleiotropic TF have been correlated with ID and autism, emphasizing the importance of ARX for brain development and functioning [7,9,13]. ...
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The X-linked gene encoding aristaless-related homeobox (ARX) is a bi-functional transcription factor capable of activating or repressing gene transcription, whose mutations have been found in a wide spectrum of neurodevelopmental disorders (NDDs); these include cortical malformations, paediatric epilepsy, intellectual disability (ID) and autism. In addition to point mutations, duplications of the ARX locus have been detected in male patients with ID. These rearrangements include telencephalon ultraconserved enhancers, whose structural alterations can interfere with the control of ARX expression in the developing brain. Here, we review the structural features of 15 gain copy-number variants (CNVs) of the ARX locus found in patients presenting wide-ranging phenotypic variations including ID, speech delay, hypotonia and psychiatric abnormalities. We also report on a further novel Xp21.3 duplication detected in a male patient with moderate ID and carrying a fully duplicated copy of the ARX locus and the ultraconserved enhancers. As consequences of this rearrangement, the patient-derived lymphoblastoid cell line shows abnormal activity of the ARX-KDM5C-SYN1 regulatory axis. Moreover, the three-dimensional (3D) structure of the Arx locus, both in mouse embryonic stem cells and cortical neurons, provides new insight for the functional consequences of ARX duplications. Finally, by comparing the clinical features of the 16 CNVs affecting the ARX locus, we conclude that—depending on the involvement of tissue-specific enhancers—the ARX duplications are ID-associated risk CNVs with variable expressivity and penetrance.
... 1 Mutations in ARX cause X-linked intellectual disability (ID) with over 44 different mutations in ARX found in over 100 families, including some sporadic cases. 1 ID is a consistent feature, with some mutations in ARX leading to a broad spectrum of seizure phenotypes, including X-linked infantile spasms (ISSX), West syndrome, infantile epileptic-dyskinetic encephalopathy, and early infantile epileptic encephalopathy (also known as Ohtahara syndrome). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Other mutations in ARX lead to severe malformations of the brain and genitalia such as Proud syndrome with agenesis of the corpus callosum and abnormal genitalia, 20 hydranencephaly with abnormal genitalia, 20,21 and X-linked lissencephaly with abnormal genitalia (XLAG). 1, [20][21][22][23][24][25][26][27][28] Mutations that lead to severe malformation phenotypes are usually protein truncation and point mutations in critical residues, leading to complete loss-of-function ARX protein. ...
Article
Mutations in the Aristaless-related homeobox gene (ARX) lead to a range of X-linked intellectual disability phenotypes, with truncating variants generally resulting in severe X-linked lissencephaly with ambiguous genitalia (XLAG), and polyalanine expansions and missense variants resulting in infantile spasms. We report two male patients with early-onset infantile spasms in whom a novel c.34G>T (p.(E12*)) variant was identified in the ARX gene. A similar variant c.81C>G (p.(Y27*)), has previously been described in two affected cousins with early-onset infantile spasms, leading to reinitiation of ARX mRNA translation resulting in an N-terminal truncated protein. We show that the novel c.34G>T (p.(E12*)) variant also reinitiated mRNA translation at the next AUG codon (c.121-123 (p.M41)), producing the same N-terminally truncated protein. The production of both of these truncated proteins was demonstrated to be at markedly reduced levels using in vitro cell assays. Using luciferase reporter assays, we demonstrate that transcriptional repression capacity of ARX was diminished by both the loss of the N-terminal corepressor octapeptide domain, as a consequence of truncation, and the marked reduction in mutant protein expression. Our study indicates that premature termination mutations very early in ARX lead to reinitiation of translation to produce N-terminally truncated protein at markedly reduced levels of expression. We conclude that even low levels of N-terminally truncated ARX is sufficient to improve the patient's phenotype compared with the severe phenotype of XLAG that includes malformations of the brain and genitalia normally seen in complete loss-of-function mutations in ARX.European Journal of Human Genetics advance online publication, 26 August 2015; doi:10.1038/ejhg.2015.176.
... ARX encodes a homeotic bi-functional TF capable of activating or repressing gene transcription [15]. Mutations in ARX have been found in a wide range of NDDs, affecting only male children and including severe cortical malformations such as X-linked Lissencephaly with agenesis of the corpus callosum and ambiguous genitalia (XLAG; MIM:300215); Agenesis of Corpus Callosum (ACC; MIM 300004; also known as Proud syndrome); severe pediatric epilepsy such as Developmental and Epileptic Encephalopathy 1 (DEE1; MIM:308350, also known as West syndrome); and mild cognition diseases including Partington syndrome (MIM 309510), autism, and non-syndromic intellectual disability [4,[16][17][18][19][20]. Previous studies conducted by us and other groups have shown that XLAG mutations abrogate the transcriptional program controlled by ARX, whereas expansions of the polyA-tracts are hypomorphic mutations with reduced transcriptional activity and binding properties [4,5,15,21,22]. ...
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Dysregulation of transcriptional pathways is observed in multiple forms of neurodevelopmental disorders (NDDs), such as intellectual disability (ID), epilepsy and autism spectrum disorder (ASD). We previously demonstrated that the NDD genes encoding lysine-specific demethylase 5C (KDM5C) and its transcriptional regulators Aristaless related-homeobox (ARX), PHD Finger Protein 8 (PHF8) and Zinc Finger Protein 711 (ZNF711) are functionally connected. Here, we show their relation to each other with respect to the expression levels in human and mouse datasets and in vivo mouse analysis indicating that the coexpression of these syntenic X-chromosomal genes is temporally regulated in brain areas and cellular sub-types. In co-immunoprecipitation assays, we found that the homeotic transcription factor ARX interacts with the histone demethylase PHF8, indicating that this transcriptional axis is highly intersected. Furthermore, the functional impact of pathogenic mutations of ARX, KDM5C, PHF8 and ZNF711 was tested in lymphoblastoid cell lines (LCLs) derived from children with varying levels of syndromic ID establishing the direct correlation between defects in the KDM5C-H3K4me3 pathway and ID severity. These findings reveal novel insights into epigenetic processes underpinning NDD pathogenesis and provide new avenues for assessing developmental timing and critical windows for potential treatments.
... ;Van Damme et al. 2011;Bettencourt et al. 2010;Faruq et al. 2015;Jodice et al. 1997;Chen et al. 2014;Bauer et al. 2004;Jenkins et al. 2005;Veneziano and Frontali 2016;Wilburn et al. 2011;Kato et al. 2007;Robinson et al. 2005;Frolov et al. 2010;Sakamoto et al. 2001;Nakano et al. 2015;Silva et al. 2015;Liquori et al. 2001;Tee and Quek 2013;Seixas et al. 2017;Cen et al. 2018; Matilla-Dueñas 2012;Obayashi et al. 2015;Steinbach et al. 1998;Koob et al. 1999). ...
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Short tandem repeats (STRs) are commonly defined as short runs of repetitive nucleotides, consisting of tandemly repeating 2–6- bp motif units, which are ubiquitously distributed throughout genomes. Functional STRs are polymorphic in the population, and their variations influence gene expression, which subsequently may result in pathogenic phenotypes. To understand STR phenotypic effects and their functional roles, we describe four different mutational mechanisms including the unequal crossing-over model, gene conversion, retrotransposition mechanism and replication slippage. Due to the multi-allelic nature, small length, abundance, high variability, codominant inheritance, nearly neutral evolution, extensive genome coverage and simple assaying of STRs, these markers are widely used in various types of biological research, including population genetics studies, genome mapping, molecular epidemiology, paternity analysis and gene flow studies. In this review, we focus on the current knowledge regarding STR genomic distribution, function, mutation and applications.
... [3][4][5] Mutations in several genes have been implicated, including ARX, STXBP1, KCNQ2, SLC25A22, and CDKL5. [6][7][8][9] Structural cerebral anomalies are often detected by brain MRI, including cerebral asymmetry, hemimegalencephaly, lissencephaly and focal-cortical dysplasia. 5,9 Hypotonia, severe developmental delay and respiratory problems are associated with these seizure types. ...
Article
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West syndrome is a severe epilepsy syndrome composed of the triad of infantile spasms, hypsarrhythmia on electroencephalography (EEG) and mental retardation. It is sometimes due to the progression of a rare and fatal condition called early infantile epileptic encephalopathy (Ohtahara syndrome). Here we describe the case of a 3 year old male, who is a known case of West syndrome, presenting with recurrent breakthrough convulsions.
... Mutations of the ARX gene are the most frequent mutations of X-linked ID (XLID), and they are responsible for a wide phenotypic spectrum including S-XLID and NS-XLID forms [12][13][14][15], as well as X-linked lissencephaly with abnormal genitalia (XLAG), hydranencephaly with abnormal genitalia (HYD-AG), X-linked infantile spasm (ISSX), X-linked myoclonic seizures, spasticity and ID (XMESID), Partington syndrome (PRTS), Ohtahara syndrome, Proud syndrome, and idiopathic infantile epileptic dyskinesia encephalopathy (IEDE) [8,[16][17][18][19][20]. ...
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Objective Intellectual Disability (ID) represents a neuropsychiatric disorder, which its etiopathogenesis remains insufficiently understood. Mutations in the Aristaless Related Homeobox gene ( ARX ) have been identified to cause syndromic and nonsyndromic (NS-ID). The most recurrent mutation of this gene is a duplication of 24pb, c.428-451dup. Epidemiological and genetic studies about ID in the Moroccan population remain very scarce, and none study is carried out on the ARX gene. This work aimed to study c.428–451dup (24 bp) mutation in the exon 2 of the ARX gene in 118 males’ Moroccan patients with milder NS-ID to evaluate if the gene screening is a good tool for identifying NS-ID. Results Our mutational analysis did not show any dup(24pb) in our patients. This is because based on findings from previous studies that found ARX mutations in 70% of families with NS-ID, and in most cases, 1.5–6.1% of individuals with NS-ID have this duplication. Since 1/118 = 0.0084 (0.84%) is not much different from 1.5%, then it is reasonable that this could a sample size artifact. A complete screening of the entire ARX gene, including the five exons, should be fulfilled. Further investigations are required to confirm these results.
... It has been linked with different early-life epilepsies, including Ohtahara syndrome and WS. The reports of patients with IS include both infants with no identifiable structural brain abnormality (which would have otherwise been classified as unknown etiology) and infants with pronounced abnormalities, such as X-linked lissencephaly with abnormal genitalia (XLAG) (Dobyns et al. 1999;Scheffer et al. 2002;Stromme et al. 2002;Kato et al. 2003Kato et al. , 2007Kato 2006;Paciorkowski et al. 2011a). ...
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The incidence of seizures and epilepsies is particularly high during the neonatal and infantile periods.We will review selected animal models of early-life epileptic encephalopathies that have addressed the dyscognitive features of frequent interictal spikes, the pathogenesis and treatments of infantile spasms (IS) or Dravet syndrome, disorders with mammalian target of rapamycin (mTOR) dysregulation, and selected early-life epilepsies with genetic defects. Potentially pathogenic mechanisms in these conditions include interneuronopathies in IS or Dravet syndrome andmTORdysregulation in brain malformations, tuberous sclerosis, and related genetic disorders, or IS of acquired etiology. These models start to generate the first therapeutic drugs, which have been specifically developed in immature animals. However, there are challenges in translating preclinical discoveries into clinically relevant findings. The advances made so far hold promise that the newinsights may potentially have curative or disease-modifying potential for many of these devastating conditions.
... Nevertheless, some cases of earlyonset epileptic encephalopathy associated with suppression-burst patterns on EEG cannot be diagnosed as either OS or EME. Both syndromes are sometimes described by inclusive terms such as "early/ neonatal epileptic encephalopathies with suppression-burst" or "severe neonatal epilepsy with suppression-burst pattern" [10] Approximately 30 years after the first description of OS, Japanese researchers identified gene abnormalities in OS; mutation in the A RX gene that is involved in the development of GABAergic interneurons, and mutations in the STX BP1 gene that is related to synaptic vesicle transmitter release and regulation of calcium channels [12,13]. Thereafter, several other gene abnormalities involving the KCNQ2 gene, SCN2A gene, GNAO1 gene and CASK gene have been reported in OS, EME, West syndrome and other cases of early-onset epilepsies. ...
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Recent advances in molecular genetics led to the discovery of several genes for childhood epileptic encephalopathies (CEEs). As the knowledge about the genes associated with this group of disorders develops, it becomes evident that CEEs present a number of specific genetic characteristics, which will influence the use of molecular testing for clinical purposes. Among these, there are the presence of marked genetic heterogeneity and the high frequency of de novo mutations. Therefore, the main objectives of this review paper are to present and discuss current knowledge regarding i) new genetic findings in CEEs, ii) phenotype-genotype correlations in different forms of CEEs; and, most importantly, iii) the impact of these new findings in clinical practice. Accompanying this text we have included a comprehensive table, containing the list of genes currently known to be involved in the etiology of CEEs.
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Epilepsies are among the most common disorders effecting children throughout infancy, childhood and adolescence. Severe forms that might be therapy-resistant account for approximately 30% whereas common forms (70%) usually go along with several treatment options. The research success regarding genetic causes of rare, devastating forms is in contrast to little knowledge on the genetic basis of frequent disorders. The formerly well-established concept of channelopathies has been questioned by recent findings. Especially high-throughput sequencing will allow large scale studies and provide promising findings. We discuss genetic findings in different forms of childhood epilepsies and provide an evaluation of available genetic tests with regard to diagnostic use and therapeutic options.
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A genetic component to epilepsy has been recognized since Antiquity and is well established through twin and familial aggregation studies, which provide convincing evidence for the heritability of epilepsy. Despite major advances in genetic studies, genetic epilepsies have not yet revealed all their secrets. This prospective study aimed to identify genetic variants of epilepsy, to document the genotype/phenotype correlations and inheritance patterns in multigenerational Algerian families. Genetic analyzes included exome sequencing, CGH-array and Southern blotting. We studied a family with a pair of monozygotic twins affected by temporal lobe epilepsy. Exome sequencing revealed that both twins carried a novel de novo mutation (p.A39E) in the GAL gene encoding the galanin neuropeptide. This latter was found to act as a potent anticonvulsant and regulates epileptic seizures in animal models. However, until now its role in human epilepsy was not established. Functional analysis showed evidence that the mutant protein disrupts galanin signalling, and strongly supports GAL as the causal gene for the TLE in this family. We identified two families with progressive myoclonus epilepsy type 1. Genetic studies by Southern blotting showed an expansion of dodecamer CCCCGCCCCGCG in EPM1 gene. In addition, two other families were analysed by CGH-array, but no pathogenic CNV was identified. The study of other multigenerational families would identify new genetic variants of epilepsy. Keywords: epilepsy, genetics, phenotype, pedigree, polymorphism, mutation, CNV, CGH-array, exome sequencing.
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Objective: Recent studies have elucidated causative roles for genetic abnormalities in early-onset epileptic encephalopathies (EOEE). Accompanying characteristic features, in addition to seizures, have also been suggested to provide important clues for an early and accurate genetic diagnosis of affected patients. In this study, we investigated the underlying genetic causes in patients with EOEE associated with infantile movement disorders. Methods: We examined 11 patients with EOEE and involuntary movements (nine with West syndrome and two with nonsyndromic epileptic encephalopathy). All showed severe developmental delay, cognitive impairment, and involuntary movements such as chorea, ballism, dyskinesia or myoclonus, and hand stereotypies. We performed whole-exome sequencing of 10 patients, while the other patient underwent high-resolution melting analysis of candidate EOEE genes. Results: We identified mutations in CDKL5, SCN2A, SETD5, ALG13, and TBL1XR1 in seven patients with West syndrome, and in SCN1A and GRIN1 in the two patients with unclassified epileptic encephalopathy. All mutations were validated as de novo events. The genetic cause was undetermined in the remaining two patients. Conclusions: We found pathogenic mutations in seven genes, in nine of 11 patients with EOEE and involuntary movements. Although the results of our study are preliminary because of the small number of patients, they nevertheless suggest that specific accompanying phenotypes such as hyperkinetic movements or hand stereotypies could be important in narrowing the disease spectrum and identifying causative genetic abnormalities.
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Introduction Rare complication chronic alcoholism, Marchiafava-Bignami disease is characterized by a demyelinating reached and necrosis of medial portion of the corpus callosum. Observation We report the case of a 48-year-old patient, with chronic alcoholism, which has consulted for progressive installation of memory disorders. Chronic dementia associated with diffuse pyramidal syndrome and an inter hemispheric disconnection syndrome have been objectified. The diagnosis was confirmed by magnetic resonance imaging (MRI). Analysis of the cerebrospinal fluid was normal. Discussion The clinical picture of this condition is nonspecific. We insist on the identification of a chronic alcoholism field and the contribution of MRI remains the primary diagnostic tool. Conclusion: Chronic alcoholism increases the risk of developing serious complications including neurological disease Marchiafava-Bignami.
Chapter
Nach Besprechung der Klassifikationen der Epilepsien sowie molekularer und zellulärer Pathomechanismen wird die Neuropathologie der Temporallappenepilepsie, der Hippokampussklerose (Ammonshornsklerose), der Epilepsie-assoziierten Tumoren, der fokalen kortikalen Dysplasien, der Rasmussen- und limbischen Enzephalitis und genetisch determinierter Epilepsien dargestellt. Außerdem wird auf Schäden durch Antikonvulsiva eingegangen.
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Epileptic encephalopathies (EE) are a group of severe childhood epilepsy disorders characterized by intractable seizures, cognitive impairment and neurological deficits. Recent whole-exome sequencing (WES) studies have implicated significant contribution of de novo mutations to EE. In this study, we utilized WES for identifying causal de novo mutations in 4 parent-offspring trios affected by West syndrome. As a result, we found two deleterious de novo mutations in DYNC1H1 and RTP1 in two trios. Expression profile analysis showed that DYNC1H1 and RTP1 are expressed in almost all brain regions and developmental stages. Interestingly, co-expression and genetic interaction network analyses suggested that DYNC1H1 and RTP1 are tightly associated with known epilepsy genes. Furthermore, we observed that the de novo mutations of DYNC1H1 were identified in several different neuropsychiatric disorders including EE, autism spectrum disorders and intellectual disabilities by previous studies, and these mutations primarily occurred in the functional domain of the protein. Taken together, these results demonstrate DYNC1H1 as a strong candidate and RTP1 as a potential candidate on the onset of EE. In addition, this work also proves WES as a powerful tool for the molecular genetic dissection of children affected by sporadic EE.
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Recent advances in genetics have determined that a number of epilepsy syndromes that occur in the first year of life are associated with genetic etiologies. These syndromes range from benign familial epilepsy syndromes to early-onset epileptic encephalopathies that lead to poor prognoses and severe psychomotor retardation. An early genetic diagnosis can save time and overall cost by reducing the amount of time and resources expended to reach a diagnosis. Furthermore, a genetic diagnosis can provide accurate prognostic information and, in certain cases, enable targeted therapy. Here, several early infantile epilepsy syndromes with strong genetic associations are briefly reviewed, and their genotype-phenotype correlations are summarized. Because the clinical presentations of these disorders frequently overlap and have heterogeneous genetic causes, next-generation sequencing (NGS)-based gene panel testing represents a more powerful diagnostic tool than single gene testing. As genetic information accumulates, genetic testing will likely play an increasingly important role in diagnosing pediatric epilepsy. However, the efforts of clinicians to classify phenotypes in nondiagnosed patients and improve their ability to interpret genetic variants remain important in the NGS era.
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Chapter
Early myoclonic epilepsy (EME) and Ohtahara syndrome (OS) or early infantile epileptic encephalopathy (EIEE) are the earliest epileptic encephalopathy syndromes. These two entities share many features, including age at presentation, a similar electroencephalographic pattern, intractable seizures, and poor prognosis. EME and EIEE are traditionally distinguished according to different type of seizures, differences in the pattern of suppression-burst, and aetiologies. In EIEE onset is within the first 3 months of age and often within the first 2 weeks. Infants acutely develop tonic spasms that can be either generalized or lateralized, can occur both isolated or in clusters, and are independent from the sleep cycle. The most specific EEG feature is the suppression-burst (SB). This pattern is characterized by high-voltage bursts alternating with almost flat suppression phases at an approximately regular rate. SB pattern differs definitely from the periodic type of hypsarrhythmia where it becomes remarkable in sleep. Early myoclonic encephalopathy (EME) can be associated with structural, metabolic, and genetic abnormalities: methylmalonic acidemia, sulphite oxidase deficiency, Menkes disease, and Zellweger syndrome, and CDG disorders. Other early-onset epileptic encephalopathies due to specific genetic aetiology include CDKL5-related epileptic encephalopathy (OMIM 300672), KCNQ2-related epileptic encephalopathy (OMIM 613720), SCN2A-related epileptic encephalopathy (OMIM 613721), and SCN8A-related epileptic encephalopathy (OMIM 614558).
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Epigenetics refers broadly to processes that influence medium to long-term gene expression by changing the readability and accessibility of the genetic code. The Neurobiology Commission of the International League Against Epilepsy (ILAE) recently convened a Task Force to explore and disseminate advances in epigenetics to better understand their role and intersection with genetics and the neurobiology of epilepsies and their co-morbidities, and to accelerate translation of these findings into the development of better therapies. Here, we provide a topic primer on epigenetics, explaining the key processes and findings to date in experimental and human epilepsy. We review the growing list of genes with epigenetic functions that have been linked with epilepsy in humans. We consider potential practical applications, including using epigenetic signals as biomarkers for tissue- and biofluid-based diagnostics and the prospects for developing epigenetic-based treatments for epilepsy. We include a glossary of terms, FAQs and other supports to facilitate a broad understanding of the topic for the non-expert. Last, we review the limitations, research gaps and the next challenges. In summary, epigenetic processes represent important mechanisms controlling the activity of genes, providing opportunities for insight into disease mechanisms, biomarkers and novel therapies for epilepsy.
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Infantile spasms (IS or epileptic spasms during infancy) were first described by Dr. William James West (aka West syndrome) in his own son in 1841. While rare by definition (occurring in 1 per 3200–3400 live births), IS represent a major social and treatment burden. The etiology of IS varies - there are many (>200) different known pathologies resulting in IS and still in about one third of cases there is no obvious reason. With the advancement of genetic analysis, role of certain genes (such as ARX or CDKL5 and others) in IS appears to be important. Current treatment strategies with incomplete efficacy and serious potential adverse effects include adrenocorticotropin (ACTH), corticosteroids (prednisone, prednisolone) and vigabatrin, more recently also a combination of hormones and vigabatrin. Second line treatments include pyridoxine (vitamin B6) and ketogenic diet. Additional treatment approaches use rapamycin, cannabidiol, valproic acid and other anti-seizure medications. Efficacy of these second line medications is variable but usually inferior to hormonal treatments and vigabatrin. Thus, new and effective models of this devastating condition are required for the search of additional treatment options as well as for better understanding the mechanisms of IS. Currently, eight models of IS are reviewed along with the ideas and mechanisms behind these models, drugs tested using the models and their efficacy and usefulness. Etiological variety of IS is somewhat reflected in the variety of the models. However, it seems that for finding precise personalized approaches, this variety is necessary as there is no “one-size-fits-all” approach possible for both IS in particular and epilepsy in general.
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Epilepsy is a progressive and disabling disease if not diagnosed early; for this reason, it has been the subject of research, specially in cases with idiopathic etiology. Approximately between 1 and 2% of the world population have epilepsy. In Mexico the prevalence is from 10 to 20 patients per 1000 inhabitants. Lately, the scientific community has been trying to create, adapt, and use biomolecular tools to study its pathophysiology so that, hopefully, in a near future we are able to intervene in the natural history of this disease. The aim of this work is to cite evidence about some of the molecular biology techniques in order to support and encourage investment in neurogenomical research; as a necessary tool in the study of epilepsy.
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Epilepsy is a network disorder driven by fundamental changes in the function of the cells which compose these networks. Driving this aberrant cellular function are large scale changes in gene expression and gene expression regulation. Recent studies have revealed rapid and persistent changes in epigenetic control of gene expression as a critical regulator of the epileptic transcriptome. Epigenetic-mediated gene output regulates many aspects of cellular physiology including neuronal structure, neurotransmitter assembly and abundance, protein abundance of ion channels and other critical neuronal processes. Thus, understanding the contribution of epigenetic-mediated gene regulation could illuminate novel regulatory mechanisms which may form the basis of novel therapeutic approaches to treat epilepsy. In this review we discuss the effects of epileptogenic brain insults on epigenetic regulation of gene expression, recent efforts to target epigenetic processes to block epileptogenesis and the prospects of an epigenetic-based therapy for epilepsy, and finally we discuss technological advancements which have facilitated the interrogation of the epigenome.
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The Aristaless-related homeobox (ARX) transcription factor is involved in the development of GABAergic and cholinergic neurons in the forebrain. ARX mutations have been associated with a wide spectrum of neurodevelopmental disorders in humans and are responsible for both malformation (in particular lissencephaly) and nonmalformation complex phenotypes. The epilepsy phenotypes related to ARX mutations are West syndrome and X-linked infantile spasms, X-linked myoclonic epilepsy with spasticity and intellectual development and Ohtahara and early infantile epileptic encephalopathy syndrome, which are related in most of the cases to intellectual disability and are often drug resistant. In this article, we shortly reviewed current knowledge of the function of ARX with a particular attention on its consequences in the development of epilepsy during early childhood.
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Background Short tandem repeat (STR) expansion disorders are an important cause of human neurological disease. They have an established role in more than 40 different phenotypes including the myotonic dystrophies, Fragile X syndrome, Huntington’s disease, the hereditary cerebellar ataxias, amyotrophic lateral sclerosis and frontotemporal dementia. Main body STR expansions are difficult to detect and may explain unsolved diseases, as highlighted by recent findings including: the discovery of a biallelic intronic ‘AAGGG’ repeat in RFC1 as the cause of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS); and the finding of ‘CGG’ repeat expansions in NOTCH2NLC as the cause of neuronal intranuclear inclusion disease and a range of clinical phenotypes. However, established laboratory techniques for diagnosis of repeat expansions (repeat-primed PCR and Southern blot) are cumbersome, low-throughput and poorly suited to parallel analysis of multiple gene regions. While next generation sequencing (NGS) has been increasingly used, established short-read NGS platforms (e.g., Illumina) are unable to genotype large and/or complex repeat expansions. Long-read sequencing platforms recently developed by Oxford Nanopore Technology and Pacific Biosciences promise to overcome these limitations to deliver enhanced diagnosis of repeat expansion disorders in a rapid and cost-effective fashion. Conclusion We anticipate that long-read sequencing will rapidly transform the detection of short tandem repeat expansion disorders for both clinical diagnosis and gene discovery.
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Epileptic encephalopathies are characterized by recurrent clinical seizures and prominent interictal epileptiform discharges seen during the early infantile period. Although epileptic encephalopathies are mostly associated with structural brain defects and inherited metabolic disorders, pathogenic gene mutations may also be involved in the development of epileptic encephalopathies even when no clear genetic inheritance patterns or consanguinity exist. The most common epileptic encephalopathies are Ohtahara syndrome, early myoclonic encephalopathy, epilepsy of infancy with migrating focal seizures, West syndrome and Dravet syndrome, which are usually unresponsive to traditional antiepileptic medication. Many of the diagnoses describe the phenotype of these electroclinical syndromes, but not the underlying causes. To date, approximately 265 genes have been defined in epilepsy and several genes including STXBP1, ARX, SLC25A22, KCNQ2, CDKL5, SCN1A, and PCDH19 have been found to be associated with early-onset epileptic encephalopathies. In this review, we aimed to present a diagnostic approach to primary genetic causes of early-onset epileptic encephalopathies. © The Author(s) 2015.
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Synpolydactyly (SPD) is a dominantly inherited congenital limb malformation. Typical cases have 3/4 finger and 4/5 toe syndactyly, with a duplicated digit in the syndactylous web, but incomplete penetrance and variable expressivity are common. The condition has recently been shown to be caused by expansions of an imperfect trinucleotide repeat sequence encoding a 15-residue polyalanine tract in HOXD13. We have studied 16 new and 4 previously published SPD families, with between 7 and 14 extra residues in the tract, to analyze the molecular basis for the observed variation in phenotype. Although there is no evidence of change in expansion size within families, even over six generations, there is a highly significant increase in the penetrance and severity of phenotype with increasing expansion size, affecting both hands (P = 0.012) and feet (P < 0. 00005). Affected individuals from a family with a 14-alanine expansion, the largest so far reported, all have a strikingly similar and unusually severe limb phenotype, involving the first digits and distal carpals. Affected males from this family also have hypospadias, not previously described in SPD, but consistent with HOXD13 expression in the developing genital tubercle. The remarkable correlation between phenotype and expansion size suggests that expansion of the tract leads to a specific gain of function in the mutant HOXD13 protein, and has interesting implications for the role of polyalanine tracts in the control of transcription.
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Mental retardation and epilepsy often occur together. They are both heterogeneous conditions with acquired and genetic causes. Where causes are primarily genetic, major advances have been made in unraveling their molecular basis. The human X chromosome alone is estimated to harbor more than 100 genes that, when mutated, cause mental retardation. At least eight autosomal genes involved in idiopathic epilepsy have been identified, and many more have been implicated in conditions where epilepsy is a feature. We have identified mutations in an X chromosome-linked, Aristaless-related, homeobox gene (ARX), in nine families with mental retardation (syndromic and nonspecific), various forms of epilepsy, including infantile spasms and myoclonic seizures, and dystonia. Two recurrent mutations, present in seven families, result in expansion of polyalanine tracts of the ARX protein. These probably cause protein aggregation, similar to other polyalanine and polyglutamine disorders. In addition, we have identified a missense mutation within the ARX homeodomain and a truncation mutation. Thus, it would seem that mutation of ARX is a major contributor to X-linked mental retardation and epilepsy.
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Investigation of a critical region for an X-linked mental retardation (XLMR) locus led us to identify a novel Aristaless related homeobox gene (ARX ). Inherited and de novo ARX mutations, including missense mutations and in frame duplications/insertions leading to expansions of polyalanine tracts in ARX, were found in nine familial and one sporadic case of MR. In contrast to other genes involved in XLMR, ARX expression is specific to the telencephalon and ventral thalamus. Notably there is an absence of expression in the cerebellum throughout development and also in adult. The absence of detectable brain malformations in patients suggests that ARX may have an essential role, in mature neurons, required for the development of cognitive abilities.
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Male embryonic mice with mutations in the X-linked aristaless-related homeobox gene (Arx) developed with small brains due to suppressed proliferation and regional deficiencies in the forebrain. These mice also showed aberrant migration and differentiation of interneurons containing gamma-aminobutyric acid (GABAergic interneurons) in the ganglionic eminence and neocortex as well as abnormal testicular differentiation. These characteristics recapitulate some of the clinical features of X-linked lissencephaly with abnormal genitalia (XLAG) in humans. We found multiple loss-of-function mutations in ARX in individuals affected with XLAG and in some female relatives, and conclude that mutation of ARX causes XLAG. The present report is, to our knowledge, the first to use phenotypic analysis of a knockout mouse to identify a gene associated with an X-linked human brain malformation.
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We recently identified mutations of ARX in nine genotypic males with X-linked lissencephaly with abnormal genitalia (XLAG), and in several female relatives with isolated agenesis of the corpus callosum (ACC). We now report 13 novel and two recurrent mutations of ARX, and one nucleotide change of uncertain significance in 20 genotypic males from 16 families. Most had XLAG, but two had hydranencephaly and abnormal genitalia, and three males from one family had Proud syndrome or ACC with abnormal genitalia. We obtained detailed clinical information on all 29 affected males, including the nine previously reported subjects. Premature termination mutations consisting of large deletions, frameshifts, nonsense mutations, and splice site mutations in exons 1 to 4 caused XLAG or hydranencephaly with abnormal genitalia. Nonconservative missense mutations within the homeobox caused less severe XLAG, while conservative substitution in the homeodomain caused Proud syndrome. A nonconservative missense mutation near the C-terminal aristaless domain caused unusually severe XLAG with microcephaly and mild cerebellar hypoplasia. In addition, several less severe phenotypes without malformations have been reported, including mental retardation with cryptogenic infantile spasms (West syndrome), other seizure types, dystonia or autism, and nonsyndromic mental retardation. The ARX mutations associated with these phenotypes have included polyalanine expansions or duplications, missense mutations, and one deletion of exon 5. Together, the group of phenotypes associated with ARX mutations demonstrates remarkable pleiotropy, but also comprises a nearly continuous series of developmental disorders that begins with hydranencephaly, lissencephaly, and agenesis of the corpus callosum, and ends with a series of overlapping syndromes with apparently normal brain structure.
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The newly identified gene, ARX, when mutated has been shown to cause both syndromic and nonsyndromic forms of mental retardation. It seems that the less severe forms are due to polyalanine expansions and missense mutations in the gene. We screened 682 developmentally retarded males for polyalanine expansions in ARX in order to examine the contribution of ARX mutations to the causes of developmental retardation. We also reinvestigated 11 putative MRX and three MR families where no cause of mental retardation had been found, by mutational analysis of ARX. Mutational analysis was also performed in 11 probands with autism from families with two or more affected males. We find that previously described polyalanine expansions of ARX are not a common cause of mental retardation.
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Poly-alanine (Ala) tract expansions in transcription factors have been shown to be associated with human birth defects such as malformations of the brain, the digits, and other structures. Expansions of a poly-Ala tract from 15 to 22 (+7)-29 (+14) Ala in Hoxd13, for example, result in the limb malformation synpolydactyly in humans and in mice [synpolydactyly homolog (spdh)]. Here, we show that an increase of the Ala repeat above a certain length (22 Ala) is associated with a shift in the localization of Hoxd13 from nuclear to cytoplasmic, where it forms large amorphous aggregates. We observed similar aggregates for expansion mutations in SOX3, RUNX2 and HOXA13, pointing to a common mechanism. Cytoplasmic aggregation of mutant Hoxd13 protein is influenced by the length of the repeat, the level of expression and the efficacy of degradation by the proteasome. Heat shock proteins Hsp70 and Hsp40 co-localize with the aggregates and activation of the chaperone system by geldanamycin leads to a reduction of aggregate formation. Furthermore, recombinant mutant Hoxd13 protein forms aggregates in vitro demonstrating spontaneous misfolding of the protein. We analyzed the mouse mutant spdh, which harbors a +7 Ala expansion in Hoxd13 similar to the human synpolydactyly mutations, as an in vivo model and were able to show a reduction of mutant Hoxd13 and, in contrast to wt Hoxd13, a primarily cytoplasmic localization of the protein. Our results provide evidence that poly-Ala repeat expansions in transcription factors result in misfolding, degradation and cytoplasmic aggregation of the mutant proteins.
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A growing number of human disorders have been associated with expansions of a tract of a single amino acid. Recently, polyalanine (polyA) tract expansions in the Aristaless-related homeobox (ARX) protein have been identified in a subset of patients with infantile spasms and mental retardation. How alanine expansions in ARX, or any other transcription factor, cause disease have not been determined. We generated a series of polyA expansions in Arx and expressed these in cell culture and brain slices. Transfection of these constructs results in nuclear protein aggregation, filamentous nuclear inclusions, and an increase in cell death. These inclusions are ubiquitinated and recruit Hsp70. Coexpressing Hsp70 decreases the percentage of cells with nuclear inclusions. Finally, we show that expressing mutant Arx in mouse brains results in neuronal nuclear inclusion formation. Our data suggest expansions in one of the ARX polyA tracts results in nuclear protein aggregation and an increase in cell death; likely underlying the pathogenesis of the associated infantile spasms and mental retardation.
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X-linked lissencephaly with abnormal genitalia is the first human disorder in which deficient tangential migration in the brain has been demonstrated. Male patients with X-linked lissencephaly with abnormal genitalia show intractable seizures, especially clonic convulsions or myoclonus from the first day of life, but neither infantile spasms nor hypsarrhythmia on electroencephalograms so far. Brain magnetic resonance imaging shows anterior pachygyria and posterior agyria with a mildly thick cortex, agenesis of the corpus callosum, and dysplastic basal ganglia. ARX, a paired-class homeobox gene with four polyalanine sequences, is a responsible gene for X-linked lissencephaly with abnormal genitalia. The brain of Arx knockout mice shows aberrant tangential migration and differentiation of gamma-aminobutyric acid (GABA)ergic interneurons. In human X-linked lissencephaly with abnormal genitalia, a neuropathologic study has suggested a loss of interneurons. Meanwhile, polyalanine expansion of ARX causes symptomatic or nonsymptomatic West's syndrome and nonsyndromic mental retardation. The striking epileptogenicity of X-linked lissencephaly with abnormal genitalia and West's syndrome associated with ARX mutations i s considered to be caused by a disorder of interneurons involving a tangentialmigration disorder. We propose "interneuronopathy" as a term for this.
Article
An early-infantile epileptic syndrome is reported. This syndrome is characterized by its early onset (less than 3 months of age), frequent tonic spasms, suppression-burst on EEG, extremely poor response to treatment and grave outcome. Out of 8 cases (5 boys and 3 girls) experienced thus far, 6 had thir onset before 1 month of age. Tonic spasms appeared in series in 4 cases, and were seen during awake and sleep period. The underlying pathologies, known in 4 cases, were porencephaly (in 2), Aicardi syndrome (in one), and subacute diffuse encephalopathy (in one). In all cases the EEG showed suppression-burst as a common denominator of this syndrome when awake or asleep, in addition to desynchronization during seizure. It is worthy of mention that hypsarhythmia was observed in 5 patients during the follow up period, and the transition to the West's syndrome in 4 cases. In most cases the suppression-burst pattern disappeared after 3 months of age. Follow up study of up to 3 years indicated the extreme ref actoriness to therapy; 4 are dead, and the remaining 4 have been suffering from severe mental and physical handicaps. Supposed pathophysiology of this syndrome studied from the burst-burst intervals was also discussed. In conclusion we would like to list this syndrome as the third specific, age-dependent childhood epileptic encephalopathy, to be entirely separated from the West's and the Lennox syndromes.
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Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disorder of late onset that commonly presents with ptosis and dysphagia. The genetic basis of the condition has been identified recently as a stable trinucleotide repeat expansion in exon 1 of the poly(A) binding protein 2 gene ( PABP2 ), in which (GCG)6 is the normal repeat length. The prevalence of OPMD is greatest in patients of French-Canadian origin. It is not clear if expansion repeat length is a reliable test in other populations. In this study, we analysed the phenotypic and genotypic characteristics of 31 patients with OPMD in the UK. Ptosis was the first reported symptom in two-thirds of the patients, and half of the subjects studied had evidence of ophthalmoplegia. All but one family had a pathological expansion in the PABP2 gene, ranging from (GCG)8 to (GCG)13. In contrast to the French-Canadian population, (GCG)10 was almost as common as (GCG)9, evidence against a strong founder effect in the UK population. There was a weak association between repeat length and age of disease onset. Patients with longer repeat lengths, such as (GCG)13, developed severe limb weakness early in the disease. We were unable to detect the (GCG)7 polymorphism in over 200 normal controls, suggesting that the frequency of this expansion is lower than that found in the French-Canadian population. One family was negative for the expansion. Affected members presented with the classical features of OPMD, namely ptosis, dysphagia and cytoplasmic inclusions on muscle biopsy, although with some atypical features, such as early age of onset, high serum levels of creatine kinase and a profound ophthalmoplegia. This family is an example of a GCG expansion-negative oculopharyngeal syndrome requiring further genetic investigation. We conclude that PABP2 analysis is a reliable non-invasive diagnostic test for OPMD in the UK population.
Article
Male embryonic mice with mutations in the X-linked aristaless-related homeobox gene (Arx) developed with small brains due to suppressed proliferation and regional deficiencies in the forebrain. These mice also showed aberrant migration and differentiation of interneurons containing γ-aminobutyric acid (GABAergic interneurons) in the ganglionic eminence and neocortex as well as abnormal testicular differentiation. These characteristics recapitulate some of the clinical features of X-linked lissencephaly with abnormal genitalia (XLAG) in humans. We found multiple loss-of-function mutations in ARX in individuals affected with XLAG and in some female relatives, and conclude that mutation of ARX causes XLAG. The present report is, to our knowledge, the first to use pheno- typic analysis of a knockout mouse to identify a gene associated with an X-linked human brain malformation.
Article
X-linked lissencephaly with absent corpus callosum and ambiguous genitalia is a newly recognized syndrome responsible for a severe neurological disorder of neonatal onset in boys. Based on the observations of 3 new cases, we confirm the phenotype in affected boys, describe additional MRI findings, report the neuropathological data, and show that carrier females may exhibit neurological and magnetic resonance imaging abnormalities. In affected boys, consistent clinical features of X-linked lissencephaly with absent corpus callosum and ambiguous genitalia are intractable epilepsy of neonatal onset, severe hypotonia, poor responsiveness, genital abnormalities, and early death. On magnetic resonance imaging, a gyration defect consisting of anterior pachygyria and posterior agyria with a moderately thickened brain cortex, dysplastic basal ganglia and complete agenesis of the corpus callosum are consistently found. Neuropathological examination of the brain shows a trilayered cortex containing exclusively pyramidal neurons, a neuronal migration defect, a disorganization of the basal ganglia, and gliotic and spongy white matter. Finally, females related to affected boys may have mental retardation and epilepsy, and they often display agenesis of the corpus callosum. These findings expand the phenotype of X-linked lissencephaly with absent corpus callosum and ambiguous genitalia, may help in the detection of carrier females in affected families, and give arguments for a semidominant X-linked mode of inheritance.
Article
A case of early infantile epileptic encephalopathy (EIEE) with suppression-bursts (Ohtahara syndrome) associated with a diffuse cerebral migrational and maturation disorder evident on microscopic examination is reported. Although virtually all reported cases of EIEE are secondary to a congenital or acquired structural malformation of cortical development, EIEE is sometimes identified only by detailed neuropathologic examination, as confirmed by this case report. In addition to the malformation of cortical development, the patient demonstrated an absence of gamma-aminobutyric acid in the cerebrospinal fluid. All children with EIEE should be thoroughly examined by magnetic resonance imaging, cerebrospinal fluid amino acid level determination, and detailed postmortem neuropathologic examination.
Article
Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disorder of late onset that commonly presents with ptosis and dysphagia. The genetic basis of the condition has been identified recently as a stable trinucleotide repeat expansion in exon 1 of the poly(A) binding protein 2 gene (PABP2), in which (GCG)(6) is the normal repeat length. The prevalence of OPMD is greatest in patients of French-Canadian origin. It is not clear if expansion repeat length is a reliable test in other populations. In this study, we analysed the phenotypic and genotypic characteristics of 31 patients with OPMD in the UK. Ptosis was the first reported symptom in two-thirds of the patients, and half of the subjects studied had evidence of ophthalmoplegia. All but one family had a pathological expansion in the PABP2 gene, ranging from (GCG)(8) to (GCG)(13). In contrast to the French-Canadian population, (GCG)(10) was almost as common as (GCG)(9), evidence against a strong founder effect in the UK population. There was a weak association between repeat length and age of disease onset. Patients with longer repeat lengths, such as (GCG)(13), developed severe limb weakness early in the disease. We were unable to detect the (GCG)(7) polymorphism in over 200 normal controls, suggesting that the frequency of this expansion is lower than that found in the French-Canadian population. One family was negative for the expansion. Affected members presented with the classical features of OPMD, namely ptosis, dysphagia and cytoplasmic inclusions on muscle biopsy, although with some atypical features, such as early age of onset, high serum levels of creatine kinase and a profound ophthalmoplegia. This family is an example of a GCG expansion-negative oculopharyngeal syndrome requiring further genetic investigation. We conclude that PABP2 analysis is a reliable non-invasive diagnostic test for OPMD in the UK population.
Article
Ohtahara syndrome (OS) is characterized by frequent tonic spasms, with or without clustering, of early onset within a few months of life, and a suppression-burst (S-B) pattern in electroencephalography (EEG). Tonic spasms occur in not only waking but also sleeping state in most cases. Partial seizures are observed in about one-third of cases. Brain imagings reveal structural abnormalities including malformations, notably asymmetric lesions in most cases.S-B pattern is persistently observed regardless of circadian cycle. Bursts of 1-3s duration alternate with nearly flat suppression phase of 2-5s at an approximately regular rate; 5-10s of burst-burst interval. Some asymmetry in S-B is noted in about two-thirds of cases. Ictal EEG of tonic spasms shows principally desynchronization with or without initial rapid activity. Tonic spasms appear concomitant with bursts. Characteristic age-dependent evolution from OS to West syndrome (WS) in many cases, and further from WS to Lennox-Gastaut syndrome (LGS) in some, proceed concomitantly with EEG transition from S-B to hypsarrhythmia at around age 3-6 months, and further from hypsarrhythmia to diffuse slow spike-waves at around age 1. Under the inclusive concept of the age-dependent epileptic encephalopathy, OS, WS, and LGS have common characteristics such as age preference, frequent minor generalized seizures, and continuous massive epileptic EEG abnormality. Mutual transition suggests the same pathophysiology among three syndromes and the age factor should be considered as the common denominator responsible for the manifestation of each of their own specific clinico-electrical features. Namely, these syndromes may be the age-specific epileptic reaction to various non-specific exogenous brain insults, acting at the specific developmental stages.
Article
Clinical data from 50 mentally retarded (MR) males in nine X-linked MR families, syndromic and non-specific, with mutations (duplication, expansion, missense, and deletion mutations) in the Aristaless related homeobox gene, ARX, were analysed. Seizures were observed with all mutations and occurred in 29 patients, including one family with a novel myoclonic epilepsy syndrome associated with the missense mutation. Seventeen patients had infantile spasms. Other phenotypes included mild to moderate MR alone, or with combinations of dystonia, ataxia or autism. These data suggest that mutations in the ARX gene are important causes of MR, often associated with diverse neurological manifestations.
Article
X-linked West syndrome, also called "X-linked infantile spasms" (ISSX), is characterized by early-onset generalized seizures, hypsarrhythmia, and mental retardation. Recently, we have shown that the majority of the X-linked families with infantile spasms carry mutations in the aristaless-related homeobox gene (ARX), which maps to the Xp21.3-p22.1 interval, and that the clinical picture in these patients can vary from mild mental retardation to severe ISSX with additional neurological abnormalities. Here, we report a study of two severely affected female patients with apparently de novo balanced X;autosome translocations, both disrupting the serine-threonine kinase 9 (STK9) gene, which maps distal to ARX in the Xp22.3 region. We show that STK9 is subject to X-inactivation in normal female somatic cells and is functionally absent in the two patients, because of preferential inactivation of the normal X. Disruption of the same gene in two unrelated patients who have identical phenotypes (consisting of early-onset severe infantile spasms, profound global developmental arrest, hypsarrhythmia, and severe mental retardation) strongly suggests that lack of functional STK9 protein causes severe ISSX and that STK9 is a second X-chromosomal locus for this disorder.
Article
Expansions of polyglutamine repeats are known to cause a variety of human neurodegenerative diseases. More recently, expansions of alanine tracts, particularly in transcription factor genes, have been shown to cause at least nine human conditions, including mental retardation and malformations of the brain, digits and other structures. Present knowledge suggests that alanine tract expansions generally, but not always, arise through unequal recombination as opposed to replication slippage, the most likely mechanism in other triplet repeat expansions. The function of alanine tracts is unknown but when alanine expansions occur in transcription factor genes, alanine tracts can result in either loss-of-function or gain of an abnormal function. Given the frequency of alanine tracts in proteins, it is likely that more alanine tract expansions will be discovered in disease genes.
Article
Expansions of trinucleotide repeats encoding polyalanine tracts have been recognized as the cause of several diseases, predominantly congenital malformation syndromes. To date, nine genes with alanine tract expansions have been described. With the exception of PABPN1, which codes for a poly(A)-binding protein, all these genes encode transcription factors that play important roles during development. Recent in vitro and in vivo findings indicate that expansions of polyalanine tracts beyond a certain threshold result in protein misfolding, aggregation and subsequent degradation. Polyalanine tracts are relatively common in the genome and occur most frequently in transcription factors and other proteins with nuclear localization. The molecular role of alanine tracts is unknown, but their strong evolutionary conservation suggests the existence of potent functional or structural constraints.
Article
The underlying genetic mutations for many inherited neurodegenerative disorders have been identified in recent years. One frequent type of mutation is trinucleotide repeat expansion. Depending on the location of the repeat expansion, the mutation might result in a loss of function of the disease gene, a toxic gain of function or both. Disease gene identification has led to the development of model systems for investigating disease mechanisms and evaluating treatments. Examination of experimental findings reveals similarities in disease mechanisms as well as possibilities for treatment.
Article
Heterozygous mutations of the PHOX2B gene account for a broad variety of disorders of the autonomic nervous system, either isolated or combined, including congenital central hypoventilation syndrome (CCHS), tumours of the sympathetic nervous system and Hirschsprung disease. In CCHS, the prevalent mutation is an expansion of a 20-alanine stretch ranging from +5 to +13 alanines, whereas frameshift and missense mutations are found occasionally. To determine the molecular basis of impaired PHOX2B function, we assayed the transactivation and DNA binding properties of wild-type and mutant PHOX2B proteins. Furthermore, we investigated aggregate formation by proteins with polyalanine tract expansions ranging from +5 to +13 alanines using immunofluorescence of transfected cells and gel filtration of in vitro translated proteins. We found that transactivation of the dopamine beta-hydroxylase promoter by PHOX2B proteins with frameshift and missense mutations was abolished or severely curtailed, as was in vitro DNA binding although the proteins localized to the nucleus. The transactivation potential of proteins with polyalanine tract expansions declined with increasing length of the polyalanine stretch, and DNA binding was affected for an expansion of +9 alanines and above. Cytoplasmic aggregation in transfected cells was only observed for the longest expansions, whereas even the short expansion mutants were prone to form multimers in vitro. Such a tendency to protein misfolding could explain loss of transactivation for alanine expansion mutations. However, additional mechanisms such as toxic gain-of-function may play a role in the pathogenic process.
Article
The Aristaless-related homeobox gene, ARX, is an important transcription factor with a crucial role in forebrain, pancreas and testes development. At least fifty-nine mutations have been described in the ARX gene in seven X-chromosome linked disorders involving mental retardation. Recent studies with ARX screening suggest that the gene is mutated in 9.5% of X-linked families with these disorders. Two different polyalanine expansion mutations represent 46% of all currently known mutations and show considerable pleiotropy. The ARX gene is emerging as one of the more important disease-causing genes on the X chromosome and ought to be considered for routine screening. Although the normal Arx protein is known to be a bifunctional transcriptional activator and repressor, the complete biochemical characterization of the normal and mutated ARX awaits further investigation. Pax4 was identified as one of the ARX target genes, and both proteins have crucial functions in endocrine mouse pancreas alpha-cell and beta-cell lineage specification.
Article
Symptomatic West syndrome has heterogeneous backgrounds. Recently, two novel genes, ARX and CDKL5, have been found to be responsible for cryptogenic West syndrome or infantile spasms. Both are located in the human chromosome Xp22 region and are mainly expressed and play roles in fetal brain. Moreover, several genes responsible for brain malformations including lissencephaly, which is frequently associated with West syndrome or infantile spasms, have been found, and the mechanisms responsible for the neural network disorders in these brain malformations are rapidly being determined. Findings of animal and in vitro studies and mutation analyses in humans are delineating the molecular and cellular basis of West syndrome.
Article
Unlabelled: Ohtahara syndrome (OS) is well known as a peculiar early onset epileptic syndrome with serious prognosis. The outline of OS, mainly in relation to the evolution with age, and differentiation from related conditions, particularly early myoclonic encephalopathy (EME) were mentioned. Results: Etiologically, structural brain lesions are most probable in OS, and non-structural/metabolic disorders in EME. Clinically, tonic spasms are the main seizures in OS, while myoclonia and frequent partial motor seizures in EME. Another difference is noted in EEG findings: suppression-bursts (SB) are consistently observed in both waking and sleeping states in OS, but suppression-bursts become more apparent in sleep in EME. The course observation clarifies differences between both syndromes; SBs evolve to hypsarrhythmia around 3-4 months of age, and sometimes further to diffuse slow spike-waves in OS. In contrast, in EME suppression-bursts may persist up to late childhood after a transient evolution to hypsarryhtmia in the middle to late infancy. Transition between syndromes is also specific; OS evolves to West syndrome, and further to Lennox-Gastaut syndrome with age, but EME persists long without such evolution excepting a transient phase of West syndrome. Conclusion: These clinicoelectrical characteristics and differential points strongly indicate the efficiency of the developmental study to delineate both syndromes.
Article
Aristaless-related homeobox gene (ARX) is an important paired-type homeobox gene involved in the development of human brain. The ARX gene mutations are a significant contributor to various forms of X-chromosome-linked mental retardation with and without additional features including epilepsy, lissencephaly with abnormal genitalia, hand dystonia or autism. Here we demonstrate that the human ARX protein is a potent transcriptional repressor, which binds to Groucho/transducin-like enhancer of split (TLE) co-factor proteins and the TLE1 in particular through its octapeptide (Engrailed homology repressor domain (eh-1) homology) domain. We show that the transcription repression activity of ARX is modulated by two strong repression domains, one located within the octapeptide domain and the second in the region of the polyalanine tract 4, and one activator domain, the aristaless domain. Importantly, we show that the transcription repression activity of ARX is affected by various naturally occurring mutations. The introduction of the c.98T>C (p.L33P) mutation results in the lack of binding to TLE1 protein and relaxed transcription repression. The introduction of the two most frequent ARX polyalanine tract expansion mutations increases the repression activity in a manner dependent on the number of extra alanines. Interestingly, deletions of alanine residues within polyalanine tracts 1 and 2 show low or no effect. In summary we demonstrate that the ARX protein is a strong transcription repressor, we identify novel ARX interacting proteins (TLE) and offer an explanation of a molecular pathogenesis of some ARX mutations, including the most frequent ARX mutations, the polyalanine tract expansion mutations, c.304ins(GCG)7 and c.428_451dup.
Polymorphism, shared functions and convergent evo-366 The American Journal of Human Genetics Volume 81 August 2007 www.ajhg.org lution of genes with sequences coding for polyalanine domains
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Lavoie H, Debeane F, Trinh QD, Turcotte JF, Corbeil-Girard LP, Dicaire MJ, Saint-Denis A, Page M, Rouleau GA, Brais B (2003) Polymorphism, shared functions and convergent evo-366 The American Journal of Human Genetics Volume 81 August 2007 www.ajhg.org lution of genes with sequences coding for polyalanine domains. Hum Mol Genet 12:2967–2979
Therapeutic effect of ACTH and gamma-globulin in 8 cases with the early-infantile epileptic encephalopathy with suppression-burst (EIEE)
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[Therapeutic effect of ACTH and gamma-globulin in 8 cases with the early-infantile epileptic encephalopathy with suppression-burst (EIEE).]
  • Miyake