Dissecting the genetic basis of myoclonic-astatic epilepsy

International League Against Epilepsy classification and definition of epilepsy syndromes with onset in childhood: Position paper by the ILAE Task Force on Nosology and Definitions

The 2017 International League Against Epilepsy classification has defined a three-tier system with epilepsy syndrome identification at the third level. Although a syndrome cannot be determined in all children with epilepsy, identification of a specific syndrome provides guidance on management and prognosis. In this paper, we describe the childhood onset epilepsy syndromes, most of which have both mandatory seizure type(s) and interictal electroencephalographic (EEG) features. Based on the 2017 Classification of Seizures and Epilepsies, some syndrome names have been updated using terms directly describing the seizure semiology. Epilepsy syndromes beginning in childhood have been divided into three categories: (1) self-limited focal epilepsies, comprising four syndromes: self-limited epilepsy with centrotemporal spikes, self-limited epilepsy with autonomic seizures, childhood occipital visual epilepsy, and photosensitive occipital lobe epilepsy; (2) generalized epilepsies, comprising three syndromes: childhood absence epilepsy, epilepsy with myoclonic absence, and epilepsy with eyelid myoclonia; and (3) developmental and/or epileptic encephalopathies, comprising five syndromes: epilepsy with myoclonic-atonic seizures, Lennox-Gastaut syndrome, developmental and/or epileptic encephalopathy with spike-and-wave activation in sleep, hemiconvulsion-hemiplegia-epilepsy syndrome, and febrile infection-related epilepsy syndrome. We define each, highlighting the mandatory seizure(s), EEG features, phenotypic variations, and findings from key investigations.

The Role of Focal Epilepsy Features in Defining SCN1A Mutation-positive Dravet Syndrome as Generalized and Focal Epilepsy

Background and Purpose

This study was aimed to describe focal epilepsy features of SCN1A mutation-positive Dravet syndrome patients.

Methods

A total of 82 SCN1A mutation-positive patients were reviewed retrospectively (39 boys and 43 girls). Seizure type and electroencephalography (EEG) findings were investigated according to the stage, disease onset, and steady state (after age 2 years). Long-term video EEG data were used to classify the seizure type.

Results

Focal seizures at onset and the steady state were found in 54.9% (45/82) and 90% (63/70) of patients, respectively. Afebrile focal seizures were an initial seizure in about one fourth of the patients (22/82, 26.8%). Of 48 seizures captured during long-term video EEG monitoring of 30 patients, 19 seizures were classified as focal onset (39.6%). Of the 19 focal seizures, 12 were either focal motor or focal non-motor seizures, and seven were focal onset bilateral tonic-clonic seizure. Focal epileptiform discharges were more frequent than generalized epileptiform discharges at seizure onset and during the clinical course on conventional EEG (3.7% vs. 0%, 52.9% vs. 32.9%, respectively).

Conclusions

Our study provides a comprehensive description of focal epilepsy features of SCN1A mutation-positive Dravet syndrome patients. Recognizing these features as defining the clinical spectrum of Dravet syndrome may lead to earlier genetic diagnosis and tailored management.

Structural brain abnormalities in epilepsy with myoclonic atonic seizures

OBJECTIVE

Epilepsy with myoclonic atonic seizure (EMAS) occurs in young children with previously normal to subnormal development. The outcome ranges from seizure freedom with preserved cognitive abilities to refractory epilepsy with intellectual disability (ID). Routine brain imaging typically shows no abnormalities. We aimed to compare the brain morphometry of EMAS patients with healthy subjects several years after epilepsy onset, and to correlate it to epilepsy severity and cognitive findings.

METHODS

Fourteen EMAS patients (4 females, 5-14 years) and 14 matched healthy controls were included. Patients were classified into three outcome groups (good, intermediate, poor) according to seizure control and cognitive and behavioral functioning. Individual anatomical data (T1-weighted sequence) were processed using the FreeSurfer pipeline. Cortical volume (CV), cortical thickness (CT), local gyrification index (LGI), and subcortical volumes were used for group-comparison and linear regression analyses.

RESULTS

Morphometric comparison between EMAS patients and healthy controls revealed that patients have 1) reduced CV in frontal, temporal and parietal lobes (p = <.001; 0.009 and 0.024 respectively); 2) reduced CT and LGI in frontal lobes (p = 0.036 and 0.032 respectively); and 3) a neat cerebellar volume reduction (p = 0.011). Neither the number of anti-seizure medication nor the duration of epilepsy was related to cerebellar volume (both p > 0.62). Poor outcome group was associated with lower LGI. Patients in good and intermediate outcome groups had a comparable LGI to their matched healthy controls (p > 0.27 for all lobes).

CONCLUSIONS

Structural brain differences were detectable in our sample of children with EMAS, mainly located in the frontal lobes and cerebellum. These findings are similar to those found in patients with genetic/idiopathic generalized epilepsies. Outcome groups correlated best with LGI. Whether these anatomical changes reflect genetically determined abnormal neuronal networks or a consequence of sustained epilepsy remains to be solved with prospective longitudinal studies.

STX1B-related epilepsy in a 24-month-old female infant

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Mutations of STX1B. can cause febrile and afebrile seizures.

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We found a heterozygous de novo variant c.733C>T (p.Arg245*) in STX1B.

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She was afebrile and presented as MAE with tonic-clonic seizures and no family history.

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One patient with the identical gene mutation had febrile and afebrile seizures but no evidence of MAE.

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Our finding adds to the phenotypic diversity of patients with STX1B. gene mutations.

We report on a 24-month-old girl with age-appropriate development and normal intellectual ability suffering from myoclonic astatic epilepsy. Panel-based sequencing of roughly 1500 genes associated with neurodevelopmental and metabolic diseases identified a heterozygous de novo point mutation in STX1B (c.733C>T or p.Arg245*). STX1B encodes Syntaxin-1B which plays a role for synaptic transmission. STX1B variants are associated with a broad phenotypic spectrum of epilepsies including febrile or afebrile seizures as well as epileptic encephalopathies. Our patient with MAE adds to the spectrum of STX1B associated phenotypes.

Epilepsy with myoclonic-atonic seizures (Doose syndrome): Clarification of diagnosis and treatment options through a large retrospective multicenter cohort

OBJECTIVE

Epilepsy with myoclonic-atonic seizures (EMAS) is a rare childhood onset epileptic encephalopathy. There is no clear consensus for recommended treatments, and pharmacoresistance is common. To better assess the clinical phenotype, most effective treatment, and determinants of cognitive and seizure outcomes, three major pediatric epilepsy centers combined data, creating the largest cohort of patients with EMAS ever studied to date.

METHODS

Authors performed a retrospective chart review of patients with EMAS who received care at the authors' institutions.

RESULTS

A total of 166 children were identified. Global developmental delay (>1 domain) was present in 2% of children at onset and 49% during the course of the disease. Afebrile seizures occurred after the age of 2 years in 88%, generalized tonic-clonic seizures in 60%, and drop attack or myoclonic seizures in 30%. At onset, electroencephalography (EEG) found 28% normal, background slowing in 20%, and epileptiform discharges or seizures in 69%. Subsequent EEG found slowing in 62% and discharges or seizures in 90%. Response (>50% seizure reduction) to the first three antiseizure drugs (ASDs) was 26% (levetiracetam, 17%; valproic acid, 31%; other ASDs combined, 26%). Diet therapy was used as a second or third therapy in 19% and ultimately used in 57%; response was 79%, significantly greater than the first three ASDs (P = .005, χ² ). Seizure freedom occurred in 57% and was less likely in the case of persistent global developmental delays (P < .001), seizure recorded on subsequent EEGs (P = .027), and failure to respond to diet therapy (P = .005). Development was normal in 47%, and 12% had delays in one domain, which was less likely in the case of global developmental delay after epilepsy onset (P < .001) and failure to achieve seizure freedom (P < .001).

SIGNIFICANCE

This large cohort of children with EMAS clarifies areas of variability in practice. Diet therapy is by far the most effective treatment; failure to respond was associated with failure to attain seizure freedom. This therapy should be used early in the treatment in EMAS. This study also identified a bidirectional link between cognitive and seizure outcomes.

Epilepsy With Myoclonic Atonic Seizures: Why Is the Yield of Genetic Testing for a "Presumed Genetic" Epilepsy Low?

Phenotypic and Genetic Spectrum of Epilepsy With Myoclonic Atonic Seizures

Tang S, Addis L, Smith A, Topp SD, Pendziwiat M, Mei D, Parker A, Agrawal S, Hughes E, Lascelles K, Williams RE, Fallon P, Robinson R, Cross HJ, Hedderly T, Eltze C, Kerr T, Desurkar A, Hussain N, Kinali M, Bagnasco I, Vassallo G, Whitehouse W, Goyal S, Absoud M, EuroEPINOMICS-RES Consortium, Møller RS, Helbig I, Weber, YG, Marini C, Guerrini R, Simpson MA, Pal DK. Epilepsia. 2020;61(5):995-1007. doi: 10.1111/epi.16508

Objective:

We aimed to describe the extent of neurodevelopmental impairments and identify the genetic etiologies in a large cohort of patients with epilepsy with myoclonic atonic seizures (MAEs).

Methods:

We deeply phenotyped patients with MAE for epilepsy features, intellectual disability, autism spectrum disorder, and attention-deficit/hyperactivity disorder using standardized neuropsychological instruments. We performed exome analysis (whole exome sequencing) filtered on epilepsy and neuropsychiatric gene sets to identify genetic etiologies.

Results:

We analyzed 101 patients with MAE (70% male). The median age of seizure onset was 34 months (range = 6-72 months). The main seizure types were myoclonic atonic or atonic in 100%, generalized tonic-clonic in 72%, myoclonic in 69%, absence in 60%, and tonic seizures in 19% of patients. We observed intellectual disability in 62% of patients, with extremely low adaptive behavioral scores in 69%. In addition, 24% exhibited symptoms of autism and 37% exhibited attention-deficit/hyperactivity symptoms. We discovered pathogenic variants in 12 (14%) of 85 patients, including 5 previously published patients. These were pathogenic genetic variants in SYNGAP1 (n = 3), KIAA2022 (n = 2), and SLC6A1 (n = 2), as well as KCNA2, SCN2A, STX1B, KCNB1, and MECP2 (n = 1 each). We also identified 3 new candidate genes, ASH1L, CHD4, and SMARCA2 in 1 patient each.

Significance:

MAE is associated with significant neurodevelopmental impairment. MAE is genetically heterogeneous, and we identified a pathogenic genetic etiology in 14% of this cohort by exome analysis. These findings suggest that MAE is a manifestation of several etiologies rather than a discrete syndromic entity.

Clinical and genetic characteristics of patients with Doose syndrome

OBJECTIVE

To elucidate the genetic background and genotype-phenotype correlations for epilepsy with myoclonic-atonic seizures, also known as myoclonic-astatic epilepsy (MAE) or Doose syndrome.

METHODS

We collected clinical information and blood samples from 29 patients with MAE. We performed whole-exome sequencing for all except one MAE case in whom custom capture sequencing identified a variant.

RESULTS

We newly identified four variants: SLC6A1 and HNRNPU missense variants and microdeletions at 2q24.2 involving SCN1A and Xp22.31 involving STS. Febrile seizures preceded epileptic or afebrile seizures in four patients, of which two patients had gene variants. Myoclonic-atonic seizures occurred at onset in four patients, of which two had variants, and during the course of disease in three patients. Variants were more commonly identified in patients with a developmental delay or intellectual disability (DD/ID), but genetic status was not associated with the severity of DD/ID. Attention-deficit/hyperactivity disorder and autistic spectrum disorder were less frequently observed in patients with variants than in those with unknown etiology.

SIGNIFICANCE

MAE patients had genetic heterogeneity, and HNRNPU and STS emerged as possible candidate causative genes. Febrile seizures prior to epileptic seizures and myoclonic-atonic seizure at onset indicate a genetic predisposition to MAE. Comorbid conditions were not related to genetic predisposition to MAE.

Dissecting the phenotypic and genetic spectrum of early childhood-onset generalized epilepsies

PURPOSE

Although the genetic and clinical aspects of epilepsy with myoclonic-atonic seizures (MAE) and early onset absence epilepsy (EOAE) have been investigated thoroughly, other early childhood-onset generalized epilepsies that share clinical features with MAE and EOAE have not been characterized. In this study, we aimed to delineate the genetic and phenotypic spectrum of early childhood-onset generalized epilepsies, including MAE and EOAE.

METHODS

We recruited 61 patients diagnosed with MAE, EOAE, genetic epilepsy with febrile seizure plus (GEFS+) and unclassified generalized epilepsies that shared seizure onset age and seizure types. Genetic causes were investigated through targeted gene panel testing, whole exome sequencing, chromosomal microarray, and single-gene Sanger sequencing.

RESULTS

We classified 11 patients with MAE, 20 with EOAE, 9 with GEFS + spectrum. Epilepsy syndrome was not specified in the remaining 21 patients. The clinical features were comparable across groups. Nevertheless, patients with EOAE tended to show better developmental and seizure outcomes. A total of 23 pathogenic sequences and copy number variants from 12 genes were identified (23/61, 37.7%). Genetic etiologies were confirmed in 36.4% (4/11) of the MAE group, 45% (9/20) of the EOAE group, 22.2% (2/9) of the GEFS + spectrum, and 38.1% (8/21) of the unclassified group. The most frequently identified genes with pathogenic variants were SLC6A1 (7 patients), SLC2A1 (4 patients), and SYNGAP1 (4 patients).

CONCLUSION

Early childhood-onset generalized epilepsy appeared to be characterized by an overlapping genetic and phenotypic spectrum. SLC6A1 and SLC2A1 appeared to be important genetic causes of early childhood-onset generalized epilepsy.

Adolescent-onset absence epilepsy years after resolution of childhood epilepsy with myoclonic-atonic seizures

We present a case series of three boys with childhood epilepsy with myoclonic–atonic seizures (EMAS) who achieved complete remission during childhood only to develop absence seizures during early adolescence. In all three cases, the recurrent seizures resolved again with antiseizure drugs, and two are currently medication-free for a second time.

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Three boys with epilepsy and myoclonic–atonic seizures were successfully controlled with antiseizure drugs.

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All three achieved controlled and were tapered off antiseizure drugs with relapse that achieved electro-clinical control.

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Two of 3 boys successfully remain off antiseizure drugs for greater than 1 year following the second relapse.

Exome sequencing findings in 27 patients with myoclonic-atonic epilepsy: Is there a major genetic factor?

Myoclonic-atonic epilepsy (MAE) is thought to have a genetic etiology. Mutations in CHD2, SLC2A1 and SLC6A1 genes have been reported in few patients showing often intellectual disability prior to MAE onset. We aimed to explore putative causal genetic factors in MAE. We performed array-CGH and whole-exome sequencing in 27 patients. We considered non-synonymous variants, splice acceptor, donor site mutations, and coding insertions/deletions. A gene was causal when its mutations have been already linked to epilepsy or other brain diseases or when it has a putative function in neuronal excitability or brain development. We identified candidate disease-causing variants in 11 patients (41%). Single variants were found in some known epilepsy-associated genes (namely CHD2, KCNT1, KCNA2 and STXBP1) but not in others (SLC2A1 and SLC6A1). One new candidate gene SUN1 requires further validation. MAE shows underlying genetic heterogeneity with only few cases linked to mutations in genes reported in developmental and epileptic encephalopathies.

Clinical spectrum of STX1B-related epileptic disorders

OBJECTIVE

The aim of this study was to expand the spectrum of epilepsy syndromes related to STX1B, encoding the presynaptic protein syntaxin-1B, and establish genotype-phenotype correlations by identifying further disease-related variants.

METHODS

We used next-generation sequencing in the framework of research projects and diagnostic testing. Clinical data and EEGs were reviewed, including already published cases. To estimate the pathogenicity of the variants, we used established and newly developed in silico prediction tools.

RESULTS

We describe 17 new variants in STX1B, which are distributed across the whole gene. We discerned 4 different phenotypic groups across the newly identified and previously published patients (49 patients in 23 families): (1) 6 sporadic patients or families (31 affected individuals) with febrile and afebrile seizures with a benign course, generally good drug response, normal development, and without permanent neurologic deficits; (2) 2 patients with genetic generalized epilepsy without febrile seizures and cognitive deficits; (3) 13 patients or families with intractable seizures, developmental regression after seizure onset and additional neuropsychiatric symptoms; (4) 2 patients with focal epilepsy. More often, we found loss-of-function mutations in benign syndromes, whereas missense variants in the SNARE motif of syntaxin-1B were associated with more severe phenotypes.

CONCLUSION

These data expand the genetic and phenotypic spectrum of STX1B-related epilepsies to a diverse range of epilepsies that span the International League Against Epilepsy classification. Variants in STX1B are protean and contribute to many different epilepsy phenotypes, similar to SCN1A, the most important gene associated with fever-associated epilepsies.

Genetic testing in a cohort of patients with potential epilepsy with myoclonic-atonic seizures

Epilepsy with myoclonic-atonic seizures (EMAS) accounts for 1-2% of all childhood-onset epilepsies. EMAS has been shown to have an underlying genetic component, however the genetics of this disorder is not yet well understood. The purpose of this study was to review genetic testing results for a cohort of EMAS patients. A retrospective chart review was conducted for 77 patients evaluated at Children's Hospital Colorado with a potential diagnosis of EMAS. Genetic testing and biochemical testing was reviewed. Family history data was also collected. Seventy-seven percent of the cohort had at least one genetic test performed, and a molecular diagnosis was reached for six patients. Thirty-seven patients had a microarray, six of which identified a copy number variant. Only one was felt to contribute to the phenotype (2p16.3 deletion including NRXN1). Fifty-one patients had an epilepsy panel, two of which were positive (likely pathogenic variant in SCN1A, pathogenic variant in GABRG2). Of the six patients who had whole exome sequencing, two were negative, three were positive or likely positive, and one had multiple variants not felt to explain the phenotype. While EMAS is widely accepted to have a strong genetic component, the diagnostic yield of genetic testing remains low. This may be because several genes now thought to be associated with EMAS are not included on the more commonly ordered epilepsy panels, or have only recently been added to them.

How do we diagnose and treat epilepsy with myoclonic-atonic seizures (Doose syndrome)? Results of the Pediatric Epilepsy Research Consortium survey

OBJECTIVE

To obtain and assess opinions on EMAS diagnostic criteria, recommended investigations, and therapeutic options, from a large group of physicians who care for children with EMAS.

METHODS

The EMAS focus group of PERC created a survey to assess the opinions of pediatric neurologists who care for children with EMAS regarding diagnosis and treatment of this condition, which was sent to members of PERC, AES, and CNS. A Likert scale was used to assess the respondents' opinions on the importance of diagnostic and exclusion criteria (five point scale), investigations (four point scale), and treatment (six point scale) of EMAS. Inclusion/exclusion criteria were then classified as critical, strong, or modest. Investigations were classified as essential, recommended, or possible. Therapies were classified as first line, beneficial, indeterminate benefit, or contraindicated.

RESULTS

Survey results from the 76 participants determined the following: EMAS inclusion criteria: history suggestive of MAS (critical), recorded or home video suggestive of MAS, generalized discharges on inter-ictal EEG, normal neuroimaging, normal development prior to seizure onset (strong). EMAS exclusionary criteria: epileptic spasms, abnormal neuroimaging, focal abnormal exam, seizure onset <six months or >six years (strong).

RECOMMENDED INVESTIGATIONS

EEG and MRI (essential), amino acids, organic acids, fatty acid/acylcarnitine profile, microarray, genetic panel, lactate/pyruvate, CSF and serum glucose/lactate (strong).

RECOMMENDED TREATMENTS

Valproic acid (first line), topiramate, zonisamide, levetiracetam, benzodiazepines, and dietary therapies (beneficial).

SIGNIFICANCE

To date, no similar surveys have been published, even though early syndrome identification and initiation of effective treatment have been associated with improved outcome in EMAS. Medications that exacerbate seizures in EMAS have also been identified. This survey identified critical and preferred diagnostic electro clinical features, investigations, and treatments for EMAS. It will guide future research and is a crucial first step in defining specific diagnostic criteria, recommended evaluation, and most effective therapies for EMAS.

Modified Atkins diet is an effective treatment for children with Doose syndrome

OBJECTIVE

Children with myoclonic astatic epilepsy (MAE; Doose syndrome) whose seizures do not respond immediately to standard antiepileptic drugs (AEDs) are at high risk of developing an epileptic encephalopathy with cognitive decline. A classic ketogenic diet (KD) is a highly effective alternative to AEDs. To date, there are only limited data on the effectiveness of the modified Atkins diet (MAD), which is less restrictive and more compatible with daily life. We report findings from a retrospective study on 30 MAE patients treated with MAD.

METHODS

Four participating centers retrospectively identified all patients with MAE in whom a MAD had been started before June 2015. Seven children were recruited from a cohort included in an open prospective controlled trial. A retrospective review of all available charts was performed in the other patients.

RESULTS

Thirty patients (24 boys) were included. Mean age at epilepsy onset was 3.1 years (range 1.5-5.6). MAD was started at a mean age of 4.5 years (range 2.2-9.1) after the children had received an average of six different AEDs (range 2-15). Mean MAD observation time was 18.7 months (range 1.5-61.5). Twenty of 30 patients were still on MAD at the end of study (duration range 1.5-61.5, mean 18.5 months). MAD was stopped without relapse in three patients after sustained seizure freedom for >2 years. For the other seven cases, ineffectiveness (three patients), loss of efficacy (two), or noncompliance (two) led to termination. No severe adverse effects were noted. By the end of the observation period, 25 (83%) of 30 patients experienced a seizure reduction by ≥50% and 14 (47%) of 30 were seizure-free. None of the evaluated factors differed significantly between the groups of seizure-free and non-seizure-free children.

SIGNIFICANCE

MAD is an effective treatment for MAE. It should be considered as an alternative to AEDs or the more restrictive classic ketogenic diet.

Haploinsufficiency of the STX1B gene is associated with myoclonic astatic epilepsy

We describe an 18-year-old male patient with myoclonic astatic epilepsy (MAE), moderate to severe intellectual disability, behavioural problems, several dysmorphisms and a 1.2-Mb de novo deletion on chromosome 16p11.2. This deletion results in haploinsufficiency of STX1B and other genes. Recently, variants in the STX1B gene have been associated with a wide spectrum of fever-related epilepsies ranging from single febrile seizures to severe epileptic encephalopathies. Two previously reported patients with a STX1B missense variant or deletion were diagnosed with MAE. Our observation of a STX1B deletion in a third patient with MAE therefore supports that STX1B gene variants or deletions can be involved in the aetiology of MAE. Furthermore, STX1B encodes for syntaxin-1B, of which interaction with the protein encoded by the STXBP1 gene is essential for the regulation of the synaptic transmission of neurotransmitters. STXBP1 gene variants have been identified in patients with many different types of epilepsy, including Dravet syndrome and epileptic encephalopathies, suggesting STX1B plays a similar role. We recommend that analysis of STX1B should be considered in the diagnostic work-up of individuals with MAE.

CHD2 mutations are a rare cause of generalized epilepsy with myoclonic-atonic seizures

Chromodomain helicase DNA-binding protein 2 (CHD2) gene mutations have been reported in patients with myoclonic-atonic epilepsy (MAE), as well as in patients with Lennox-Gastaut, Dravet, and Jeavons syndromes and other epileptic encephalopathies featuring generalized epilepsy and intellectual disability. The aim of this study was to assess the impact of CHD2 mutations in a series of patients with MAE. Twenty patients affected by MAE were included in the study. We analyzed antecedents, age at onset, seizure semiology and frequency, EEG, treatment, and neuropsychological outcome. We sequenced the CHD2 gene with Sanger technology. We identified a CHD2 frameshift mutation in one patient (c.4256del19). He was a 17-year-old boy with no familial history for epilepsy and normal development before epilepsy onset. Epilepsy onset was at 3years and 5months: he presented with myoclonic-atonic seizures, head drops, myoclonic jerks, and absences. Interictal EEGs revealed slow background activity associated with generalized epileptiform abnormalities and photoparoxysmal response. His seizures were highly responsive to valproic acid, and an attempt to withdraw it led to seizure recurrence. Neuropsychological evaluation revealed moderate intellectual disability. Chromodomain-helicase-DNA-binding protein 2 is not the major gene associated with MAE. Conversely, CHD2 could be responsible for a proper phenotype characterized by infantile-onset generalized epilepsy, intellectual disability, and photosensitivity, which might overlap with MAE, Lennox-Gastaut, Dravet, and Jeavons syndromes.