Genetic epilepsy with febrile seizures plus: Refining the spectrum

Identifying individuals with rare disease variants by inferring shared ancestral haplotypes from SNP array data

We describe FoundHaplo, an identity-by-descent algorithm that can be used to screen untyped disease-causing variants using single nucleotide polymorphism (SNP) array data. FoundHaplo leverages knowledge of shared disease haplotypes for inherited variants to identify those who share the disease haplotype and are, therefore, likely to carry the rare [minor allele frequency (MAF) ≤ 0.01%] variant. We performed a simulation study to evaluate the performance of FoundHaplo across 33 disease-harbouring loci. FoundHaplo was used to infer the presence of two rare (MAF ≤ 0.01%) pathogenic variants, SCN1B c.363C>G (p.Cys121Trp) and WWOX c.49G>A (p.E17K), which can cause mild dominant and severe recessive epilepsy, respectively, in the Epi25 cohort and the UK Biobank. FoundHaplo demonstrated substantially better sensitivity at inferring the presence of these rare variants than existing genome-wide imputation. FoundHaplo is a valuable screening tool for searching disease-causing variants with known founder effects using only SNP genotyping data. It is also applicable to nonhuman applications and nondisease-causing traits, including rare-variant drivers of quantitative traits. The FoundHaplo algorithm is available at https://github.com/bahlolab/FoundHaplo (DOI:10.5281/zenodo.8058286).

Epilepsy with myoclonic-atonic seizures: an update on genetic causes, nosological limits, and treatment strategies

Epilepsy with myoclonic-atonic seizures is a childhood-onset epilepsy syndrome characterised by a range of seizure types, including myoclonic-atonic, atonic, myoclonic, absence, and generalised tonic-clonic seizures. The causes and outcomes of this syndrome are highly variable, with many uncertainties surrounding its classification and prognosis. Traditional antiseizure medications and the ketogenic diet remain the main treatment options. Although two-thirds of children attain remission from seizures without cognitive or behavioural sequelae, some continue to have drug-resistant seizures, intellectual disability, and behavioural problems. The identification of single-gene causes in a substantial subset of patients highlights the importance of genetic testing for development of personalised treatment strategies. However, diagnostic complexities have hindered the development of trials for new therapies. Better recognition of the distinct features of epilepsy with myoclonic-atonic seizures, combined with advances in molecular genetic testing, will pave the way for more focused clinical research and drug development. Future studies should aim to identify genetic causes and tailor treatment options, offering hope for improved long-term outcomes.

ADGRL1 variants: From developmental and epileptic encephalopathy to genetic epilepsy with febrile seizures plus

AIM

To expand the phenotypic spectrum of ADGRL1 and explore the correlation between epilepsy and the ADGRL1 genotype.

METHOD

We performed whole-exome sequencing in a cohort of 115 families (including 195 males and 150 females) with familial febrile seizure or epilepsy with unexplained aetiology. The damaging effects of variants was predicted using protein modelling and multiple in silico tools. All reported patients with ADGRL1 pathogenic variants were analysed.

RESULTS

One new ADGRL1 variant (p.Pro753Leu) was identified in one family with genetic epilepsy with febrile seizures. Further analysis of 12 ADGRL1 variants in 16 patients revealed that six patients had epilepsy. Epilepsy types ranged from early-onset epileptic encephalopathy to genetic epilepsy with febrile seizures plus (GEFS+). All four variants associated with epilepsy were located in the non-helix or sheet region of ADGRL1. Three of the four epilepsy-associated variants were missense variants. Thus, all three variants located in the G-protein-coupled receptor autoproteolytic-inducing domain exhibited epilepsy.

INTERPRETATION

We found one new missense variant of ADGRL1 in one family with GEFS+. ADGRL1 may be a potential candidate or susceptibility gene for epilepsy. ADGRL1-associated epilepsy ranged from benign GEFS+ to severe epileptic encephalopathy; the genotypes and variant locations may help explain the phenotypic heterogeneity of patients with the ADGRL1 variant.

Voltage-gated sodium channels in genetic epilepsy: up and down of excitability

The past two decades have witnessed a wide range of studies investigating genetic variants of voltage-gated sodium (NaV) channels, which are involved in a broad spectrum of diseases, including several types of epilepsy. We have reviewed here phenotypes and pathological mechanisms of genetic epilepsies caused by variants in NaV α and β subunits, as well as of some relevant interacting proteins (FGF12/FHF1, PRRT2, and Ankyrin-G). Notably, variants of all these genes can induce either gain- or loss-of-function of NaV leading to either neuronal hyperexcitability or hypoexcitability. We present the results of functional studies obtained with different experimental models, highlighting that they should be interpreted considering the features of the experimental system used. These systems are models, but they have allowed us to better understand pathophysiological issues, ameliorate diagnostics, orientate genetic counseling, and select/develop therapies within a precision medicine framework. These studies have also allowed us to gain insights into the physiological roles of different NaV channels and of the cells that express them. Overall, our review shows the progress that has been made, but also the need for further studies on aspects that have not yet been clarified. Finally, we conclude by highlighting some significant themes of general interest that can be gleaned from the results of the work of the last two decades.

Investigating the effect of polygenic background on epilepsy phenotype in 'monogenic' families

BACKGROUND

Phenotypic variability within families with epilepsy is often observed, even when relatives share the same monogenic cause. We aimed to investigate whether common polygenic risk for epilepsy could explain the penetrance and phenotypic expression of rare pathogenic variants in familial epilepsies.

METHODS

We studied 58 clinically heterogeneous families with genetic epilepsy with febrile seizures plus (GEFS+). Relatives were coded as either unaffected or affected with epilepsy, and graded according to phenotype severity: no seizures, febrile seizures (FS) only, febrile seizures plus (FS+), generalised/focal epilepsy, or developmental and epileptic encephalopathy (DEE). Epilepsy polygenic risk scores (PRSs) were tested for association with epilepsy phenotype. Within families, the mean PRS difference was compared between pairs concordant versus discordant for phenotype severity. Statistical analyses were performed using mixed-effect regression models.

FINDINGS

304 individuals segregating a known, or presumed, rare variant of large effect, were studied. Within families, higher epilepsy polygenic risk was associated with an epilepsy diagnosis (OR = 1.39, 95% CI 1.08, 1.80, padj = 0.040). Relatives with a more severe phenotype had a mean pairwise PRS difference of +0.19 higher than relatives with a milder phenotype (padj = 0.010). The difference increased with greater phenotype discordance between relatives. As the cohort included two rare variants with >30 relatives each, variant-specific genotype-phenotype associations could also be analysed. Whilst the epilepsy PRS effect was strong for relatives segregating the GABRG2 p.Arg82Gln pathogenic variant (padj = 0.0010), the effect was not significant for SCN1B p.Cys121Trp.

INTERPRETATION

We provide support for genetic background modifying the penetrance and phenotypic expression of rare variants associated with 'monogenic' epilepsies. In GEFS+ families, relatives with higher epilepsy PRSs were more likely to show penetrance (epilepsy diagnosis) and a more severe phenotype. Variant-specific analyses suggest that some rare variants may be more susceptible to PRS modification, carrying important genetic counselling and disease prognostication implications for patients.

FUNDING

National Health and Medical Research Council of Australia, Medical Research Future Fund of Australia.

Developmental and epileptic encephalopathy 56 due to YWHAG variants: 12 new cases and review of the literature

BACKGROUND AND OBJECTIVES

Developmental and epileptic encephalopathy 56 (DEE-56) is caused by pathogenic variants in YWHAG and is characterized by early-onset epilepsy and neurodevelopmental delay. This study reports on a cohort of DEE-56 individuals, correlating antiseizure medication usage and comorbidities, to aid in understanding disease evolution.

METHODS

We analyzed data from thirty-nine individuals aged 3-40 years with YWHAG variants, including 12 previously unreported individuals (2 of these with recurrent distal 7q11.23 deletions) and 27 previously published cases (21 families, including 3 adult individuals reported in a family case). Our assessments encompassed clinical, radiological, and genetic evaluations. All procedures adhered to standardized protocols for patient approvals, registrations, and data collection.

RESULTS

Individuals with YWHAG variants exhibited variable psychomotor delay, with the majority experiencing mild intellectual disability. Early-onset seizures, particularly febrile seizures, were common, with various seizure types reported. Valproic acid has emerged as an effective antiseizure medication. Movement disorders were present in a subset of individuals, primarily manifesting as ataxia and tremor. Comorbidities such as autism spectrum disorders and attention deficit-hyperreactivity disorder were observed in a proportion of individuals. We identified a novel YWHAG variant (c.634_645del/p.Asn212_Ser215del) and expanded the genotypic spectrum of the disease.

CONCLUSIONS

We provide insights into the clinical, radiological, and genetic features of YWHAG-related epileptic encephalopathy. Despite mild clinical symptoms, affected individuals face challenges in daily functioning, underscoring the need for comprehensive care. Valproic acid has been used for seizure control with variable results.

Clinical and genetic analysis of 23 Chinese children with epilepsy associated with KCNQ2 gene mutations

OBJECTIVE

To summarize the clinical features and genetic mutation characteristics of Chinese children with KCNQ2-related epilepsy.

METHODS

A cohort of children with genetically caused epilepsy was evaluated at Linyi People's Hospital from January 2017 to December 2023. After next-generation sequencing and pathogenicity analysis, we summarized the medical records and genetic testing data of the children who had KCNQ2 gene mutations.

RESULTS

We identified 23 KCNQ2 gene mutations. 73.9% (n = 17) of the mutation sites were located in S5-S6 segments and the C-terminal region. In addition to the common phenotypes, 2 new phenotypes were identified: infantile convulsion with paroxysmal choreoathetosis (ICCA) and febrile seizure plus (FS+). Of all the cases with abnormal video-electro-encephalography, three cases with self-limited familial infantile epilepsy (SeLNE) exhibited a small number of multifocal discharges. Of the patients who have taken a particular antiepileptic drug, the statistics on the number of patients who have responded to the drug are as follows: oxcarbazepine (8/9, 88.9%), levetiracetam (5/7, 71.4%), phenobarbital (9/16, 56.3%), and topiramate (2/5, 40.0%). However, the efficacy of phenobarbital varied widely in treating SeLNE and KCNQ2-DEE. At the final follow-up, 1 case with SeLNE had a transient developmental regression and 7 cases with KCNQ2-DEE had mild to severe developmental backwardness.

SIGNIFICANCE

Although clinically rare, we report 10 new KCNQ2 mutations and two new phenotypes: ICCA and FS+. This further expands genetic and phenotypic spectrum of KCNQ2-related epilepsy. The gene mutation sites are mostly located in S5-S6 segments and the C-terminal region, and the former is usually associated with KCNQ2-DEE. Sodium channel blockers (including oxcarbazepine and topiramate) and levetiracetam should be prioritized over phenobarbital for KCNQ2-DEE. Some cases with KCNQ2-related epilepsy may have transient developmental regression during periods of frequent seizures. Early treatment and early seizure control may be beneficial for willing outcomes in children with KCNQ2-DEE.

PLAIN LANGUAGE SUMMARY

This article reports 23 cases of children with KCNQ2-related epilepsy, including 10 new mutation sites and 2 new phenotypes. It further expands the genetic and phenotypic spectrum of KCNQ2-related epilepsy. In addition, the article summarizes the gene mutation characteristics and clinical manifestations of children with KCNQ2-related epilepsy, with the expectation of providing a certain theoretical basis for the diagnosis and treatment of such patients.

Developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies, the most severe group of epilepsies, are characterized by seizures and frequent epileptiform activity associated with developmental slowing or regression. Onset typically occurs in infancy or childhood and includes many well-defined epilepsy syndromes. Patients have wide-ranging comorbidities including intellectual disability, psychiatric features, such as autism spectrum disorder and behavioural problems, movement and musculoskeletal disorders, gastrointestinal and sleep problems, together with an increased mortality rate. Problems change with age and patients require substantial support throughout life, placing a high psychosocial burden on parents, carers and the community. In many patients, the aetiology can be identified, and a genetic cause is found in >50% of patients using next-generation sequencing technologies. More than 900 genes have been identified as monogenic causes of developmental and epileptic encephalopathies and many cell components and processes have been implicated in their pathophysiology, including ion channels and transporters, synaptic proteins, cell signalling and metabolism and epigenetic regulation. Polygenic risk score analyses have shown that common variants also contribute to phenotypic variability. Holistic management, which encompasses antiseizure therapies and care for multimorbidities, is determined both by epilepsy syndrome and aetiology. Identification of the underlying aetiology enables the development of precision medicines to improve the long-term outcome of patients with these devastating diseases.

Voltage-gated sodium channel epilepsies in a tertiary care center: Phenotypic spectrum with correlation to predicted functional effects

BACKGROUND

Variants in sodium channel genes (SCN) are strongly associated with epilepsy phenotypes. Our aim in this study to evaluate the genotype and phenotype correlation of patients with SCN variants in our tertiary care center.

METHODS

In this retrospective study, patients with SCN variants and epilepsy who were followed up at our clinic between 2018 and 2022 were evaluated. Our study discussed the demographics of the patients, the seizure types, the age of seizure onset, the SCN variants, the domains and the functions of the variants, the magnetic resonance imaging findings, the motor, cognitive, and psychiatric comorbidities, and the response to anti-seizure medication. Genetic testing was conducted using a next-generation sequencing gene panel (epilepsy panel) or a whole-exome sequencing. For evaluating variant function, we used a prediction tool (https://funnc.shinyapps.io/shinyappweb/ site). To assess protein domains, we used the PER viewer (http://per.broadinstitute.org/).

RESULTS

Twenty-three patients with SCN variants and epilepsy have been identified. Sixteen patients had variants in the SCN1A, six patients had variants in the SCN2A, and one patient had a variant in the SCN3A. Two novel SCN1A variants and two novel SCN2A variants were identified. The analysis revealed 14/23 missense, 6/23 nonsense, 2/23 frameshift, and 1/23 splice site variants in the SCN. There are seven variants predicted to be gain-of-function and 13 predicted to be loss-of-function. Among 23 patients; 11 had Dravet Syndrome, 6 had early infantile developmental and epileptic encephalopathy, three had genetic epilepsy with febrile seizures plus spectrum disorder, one had self-limited familial neonatal-infantile epilepsy, one had self-limited infantile epilepsy and one had infantile childhood development epileptic encephalopathy.

CONCLUSION

Our cohort consists of mainly SCN1 variants, most of them were predicted to be loss of function. Dravet syndrome was the most common phenotype. The prediction tool used in our study demonstrated overall compatibility with clinical findings. Due to the diverse clinical manifestations of variant functions, it may assist in guiding medication selection and predicting outcomes. We believe that such a tool will help the clinician in both prognosis prediction and solving therapeutic challenges in this group where refractory seizures are common.

Insights into clinical phenotypes and treatment responses in a Small cohort of Taiwanese patients with SCN1A variants: A Preliminary study

BACKGROUND

SCN1A channelopathy is the most well-known cause for epileptic encephalopathies and contributes to a wide phenotypic spectrum. The variable expressivity is troublesome for the interpretation of clinical significance and prognoses. To investigate the clinical manifestations, medications and outcomes of patients with SCN1A channelopathies, we conducted this observation retrospective study in Taiwan.

METHODS

A cohort consisting of 16 patients (5 males and 11 females) from multiple centers with identified SCN1A variants was investigated and phenotypically relevant factors were recorded. The variants were identified using NGS and confirmed by Sanger sequencing. A panel of 90 epileptic-related genes was used to identify SCN1A variants and to evaluate some of the potential SCN1A modifier genes.

RESULTS

The mean age of seizure onset was 10.4 months. Twelve of the sixteen patients (75%) had different degrees of neurocognitive sequela and psychobehavioral comorbidity in our cohort. Cognitive impairment was noted in all ten patients with Dravet syndrome (DS) and in two of the patients with non-DS phenotypes. A lower response rate to medications was also noted in patients with DS. Notably, a medication-specific tendency towards valproic acid (VPA), clobazam (CLB), and levetiracetam (LEV) was observed, revealing the effective pharmacotherapies for SCN1A-related seizures. An asymptomatic carrier with a reported pathogenic SCN1A variant was reviewed along with her monozygotic twin sister with DS. Nine novel SCN1A mutations are herein reported, eight of which being classified as pathogenic.

CONCLUSION

Our study revealed unfavorable outcomes for patients with SCN1A variants. Some patients with SCN1A channelopathy showed specific responsiveness to the pharmacotherapies previously either recommended or contraindicated for these patients. Our study also expands the genotype and provides valuable prognostic insights in patients with SCN1A channelopathy.

GABRG2 mutations in genetic epilepsy with febrile seizures plus: structure, roles, and molecular genetics

Genetic epilepsy with febrile seizures plus (GEFS+) is a genetic epilepsy syndrome characterized by a marked hereditary tendency inherited as an autosomal dominant trait. Patients with GEFS+ may develop typical febrile seizures (FS), while generalized tonic-clonic seizures (GTCSs) with fever commonly occur between 3 months and 6 years of age, which is generally followed by febrile seizure plus (FS+), with or without absence seizures, focal seizures, or GTCSs. GEFS+ exhibits significant genetic heterogeneity, with polymerase chain reaction, exon sequencing, and single nucleotide polymorphism analyses all showing that the occurrence of GEFS+ is mainly related to mutations in the gamma-aminobutyric acid type A receptor gamma 2 subunit (GABRG2) gene. The most common mutations in GABRG2 are separated in large autosomal dominant families, but their pathogenesis remains unclear. The predominant types of GABRG2 mutations include missense (c.983A → T, c.245G → A, p.Met199Val), nonsense (R136*, Q390*, W429*), frameshift (c.1329delC, p.Val462fs*33, p.Pro59fs*12), point (P83S), and splice site (IVS6+2T → G) mutations. All of these mutations types can reduce the function of ion channels on the cell membrane; however, the degree and mechanism underlying these dysfunctions are different and could be linked to the main mechanism of epilepsy. The γ2 subunit plays a special role in receptor trafficking and is closely related to its structural specificity. This review focused on investigating the relationship between GEFS+ and GABRG2 mutation types in recent years, discussing novel aspects deemed to be great significance for clinically accurate diagnosis, anti-epileptic treatment strategies, and new drug development.

Channelopathies in epilepsy: an overview of clinical presentations, pathogenic mechanisms, and therapeutic insights

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders.

Genotype-phenotype associations in 1018 individuals with SCN1A-related epilepsies

OBJECTIVE

SCN1A variants are associated with epilepsy syndromes ranging from mild genetic epilepsy with febrile seizures plus (GEFS+) to severe Dravet syndrome (DS). Many variants are de novo, making early phenotype prediction difficult, and genotype-phenotype associations remain poorly understood.

METHODS

We assessed data from a retrospective cohort of 1018 individuals with SCN1A-related epilepsies. We explored relationships between variant characteristics (position, in silico prediction scores: Combined Annotation Dependent Depletion (CADD), Rare Exome Variant Ensemble Learner (REVEL), SCN1A genetic score), seizure characteristics, and epilepsy phenotype.

RESULTS

DS had earlier seizure onset than other GEFS+ phenotypes (5.3 vs. 12.0 months, p < .001). In silico variant scores were higher in DS versus GEFS+ (p < .001). Patients with missense variants in functionally important regions (conserved N-terminus, S4-S6) exhibited earlier seizure onset (6.0 vs. 7.0 months, p = .003) and were more likely to have DS (280/340); those with missense variants in nonconserved regions had later onset (10.0 vs. 7.0 months, p = .036) and were more likely to have GEFS+ (15/29, χ2 = 19.16, p < .001). A minority of protein-truncating variants were associated with GEFS+ (10/393) and more likely to be located in the proximal first and last exon coding regions than elsewhere in the gene (9.7% vs. 1.0%, p < .001). Carriers of the same missense variant exhibited less variability in age at seizure onset compared with carriers of different missense variants for both DS (1.9 vs. 2.9 months, p = .001) and GEFS+ (8.0 vs. 11.0 months, p = .043). Status epilepticus as presenting seizure type is a highly specific (95.2%) but nonsensitive (32.7%) feature of DS.

SIGNIFICANCE

Understanding genotype-phenotype associations in SCN1A-related epilepsies is critical for early diagnosis and management. We demonstrate an earlier disease onset in patients with missense variants in important functional regions, the occurrence of GEFS+ truncating variants, and the value of in silico prediction scores. Status epilepticus as initial seizure type is a highly specific, but not sensitive, early feature of DS.

Drug-resistant generalized epilepsies: Revisiting the frontiers of idiopathic generalized epilepsies

The 2017 International League Against Epilepsy (ILAE) classification suggested that the term "genetic generalized epilepsies" (GGEs) should be used for the broad group of epilepsies with so-called "generalized" seizure types and "generalized" spike-wave activity on EEG, based on a presumed genetic etiology. Within this framework, idiopathic generalized epilepsies (IGEs) are described as a subset of GGEs and include only four epileptic syndromes: childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with generalized tonic-clonic seizures alone. The recent 2022 ILAE definition of IGEs is based on the current state of knowledge and reflects a community consensus and is designed to evolve as knowledge advances. The term "frontiers of IGEs" refers to the actual limits of our understanding of these four syndromes. Indeed, among patients presenting with a syndrome compatible with the 2022 definition of IGEs, we still observe a significant proportion of patients presenting with specific clinical features, refractory seizures, or drug-resistant epilepsies. This leads to the discussion of the boundaries of IGEs and GGEs, or what is accepted within a clinical spectrum of a definite IGE. Here, we discuss several entities that have been described in the literature for many years and that may either constitute rare features of IGEs or a distinct differential diagnosis. Their recognition by clinicians may allow a more individualized approach and improve the management of patients presenting with such entities.

CRISPR/Cas9 system and its applications in nervous system diseases

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is an acquired immune system of many bacteria and archaea, comprising CRISPR loci, Cas genes, and its associated proteins. This system can recognize exogenous DNA and utilize the Cas9 protein's nuclease activity to break DNA double-strand and to achieve base insertion or deletion by subsequent DNA repair. In recent years, multiple laboratory and clinical studies have revealed the therapeutic role of the CRISPR/Cas9 system in neurological diseases. This article reviews the CRISPR/Cas9-mediated gene editing technology and its potential for clinical application against neurological diseases.

Identification of potential disease-associated variants in idiopathic generalized epilepsy using targeted sequencing

Many questions remain regarding the genetics of idiopathic generalized epilepsy (IGE), a subset of genetic generalized epilepsy (GGE). We aimed to identify the candidate coding variants of epilepsy panel genes in a cohort of affected individuals, using variant frequency information from a control cohort of the same region. We performed whole-exome sequencing analysis of 121 individuals and 10 affected relatives, focusing on variants of 950 candidate genes associated with epilepsy according to the Genes4Epilepsy curated panel. We identified 168 candidate variants (CVs) in 137 of 950 candidate genes in 88 of 121 affected individuals with IGE, of which 61 were novel variants. Notably, we identified five CVs in known GGE-associated genes (CHD2, GABRA1, RORB, SCN1A, and SCN1B) in five individuals and CVs shared by affected individuals in each of four family cases for other epilepsy candidate genes. The results of this study demonstrate that IGE is a disease with high heterogeneity and provide IGE-associated CVs whose pathogenicity should be proven by future studies, including advanced functional analysis. The low detection rate of CVs in the GGE-associated genes (4.1%) in this study suggests the current incompleteness of the Genes4Epilepsy panel for the diagnosis of IGE in clinical practice.

Epilepsies

Recent advances in genetic diagnosis have revealed the underlying etiology of many epilepsies and have identified pathogenic, causative variants in numerous ion and ligand-gated channel genes. This chapter describes the clinical presentations of epilepsy associated with different channelopathies including classic electroclinical syndromes and emerging gene-specific phenotypes. Also discussed are the archetypal epilepsy channelopathy, SCN1A-Dravet syndrome, considering the expanding phenotype. Clinical presentations where a channelopathy is suspected, such as sleep-related hypermotor epilepsy and epilepsy in association with movement disorders, are reviewed. Channelopathies pose an intriguing problem for the development of gene therapies. Design of targeted therapies requires physiologic insights into the often multifaceted impact of a pathogenic variant, coupled with an understanding of the phenotypic spectrum of a gene. As gene-specific novel therapies come online for the channelopathies, it is essential that clinicians are able to recognize epilepsy phenotypes likely to be due to channelopathy and institute early genetic testing in both children and adults. These findings are likely to have immediate management implications and to inform prognostic and reproductive counseling.

Prediction of molecular phenotypes for novel SCN1A variants from a Turkish genetic epilepsy syndromes cohort and report of two new patients with recessive Dravet syndrome

Dravet syndrome and genetic epilepsy with febrile seizures plus (GEFS+) are both epilepsy syndromes that can be attributed to deleterious mutations occurring in SCN1A, the gene encoding the pore-forming α-subunit of the NaV 1.1 voltage-gated sodium channel predominantly expressed in the central nervous system. In this research endeavor, our goal is to expand our prior cohort of Turkish patients affected by SCN1A-positive genetic epilepsy disorders. This will be accomplished by incorporating two recently discovered and infrequent index cases who possess a novel biallelic (homozygous) SCN1A missense variant, namely E158G, associated with Dravet syndrome. Furthermore, our intention is to use computational techniques to predict the molecular phenotypes of each distinct SCN1A variant that has been detected to date within our center. The correlation between genotype and phenotype in Dravet syndrome/GEFS+ is intricate and necessitates meticulous clinical investigation as well as advanced scientific exploration. Broadened mechanistic and structural insights into NaV 1.1 dysfunction offer significant promise in facilitating the development of targeted and effective therapies, which will ultimately enhance clinical outcomes in the treatment of epilepsy.

Familial Mesial Temporal Lobe Epilepsy: Clinical Spectrum and Genetic Evidence for a Polygenic Architecture

OBJECTIVE

Familial mesial temporal lobe epilepsy (FMTLE) is an important focal epilepsy syndrome; its molecular genetic basis is unknown. Clinical descriptions of FMTLE vary between a mild syndrome with prominent déjà vu to a more severe phenotype with febrile seizures and hippocampal sclerosis. We aimed to refine the phenotype of FMTLE by analyzing a large cohort of patients and asked whether common risk variants for focal epilepsy and/or febrile seizures, measured by polygenic risk scores (PRS), are enriched in individuals with FMTLE.

METHODS

We studied 134 families with ≥ 2 first or second-degree relatives with temporal lobe epilepsy, with clear mesial ictal semiology required in at least one individual. PRS were calculated for 227 FMTLE cases, 124 unaffected relatives, and 16,077 population controls.

RESULTS

The age of patients with FMTLE onset ranged from 2.5 to 70 years (median = 18, interquartile range = 13-28 years). The most common focal seizure symptom was déjà vu (62% of cases), followed by epigastric rising sensation (34%), and fear or anxiety (22%). The clinical spectrum included rare cases with drug-resistance and/or hippocampal sclerosis. FMTLE cases had a higher mean focal epilepsy PRS than population controls (odds ratio = 1.24, 95% confidence interval = 1.06, 1.46, p = 0.007); in contrast, no enrichment for the febrile seizure PRS was observed.

INTERPRETATION

FMTLE is a generally mild drug-responsive syndrome with déjà vu being the commonest symptom. In contrast to dominant monogenic focal epilepsy syndromes, our molecular data support a polygenic basis for FMTLE. Furthermore, the PRS data suggest that sub-genome-wide significant focal epilepsy genome-wide association study single nucleotide polymorphisms are important risk variants for FMTLE. ANN NEUROL 2023;94:825-835.

Widespread genomic influences on phenotype in Dravet syndrome, a 'monogenic' condition

Dravet syndrome is an archetypal rare severe epilepsy, considered 'monogenic', typically caused by loss-of-function SCN1A variants. Despite a recognizable core phenotype, its marked phenotypic heterogeneity is incompletely explained by differences in the causal SCN1A variant or clinical factors. In 34 adults with SCN1A-related Dravet syndrome, we show additional genomic variation beyond SCN1A contributes to phenotype and its diversity, with an excess of rare variants in epilepsy-related genes as a set and examples of blended phenotypes, including one individual with an ultra-rare DEPDC5 variant and focal cortical dysplasia. The polygenic risk score for intelligence was lower, and for longevity, higher, in Dravet syndrome than in epilepsy controls. The causal, major-effect, SCN1A variant may need to act against a broadly compromised genomic background to generate the full Dravet syndrome phenotype, whilst genomic resilience may help to ameliorate the risk of premature mortality in adult Dravet syndrome survivors.

An SCN1A gene missense variant in a Chinese Tujia ethnic family with genetic epilepsy with febrile seizures plus

Genetic epilepsy with febrile seizures plus (GEFSP) is a familial epileptic syndrome that is genetically heterogeneous and inherited in an autosomal dominant form in most cases. To date, at least seven genes have been reported to associate with GEFSP. This study aimed to identify the disease-causing variant in a Chinese Tujia ethnic family with GEFSP by using whole exome sequencing, Sanger sequencing, and in silico prediction. A heterozygous missense variant c.5725A>G (p.T1909A) was identified in the sodium voltage-gated channel alpha subunit 1 gene (SCN1A) coding region. The variant co-segregated with the GEFSP phenotype in this family, and it was predicted as disease-causing by multiple in silico programs, which was proposed as the genetic cause of GEFSP, further genetically diagnosed as GEFSP2. These findings expand the genetic and phenotypic spectrum of GEFSP and should contribute to genetic diagnoses, personalized therapies, and prognoses.

Gain of function SCN1A disease-causing variants: Expanding the phenotypic spectrum and functional studies guiding the choice of effective antiseizure medication

OBJECTIVE

This study was undertaken to refine the spectrum of SCN1A epileptic disorders other than Dravet syndrome (DS) and genetic epilepsy with febrile seizures plus (GEFS+) and optimize antiseizure management by correlating phenotype-genotype relationship and functional consequences of SCN1A variants in a cohort of patients.

METHODS

Sixteen probands carrying SCN1A pathogenic variants were ascertained via a national collaborative network. We also performed a literature review including individuals with SCN1A variants causing non-DS and non-GEFS+ phenotypes and compared the features of the two cohorts. Whole cell patch clamp experiments were performed for three representative SCN1A pathogenic variants.

RESULTS

Nine of the 16 probands (56%) had de novo pathogenic variants causing developmental and epileptic encephalopathy (DEE) with seizure onset at a median age of 2 months and severe intellectual disability. Seven of the 16 probands (54%), five with inherited and two with de novo variants, manifested focal epilepsies with mild or no intellectual disability. Sodium channel blockers never worsened seizures, and 50% of patients experienced long periods of seizure freedom. We found 13 SCN1A missense variants; eight of them were novel and never reported. Functional studies of three representative variants showed a gain of channel function. The literature review led to the identification of 44 individuals with SCN1A variants and non-DS, non-GEFS+ phenotypes. The comparison with our cohort highlighted that DEE phenotypes are a common feature.

SIGNIFICANCE

The boundaries of SCN1A disorders are wide and still expanding. In our cohort, >50% of patients manifested focal epilepsies, which are thus a frequent feature of SCN1A pathogenic variants beyond DS and GEFS+. SCN1A testing should therefore be included in the diagnostic workup of pediatric, familial and nonfamilial, focal epilepsies. Alternatively, non-DS/non-GEFS+ phenotypes might be associated with gain of channel function, and sodium channel blockers could control seizures by counteracting excessive channel function. Functional analysis evaluating the consequences of pathogenic SCN1A variants is thus relevant to tailor the appropriate antiseizure medication.

Pathogenetic and etiologic considerations of febrile seizures

Febrile seizure (FS), which occurs in febrile children without underlying health problems, is the most common type of seizure disorder in children. The suggested pathogenesis of FS derived from several animal and human studies is multifactorial and debatable. Neuronal hyperexcitability, which develops during inflammatory responses that accompany fever, provokes seizures. However, the exact role of each inflammatory mediator (e.g., cytokines) is undefined in terms of the connection between systemic or local inflammation and the central nervous system, and the mechanisms by which cytokines increase neuronal excitability remain unclear. In contrast, the cause of fever in most children with FS is usually mild respiratory virus infection (e.g., rhinovirus, influenza virus, adenovirus, and enterovirus) rather than severe bacterial infections. In temperate regions, the major causative respiratory viruses seem to mirror seasonally prevalent respiratory viruses in the community. Therefore, vigorous efforts to identify the causative pathogen of fever may not be necessary in children with FS. Genetic factors seem to play a role in neuronal hyperexcitability, and some types of genetic variation have been identified in several genes encoding ion channels of neurons that participate in neuronal excitation. Although most children with FS have benign outcomes, some characteristics such as complex FS, febrile status epilepticus, consecutive afebrile seizures, and the presence of neurodevelopmental disabilities may require further genetic and neurologic evaluations.

Fundamental Neurochemistry Review: GABAA receptor neurotransmission and epilepsy: Principles, disease mechanisms and pharmacotherapy

Epilepsy is a common neurological disorder associated with alterations of excitation-inhibition balance within brain neuronal networks. GABA_A receptor neurotransmission is the most prevalent form of inhibitory neurotransmission and is strongly implicated in both the pathophysiology and treatment of epilepsy, serving as a primary target for antiseizure medications for over a century. It is now established that GABA exerts a multifaceted influence through an array of GABA_A receptor subtypes that extends far beyond simply negating excitatory activity. As the role of GABA_A neurotransmission within inhibitory circuits is elaborated, this will enable the development of precision therapies that correct the network dysfunction underlying epileptic pathology.

SCN1A channelopathies: Navigating from genotype to neural circuit dysfunction

The SCN1A gene is strongly associated with epilepsy and plays a central role for supporting cortical excitation-inhibition balance through the expression of Na_V1.1 within inhibitory interneurons. The phenotype of SCN1A disorders has been conceptualized as driven primarily by impaired interneuron function that predisposes to disinhibition and cortical hyperexcitability. However, recent studies have identified SCN1A gain-of-function variants associated with epilepsy, and the presence of cellular and synaptic changes in mouse models that point toward homeostatic adaptations and complex network remodeling. These findings highlight the need to understand microcircuit-scale dysfunction in SCN1A disorders to contextualize genetic and cellular disease mechanisms. Targeting the restoration of microcircuit properties may be a fruitful strategy for the development of novel therapies.

The gain of function SCN1A disorder spectrum: novel epilepsy phenotypes and therapeutic implications

Brain voltage-gated sodium channel NaV1.1 (SCN1A) loss-of-function variants cause the severe epilepsy Dravet syndrome, as well as milder phenotypes associated with genetic epilepsy with febrile seizures plus. Gain of function SCN1A variants are associated with familial hemiplegic migraine type 3. Novel SCN1A-related phenotypes have been described including early infantile developmental and epileptic encephalopathy with movement disorder, and more recently neonatal presentations with arthrogryposis. Here we describe the clinical, genetic and functional evaluation of affected individuals. Thirty-five patients were ascertained via an international collaborative network using a structured clinical questionnaire and from the literature. We performed whole-cell voltage-clamp electrophysiological recordings comparing sodium channels containing wild-type versus variant NaV1.1 subunits. Findings were related to Dravet syndrome and familial hemiplegic migraine type 3 variants. We identified three distinct clinical presentations differing by age at onset and presence of arthrogryposis and/or movement disorder. The most severely affected infants (n = 13) presented with congenital arthrogryposis, neonatal onset epilepsy in the first 3 days of life, tonic seizures and apnoeas, accompanied by a significant movement disorder and profound intellectual disability. Twenty-one patients presented later, between 2 weeks and 3 months of age, with a severe early infantile developmental and epileptic encephalopathy and a movement disorder. One patient presented after 3 months with developmental and epileptic encephalopathy only. Associated SCN1A variants cluster in regions of channel inactivation associated with gain of function, different to Dravet syndrome variants (odds ratio = 17.8; confidence interval = 5.4-69.3; P = 1.3 × 10-7). Functional studies of both epilepsy and familial hemiplegic migraine type 3 variants reveal alterations of gating properties in keeping with neuronal hyperexcitability. While epilepsy variants result in a moderate increase in action current amplitude consistent with mild gain of function, familial hemiplegic migraine type 3 variants induce a larger effect on gating properties, in particular the increase of persistent current, resulting in a large increase of action current amplitude, consistent with stronger gain of function. Clinically, 13 out of 16 (81%) gain of function variants were associated with a reduction in seizures in response to sodium channel blocker treatment (carbamazepine, oxcarbazepine, phenytoin, lamotrigine or lacosamide) without evidence of symptom exacerbation. Our study expands the spectrum of gain of function SCN1A-related epilepsy phenotypes, defines key clinical features, provides novel insights into the underlying disease mechanisms between SCN1A-related epilepsy and familial hemiplegic migraine type 3, and identifies sodium channel blockers as potentially efficacious therapies. Gain of function disease should be considered in early onset epilepsies with a pathogenic SCN1A variant and non-Dravet syndrome phenotype.

A founder event causing a dominant childhood epilepsy survives 800 years through weak selective pressure

Genetic epilepsy with febrile seizures plus (GEFS+) is an autosomal dominant familial epilepsy syndrome characterized by distinctive phenotypic heterogeneity within families. The SCN1B c.363C>G (p.Cys121Trp) variant has been identified in independent, multi-generational families with GEFS+. Although the variant is present in population databases (at very low frequency), there is strong clinical, genetic, and functional evidence to support pathogenicity. Recurrent variants may be due to a founder event in which the variant has been inherited from a common ancestor. Here, we report evidence of a single founder event giving rise to the SCN1B c.363C>G variant in 14 independent families with epilepsy. A common haplotype was observed in all families, and the age of the most recent common ancestor was estimated to be approximately 800 years ago. Analysis of UK Biobank whole-exome-sequencing data identified 74 individuals with the same variant. All individuals carried haplotypes matching the epilepsy-affected families, suggesting all instances of the variant derive from a single mutational event. This unusual finding of a variant causing an autosomal dominant, early-onset disease in an outbred population that has persisted over many generations can be attributed to the relatively mild phenotype in most carriers and incomplete penetrance. Founder events are well established in autosomal recessive and late-onset disorders but are rarely observed in early-onset, autosomal dominant diseases. These findings suggest variants present in the population at low frequencies should be considered potentially pathogenic in mild phenotypes with incomplete penetrance and may be more important contributors to the genetic landscape than previously thought.

Does long-term phenytoin have a place in Dravet syndrome?

Anti-seizure medications that block sodium channels are generally considered contraindicated in Dravet syndrome. There is, however, considerable debate about the sodium-channel blocker phenytoin, which is often used for status epilepticus, a frequent feature of Dravet syndrome. We describe four patients with Dravet syndrome in whom long-term phenytoin therapy reduced seizure frequency and duration. In two patients, phenytoin produced prolonged periods without status epilepticus for the first time. Attempting to wean phenytoin in all patients after 1 to 20 years of use resulted in seizure exacerbation. Reintroducing phenytoin improved seizure control, suggesting phenytoin is beneficial in some patients with Dravet syndrome.

SCN1A overexpression, associated with a genomic region marked by a risk variant for a common epilepsy, raises seizure susceptibility

Mesial temporal lobe epilepsy with hippocampal sclerosis and a history of febrile seizures is associated with common variation at rs7587026, located in the promoter region of SCN1A. We sought to explore possible underlying mechanisms. SCN1A expression was analysed in hippocampal biopsy specimens of individuals with mesial temporal lobe epilepsy with hippocampal sclerosis who underwent surgical treatment, and hippocampal neuronal cell loss was quantitatively assessed using immunohistochemistry. In healthy individuals, hippocampal volume was measured using MRI. Analyses were performed stratified by rs7587026 type. To study the functional consequences of increased SCN1A expression, we generated, using transposon-mediated bacterial artificial chromosome transgenesis, a zebrafish line expressing exogenous scn1a, and performed EEG analysis on larval optic tecta at 4 day post-fertilization. Finally, we used an in vitro promoter analysis to study whether the genetic motif containing rs7587026 influences promoter activity. Hippocampal SCN1A expression differed by rs7587026 genotype (Kruskal-Wallis test P = 0.004). Individuals homozygous for the minor allele showed significantly increased expression compared to those homozygous for the major allele (Dunn's test P = 0.003), and to heterozygotes (Dunn's test P = 0.035). No statistically significant differences in hippocampal neuronal cell loss were observed between the three genotypes. Among 597 healthy participants, individuals homozygous for the minor allele at rs7587026 displayed significantly reduced mean hippocampal volume compared to major allele homozygotes (Cohen's D = - 0.28, P = 0.02), and to heterozygotes (Cohen's D = - 0.36, P = 0.009). Compared to wild type, scn1lab-overexpressing zebrafish larvae exhibited more frequent spontaneous seizures [one-way ANOVA F(4,54) = 6.95 (P < 0.001)]. The number of EEG discharges correlated with the level of scn1lab overexpression [one-way ANOVA F(4,15) = 10.75 (P < 0.001]. Finally, we showed that a 50 bp promoter motif containing rs7587026 exerts a strong regulatory role on SCN1A expression, though we could not directly link this to rs7587026 itself. Our results develop the mechanistic link between rs7587026 and mesial temporal lobe epilepsy with hippocampal sclerosis and a history of febrile seizures. Furthermore, we propose that quantitative precision may be important when increasing SCN1A expression in current strategies aiming to treat seizures in conditions involving SCN1A haploinsufficiency, such as Dravet syndrome.

ILAE definition of the Idiopathic Generalized Epilepsy Syndromes: Position statement by the ILAE Task Force on Nosology and Definitions

In 2017, the International League Against Epilepsy (ILAE) Classification of Epilepsies described the "genetic generalized epilepsies" (GGEs), which contained the "idiopathic generalized epilepsies" (IGEs). The goal of this paper is to delineate the four syndromes comprising the IGEs, namely childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with generalized tonic-clonic seizures alone. We provide updated diagnostic criteria for these IGE syndromes determined by the expert consensus opinion of the ILAE's Task Force on Nosology and Definitions (2017-2021) and international external experts outside our Task Force. We incorporate current knowledge from recent advances in genetic, imaging, and electroencephalographic studies, together with current terminology and classification of seizures and epilepsies. Patients that do not fulfill criteria for one of these syndromes, but that have one, or a combination, of the following generalized seizure types: absence, myoclonic, tonic-clonic and myoclonic-tonic-clonic seizures, with 2.5-5.5 Hz generalized spike-wave should be classified as having GGE. Recognizing these four IGE syndromes as a special grouping among the GGEs is helpful, as they carry prognostic and therapeutic implications.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

Methodology for classification and definition of epilepsy syndromes with list of syndromes: Report of the ILAE Task Force on Nosology and Definitions

Epilepsy syndromes have been recognized for >50 years, as distinct electroclinical phenotypes with therapeutic and prognostic implications. Nonetheless, no formally accepted International League Against Epilepsy (ILAE) classification of epilepsy syndromes has existed. The ILAE Task Force on Nosology and Definitions was established to reach consensus regarding which entities fulfilled criteria for an epilepsy syndrome and to provide definitions for each syndrome. We defined an epilepsy syndrome as "a characteristic cluster of clinical and electroencephalographic features, often supported by specific etiological findings (structural, genetic, metabolic, immune, and infectious)." The diagnosis of a syndrome in an individual with epilepsy frequently carries prognostic and treatment implications. Syndromes often have age-dependent presentations and a range of specific comorbidities. This paper describes the guiding principles and process for syndrome identification in both children and adults, and the template of clinical data included for each syndrome. We divided syndromes into typical age at onset, and further characterized them based on seizure and epilepsy types and association with developmental and/or epileptic encephalopathy or progressive neurological deterioration. Definitions for each specific syndrome are contained within the corresponding position papers.

Phenotypic and Genotypic Characteristics of SCN1A Associated Seizure Diseases

Although SCN1A variants result in a wide range of phenotypes, genotype-phenotype associations are not well established. We aimed to explore the phenotypic characteristics of SCN1A associated seizure diseases and establish genotype-phenotype correlations. We retrospectively analyzed clinical data and results of genetic testing in 41 patients carrying SCN1A variants. Patients were divided into two groups based on their clinical manifestations: the Dravet Syndrome (DS) and non-DS groups. In the DS group, the age of seizure onset was significantly earlier and ranged from 3 to 11 months, with a median age of 6 months, than in the non-DS group, where it ranged from 7 months to 2 years, with a median age of 10 and a half months. In DS group, onset of seizures in 11 patients was febrile, in seven was afebrile, in two was febrile/afebrile and one patient developed fever post seizure. In the non-DS group, onset in all patients was febrile. While in the DS group, three patients had unilateral clonic seizures at onset, and the rest had generalized or secondary generalized seizures at onset, while in the non-DS group, all patients had generalized or secondary generalized seizures without unilateral clonic seizures. The duration of seizure in the DS group was significantly longer and ranged from 2 to 70 min (median, 20 min), than in the non-DS group where it ranged from 1 to 30 min (median, 5 min). Thirty-one patients harbored de novo variants, and nine patients had inherited variants. Localization of missense variants in the voltage sensor region (S4) or pore-forming region (S5–S6) was seen in seven of the 11 patients in the DS group and seven of the 17 patients in the non-DS group. The phenotypes of SCN1A-related seizure disease were diverse and spread over a continuous spectrum from mild to severe. The phenotypes demonstrate commonalities and individualistic differences and are not solely determined by variant location or type, but also due to functional changes, genetic modifiers as well as other known and unknown factors.

Shared Etiology in Autism Spectrum Disorder and Epilepsy with Functional Disability

Autism spectrum disorders and epilepsies are heterogeneous human disorders that have miscellaneous etiologies and pathophysiology. There is considerable risk of frequent epilepsy in autism that facilitates amplified morbidity and mortality. Several biological pathways appear to be involved in disease progression, including gene transcription regulation, cellular growth, synaptic channel function, and maintenance of synaptic structure. Here, abnormalities in excitatory/inhibitory (E/I) balance ratio are reviewed along with part of an epileptiform activity that may drive both overconnectivity and genetic disorders where autism spectrum disorders and epilepsy frequently co-occur. The most current ideas concerning common etiological and molecular mechanisms for co-occurrence of both autism spectrum disorders and epilepsy are discussed along with the powerful pharmacological therapies that protect the cognition and behavior of patients. Better understanding is necessary to identify a biological mechanism that might lead to possible treatments for these neurological disorders.

Long-term outcome of developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies are conditions where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. Usually they have multiple etiologies. Therefore, long-term outcome is related to both etiology-related factors and epilepsy-related factors-age at onset of epilepsy, type(s) of seizure(s), type of electroencephalographic abnormalities, duration of the epileptic disorder. This paper focuses on long-term outcome of six developmental and epileptic encephalopathies with onset from the neonatal period to childhood: early epileptic encephalopathy with suppression bursts, West syndrome, Dravet syndrome, Lennox-Gastaut syndrome, epilepsy with myoclonic atonic seizures and epileptic encephalopathy with continuous spike and waves during slow-wave sleep including Landau-Kleffner syndrome. For each syndrome, definition, main etiologies if multiple, and long-term outcome are discussed.

SCN1A Variants as the Underlying Cause of Genetic Epilepsy with Febrile Seizures Plus in Two Multi-Generational Colombian Families

Genetic epilepsy with febrile seizures plus (GEFS+) is an autosomal dominant disorder with febrile or afebrile seizures that exhibits phenotypic variability. Only a few variants in SCN1A have been previously characterized for GEFS+, in Latin American populations where studies on the genetic and phenotypic spectrum of GEFS+ are scarce. We evaluated members in two multi-generational Colombian Paisa families whose affected members present with classic GEFS+. Exome and Sanger sequencing were used to detect the causal variants in these families. In each of these families, we identified variants in SCN1A causing GEFS+ with incomplete penetrance. In Family 047, we identified a heterozygous variant (c.3530C > G; p.(Pro1177Arg)) that segregates with GEFS+ in 15 affected individuals. In Family 167, we identified a previously unreported variant (c.725A > G; p.(Gln242Arg)) that segregates with the disease in a family with four affected members. Both variants are located in a cytoplasmic loop region in SCN1A and based on our findings the variants are classified as pathogenic and likely pathogenic, respectively. Our results expand the genotypic and phenotypic spectrum associated with SCN1A variants and will aid in improving molecular diagnostics and counseling in Latin American and other populations.

Genetic Epilepsy Syndromes

PURPOSE OF REVIEW

This article reviews the clinical features, typical EEG findings, treatment, prognosis, and underlying molecular etiologies of the more common genetic epilepsy syndromes. Genetic generalized epilepsy, self-limited focal epilepsy of childhood, self-limited neonatal and infantile epilepsy, select developmental and epileptic encephalopathies, progressive myoclonus epilepsies, sleep-related hypermotor epilepsy, photosensitive occipital lobe epilepsy, and focal epilepsy with auditory features are discussed. Also reviewed are two familial epilepsy syndromes: genetic epilepsy with febrile seizures plus and familial focal epilepsy with variable foci.

RECENT FINDINGS

Recent years have seen considerable advances in our understanding of the genetic factors underlying genetic epilepsy syndromes. New therapies are emerging for some of these conditions; in some cases, these precision medicine approaches may dramatically improve the prognosis.

SUMMARY

Many recognizable genetic epilepsy syndromes exist, the identification of which is a crucial skill for neurologists, particularly those who work with children. Proper diagnosis of the electroclinical syndrome allows for appropriate treatment choices and counseling regarding prognosis and possible comorbidities.

Auditory phoneme discrimination, articulation, and language disorders in patients with genetic epilepsy with febrile seizures plus: A case-control study

INTRODUCTION

Genetic epilepsy with febrile seizures plus (GEFS+) is an epilepsy syndrome with clinical heterogeneity that was first described in 1997. Central auditory processing (CAP) is defined as the neurophysiological process in decoding sound waves from the outer ear to the auditory cortex. The present study aimed to analyze CAP and phonological disorders in preschool-age children with GEFS+.

MATERIAL AND METHOD

This is a prospective case-control study. Twenty-seven patients diagnosed with GEFS+ aged between 4 years and 6 years and 6 months and 31 healthy controls in the same age range were included in the study. Phonological sensitivity test (SAT) and auditory discrimination test (İAT) were applied to both groups, and the results of both groups were statistically compared.

RESULTS

The SAT and İAT raw and Z scores of the subjects in the study group were found to be significantly higher than those of the control group (p = 0.001; p < 0.01). Electroencephalography (EEG) status of the patients or the duration of antiseizure medication use did not have a statistically significant effect on the outcome.

CONCLUSION

Patients with GEFS+ have a significantly high impairment in both articulation and auditory discrimination of phonemes compared with the healthy population. Early diagnosis and early treatment of this condition can prevent potential literacy problems and the development of dyslexia in the future.

Development and Validation of a Prediction Model for Early Diagnosis of SCN1A-Related Epilepsies

BACKGROUND AND OBJECTIVES

Pathogenic variants in the neuronal sodium channel α1 subunit gene (SCN1A) are the most frequent monogenic cause of epilepsy. Phenotypes comprise a wide clinical spectrum, including severe childhood epilepsy; Dravet syndrome, characterized by drug-resistant seizures, intellectual disability, and high mortality; and the milder genetic epilepsy with febrile seizures plus (GEFS+), characterized by normal cognition. Early recognition of a child's risk for developing Dravet syndrome vs GEFS+ is key for implementing disease-modifying therapies when available before cognitive impairment emerges. Our objective was to develop and validate a prediction model using clinical and genetic biomarkers for early diagnosis of SCN1A-related epilepsies.

METHODS

We performed a retrospective multicenter cohort study comprising data from patients with SCN1A-positive Dravet syndrome and patients with GEFS+ consecutively referred for genetic testing (March 2001-June 2020) including age at seizure onset and a newly developed SCN1A genetic score. A training cohort was used to develop multiple prediction models that were validated using 2 independent blinded cohorts. Primary outcome was the discriminative accuracy of the model predicting Dravet syndrome vs other GEFS+ phenotypes.

RESULTS

A total of 1,018 participants were included. The frequency of Dravet syndrome was 616/743 (83%) in the training cohort, 147/203 (72%) in validation cohort 1, and 60/72 (83%) in validation cohort 2. A high SCN1A genetic score (133.4 [SD 78.5] vs 52.0 [SD 57.5]; p < 0.001) and young age at onset (6.0 [SD 3.0] vs 14.8 [SD 11.8] months; p < 0.001) were each associated with Dravet syndrome vs GEFS+. A combined SCN1A genetic score and seizure onset model separated Dravet syndrome from GEFS+ more effectively (area under the curve [AUC] 0.89 [95% CI 0.86-0.92]) and outperformed all other models (AUC 0.79-0.85; p < 0.001). Model performance was replicated in both validation cohorts 1 (AUC 0.94 [95% CI 0.91-0.97]) and 2 (AUC 0.92 [95% CI 0.82-1.00]).

DISCUSSION

The prediction model allows objective estimation at disease onset whether a child will develop Dravet syndrome vs GEFS+, assisting clinicians with prognostic counseling and decisions on early institution of precision therapies (http://scn1a-prediction-model.broadinstitute.org/).

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that a combined SCN1A genetic score and seizure onset model distinguishes Dravet syndrome from other GEFS+ phenotypes.

Generalized Fast Discharges Along the Genetic Generalized Epilepsy Spectrum: Clinical and Prognostic Significance

Objective

To investigate the electroclinical characteristics and the prognostic impact of generalized fast discharges in a large cohort of genetic generalized epilepsy (GGE) patients studied with 24-h prolonged ambulatory electroencephalography (paEEG).

Methods

This retrospective multicenter cohort study included 202 GGE patients. The occurrence of generalized paroxysmal fast activity (GPFA) and generalized polyspike train (GPT) was reviewed. GGE patients were classified as having idiopathic generalized epilepsy (IGE) or another GGE syndrome (namely perioral myoclonia with absences, eyelid myoclonia with absences, epilepsy with myoclonic absences, generalized epilepsy with febrile seizures plus, or GGE without a specific epilepsy syndrome) according to recent classification proposals.

Results

GPFA/GPT was found in overall 25 (12.4%) patients, though it was significantly less frequent in IGE compared with other GGE syndromes (9.3 vs. 25%, p = 0.007). GPFA/GPT was found independently of seizure type experienced during history, the presence of mild intellectual disability/borderline intellectual functioning, or EEG features. At multivariable analysis, GPFA/GPT was significantly associated with drug resistance (p = 0.04) and with a higher number of antiseizure medications (ASMs) at the time of paEEG (p < 0.001) and at the last medical observation (p < 0.001). Similarly, GPFA/GPT, frequent/abundant generalized spike-wave discharges during sleep, and a higher number of seizure types during history were the only factors independently associated with a lower chance of achieving 2-year seizure remission at the last medical observation. Additionally, a greater number of GPFA/GPT discharges significantly discriminated between patients who achieved 2-year seizure remission at the last medical observation and those who did not (area under the curve = 0.77, 95% confidence interval 0.57-0.97, p = 0.02).

Conclusion

We found that generalized fast discharges were more common than expected in GGE patients when considering the entire GGE spectrum. In addition, our study highlighted that GPFA/GPT could be found along the entire GGE continuum, though their occurrence was more common in less benign GGE syndromes. Finally, we confirmed that GPFA/GPT was associated with difficult-to-treat GGE, as evidenced by the multivariable analysis and the higher ASM load during history.

The Broad Clinical Spectrum of Epilepsies Associated With Protocadherin 19 Gene Mutation

Protocadherin 19 (PCDH19) gene is one of the most common genes involved in epilepsy syndromes. According to literature data PCDH19 is among the 6 genes most involved in genetic epilepsies. PCDH19 is located on chromosome Xq22.1 and is involved in neuronal connections and signal transduction. The most frequent clinical expression of PCDH19 mutation is epilepsy and mental retardation limited to female (EFMR) characterized by epileptic and non-epileptic symptoms affecting mainly females. However, the phenotypic spectrum of these mutations is considerably variable from genetic epilepsy with febrile seizure plus to epileptic encephalopathies. The peculiar exclusive involvement of females seems to be caused by a cellular interference in heterozygosity, however, affected mosaic-males have been reported. Seizure types range from focal seizure to generalized tonic-clonic, tonic, atonic, absences, and myoclonic jerks. Treatment of PCDH19-related epilepsy is limited by drug resistance and by the absence of specific treatment indications. However, seizures become less severe with adolescence and some patients may even become seizure-free. Non-epileptic symptoms represent the main disabilities of adult patients with PCDH19 mutation. This review aims to analyze the highly variable phenotypic expression of PCDH19 gene mutation associated with epilepsy.

Risk factors of epilepsy in children with complex febrile seizures: A retrospective cohort study

BACKGROUND

Febrile seizures are the most common seizures in children. Children with complex febrile seizures have a higher risk of subsequent epilepsy compared with children with simple febrile seizures. Multiple risks factors for epilepsy, including focal status epilepticus, family history of epilepsy, neurodevelopmental abnormalities and abnormal electroencephalogram findings, have been found with inconsistent results. The aim of this study is to identify risk factors for developing epilepsy in children with complex febrile seizures.

METHODS

The study included 248 children aged 3-72-months, diagnosed with complex febrile seizures at Chiang Mai University Hospital. Demographic data, seizure characteristics, electroencephalogram and neuroimaging findings were identified, and assessed to establish whether they were risk factors for subsequent epilepsy.

RESULTS

Fifty-five patients (22.1%) had subsequent epilepsy. Using Cox regression-survival analysis, factors associated with epilepsy were prolonged seizures >15 min (P = 0.006; Hazard Ratio (HR): 2.475; 95% Confidence Interval (CI): 1.294-4.735), developmental delay (P = 0.019; HR: 4.476; 95% CI: 2.280-15.646), epileptiform discharges on electroencephalogram (P = 0.023; HR: 1.391; 95%CI: 1.174-1.876), and abnormal neuroimaging (computed tomography or magnetic resonance imaging; P = 0.028; HR: 1.355; 95% CI: 1.034-1.776). Age at onset, peak febrile temperature, duration between the onset of fever and the occurrence of seizure, recurrent seizures within 24 h, focal seizures, abnormal neurological exams and family history of febrile seizure or epilepsy were not associated with increased risk of subsequent epilepsy in this study.

CONCLUSIONS

Risk factors associated with increased risk of epilepsy in children with complex febrile seizures are prolonged seizures or febrile status epilepticus, developmental delay, electroencephalogram epileptiform discharges, and abnormal neuroimaging. Their presence would merit close clinical monitoring.

Role of SCN2A c.56G/A Gene Polymorphism in Egyptian Children with Genetic Epilepsy with Febrile Seizure Plus

BACKGROUND

Febrile Seizures (FS) are the most common seizures in children younger than 5 years. In the last decade, various coding and noncoding sequence variations of voltage-gated sodium channels SCN2A have been identified in patients with seizures, implying their genetic base. We aimed to evaluate the association between SCN2A c. G/A genetic polymorphism among Egyptian children with febrile seizure plus.

METHODS

The present cross-sectional study was carried out on 100 epileptic infants and children, attendants of the Neurology Unit, pediatric department, Menoufia University Hospitals (Group Ι). The patients were sub-classified into two groups, according to response to anti-epileptic treatment; Group Ι a (drug responder) and Group Ι b (drug-resistant). Evenly divided number of apparently healthy, age and gender-matched children were selected as controls (Group II). A complete history, throughout the systemic examination and radiological & metabolic assessment, whenever needed was provided, all participants were genotyped for SCN2A rs17183814 polymorphism by Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

Both of A allele and AA, GA genotypes of SCN2A c. 56 G/A were detected more in patients with febrile seizure plus comparison to the control group with a statistically significant difference at frequencies of 17% and 11% and 12% respectively; OR (CI95%): 10.04 (3.49-28.87) and p <0.001. On classifying epileptic patients into 2 subgroups, carriers of SCN2A rs17183814 AA genotype tended to respond poorly to Anti-epileptic Drugs (AEDs). Moreover, multivariate analysis revealed that rs17183814 A allele and positive family history of epilepsy were considered the highest predicted risk factors for the development of epilepsy; p<0.05.

CONCLUSION

SCN2A rs17183814 (A) allele was specifically associated with developing febrile seizure plus and could modulate the patient's response to anti-epileptic medications.

Fever-Associated Seizures or Epilepsy: An Overview of Old and Recent Literature Acquisitions

In addition to central nervous system infections, seizures and fever may occur together in several neurological disorders. Formerly, based on the clinical features and prognostic evolution, the co-association of seizure and fever included classical febrile seizures (FS) divided into simple, complex, and prolonged FS (also called febrile status epilepticus). Later, this group of disorders has been progressively indicated, with a more inclusive term, as "fever-associated seizures or epilepsy" (FASE) that encompasses: (a) FS divided into simple, complex, and prolonged FS; (b) FS plus; (c) severe myoclonic epilepsy in infancy (Dravet syndrome); (d) genetic epilepsy with FS plus; and (e) febrile infection-related epilepsy syndrome (FIRES). Among the FASE disorders, simple FS, the most common and benign condition, is rarely associated with subsequent epileptic seizures. The correlation of FS with epilepsy and other neurological disorders is highly variable. The pathogenesis of FASE is unclear but immunological and genetic factors play a relevant role and the disorders belonging to the FASE group show to have an underlying common clinical, immunological, and genetic pathway. In this study, we have reviewed and analyzed the clinical data of each of the heterogeneous group of disorders belonging to FASE.

De novo mutations in childhood cases of sudden unexplained death that disrupt intracellular Ca2+ regulation

Approximately 400 United States children 1 y of age and older die suddenly from unexplained causes annually. We studied whole-exome sequence data from 124 “trios” (decedent child and living parents) to identify genetic risk factors. Nonsynonymous mutations, mostly de novo (present in child but absent in both biological parents), were highly enriched in genes associated with cardiac and seizure disorders relative to controls, and contributed to 9% of deaths. We found significant overtransmission of loss-of-function or pathogenic missense variants in cardiac and seizure disorder genes. Most pathogenic variants were de novo in origin, highlighting the importance of trio studies. Many of these pathogenic de novo mutations altered a protein network regulating calcium-related excitability at submembrane junctions in cardiomyocytes and neurons.

Sudden unexplained death in childhood (SUDC) is an understudied problem. Whole-exome sequence data from 124 “trios” (decedent child, living parents) was used to test for excessive de novo mutations (DNMs) in genes involved in cardiac arrhythmias, epilepsy, and other disorders. Among decedents, nonsynonymous DNMs were enriched in genes associated with cardiac and seizure disorders relative to controls (odds ratio = 9.76, P = 2.15 × 10⁻⁴). We also found evidence for overtransmission of loss-of-function (LoF) or previously reported pathogenic variants in these same genes from heterozygous carrier parents (11 of 14 transmitted, P = 0.03). We identified a total of 11 SUDC proband genotypes (7 de novo, 1 transmitted parental mosaic, 2 transmitted parental heterozygous, and 1 compound heterozygous) as pathogenic and likely contributory to death, a genetic finding in 8.9% of our cohort. Two genes had recurrent missense DNMs, RYR2 and CACNA1C. Both RYR2 mutations are pathogenic (P = 1.7 × 10⁻⁷) and were previously studied in mouse models. Both CACNA1C mutations lie within a 104-nt exon (P = 1.0 × 10⁻⁷) and result in slowed L-type calcium channel inactivation and lower current density. In total, six pathogenic DNMs can alter calcium-related regulation of cardiomyocyte and neuronal excitability at a submembrane junction, suggesting a pathway conferring susceptibility to sudden death. There was a trend for excess LoF mutations in LoF intolerant genes, where ≥1 nonhealthy sample in denovo-db has a similar variant (odds ratio = 6.73, P = 0.02); additional uncharacterized genetic causes of sudden death in children might be discovered with larger cohorts.

SUDEP risk and autonomic dysfunction in genetic epilepsies

The underlying pathophysiology of sudden unexpected death in epilepsy (SUDEP) remains unclear. This phenomenon is likely multifactorial, and there is considerable evidence that genetic factors play a role. There are certain genetic causes of epilepsy in which the risk of SUDEP appears to be increased relative to epilepsy overall. For individuals with pathogenic variants in genes including SCN1A, SCN1B, SCN8A, SCN2A, GNB5, KCNA1 and DEPDC5, there are varying degrees of evidence to suggest an increased risk for sudden death. Why the risk for sudden death is higher is not completely clear; however, in many cases pathogenic variants in these genes are also associated with autonomic dysfunction, which is hypothesized as a contributing factor to SUDEP. We review the evidence for increased SUDEP risk for patients with epilepsy due to pathogenic variants in these genes, and also discuss what is known about autonomic dysfunction in these contexts.

Initiation of migraine-related cortical spreading depolarization by hyperactivity of GABAergic neurons and NaV1.1 channels

Spreading depolarizations (SDs) are involved in migraine, epilepsy, stroke, traumatic brain injury, and subarachnoid hemorrhage. However, the cellular origin and specific differential mechanisms are not clear. Increased glutamatergic activity is thought to be the key factor for generating cortical spreading depression (CSD), a pathological mechanism of migraine. Here, we show that acute pharmacological activation of NaV1.1 (the main Na+ channel of interneurons) or optogenetic-induced hyperactivity of GABAergic interneurons is sufficient to ignite CSD in the neocortex by spiking-generated extracellular K+ build-up. Neither GABAergic nor glutamatergic synaptic transmission were required for CSD initiation. CSD was not generated in other brain areas, suggesting that this is a neocortex-specific mechanism of CSD initiation. Gain-of-function mutations of NaV1.1 (SCN1A) cause familial hemiplegic migraine type-3 (FHM3), a subtype of migraine with aura, of which CSD is the neurophysiological correlate. Our results provide the mechanism linking NaV1.1 gain of function to CSD generation in FHM3. Thus, we reveal the key role of hyperactivity of GABAergic interneurons in a mechanism of CSD initiation, which is relevant as a pathological mechanism of Nav1.1 FHM3 mutations, and possibly also for other types of migraine and diseases in which SDs are involved.

Dravet syndrome: A quick transition guide for the adult neurologist

INTRODUCTION

Dravet syndrome (DS) is still seen as a "pediatric disease", where patients receive excellent care in pediatric centers, but care is less than optimal in adult health care systems (HCS). This creates a barrier when young adults need to leave the family-centered pediatric system and enter the adult, patient-centered HCS. Here we create a guide to help with the transition from pediatric to adult for patients with DS.

METHODS

Experts in Dravet syndrome flagged the main barriers in caring for adults with DS and created a 2-page transition summary guide based on their expertise and a literature review.

RESULTS

The 2-page guide addresses: DS diagnosis in children and adults; clinical manifestations, including the differences in seizures types and frequencies between children and adults with DS; the natural history of intellectual disability, behavior, gait, motor disorders and dysautonomia; a review of optimal treatments (including medications not commonly used in adult epilepsy settings such as stiripentol and fenfluramine), as well as emergency seizure management; avoidance of triggers, preventive measures, and vaccine administration in adults with DS.

CONCLUSION

Several young adults with DS are still followed by their child neurologist. This 2-page transition guide should help facilitate the transition of patients with DS to the adult HCS and should be given to families as well as adult health care providers that may not be familiar with DS.