Familial occurrence of febrile seizures and epilepsy in severe myoclonic epilepsy of infancy (SMEI) patients with SCN1A mutations

SCN1A intronic variants impact on Nav1.1 protein expression and sodium channel function, and associated with epilepsy phenotypic severity

High-throughput sequencing has identified numerous intronic variants in the SCN1A gene in epilepsy patients. Abnormal mRNA splicing caused by these variants can lead to significant phenotypic differences, but the mechanisms of epileptogenicity and phenotypic differences remain unknown. Two variants, c.4853-1 G>C and c.4853-25 T>A, were identified in intron 25 of SCN1A, which were associated with severe Dravet syndrome (DS) and mild focal epilepsy with febrile seizures plus (FEFS+), respectively. The impact of these variants on protein expression, electrophysiological properties of sodium channels and their correlation with epilepsy severity was investigated through plasmid construction and transfection based on the aberrant spliced mRNA. We found that the expression of truncated mutant proteins was significantly reduced on the cell membrane, and retained in the cytoplasmic endoplasmic reticulum. The mutants caused a decrease in current density, voltage sensitivity, and an increased vulnerability of channel, leading to a partial impairment of sodium channel function. Notably, the expression of DS-related mutant protein on the cell membrane was higher compared to that of FEFS+-related mutant, whereas the sodium channel function impairment caused by DS-related mutant was comparatively milder than that caused by FEFS+-related mutant. Our study suggests that differences in protein expression levels and altered electrophysiological properties of sodium channels play important roles in the manifestation of diverse epileptic phenotypes. The presence of intronic splice site variants may result in severe phenotypes due to the dominant-negative effects, whereas non-canonical splice site variants leading to haploinsufficiency could potentially cause milder phenotypes.

Customized targeted massively parallel sequencing enables the identification of novel pathogenic variants in Tunisian patients with developmental and epileptic encephalopathy

OBJECTIVE

To develop a high-throughput sequencing panel for the diagnosis of developmental and epileptic encephalopathy in Tunisia and to clarify the frequency of disease-causing genes in this region.

METHODS

We developed a custom panel for next-generation sequencing of the coding sequences of 116 genes in individuals with developmental and epileptic encephalopathy from the Tunisian population. Segregation analyses and in silico studies have been conducted to assess the identified variants' pathogenicity.

RESULTS

We report 12 pathogenic variants in SCN1A, CHD2, CDKL5, SZT2, KCNT1, GNAO1, PCDH19, MECP2, GRIN2A, and SYNGAP1 in patients with developmental and epileptic encephalopathy. Five of these variants are novel: "c.149delA, p.(Asn50MetfsTer26)" in CDKL5; "c.3616C > T, p.(Arg1206Ter)" in SZT2; "c.111_113del, p.(Leu39del)" in GNAO1; "c.1435G>C, p.(Asp479His)" in PCDH19; and "c.2143delC, p.(Arg716GlyfsTer10)" in SYNGAP1. Additionally, for four of our patients, the genetic result facilitated the choice of the appropriate treatment.

SIGNIFICANCE

This is the first report of a custom gene panel to identify genetic variants implicated in developmental and epileptic encephalopathy in the Tunisian population as well as the North African region (Tunisia, Egypt, Libya, Algeria, Morocco) with a diagnostic rate of 30%. This high-throughput sequencing panel has considerably improved the rate of positive diagnosis of developmental and epileptic encephalopathy in the Tunisian population, which was less than 15% using Sanger sequencing. The benefit of genetic testing in these patients was approved by both physicians and parents.

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.

Best practices for the management of febrile seizures in children

Febrile seizures (FS) are commonly perceived by healthcare professionals as a self-limited condition with a generally 'benign' nature. Nonetheless, they frequently lead to pediatric consultations, and their management can vary depending on the clinical context. For parents and caregivers, witnessing a seizure can be a distressing experience, significantly impacting their quality of life. In this review, we offer an in-depth exploration of FS management, therapeutic interventions, and prognostic factors, with the aim of providing support for physicians and enhancing communication with families. We conducted a comprehensive literature search using the PubMed and Web of Science databases, spanning the past 50 years. The search terms utilized included "febrile seizure," "complex febrile seizure," "simple febrile seizure," in conjunction with "children" or "infant." Only studies published in English or those presenting evidence-based data were included in our assessment. Additionally, we conducted a cross-reference search to identify any additional relevant data sources. Our thorough literature search resulted in a compilation of references, with carefully selected papers thoughtfully integrated into this review.

Heat-induced seizures, premature mortality, and hyperactivity in a novel Scn1a nonsense model for Dravet syndrome

Dravet syndrome (Dravet) is a severe congenital developmental genetic epilepsy caused by de novo mutations in the SCN1A gene. Nonsense mutations are found in ∼20% of the patients, and the R613X mutation was identified in multiple patients. Here we characterized the epileptic and non-epileptic phenotypes of a novel preclinical Dravet mouse model harboring the R613X nonsense Scn1a mutation. Scn1a^WT/R613X mice, on a mixed C57BL/6J:129S1/SvImJ background, exhibited spontaneous seizures, susceptibility to heat-induced seizures, and premature mortality, recapitulating the core epileptic phenotypes of Dravet. In addition, these mice, available as an open-access model, demonstrated increased locomotor activity in the open-field test, modeling some non-epileptic Dravet-associated phenotypes. Conversely, Scn1a^WT/R613X mice, on the pure 129S1/SvImJ background, had a normal life span and were easy to breed. Homozygous Scn1a^R613X/R613X mice (pure 129S1/SvImJ background) died before P16. Our molecular analyses of hippocampal and cortical expression demonstrated that the premature stop codon induced by the R613X mutation reduced Scn1a mRNA and Na_V1.1 protein levels to ∼50% in heterozygous Scn1a^WT/R613X mice (on either genetic background), with marginal expression in homozygous Scn1a^R613X/R613X mice. Together, we introduce a novel Dravet model carrying the R613X Scn1a nonsense mutation that can be used to study the molecular and neuronal basis of Dravet, as well as the development of new therapies associated with SCN1A nonsense mutations in Dravet.

Unwinding and spiral sliding of S4 and domain rotation of VSD during the electromechanical coupling in Nav1.7

Na_v1.7 has been targeted for pain management for its well-established role in pain sensation. Hundreds of mutations of Na_v1.7 have been found in patients with pain disorders. Structures of Na_v1.7 captured in different conformations will reveal its working mechanism and facilitate drug discovery. Here we present the rational design of a Na_v1.7 variant, Na_v1.7-M11, that may be trapped in the closed-state inactivation conformation at 0 mV. Cryoelectron microscopy analysis of Na_v1.7-M11 reveals voltage-sensing domain in the first repeat (VSD_I) in the completely down conformation, VSD_II at an intermediate state, and the pore domain tightly closed. Structural comparison of Na_v1.7-M11 with the WT channel provides unprecedented insight into the electromechanical coupling details and affords mechanistic interpretation for a number of pain-related mutations.

Voltage-gated sodium (Na_v) channel Na_v1.7 has been targeted for the development of nonaddictive pain killers. Structures of Na_v1.7 in distinct functional states will offer an advanced mechanistic understanding and aid drug discovery. Here we report the cryoelectron microscopy analysis of a human Na_v1.7 variant that, with 11 rationally introduced point mutations, has a markedly right-shifted activation voltage curve with V_1/2 reaching 69 mV. The voltage-sensing domain in the first repeat (VSD_I) in a 2.7-Å resolution structure displays a completely down (deactivated) conformation. Compared to the structure of WT Na_v1.7, three gating charge (GC) residues in VSD_I are transferred to the cytosolic side through a combination of helix unwinding and spiral sliding of S4_I and ∼20° domain rotation. A conserved WNФФD motif on the cytoplasmic end of S3_I stabilizes the down conformation of VSD_I. One GC residue is transferred in VSD_II mainly through helix sliding. Accompanying GC transfer in VSD_I and VSD_II, rearrangement and contraction of the intracellular gate is achieved through concerted movements of adjacent segments, including S4-5_I, S4-5_II, S5_II, and all S6 segments. Our studies provide important insight into the electromechanical coupling mechanism of the single-chain voltage-gated ion channels and afford molecular interpretations for a number of pain-associated mutations whose pathogenic mechanism cannot be revealed from previously reported Na_v structures.

Clinical and Functional Features of Epilepsy-Associated In-Frame Deletion Variants in SCN1A

Objective

Naturally occurring in-frame deletion is a unique type of genetic variations, causing the loss of one or more amino acids of proteins. A number of in-frame deletion variants in an epilepsy-associated gene SCN1A, encoding voltage gated sodium channel alpha unit 1.1 (Na_v1.1), have been reported in public database. In contrast to the missense and truncation variants, the in-frame deletions in SCN1A remains largely uncharacterized.

Methods

We summarized the basic information of forty-four SCN1A in-frame deletion variants and performed further analysis on six variants identified in our cases with epilepsy. Mutants of the six in-frame deletions and one truncating variant used as comparison were generated and co-transfected with beta-1 and -2 subunits in tsA201 cells, followed by patch clamp recordings.

Results

Reviewing all the in-frame deletions showed that they spread over the entire Na_v1.1 protein, without obvious “hot spots.” The dominant type (54%) was single residue loss. There was no obvious relationship between the length or locations of deletions and their clinical phenotypes. The six in-frame deletions were two single residue deletions (p.M400del and p.I1772del), one microdeletion (p.S128_F130del) and three macrodeletions (p.T303_R322del, p.T160_Y202del, and p.V1335_V1428del). They scatter and affect different functional domains, including transmembrane helices, pore region, and P-loop. Electrophysiological recordings revealed no measurable sodium current in all of the six mutants. In contrast, the truncating mutant p.M1619Ifs*7 that loses a long stretch of peptides retains partial function.

Significance

The complete loss-of-function in these shortened, abnormal mutants indicates that Na_v1.1 protein is a highly accurate structure, and many of the residues have no redundancy to ion conductance. In-frame deletions caused particularly deleterious effect on protein function possibly due to the disruption of ordered residues.

The study of sodium and potassium channel gene single-nucleotide variation significance in non-mechanical forms of epilepsy

Background

Epilepsy is one of the most common and heterogeneous neurological diseases. The main clinical signs of the disease are repeated symptomatic or idiopathic epileptic seizures of both convulsive and non-convulsive nature that develop against a background of lost or preserved consciousness. The genetic component plays a large role in the etiology of idiopathic forms of epilepsy. The study of the molecular genetic basis of neurological disorders has led to a rapidly growing number of gene mutations known to be involved in hereditary ion channel dysfunction. The aim of this research was to evaluate the involvement of single-nucleotide variants that modify the function of genes (SCN1A, KCNT1, KCNTС1, and KCNQ2) encoding sodium and potassium ion channel polypeptides in the development of epilepsy.

Results

De novo mutations in the sodium channel gene SCN1A c.5347G>A (p. Ala1783Thr) were detected in two patients with Dravet syndrome, with a deletion in exon 26 found in one. Three de novo mutations in the potassium channel gene KCNT1 c.2800G>A (p. Ala934Thr), were observed in two patients with temporal lobe epilepsy (TLE) and one patient with residual encephalopathy. Moreover, a control cohort matched to the case cohort did not reveal any SNVs among conditionally healthy individuals, supporting the pathogenic significance of the studied SNVs.

Conclusion

Our results are supported by literature data showing that the sodium ion channel gene SCN1A c.5347G>A mutation may be involved in the pathogenesis of Dravet syndrome. We also note that the c.2800G>A mutation in the potassium channel gene KCNT1 can cause not only autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) but also other forms of epilepsy. To treat pathogenetic mutations that accelerate the function of sodium and potassium ion channels, we recommend ion channel blockade drug therapy.

Differences in SCN1A intronic variants result in diverse aberrant splicing patterns and are related to the phenotypes of epilepsy with febrile seizures

OBJECTIVE

Intronic variants of the SCN1A gene are detected in patients with epilepsy with febrile seizures (EFS), which includes a series of phenotypes with different severities. However, the pathogenicity of intronic variants and their genotype-phenotype correlation remain under characterized. The purpose of this study was to determine the changes in mRNA splicing caused by SCN1A intronic variants associated with EFS and their association with phenotypes.

METHODS

Five SCN1A intronic variants detected in patients with focal epilepsy with antecedent febrile seizures plus (FEFS+) and Dravet syndrome (DS) were molecularly cloned. Through an in vitro minigene splicing assay, their influence on mRNA splicing was qualitatively and quantitatively compared and analyzed using reverse-transcription polymerase chain reaction (RT-PCR) and fluorescence quantitative PCR (Q-PCR).

RESULTS

The severe phenotype of DS-associated variants c.602 + 1G > A and c.4853-1G > C, which occurred in canonical splice sites of introns, caused exon skipping and little retention of full-length mRNA, while the milder phenotype of FEFS+-associated variants c.473 + 5G > A, c.473 + 5G > C and c.4853-25T > A, which occurred in potential splice sites or in deep intronic regions, presented partial exon skipping or intronic insertion and significantly higher retention of full-length mRNA at different levels. Full-length mRNA retention was negatively correlated with the location of intronic variants and phenotype severity.

CONCLUSION

The different aberrant splicing patterns resulting from SCN1A intronic variants with different positions represent a potential molecular mechanism for phenotypic differences in EFS. This research provides valuable clues for functional studies on the pathogenicity of intronic variants and for the evaluation of genotype-phenotype correlations.

Functional analysis of three Nav1.6 mutations causing early infantile epileptic encephalopathy

The voltage-gated sodium channel Na_v1.6 is associated with more than 300 cases of epileptic encephalopathy. Na_v1.6 epilepsy-causing mutations are spread over the entire channel's structure and only 10% of mutations have been characterized at the molecular level, with most of them being gain of function mutations. In this study, we analyzed three previously uncharacterized Na_v1.6 epilepsy-causing mutations: G214D, N215D and V216D, located within a mutation hot-spot at the S3-S4 extracellular loop of Domain1. Voltage clamp experiments showed a 6-16 mV hyperpolarizing shift in the activation mid-point for all three mutants. V216D presented the largest shift along with decreased current amplitude, enhanced inactivation and a lack of persistent current. Recordings at hyperpolarized potentials indicated that all three mutants presented gating pore currents. Furthermore, trafficking experiments performed in cultured hippocampal neurons demonstrated that the mutants trafficked properly to the cell surface, with no significant differences regarding surface expression within the axon initial segment or soma compared to wild-type. These trafficking data suggest that the disease-causing consequences are due to only changes in the biophysical properties of the channel. Interestingly, the patient carrying the V216D mutation, which is the mutant with the greatest electrophysiological changes as compared to wild-type, exhibited the most severe phenotype. These results emphasize that these mutations will mandate unique treatment approaches, for normal sodium channel blockers may not work given that the studied mutations present gating pore currents. This study emphasizes the importance of molecular characterization of disease-causing mutations in order to improve the pharmacological treatment of patients.

A Study among the Genotype, Functional Alternations, and Phenotype of 9 SCN1A Mutations in Epilepsy Patients

Mutations in the voltage-gated sodium channel Nav1.1 (SCN1A) are linked to various epileptic phenotypes with different severities, however, the consequences of newly identified SCN1A variants on patient phenotype is uncertain so far. The functional impact of nine SCN1A variants, including five novel variants identified in this study, was studied using whole-cell patch-clamp recordings measurement of mutant Nav1.1 channels expressed in HEK293T mammalian cells. E78X, W384X, E1587K, and R1596C channels failed to produce measurable sodium currents, indicating complete loss of channel function. E788K and M909K variants resulted in partial loss of function by exhibiting reduced current density, depolarizing shifts of the activation and hyperpolarizing shifts of the inactivation curves, and slower recovery from inactivation. Hyperpolarizing shifts of the activation and inactivation curves were observed in D249E channels along with slower recovery from inactivation. Slower recovery from inactivation was observed in E78D and T1934I with reduced current density in T1934I channels. Various functional effects were observed with the lack of sodium current being mainly associated with severe phenotypes and milder symptoms with less damaging channel alteration. In vitro functional analysis is thus fundamental for elucidation of the molecular mechanisms of epilepsy, to guide patients' treatment, and finally indicate misdiagnosis of SCN1A related epilepsies.

Rare Variants in 48 Genes Account for 42% of Cases of Epilepsy With or Without Neurodevelopmental Delay in 246 Pediatric Patients

In order to characterize the genetic architecture of epilepsy in a pediatric population from the Iberian Peninsula (including the Canary Islands), we conducted targeted exome sequencing of 246 patients with infantile-onset seizures with or without neurodevelopmental delay. We detected 107 variants in 48 different genes, which were implicated in neuronal excitability, neurodevelopment, synaptic transmission, and metabolic pathways. In 104 cases (42%) we detected variant(s) that we classified as pathogenic or likely pathogenic. Of the 48 mutated genes, 32 were dominant, 8 recessive and 8 X-linked. Of the patients for whom family studies could be performed and in whom pathogenic variants were identified in dominant or X-linked genes, 82% carried de novo mutations. The involvement of small copy number variations (CNVs) is 9%. The use of progressively updated custom panels with high mean vertical coverage enabled establishment of a definitive diagnosis in a large proportion of cases (42%) and detection of CNVs (even duplications) with high fidelity. In 10.5% of patients we detected associations that are pending confirmation via functional and/or familial studies. Our findings had important consequences for the clinical management of the probands, since a large proportion of the cohort had been clinically misdiagnosed, and their families were subsequently able to avail of genetic counseling. In some cases, a more appropriate treatment was selected for the patient in question, or an inappropriate treatment discontinued. Our findings suggest the existence of modifier genes that may explain the incomplete penetrance of some epilepsy-related genes. We discuss possible reasons for non-diagnosis and future research directions. Further studies will be required to uncover the roles of structural variants, epimutations, and oligogenic inheritance in epilepsy, thereby providing a more complete molecular picture of this disease. In summary, given the broad phenotypic spectrum of most epilepsy-related genes, efficient genomic tools like the targeted exome sequencing panel described here are essential for early diagnosis and treatment, and should be implemented as first-tier diagnostic tools for children with epilepsy without a clear etiologic basis.

Clinical exome sequencing identifies two novel mutations of the SCN1A and SCN2A genes in Moroccan patients with epilepsy: a case series

BACKGROUND

Epilepsy is the most common neurological disorder that causes spontaneous, unprovoked, and recurrent seizures. Epilepsy is clinically and genetically heterogeneous with various modes of inheritance. The complexity of epilepsy presents a challenge and identification of the causal genetic mutation allows diagnosis, genetic counseling, predicting prognosis, and, in some cases, treatment decisions. Clinical exome sequencing is actually becoming a powerful approach for molecular diagnosis of heterogeneous neurological disorders in clinical practice.

CASE PRESENTATION

We report our observations of three unrelated Moroccan patients referred to our genetics department for molecular diagnosis of epilepsy: a 4-year-old Moroccan boy, a 3-year-old Moroccan girl, and a 7-year-old Moroccan boy. Due to the heterogeneity and complexity of epilepsy, we performed clinical exome sequencing followed by targeted analysis of 936 epilepsy genes. A total of three mutations were identified in known epilepsy genes (SCN1A, SCN2A). By clinical exome sequencing, we identified two novel mutations: c.4973C>A (p.Thr1658Lys) in SCN1A gene and c.1283A>G (p.Tyr428Cys) in the SCN2A gene, whereas the third mutation c.3295G>T (p.Glu1099*) was already described in patients with Dravet syndrome.

CONCLUSION

This study demonstrates that clinical exome sequencing is an effective diagnosis tool to investigate this group of diseases with huge diversity and defends its use in clinical routine.

Clinical and molecular analysis of epilepsy-related genes in patients with Dravet syndrome

Dravet syndrome is considered to be one of the most severe types of genetic epilepsy. Mutations in SCN1A gene have been found to be responsible for at least 80% of patients with Dravet syndrome, and 90% of these mutations arise de novo. The variable clinical phenotype is commonly observed among these patients with SCN1A mutations, suggesting that genetic modifiers may influence the phenotypic expression of Dravet syndrome. In the present study, we described the clinical, pathological, and molecular characteristics of 13 Han Chinese pedigrees clinically diagnosed with Dravet syndrome. By targeted-exome sequencing, bioinformatics analysis and Sanger sequencing verification, 11 variants were identified in SCN1A gene among 11 pedigrees including 7 missense mutations, 2 splice site mutations, and 2 frameshift mutations (9 novel variants and 2 reported mutations). Particularly, 2 of these Dravet syndrome patients with SCN1A variants also harbored SCN9A, KCNQ2, or SLC6A8 variants. In addition, 2 subjects were failed to detect any pathogenic mutations in SCN1A and other epilepsy-related genes. These data suggested that SCN1A variants account for about 84.6% of Dravet syndrome in our cohort. This study expanded the mutational spectrum for the SCN1A gene, and also provided clinical and genetic evidence for the hypothesis that genetic modifiers may contribute to the variable manifestation of Dravet syndrome patients with SCN1A mutations. Thus, targeted-exome sequencing will make it possible to detect the interactions of epilepsy-related genes and reveal their modification on the severity of SCN1A mutation-related Dravet syndrome.

Pathogenic significance of SCN1A splicing variants causing Dravet syndrome: Improving diagnosis with targeted sequencing for variants by in silico analysis

OBJECTIVES

Genetic heterogeneity of epileptic encephalopathy (IEE) mandates the use of gene-panels for diagnosis.

PATIENTS AND METHODS

A 36-gene-panel next-generation sequencing was applied for IEE in two Iranian families. A literature search was performed using keywords to identify reported splicing mutations in SCN1A and perform genotype-phenotype correlation.

RESULTS

An update of splicing mutations revealed 147 variants with 65.75% of them de novo mutations. Most of the familial variants were of parental origin. The structure of the protein was often affected in the linker and transmembrane segments. 92% of intronic variants were pathogenic. A de novo heterozygous mutation was found in the first patient, but not in her sibling and parents. In the second family, a novel de novo heterozygous mutation was found at position c.1210insT leading to a truncated protein.

CONCLUSION

Gene-panel sequencing is helpful for reducing the time and cost, guiding early treatment, and estimating the recurrence risks. The importance of characterization of intronic variants was noticed; though bioinformatics analysis of novel intronic variants should be of concern for rapid reporting the pathogenic effect of variants.

Novel SCN1A and GABRA1 Gene Mutations With Diverse Phenotypic Features and the Question on the Existence of a Broader Spectrum of Dravet Syndrome

In the light of modern molecular technologies, the understanding of the complexity of the numerous genotype-phenotype correlations regarding Dravet syndrome is mandatory. Motivated by 2 patients, whose whole-exome sequencing revealed novel mutations that exemplify the phenotypic and genetic heterogeneities associated with typical and atypical Dravet syndrome presentations, the authors discuss the existence of a broader spectrum of Dravet syndrome. The first patient is a 4-year-old boy with fairly typical Dravet syndrome and a novel sodium channel α1 subunit gene mutation of high-predicted combined pathogenicity likelihood. The second patient is a 15-year-old boy with some atypical features of Dravet syndrome, harboring a novel mutation of the γ-aminobutyric acid receptor α1 subunit gene, whose role in this syndrome pathogenesis has recently been highlighted. A brief review of the literature reveals that none of the current diagnostic criteria is thoroughly predictive of the disease, and phenotypic discrepancies are common among patients carrying atypical Dravet syndrome mutations. The authors conclude that the discussion of a Dravet syndrome spectrum is relevant.

Gene Panel Testing in Epileptic Encephalopathies and Familial Epilepsies

In recent years, several genes have been causally associated with epilepsy. However, making a genetic diagnosis in a patient can still be difficult, since extensive phenotypic and genetic heterogeneity has been observed in many monogenic epilepsies. This study aimed to analyze the genetic basis of a wide spectrum of epilepsies with age of onset spanning from the neonatal period to adulthood. A gene panel targeting 46 epilepsy genes was used on a cohort of 216 patients consecutively referred for panel testing. The patients had a range of different epilepsies from benign neonatal seizures to epileptic encephalopathies (EEs). Potentially causative variants were evaluated by literature and database searches, submitted to bioinformatic prediction algorithms, and validated by Sanger sequencing. If possible, parents were included for segregation analysis. We identified a presumed disease-causing variant in 49 (23%) of the 216 patients. The variants were found in 19 different genes including SCN1A, STXBP1, CDKL5, SCN2A, SCN8A, GABRA1, KCNA2, and STX1B. Patients with neonatal-onset epilepsies had the highest rate of positive findings (57%). The overall yield for patients with EEs was 32%, compared to 17% among patients with generalized epilepsies and 16% in patients with focal or multifocal epilepsies. By the use of a gene panel consisting of 46 epilepsy genes, we were able to find a disease-causing genetic variation in 23% of the analyzed patients. The highest yield was found among patients with neonatal-onset epilepsies and EEs.

Phenotypic Variability from Benign Infantile Epilepsy to Ohtahara Syndrome Associated with a Novel Mutation in SCN2A

Mutations in SCN2A have been associated with benign familial neonatal-infantile seizures (BFNIS) as well as infantile-onset epileptic encephalopathy, such as Ohtahara syndrome (OS). We describe a family with 3 affected individuals carrying the novel SCN2A missense variant c.1147C>G, p.Q383E affecting a residue proximal to the highly conserved selectivity filter in the P-loop of the voltage-gated sodium channel (Na_v1.2). All 3 individuals presented with seizures in early infancy. However, there were striking differences in the spectrum of clinical presentations, ranging from BFNIS to OS. A change of ion selectivity of Na_v1.2 is considered to be the potential pathomechanism underlying this Na_v1.2 channel dysfunction. The observation of benign and severe phenotypes due to an identical mutation within one family contradicts the hypothesis of different modes of inheritance as a mandatory feature discriminating BFNIS from SCN2A encephalopathy.

Amplicon Resequencing Identified Parental Mosaicism for Approximately 10% of "de novo" SCN1A Mutations in Children with Dravet Syndrome

The majority of children with Dravet syndrome (DS) are caused by de novo SCN1A mutations. To investigate the origin of the mutations, we developed and applied a new method that combined deep amplicon resequencing with a Bayesian model to detect and quantify allelic fractions with improved sensitivity. Of 174 SCN1A mutations in DS probands which were considered "de novo" by Sanger sequencing, we identified 15 cases (8.6%) of parental mosaicism. We identified another five cases of parental mosaicism that were also detectable by Sanger sequencing. Fraction of mutant alleles in the 20 cases of parental mosaicism ranged from 1.1% to 32.6%. Thirteen (65% of 20) mutations originated paternally and seven (35% of 20) maternally. Twelve (60% of 20) mosaic parents did not have any epileptic symptoms. Their mutant allelic fractions were significantly lower than those in mosaic parents with epileptic symptoms (P = 0.016). We identified mosaicism with varied allelic fractions in blood, saliva, urine, hair follicle, oral epithelium, and semen, demonstrating that postzygotic mutations could affect multiple somatic cells as well as germ cells. Our results suggest that more sensitive tools for detecting low-level mosaicism in parents of families with seemingly "de novo" mutations will allow for better informed genetic counseling.

Dravet syndrome in Sweden: a population-based study

AIM

To assess the prevalence and incidence of Dravet syndrome in children diagnosed in Sweden between 2007 and 2011, and to describe neurological comorbidity, disease course, phenotypes, and treatment effects.

METHOD

All neuropaediatricians at university and county hospitals were asked to supply information for patients that matched the electro-clinical profile of Dravet syndrome. Genetic laboratories and referral clinicians were also contacted and requested to supply information.

RESULTS

The estimated incidence was one in 33 000 live births (95% CI 1:20 400-1:56 200) and prevalence on December 31, 2011 was one in 45 700 children aged less than 18 years of age (95% CI 1:33 800-1:63 400). The median age of the 42 children (18 males, 24 females) was 7 years (range 1-17y), the median age at seizure onset was 6 months (range 0-12mo), and the median age at diagnosis was 3 years (range 1-14y). A mutation in the SCN1A gene was found in 37 patients (88%), four were familial. Intellectual disability was diagnosed in 28 (67%) children, and 18 out of 30 patients investigated had autism spectrum disorder. Thirty participants had neurological deficits. Stiripentol, as an add-on medication, was used in 18 patients. Among these patients, seven were seizure free, six had >50% seizure reduction, and five <50% seizure reduction.

INTERPRETATION

This is the first population-based study of Dravet syndrome in Sweden. Our data confirm international findings of incidence and highlights the severe and progressive course of this genetic epilepsy syndrome.

Functional and structural deficits of the dentate gyrus network coincide with emerging spontaneous seizures in an Scn1a mutant Dravet Syndrome model during development

Dravet syndrome (DS) is characterized by severe infant-onset myoclonic epilepsy along with delayed psychomotor development and heightened premature mortality. A primary monogenic cause is mutation of the SCN1A gene, which encodes the voltage-gated sodium channel subunit Nav1.1. The nature and timing of changes caused by SCN1A mutation in the hippocampal dentate gyrus (DG) network, a core area for gating major excitatory input to hippocampus and a classic epileptogenic zone, are not well known. In particularly, it is still not clear whether the developmental deficit of this epileptogenic neural network temporally matches with the progress of seizure development. Here, we investigated the emerging functional and structural deficits of the DG network in a novel mouse model (Scn1a(E1099X/+)) that mimics the genetic deficit of human DS. Scn1a(E1099X/+) (Het) mice, similarly to human DS patients, exhibited early spontaneous seizures and were more susceptible to hyperthermia-induced seizures starting at postnatal week (PW) 3, with seizures peaking at PW4. During the same period, the Het DG exhibited a greater reduction of Nav1.1-expressing GABAergic neurons compared to other hippocampal areas. Het DG GABAergic neurons showed altered action potential kinetics, reduced excitability, and generated fewer spontaneous inhibitory inputs into DG granule cells. The effect of reduced inhibitory input to DG granule cells was exacerbated by heightened spontaneous excitatory transmission and elevated excitatory release probability in these cells. In addition to electrophysiological deficit, we observed emerging morphological abnormalities of DG granule cells. Het granule cells exhibited progressively reduced dendritic arborization and excessive spines, which coincided with imbalanced network activity and the developmental onset of spontaneous seizures. Taken together, our results establish the existence of significant structural and functional developmental deficits of the DG network and the temporal correlation between emergence of these deficits and the onset of seizures in Het animals. Most importantly, our results uncover the developmental deficits of neural connectivity in Het mice. Such structural abnormalities likely further exacerbate network instability and compromise higher-order cognitive processing later in development, and thus highlight the multifaceted impacts of Scn1a deficiency on neural development.

Genetic epileptic encephalopathies: is all written into the DNA?

Epileptic encephalopathy is a condition in which epileptic activity, clinical or subclinical, is thought to be responsible for any disturbance of cognition, behavior, or motor control. However, experimental evidence supporting this clinical observation are still poor and the causal relationship between pharmacoresistant seizures and cognitive outcome is controversial. In the past two decades, genetic studies shed new light onto complex mechanisms underlying different severe epileptic conditions associated with intellectual disability and behavioral abnormalities, thereby providing important clues on the relationship between seizures and cognitive outcome. Dravet syndrome is a childhood disorder associated with loss-of-function mutations in SCN1A and is characterized by frequent seizures and severe cognitive impairment, thus well illustrating the concept of epileptic encephalopathy. However, it is difficult to determine the causative role of the underlying sodium channel dysfunction and that of the consequent seizures in influencing cognitive outcome in these children. It is also difficult to demonstrate whether a recognizable profile of cognitive impairment or a definite behavioral phenotype exists. Data from the laboratory and the clinics may provide greater insight into the degree to which epileptic activity may contribute to cognitive impairment in individual syndromes.

Long-term course of Dravet syndrome: a study from an epilepsy center in Japan

OBJECTIVE

This study attempted to clarify the long-term course of Dravet syndrome (DS).

METHODS

Sixty-four patients diagnosed with DS (44 with typical DS, and 20 with atypical DS) were studied. The long-term outcomes of clinical seizures, electroencephalographic findings, neuropsychological findings, and social situation were analyzed. The follow-up period ranged from 11 to 34 years 5 months (median 24 years).

RESULTS

At the last visit, the ages ranged from 19 years to 45 years (median 30 years). Fifty-nine patients continued to have generalized tonic-clonic seizures (GTCS). Status epilepticus and unilateral seizures were not observed and myoclonic seizures, atypical absence seizures, and photosensitive seizures were resolved in most patients. The frequency of complex partial seizures was equally low, with five patients at presentation and six patients at the last visit, respectively. Five patients achieved seizure remission (seizure-free for 1 year or longer). Only 1 of 44 patients with typical DS had seizure remission, whereas 4 of 20 patients with atypical DS remitted, with a statistically significant difference between the two phenotypes (p = 0.03). Intellectual disability was found in all patients; especially, severe intellectual disability was prevalent. Patients with atypical DS tended to have milder intellectual disability compared to those with typical DS (p = 0.0283). Occipital alpha rhythm in the basic activity was associated with milder intellectual disability (p = 0.0085). The freedom from seizures correlated with appearance of occipital alpha rhythms (p = 0.0008) and disappearance of epileptic discharges (p = 0.0004). Two patients with GTCS died. Mutations of the neuronal voltage-gated sodium channel alpha subunit type 1 gene were detected at a high frequency (33 of 36 patients examined). Seizure remission was found only in the missense mutation group.

SIGNIFICANCE

The long-term seizure and intellectual outcomes are extremely poor in patients with typical DS compared to those with atypical DS. Epilepsy phenotype may influence long-term course of DS.

Prognostic factors for subsequent epilepsy in children with febrile seizures

OBJECTIVE

Epilepsy following febrile seizures (FS) has been estimated between 2% and 7%. It concerns a prospective study in a large sample of children with a long-term follow-up. The aim of this study is to identify the prognostic factors that can lead children with FS to epilepsy.

METHODS

Children with a first episode of FS were included. We gathered information about prenatal and perinatal history, family history of FS and epilepsy in first- and second degree relatives, age at the time of the initial FS, dates of FS recurrences, focality, duration of the FS and recurrent episodes within the same febrile illness, height and duration of fever prior to the seizure, cause of the fever, and frequency of febrile illnesses. Patients were seen every 4-6 months and also at each recurrence.

KEY FINDINGS

A group of 560 children with a first FS met all entry criteria. Epilepsy was recorded at 5.4%. Statistical analysis was performed between children with epilepsy and those with no afebrile seizure. We analyzed FS recurrences in accordance with the occurrence of epilepsy. From the third FS recurrence and beyond, only focality continued to have prognostic value.

SIGNIFICANCE

Main prognostic factors for the development of epilepsy after FS are: (1) complex FS that increased the risk for epilepsy 3.6 times, (2) age at onset of FS beyond the third year of life that raised the risk 3.8 times, (3) positive family history of epilepsy 7.3 times, and (4) multiple episodes of FS about 10 times. Focality at the first and the second FS recurrence increased the risk of epilepsy about 9.7 and 11.7 times, respectively. Focality was the only factor that continued to be significant in further FS recurrences. A prognostic profile of each child with FS would be very useful for the follow-up of these children.

Identification of SCN1A and PCDH19 mutations in Chinese children with Dravet syndrome

BACKGROUND

Dravet syndrome is a severe form of epilepsy. Majority of patients have a mutation in SCN1A gene, which encodes a voltage-gated sodium channel. A recent study has demonstrated that 16% of SCN1A-negative patients have a mutation in PCDH19, the gene encoding protocadherin-19. Mutations in other genes account for only a very small proportion of families. TSPYL4 is a novel candidate gene within the locus 6q16.3-q22.31 identified by linkage study.

OBJECTIVE

The present study examined the mutations in epileptic Chinese children with emphasis on Dravet syndrome.

METHODS

A hundred children with severe epilepsy were divided into Dravet syndrome and non-Dravet syndrome groups and screened for SCN1A mutations by direct sequencing. SCN1A-negative Dravet syndrome patients and patients with phenotypes resembling Dravet syndrome were checked for PCDH19 and TSPYL4 mutations.

RESULTS

Eighteen patients (9 males, 9 females) were diagnosed to have Dravet syndrome. Among them, 83% (15/18) had SCN1A mutations including truncating (7), splice site (2) and missense mutations (6). The truncating/splice site mutations were associated with moderate to severe degree of intellectual disability (p<0.05). During the progression of disease, 73% (11/15) had features fitting into the diagnostic criteria of autism spectrum disorder and 53% (8/15) had history of vaccination-induced seizures. A novel PCDH19 p.D377N mutation was identified in one SCN1A-negative female patient with Dravet syndrome and a known PCDH19 p.N340S mutation in a female non-Dravet syndrome patient. The former also inherited a TSPYL4 p.G60R variant.

CONCLUSION

A high percentage of SCN1A mutations was identified in our Chinese cohort of Dravet syndrome patients but none in the rest of patients. We demonstrated that truncating/splice site mutations were linked to moderate to severe intellectual disability in these patients. A de novo PCDH19 missense mutation together with an inherited TSPYL4 missense variant were identified in a patient with Dravet syndrome.

Dravet syndrome: patients with co-morbid SCN1A gene mutations and mitochondrial electron transport chain defects

PURPOSE

To review our cohort of patients with Dravet syndrome and determine if patients with SCN1A mutations can also express mitochondrial disease due to electron transport chain dysfunction.

METHODS

A retrospective chart review was used to describe clinical manifestations and retrieve biochemical testing, neuroimaging, gene sequencing, and electroencephalographic results of patients expressing both mitochondrial disease and Dravet syndrome.

RESULTS

Two children were found to have pathological mutations in the SCN1A gene and defects in mitochondrial electron transport chain complex activity. Both developed early febrile and medically intractable afebrile seizures with resulting neurocognitive decline. In the first patient, a muscle biopsy demonstrated complex IV dysfunction and in the second patient, complex III dysfunction. Patient 1 had more difficult to control seizures, and had features consistent with severe autism. Patient 2, who had earlier control and less severe seizures, did not have features of autism. Patient 1 had SCN1A missense mutation, c. 3734 G>A and patient 2 had a mutation, c. 3733 C>T, which produces a truncation mutation.

CONCLUSION

Our two patients underscore the need to rule out possible co-morbid mitochondrial disease and Dravet syndrome. The treatment of seizures for each is different, with valproic acid being first line treatment in Dravet syndrome and contraindicated in many mitochondrial diseases, due to possible induction of liver failure and death. Failure to pursue complete diagnostic evaluation might influence medication choice, possible seizure control, and developmental outcomes.

Dravet syndrome as epileptic encephalopathy: evidence from long-term course and neuropathology

Dravet syndrome is an epilepsy syndrome of infantile onset, frequently caused by SCN1A mutations or deletions. Its prevalence, long-term evolution in adults and neuropathology are not well known. We identified a series of 22 adult patients, including three adult post-mortem cases with Dravet syndrome. For all patients, we reviewed the clinical history, seizure types and frequency, antiepileptic drugs, cognitive, social and functional outcome and results of investigations. A systematic neuropathology study was performed, with post-mortem material from three adult cases with Dravet syndrome, in comparison with controls and a range of relevant paediatric tissue. Twenty-two adults with Dravet syndrome, 10 female, were included, median age 39 years (range 20-66). SCN1A structural variation was found in 60% of the adult Dravet patients tested, including one post-mortem case with DNA extracted from brain tissue. Novel mutations were described for 11 adult patients; one patient had three SCN1A mutations. Features of Dravet syndrome in adulthood include multiple seizure types despite polytherapy, and age-dependent evolution in seizure semiology and electroencephalographic pattern. Fever sensitivity persisted through adulthood in 11 cases. Neurological decline occurred in adulthood with cognitive and motor deterioration. Dysphagia may develop in or after the fourth decade of life, leading to significant morbidity, or death. The correct diagnosis at an older age made an impact at several levels. Treatment changes improved seizure control even after years of drug resistance in all three cases with sufficient follow-up after drug changes were instituted; better control led to significant improvement in cognitive performance and quality of life in adulthood in two cases. There was no histopathological hallmark feature of Dravet syndrome in this series. Strikingly, there was remarkable preservation of neurons and interneurons in the neocortex and hippocampi of Dravet adult post-mortem cases. Our study provides evidence that Dravet syndrome is at least in part an epileptic encephalopathy.

Genotype-phenotype correlations in a group of 15 SCN1A-mutated Italian patients with GEFS+ spectrum (seizures plus, classical and borderline severe myoclonic epilepsy of infancy)

Mutations in SCN1A gene have been associated with the spectrum of generalized/genetic epilepsy with febrile seizures plus. Recently, databases reporting SCN1A mutations and clinical details of patients have been created to facilitate genotype- phenotype correlations, actually not completely defined, particularly if a specific mutation underlies phenotypes. We report on a group of 15 patients with clinical features of GEFS+ (3), classical (7), or borderline severe myoclonic epilepsy of infancy (5), in whom genetic analysis of patients and parents and follow-up period were performed to establish genotype-phenotype correlations, to enrich literature and databases data. We found 11 pathogenic mutations (5 novel: c.80 G>C exon 1; c.187 T>C exon 1; c.3061 G>T exon 16; c.4297 G>A exon 22; c.5579 delA ins TCTCC exon 26) and 4 novel nucleotidic variants (IVS5+38 C>T intron 5; IVS8-19 C>T intron 18; c.4945 C>T exon 25; c.5127 C>A exon 26). Paternal inheritance was observed in 4/4 cases.

A catalog of SCN1A variants

Over the past 10 years mutations in voltage-gated sodium channels (Na(v)s) have become closely associated with inheritable forms of epilepsy. One isoform in particular, Na(v)1.1 (gene symbol SCN1A), appears to be a superculprit, registering with more than 330 mutations to date. The associated phenotypes range from benign febrile seizures to extremely serious conditions, such as Dravet's syndrome (SMEI). Despite the wealth of information, mutational analyses are cumbersome, owing to inconsistencies among the Na(v)1.1 sequences to which different research groups refer. Splicing variability is the core problem: Na(v)1.1 co-exists in three isoforms, two of them lack 11 or 28 amino acids compared to full-length Na(v).1.1. This review establishes a standardized nomenclature for Na(v)1.1 variants so as to provide a platform from which future mutation analyses can be started without need for up-front data normalization. An online resource--SCN1A infobase--is introduced.

SCN1A, SCN1B, and GABRG2 gene mutation analysis in Chinese families with generalized epilepsy with febrile seizures plus

Generalized epilepsy with febrile seizures plus (GEFS+; MIM#604233) is a familial epilepsy syndrome characterized by phenotypic and genetic heterogeneity. It was associated with mutations in the neuronal voltage-gated sodium channel subunit gene (SCN1A, SCN2A, SCN1B) and ligand-gated gamma aminobutyric acid receptors genes (GABRG2, GABRD). We investigated the roles of SCN1A, SCN1B, and GABRG2 mutations in the etiology of Chinese GEFS+ families. Genomic deoxyribonucleic acid (DNA) was extracted from peripheral blood lymphocytes of 23 probands and their family members. The sequences of SCN1A, SCN1B, and GABRG2 genes were analyzed by polymerase chain reaction (PCR) and direct sequencing. The major phenotypes of affected members in the 23 GEFS+ families exhibited FS and FS+, whereas rare phenotypes afebrile generalized tonic-clonic seizures (AGTCS), myoclonic-astatic epilepsy (MAE), and partial seizures were also observed. A novel SCN1A mutation, p.N935H, was identified in one family and another novel mutation in GABRG2, p.W390X, in another family. However, no SCN1B mutation was identified. The combined frequency of SCN1A, SCN1B, and GABRG2 mutations was 8.7% (2/23), extending the distribution of SCN1A and GABRG2 mutations to Chinese GEFS+ families. There were still unidentified genes contributing to the pathogenesis of GEFS+.

The spectrum of SCN1A-related infantile epileptic encephalopathies

The relationship between severe myoclonic epilepsy of infancy (SMEI or Dravet syndrome) and the related syndrome SMEI-borderland (SMEB) with mutations in the sodium channel alpha 1 subunit gene SCN1A is well established. To explore the phenotypic variability associated with SCN1A mutations, 188 patients with a range of epileptic encephalopathies were examined for SCN1A sequence variations by denaturing high performance liquid chromatography and sequencing. All patients had seizure onset within the first 2 years of life. A higher proportion of mutations were identified in patients with SMEI (52/66; 79%) compared to patients with SMEB (25/36; 69%). By studying a broader spectrum of infantile epileptic encephalopathies, we identified mutations in other syndromes including cryptogenic generalized epilepsy (24%) and cryptogenic focal epilepsy (22%). Within the latter group, a distinctive subgroup designated as severe infantile multifocal epilepsy had SCN1A mutations in three of five cases. This phenotype is characterized by early onset multifocal seizures and later cognitive decline. Knowledge of an expanded spectrum of epileptic encephalopathies associated with SCN1A mutations allows earlier diagnostic confirmation for children with these devastating disorders.