Clustered de novo start-loss variants in GLUL result in a developmental and epileptic encephalopathy via stabilization of glutamine synthetase

Glutamine synthetase (GS), encoded by GLUL, catalyzes the conversion of glutamate to glutamine. GS is pivotal for the generation of the neurotransmitters glutamate and gamma-aminobutyric acid and is the primary mechanism of ammonia detoxification in the brain. GS levels are regulated post-translationally by an N-terminal degron that enables the ubiquitin-mediated degradation of GS in a glutamine-induced manner. GS deficiency in humans is known to lead to neurological defects and death in infancy, yet how dysregulation of the degron-mediated control of GS levels might affect neurodevelopment is unknown. We ascertained nine individuals with severe developmental delay, seizures, and white matter abnormalities but normal plasma and cerebrospinal fluid biochemistry with de novo variants in GLUL. Seven out of nine were start-loss variants and two out of nine disrupted 5' UTR splicing resulting in splice exclusion of the initiation codon. Using transfection-based expression systems and mass spectrometry, these variants were shown to lead to translation initiation of GS from methionine 18, downstream of the N-terminal degron motif, resulting in a protein that is stable and enzymatically competent but insensitive to negative feedback by glutamine. Analysis of human single-cell transcriptomes demonstrated that GLUL is widely expressed in neuro- and glial-progenitor cells and mature astrocytes but not in post-mitotic neurons. One individual with a start-loss GLUL variant demonstrated periventricular nodular heterotopia, a neuronal migration disorder, yet overexpression of stabilized GS in mice using in utero electroporation demonstrated no migratory deficits. These findings underline the importance of tight regulation of glutamine metabolism during neurodevelopment in humans.

Cannabidiol: metabolism and clinical efficacy in epileptic patients

INTRODUCTION

The landscape of epilepsy treatment has undergone a significant transformation with the emergence of cannabidiol as a potential therapeutic agent. Epidiolex, a pharmaceutical formulation of highly purified CBD, garnered significant attention not just for its therapeutic potential but also for being the first cannabis-derived medication to obtain approval from regulatory bodies.

AREA COVERED

In this narrative review the authors explore the intricate landscape of CBD as an antiseizure medication, deepening into its pharmacological mechanisms and clinical trials involving various epileptic encephalopathies. This exploration serves as a comprehensive guide, shedding light on a compound that holds promise for individuals contending with the significant challenges of drug-resistant epilepsy.

EXPERT OPINION

Rigorous studies highlight cannabidiol's efficacy, safety profile, and potential cognitive benefits, warranting further exploration for its approval in various drug-resistant epilepsy forms. As a promising therapeutic option, cannabidiol not only demonstrates efficacy in seizure control but also holds the potential for broader enhancements in the quality of life, especially for patients with epileptic encephalopathies.

Continuous Spike-Waves during Slow Sleep Today: An Update

In the context of childhood epilepsy, the concept of continuous spike-waves during slow sleep (CSWS) includes several childhood-onset heterogeneous conditions that share electroencephalograms (EEGs) characterized by a high frequency of paroxysmal abnormalities during sleep, which have negative effects on the cognitive development and behavior of the child. These negative effects may have the characteristics of a clear regression or of a slowdown in development. Seizures are very often present, but not constantly. The above makes it clear why CSWS have been included in epileptic encephalopathies, in which, by definition, frequent EEG paroxysmal abnormalities have an unfavorable impact on cognitive functions, including socio-communicative skills, causing autistic features, even regardless of the presence of clinically overt seizures. Although several decades have passed since the original descriptions of the electroclinical condition of CSWS, there are still many areas that are little-known and deserve to be further studied, including the EEG diagnostic criteria, the most effective electrophysiological parameter for monitoring the role of the thalamus in CSWS pathogenesis, its long-term evolution, the nosographic location of Landau-Kleffner syndrome, standardized neuropsychological and behavioral assessments, and pharmacological and non-pharmacological therapies.

Epileptic Encephalopathy GABRB Structural Variants Share Common Gating and Trafficking Defects

Variants in the GABRB gene, which encodes the β subunit of the GABAA receptor, have been implicated in various epileptic encephalopathies and related neurodevelopmental disorders such as Dravet syndrome and Angelman syndrome. These conditions are often associated with early-onset seizures, developmental regression, and cognitive impairments. The severity and specific features of these encephalopathies can differ based on the nature of the genetic variant and its impact on GABAA receptor function. These variants can lead to dysfunction in GABAA receptor-mediated inhibition, resulting in an imbalance between neuronal excitation and inhibition that contributes to the development of seizures. Here, 13 de novo EE-associated GABRB variants, occurring as missense mutations, were analyzed to determine their impact on protein stability and flexibility, channel function, and receptor biogenesis. Our results showed that all mutations studied significantly impact the protein structure, altering protein stability, flexibility, and function to varying degrees. Variants mapped to the GABA-binding domain, coupling zone, and pore domain significantly impact the protein structure, modifying the β+/α- interface of the receptor and altering channel activation and receptor trafficking. Our study proposes that the extent of loss or gain of GABAA receptor function can be elucidated by identifying the specific structural domain impacted by mutation and assessing the variability in receptor structural dynamics. This paves the way for future studies to explore and uncover links between the incidence of a variant in the receptor topology and the severity of the related disease.

Respiratory Dysfunction in Epileptic Encephalopathies: Insights and Challenges

Epileptic encephalopathies constitute a group of severe epileptic disorders characterized by intractable seizures and cognitive regression. Beyond the hallmark neurological manifestations, these disorders frequently exhibit associated respiratory dysfunction, which is increasingly recognized as a critical aspect of their pathophysiology. Respiratory abnormalities in epileptic encephalopathies encompass a spectrum of manifestations, ranging from subtle alterations in breathing patterns to life-threatening events such as apneas and hypoventilation. These respiratory disturbances often occur during seizures, the interictal period, or even persist chronically, leading to significant morbidity and mortality. We explore the varied clinical presentations and their implications on patient outcomes, emphasizing the need for heightened awareness among clinicians. This review unravels the intricate mechanisms linking epilepsy and respiratory dysfunction. GABAergic and glutamatergic imbalances, alterations in central respiratory centers, and abnormal autonomic control are among the key factors contributing to respiratory disturbances in these patients. We elucidate the neurobiological intricacies that underlie these processes and their relevance to therapeutic interventions. Accurate diagnosis of respiratory dysfunction in epileptic encephalopathies is often hindered by its diverse clinical phenotypes and the absence of routine screening protocols. We scrutinize the diagnostic hurdles, highlighting the necessity of comprehensive respiratory assessments in managing these patients. Timely recognition of respiratory issues may guide treatment decisions and mitigate complications. Management of respiratory dysfunction in epileptic encephalopathies is complex and necessitates a multidisciplinary approach. We explore various therapeutic modalities, including antiepileptic drugs (AEDs), ventilatory support, and novel interventions like neuromodulation techniques. The review emphasizes the individualized nature of treatment strategies tailored to each patient's specific needs. In conclusion, this narrative review offers a comprehensive overview of respiratory dysfunction in epileptic encephalopathies, shedding light on its clinical importance, underlying mechanisms, diagnostic challenges, and therapeutic considerations. By addressing these insights and challenges, we hope to inspire further research and innovation to enhance the care and outcomes of patients with epileptic encephalopathies.

GABRG1 variant as a potential novel cause of epileptic encephalopathy, hypotonia, and global developmental delay

Epileptic encephalopathies (EEs) are severe brain disorders with excessive ictal (seizure) and interictal (electrographic epileptiform discharges) activity in developing brain which may result in progressive cognitive and neuropsychological deterioration. In contrast to regular epilepsy where the treatment goal is to prevent the seizure (ictal) recurrence, in patients with EE the goal is to treat both ictal as well as interictal activity to prevent further progression. With the introduction of genetic sequencing technologies over the past 20 years, there is growing recognition of the genetic basis of EE, with the majority due to monogenic causes. Monogenic etiologies of EE include pathogenic variants in the γ-aminobutyric acid type A receptor (GABA-A) encoding gene family. We present a 2-year-old patient with EE, hypotonia, and global developmental delays. Clinical trio exome sequencing showed a novel, de novo variant in GABRG1. GABRG1 encodes the γ1 subunit of the GABA-A receptor. To date, there has not been an association of EE with pathogenic variants in GABRG1. This variant is predicted to be damaging to protein structure and function, and the patient's phenotype is similar to those with pathogenic variants in other members of the GABA-A receptor encoding gene family.

Myoclonic Epilepsy: Case Report of a Mild Phenotype in a Pediatric Patient Expanding Clinical Spectrum of KCNA2 Pathogenic Variants

We report on the rare case of a male toddler presenting with myoclonic epilepsy characterized by daily episodes of upward movements of the eyebrows, and myoclonic jerks of both head and upper limbs. In addition, the child showed speech delay, tremors, and lack of motor coordination. Next Generation Sequencing analysis (NGS) performed in trio revealed in the proband the c.889C>T de novo missense variant in the KCNA2 gene in heterozygous state. This is the first case of myoclonic epilepsy in a toddler due to a c.889C>T KCNA2 missense variant. The patient was treated with valproic acid and ethosuximide with a good clinical response. At 6 years old, follow-up revealed that the proband was seizure-free with tremors and clumsiness in movements. According to the literature, this case supports the correlation between myoclonic epilepsy and KCNA2 alterations. This evidence suggests that performing genomic testing including the KCNA2 gene in preschool patients affected by myoclonic epilepsy, especially when associated with delayed neurodevelopment. Our goal is to expand the phenotypical spectrum of this rare condition and adding clinical features following a genotype-first approach.

Epileptic Phenotypes Associated With SNAREs and Related Synaptic Vesicle Exocytosis Machinery

SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptor) are an heterogeneous family of proteins that, together with their key regulators, are implicated in synaptic vesicle exocytosis and synaptic transmission. SNAREs represent the core component of this protein complex. Although the specific mechanisms of the SNARE machinery is still not completely uncovered, studies in recent years have provided a clearer understanding of the interactions regulating the essential fusion machinery for neurotransmitter release. Mutations in genes encoding SNARE proteins or SNARE complex associated proteins have been associated with a variable spectrum of neurological conditions that have been recently defined as “SNAREopathies.” These include neurodevelopmental disorder, autism spectrum disorder (ASD), movement disorders, seizures and epileptiform abnormalities. The SNARE phenotypic spectrum associated with seizures ranges from simple febrile seizures and infantile spasms, to severe early-onset epileptic encephalopathies. Our study aims to review and delineate the epileptic phenotypes associated with dysregulation of synaptic vesicle exocytosis and transmission, focusing on the main proteins of the SNARE core complex (STX1B, VAMP2, SNAP25), tethering complex (STXBP1), and related downstream regulators.

Novel treatments in epilepsy guided by genetic diagnosis

In recent years, precision medicine has emerged as a new paradigm for improved and more individualized patient care. Its key objective is to provide the right treatment, to the right patient at the right time, by basing medical decisions on individual characteristics, including specific genetic biomarkers. In order to realize this objective researchers and physicians must first identify the underlying genetic cause; over the last 10 years, advances in genetics have made this possible for several monogenic epilepsies. Through next generation techniques, a precise genetic aetiology is attainable in 30-50% of genetic epilepsies beginning in the paediatric age. While committed in such search for novel genes carrying disease-causing variants, progress in the study of experimental models of epilepsy has also provided a better understanding of the mechanisms underlying the condition. Such advances are already being translated into improving care, management and treatment of some patients. Identification of a precise genetic aetiology can already direct physicians to prescribe treatments correcting specific metabolic defects, avoid antiseizure medicines that might aggravate functional consequences of the disease-causing variant or select the drugs that counteract the underlying, genetically determined, functional disturbance. Personalized, tailored treatments should not just focus on how to stop seizures but possibly prevent their onset and cure the disorder, often consisting of seizures and its comorbidities including cognitive, motor and behaviour deficiencies. This review discusses the therapeutic implications following a specific genetic diagnosis and the correlation between genetic findings, pathophysiological mechanisms and tailored seizure treatment, emphasizing the impact on current clinical practice.

Early vagus nerve stimulator implantation as a main predictor of positive outcome in pediatric patients with epileptic encephalopathy

We describe a multicenter experience with VNS implantation in pediatric patients with epileptic encephalopathy. Our goal was to assess VNS efficacy and identify potential predictors of favorable outcome. This was a retrospective study. Inclusion criteria were: ≤18 years at the time of VNS implantation and at least one year of follow-up. All patients were non-candidates for excisional procedures. Favorable clinical outcome and effective VNS therapy were defined as seizure reduction >50%. Outcome data were reviewed at one, two, three and five years after VNS implantation. Fisher's exact test, Kaplan-Meier and multiple logistic regression analysis were employed. Twenty-seven patients met inclusion criteria. Responder rate (seizure frequency reduction ≥ 50%) at one-year follow-up was 25.9%, and 15.3% at last follow-up visit. The only variable significantly predicting favorable outcome was time to VNS implantation, with the best outcome achieved when VNS implantation was performed within five years of seizure onset (overall response rate of 83.3% at one year of follow-up and 100% at five years). In total, 63% of patients evidenced improved QOL at last follow-up visit. Only one patient exited the study due to an adverse event at two years from implantation. Early VNS implantation within five years of seizure onset was the only predictor of favorable clinical outcome in pediatric patients with epileptic encephalopathy. Improved QOL and a very low incidence of adverse events were observed.

KCNT1-related epilepsies and epileptic encephalopathies: phenotypic and mutational spectrum

Variants in KCNT1, encoding a sodium-gated potassium channel (subfamily T member 1), have been associated with a spectrum of epilepsies and neurodevelopmental disorders. These range from familial autosomal dominant or sporadic sleep-related hypermotor epilepsy ((AD)SHE) to epilepsy of infancy with migrating focal seizures (EIMFS) and include developmental and epileptic encephalopathies (DEE). This study aims to provide a comprehensive overview of the phenotypic and genotypic spectrum of KCNT1 mutation-related epileptic disorders in 248 individuals, including 66 unpreviously published and 182 published cases, the largest cohort reported so far. Four phenotypic groups emerged from our analysis: i) EIMFS (152 individuals, 33 previously unpublished); ii) DEE other than EIMFS (non-EIMFS DEE) (37 individuals, 17 unpublished); iii) (AD)SHE (53 patients, 14 unpublished); iv) other phenotypes (6 individuals, 2 unpublished). In our cohort of 66 new cases, the most common phenotypic features were: a) in EIMFS, heterogeneity of seizure types, including epileptic spasms, epilepsy improvement over time, no epilepsy-related deaths; b) in non-EIMFS DEE, possible onset with West syndrome, occurrence of atypical absences, possible evolution to DEE with SHE features; one case of sudden unexplained death in epilepsy (SUDEP); c) in (AD)SHE, we observed a high prevalence of drug-resistance, although seizure frequency improved with age in some individuals, appearance of cognitive regression after seizure onset in all patients, no reported severe psychiatric disorders, although behavioural/psychiatric comorbidities were reported in about 50% of the patients, SUDEP in one individual; d) other phenotypes in individuals with mutation of KCNT1 included temporal lobe epilepsy, and epilepsy with tonic-clonic seizures and cognitive regression. Genotypic analysis of the whole cohort of 248 individuals showed only missense mutations and one inframe deletion in KCNT1. Although the KCNT1 mutations in affected individuals were seen to be distributed among the different domains of the KCNT1 protein, genotype-phenotype considerations showed many of the (AD)SHE-associated mutations to be clustered around the RCK2 domain in the C-terminus, distal to the NADP domain. Mutations associated with EIMFS/non-EIMFS DEE did not show a particular pattern of distribution in the KCNT1 protein. Recurrent KCNT1 mutations were seen to be associated with both severe and less severe phenotypes. Our study further defines and broadens the phenotypic and genotypic spectrums of KCNT1-related epileptic conditions and emphasizes the increasingly important role of this gene in the pathogenesis of early onset DEEs as well as in focal epilepsies, namely (AD)SHE.

The Heat Sensing Trpv1 Receptor Is Not a Viable Anticonvulsant Drug Target in the Scn1a +/- Mouse Model of Dravet Syndrome

Cannabidiol has been approved for the treatment of drug-resistant childhood epilepsies including Dravet syndrome (DS). Although the mechanism of anticonvulsant action of cannabidiol is unknown, emerging data suggests involvement of the transient receptor potential cation channel subfamily V member 1 (Trpv1). Pharmacological and genetic studies in conventional seizure models suggest Trpv1 is a novel anticonvulsant target. However, whether targeting Trpv1 is anticonvulsant in animal models of drug-resistant epilepsies is not known. Thus, we examined whether Trpv1 affects the epilepsy phenotype of the F1.Scn1a ^+/- mouse model of DS. We found that cortical Trpv1 mRNA expression was increased in seizure susceptible F1.Scn1a ^+/- mice with a hybrid genetic background compared to seizure resistant 129.Scn1a ^+/- mice isogenic on 129S6/SvEvTac background, suggesting Trpv1 could be a genetic modifier. Previous studies show functional loss of Trpv1 is anticonvulsant. However, Trpv1 selective antagonist SB-705498 did not affect hyperthermia-induced seizure threshold, frequency of spontaneous seizures or survival of F1.Scn1a ^+/- mice. Surprisingly, Trpv1 deletion had both pro- and anti-seizure effects. Trpv1 deletion did not affect hyperthermia-induced seizure temperature thresholds of F1.Scn1a ^+/- ; Trpv1 ^+/- at P14-16 but was proconvulsant at P18 as it reduced seizure temperature thresholds. Conversely, Trpv1 deletion did not alter the frequency of spontaneous seizures but reduced their severity. These results suggest that Trpv1 is a modest genetic modifier of spontaneous seizure severity in the F1.Scn1a ^+/- model of DS. However, the opposing pro- and anti-seizure effects of Trpv1 deletion and the lack of effects of Trpv1 inhibition suggest that Trpv1 is unlikely a viable anticonvulsant drug target in DS.

Bad Timing for Epileptic Networks: Role of Temporal Dynamics in Seizures and Cognitive Deficits

The precise coordination of neuronal activity is critical for optimal brain function. When such coordination fails, this can lead to dire consequences. In this review, I will present evidence that in epilepsy, failed coordination leads not only to seizures but also to alterations of the rhythmical patterns observed in the electroencephalogram and cognitive deficits. Restoring the dynamic coordination of epileptic networks could therefore both improve seizures and cognitive outcomes.

Detection of Disease-Causing SNVs/Indels and CNVs in Single Test Based on Whole Exome Sequencing: A Retrospective Case Study in Epileptic Encephalopathies

Background: Epileptic encephalopathies (EEs) are a pediatric entity with highly phenotypic and genetic heterogeneity. Both single nucleotide variants (SNVs)/Indels and copy number variations (CNVs) could be the causes. Whole exome sequencing (WES) is widely applied to detect SNVs/Indels, but the bioinformatics approach for detecting CNVs is still limited and weak. In the current study, the possibility of profiling both disease-causing SNVs/Indels and CNVs in a single test based on WES in EEs was evaluated. Methods: The infants diagnosed with EEs were enrolled from a single pediatric epilepsy center between January 2018 and February 2020. Demographic and clinical data were collected. In WES data, the pathogenic SNVs were identified through an in-house pipeline, and pathogenic CNVs were identified by CNVkit. The diagnostic rate was evaluated, and the molecular findings were characterized. Results: A total of 73 infants were included; 36 (49.32%) of them were males. The median age was 7 months. Thirty-two (43.84%) infants had been diagnosed with epilepsy syndrome. The most common type of syndrome was West syndrome (22/73, 30.1%), followed by Dravet syndrome (20/77, 27.4%). Fifty-four (73.97%) had intellectual development delay. The genetic cause of EEs, pathogenic or likely pathogenic variants, were successfully discovered in 46.6% (34/73) of the infants, and 29 (39.7%) infants carried SNVs/Indels, while 5 (6.8%) carried CNVs. The majority of the disease-causing variants were inherited in de novo pattern (25, 71.4%). In addition to showing that the variants in the ion channel encoding genes accounted for the main etiology, we discovered and confirmed two new disease-causing genes, CACNA1E and WDR26. Five discovered CNVs were deletions of 2q24.3, 1p36, 15q11-q13, 16p11.2, and 17p13.3, and all were confirmed by array comparative genomic hybridization. Conclusion: The application of both SNVs/Indels and CNVs detection in a single test based on WES yielded a high diagnosis rate in EEs. WES may serve as a first-tier test with cost-effective benefit in EEs.

De novo STXBP1 mutation in a child with developmental delay and spasticity reveals a major structural alteration in the interface with syntaxin 1A

STXBP1, also known as Munc-18, is a master regulator of neurotransmitter release and synaptic function in the human brain through its direct interaction with syntaxin 1A. STXBP1 binds syntaxin 1A is an inactive conformational state. STXBP1 decreases its binding affinity to syntaxin upon phosphorylation, enabling syntaxin 1A to engage in the SNARE complex, leading to neurotransmitter release. STXBP1-related disorders are well characterized by encephalopathy with epilepsy, and a diverse range of neurological and neurodevelopmental conditions. Through exome sequencing of a child with developmental delay, hypotonia, and spasticity, we found a novel de novo insertion mutation of three nucleotides in the STXBP1 coding region, resulting in an additional arginine after position 39 (R39dup). Inconclusive results from state-of-the-art variant prediction tools mandated a structure-based approach using molecular dynamics (MD) simulations of the STXBP1-syntaxin 1A complex. Comparison of the interaction interfaces of the wild-type and the R39dup complexes revealed a reduced interaction surface area in the mutant, leading to destabilization of the protein complex. Moreover, the decrease in affinity toward syntaxin 1A is similar for the phosphorylated STXBP1 and the R39dup. We applied the same MD methodology to seven additional previously reported STXBP1 mutations and reveal that the stability of the STXBP1-syntaxin 1A interface correlates with the reported clinical phenotypes. This study provides a direct link between the outcome of a novel variant in STXBP1 and protein structure and dynamics. The structural change upon mutation drives an alteration in synaptic function.

Seizures in Mouse Models of Rare Neurodevelopmental Disorders

Genetic neurodevelopmental disorders - that often include epilepsy as part of their phenotype - are a heterogeneous and clinically challenging spectrum of disorders in children. Although seizures often contribute significantly to morbidity in these affected populations, the mechanisms of epileptogenesis in these conditions remain poorly understood. Different model systems have been developed to aid in unraveling these mechanisms, which include a number of specific mutant mouse lines which genocopy specific general types of mutations present in patients. These mouse models have not only allowed for assessments of behavioral and electrographic seizure phenotypes to be ascertained, but also have allowed effects on the neurodevelopmental alterations and cognitive impairments associated with these disorders to be examined. In addition, these models play a role in advancing our understanding of these epileptic processes and developing preclinical therapeutics. The concordance of seizure phenotypes - in a select group of rare, genetic, neurodevelopmental disorders and epileptic encephalopathies - found between human patients and their model counterparts will be summarized. This review aims to assess whether models of Rett syndrome, CDKL5 deficiency disorder, Fragile-X syndrome, Dravet syndrome, and Ohtahara syndrome phenocopy the seizures seen in human patients.

Cannabinoids in the Treatment of Epilepsy: Current Status and Future Prospects

Cannabidiol (CBD) is one of the prominent phytocannabinoids found in Cannabis sativa, differentiating from Δ9-tetrahydrocannabinol (THC) for its non-intoxicating profile and its antianxiety/antipsychotic effects. CBD is a multi-target drug whose anti-convulsant properties are supposed to be independent of endocannabinoid receptor CB1 and might be related to several underlying mechanisms, such as antagonism on the orphan GPR55 receptor, regulation of adenosine tone, activation of 5HT1A receptors and modulation of calcium intracellular levels. CBD is a lipophilic compound with low oral bioavailability (6%) due to poor intestinal absorption and high first-pass metabolism. Its exposure parameters are greatly influenced by feeding status (ie, high fat-containing meals). It is mainly metabolized by cytochrome P 450 (CYP) 3A4 and 2C19, which it strongly inhibits. A proprietary formulation of highly purified, plant-derived CBD has been recently licensed as an adjunctive treatment for Dravet syndrome (DS) and Lennox-Gastaut syndrome (LGS), while it is being currently investigated in tuberous sclerosis complex. The regulatory agencies' approval was granted based on four pivotal double-blind, placebo-controlled, randomized clinical trials (RCTs) on overall 154 DS patients and 396 LGS ones, receiving CBD 10 or 20 mg/kg/day BID as active treatment. The primary endpoint (reduction in monthly seizure frequency) was met by both CBD doses. Most patients reported adverse events (AEs), generally from mild to moderate and transient, which mainly consisted of somnolence, sedation, decreased appetite, diarrhea and elevation in aminotransferase levels, the last being documented only in subjects on concomitant valproate therapy. The interaction between CBD and clobazam, likely due to CYP2C19 inhibition, might contribute to some AEs, especially somnolence, but also to CBD clinical effectiveness. Cannabidivarin (CBDV), the propyl analogue of CBD, showed anti-convulsant properties in pre-clinical studies, but a plant-derived, purified proprietary formulation of CBDV recently failed the Phase II RCT in patients with uncontrolled focal seizures.

Both gain-of-function and loss-of-function de novo CACNA1A mutations cause severe developmental epileptic encephalopathies in the spectrum of Lennox-Gastaut syndrome

OBJECTIVE

Developmental epileptic encephalopathies (DEEs) are genetically heterogeneous severe childhood-onset epilepsies with developmental delay or cognitive deficits. In this study, we explored the pathogenic mechanisms of DEE-associated de novo mutations in the CACNA1A gene.

METHODS

We studied the functional impact of four de novo DEE-associated CACNA1A mutations, including the previously described p.A713T variant and three novel variants (p.V1396M, p.G230V, and p.I1357S). Mutant cDNAs were expressed in HEK293 cells, and whole-cell voltage-clamp recordings were conducted to test the impacts on Ca_V 2.1 channel function. Channel localization and structure were assessed with immunofluorescence microscopy and three-dimensional (3D) modeling.

RESULTS

We find that the G230V and I1357S mutations result in loss-of-function effects with reduced whole-cell current densities and decreased channel expression at the cell membrane. By contrast, the A713T and V1396M variants resulted in gain-of-function effects with increased whole-cell currents and facilitated current activation (hyperpolarized shift). The A713T variant also resulted in slower current decay. 3D modeling predicts conformational changes favoring channel opening for A713T and V1396M.

SIGNIFICANCE

Our findings suggest that both gain-of-function and loss-of-function CACNA1A mutations are associated with similarly severe DEEs and that functional validation is required to clarify the underlying molecular mechanisms and to guide therapies.

Update on the treatment of vitamin B6 dependent epilepsies

Introduction: Vitamin B6 dependent epilepsies are a group of treatable diseases (ALDH7A1 deficiency, PNPO deficiency, PLP binding protein deficiency, hyperprolinaemia type II and hypophosphatasia and glycosylphosphatidylinositol anchor synthesis defects) responding to pyridoxine or pyridoxal-5^I-phosphate. Areas covered: A critical review was conducted on the therapeutic management of all the reported patients with genetically confirmed diagnoses of diseases affecting vitamin B6 metabolism and presenting with pyridoxine or pyridoxal-5^I-phosphate dependent-seizures. Data about safety and efficacy were analyzed as well as the management of supplementation with pyridoxine or pyridoxal-5^I-phosphate both in the acute phases and in the maintenance therapies. The authors also analyzed alternative therapeutic strategies for ALDH7A1 deficiency (lysine-restricted diet, arginine supplementation, oligonucleotide antisense therapy, upstream inhibition of aminoadipic semialdehyde synthase). Expert opinion: The administration of pyridoxine or pyridoxal-5^I-phosphate should be considered in all intractable seizures also beyond the first year of life. Lysine restricted diet and arginine supplementation should be introduced in all the confirmed ALDH7A1 deficient patients. Pre or post-natal supplementation with pyridoxine should be given in familial cases until an eventual molecular genetic disconfirmation. Minor data about alternative therapies are available for other disorders of vitamin B6 metabolism.

Parental mosaicism in epilepsies due to alleged de novo variants

Severe early onset epilepsies are often caused by de novo pathogenic variants. Few studies have reported the frequency of somatic mosaicism in parents of children with severe epileptic encephalopathies. Here we aim to investigate the frequency of mosaicism in the parents of children with epilepsy caused by alleged de novo variants. We tested parental genomic DNA derived from different tissues for 75 cases using targeted next-generation sequencing. Five parents (6.6%) showed mosaicism at minor allele frequencies of 0.8%-29% for the pathogenic variant detected in their offspring. Parental mosaicism was observed in the following genes: SCN1A, SCN2A, SCN8A, and STXBP1. One of the identified parents had epilepsy himself. Our results show that de novo events can occur already in parental tissue and in some cases can be detected in peripheral blood. Consequently, parents affected by low-grade mosaicism are faced with an increased recurrence risk for transmitting the pathogenic variant, compared to the overall recurrence risk for a second affected child estimated at approximately 1%. However, testing for parental somatic mosaicism will help identifying those parents who truly are at higher risk and will significantly improve genetic counseling in the respective families.

Current Perspectives On The Role Of The Ketogenic Diet In Epilepsy Management

Drug-refractory epilepsy is a commonly prevalent pediatric neurological illness of global significance. Ketogenic diet (KD) is a time-tested therapeutic modality for refractory epilepsy, which has reemerged as a robust alternative to anti-epileptic pharmacotherapy. There is a growing body of evidence which supports the anti-seizure efficacy, safety profile and feasibility of KD use in childhood epilepsy. In addition, this modality has been recognized to reduce anti-epileptic exposure, improve cognition and behavioral profile of patients as well as improve the quality-of-life of care-givers. Current indications of KD include refractory epilepsy syndromes, selected metabolic disorders (such as pyruvate dehydrogenase deficiency) and a host of varied neurological entities. KD research has broadened the knowledge-base about its mechanisms of action. Four types of KD are in vogue currently with varying nutritional constitution, palatability, administration protocols and comparable efficacy. KD initiation and maintenance are the result of concerted effort of a team of pediatric neurologist/epileptologist, nutritionist and patient's primary care-giver. Consensus is being formulated about various practical aspects of KD such as patient-selection, parental counseling, baseline work-up, dietary prescription, nutritional supplementation, concurrent anti-epileptic drug administration, follow-up and treatment-duration. Novel applications of KD include its use in neonatal epilepsy and super-refractory status epilepticus and tailor-made formulations such as cooking oil-based KD in predominantly rice-fed populations. Increasing body of clinical experience, improved nutritional designs and translational research are promoting KD as a major therapeutic modality. Currently, KD forms a core essence in the armamentarium against refractory epilepsy. In this review, we summarize the recent advances and current perspectives in the use of KD in refractory epilepsy.

Efficacy, Retention, and Tolerability of Brivaracetam in Patients With Epileptic Encephalopathies: A Multicenter Cohort Study From Germany

Objective: To evaluate the efficacy and tolerability of brivaracetam (BRV) in a severely drug refractory cohort of patients with epileptic encephalopathies (EE).

Method: A multicenter, retrospective cohort study recruiting all patients treated with EE who began treatment with BRV in an enrolling epilepsy center between 2016 and 2017.

Results: Forty-four patients (27 male [61%], mean age 29 years, range 6 to 62) were treated with BRV. The retention rate was 65% at 3 months, 52% at 6 months and 41% at 12 months. A mean retention time of 5 months resulted in a cumulative exposure to BRV of 310 months. Three patients were seizure free during the baseline. At 3 months, 20 (45%, 20/44 as per intention-to-treat analysis considering all patients that started BRV including three who were seizure free during baseline) were either seizure free (n = 4; 9%, three of them already seizure-free at baseline) or reported at least 25% (n = 4; 9%) or 50% (n = 12; 27%) reduction in seizures. An increase in seizure frequency was reported in two (5%) patients, while there was no change in the seizure frequency of the other patients. A 50% long-term responder rate was apparent in 19 patients (43%), with two (5%) free from seizures for more than six months and in nine patients (20%, with one [2 %] free from seizures) for more than 12 months. Treatment-emergent adverse events were predominantly of psychobehavioural nature and were observed in 16%.

Significance: In this retrospective analysis the rate of patients with a 50% seizure reduction under BRV proofed to be similar to those seen in regulatory trials for focal epilepsies. BRV appears to be safe and relatively well tolerated in EE and might be considered in patients with psychobehavioral adverse events while on levetiracetam.

Novel mutations and phenotypes of epilepsy-associated genes in epileptic encephalopathies

Epileptic encephalopathies are severe epilepsy disorders with strong genetic bases. We performed targeted next-generation sequencing (NGS) in 70 patients with epileptic encephalopathies. The likely pathogenicity of variants in candidate genes was evaluated by American College of Medical Genetics and Genomics (ACMG) scoring taken together with the accepted clinical presentation. Thirty-three candidate variants were detected after population filtration and computational prediction. According to ACMG, 21 candidate variants, including 18 de novo variants, were assessed to be pathogenic/likely pathogenic with clinical concordance. Twelve variants were initially assessed as uncertain significance by ACMG, among which 3 were considered causative and 3 others were considered possibly causative after analysis of clinical concordance. In total, 24 variants were identified as putatively causative, among which 19 were novel findings. SCN1A mutations were identified in 50% of patients with Dravet syndrome. TSC1/TSC2 mutations were detected in 66.7% of patients with tuberous sclerosis. STXBP1 mutations were the main findings in patients with West syndrome. Mutations in SCN2A, KCNT1, KCNQ2 and CLCN4 were identified in patients with epileptic infantile with migrating focal seizures; among them, KCNQ2 and CLCN4 were first identified as potential causative genes. Only one CHD2 mutation was detected in patients with Lennox-Gastaut syndrome. This study highlighted the utility of targeted NGS in genetic diagnoses of epileptic encephalopathies and a comprehensive evaluation of the pathogenicity of variants based on ACMG scoring and assessment of clinical concordance. Epileptic encephalopathies differ in genetic causes, and the genotype-phenotype correlations would provide insights into the underlying pathogenic mechanisms.

Genetic basis of pediatric epilepsy syndromes

Childhood epilepsy affects ~0.5-1% in the general population worldwide. Early-onset epileptic encephalopathies are considered to be severe neurological disorders, which lead to impaired motor, cognitive, and sensory development due to recurrence of seizures. Many of the observed epilepsy phenotypes are associated with specific chromosomal imbalances and thus display gene dosage effects, and also specific mutations of a variety of genes ranging from ion channels to transcription factors. High throughput sequencing technologies and whole exome sequencing have led to the recognition of several new candidate genes with a possible role in the pathogenesis of epileptic encephalopathies. The mutations causing channelopathies can be either a gain or a loss of ion channel function and contribute to the pathogenesis of epilepsy syndrome. Nearly 300 mutations of SCN1A gene coding for the Nav1.1 channel protein have been identified that contribute to the pathology of epilepsy. Besides Na, potassium and calcium channels are also implicated in epileptic encephalopathies. Therapeutic management of epileptic encephalopathies has been challenging as the majority of the medications are not efficient and often have many undesirable side effects. A better understanding of the molecular nature of epilepsy in an individual is important to design a personalized medication, considering the number of possible genetic mutations that can contribute to epileptic encephalopathies.

Entropy measures to study and model long term simultaneous evolution of children in Doose and Lennox-Gastaut syndromes

Doose and Lennox-Gastaut (syndromes) are rare generalized electroclinical affections of early infancy of variable prognosis which manifest with very diverse kinds of seizures. Very frequently, these types of epilepsy become drug resistant and finding reliable treatment results is very difficult. As a result of this, fighting against these syndromes becomes a long term (or endless) event for the little patient, the neurologist and the parents. A lot of Electroencephalographic (EEG) records are so accumulated during the child's life in order to monitor evolution and correlate it with medications. So, given a bunch of EEG, three questions arise: (a) On which year was the child healthier (less affected by seizures)? (b) Which area of the brain has been the most affected? (c) What is the status of the child with respect to others (which also have a bunch of EEG, each)? Answering these interrogations by traditional scrutinizing of the whole database becomes subjective, if not impossible. We propose to answer these questions objectively by means of time series entropies. We start with our modified version of the Multiscale Entropy (MSE) in order to generalize it as a Bivariate MSE (BMSE) and from them, we compute two indices. All were tested in a series of patients and coincide with medical conclusions. As far as we are concerned, our contribution is new.

Early-onset epileptic encephalopathy caused by gain-of-function mutations in the voltage sensor of Kv7.2 and Kv7.3 potassium channel subunits

Mutations in Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3) genes, encoding for voltage-gated K(+) channel subunits underlying the neuronal M-current, have been associated with a wide spectrum of early-onset epileptic disorders ranging from benign familial neonatal seizures to severe epileptic encephalopathies. The aim of the present work has been to investigate the molecular mechanisms of channel dysfunction caused by voltage-sensing domain mutations in Kv7.2 (R144Q, R201C, and R201H) or Kv7.3 (R230C) recently found in patients with epileptic encephalopathies and/or intellectual disability. Electrophysiological studies in mammalian cells transfected with human Kv7.2 and/or Kv7.3 cDNAs revealed that each of these four mutations stabilized the activated state of the channel, thereby producing gain-of-function effects, which are opposite to the loss-of-function effects produced by previously found mutations. Multistate structural modeling revealed that the R201 residue in Kv7.2, corresponding to R230 in Kv7.3, stabilized the resting and nearby voltage-sensing domain states by forming an intricate network of electrostatic interactions with neighboring negatively charged residues, a result also confirmed by disulfide trapping experiments. Using a realistic model of a feedforward inhibitory microcircuit in the hippocampal CA1 region, an increased excitability of pyramidal neurons was found upon incorporation of the experimentally defined parameters for mutant M-current, suggesting that changes in network interactions rather than in intrinsic cell properties may be responsible for the neuronal hyperexcitability by these gain-of-function mutations. Together, the present results suggest that gain-of-function mutations in Kv7.2/3 currents may cause human epilepsy with a severe clinical course, thus revealing a previously unexplored level of complexity in disease pathogenetic mechanisms.

Epileptic encephalopathies: new genes and new pathways

Epileptic encephalopathies represent a group of devastating epileptic disorders that occur early in life and are often characterized by pharmaco-resistant epilepsy, persistent severe electroencephalographic abnormalities, and cognitive dysfunction or decline. Next generation sequencing technologies have increased the speed of gene discovery tremendously. Whereas ion channel genes were long considered to be the only significant group of genes implicated in the genetic epilepsies, a growing number of non-ion-channel genes are now being identified. As a subgroup of the genetically mediated epilepsies, epileptic encephalopathies are complex and heterogeneous disorders, making diagnosis and treatment decisions difficult. Recent exome sequencing data suggest that mutations causing epileptic encephalopathies are often sporadic, typically resulting from de novo dominant mutations in a single autosomal gene, although inherited autosomal recessive and X-linked forms also exist. In this review we provide a summary of the key features of several early- and mid-childhood onset epileptic encephalopathies including Ohtahara syndrome, Dravet syndrome, Infantile spasms and Lennox Gastaut syndrome. We review the recent next generation sequencing findings that may impact treatment choices. We also describe the use of conventional and newer anti-epileptic and hormonal medications in the various syndromes based on their genetic profile. At a biological level, developments in cellular reprogramming and genome editing represent a new direction in modeling these pediatric epilepsies and could be used in the development of novel and repurposed therapies.

Genetic epilepsy syndromes without structural brain abnormalities: clinical features and experimental models

Research in genetics of epilepsy represents an area of great interest both for clinical purposes and for understanding the basic mechanisms of epilepsy. Most mutations in epilepsies without structural brain abnormalities have been identified in ion channel genes, but an increasing number of genes involved in a diversity of functional and developmental processes are being recognized through whole exome or genome sequencing. Targeted molecular diagnosis is now available for different forms of epilepsy. The identification of epileptogenic mutations in patients before epilepsy onset and the possibility of developing therapeutic strategies tested in experimental models may facilitate experimental approaches that prevent epilepsy or decrease its severity. Functional analysis is essential for better understanding pathogenic mechanisms and gene interactions. In vitro experimental systems are either cells that usually do not express the protein of interest or neurons in primary cultures. In vivo/ex vivo systems are organisms or preparations obtained from them (e.g., brain slices), which should better model the complexity of brain circuits and actual pathophysiological conditions. Neurons differentiated from induced pluripotent stem cells generated from the skin fibroblasts of patients have recently allowed the study of mutations in human neurons having the genetic background of a given patient. However, there is remarkable complexity underlying epileptogenesis in the clinical dimension, as reflected by the fact that experimental models have not provided yet results having clinical translation and that, with a few exceptions concerning rare conditions, no new curative treatment has emerged from any genetic finding in epilepsy.

TBC1D24 regulates neuronal migration and maturation through modulation of the ARF6-dependent pathway

Alterations in the formation of brain networks are associated with several neurodevelopmental disorders. Mutations in TBC1 domain family member 24 (TBC1D24) are responsible for syndromes that combine cortical malformations, intellectual disability, and epilepsy, but the function of TBC1D24 in the brain remains unknown. We report here that in utero TBC1D24 knockdown in the rat developing neocortex affects the multipolar-bipolar transition of neurons leading to delayed radial migration. Furthermore, we find that TBC1D24-knockdown neurons display an abnormal maturation and retain immature morphofunctional properties. TBC1D24 interacts with ADP ribosylation factor (ARF)6, a small GTPase crucial for membrane trafficking. We show that in vivo, overexpression of the dominant-negative form of ARF6 rescues the neuronal migration and dendritic outgrowth defects induced by TBC1D24 knockdown, suggesting that TBC1D24 prevents ARF6 activation. Overall, our findings demonstrate an essential role of TBC1D24 in neuronal migration and maturation and highlight the physiological relevance of the ARF6-dependent membrane-trafficking pathway in brain development.

Treatment of Lennox-Gastaut syndrome: overview and recent findings

Lennox-Gastaut syndrome (LGS) is a rare, age-related syndrome, characterized by multiple seizure types, a specific electro-encephalographic pattern, and mental regression. However, published data on the etiology, evolution, and therapeutic approach of LGS are contradictory, partly because the precise definition of LGS used in the literature varies. In the most recent classification, LGS belongs to the epileptic encephalopathies and is highly refractory to all antiepileptic drugs. Numerous treatments, medical and non-medical, have been proposed and results mostly from open studies or case series have been published. Sometimes, patients with LGS are included in a more global group of patients with refractory epilepsy. Only 6 randomized double-blind controlled trials of medical treatments, which included patients with LGS, have been published. Overall, treatment is rarely effective and the final prognosis remains poor in spite of new therapeutic strategies. Co-morbidities need specific treatment. This paper summarizes the definition, diagnosis and therapeutic approach to LGS, including not only recognized antiepileptic drugs, but also "off label" medications, immune therapy, diet, surgery and some perspectives for the future.