Epidemiology of Developmental and Epileptic Encephalopathy and of Intellectual Disability and Epilepsy in Children

Operational definition of developmental and epileptic encephalopathies to underpin the design of therapeutic trials

Developmental and epileptic encephalopathies (DEEs) are the most severe group of epilepsies, characterized by drug-resistant seizures and developmental slowing or regression. DEEs encompass many epilepsy syndromes, although not all patients with a DEE can be classified into a specific syndrome. Our understanding of the etiologies of DEEs has been revolutionized with next-generation sequencing, with more than 900 genes implicated, in addition to structural causes. It is therefore now possible to consider precision medicine and novel therapeutic approaches for these devastating diseases with trials of repurposed and new drugs, including gene therapies. Trials are being designed to target either DEE diseases more broadly, specific DEE syndromes, or specific genetic DEEs. To serve this purpose, a clear operational definition of DEEs is needed to ensure that appropriate patients are selected for trials with precisely defined, targeted outcome measures. Herein we propose the operational definition of DEEs to set the stage for the development of DEE therapies.

Anticipatory guidance and care in pediatric and adult neurology for people with epilepsy who became pregnant

OBJECTIVE

To assess documentation of pregnancy-related counseling and care for people with epilepsy of childbearing potential (PWECP) in pediatric and adult neurology who became pregnant.

METHODS

We reviewed health records for primigravida PWECP prescribed an antiseizure medication (ASM) who delivered between June 2014 and May 2024 within one academic medical center. We used chi-squared tests to compare counseling, ASM prescriptions, and recommendations for supplemental folic acid between individuals in pediatric and adult neurology care before pregnancy. We performed logistic regression for these outcomes of pre-pregnancy counseling associated with type of neurology care, race, ethnicity, intellectual disability (ID), teratogenic profile of ASMs prescribed, and ASM polytherapy.

RESULTS

173 PWECP (84 % White non-Hispanic, 9 % with intellectual disability (ID) were included. Twenty-one (12 %) transferred from pediatric to adult neurology care due to pregnancy ("pediatric group") and 152 (88 %) were previously established with adult neurology ("adult group"). PWECP in the pediatric group compared to the adult group had lower rates of documentation of clinician discussion of ASM teratogenicity (43 % vs 66 %, p = 0.041) and folic acid use (24 % vs 63 %, p = 0.001) before pregnancy. PWECP established with adult neurology prior to pregnancy were significantly more likely to have been taking folic acid before pregnancy (OR 5.21, 95 % CI 1.78-15.3). Individuals with ID were significantly less likely to have documentation of discussion of ASM teratogenicity (OR 0.18, 95 % CI 0.05-0.62).

CONCLUSION

Our findings suggest a need for improvement in providing pre-pregnancy guidance and care for PWECP, especially for PWECP in pediatric neurology care and those with ID.

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

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

SCN8A Epileptic Encephalopathy Mutation Displays a Loss-of-Function Phenotype and Distinct Insensitivity to Valproate

Voltage-gated sodium channels are the main targets of antiepileptic drugs, such as sodium valproate (VPA). Single nucleotide polymorphisms (SNPs) in the Nav1.6 isoform (SCN8A) have been reported to be closely associated with motor dysfunction in pediatric akathisia epileptica. In this study, we conducted a genetic screening of pediatric patients with seizures treated solely with VPA and identified two novel missense mutations of SCN8A (A1534V and Q1853H). Electrophysiological results revealed that the peak currents of the A1534V variant were smaller compared to that of the wild-type (WT) channel. The A1534V variant also caused a positive shift in the I-V curve, indicating a change in the voltage dependence of activation compared to the WT channels. In contrast, VPA induced a significant negative shift in the inactivation of both WT and A1534V mutant. However, the inhibition of currents by VPA was weaker in the A1534V variant than in WT. Furthermore, the recovery time constant of the A1534V variant was shorter than that of WT when treated with VPA. Regrettably, although the Q1853H variant can be expressed in HEK293T cells, the detected current is too small (approximately 50 pA). In conclusion, our results suggest that the A1534V mutation is a novel loss-of-function variant that exhibits moderate insensitivity to VPA. These results underscore the importance of Nav1.6 as a key target in epilepsy and highlight the necessity of analyzing its role in the pathological process.

Motor phenotyping in a Greek cohort of patients with neonatal and infantile onset developmental and epileptic encephalopathy

BACKGROUND

Developmental and epileptic encephalopathy (DEE) includes diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. Patients often present with movement disorders (MD). This study aims to delineate the motor phenotype in a cohort of patients with DEE.

METHODS

Retrospective review of 82 patients with DEE. MD type and distribution were documented and when available, video recordings were reviewed.

RESULTS

Patients were classified into five etiological groups: 30.5 % had a likely genetic diagnosis, 29.3 % a confirmed genetic diagnosis, 18.3 % an inborn error of metabolism (IEM), 14.6 % an acquired brain lesion, and 7.3 % a brain dysplasia. Hyperkinetic MDs were present in 85.4 % of patients, including dystonia (48.8 %), stereotypies (22.0 %), chorea (20.7 %), hyperekplexia (15.9 %), tremor (14.6 %), and myoclonus (6.1 %). Parkinsonism was observed in 11 % of patients, ataxia in 8.5 % and multiple MDs in 50 %. Paroxysmal episodes of MD exacerbation occurred in 6 patients, and transient MD in 8. Dystonia was most frequent in patients with acquired brain lesions (p = 0.003). Parkinsonism was more frequent in patients with brain dysplasias and IEM (p = 0.043).

CONCLUSIONS

This study confirms the high frequency of hyperkinetic and combined MD in DEE, and identifies characteristic MDs in conditions such SCN8A, FOXG1 and ARX related DEE, as well as ataxia and tremor in STXBP1, SCN1A, MTRFR, KCTD7 and 15q111-13 deletion. Novel observations, include the occurrence of paroxysmal dyskinetic exacerbations in FOXG1, axial stereotypies in KCNQ2, hyperekplexia in cortical dysplasia and Parkinsonism in ECHS1 with DEE.

Adult phenotypes of genetic developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies constitute a group of severe epilepsies, with seizure onset typically occurring in infancy or childhood, and diverse clinical manifestations, including neurodevelopmental deficits and multimorbidities. Many have genetic aetiologies, identified in up to 50% of individuals. Whilst classically considered paediatric disorders, most are compatible with survival into adulthood, but their adult phenotypes remain inadequately understood. This cross-sectional study presents detailed phenotypes of 129 adults (age range 17-71 years), with genetic developmental and epileptic encephalopathies involving causal variants in 42 genes. We describe diverse disease aspects, and we sought genetic insights from the age-related trends of expression of the genes involved. Most developmental and epileptic encephalopathies (69.7%) are epileptic encephalopathies in adulthood, with the presence of epileptic encephalopathy correlating with worse cognitive phenotypes (P = 0.0007). However, phenotypic variability was observed, ranging from those with epileptic encephalopathy to seizure-free individuals with normal EEG or intermediate clinical and EEG phenotypes. This variability was found across individual genes and age-related gene expression trends, suggesting that other influential factors are likely at play. Mobility, feeding and communication impairments were common, with significant dependence on others for activities of daily living. Neurological and psychiatric comorbidities were most prevalent, along with additional systemic comorbidities observed, particularly musculoskeletal, cardiac and gastrointestinal conditions, highlighting the need for comprehensive and multisystemic monitoring. Despite an average diagnostic delay of 25.2 years, aetiology-based therapeutic interventions were feasible for 54.8% of the cohort, underscoring the critical need for genome-wide genetic testing for adults with these phenotypes. Optimizing seizure control remains necessary, but it may not be sufficient to ensure good outcomes, which may differ significantly from childhood metrics, like cognitive function and independence in daily living. Therapies addressing additional aspects beyond seizures are necessary for improving overall outcomes. Understanding the intricate relationship between molecular pathways and the age-related trends of gene expression is crucial for development of appropriate gene-specific therapies and timely intervention. Whilst prospective data are also needed to define these complexities, such studies of necessity take years to acquire: insights from adults can inform care strategies for both paediatric and adult populations now.

Infantile epileptic spasms syndrome: an etiologic study of 361 patients with infantile epileptic spasms syndrome

Introduction

Infantile Epileptic Spasms Syndrome (IESS) typically has a profound impact on the neurodevelopment of patients. The study on IESS indicates possible geographical variation in etiology and a lack of data from China. Our study intends to summarize the etiology of IESS and analyze its characteristics.

Methods

A retrospective analysis was performed to gather clinical data from patients diagnosed with IESS at the Department of Neurology of Qilu Hospital of Shandong University and the Children's Hospital Affiliated to Shandong University between June 2017 to May 2024.

Results

A total of 361 patients with IESS were included, comprising 115 structural cases (31.9%), 37 genetic cases (10.2%), 32 genetic-structural cases (8.9%), 9 metabolic cases (2.5%), 3 infectious cases (0.8%), and 165 cases with unknown etiology (45.7%). No immunological cause was determined. The primary cause of the condition was linked to hypoxic-ischemic encephalopathy (HIE), with structural brain abnormalities following closely. The predominant pathogenic genes identified were TSC2, NF1, SCN8A, and KCNQ2. Male gender, preterm infants, low birth weight infants, and developmental regression in patients were associated with a higher likelihood of structural etiology. Patients exhibiting developmental regression before the commencement demonstrated inferior outcomes. Patients administered adrenocorticotropic hormone (ACTH) exhibited a higher likelihood of attaining seizure control, and those who responded favorably to the medication saw improved results.

Conclusion

The predominant etiology of IESS is structural, succeeded by genetic factors, with significant pathogenic genes comprising TSC2, NF1, SCN8A, and KCNQ2. The genetic classifications exhibit geographic variability. Genetic and structural etiologies are frequently linked to an unfavorable prognosis. Genetic testing can help clarify the etiology of IESS when metabolic screening and brain MRI results are negative. The advancement of genetic testing is crucial for future targeted and individualized diagnosis and therapy.

Fulfilling the needs of caregivers in delivering health services to children with developmental and epileptic encephalopathies

INTRODUCTION

Patients with developmental and epileptic encephalopathies (DEEs) have multiple comorbidities and high healthcare needs. Whether health services meet the needs of this patient population and their families is not well understood. We explored caregiver perspectives on their child's health service use, satisfaction with health services, and priorities for improvement.

METHODS

Caregivers of patients with DEEs completed online questionnaires containing specifically designed quantitative and qualitative questions to assess their perceptions of their child's health service use over a 12-month period. We analysed the quantitative data using descriptive and non-parametric statistics and the qualitative data using content analysis.

RESULTS

Seventy-five caregivers participated. Over 12-months, 52 (69.3 %) patients presented to the emergency department, 70 (93.3 %) saw ≥3 medical professionals, and 45 (60 %) saw ≥3 allied health professionals (n = 45, 60.0 %). Caregivers were satisfied with their child's healthcare when they perceived healthcare professionals to be compassionate and knowledgeable. Caregivers were dissatisfied when they perceived that healthcare professionals were not knowledgeable about DEEs, or they felt unheard, unsupported, needed to advocate for their child's healthcare and disability funding, and perceived care coordination to be lacking. Hospital care and parent psychological support were caregivers' top priorities for improvement to the healthcare system.

DISCUSSION

Care coordination and access to knowledgeable healthcare professionals and psychological supports should be prioritised to achieve more appropriate models of care for patients with DEEs. Further research should evaluate models of care which incorporate these features to determine if they provide high value healthcare and improve the patient and family journey.

Association between maternal usage of volatile organic compounds and West syndrome, the Japan Environment and Children's study

Multiple etiologies of West syndrome have been reported; however, there are cases of unknown etiologies. Exposure to volatile organic compounds (VOCs) increases the risk of epilepsy; however, their effects on children remain unknown. This study aimed to investigate the association between maternal occupational usage of VOCs and West syndrome development in children. Using data from a cohort of 88,280 children, we extracted children born to mothers who had used VOCs during pregnancy. Based on an epilepsy diagnosis by the age of 2 years, the frequency of usage of VOCs was comparatively analyzed among the following groups: never diagnosed with epilepsy, West syndrome, and other epileptic syndromes. A total of 15, 154, and 88,111 children were categorized into the West syndrome, other epileptic syndrome, and never diagnosed with epilepsy groups, respectively. The odds ratio (OR) for West syndrome development increased with the frequency of permanent marker usage (one to three times a month: OR = 2.58, 95% confidence interval [CI] 0.75-8.90; one or more times a week: OR = 4.34, 95% CI 1.23-15.26). These results suggested an association between maternal occupational frequent usage of permanent marker and West syndrome development in children.

Unveiling the disease progression in developmental and epileptic encephalopathies: Insights from EEG and neuropsychology

OBJECTIVE

Developmental and epileptic encephalopathies (DEEs) are neurological disorders characterized by developmental impairment and epilepsy. Our study aims to assess disease progression by comparing clinical findings, electroencephalography (EEG), and neuropsychological data from seizure onset to the last follow-up evaluation.

METHODS

We retrospectively reviewed patients with genetic DEEs who were followed-up at the epilepsy unit of Bambino Gesù Children's Hospital, Rome. We collected information regarding gender, family history, genetic variant, age at onset and at last follow-up, neurological examination, type of seizure, drug resistance, occurrence of status epilepticus, and movement and cognitive and behavioral disorders. We compared EEG background activity, epileptiform abnormalities, and cognitive functions between seizure onset and the last follow-up evaluation using the McNemar-Bowker test (α = 5%).

RESULTS

A total of 160 patients (94 female) were included. Genetic analysis revealed a spectrum of pathogenic variants, with SCN1A being the most prevalent (25%). The median age at seizure onset and at the last follow-up was 0.37 (interquartile range [IQR]: 0.09-0.75) and 8.54 years (IQR: 4.32-14.55), respectively. We documented a statistically significant difference in EEG background activity (p = .017) and cognitive impairment (p = .01) from seizure onset to the last follow-up evaluation. No significant differences were detected for epileptiform abnormalities (p = .2). In addition, high prevalence rates were observed for drug resistance (81.9%), movement disorders (60.6%), behavioral and autism spectrum disorders (45%), neurological deficits (31.3%), and occurrence of status epilepticus (23.1%).

SIGNIFICANCE

Our study provides evidence that a clinical progression may appear in genetic DEEs, manifesting as development or worsening of cognitive impairment and disruption of EEG background activity. These results highlight the challenging clinical course and the importance of early intervention and personalized care in the management of patients with DEEs.

The expanding field of genetic developmental and epileptic encephalopathies: current understanding and future perspectives

Recent advances in genetic testing technologies have revolutionised the identification of genetic abnormalities in early onset developmental and epileptic encephalopathies (DEEs). In this Review, we provide an update on the expanding landscape of genetic factors contributing to DEEs, encompassing over 800 reported genes. We focus on the cellular and molecular mechanisms driving epileptogenesis, with an emphasis on emerging therapeutic strategies and effective treatment options. We explore noteworthy, novel genes linked to DEE phenotypes, such as gBRAT-1 and GNAO1, and gene families such as GRIN and HCN. Understanding the network-level effects of gene variants will pave the way for potential gene therapy applications. Given the diverse comorbidities associated with DEEs, a multidisciplinary team approach is essential. Despite ongoing efforts and improved genetic testing, DEEs lack a cure, and treatment complexities persist. This Review underscores the necessity for larger international prospective studies focusing on both seizure outcomes and developmental trajectories.

Voltage-Gated Ion Channel Compensatory Effect in DEE: Implications for Future Therapies

Developmental and Epileptic Encephalopathies (DEEs) represent a clinically and genetically heterogeneous group of rare and severe epilepsies. DEEs commonly begin early in infancy with frequent seizures of various types associated with intellectual disability and leading to a neurodevelopmental delay or regression. Disease-causing genomic variants have been identified in numerous genes and are implicated in over 100 types of DEEs. In this context, genes encoding voltage-gated ion channels (VGCs) play a significant role, and part of the large phenotypic variability observed in DEE patients carrying VGC mutations could be explained by the presence of genetic modifier alleles that can compensate for these mutations. This review will focus on the current knowledge of the compensatory effect of DEE-associated voltage-gated ion channels and their therapeutic implications in DEE. We will enter into detailed considerations regarding the sodium channels SCN1A, SCN2A, and SCN8A; the potassium channels KCNA1, KCNQ2, and KCNT1; and the calcium channels CACNA1A and CACNA1G.

Pharmacokinetic Variability of Rufinamide and Stiripentol in Children With Refractory Epilepsy: A Retrospective Study of Therapeutic Drug Monitoring From the National Epilepsy Centers in Denmark and Norway

BACKGROUND

Rufinamide and stiripentol, orphan drugs used in Lennox-Gastaut and Dravet syndromes, respectively, are antiseizure medications (ASMs), often administered to children; however, pharmacokinetic studies are lacking. The authors compared the pharmacokinetic variability of these drugs with respect to the dose, serum concentrations, comedication, age, and duration of treatment.

METHODS

Children and adolescents (<18 years) whose serum concentrations were measured were retrospectively identified from the therapeutic drug monitoring (TDM) databases at 2 national epilepsy centers in Norway and Denmark (2012-2021).

RESULTS

Data from 165 patients (56% boys/44% girls) treated with rufinamide and 52 patients (50% boys/50% girls) treated with stiripentol were included. For rufinamide, the median age was 10 (range 2-17) years, dose 23 (3-73) mg/d, and serum concentration 34 (3-227) µmol/L [8.1 mg/L (0.71-54.0 mg/L)]. For stiripentol, the median age was 8.5 (range 1-17) years, dose 37 (18-76) mg/d, and serum concentration 33 (4-113) µmol/L [7.7 mg/L (0.93-26.3 mg/L)]. The concomitant use of 1-9 other ASMs during the data collection was noted. Pharmacokinetic variability, calculated as the concentration/(dose/kg) ratio, ranged from 0.26 to 11.31 (µmol/L)/(mg/kg) for rufinamide and 0.17-1.52 (µmol/L)/(mg/kg) for stiripentol. The intraindividual coefficients of variation ranged widely, from 5% to 110% for rufinamide and 11%-117% for stiripentol. The treatment period was at least 5 years in 50% of patients. No statistically significant effects of age, sex, or ASM comedication were observed, possibly due to the small sample size and heterogeneous groups with variable seizure situations, comorbidities, and changes in comedication and physiology.

CONCLUSIONS

This study demonstrates considerable pharmacokinetic variability in and between patients for both drugs and similar use in terms of age, burden of comedication and retention rates. TDM may be useful in the clinical setting to monitor and optimize treatment in this vulnerable patient group.

Epilepsy surgery in developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies (DEEs) present significant treatment challenges due to frequent, drug-resistant seizures and comorbidities that impact quality of life. DEEs include both developmental encephalopathy from underlying pathology and epileptic encephalopathy where seizures exacerbate cognitive and behavioral impairments. Classification by syndrome and etiology is essential for therapy and prognosis, with common syndromes like infantile epileptic spasms syndrome and Dravet syndrome having specific first-line treatments. Etiologies are predominantly genetic, structural, or combined, with targeted therapies increasingly available. Surgery aims to improve seizure control but also may improve development, if the epileptic encephalopathy can be ameliorated. Timely intervention can reduce seizures and epileptiform discharges, maximizing developmental potential and allowing reduction in antiseizure medication. In cases requiring extensive resections, new deficits may be offset by developmental gains. Studies indicate that parents are generally willing to accept some deficits for significant seizure reduction.

Overview of clinical and physiologic aspects of status epilepticus in the developmental and epileptic encephalopathies

The Developmental and Epileptic Encephalopathies are a group of severe epilepsies which onset in early life and are characterized by recurrent, drug-resistant seizures and multiple comorbidities including intellectual disability, behavior and sleep problems, gait concerns, amongst others. Both convulsive and nonconvulsive status epilepticus are frequently seen, however the exact risk and type of status epilepticus depends on the underlying syndrome or etiology. The baseline degree of developmental impairment and EEG features characterized by background slowing and persistent, and at times, near-continuous high-amplitude epileptiform discharges can make a clearcut diagnosis of nonconvulsive status epilepticus, in a timely manner, very challenging. Furthermore, there is limited guidance on best management of nonconvulsive status epilepticus, and success of therapy is often suboptimal.

Promoting medication compliance in epileptic children: a cross sectional survey

BACKGROUND

Compliance with medication is crucial for the favorable prognosis of children with epilepsy. The objective of this study was to assess the determinants of medication compliance and to construct a predictive model for the risk of non-compliance among pediatric epilepsy patients.

METHODS

The study included children diagnosed with epilepsy and treated at our hospital between February 1 and September 30, 2023. We evaluated the demographic characteristics and medication compliance profiles of these patients. The predictive model's performance was assessed using the receiver operating characteristic (ROC) curve to determine its sensitivity and specificity.

RESULTS

A total of 168 children with epilepsy were analyzed. The rate of non-compliance with medication was found to be 32.74% (55 out of 168). Logistic regression identified the educational level of parents (OR = 2.844, 95% CI: 2.182-3.214), monthly household income (OR = 1.945, 95% CI: 1.203-2.422), the number of medications taken (OR = 1.883, 95% CI: 1.314-2.201), and the level of epilepsy knowledge received (OR = 2.517, 95% CI: 1.852-3.009) as significant factors influencing non-compliance (all p < 0.05). A total score threshold of 6 was set for the predictive model. The area under the ROC curve was 0.713 (95% CI: 0.686-0.751), indicating the model's discriminative ability.

CONCLUSIONS

The compliance to medication regimens among children with epilepsy is suboptimal and influenced by a multitude of factors. This study has developed a predictive model for medication compliance, which could serve as a valuable tool for clinical assessment and intervention planning regarding medication compliance in pediatric epilepsy patients.

Developmental and epileptic encephalopathies

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

In Vivo Evaluation of Self-assembled nano-Saikosaponin-a for Epilepsy Treatment

Saikosaponin-a (SSa) exhibits antiepileptic effects. However, its poor water solubility and inability to pass through the blood-brain barrier greatly limit its clinical development and application. In this study, SSa-loaded Methoxy poly (ethylene glycol)-poly(ε-caprolactone) (MePEG-SSa-PCL) NPs were successfully prepared and characterized. Our objective was to further investigate the effect of this composite on acute seizure in mice. First, we confirmed the particle size and surface potential of the composite (51.00 ± 0.25 nm and - 33.77 ± 2.04 mV, respectively). Further, we compared the effects of various MePEG-SSa-PCL doses (low, medium, and high) with those of free SSa, valproic acid (VPA - positive control), and saline only (model group) on acute seizure using three different acute epilepsy mouse models. We observed that compared with the model group, the three MePEG-SSa-PCL treatments showed significantly lowered seizure frequency in mice belonging to the maximum electroconvulsive model group. In the pentylenetetrazol and kainic acid (KA) acute epilepsy models, MePEG-SSa-PCL increased both clonic and convulsion latency periods and shortened convulsion duration more effectively than equivalent SSa-only doses. Furthermore, hematoxylin-eosin and Nissl staining revealed considerably less neuronal damage in the hippocampal CA3 area of KA mice in the SSa, VPA, and three MePEG-SSa-PCL groups relative to mice in the model group. Hippocampal gamma-aminobutyric acid-A (GABA-A) receptor and cleaved caspase-3 expression levels in KA mice were significantly higher and lower, respectively, in the three MePEG-SSa-PCL treatment groups than in the model group. Thus, MePEG-SSa-PCL exhibited a more potent antiepileptic effect than SSa in acute mouse epilepsy models and could alleviate neuronal damage in the hippocampus following epileptic seizures, possibly via GABA-A receptor expression upregulation.

Diagnostic utility of DNA methylation analysis in genetically unsolved pediatric epilepsies and CHD2 episignature refinement

Sequence-based genetic testing identifies causative variants in ~ 50% of individuals with developmental and epileptic encephalopathies (DEEs). Aberrant changes in DNA methylation are implicated in various neurodevelopmental disorders but remain unstudied in DEEs. We interrogate the diagnostic utility of genome-wide DNA methylation array analysis on peripheral blood samples from 582 individuals with genetically unsolved DEEs. We identify rare differentially methylated regions (DMRs) and explanatory episignatures to uncover causative and candidate genetic etiologies in 12 individuals. Using long-read sequencing, we identify DNA variants underlying rare DMRs, including one balanced translocation, three CG-rich repeat expansions, and four copy number variants. We also identify pathogenic variants associated with episignatures. Finally, we refine the CHD2 episignature using an 850 K methylation array and bisulfite sequencing to investigate potential insights into CHD2 pathophysiology. Our study demonstrates the diagnostic yield of genome-wide DNA methylation analysis to identify causal and candidate variants as 2% (12/582) for unsolved DEE cases.

Clinical features and underlying etiology of children with Lennox-Gastaut syndrome

OBJECTIVE

Lennox-Gastaut Syndrome (LGS) is characterized by the presence of multiple seizure types and encompasses a heterogenous group of etiologies. The aim of our study was to evaluate the etiological profile of LGS and investigate seizure outcomes based on different clinical variables.

METHODS

The clinical features, neuroimaging findings, genetic testing and other testing results of LGS patients were systematically reviewed. The identifiable etiology was categorized as either acquired or nonacquired. Univariate and multivariate regression analyses were performed to explore the association between clinical variables and seizure outcome at the last follow-up.

RESULTS

We enrolled 156 patients diagnosed with LGS, of whom 66% were male. The mean age of patients was 34.2 months and the median follow-up duration was 29.5 months (interquartile range = 14-56.25 months). The initial seizure type was epileptic spasm in 61 patients, among which 33 of them met the criteria for infantile epileptic spasm syndrome. All patients underwent neuroimaging test, with 25% falling into the acquired structural category. Etiology could be identified in 84 individuals, including pathogenetic variants found in 34 out of 117 patients with nonacquired etiology. CHD2 mutations were most frequently observed among these pathogenetic variants. At the last follow-up, favorable outcomes were observed in 27 patients. The identification of etiology emerged as a significant determinant influencing LGS outcome; specifically, patients with unknown etiology had a higher likelihood of experiencing favorable outcomes compared to those with known cause (p = 0.041). Early onset age and longer epilepsy duration significantly increased the odds of an unfavorable outcome (p = 0.006 and 0.024).

SIGNIFICANCE

We present novel data on the clinical and etiological spectrum of LGS, with determined etiology observed in over half of the patients. Epileptic spasms were found to be more prevalent than tonic seizures as seizure onset types in LGS. The presence of a known etiology, earlier age at onset, and longer duration of epilepsy were associated with a poorer long-term epileptological outcome.

Knockdown of NeuroD2 leads to seizure-like behavior, brain neuronal hyperactivity and a leaky blood-brain barrier in a Xenopus laevis tadpole model of DEE75

Developmental and Epileptic Encephalopathies (DEE) are a genetically diverse group of severe, early onset seizure disorders. DEE are normally identified clinically in the first six months of life by the presence of frequent, difficult to control seizures and accompanying stalling or regression of development. DEE75 results from de novo mutations of the NEUROD2 gene that result in loss of activity of the encoded transcription factor, and the seizure phenotype was shown to be recapitulated in Xenopus tropicalis tadpoles. We used CRISPR/Cas9 to make a DEE75 model in Xenopus laevis, to further investigate the developmental etiology. NeuroD2.S CRISPR/Cas9 edited tadpoles were more active, swam faster on average, and had more seizures (C-shaped contractions resembling unprovoked C-start escape responses) than their sibling controls. Live imaging of Ca2+ signaling revealed prolongued, strong signals sweeping through the brain, indicative of neuronal hyperactivity. While the resulting tadpole brain appeared grossly normal, the blood-brain barrier (BBB) was found to be leakier than that of controls. Additionally, the TGFβ antagonist Losartan was shown to have a short-term protective effect, reducing neuronal hyperactivity and reducing permeability of the BBB. Treatment of NeuroD2 CRISPant tadpoles with 5 mM Losartan decreased seizure events by more than 4-fold compared to the baseline. Our results support a model of DEE75 resulting from reduced NeuroD2 activity during vertebrate brain development, and indicate that a leaky BBB contributes to epileptogenesis.

Improving epilepsy diagnosis across the lifespan: approaches and innovations

Epilepsy diagnosis is often delayed or inaccurate, exposing people to ongoing seizures and their substantial consequences until effective treatment is initiated. Important factors contributing to this problem include delayed recognition of seizure symptoms by patients and eyewitnesses; cultural, geographical, and financial barriers to seeking health care; and missed or delayed diagnosis by health-care providers. Epilepsy diagnosis involves several steps. The first step is recognition of epileptic seizures; next is classification of epilepsy type and whether an epilepsy syndrome is present; finally, the underlying epilepsy-associated comorbidities and potential causes must be identified, which differ across the lifespan. Clinical history, elicited from patients and eyewitnesses, is a fundamental component of the diagnostic pathway. Recent technological advances, including smartphone videography and genetic testing, are increasingly used in routine practice. Innovations in technology, such as artificial intelligence, could provide new possibilities for directly and indirectly detecting epilepsy and might make valuable contributions to diagnostic algorithms in the future.

Neuropsychology of late-onset epilepsies

In an increasingly ageing society, patients ageing with epilepsy and those with late-onset epilepsies (LOE) represent a challenge for epilepsy care and treatment. Senescence itself bears risks of pathologies which in the form of acute focal damage (e.g. stroke) or slowly progressive degenerative damage can cause seizures and substantial cognitive impairment. There is converging evidence from studies in LOE that cognitive impairments are present from epilepsy onset before treatment is initiated and may even precede the emergence of seizures. This suggests that these impairments (like the seizures) are expressions of the underlying disease. Indeed, both seizures and cognitive impairments can be early indicators of disease conditions which lead to mental decline. Cognitive decline over time poses the challenge of disentangling the interrelation between seizures, treatment effects and underlying disease. This issue must be considered as some of the etiologies for causing neuropsychological decline can be addressed. Medication and active epilepsy can contribute to impairments and their impact may be reversible. Dementia is rare if seizures are what has brought the person to attention, and if this is not accompanied by other slowly developing features (such as cognitive of psychiatric changes). From a neuropsychological point of view choosing the right screening tools or assessments, obtaining the history and timeline of impairments in relation to epilepsy, and most importantly longitudinally following the patients regardless of whether epilepsy is ultimately controlled or not appear essential.

Identification of a novel KCNT2 variant in a family with developmental and epileptic encephalopathies: a case report and literature review

Background: Developmental and epileptic encephalopathies (DEEs) are a group of heterogeneous neurodevelopmental diseases characterized mainly by developmental delay/intellectual disability and early-onset epilepsy. Researchers have identified variations in the KCNT2 gene (OMIM* 610044) as the cause of DEE type 57 (MIM# 617771). Case presentation: We report in this study a 46-year-old woman who presented with early-onset epilepsy, intellectual disability, hypertrichosis, coarse facial features, and short stature. Besides, there were four other affected individuals in her family history, including two elder brothers, a younger brother, and their mother. We collected blood samples from the proband, her two affected brothers, and her clinically normal daughter for genetic analysis. Clinical exome sequencing revealed a novel heterozygous variant in the KCNT2 gene (NM_198503: c.188G>A, p.Arg63His) in the proband and her two affected brothers, while her daughter did not carry this variant. Furthermore, we reviewed all 25 patients identified in the literature with KCNT2 variants and compared their phenotypes. Conclusion: Epilepsy and intellectual disability/developmental delay occur in almost all patients with KCNT2 variants. KCNT2-relevant DEEs partially overlap with the clinical phenotypes of KATP channel diseases, particularly in hypertrichosis and distinctive coarse facial features.

Istore: a project on innovative statistical methodologies to improve rare diseases clinical trials in limited populations

BACKGROUND

The conduct of rare disease clinical trials is still hampered by methodological problems. The number of patients suffering from a rare condition is variable, but may be very small and unfortunately statistical problems for small and finite populations have received less consideration. This paper describes the outline of the iSTORE project, its ambitions, and its methodological approaches.

METHODS

In very small populations, methodological challenges exacerbate. iSTORE's ambition is to develop a comprehensive perspective on natural history course modelling through multiple endpoint methodologies, subgroup similarity identification, and improving level of evidence.

RESULTS

The methodological approaches cover methods for sound scientific modeling of natural history course data, showing similarity between subgroups, defining, and analyzing multiple endpoints and quantifying the level of evidence in multiple endpoint trials that are often hampered by bias.

CONCLUSION

Through its expected results, iSTORE will contribute to the rare diseases research field by providing an approach to better inform about and thus being able to plan a clinical trial. The methodological derivations can be synchronized and transferability will be outlined.

The burden of epilepsy on long-term outcome of genetic developmental and epileptic encephalopathies: A single tertiary center longitudinal retrospective cohort study

BACKGROUND

This retrospective cohort analysis highlighted neurodevelopmental outcome predictors of genetic developmental and epileptic encephalopathies (DEE).

PATIENTS AND METHODS

Patients' demographic, clinical and molecular genetics data were collected. All patients underwent clinical, developmental, and neuropsychological assessments.

RESULTS

We recruited 100 participants (53 males, 47 females) with a mean follow-up lasting 10.46 ± 8.37 years. Age at epilepsy-onset was predictive of poor adaptive and cognitive functions (VABS-II score, r = 0.350, p = 0.001; BRIEF control subscale, r = -0.253; p = 0.031). Duration of epilepsy correlated negatively with IQ (r = -0.234, p = 0.019) and VABS-II score (r = -0.367, p = 0.001). Correlations were found between delayed/lacking EEG maturation/organization and IQ (r = 0.587, p = 0.001), VABS-II score (r = 0.658, p = 0.001), BRIEF-MI and BRIEF-GEC scores (r = -0.375, p = 0.001; r = -0.236, p = 0.033), ASEBA anxiety (r = -0.220, p = 0.047) and ADHD (r = -0.233, p = 0.035) scores. The number of antiseizure medications (ASMs) correlated with IQ (r = -0.414, p = 0.001), VABS-II (r = -0.496, p = 0.001), and BRIEF-MI (r = 0.294, p = 0.012) scores; while age at the beginning of therapy with ASEBA anxiety score (r = 0.272, p = 0.013). The occurrence of status epilepticus was associated with worse adaptive performances. The linear regression analysis model showed that delayed/lacking EEG maturation/organization had a significant influence on the IQ (R2 = 0.252, p < 0.001) and the BRIEF-GEC variability (R2 = 0.042, p = 0.036). The delayed/lacking EEG maturation/organization and the duration of epilepsy also had a significant influence on the VABS-II score (R2 = 0.455, p = 0.005).

CONCLUSIONS

Age at seizure-onset, EEG maturation/organization, duration of epilepsy, occurrence of status epilepticus, age at the introduction and number of ASMs used are reliable predictors of long-term outcomes in patients with genetic DEE.

[A multicentre epilepsy registry in Mexico]

INTRODUCTION

The National Epilepsy Registry in Mexico was carried out, from March 2021 to December 2022, in public hospitals of the Priority Epilepsy Program 'PPE', with the aim of describing the current situation in our pediatric and adult population.

PATIENTS AND METHODS

Observational, cross-sectional, multicenter study. We used a database, according to classifications of the International League Against Epilepsy (ILAE) 2017. Patients of all ages were included, with a diagnosis of epilepsy according to the practical clinical definition ILAE 2014.

RESULTS

We registered 10,852 patients, 5,495 men (50.6%) and 5,357 women (49.4%). Family history of epilepsy in 1,714 patients (15.8%), febrile seizures in 987 (9.1%). Type of seizure: 5,542 (51.1%) presented focal onset, of which 1,889 (34.1%) evolved to bilateral tonic-clonic seizures; generalized onset 4,861 (44.8%), unknown 33 (3.1%) and unclassified 115 (1.1%). Almost half had unknown etiology and 40% were structural, of which hypoxic ischemic encephalopathy was the most frequent (21.6%) and neurocysticercosis was 1%. Comorbidities appeared in 6,326 patients (58.3%). Anti-seizure medications (ASM) were used in 96.4% patients, mainly valproate. Status epilepticus was found in 1,383 patients (12.7%) and drug-resistant epilepsy in 18.9%. Paraclinical studies: 79.3% with at least one electroencephalogram and 76.9% with a neuroimaging study. Epilepsy surgery occurred in 275 patients (2.5%).

CONCLUSIONS

Despite the efforts of the Pan American Health Organization in its Strategy and Action Plan on epilepsy, diagnostic technologies and ASM supply are still lagging behind.

Epilepsy Surgery for Cognitive Improvement in Epileptic Encephalopathy

Epileptic encephalopathies are defined by the presence of frequent epileptiform activity that causes neurodevelopmental slowing or regression. Here, we review evidence that epilepsy surgery improves neurodevelopment in children with epileptic encephalopathies. We describe an example patient with epileptic encephalopathy without drug refractory seizures, who underwent successful diagnostic and therapeutic surgeries. In patients with epileptic encephalopathy, cognitive improvement alone is a sufficient indication to recommend surgical intervention in experienced centers.

Epilepsies

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

STXBP6 Gene Mutation: A New Form of SNAREopathy Leads to Developmental Epileptic Encephalopathy

Syntaxin-binding protein 6 (STXBP6), also known as amysin, is an essential component of the SNAP receptor (SNARE) complex and plays a crucial role in neuronal vesicle trafficking. Mutations in genes encoding SNARE proteins are often associated with a broad spectrum of neurological conditions defined as "SNAREopathies", including epilepsy, intellectual disability, and neurodevelopmental disorders such as autism spectrum disorders. The present whole exome sequencing (WES) study describes, for the first time, the occurrence of developmental epileptic encephalopathy and autism spectrum disorders as a result of a de novo deletion within the STXBP6 gene. The truncated protein in the STXBP6 gene leading to a premature stop codon could negatively modulate the synaptic vesicles' exocytosis. Our research aimed to elucidate a plausible, robust correlation between STXBP6 gene deletion and the manifestation of developmental epileptic encephalopathy.

Intellectual Disability and Epilepsy: The High Incidence and the Risks of Status Epilepticus and Sudden Death Require Improved Therapies

Epidemiology of Developmental and Epileptic Encephalopathy and of Intellectual Disability and Epilepsy in Children Poke G, Stanley J, Scheffer IE, Sadleir LG. Neurology. 2023;100(13):e1363-e1375. doi:10.1212/WNL.0000000000206758 Background and Objectives: We aimed to determine the population-based cumulative incidence and prevalence of developmental and epileptic encephalopathies (DEEs) and intellectual disability and epilepsy (ID+E) in children. We analyzed the cumulative incidence of specific epilepsy syndromes. Methods: Children younger than 16 years with a DEE or ID+E were ascertained using EEG records from 2000 to 2016 in the Wellington region of New Zealand. Epilepsy syndromes were diagnosed on medical record and EEG review. Point prevalence and cumulative incidence for children with epilepsy and developmental impairment, DEE and ID+E were calculated. Cumulative incidence for each epilepsy syndrome was calculated. Results: The cohort comprised 235 children (58% male) with developmental impairment and epilepsy, including 152 (65%) with DEE and 83 (35%) with ID+E. The median age of seizure onset was 15.4 months (range day 1-15 years). The median follow-up from seizure onset was 7.9 years (range 0-18.2 years). Point prevalence for the broad group of children with epilepsy and developmental impairment was 175/100,000 children (95% CI 149-203; DEE 112 and ID+E 63/100,000 children). Cumulative incidence for DEE was 169/100,000 children (95% CI 144-199) and that for ID+E was 125/100,000 children (95% CI 95.4-165). Cumulative incidence per 100,000 children was as follows: infantile epileptic spasms syndrome 58.2 (95% CI 45.0-75.3), epilepsy with myoclonic-atonic seizures 16.4 (95% CI 9.69-27.7), Lennox-Gastaut syndrome 13.2 (95% CI 4.1-41.9), and Dravet syndrome 5.1 (95% CI 2.1-12.2). Fifty/152 (33%) of children with DEE and 70/83 (84%) with ID+E could not be diagnosed with a known epilepsy syndrome. Discussion: Epilepsy and developmental impairment before the age of 16 years occurs in 1 in 340 children, with 1 in 590 having a DEE and 1 in 800 having ID+E. These individuals require significant health and community resources; therefore, these data will inform complex health service and education planning. Epidemiologic studies have focused on early childhood-onset DEEs. These do not fully reflect the burden of these disorders because 27% of DEEs and 70% of ID+E begin later, with seizure onset after the age of 3 years. Understanding the cumulative incidence of specific syndromes together with the broad group of DEEs is essential for the planning of therapeutic trials. Given trials focus on specific syndromes, there is a risk that effective therapies will not be developed for one-third of children with DEE.

Rates of Status Epilepticus and Sudden Unexplained Death in Epilepsy in People With Genetic Developmental and Epileptic Encephalopathies Donnan AM, Schneider AL, Russ-Hall S, Churilov L, Scheffer IE. Neurology. 2023;100(16): e1712-e1722. doi:10.1212/WNL.0000000000207080 Background and Objectives: The genetic developmental and epileptic encephalopathies (DEEs) comprise a large group of severe epilepsy syndromes, with a wide phenotypic spectrum. Currently, the rates of convulsive status epilepticus (CSE), nonconvulsive status epilepticus (NCSE), and sudden unexplained death in epilepsy (SUDEP) in these diseases are not well understood. We aimed to describe the proportions of patients with frequently observed genetic DEEs who developed CSE, NCSE, mortality, and SUDEP. Understanding the risks of these serious presentations in each genetic DEE will enable earlier diagnosis and appropriate management. Methods: In this retrospective analysis of patients with a genetic DEE, we estimated the proportions with CSE, NCSE, and SUDEP and the overall and SUDEP-specific mortality rates for each genetic diagnosis. We included patients with a pathogenic variant in the genes SCN1A, SCN2A, SCN8A, SYNGAP1, NEXMIF, CHD2, PCDH19, STXBP1, GRIN2A, KCNT1, and KCNQ2 and with Angelman syndrome (AS). Results: The cohort comprised 510 individuals with a genetic DEE, in whom we observed CSE in 47% and NCSE in 19%. The highest proportion of CSE occurred in patients with SCN1A-associated DEEs, including 181/203 (89%; 95% CI 84-93) patients with Dravet syndrome and 8/15 (53%; 95% CI 27-79) non-Dravet SCN1A-DEEs. CSE was also notable in patients with pathogenic variants in KCNT1 (6/10; 60%; 95% CI 26-88) and SCN2A (8/15; 53%; 95% CI 27-79). NCSE was common in patients with non-Dravet SCN1A-DEEs (8/15; 53%; 95% CI 27-79) and was notable in patients with CHD2-DEEs (6/14; 43%; 95% CI 18-71) and AS (6/19; 32%; 95% CI 13-57). There were 42/510 (8%) deaths among the cohort, producing a mortality rate of 6.1 per 1,000 person-years (95% CI 4.4-8.3). Cases of SUDEP accounted for 19/42 (48%) deaths. Four genes were associated with SUDEP: SCN1A, SCN2A, SCN8A, and STXBP1. The estimated SUDEP rate was 2.8 per 1,000 person-years (95% CI 1.6-4.3). Discussion: We showed that proportions of patients with CSE, NCSE, and SUDEP differ for commonly encountered genetic DEEs. The estimates for each genetic DEE studied will inform early diagnosis and management of status epilepticus and SUDEP and inform disease-specific counseling for patients and families in this high-risk group of conditions.

Diagnostic Utility of Genome-wide DNA Methylation Analysis in Genetically Unsolved Developmental and Epileptic Encephalopathies and Refinement of a CHD2 Episignature

Sequence-based genetic testing currently identifies causative genetic variants in ∼50% of individuals with developmental and epileptic encephalopathies (DEEs). Aberrant changes in DNA methylation are implicated in various neurodevelopmental disorders but remain unstudied in DEEs. Rare epigenetic variations ("epivariants") can drive disease by modulating gene expression at single loci, whereas genome-wide DNA methylation changes can result in distinct "episignature" biomarkers for monogenic disorders in a growing number of rare diseases. Here, we interrogate the diagnostic utility of genome-wide DNA methylation array analysis on peripheral blood samples from 516 individuals with genetically unsolved DEEs who had previously undergone extensive genetic testing. We identified rare differentially methylated regions (DMRs) and explanatory episignatures to discover causative and candidate genetic etiologies in 10 individuals. We then used long-read sequencing to identify DNA variants underlying rare DMRs, including one balanced translocation, three CG-rich repeat expansions, and two copy number variants. We also identify pathogenic sequence variants associated with episignatures; some had been missed by previous exome sequencing. Although most DEE genes lack known episignatures, the increase in diagnostic yield for DNA methylation analysis in DEEs is comparable to the added yield of genome sequencing. Finally, we refine an episignature for CHD2 using an 850K methylation array which was further refined at higher CpG resolution using bisulfite sequencing to investigate potential insights into CHD2 pathophysiology. Our study demonstrates the diagnostic yield of genome-wide DNA methylation analysis to identify causal and candidate genetic causes as ∼2% (10/516) for unsolved DEE cases.

Pharmacological diversity amongst approved and emerging antiseizure medications for the treatment of developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies (DEEs) are rare neurodevelopmental disorders characterised by early-onset and often intractable seizures and developmental delay/regression, and include Dravet syndrome and Lennox-Gastaut syndrome (LGS). Rufinamide, fenfluramine, stiripentol, cannabidiol and ganaxolone are antiseizure medications (ASMs) with diverse mechanisms of action that have been approved for treating specific DEEs. Rufinamide is thought to suppress neuronal hyperexcitability by preventing the functional recycling of voltage-gated sodium channels from the inactivated to resting state. It is licensed for adjunctive treatment of seizures associated with LGS. Fenfluramine increases extracellular serotonin levels and may reduce seizures via activation of specific serotonin receptors and positive modulation of the sigma-1 receptor. Fenfluramine is licensed for adjunctive treatment of seizures associated with Dravet syndrome and LGS. Stiripentol is a positive allosteric modulator of type-A gamma-aminobutyric acid (GABAA) receptors. As a broad-spectrum inhibitor of cytochrome P450 enzymes, its antiseizure effects may additionally arise through pharmacokinetic interactions with co-administered ASMs. Stiripentol is licensed for treating seizures associated with Dravet syndrome in patients taking clobazam and/or valproate. The mechanism(s) of action of cannabidiol remains largely unclear although multiple targets have been proposed, including transient receptor potential vanilloid 1, G protein-coupled receptor 55 and equilibrative nucleoside transporter 1. Cannabidiol is licensed as adjunctive treatment in conjunction with clobazam for seizures associated with Dravet syndrome and LGS, and as adjunctive treatment of seizures associated with tuberous sclerosis complex. Like stiripentol, ganaxolone is a positive allosteric modulator at GABAA receptors. It has recently been licensed in the USA for the treatment of seizures associated with cyclin-dependent kinase-like 5 deficiency disorder. Greater understanding of the causes of DEEs has driven research into the potential use of other novel and repurposed agents. Putative ASMs currently in clinical development for use in DEEs include soticlestat, carisbamate, verapamil, radiprodil, clemizole and lorcaserin.