SUDEP risk and autonomic dysfunction in genetic epilepsies

Response to Singh et al. 2023: It is premature for a unified hypothesis of sudden unexpected death in epilepsy: A great amount of research is still needed to understand the multisystem cascade

In response to the comments by Singh and colleagues about our recent paper proposing a unified hypothesis of SUDEP, we definitely agree that more research is needed. This research should include studies in other models, including Dravet mice, emphasized by Singh et al. However, we strongly believe the hypothesis is timely, because it is based on the continuing progress on SUDEP-related research on serotonin (5-HT) and adenosine as well as neuroanatomical findings.We propose testing of 5-HT enhancing drugs, neurotoxicity blocking drugs, such as N-methyl-D-aspartate (NMDA) antagonists and periaqueductal gray (PAG) electrical stimulation for SUDEP prevention. There are FDA-approved drugs that enhance the action of 5-HT, including fluoxetine and fenfluramine, which is approved for Dravet syndrome. NMDA antagonists, including memantine and ketamine, are also approved for other disorders. PAG electrical stimulation, which is proposed to activate a suffocation alarm, is also approved to treat other conditions and is known to enhance respiration. Experiments using these methods are currently being carried out in animal studies. If these approaches are validated in SUDEP models, treatments could be evaluated relatively quickly in patients with epilepsy (PWE) who exhibit a biomarker for high SUDEP risk, such as peri-ictal respiratory abnormalities. An example of such a study is the ongoing clinical trial of a selective serotonin reuptake inhibitor in PWE. Although, gene-based therapies may ultimately become treatments of choice to prevent SUDEP, as Singh et al suggested, one or more of the approaches we proposed could become temporizing treatments before gene-based therapies can be available. Establishing genetic treatments would require extensive time for each of the genetic abnormalities associated with SUDEP, and too many PWE are likely to die in the meantime.The temporizing treatments may help to reduce the incidence of SUDEP sooner, which is urgently needed.

Audiogenic epileptic DBA/2 mice strain as a model of genetic reflex seizures and SUDEP

Epilepsy is a chronic neurological disease characterized by abnormal brain activity, which results in repeated spontaneous seizures. Sudden unexpected death in epilepsy (SUDEP) is the leading cause of seizure-related premature death, particularly in drug-resistant epilepsy patients. The etiology of SUDEP is a structural injury to the brain that is not fully understood, but it is frequently associated with poorly controlled and repeated generalized tonic-clonic seizures (GTCSs) that cause cardiorespiratory and autonomic dysfunctions, indicating the involvement of the brainstem. Both respiratory and cardiac abnormalities have been observed in SUDEP, but not much progress has been made in their prevention. Owing to the complexity of SUDEP, experimental animal models have been used to investigate cardiac and/or respiratory dysregulation due to or associated with epileptic seizures that may contribute to death in humans. Numerous rodent models, especially mouse models, have been developed to better understand epilepsy and SUDEP physiopathology. This review synthesizes the current knowledge about dilute brown agouti coat color (DBA/2) mice as a possible SUDEP model because respiratory arrest (RA) and sudden death induced by audiogenic generalized seizures (AGSs) have been observed in these animals. Respiratory/cardiac dysfunction, brainstem arousal system dysfunction, and alteration of the neurotransmitter systems, which are observed in human SUDEP, have also been observed in these mice. In particular, serotonin (5-HT) alteration and adenosine neurotransmission appear to contribute to not only the pathophysiological mechanisms of medication but also seizure-related respiratory dysfunctions in this animal model. These neurotransmitter systems could be the relevant targets for medication development for chronic epilepsy and SUDEP prevention. We reviewed data on AGSs in DBA/2 mice and the relevance of this model of generalized tonic-clonic epilepsy to human SUDEP. Furthermore, the advantages of using this strain prone to AGSs for the identification of possible new therapeutic targets and treatment options have also been assessed.

Genetics and SUDEP: Challenges and Future Directions

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related deaths in children and adults with epilepsy. The incidence of SUDEP in children and adults is equal, approximately 1.2 per 1000-person years. Although inroads have been made in our understanding of SUDEP, its pathophysiology remains unknown. The most important risk factor for SUDEP is the presence of tonic-clonic seizures. Recently there has been growing interest in the contribution of genetic risk factors to SUDEP deaths. Pathogenic variants in epilepsy-related and cardiac genes have been found in some cases of SUDEP post-mortem. Pleiotropy may occur in which a single gene when altered may cause multiple phenotypes (i.e., epilepsy and cardiac arrhythmia). Recently it has been shown that some developmental and epileptic encephalopathies (DEEs) may also be at heightened risk of SUDEP. In addition, polygenic risk has been postulated to effect SUDEP risk with current models evaluating the additive effect of variants in multiple genes. However, the mechanisms underpinning polygenic risk in SUDEP are likely more complex than this. Some preliminary studies also highlight the feasibility of detecting genetic variants in brain tissue post-mortem. Despite the advances in the field of SUDEP genetics, the use of molecular autopsy remains underutilized in SUDEP cases. Several challenges exist concerning genetic testing post-mortem in SUDEP cases, such as interpretation, cost of testing, and availability. In this focused review, we highlight the current landscape of genetic testing in SUDEP cases, its challenges, and future directions.

Strain-dependent effects on neurobehavioral and seizure phenotypes in Scn2aK1422E mice

Pathogenic variants in SCN2A are associated with a range of neurodevelopmental disorders (NDD). Despite being largely monogenic, SCN2A-related NDD show considerable phenotypic variation and complex genotype-phenotype correlations. Genetic modifiers can contribute to variability in disease phenotypes associated with rare driver mutations. Accordingly, different genetic backgrounds across inbred rodent strains have been shown to influence disease-related phenotypes, including those associated with SCN2A-related NDD. Recently, we developed a mouse model of the variant SCN2A-p.K1422E that was maintained as an isogenic line on the C57BL/6J (B6) strain. Our initial characterization of NDD phenotypes in heterozygous Scn2aK1422E mice revealed alterations in anxiety-related behavior and seizure susceptibility. To determine if background strain affects phenotype severity in the Scn2aK1422E mouse model, phenotypes of mice on B6 and [DBA/2J×B6]F1 hybrid (F1D2) strains were compared. Convergent evidence from neurobehavioral assays demonstrated lower anxiety-like behavior in Scn2aK1422E mice compared to wild-type and further suggested that this effect is more pronounced on the B6 background compared to the F1D2 background. Although there were no strain-dependent differences in occurrence of rare spontaneous seizures, response to the chemoconvulsant kainic acid revealed differences in seizure generalization and lethality risk, with variation based on strain and sex. Continued examination of strain-dependent effects in the Scn2aK1422E mouse model could reveal genetic backgrounds with unique susceptibility profiles that would be relevant for future studies on specific traits and enable the identification of highly penetrant phenotypes and modifier genes that could provide clues about the primary pathogenic mechanism of the K1422E variant.

Sudden unexpected death in epilepsy in children

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related mortality in children and adults living with epilepsy. The incidence of SUDEP is comparable in both children and adults; it is approximately 1.2 per 1000 person years. The pathophysiology of SUDEP is not well understood but may involve mechanisms such as cerebral shutdown, autonomic dysfunction, altered brainstem function, and cardiorespiratory demise. Risk factors for SUDEP include the presence of generalized tonic-clonic seizures, nocturnal seizures, possible genetic predisposition, and non-adherence to antiseizure medications. Pediatric-specific risk factors are not fully elucidated. Despite recommendations from consensus guidelines, many clinicians still do not follow the practice of counseling their patients about SUDEP. SUDEP prevention has been an area of important research focus and includes several strategies, such as obtaining seizure control, optimizing treatment regimens, nocturnal supervision, and seizure detection devices. This review discusses what is currently known about SUDEP risk factors and reviews current and future preventive strategies for SUDEP.

Sudden unexpected death in epilepsy: Investigation of autopsy-based studies

Epilepsy is a common neurological disorder that is associated with increased morbidity and mortality. Sudden unexpected death in epilepsy (SUDEP) is one of the most common causes for epilepsy-related deaths and its characteristics remain largely unknown, particularly from a forensic autopsy perspective. The present study aimed to investigate the neurological, cardiac, and pulmonary findings for a total of 388 SUDEP decedents, encompassing three cases from our forensic center during 2011-2020 and 385 literature-reported autopsy cases. In the cases mentioned in this study, two of them presented with only mild cardiac abnormalities, such as focal myocarditis and mild coronary atherosclerosis of the left anterior coronary artery. The third one was negative of any pathological findings. After pooling together these SUDEP cases, we found that neurological changes (n = 218 cases, 56.2%) were the most common postmortem findings associated with SUDEP, with cerebral edema/congestion (n = 60 cases, 15.5%) and old traumatic brain injury (n = 58 cases, 14.9%) being the major findings. Interstitial fibrosis, myocyte disarray/hypertrophy, and mild coronary artery atherosclerosis were the most common findings related to primary cardiac pathology, documented in 49 (12.6%), 18 (4.6%), and 15 (3.9%) cases, respectively. Non-specific pulmonary edema was the major finding in the lungs. This is an autopsy-based study that reports the scenario of postmortem findings for SUDEP cases. Our study paves the way for understanding the pathogenesis of SUDEP and the interpretation of death.

Updates on the diagnostic evaluation, genotype-phenotype correlation, and treatments of genetic epilepsies

PURPOSE OF REVIEW

This article reviews the latest publications in genetic epilepsies, with an eye on publications that have had a translational impact. This review is both timely and relevant as translational discoveries in genetic epilepsies are becoming so frequent that it is difficult for the general pediatrician and even the general child neurologist to keep up.

RECENT FINDINGS

We divide these publications from 2021 and 2022 into three categories: diagnostic testing, genotype-phenotype correlation, and therapies. We also summarize ongoing and upcoming clinical trials.

SUMMARY

Two meta-analyses and systematic reviews suggest that exome and genome sequencing offer higher diagnostic yield than gene panels. Genotype-phenotype correlation studies continue to increase our knowledge of the clinical evolution of genetic epilepsy syndromes, particularly with regards to sudden death, auditory dysfunction, neonatal presentation, and magnetoencephalographic manifestations. Pyridoxine supplementation may be helpful in seizure management for various genetic epilepsies. There has been interest in using the neurosteroid ganaxolone for various genetic epilepsy syndromes, with clear efficacy in certain trials. Triheptanoin for epilepsy secondary to glucose transporter 1 ( GLUT1 ) deficiency syndrome is not clearly effective but further studies will be needed.

Reversibility and therapeutic development for neurodevelopmental disorders, insights from genetic animal models

Neurodevelopmental Disorders (NDDs) encompass a broad spectrum of conditions resulting from atypical brain development. Over the past decades, we have had the fortune to witness enormous progress in diagnosis, etiology discovery, modeling, and mechanistic understanding of NDDs from both fundamental and clinical research. Here, we review recent neurobiological advances from experimental models of NDDs. We introduce several examples and highlight breakthroughs in reversal studies of phenotypes using genetically engineered models of NDDs. The in-depth understanding of brain pathophysiology underlying NDDs and evaluations of reversibility in animal models paves the foundation for discovering novel treatment options. We discuss how the expanding property of cutting-edge technologies, such as gene editing and AAV-mediated gene delivery, are leveraged in animal models for the therapeutic development of NDDs. We envision opportunities and challenges toward faithful modeling and fruitful clinical translation.

Epilepsy and Electroencephalogram Characteristics in Children with Neurofibromatosis Type 1, What We Have Learned from a Tertiary Center Five Years' Experience

Introduction: Neurofibromatosis type 1(NF-1) is the commonest neurocutaneous phacomatosis in children. Epilepsy is an infrequent comorbidity. Reports of seizure and Electroencephalogram (EEG) characteristics in children are sparse. Methods: A retrospective review was performed on patients with NF-1 seen between 2016-2020. Patients with co-existing epilepsy were identified. Demographic, clinical, radiological and neurophysiological data were reviewed and analyzed. Results: Out of 118 children with NF1, 16 had epilepsy. 11 patients had focal onset seizures, whereas 5 had generalized onset seizures. Most patients had easy seizure control. Focal epileptiform discharges were the most prevalent EEG abnormality. There was no significant correlation between seizure patterns and presence of intracranial tumors. Conclusion: Epilepsy is a relatively uncommon in pediatric NF-1. Seizures are often of focal semiology and likely to be easily controlled. Focal and multifocal spike epileptiform discharges are the typical interictal EEG findings. Correlation of clinical and EEG findings with intracranial lesions is poor.

Cortical neuronal hypertrophy and mTOR pathway activation in CAN regions in SUDEP

OBJECTIVES

Dysfunctional connectivity and preexisting structural abnormalities of central autonomic network (CAN) regions have been shown on magnetic resonance imaging (MRI) in sudden unexpected death in epilepsy (SUDEP) and may be mechanistically relevant. In a previous postmortem study we reported increased microglia in CAN regions, including the superior temporal gyrus (STG) in SUDEP. In this current study we investigated mammalian target of rapamycin (mTOR) pathway activation and neuronal c-Fos activation in CAN regions in SUDEP compared to control groups.

METHODS

In a series of 59 postmortem cases (SUDEP, n = 26; epilepsy controls [EPCs], n = 14; and nonepilepsy controls [NECs], n = 19), we quantified pS6-240/4, pS6-235/6 (markers of mTOR activation) and c-Fos neuronal densities and labeling index in the STG, anterior cingulate, insula, frontobasal, and pulvinar regions using immunohistochemistry with whole-slide automated image analysis.

RESULTS

Significantly more pS6-positive neurons were present in the STG in cases with a history of recent seizures prior to death and also in SUDEP compared to other cause of death groups. No differences were noted for c-Fos neuronal labeling in any region between cause of death groups. Cortical neuronal hypertrophy in the STG was observed in some SUDEP cases and associated with pS6-240/4 expression. pS6-235/6 highlighted neuronal intranuclear inclusions, mainly in SUDEP cases and in the STG region.

SIGNIFICANCE

Neuronal labeling for pS6 in the STG correlated with both seizure activity in the period prior to death and SUDEP. Further investigations are required to explore the significance of this region in terms of autonomic network dysfunction that may increase the vulnerability for SUDEP.

SCN2A-Related Epilepsy: The Phenotypic Spectrum, Treatment and Prognosis

OBJECTIVE

The aim of this study was to analyze the phenotypic spectrum, treatment, and prognosis of 72 Chinese children with SCN2A variants.

METHODS

The SCN2A variants were detected by next-generation sequencing. All patients were followed up at a pediatric neurology clinic in our hospital or by telephone.

RESULTS

In 72 patients with SCN2A variants, the seizure onset age ranged from the first day of life to 2 years and 6 months. The epilepsy phenotypes included febrile seizures (plus) (n = 2), benign (familial) infantile epilepsy (n = 9), benign familial neonatal-infantile epilepsy (n = 3), benign neonatal epilepsy (n = 1), West syndrome (n = 16), Ohtahara syndrome (n = 15), epilepsy of infancy with migrating focal seizures (n = 2), Dravet syndrome (n = 1), early infantile epileptic encephalopathy (n = 15), and unclassifiable developmental and epileptic encephalopathy (n = 8). Approximately 79.2% (57/72) patients had varying degrees of developmental delay. All patients had abnormal MRI findings with developmental delay. 91.7% (55/60) patients with de novo SCN2A variants had development delay, while only 16.7% (2/12) patients with inherited SCN2A variants had abnormal development. 83.9% (26/31) SCN2A variants that were located in transmembrane regions of the protein were detected in patients with development delay. Approximately 69.2% (9/13) SCN2A variants detected in patients with normal development were located in the non-transmembrane regions. Approximately 54.2% (39/72) patients were seizure-free at a median age of 8 months. Oxcarbazepine has been used by 38 patients, and seizure-free was observed in 11 of them (11/38, 28.9%), while 6 patients had seizure worsening by oxcarbazepine. All 3 patients used oxcarbazepine and with seizure onset age > 1 year presented seizure exacerbation after taking oxcarbazepine. Valproate has been used by 53 patients, seizure-free was observed in 22.6% (12/53) of them.

CONCLUSION

The phenotypic spectrum of SCN2A-related epilepsy was broad, ranging from benign epilepsy in neonate and infancy to severe epileptic encephalopathy. Oxcarbazepine and valproate were the most effective drugs in epilepsy patients with SCN2A variants. Sodium channel blockers often worsen seizures in patients with seizure onset beyond 1 year of age. Abnormal brain MRI findings and de novo variations were often related to poor prognosis. Most SCN2A variants located in transmembrane regions were related to patients with developmental delay.