Mechanisms of infantile epileptic spasms syndrome: What have we learned from animal models?

Association Between Scalp High-Frequency Oscillations and Burden of Amplitudes and Epileptiform Discharges (BASED) Scores in Infantile Epileptic Spasms Syndrome

Tools for measuring the likelihood of relapse in infantile epileptic spasms syndrome (IESS) treatment could aid clinicians in making critical management decisions. High-frequency oscillations (HFOs), transient bursts of electroencephalography (EEG) activity with frequencies beyond 80 Hz, are a new and promising noninvasive biomarker. The present study aimed to investigate the association between the Burden of Amplitudes and Epileptiform Discharges (BASED) scores, an interictal EEG grading scale for IESS, and scalp HFOs in patients with IESS. The study enrolled 50 patients, 25 with a clinical diagnosis of IESS and 25 without epilepsy. The percentage of patients with at least one scalp HFO detected, stratified by BASED scores, differed significantly: for BASED scores ≤ 2, 7.7%; for 3, 16.7%; for 4, 87.5%; and for 5, 100% (p < 0.001). Compared with BASED scores ≤ 2, the median scalp HFO detection rate was significantly highest for BASED scores of 5 (median [IQR]: 6.24 [2.25-8.32], p < 0.001), followed by BASED scores of 4. The scalp HFO detection rates showed a better performance in estimating patients with BASED scores of 4 and 5. It is hoped that scalp HFOs can be used as an objective indicator to validate the results of BASED scores.

The role of CSNK1A1 and its de novo mutations in infantile spasms syndrome

Infantile spasms syndrome (ISS) is an early-onset epileptic encephalopathy characterized by uncontrollable seizures, severe electroencephalogram abnormalities, as well as delayed cognitive and behavioral development. Independent studies have shown that a variety of genes are involved in ISS and genetic factors play a critical role in its pathogenesis. Here we report two de novo mutations in the casein kinase 1 isoform alpha (CSNK1A1) gene which underlie severe epilepsy with similar clinical presentation in two patients. The identified variants are one missense mutation c.646G > C (p.Ala216Pro, Mut) in NM_001025105.3 and one deletion c.599_604delACATAC (p.His200_Ile201del, Del). In vitro analyses indicated that the Mut causes significant decreases in both mRNA and protein expression, while the Del demonstrated no significant impact on gene expression level. However, co-immunoprecipitation studies have shown that both mutations lead to reduced interactions between CSNK1A1 and β-catenin, resulting in excessive intracellular β-catenin and aberrant expression of several downstream genes. Compared with the wild type (WT), the EdU positive rates in cells transfected with Mut plasmid or Del plasmid were both elevated. Wnt/β-catenin signaling pathway is crucial to neurogenesis. An abnormal rise in β-catenin level has been utilized to generate genetic models for ISS. Our results not only elucidate the role of a novel candidate gene CSNK1A1 in the pathology of ISS, but also provide further evidence for the findings that mediating Wnt/β-catenin signaling is a potential mechanism causing ISS.

New insights into epileptic spasm generation and treatment from the TTX animal model

Currently, we have an incomplete understanding of the mechanisms underlying infantile epileptic spasms syndrome (IESS). However, over the past decade, significant efforts have been made to develop IESS animal models to provide much-needed mechanistic information for therapy development. Our laboratory has focused on the TTX model and in this paper, we review some of our findings. To induce spasms, tetrodotoxin (TTX) is infused into the neocortex of infant rats. TTX produces a lesion at its infusion site and thus mimics IESS resulting from acquired structural brain abnormalities. Subsequent electrophysiological studies showed that the epileptic spasms originate from neocortical layer V pyramidal cells. Importantly, experimental maneuvers that increase the excitability of these cells produce focal seizures in non-epileptic control animals but never produce them in TTX-infused epileptic rats; instead, epileptic spasms are produced in epileptic rats, indicating a significant transformation in the operations of neocortical networks. At the molecular level, studies showed that the expression of insulin-like growth factor 1 was markedly reduced in the cortex and this corresponded with a loss of presynaptic GABAergic nerve terminals. Very similar observations were made in surgically resected tissue from IESS patients with a history of perinatal strokes. Other experiments in conditional knockout mice indicated that IGF-1 plays a critical role in the maturation of neocortical inhibitory connectivity. This finding led to our hypothesis that the loss of IGF-1 in epileptic animals impairs inhibitory interneuron synaptogenesis and is responsible for spasms. To test this idea, we treated epileptic rats with the IGF-1-derived tripeptide (1-3)IGF-1, which was shown to act through IGF-1's receptor. (1-3)IGF-1 rescued inhibitory interneuron connectivity, restored IGF-1 levels, and abolished spasms. Thus, (1-3)IGF-1 or its analogs are potential novel treatments for IESS following perinatal brain injury. We conclude by discussing our findings in the broader context of the often-debated final common pathway hypothesis for IESS. PLAIN LANGUAGE SUMMARY: We review findings from the TTX animal model of infantile epileptic spasms syndrome, which show that these seizures come from an area of the brain called the neocortex. In this area, the amount of an important growth factor called IGF-1 is reduced, as is the number of inhibitory synapses that play an important role in preventing seizures. Other results indicate that the loss of IGF-1 prevents the normal development of these inhibitory synapses. Treatment of epileptic animals with (1-3)IGF-1 restored IGF-1 levels and inhibitory synapses and abolished spasms. Thus, (1-3)IGF-1 or an analog is a potential new therapy for epileptic spasms.

Intestinal microbiome alterations in pediatric epilepsy: Implications for seizures and therapeutic approaches

The intestinal microbiome plays a pivotal role in maintaining host health through its involvement in gastrointestinal, immune, and central nervous system (CNS) functions. Recent evidence underscores the bidirectional communication between the microbiota, the gut, and the brain and the impact of this axis on neurological diseases, including epilepsy. In pediatric patients, alterations in gut microbiota composition-called intestinal dysbiosis-have been linked to seizure susceptibility. Preclinical models revealed that gut dysbiosis may exacerbate seizures, while microbiome-targeted therapies, including fecal microbiota transplantation, pre/pro-biotics, and ketogenic diets, show promise in reducing seizures. Focusing on clinical and preclinical studies, this review examines the role of the gut microbiota in pediatric epilepsy with the aim of exploring its implications for seizure control and management of epilepsy. We also discuss mechanisms that may underlie mutual gut-brain communication and emerging therapeutic strategies targeting the gut microbiome as a novel approach to improve outcomes in pediatric epilepsy. PLAIN LANGUAGE SUMMARY: Reciprocal communication between the brain and the gut appears to be dysfunctional in pediatric epilepsy. The composition of bacteria in the intestine -known as microbiota- and the gastrointestinal functions are altered in children with drug-resistant epilepsy and animal models of pediatric epilepsies. Microbiota-targeted interventions, such as ketogenic diets, pre-/post-biotics administration, and fecal microbiota transplantation, improve both gastrointestinal dysfunctions and seizures in pediatric epilepsy. These findings suggest that the gut and its microbiota represent potential therapeutic targets for reducing drug-resistant seizures in pediatric epilepsy.

Hypotheses of pathophysiological mechanisms in epileptic encephalopathies: A review

INTRODUCTION

Epileptic encephalopathy (EE) is a serious clinical issue that manifests as part of developmental and epileptic encephalopathy (DEE), particularly in childhood epilepsy. In EE, neurocognitive functions and behavior are impaired by intense epileptiform electroencephalogram (EEG) activity. Hypotheses of pathophysiological mechanisms behind EE are reviewed to contribute to an effective solution for EE.

REVIEW

Current hypotheses are as follows: 1) neuronal dysfunction based on genetic abnormalities that may affect neurocognitive functions and epilepsy separately; 2) impairment of synaptic homeostasis during sleep that may be responsible for DEE/EE with spike-and-wave activation in sleep; 3) abnormal subcortical regulation of the cerebral cortex; 4) abnormal cortical metabolism and hemodynamics with impairment of the neural network including default mode network; 5) neurotransmitter imbalance and disordered neural excitability; 6) the effects of neuroinflammation that may be caused by epileptic seizures and in turn aggravate epileptogenesis; 7) the interaction between physiological and pathological high-frequency EEG activity; etc. The causal relationship between epileptiform EEG activity and neurocognitive dysfunctions is small in DEE based on genetic abnormalities and it is largely unestablished in the other hypothetical mechanisms.

CONCLUSION

We have not yet found answers to the question of whether the single-central or multiple derangements are present and what seizures and intense epileptiform EEG abnormalities mean in EE. We need to continue our best efforts in both aspects to elucidate the pathophysiological mechanisms of DEE/EE and further develop epilepsy treatment and precision medicine.

Infantile Spasms in Pediatric Down Syndrome: Potential Mechanisms Driving Therapeutic Considerations

Infantile spasms are common in Down Syndrome (DS), but the mechanisms by which DS predisposes to this devastating epilepsy syndrome are unclear. In general, neuronal excitability and therefore seizure predisposition results from an imbalance of excitation over inhibition in neurons and neural networks of the brain. Animal models provide clues to mechanisms and thereby provide potential therapeutic approaches. Ts65Dn mice have been the most widely used animal model of DS. In this model, there is evidence for both abnormal cerebral excitation and inhibition: infantile spasms-like clinical and electrographic activity can be elicited by the administration of gamma-aminobutyric acid (GABA)-B receptor agonist, gamma-butyrolactone (GBL), and depolarizing GABA-A responses persist beyond the age of their usual switch to hyperpolarized responses. But despite its widespread use, the Ts65Dn model may be suboptimal because of the absence of numerous genes that are triplicated in human DS and the presence of numerous genes that are not triplicated in human DS. Recently, a transchromosomic mouse artificial chromosome 21 (TcMAC21) mouse model has been developed, which carries a copy of human chromosome 21 and therefore has a genetic composition more similar to human DS. As in Ts65Dn mice, exposure of TcMAC21 mice to GBL results in epileptic spasms, and aberrant excitation has also been demonstrated. This review summarizes excitatory and inhibitory dysfunction in models of DS that may play a role in the generation of seizures and infantile spasms, providing a perspective on past studies and a prelude for future ones. Further elucidation will hopefully lead to rational therapeutic options for DS children with infantile spasms.

Genetic Advancements in Infantile Epileptic Spasms Syndrome and Opportunities for Precision Medicine

Infantile epileptic spasms syndrome (IESS) is a devastating developmental epileptic encephalopathy (DEE) consisting of epileptic spasms, as well as one or both of developmental regression or stagnation and hypsarrhythmia on EEG. A myriad of aetiologies are associated with the development of IESS; broadly, 60% of cases are thought to be structural, metabolic or infectious in nature, with the remainder genetic or of unknown cause. Epilepsy genetics is a growing field, and over 28 copy number variants and 70 single gene pathogenic variants related to IESS have been discovered to date. While not exhaustive, some of the most commonly reported genetic aetiologies include trisomy 21 and pathogenic variants in genes such as TSC1, TSC2, CDKL5, ARX, KCNQ2, STXBP1 and SCN2A. Understanding the genetic mechanisms of IESS may provide the opportunity to better discern IESS pathophysiology and improve treatments for this condition. This narrative review presents an overview of our current understanding of IESS genetics, with an emphasis on animal models of IESS pathogenesis, the spectrum of genetic aetiologies of IESS (i.e., chromosomal disorders, single-gene disorders, trinucleotide repeat disorders and mitochondrial disorders), as well as available genetic testing methods and their respective diagnostic yields. Future opportunities as they relate to precision medicine and epilepsy genetics in the treatment of IESS are also explored.