Defining the latent period of epileptogenesis and epileptogenic zone in a focal cortical dysplasia type II (FCDII) rat model

Long-Term Downregulation of the Sodium Channel Gene Scn8a Is Therapeutic in Mouse Models of SCN8A Epilepsy

OBJECTIVE

De novo mutations of the voltage-gated sodium channel gene SCN8A cause developmental and epileptic encephalopathy (DEE). Most pathogenic variants result in gain-of-function changes in activity of the sodium channel Nav1.6, poorly controlled seizures, and significant comorbidities. In previous work, an antisense oligonucleotide (ASO) reduced Scn8a transcripts and increased lifespan after neonatal administration to a mouse model. Here, we tested long-term ASO treatment initiated after seizure onset, as required for clinical application.

METHODS

ASO treatment was initiated after observation of a convulsive seizure and repeated at 4 to 6 week intervals for 1 year. We also tested the long-term efficacy of an AAV10-short hairpin RNA (shRNA) virus administered on P1.

RESULTS

Repeated treatment with the Scn8a ASO initiated after seizure onset provided long-term survival and reduced seizure frequency during a 12 month observation period. A single treatment with viral shRNA was also protective during 12 months of observation.

INTERPRETATION

Downregulation of Scn8a expression that is initiated after the onset of seizures is effective for long-term treatment in a model of SCN8A-DEE. Repeated ASO administration or a single dose of viral shRNA prevented seizures and extended survival through 12 months of observation. ANN NEUROL 2024;95:754-759.

Distinct patterns of interictal intracranial EEG in focal cortical dysplasia type I and II

OBJECTIVE

Focal cortical dysplasia (FCD) is the most common malformation causing refractory focal epilepsy. Surgical removal of the entire dysplastic cortex is crucial for achieving a seizure-free outcome. Precise presurgical distinctions between FCD types by neuroimaging are difficult, mainly in patients with normal magnetic resonance imaging findings. However, the FCD type is important for planning the extent of surgical approach and counselling.

METHODS

This study included patients with focal drug-resistant epilepsy and definite histopathological FCD type I or II diagnoses who underwent intracranial electroencephalography (iEEG). We detected interictal epileptiform discharges (IEDs) and their recruitment into repetitive discharges (RDs) to compare electrophysiological patterns characterizing FCD types.

RESULTS

Patients with FCD type II had a significantly higher IED rate (p < 0.005), a shorter inter-discharge interval within RD episodes (p < 0.003), sleep influence on decreased RD periodicity (p < 0.036), and longer RD episode duration (p < 0.003) than patients with type I. A Bayesian classifier stratified FCD types with 82% accuracy.

CONCLUSION

Temporal characteristics of IEDs and RDs reflect the histological findings of FCD subtypes and can differentiate FCD types I and II.

SIGNIFICANCE

Presurgical prediction of FCD type can help to plan a more tailored surgical approach in patients with normal magnetic resonance findings.

Advances in in utero electroporation

In utero electroporation (IUE) is a technique developed in the early 2000s to transfect the neurons and neural progenitors of embryonic brains, thus enabling continued development in utero and subsequent analyses of neural development. Early IUE experiments focused on ectopic expression of plasmid DNA to analyze parameters such as neuron morphology and migration. Recent advances made in other fields, such as CRISPR/CAS9 genome editing, have been incorporated into IUE techniques as they were developed. Here, we provide a general review of the mechanics and techniques involved in IUE and explore the breadth of approaches that can be used in conjunction with IUE to study cortical development in a rodent model, with a focus on the novel advances in IUE techniques. We also highlight a few cases that exemplify the potential of IUE to study a broad range of questions in neural development.

Early suppression of excitability in subcortical band heterotopia modifies epileptogenesis in rats

Malformations of cortical development represent a major cause of epilepsy in childhood. However, the pathological substrate and dynamic changes leading to the development and progression of epilepsy remain unclear. Here, we characterized an etiology-relevant rat model of subcortical band heterotopia (SBH), a diffuse type of cortical malformation associated with drug-resistant seizures in humans. We used longitudinal electrographic recordings to monitor the age-dependent evolution of epileptiform discharges during the course of epileptogenesis in this model. We found both quantitative and qualitative age-related changes in seizures properties and patterns, accompanying a gradual progression towards a fully developed seizure pattern seen in adulthood. We also dissected the relative contribution of the band heterotopia and the overlying cortex to the development and age-dependent progression of epilepsy using timed and spatially targeted manipulation of neuronal excitability. We found that an early suppression of neuronal excitability in SBH slows down epileptogenesis in juvenile rats, whereas epileptogenesis is paradoxically exacerbated when excitability is suppressed in the overlying cortex. However, in rats with active epilepsy, similar manipulations of excitability have no effect on chronic spontaneous seizures. Together, our data support the notion that complex developmental alterations occurring in both the SBH and the overlying cortex concur to creating pathogenic circuits prone to generate seizures. Our study also suggests that early and targeted interventions could potentially influence the course of these altered developmental trajectories, and favorably modify epileptogenesis in malformations of cortical development.

Focal cortical dysplasia links to sleep-related epilepsy in symptomatic focal epilepsy

OBJECTIVE

In sleep-related epilepsy (SRE), epileptic seizures predominantly occur during sleep, but the clinical characteristics of SRE remain elusive. We aimed to identify the clinical features associated with the occurrence of SRE in a large cohort of symptomatic focal epilepsy.

METHODS

We retrospectively included patients with four etiologies, including focal cortical dysplasia (FCD), low-grade tumors (LGT), temporal lobe epilepsy with hippocampal sclerosis (TLE-HS), and encephalomalacia. SRE was defined as more than 70% of seizures occurring during sleep according to the seizure diary. The correlation between SRE and other clinical variables, such as etiology of epilepsy, pharmacoresistance, seizure frequency, history of bilateral tonic-clonic seizures, and seizure localization was analyzed.

RESULTS

A total of 376 patients were included. Among them 95 (25.3%) were classified as SRE and the other 281(74.7%) as non-SRE. The incidence of SRE was 53.5% in the FCD group, which was significantly higher than the other three groups (LGT: 19.0%; TLE-HS: 9.9%; encephalomalacia: 16.7%; P < 0.001). The etiology of FCD (p < 0.001) was significantly associated with SRE (OR: 9.71, 95% CI: 3.35-28.14) as an independent risk factor. In addition, small lesion size (p = 0.009) of FCD further increased the risk of SRE (OR: 3.18, 95% CI: 1.33-7.62) in the FCD group.

SIGNIFICANCE

Our data highlight that FCD markedly increased the risk of sleep-related epilepsy independently of seizure localization. A small lesion of FCD further increased the risk of sleep-related epilepsy by 2.18 times in the FCD group.

Early and Bi-hemispheric seizure onset in a rat glioblastoma Multiforme model

GBM is the most life-threatening neurological disease with annual incidence of ∼ 5 cases per 100,000 people and a median survival of less than 15 months. Seizures are the first clinical symptoms in 40%-45% of patients with GBM and its epileptogenic mechanisms are poorly understood, largely due to the challenge to develop a clinically-relevant animal model and the unknown latent period. In this study, we used continuous video-EEG monitoring to detect the earliest interictal and ictal events in a CRISPR- IUE GBM rat model that shares pathological and clinical features with those observed in human patients. To our best knowledge, we showed for the first time that interictal epileptiform discharges emerged during early postnatal weeks and the first ictal event occurred during the fourth postnatal week. We also showed GBM animals showed independent bi-hemispheric epileptogenic events, suggesting a widespread circuitry dysregulation. Together, our work identified the temporal- and spatial frame of epileptogenic network in a highly clinically-relevant GBM animal model, paving ways for mechanistic studies at molecular, cellular and circuitry levels.