Mice harboring the T316N variant in the GABAAR γ2 subunit exhibit sleep-related hypermotor epilepsy phenotypes and hypersynchronization in the thalamocortical pathway

OBJECTIVE

Sleep-related hypermotor epilepsy (SHE) is a focal epilepsy syndrome characterized by seizures that predominantly occur during sleep. The pathogenesis of these seizures remains unclear. We previously detected rare variants in GABRG2, which encodes the γ2 subunit of γ-aminobutyric acid type A receptor (GABAAR), in patients with SHE and demonstrated that these variants impaired GABAAR function in vitro. However, the mechanisms by which GABRG2 variants contribute to seizure attacks during sleep remain unclear.

METHODS

In this study, we designed a knock-in (KI) mouse expressing the mouse Gabrg2 T316N variant, corresponding to human GABRG2 T317N variant, using CRISPR/Cas9. Continuous video-electroencephalogram monitoring and in vivo multichannel electrophysiological recordings were performed to explore seizure susceptibility to pentylenetetrazol (PTZ), alterations in the sleep-wake cycle, spontaneous seizure patterns, and synchronized activity in the motor thalamic nuclei (MoTN) and secondary motor cortex (M2). Circadian variations in the expression of total, membrane-bound, and synaptic GABAAR subunits were also investigated.

RESULTS

No obvious changes in gross morphology were detected in Gabrg2T316N/+ mice compared to their wild-type (Gabrg2+/+) littermates. Gabrg2T316N/+ mice share key phenotypes with patients, including sleep fragmentation and spontaneous seizures during sleep. Gabrg2T316N/+ mice showed increased susceptibility to PTZ-induced seizures and higher mortality after seizures. Synchronization of the local field potentials between the MoTN and M2 was abnormally enhanced in Gabrg2T316N/+ mice during light phase, when sleep dominates, accompanied by increased local activities in the MoTN and M2. Interestingly, in Gabrg2+/+ mice, GABAAR γ2 subunits showed a circadian increase on the neuronal membrane and synaptosomes in the transition from dark phase to light phase, which was absent in Gabrg2T316N/+ mice.

CONCLUSION

We generated a new SHE mouse model and provided in vivo evidence that rare variants of GABRG2 contribute to seizure attacks during sleep in SHE.

Epilepsy surgery outcomes in patients with GATOR1 gene complex variants: Report of new cases and review of literature

AIM

To report seizure outcomes in children with GATOR1 gene complex disorders who underwent epilepsy surgery and perform a systematic literature search to study the available evidence.

METHODS

The records of children with pathogenic/likely pathogenic variants in GATOR1 gene complex who underwent epilepsy surgery were reviewed. Clinical, radiological, neurophysiological, and histological data were extracted/summarized. The systematic review included all case series/reports and observational studies reporting on children or adults with genetic (germline or somatic) variants in the GATOR1 complex genes (DEPDC5, NPRL2, NPRL3) with focal epilepsy with/without focal cortical dysplasia who underwent epilepsy surgery; seizure outcomes were analyzed.

RESULTS

Eight children with pathogenic/likely pathogenic variants in GATOR1 complex genes were included. All had drug-resistant epilepsy. Six children had significant neurodevelopmental delay. Epilepsy surgery was performed in all; clinical seizure freedom was noted in 4 children (50%). Systematic literature search identified 17 eligible articles; additional 30 cases with patient-level data were studied. Lesional MRI brain was seen in 80% cases. The pooled rate of seizure freedom following surgery was 60%; FCD IIa was the most encountered pathology.

INTERPRETATION

Epilepsy surgery may be effective in some children with GATOR1 complex gene variants. Seizure outcomes may be compromised by extensive epileptogenic zones.

Nicotinic acetylcholine receptors and epilepsy

Despite recent advances in understanding the causes of epilepsy, especially the genetic, comprehending the biological mechanisms that lead to the epileptic phenotype remains difficult. A paradigmatic case is constituted by the epilepsies caused by altered neuronal nicotinic acetylcholine receptors (nAChRs), which exert complex physiological functions in mature as well as developing brain. The ascending cholinergic projections exert potent control of forebrain excitability, and wide evidence implicates nAChR dysregulation as both cause and effect of epileptiform activity. First, tonic-clonic seizures are triggered by administration of high doses of nicotinic agonists, whereas non-convulsive doses have kindling effects. Second, sleep-related epilepsy can be caused by mutations on genes encoding nAChR subunits widely expressed in the forebrain (CHRNA4, CHRNB2, CHRNA2). Third, in animal models of acquired epilepsy, complex time-dependent alterations in cholinergic innervation are observed following repeated seizures. Heteromeric nAChRs are central players in epileptogenesis. Evidence is wide for autosomal dominant sleep-related hypermotor epilepsy (ADSHE). Studies of ADSHE-linked nAChR subunits in expression systems suggest that the epileptogenic process is promoted by overactive receptors. Investigation in animal models of ADSHE indicates that expression of mutant nAChRs can lead to lifelong hyperexcitability by altering i) the function of GABAergic populations in the mature neocortex and thalamus, ii) synaptic architecture during synaptogenesis. Understanding the balance of the epileptogenic effects in adult and developing networks is essential to plan rational therapy at different ages. Combining this knowledge with a deeper understanding of the functional and pharmacological properties of individual mutations will advance precision and personalized medicine in nAChR-dependent epilepsy.

Rare variants in GABRG2 associated with sleep-related hypermotor epilepsy

Sleep-related hypermotor epilepsy (SHE) is a focal epilepsy syndrome. The underlying pathophysiology is presumed to be closely related with disruption of GABAergic neurotransmission, which is mainly medicated by γ-aminobutyric acid type A receptor (GABA_AR). Thus, it is reasonable to assume that rare GABA_AR variants might contribute to the pathogenesis of SHE. To test this hypothesis, we performed next-generation sequencing in 58 SHE patients and analyzed the functional effects of the identified variants in both neuronal and non-neuronal cells using a combination of electrophysiology recordings, western blot, flow cytometry, and confocal microscopy. In our study, we detected three rare variants (NM_198904.2: c.269C > T, p.T90M; NM_198904.2: c.950C > A, p.T317N and NM_198903.2: c.649C > T, p.Q217X) in GABRG2 (MIM:137,164, encoding GABA_AR γ₂ subunit) in three unrelated patients. Two of the three rare variants were transmitted unaffected maternally (T90M) or unaffected paternally (Q217X), whereas the T317N variant arose de novo. The mother of proband carrying the T90M variant was unaffected and being mosaicism for this variant. Functional analysis showed that T90M and T317N variants decreased GABA-evoked current amplitudes by diverse mechanisms including impaired surface expression, endoplasmic reticulum retention, and channel gating defects. And Q217X variant reduced synaptic clustering and distribution of GABA_AR. While a causal role of these variants cannot be established directly from these results, the functional assessment together with the genetic sequencing suggests that these rare GABRG2 variants may constitute genetic risk factors for SHE. Our study further expands the GABRG2 phenotypic spectrum and supports the view that GABAergic neurotransmission participates in the epileptogenesis of SHE.

Sleep and Epilepsy, Clinical Spectrum and Updated Review

Electroencephalogram (EEG) recording is essential in the evaluation of complex movement and behaviors during sleep, but in particular for differentiating epileptic versus nonepileptic events. In general, epileptiform discharges occur with greater density in the first few nonerapid eye movement cycles, and approximately 12% to 20% of seizures occur exclusively at night. This review examines the epilepsy types and syndromes whose presentation is strongly influenced by the sleep state, with an appraisal about the role that sleep plays in facilitating seizures, while deleaneatign EEG findings and clinical manifestation. The review will summarize the typical semiology of sleep-related hypermotor seizures and contrasted with those occurring during none/rapid eye movement parasomnias and sleep-related movement disorders.

Seizure worsening in pregnancy in women with sleep-related hypermotor epilepsy (SHE): A historical cohort study

INTRODUCTION

Data on seizure course during pregnancy in women with epilepsy are limited. In particular, little is known about the causes underlying possible seizure worsening in this population. We therefore set out to explore worsening, in pregnancy, of sleep-related hypermotor epilepsy (SHE), a syndrome in which seizures are known to be triggered by sleep fragmentation, a condition common in pregnancy.

METHODS

From a cohort of consecutive patients with epilepsy who had one or more deliveries between January 2008 and March 2018, we retrospectively compared the rates of seizure worsening during pregnancy in SHE versus other epilepsies (NSHE). Worsening was defined as an increase in seizure frequency compared with the rate for the year prior to conception, including seizure recurrence after a year of seizure freedom, and/or new occurrence of tonic-clonic seizures.

RESULTS

We considered data on 11 pregnancies in women with SHE and 104 pregnancies in women with NSHE. Seizures worsened in six SHE pregnancies (54.5%) versus 18 NSHE ones (17.3%) (OR adjusted for preconception seizure frequency and polytherapy = 5.7, 95% CI = 1.6-20.8, p = 0.019).

CONCLUSIONS

Women with SHE have a higher risk of seizure worsening in pregnancy. This finding should be considered from the perspective of patient counseling.

Treatment of pharmacoresistant sleep-related hypermotor epilepsy (SHE) with the selective AMPA receptor antagonist perampanel

This study aimed to evaluate the efficacy and tolerability of perampanel (PER) as adjunctive therapy in patients with pharmacoresistant sleep-related hypermotor epilepsy (SHE). Patients diagnosed with SHE who received PER treatment between 2016 and 2019 were included, and their data were reviewed retrospectively. Diagnosis was based on reports of patients or family members witnessing the events and clinical characteristics of seizures captured by video or during video-electroencephalography monitoring. Among 36 SHE patients, 20 with pharmacoresistant SHE (six female; mean age: 34.1 ± 9.0 years) who received PER as adjunctive therapy were included in this study. Fourteen out of the 20 patients received PER with mean length of PER exposure of 24.6 ± 15.7 months: 10 of them were responders and four non-responders. The remaining six patients discontinued PER for adverse events (n = 5) and patient choice (n = 1). Among the 10 responders, six (60%) reported seizure-free periods lasting ≥6 months. The most common PER-associated adverse event was dizziness (25%) followed by malaise (10%). Clinical experience with these patients demonstrated that PER might be considered as an add-on anti-seizure medication for patients with highly pharmacoresistant SHE.

The Arousal Disorders Questionnaire: a new and effective screening tool for confusional arousals, Sleepwalking and Sleep Terrors in epilepsy and sleep disorders units

BACKGROUND

Arousal Disorders (DoA) include Confusional Arousals, Sleepwalking and Sleep Terrors. DoA diagnosis is mainly clinical but no validated questionnaires exist for DoA screening according to the criteria of the International Classification of Sleep Disorders, Third Edition. Recently our group proposed the Arousal Disorders Questionnaire (ADQ) as a new diagnostic tool for DoA diagnosis. The objective of this study was to evaluate the diagnostic accuracy of the ADQ in a sleep and epilepsy center.

METHODS

One interviewer blinded to clinical and video-polysomnographic (VPSG) data administered the ADQ to 150 patients consecutively admitted to our Sleep and Epilepsy Centers for a follow-up visit. The final diagnosis, according to VPSG recordings of at least one major episode, classified patients either with DoA (DoA group) or with other sleep-related motor behaviors confounding for DoA (nDoA group).

RESULTS

47 patients (31%) composed the DoA group; 56 patients with REM sleep behavior disorder, 39 with sleep-hypermotor epilepsy, six with night eating syndrome, and two with drug-induced DoA composed the nDoA group. The ADQ had a sensitivity of 72% (95% CI: 60-82) and a specificity of 96% (95% CI: 89-98) for DoA diagnosis; excluding the items regarding consciousness and episode recall, sensitivity was 83% (95% CI: 71-90) and specificity 93% (95% CI: 86-97).

CONCLUSIONS

The ADQ showed good accuracy in screening patients with DoA in a sleep and epilepsy center setting. Diagnostic criteria related to cognition and episode recall reduced ADQ sensitivity, therefore a better definition of these criteria is required, especially in adults.

[Advances in sleep-related hypermotor epilepsy]

Sleep-related hypermotor epilepsy (SHE), formerly known as nocturnal frontal epilepsy, is characterized by asymmetrical tonic or complex hypermotor seizures during sleep, with transient, frequent and clustering attack. The accurate incidence is not known but somehow low, which is estimated about 1.8/100 000. The differential diagnosis between SHE and parasomnias may be challenging due to possible similarities between the two sleep-related manifestations. In a majority of patients, the etiology is unknown. Identified etiologies are heterogeneous and structural abnormalities,which are involved in the severity and prognosis of SHE. In terms of treatment, it mainly includes pharmacological therapy and surgery. Carbamazepine seems to be the drug of choice in SHE patients, and epilepsy surgery provides excellent results in selected drug-resistant SHE cases. This review will focus on diagnosis, pathogenesis, treatment and prognosis of SHE, aiming to promote its early diagnosis and appropriate treatment.

Sleep-related hypermotor epilepsy (SHE): Contribution of known genes in 103 patients

PURPOSE

Genetics of Sleep-related Hypermotor Epilepsy (SHE) includes mutations in several genes that cumulatively account for 30 % of families. This approximate estimate comes from different case-series, each focused on the screening of a single gene. We systematically investigated a large cohort of SHE patients to estimate the frequency of pathogenic variants in the main genes thus far implicated in this epilepsy syndrome.

METHODS

We selected familial and isolated cases diagnosed with clinical/confirmed SHE who underwent genetic analysis by comparable next generation sequencing (NGS) techniques (WES/ multigene epilepsy panel). The identified heterozygous variants were classified according to the American College of Medical Genetics and Genomics guidelines.

RESULTS

We included 103 SHE patients (M/F:61/42) who underwent NGS. Sixteen (15.5 %) were familial cases, 16.5 % had focal cortical dysplasia (FCD). We identified three pathogenic variants in CHRNA4 (2.9 %, CI: 0.6-8.3 %), two of whom novel; one pathogenic variant in KCNT1 (1 %, CI: 0.02-5.29 %); four loss-of-function variants in DEPDC5 (3.9 %, CI: 1.1-9.7 %), one of whom never reported; finally, one missense change in NPRL2 (1 %, CI: 0.02-5.29 %), already reported as pathogenic. Three out of the four patients with DEPDC5 variants had FCD.

CONCLUSIONS

The overall frequency of pathogenic variants in our SHE cohort was 8.7 %, 19 % and 7 % considering familial and sporadic cases, respectively. Pathogenic variants in the GATOR1-complex genes account for 5 % of the cases. DEPDC5 shows the highest variants frequency, especially in patients with genetic-structural etiology. From a practical perspective, analysis of this gene is recommended even in isolated cases, because of possible implications for patient management.

Brain functional connectivity in sleep-related hypermotor epilepsy

Objectives

To evaluate functional connectivity (FC) in patients with sleep-related hypermotor epilepsy (SHE) compared to healthy controls.

Methods

Resting state fMRI was performed in 13 patients with a clinical diagnosis of SHE (age = 38.3 ± 11.8 years, 6 M) and 13 matched healthy controls (age = 38.5 ± 10.8 years, 6 M).

Data were first analysed using probabilistic independent component analysis (ICA), then a graph theoretical approach was applied to assess topological and organizational properties at the whole brain level. We evaluated node degree (ND), betweenness centrality (BC), clustering coefficient (CC), local efficiency (LE) and global efficiency (GE). The differences between the two groups were evaluated non-parametrically.

Results

At the group level, we distinguished 16 RSNs (Resting State Networks). Patients showed a significantly higher FC in sensorimotor and thalamic regions (p < 0.05 corrected). Compared to controls, SHE patients showed no significant differences in network global efficiency, while ND and BC were higher in regions of the limbic system and lower in the occipital cortex, while CC and LE were higher in regions of basal ganglia and lower in limbic areas (p < 0.05 uncorrected).

Discussion and conclusions

The higher FC of the sensorimotor cortex and thalamus might be in agreement with the hypothesis of a peculiar excitability of the motor cortex during thalamic K-complexes. This sensorimotor-thalamic hyperconnection might be regarded as a consequence of an alteration of the arousal regulatory system in SHE. An altered topology has been found in structures like basal ganglia and limbic system, hypothesized to be involved in the pathophysiology of the disease as suggested by the dystonic-dyskinetic features and primitive behaviours observed during the seizures.

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Resting state functional connectivity was studied for the first time in SHE.

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SHE patients showed higher connectivity in thalamic and motor regions.

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Motor cortex might show a higher excitability in response to thalamic projections.

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Brain network topology was altered mainly in basal ganglia and limbic system.