Nocturnal Frontal Lobe Epilepsy: New pathophysiological interpretations

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.

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.

Epilepsy in ring chromosome 20 syndrome

OBJECTIVE

Ring chromosome 20 syndrome is characterized by severe, drug resistant childhood onset epilepsy, often accompanied by cognitive impairment. We characterized the electro-clinical phenotype and the long-term course of epilepsy in a large series.

METHODS

We reviewed the electro-clinical phenotype of 25 patients (aged 8-59 years), and assessed the relationship between epilepsy severity and clinical and/or genetic variables. We also searched for reports of patients diagnosed with r(20) syndrome in the literature, included those whose clinical information was sufficiently accurate, and compared their clinical features with the ones of our patients.

RESULTS

Epilepsy exhibited an age dependent course. When seizure onset occurred in childhood (21 patients), terrifying hallucinations associated with focal motor seizures, often sleep-related (8 patients), or dyscognitive seizures (13 patients), were prominent features, often evolving into epileptic encephalopathy associated with non-convulsive status epilepticus (11 patients). In the long-term, progressive stabilization of drug resistant epilepsy associated with non-convulsive status epilepticus, focal seizures with motor and autonomic features, and eyelid myoclonia were noticed. Epilepsy onset in adolescence (3 patients) was accompanied by a milder developmental course, dyscognitive seizures and non-convulsive status epilepticus, and no cognitive decline. Only three older patients became seizure free (>5 years) We found statistically significant correlations between age at epilepsy onset and cognitive level. Although in the study cohort the relationship between r(20) ratio, age at epilepsy onset and cognitive level was non-statistically significant, it reached significance evaluating the larger cohort of patients previously published.

SIGNIFICANCE

In ring(20) syndrome, epilepsy has an age dependent course and a worse outcome when age at seizure onset is earlier. The r(20) ratio and severity of cognitive impairment appear to be directly related to each other and inversely correlated with the age at epilepsy onset.

The cooccurrence of interictal discharges and seizures in pediatric sleep-disordered breathing

Studies in the literature data have shown that the prevalence of obstructive sleep apnea (OSA) in children with epilepsy is high and that treatment for OSA leads to a reduction in the number of seizures; by contrast, few studies have demonstrated an increased prevalence of interictal epileptiform discharges (IEDs) or epilepsy in children with sleep-disordered breathing (SDB). The aim of the present study was to confirm the high prevalence of IEDs or epilepsy in a large sample of children with SDB and to collect follow-up data. Children were recruited prospectively and underwent their first video-polysomnography (video-PSG) for SDB in a teaching hospital sleep center. Of the 298 children who fulfilled the diagnostic criteria for sleep-disordered breathing, 48 (16.1%) children were found to have IEDs, three of these 48 children were also found to have nocturnal seizures (two females diagnosed with rolandic epilepsy and a male diagnosed with frontal lobe epilepsy). Only 11 subjects underwent a second video-PSG after 6months; at the second video-PSG, the IEDs had disappeared in six subjects, who also displayed a reduced AHI and an increased mean overnight saturation. Thirty-eight of the 250 children without IEDs underwent a second video-PSG after 6months. Of these 250 children, four, who did not display any improvement in the respiratory parameters and were found to experience numerous stereotyped movements during sleep, were diagnosed with nocturnal frontal lobe epilepsy. Our study confirms the high prevalence of IEDs in children with SDB. Follow-up data indicate that they may recede over time, accompanied by an improvement of sleep respiratory parameters.

Childhood parasomnia--a disorder of sleep maturation?

BACKGROUND

Childhood parasomnias are believed to be a benign disorder due to immaturity of some neural circuits, synapses and receptors. The aim of our study was to explore a possible connection with other neurological developmental disorders.

METHODS

72 children (mean age 9.9 ± 5.0 years, 47 boys) were clinically examined and 88 nocturnal v-PSG and 22 v-EEG recordings were evaluated. The most frequent diagnostic findings were: sleepwalking in 24 children, confusional arousal in 21, sleep terror in 8, groaning and enuresis each in 7, non-specific arousal disorder in 4 patients, and REM-related parasomnia in only one child. For statistical evaluation chi-square test, the two-sample t-test and Mann-Whitney rank test were used.

RESULTS

Perinatal risk history was found in 38% of the cohort. Developmental disorders were diagnosed in 30 children (41.7%), more frequently in combinations with: attention-hyperactivity disorder (30.6%), dyslexia and dysgraphia (13.9%), developmental dysphasia (9.7%), mild motor and/or intellectual dysfunction (6.9%). Abnormal movements in sleep, some of them also regarded as developmental, were diagnosed in 37 children (51.4%). Sleep-related breathing disorders were found in 29 patients (40.3%) -snoring (29.2%) and/or sleep apnea (11.1%). Only 16.7% had no comorbidity. Most of the children (60%) showed 2 or 3, exceptionally up to 5 comorbidities. Children, in whom no parasomnia was found in close relatives, had a mild but non-significant earlier onset of the disease (4.4 ± 4.0 against 6.3 ± 4.3 years).

CONCLUSION

Childhood parasomnias are frequently associated with perinatal risk factors and developmental comorbidities, and can be regarded as a disorder of sleep maturation.

Sleep and epilepsy

The intimate relationship between sleep and epilepsy has long been recognized, yet our understanding of the relationship is incomplete. In this article we address four key issues in this area. First, we consider the reciprocal interaction between sleep and epilepsy. Sleep state clearly influences seizure onset, particularly in certain epilepsy syndromes. The converse is also true; epilepsy may disrupt sleep, either directly through seizures and epileptiform activity, or indirectly through medication-related effects. Unraveling the influences of sleep stage, epilepsy syndrome, and drug effects is challenging, and the current state of knowledge is reviewed. Secondly, accurate diagnosis of sleep-related epilepsy can be difficult, particularly the distinction of nocturnal frontal lobe epilepsy (NFLE) from arousal parasomnias. The challenges in this area, along with work from the authors, are discussed. Thirdly, we will explore the putative relationship between obstructive sleep apnea (OSA) and epilepsy, including the effect of OSA on quality of life; this will lead us to a brief exploration of the effects of OSA on neuroendocrine function. Finally, we will review the evidence surrounding the role of sleep in sudden unexpected death in epilepsy (SUDEP).

Neuronal nicotinic receptors in sleep-related epilepsy: studies in integrative biology

Although Mendelian diseases are rare, when considered one by one, overall they constitute a significant social burden. Besides the medical aspects, they propose us one of the most general biological problems. Given the simplest physiological perturbation of an organism, that is, a single gene mutation, how do its effects percolate through the hierarchical biological levels to determine the pathogenesis? And how robust is the physiological system to this perturbation? To solve these problems, the study of genetic epilepsies caused by mutant ion channels presents special advantages, as it can exploit the full range of modern experimental methods. These allow to extend the functional analysis from single channels to whole brains. An instructive example is autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), which can be caused by mutations in neuronal nicotinic acetylcholine receptors. In vitro, such mutations often produce hyperfunctional receptors, at least in heterozygous condition. However, understanding how this leads to sleep-related frontal epilepsy is all but straightforward. Several available animal models are helping us to determine the effects of ADNFLE mutations on the mammalian brain. Because of the complexity of the cholinergic regulation in both developing and mature brains, several pathogenic mechanisms are possible, which also present different therapeutic implications.