Narrative review of brivaracetam for genetic generalized epilepsies.

BACKGROUND: The licensed treatment options for genetic generalized epilepsies are limited although many patients with these conditions require chronic pharmacological management with antiseizure medications and there are no curative surgical treatment options. Brivaracetam is being studied as a new therapeutic option for genetic generalized epilepsies. METHOD: In order to carry out a narrative review on the efficacy and safety of brivaracetam in genetic generalized epilepsies, a literature research was performed in Pubmed, EMBASE, Cochrane and Clinical Trials.gov databases. RESULTS: Promising results were found with doses ranging from 50 to 200 mg/day in terms of efficacy (with > 50% responder rates between 36 and 84%), tolerability, and short and long-term safety (24-57% drug-associated adverse effects), with most studies reporting adequate retention rates and an absence of serious adverse effects, in monotherapy or as adjuvant therapy, even in refractory epilepsies, special populations and in patients with previous use and/or therapeutic failure with levetiracetam. CONCLUSION: According to our review, brivaracetam is a valid treatment alternative in patients with genetic generalized epilepsies capable of improving patients' quality of life by reducing seizure frequency with minimal adverse effects.

The role of thalamic nuclei in genetic generalized epilepsies.

There is no doubt on the participation of the thalamus in the various types of genetic generalized epilepsies as evidenced by multiple non-invasive imaging studies in humans as well as invasive studies in animal models of GGE. Based on human and mostly animal data gathered in early 2000 a so called 'three compartment model' on seizure generation was proposed conceptualizing the existence of a hyperexcitable cortical seizure onset zone providing excitation to relay cells of the relay thalamus and the inhibitory reticular thalamic nucleus (RTn). The interplay of corticothalamic excitation and feedforward inhibition via RTn is supposed to entrain thalamic relay neurons into synchronous, oscillatory activity for SWD sustainment. With the emergence of more fine-tuned experimental techniques and analyses, however, it becomes apparent that this model is too simplistic as the thalamus cannot be regarded as unity. Rather, different thalamic nuclei, being integrated in different thalamocortical and other subcortical subloops, need to be differentiated, which take over different functions for seizure generation, generalization and maintenance. Moreover, these networks are not necessarily the same for different classes of patients with GGE and can even be antagonistic between seizure types. This review will summarize data concerning different nuclei and their participation in GGE in order to extend this model and create a more detailed concept on seizure generation, generalization and maintenance.

Additional observation of a de novo pathogenic variant in KCNT2 leading to epileptic encephalopathy with clinical features of frontal lobe epilepsy.

INTRODUCTION: KCNT2 was recently recognized as a gene associated with neurodevelopmental disorder and epilepsy. CASE REPORT: We present an additional observation of a 16-year-old male patient with a novel de novo KCNT2 likely pathogenic variant and review the five previously reported cases of de novo variants in this gene. DISCUSSION: Whole exome sequencing identified the missense variant c.725C > A p.(Thr242Asn), which was confirmed by Sanger sequencing. Our patient has a refractory stereotyped and monomorphic type of hyperkinetic focal motor seizure, similar to what is seen in frontal lobe epilepsy, occurring only during sleep. This type of seizure is not usually seen in epileptic encephalopathies.

Clinical features and outcome of Wilson's disease with generalized epilepsy in Chinese patients.

OBJECTIVE: Generalized epilepsy is rarely reported in patients with Wilson disease (WD) and lacks experience in clinical practice. We aim to provide better experience for the diagnosis and treatment for WD patients with epilepsy in the future. METHODS: A retrospective study was performed in 13 Chinese WD patients with generalized epilepsy. Each patient was diagnosed with WD by clinical evaluation and genetic screening. Patients were given small doses of antiepileptic drugs (AEDs), followed by copper-chelation therapy when the seizures stabilized. Clinical manifestations, brain imaging changes, and treatment and outcome after a long-term follow-up were analyzed. RESULTS: Four out of 13 (30.8%) patients stopped taking copper-chelation drugs for more than 1 year before they were admitted for epilepsy. The incidence of epilepsy of WD patients in our cohort is 1.43% (13/910), lower than those (4.5%-5.9%) in other populations. After the attack of epilepsy, frontal lobes were the most common abnormalities (13/13, 100%) in patients, followed by brain stem (8/13, 61.5%) and thalamus (7/13, 53.8%). After a long-term follow-up, brain imaging and clinical manifestations of 8 (8/9, 88.9%) WD patients were significantly improved. CONCLUSIONS: We firstly described WD patients with generalized epilepsy in the Chinese population. WD patients with aggravation of neuropsychiatric symptoms are prone to occur epilepsy; thus, brain MRI should be performed regularly in those patients. Cortical abnormality in brain MRI is a warning sign of epilepsy. Irregular use of copper-chelation drugs and excessive copper deposition in the brain may be the cause of seizures. Long-term standardized treatment for WD can effectively prevent the extensive brain damage and reduce the incidence of epilepsy in WD patients.

Thalamic volume reduction in drug-naive patients with new-onset genetic generalized epilepsy.

OBJECTIVE: Patients with genetic generalized epilepsy (GGE) have subtle morphologic abnormalities of the brain revealed with magnetic resonance imaging (MRI), particularly in the thalamus. However, it is unclear whether morphologic abnormalities of the brain in GGE are a consequence of repeated seizures over the duration of the disease, or are a consequence of treatment with antiepileptic drugs (AEDs), or are independent of these factors. Therefore, we measured brain morphometry in a cohort of AED-naive patients with GGE at disease onset. We hypothesize that drug-naive patients at disease onset have gray matter changes compared to age-matched healthy controls. METHODS: We performed quantitative measures of gray matter volume in the thalamus, putamen, caudate, pallidum, hippocampus, precuneus, prefrontal cortex, precentral cortex, and cingulate in 29 AED-naive patients with new-onset GGE and compared them to 32 age-matched healthy controls. We subsequently compared the shape of any brain structures found to differ in gray matter volume between the groups. RESULTS: The thalamus was the only structure to show reduced gray matter volume in AED-naive patients with new-onset GGE compared to healthy controls. Shape analysis revealed that the thalamus showed deflation, which was not uniformly distributed, but particularly affected a circumferential strip involving anterior, superior, posterior, and inferior regions with sparing of medial and lateral regions. SIGNIFICANCE: Structural abnormalities in the thalamus are present at the initial onset of GGE in AED-naive patients, suggesting that thalamic structural abnormality is an intrinsic feature of GGE and not a consequence of AEDs or disease duration.

Gain-of-function HCN2 variants in genetic epilepsy.

Genetic generalized epilepsy (GGE) is a common epilepsy syndrome that encompasses seizure disorders characterized by spike-and-wave discharges (SWDs). Pacemaker hyperpolarization-activated cyclic nucleotide-gated channels (HCN) are considered integral to SWD genesis, making them an ideal gene candidate for GGE. We identified HCN2 missense variants from a large cohort of 585 GGE patients, recruited by the Epilepsy Phenome-Genome Project (EPGP), and performed functional analysis using two-electrode voltage clamp recordings from Xenopus oocytes. The p.S632W variant was identified in a patient with idiopathic photosensitive occipital epilepsy and segregated in the family. This variant was also independently identified in an unrelated patient with childhood absence seizures from a European cohort of 238 familial GGE cases. The p.V246M variant was identified in a patient with photo-sensitive GGE and his father diagnosed with juvenile myoclonic epilepsy. Functional studies revealed that both p.S632W and p.V246M had an identical functional impact including a depolarizing shift in the voltage dependence of activation that is consistent with a gain-of-function. In contrast, no biophysical changes resulted from the introduction of common population variants, p.E280K and p.A705T, and the p.R756C variant from EPGP that did not segregate with disease. Our data suggest that HCN2 variants can confer susceptibility to GGE via a gain-of-function mechanism.

Triheptanoin reduces seizure susceptibility in a syndrome-specific mouse model of generalized epilepsy.

Triheptanoin is a triglyceride containing heptanoate, an odd-chained medium fatty acid that is metabolized to produce propionyl-CoA and subsequently C4 intermediates of the citric acid cycle and therefore capable of anaplerosis. These metabolic products are believed to underlie triheptanoin's anticonvulsant effects in rodent seizure models. Here we investigate the anticonvulsive effects of oral triheptanoin in a syndrome-specific genetic mouse model of generalized epilepsy based on the GABA(A)γ2(R43Q) mutation. Mice were fed a diet supplemented with triheptanoin from weaning for three weeks prior to electrocortical recordings. Occurrence and durations of spike and wave discharges (SWDs) were measured. Triheptanoin did not alter body weight or basal blood glucose levels suggesting that it was well tolerated. Triheptanoin supplementation halved the time spent in seizures due to a reduction in both SWD occurrence and duration. An injection of insulin was used to reduce blood glucose, a metabolic stress known to precipitate seizures in the GABA(A)γ2(R43Q) mouse. The reduction in seizure count was also evident following insulin induced hypoglycemia with the triheptanoin treated group having significantly less SWDs than control animals under similar low blood glucose conditions. In summary, triheptanoin may be an effective and well tolerated dietary therapy for generalized epilepsy.

New vistas and views in the concept of generalized epilepsies.

The aim of this work is to show explicitly why the "idiopathic generalized epilepsy" concept becomes outfashioned and untenable. As the concept of "generalized epilepsies" is from long ago closely related to the thalamo-cortical system, we briefly summarize the functional anatomy, the double working mode of the thalamo-cortical system in different vigilance states and it's role in development of the spike-wave pattern. The next part shows weaknesses of this concept from the EEG, seizure semiology, and neuroimaging point of view. Further experimental and clinical arguments are accumulated from the reflex epileptic features in IGE, indicating local/regional cortical hyperexcitability. A separate part is devoted to genetic aspects of the question. Lastly implications to epilepsy classification are shown and an outlook toward a unified epilepsy concept is provided. The epileptic disorder of the thalamo-cortical system is responsible for the development of "generalized", synchronous spike-wave paroxysms as the common neurophysiological background in "primary" - idiopathic and in "secondary" generalized epilepsies. This disorder is specifically related to the burstfiring working mode of the thalamo-cortical system during NREM sleep (is an epileptic exageration of it). The "generalized" epilepsy category should be abandoned, being misleading. Epilepsies are proposed to be classified according to their network properties and relations to different physiological systems of the brain. The different phenotypes, named earlier idiopathic (primary) generalized, or symptomatic (secondary) generalized (with encephalopathic features), should be delineated depending on the following factors: 1. speed and extent of syncronization within the thalamo-cortical system, 2. the way how the thalamo-cortical system is involved, 3. which kind of cortical triggers play role, 4. the degree and level of the disorder (restricted to the molecular level or extended to the level of structural alterations - in the cortex or more diffusely, 5. genetic targets and features.

vGLUT2 heterozygous mice show more susceptibility to clonic seizures induced by pentylenetetrazol.

Glutamate, the most abundant excitatory neurotransmitter in the central nervous system, is well known to be implicated in epileptic seizures. Therefore, impairments in glutamate transport could have an involvement in the mechanism of epileptogenesis. The uptake of glutamate into synaptic vesicles is mediated by vesicular glutamate transporters (vGLUTs). There are three known vGLUT isoforms, vGLUT1-3. In this study, we are particularly interested in the vGLUT2 isoform. We investigated the possible role of vGLUT2 in pentylenetetrazol (PTZ)-induced seizure generation. Seizure threshold of PTZ was compared in vGLUT2 heterozygous knock out (HET) and wild type (WT) mice. In comparison with their WT littermates a lower dose of PTZ was needed in the vGLUT2 HET mice until the onset of the first myoclonic jerk. The threshold for PTZ-induced clonic seizure activity was also lower in the vGLUT2 HET mice. These results indicate, for the first time, that vGLUT2 is likely involved in the epileptogenesis of generalized seizures.

Pyridoxine-dependent seizures: a family phenotype that leads to severe cognitive deficits, regardless of treatment regime.

The neuropsychological and clinical histories of three male siblings affected by pyridoxine-dependent seizures with known homozygous antiquitin mutations are presented. Neuropsychological evaluation is reported from when the siblings were 11, 9, and 7 years of age. Two of the siblings had received early pyridoxine treatment (antenatal, 2-4 wks into pregnancy) and one had received late treatment (2mo postnatal). However, there was no differential effect on cognitive outcome, with all three siblings having moderate to severe learning disability. Unlike previously reported cases that received early postnatal treatment, none of the siblings had relatively preserved non-verbal cognitive skills. Equally, their intellectual performance over time did not increase above the 1st centile despite high maintenance doses of vitamin B6 (range 16-26 mg/kg/d), and mild sensory neuropathy was reported on nerve conduction studies. The findings in these siblings challenge assumptions that early and high dose pyridoxine treatment can benefit cognition in this population and suggest routine electromyography monitoring may be beneficial.

Ion channel defects in idiopathic epilepsies.

Idiopathic epilepsies are genetically determined diseases of the central nervous system characterized by typical epileptic seizures and EEG abnormalities but not associated with structural brain lesions. In recent years, an increasing number of mutations associated with idiopathic epilepsy syndromes were identified in genes encoding subunits of voltage- or ligand-gated ion channels. These encouraging results provide a plausible pathophysiological concept, since ion channels form the basis for neuronal excitability and are the major targets for anticonvulsive pharmacotherapy. The first epilepsy genes were identified for rare autosomal dominant syndromes within large pedigrees. Recently, a few mutations were also found for the frequent classical forms of idiopathic generalized epilepsies (IGE), for example absence or juvenile myoclonic epilepsy. The mutations can affect ion channels which on one hand have been known since several decades to be crucial for neuronal function, such as the voltage-gated sodium channel or the GABA(A) receptor, or on the other hand were newly identified within the last decade as KCNQ potassium channels or the ClC-2 chloride channel. Functional studies characterizing the molecular defects of the mutant channels point to a central role of GABAergic synaptic inhibition in the pathophysiology of IGE. Furthermore, newly discovered genes may be suitable as novel targets for pharmacotherapy such as KCNQ channels for the anticonvulsant drug retigabine. Altogether, these genetic and pathophysiological investigations will enhance our knowledge about the understanding of epileptogenesis and can help to improve anticonvulsive therapy.

Effects of Cav3.2 channel mutations linked to idiopathic generalized epilepsy.

Heron and colleagues (Ann Neurol 2004;55:595-596) identified three missense mutations in the Cav3.2 T-type calcium channel gene (CACNA1H) in patients with idiopathic generalized epilepsy. None of the variants were associated with a specific epilepsy phenotype and were not found in patients with juvenile absence epilepsy or childhood absence epilepsy. Here, we introduced and functionally characterized these three mutations using transiently expressed human Cav3.2 channels. Two of the mutations exhibited functional changes that are consistent with increased channel function. Taken together, these findings along with previous reports, strongly implicate CACNA1H as a susceptibility gene in complex idiopathic generalized epilepsy.

Pyridoxine-dependent seizures: magnetic resonance spectroscopy findings.

Pyridoxine-dependent seizures are an extremely rare genetic disorder. Early diagnosis and treatment are important for the prevention of permanent brain damage. Elevated levels of glutamate and decreased levels of gamma-aminobutyric acid (GABA) in the frontal and parietal cortices are among the characteristic features of this disorder. These metabolic abnormalities eventually lead to seizures and neuronal loss. In this case report, we present magnetic resonance spectroscopy findings of a 9-year-old girl with pyridoxine-dependent seizures with mental retardation. The N-acetylaspartate-to-creatine ratio was found to be decreased in the frontal and parieto-occipital cortices, which could indicate neuronal loss. Magnetic resonance spectroscopy could be a useful tool in the neuroimaging evaluation for assessment of parenchymal changes despite a normal-appearing brain magnetic resonance image in patients with pyridoxine-dependent seizures.

Mutations in CLCN2 encoding a voltage-gated chloride channel are associated with idiopathic generalized epilepsies.

Idiopathic generalized epilepsy (IGE) is an inherited neurological disorder affecting about 0.4% of the world's population. Mutations in ten genes causing distinct forms of idiopathic epilepsy have been identified so far, but the genetic basis of many IGE subtypes is still unknown. Here we report a gene associated with the four most common IGE subtypes: childhood and juvenile absence epilepsy (CAE and JAE), juvenile myoclonic epilepsy (JME), and epilepsy with grand mal seizures on awakening (EGMA; ref. 8). We identified three different heterozygous mutations in the chloride-channel gene CLCN2 in three unrelated families with IGE. These mutations result in (i) a premature stop codon (M200fsX231), (ii) an atypical splicing (del74-117) and (iii) a single amino-acid substitution (G715E). All mutations produce functional alterations that provide distinct explanations for their pathogenic phenotypes. M200fsX231 and del74-117 cause a loss of function of ClC-2 channels and are expected to lower the transmembrane chloride gradient essential for GABAergic inhibition. G715E alters voltage-dependent gating, which may cause membrane depolarization and hyperexcitability.

Molecular genetics of human familial epilepsy syndromes.

Genetic defects have been recently identified in certain inherited epilepsy syndromes in which the phenotypes are similar to those of common idiopathic epilepsies. Mutations in the neuronal nicotinic acetylcholine receptor alpha4 and beta2 subunit genes have been detected in families with autosomal dominant nocturnal frontal lobe epilepsy. Both receptors are components of neuronal acetylcholine receptor, a ligand-gated ion channel in the brain. Furthermore, mutations of two K+ channel genes also were identified as the underlying genetic abnormalities of benign familial neonatal convulsions. Mutations in the voltage-gated Na+-channel alpha1 and beta1 subunit genes were found as the cause of generalized epilepsy with febrile seizures plus, a clinical subset of febrile convulsions. Mutation of a voltage-gated K+-channel gene can cause partial seizures associated with periodic ataxia type 1 and some forms of juvenile myoclonic epilepsy can result from mutations of a Ca2+ channel. This line of evidence suggests the involvement of channels expressed in the brain in the pathogenesis of certain types of epilepsy. Our working hypothesis is to view certain idiopathic epilepsies as disorders of ion channels (i.e., "channelopathies"). Such a hypothesis should provide a new insight into our understanding of the genetic background of epilepsy.

Spike-wave discharge and the microstructure of sleep-wake continuum in idiopathic generalised epilepsy.

This review summarises all the evidences about the influence of different vigilance states on the occurrence of spike wave discharge (SWD) in idiopathic generalised epilepsy (IGE) patients. Numerous converging observations showed that full REM-sleep and alert wakefulness exert strong inhibition. A critical zone of vigilance which is a transitional state between waking and non-REM (NREM) sleep, and NREM sleep and REM sleep, has a promoting effect on the absence type spike wave discharge. Spike wave discharges are associated with phasic arousals without awakening and are attached to oscillation son the microstructural level of sleep, perpetuated by cyclic arousal events known as 'cyclic alternating pattern' (CAP), especially within the critical zone, but also along the whole sleep process. More specifically SWD seems to be attached to the 'A-phase' of CAP which is a reactive one and reflects synchronised NREM sleep EEG elements, like K-complexes, spindles and delta groups. The more slow wave elements are found in phase A--like in subtype A1--the more the coincidence with SWD occurs, and the more it is characterised by fast rhythms--as in subtype A2 and A3--the less the association with SWD could be observed. Since subtype A1 is associated with the first sleep cycle and with the descending branches of cycles, it is concluded that SWD appear in those dynamic moments of vigilance level oscillations which were characterised by strong sleep-like answers to arousal influences in high sleep pressure periods of sleep cyclicity. These data harmonize with another line of evidence suggesting that SWD represent the epileptic variant of the complex thalamocortical system function which is the substrate of NREM sleep EEG phenomena. In idiopathic generalised epilepsy there is a growing body of evidence that--as it was assumed by Gloor--spindles transform to SWD pattern. These data explain why those dynamic changes which evoke sleep responses are promoting for the occurrence of SWD. Adapting these data we offer a new interpretation to explain the strong activation effect of sleep deprivation in this kind of epilepsy. We assume that it is mainly due to the forced vigilance level oscillations, especially in morning, when elevated sleep pressure and circadian wake promoting forces, representing opposite tendencies, increase the amount of oscillations.

Ion channels and epilepsy.

Ion channels provide the basis for the regulation of excitability in the central nervous system and in other excitable tissues such as skeletal and heart muscle. Consequently, mutations in ion channel encoding genes are found in a variety of inherited diseases associated with hyper- or hypoexcitability of the affected tissue, the so-called 'channelopathies.' An increasing number of epileptic syndromes belongs to this group of rare disorders: Autosomal dominant nocturnal frontal lobe epilepsy is caused by mutations in a neuronal nicotinic acetylcholine receptor (affected genes: CHRNA4, CHRNB2), benign familial neonatal convulsions by mutations in potassium channels constituting the M-current (KCNQ2, KCNQ3), generalized epilepsy with febrile seizures plus by mutations in subunits of the voltage-gated sodium channel or the GABA(A) receptor (SCN1B, SCN1A, GABRG2), and episodic ataxia type 1-which is associated with epilepsy in a few patients--by mutations within another voltage-gated potassium channel (KCNA1). These rare disorders provide interesting models to study the etiology and pathophysiology of disturbed excitability in molecular detail. On the basis of genetic and electrophysiologic studies of the channelopathies, novel therapeutic strategies can be developed, as has been shown recently for the antiepileptic drug retigabine activating neuronal KCNQ potassium channels.