Genetic epilepsy syndromes without structural brain abnormalities: clinical features and experimental models

Clinical description and evaluation of 30 pediatric patients with ultra-rare diseases: A multicenter study with real-world data from Saudi Arabia

BACKGROUND

With the advancement of next-generation sequencing, clinicians are now able to detect ultra-rare mutations that are barely encountered by the majority of physicians. Ultra-rare and rare diseases cumulatively acquire a prevalence equivalent to type 2 diabetes with 80% being genetic in origin and more prevalent among high consanguinity communities including Saudi Arabia. The challenge of these diseases is the ability to predict their prevalence and define clear phenotypic features.

METHODS

This is a non-interventional retrospective multicenter study. We included pediatric patients with a pathogenic variant designated as ultra-rare according to the National Institute for Clinical Excellence's criteria. Demographic, clinical, laboratory, and radiological data of all patients were collected and analyzed using multinomial regression models.

RESULTS

We included 30 patients. Their mean age of diagnosis was 16.77 months (range 3-96 months) and their current age was 8.83 years (range = 2-15 years). Eleven patients were females and 19 were males. The majority were of Arab ethnicity (96.77%). Twelve patients were West-Saudis and 8 patients were South-Saudis. SCN1A mutation was reported among 19 patients. Other mutations included SZT2, ROGDI, PRF1, ATP1A3, and SHANK3. The heterozygous mutation was reported among 67.86%. Twenty-nine patients experienced seizures with GTC being the most frequently reported semiology. The mean response to ASMs was 45.50% (range 0-100%).

CONCLUSION

The results suggest that ultra-rare diseases must be viewed as a distinct category from rare diseases with potential demographic and clinical hallmarks. Additional objective and descriptive criteria to detect such cases are needed.

Nanotechnology-based Nose-to-brain Delivery in Epilepsy: A NovelApproach to Diagnosis and Treatment

Epilepsy is a serious neurological disease, and scientists have a significant challenge in developing a noninvasive treatment for the treatment of epilepsy. The goal is to provide novel ideas for improving existing and future anti-epileptic medications. The injection of nano treatment via the nose to the brain is being considered as a possible seizure control method. Various nasal medicine nanoformulations have the potential to cure epilepsy. Investigations with a variety of nose-to-brain dosing methods for epilepsy treatment have yielded promising results. After examining global literature on nanotechnology and studies, the authors propose nasal administration with nanoformulations as a means to successfully treat epilepsy. The goal of this review is to look at the innovative application of nanomedicine for epilepsy treatment via nose-to-brain transfer, with a focus on the use of nanoparticles for load medicines. When nanotechnology is combined with the nose to brain approach, treatment efficacy can be improved through site specific delivery. Furthermore, this technique of administration decreases adverse effects and patient noncompliance encountered with more traditional procedures.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Generation of a human iPSC line CIPi001-A from a benign familial infantile epilepsy patient related 16p11.2 deletion

The features of 16p11.2 deletion phenotype is developmental delay, intellectual disability, and autism spectrum disorder. Seizures are observed in approximately 20% of individuals with the microdeletion. Induced pluripotent stem cells (iPSCs) were generated from erythroblasts obtained from a child diagnosed with benign familial infantile epilepsy, caused by 16p11.2 deletion. These iPSCs exhibited stable amplification, expressed pluripotent markers, and differentiated spontaneously into three germ layers in vitro.

Mechanisms of microRNA‑142 in mitochondrial autophagy and hippocampal damage in a rat model of epilepsy

Researchers have confirmed the microRNA (miRNA/miR)‑epilepsy association in rodent models of human epilepsy via a comprehensive database. However, the mechanisms of miR‑142 in epilepsy have not been extensively studied. In the present study, a rat model of epilepsy was first established by an injection of lithium chloride‑pilocarpine and the successful establishment of the model was verified via electroencephalogram monitoring. The levels of miR‑142, phosphatase and tensin homolog deleted on chromosome 10 (PTEN)‑induced putative kinase 1 (PINK1), marker proteins of mitochondrial autophagy, and apoptosis‑related proteins were measured. Additionally, the pathological changes in the hippocampus, the ultrastructure of the mitochondria, and degeneration and the apoptosis of neurons were observed using different staining methods. The malondialdehyde (MDA) content and superoxide dismutase (SOD) activity in the hippocampus, mitochondrial membrane potential (MTP) and reactive oxygen species (ROS) generation were detected. Furthermore, the targeting association between miR‑142 and PINK1 was predicted and verified. Consequently, apoptosis increased, and mitochondrial autophagy decreased, in the hippocampus of epileptic rats. Following miR‑142 inhibition, the epileptic rats exhibited an increased Bax expression, a decreased Bcl‑2 expression, upregulated marker protein levels of mitochondrial autophagy, a reduced MDA content, an enhanced SOD activity, an increased MTP and decreased ROS generation. PINK1 is a target gene of miR‑142, and its overexpression protected against hippocampal damage. Taken together, the results of the present study demonstrated that miR‑142 inhibition promotes mitochondrial autophagy and reduces hippocampal damage in epileptic rats by targeting PINK1. These findings may provide useful information for the treatment of epilepsy.

Sodium channelopathies of skeletal muscle and brain

Voltage-gated sodium channels initiate action potentials in nerve, skeletal muscle, and other electrically excitable cells. Mutations in them cause a wide range of diseases. These channelopathy mutations affect every aspect of sodium channel function, including voltage sensing, voltage-dependent activation, ion conductance, fast and slow inactivation, and both biosynthesis and assembly. Mutations that cause different forms of periodic paralysis in skeletal muscle were discovered first and have provided a template for understanding structure, function, and pathophysiology at the molecular level. More recent work has revealed multiple sodium channelopathies in the brain. Here we review the well-characterized genetics and pathophysiology of the periodic paralyses of skeletal muscle and then use this information as a foundation for advancing our understanding of mutations in the structurally homologous α-subunits of brain sodium channels that cause epilepsy, migraine, autism, and related comorbidities. We include studies based on molecular and structural biology, cell biology and physiology, pharmacology, and mouse genetics. Our review reveals unexpected connections among these different types of sodium channelopathies.

Venom-derived modulators of epilepsy-related ion channels

Epilepsy is characterised by spontaneous recurrent seizures that are caused by an imbalance between neuronal excitability and inhibition. Since ion channels play fundamental roles in the generation and propagation of action potentials as well as neurotransmitter release at a subset of excitatory and inhibitory synapses, their dysfunction has been linked to a wide variety of epilepsies. Indeed, these unique proteins are the major biological targets for antiepileptic drugs. Selective targeting of a specific ion channel subtype remains challenging for small molecules, due to the high level of homology among members of the same channel family. As a consequence, there is a growing trend to target ion channels with biologics. Venoms are the best known natural source of ion channel modulators, and venom peptides are increasingly recognised as potential therapeutics due to their high selectivity and potency gained through millions of years of evolutionary selection pressure. Here we describe the major ion channel families involved in the pathogenesis of various types of epilepsy, including voltage-gated Na⁺, K⁺, Ca²⁺ channels, Cys-loop receptors, ionotropic glutamate receptors and P2X receptors, and currently available venom-derived peptides that target these channel proteins. Although only a small number of venom peptides have successfully progressed to the clinic, there is reason to be optimistic about their development as antiepileptic drugs, notwithstanding the challenges associated with development of any class of peptide drug.

SCN1A/NaV 1.1 channelopathies: Mechanisms in expression systems, animal models, and human iPSC models

Pathogenic SCN1A/Na_V 1.1 mutations cause well-defined epilepsies, including genetic epilepsy with febrile seizures plus (GEFS+) and the severe epileptic encephalopathy Dravet syndrome. In addition, they cause a severe form of migraine with aura, familial hemiplegic migraine. Moreover, SCN1A/Na_V 1.1 variants have been inferred as risk factors in other types of epilepsy. We review here the advancements obtained studying pathologic mechanisms of SCN1A/Na_V 1.1 mutations with experimental systems. We present results gained with in vitro expression systems, gene-targeted animal models, and the induced pluripotent stem cell (iPSC) technology, highlighting advantages, limits, and pitfalls for each of these systems. Overall, the results obtained in the last two decades confirm that the initial pathologic mechanism of epileptogenic SCN1A/Na_V 1.1 mutations is loss-of-function of Na_V 1.1 leading to hypoexcitability of at least some types of γ-aminobutyric acid (GABA)ergic neurons (including cortical and hippocampal parvalbumin-positive and somatostatin-positive ones). Conversely, more limited results point to Na_V 1.1 gain-of-function for familial hemiplegic migraine (FHM) mutations. Behind these relatively simple pathologic mechanisms, an unexpected complexity has been observed, in part generated by technical issues in experimental studies and in part related to intrinsically complex pathophysiologic responses and remodeling, which yet remain to be fully disentangled.

Analysis of gene variants in the GASH/Sal model of epilepsy

Epilepsy is a complex neurological disorder characterized by sudden and recurrent seizures, which are caused by various factors, including genetic abnormalities. Several animal models of epilepsy mimic the different symptoms of this disorder. In particular, the genetic audiogenic seizure hamster from Salamanca (GASH/Sal) animals exhibit sound-induced seizures similar to the generalized tonic seizures observed in epileptic patients. However, the genetic alterations underlying the audiogenic seizure susceptibility of the GASH/Sal model remain unknown. In addition, gene variations in the GASH/Sal might have a close resemblance with those described in humans with epilepsy, which is a prerequisite for any new preclinical studies that target genetic abnormalities. Here, we performed whole exome sequencing (WES) in GASH/Sal animals and their corresponding controls to identify and characterize the mutational landscape of the GASH/Sal strain. After filtering the results, moderate- and high-impact variants were validated by Sanger sequencing, assessing the possible impact of the mutations by “in silico” reconstruction of the encoded proteins and analyzing their corresponding biological pathways. Lastly, we quantified gene expression levels by RT-qPCR. In the GASH/Sal model, WES showed the presence of 342 variations, in which 21 were classified as high-impact mutations. After a full bioinformatics analysis to highlight the high quality and reliable variants, the presence of 3 high-impact and 15 moderate-impact variants were identified. Gene expression analysis of the high-impact variants of Asb14 (ankyrin repeat and SOCS Box Containing 14), Msh3 (MutS Homolog 3) and Arhgef38 (Rho Guanine Nucleotide Exchange Factor 38) genes showed a higher expression in the GASH/Sal than in control hamsters. In silico analysis of the functional consequences indicated that those mutations in the three encoded proteins would have severe functional alterations. By functional analysis of the variants, we detected 44 significantly enriched pathways, including the glutamatergic synapse pathway. The data show three high-impact mutations with a major impact on the function of the proteins encoded by these genes, although no mutation in these three genes has been associated with some type of epilepsy until now. Furthermore, GASH/Sal animals also showed gene variants associated with different types of epilepsy that has been extensively documented, as well as mutations in other genes that encode proteins with functions related to neuronal excitability, which could be implied in the phenotype of the GASH/Sal. Our findings provide valuable genetic and biological pathway data associated to the genetic burden of the audiogenic seizure susceptibility and reinforce the need to validate the role of each key mutation in the phenotype of the GASH/Sal model.

Modeling cortical spreading depression induced by the hyperactivity of interneurons

Cortical spreading depression (CSD) is a wave of transient intense neuronal firing leading to a long lasting depolarizing block of neuronal activity. It is a proposed pathological mechanism of migraine with aura. Some forms of migraine are associated with a genetic mutation of the Na_v1.1 channel, resulting in its gain of function and implying hyperexcitability of interneurons. This leads to the counterintuitive hypothesis that intense firing of interneurons can cause CSD ignition. To test this hypothesis in silico, we developed a computational model of an E-I pair (a pyramidal cell and an interneuron), in which the coupling between the cells in not just synaptic, but takes into account also the effects of the accumulation of extracellular potassium caused by the activity of the neurons and of the synapses. In the context of this model, we show that the intense firing of the interneuron can lead to CSD. We have investigated the effect of various biophysical parameters on the transition to CSD, including the levels of glutamate or GABA, frequency of the interneuron firing and the efficacy of the KCC2 co-transporter. The key element for CSD ignition in our model was the frequency of interneuron firing and the related accumulation of extracellular potassium, which induced a depolarizing block of the pyramidal cell. This constitutes a new mechanism of CSD ignition.

Building Bridges Between the Clinic and the Laboratory: A Meeting Review - Brain Malformations: A Roadmap for Future Research

In the middle of March 2019, a group of scientists and clinicians (as well as those who wear both hats) gathered in the green campus of the Weizmann Institute of Science to share recent scientific findings, to establish collaborations, and to discuss future directions for better diagnosis, etiology modeling and treatment of brain malformations. One hundred fifty scientists from twenty-two countries took part in this meeting. Thirty-eight talks were presented and as many as twenty-five posters were displayed. This review is aimed at presenting some of the highlights that the audience was exposed to during the three-day meeting.

NaV1.2 haploinsufficiency in Scn2a knock-out mice causes an autistic-like phenotype attenuated with age

Mutations of the SCN2A gene, encoding the voltage gated sodium channel Na_V1.2, have been associated to a wide spectrum of epileptic disorders ranging from benign familial neonatal-infantile seizures to early onset epileptic encephalopathies such as Ohtahara syndrome. These phenotypes may be caused by either gain-of-function or loss-of-function mutations. More recently, loss-of-function SCN2A mutations have also been identified in patients with autism spectrum disorder (ASD) without overt epileptic phenotypes. Heterozygous Scn2a knock-out mice (Scn2a^+/−) may be a model of this phenotype. Because ASD develops in childhood, we performed a detailed behavioral characterization of Scn2a^+/− mice comparing the juvenile/adolescent period of development and adulthood. We used tasks relevant to ASD and the different comorbidities frequently found in this disorder, such as anxiety or intellectual disability. Our data demonstrate that young Scn2a^+/− mice display autistic-like phenotype associated to impaired memory and reduced reactivity to stressful stimuli. Interestingly, these dysfunctions are attenuated with age since adult mice show only communicative deficits. Considering the clinical data available on patients with loss-of-function SCN2A mutations, our results indicate that Scn2a^+/− mice constitute an ASD model with construct and face validity during the juvenile/adolescent period of development. However, more information about the clinical features of adult carriers of SCN2A mutations is needed to evaluate comparatively the phenotype of adult Scn2a^+/− mice.

Epilepsy Disease and Nose-to-Brain Delivery of Polymeric Nanoparticles: An Overview

Epilepsy is the fourth most common global neurological problem, which can be considered a spectrum disorder because of its various causes, seizure types, its ability to vary in severity and the impact from person to person, as well as its range of co-existing conditions. The approaches to drug therapy of epilepsy are directed at the control of symptoms by chronic administration of antiepileptic drugs (AEDs). These AEDs are administered orally or intravenously but alternative routes of administration are needed to overcome some important limits. Intranasal (IN) administration represents an attractive route because it is possible to reach the brain bypassing the blood brain barrier while the drug avoids first-pass metabolism. It is possible to obtain an increase in patient compliance for the easy and non-invasive route of administration. This route, however, has some drawbacks such as mucociliary clearance and the small volume that can be administered, in fact, only drugs that are efficacious at low doses can be considered. The drug also needs excellent aqueous solubility or must be able to be formulated using solubilizing agents. The use of nanomedicine formulations able to encapsulate active molecules represents a good strategy to overcome several limitations of this route and of conventional drugs. The aim of this review is to discuss the innovative application of nanomedicine for epilepsy treatment using nose-to-brain delivery with particular attention focused on polymeric nanoparticles to load drugs.

HDAC4 gene silencing alleviates epilepsy by inhibition of GABA in a rat model

OBJECTIVES

Despite the availability of effective antiepileptic drugs, epileptic patients still suffer from intractable seizures and adverse events. Better control of both seizures and fewer side effects is needed in order to enhance the patient's quality of life. We performed the present study with an attempt to explore the effect that HDAC4 gene silencing would have on epilepsy simulated by model rats. Furthermore, the study made additional analysis on the relativity of the HDAC4 gene in regard to its relationship with the gamma-aminobutyric acid (GABA) signaling pathway.

MATERIALS AND METHODS

Tremor rats were prepared in order to establish the epilepsy model. The rats would go on to be treated with si-HDAC4 in order to identify roles of the HDAC4 in levels of GABAARα1, GABAARα4, GAD65, GAT-1, and GAT-3. Finally, both electroencephalogram behavior and cognitive function of the rats following the treatment of si-HDAC4 were observed.

RESULTS

Levels of the GABAARα1 and GABAARα4 showed an evident increase, while GAD65, GAT-1, and GAT-3 displayed a decline in the epilepsy rats treated with the aforementioned si-HDAC4 when compared with the epilepsy rats. After injection of si-HDAC4, the epilepsy rats presented with a reduction in seizure degree, latency and duration of seizure, amount of scattered epileptic waves, and occurrence of epilepsy, with an improvement in their cognitive function.

CONCLUSION

The study highlighted the role that HDAC4 gene silencing played in easing the cases of epilepsy found in the model rats. This was shown to have occurred through the upregulation of both GABAARα1 and GABAARα4 levels, as well as in the downregulation of GAD65, GAT-1, and GAT-3 levels. The evidence provided shows that the HDAC4 gene is likely to present as a new objective in further experimentation in the treatment of epilepsy.

p53-Sensitive Epileptic Behavior and Inflammation in Ft1 Hypomorphic Mice

Epilepsy is a complex clinical condition characterized by repeated spontaneous seizures. Seizures have been linked to multiple drivers including DNA damage accumulation. Investigation of epilepsy physiopathology in humans imposes ethical and practical limitations, for this reason model systems are mostly preferred. Among animal models, mouse mutants are particularly valuable since they allow conjoint behavioral, organismal, and genetic analyses. Along with this, since aging has been associated with higher frequency of seizures, prematurely aging mice, simulating human progeroid diseases, offer a further useful modeling element as they recapitulate aging over a short time-window. Here we report on a mouse mutant with progeroid traits that displays repeated spontaneous seizures. Mutant mice were produced by reducing the expression of the gene Ft1 (AKTIP in humans). In vitro, AKTIP/Ft1 depletion causes telomere aberrations, DNA damage, and cell senescence. AKTIP/Ft1 interacts with lamins, which control nuclear architecture and DNA function. Premature aging defects of Ft1 mutant mice include skeletal alterations and lipodystrophy. The epileptic behavior of Ft1 mutant animals was age and sex linked. Seizures were observed in 18 mutant mice (23.6% of aged ≥ 21 weeks), at an average frequency of 2.33 events/mouse. Time distribution of seizures indicated non-random enrichment of seizures over the follow-up period, with 75% of seizures happening in consecutive weeks. The analysis of epileptic brains did not reveal overt brain morphological alterations or severe neurodegeneration, however, Ft1 reduction induced expression of the inflammatory markers IL-6 and TGF-β. Importantly, Ft1 mutant mice with concomitant genetic reduction of the guardian of the genome, p53, showed no seizures or inflammatory marker activation, implicating the DNA damage response into these phenotypes. This work adds insights into the connection among DNA damage, brain function, and aging. In addition, it further underscores the importance of model organisms for studying specific phenotypes, along with permitting the analysis of genetic interactions at the organismal level.

Gain of Function for the SCN1A/hNav1.1-L1670W Mutation Responsible for Familial Hemiplegic Migraine

The SCN1A gene encodes for the voltage-dependent Na_v1.1 Na⁺ channel, an isoform mainly expressed in GABAergic neurons that is the target of hundreds of epileptogenic mutations. More recently, it has been shown that the SCN1A gene is also the target of mutations responsible for familial hemiplegic migraine (FHM-3), a rare autosomal dominant subtype of migraine with aura. Studies of these mutations indicate that they induce gain of function of the channel. Surprisingly, the mutation L1649Q responsible for pure FHM-3 showed a complete loss of function, but, when partially rescued it induced an overall gain of function because of modification of the gating properties of the mutant channel. Here, we report the characterization of the L1670W SCN1A mutation that has been previously identified in a Chinese family with pure FHM-3, and that we have identified also in a Caucasian American family with pure FHM-3. Notably, one patient in our family had severe neurological deterioration after brain radiation for cancer treatment. Functional analysis of L1670W reveals that the mutation is responsible for folding/trafficking defects and, when they are rescued by incubation at lower temperature or by expression in neurons, modifications of the gating properties lead to an overall gain of function. Therefore, L1670W is the second mutation responsible for FHM-3 with this pathophysiological mechanism, showing that it may be a recurrent mechanism for Na_v1.1 hemiplegic migraine mutations.

Epilepsy and migraine-Are they comorbidity?

Epilepsy and migraine often co-occur. From the clinical symptoms, they often have some signs of symptoms before onset; from the pathogenesis of epilepsy and migraine, both of them have a high degree of neuronal excitement and ion channel abnormalities; in terms of treatment, many antiepileptic drugs are work in migraine. All of this indicates that they interact with each other. But it is undeniable that there are interactions and relationships between them, and there are also some differences such as the different clinical episodes, the different ways of neuronal haperexcitability and the different drug treatment programs. And are they comorbidity? If we can better understand the correlation between seizures and migraines, then this will help develop better guidelines for clinical diagnosis and treatment.

Pathophysiological mechanisms of migraine and epilepsy: Similarities and differences

Migraine and epilepsy are episodic disorders with distinct features, but they have some clinical and pathophysiological overlaps. We review here clinical overlaps between seizures and migraine attacks, activities of neuronal networks observed during seizures and migraine attacks, and molecular and cellular mechanisms of migraine identified in genetic forms, focusing on genetic variants identified in hemiplegic migraine and their functional effects. Epilepsy and migraine can be generated by dysfunctions of the same neuronal networks, but these dysfunctions can be disease-specific, even if pathogenic mutations target the same protein. Studies of rare monogenic forms have allowed the identification of some molecular/cellular dysfunctions that provide a window on pathological mechanisms: we have begun to disclose the tip of the iceberg.

Models for discovery of targeted therapy in genetic epileptic encephalopathies

Epileptic encephalopathies are severe disorders emerging in the first days to years of life that commonly include refractory seizures, various types of movement disorders, and different levels of developmental delay. In recent years, many de novo occurring variants have been identified in individuals with these devastating disorders. To unravel disease mechanisms, the functional impact of detected variants associated with epileptic encephalopathies is investigated in a range of cellular and animal models. This review addresses efforts to advance and use such models to identify specific molecular and cellular targets for the development of novel therapies. We focus on ion channels as the best-studied group of epilepsy genes. Given the clinical and genetic heterogeneity of epileptic encephalopathy disorders, experimental models that can reflect this complexity are critical for the development of disease mechanisms-based targeted therapy. The convergence of technological advances in gene sequencing, stem cell biology, genome editing, and high throughput functional screening together with massive unmet clinical needs provides unprecedented opportunities and imperatives for precision medicine in epileptic encephalopathies.

Post-translational dysfunctions in channelopathies of the nervous system

Channelopathies comprise various diseases caused by defects of ion channels. Modifications of their biophysical properties are common and have been widely studied. However, ion channels are heterogeneous multi-molecular complexes that are extensively modulated and undergo a maturation process comprising numerous steps of structural modifications and intracellular trafficking. Perturbations of these processes can give rise to aberrant channels that cause pathologies. Here we review channelopathies of the nervous system associated with dysfunctions at the post-translational level (folding, trafficking, degradation, subcellular localization, interactions with associated proteins and structural post-translational modifications). We briefly outline the physiology of ion channels' maturation and discuss examples of defective mechanisms, focusing in particular on voltage-gated sodium channels, which are implicated in numerous neurological disorders. We also shortly introduce possible strategies to develop therapeutic approaches that target these processes. This article is part of the Special Issue entitled 'Channelopathies.'

The impact of genetic and experimental studies on classification and therapy of the epilepsies

Different types of epilepsy are associated with gene mutations, in which seizures can be the only symptom (genetic epilepsies) or be one of the elements of complex clinical pictures that are often progressive over time (epileptic or epileptogenic encephalopathies). In epileptogenic encephalopathies, epileptic seizures and other neurological and cognitive signs are symptoms of genetically determined neuropathological or neurochemical disorders. In epileptic encephalopathies, epileptic activity itself is thought to contribute to severe cognitive and behavioral impairments above and beyond what might be expected from the underlying pathology alone. The distinction is conceptually clear and clinically relevant, as the different categories have a different prognosis in terms of both epilepsy and associated neurological and cognitive picture, but the boundaries are sometimes difficult to define in the clinical practice. Here we review the genetic epilepsies from the clinician perspective. A monogenic inheritance has been defined only in a minority of idiopathic epilepsies making improper to rename genetic the category of idiopathic epilepsies, until the presumptive multigenic mechanism will be demonstrated. A search for gene mutations must be done in any patient with candidate genetic types of epilepsy or epileptic/epileptogenic encephalopathy (e.g. familial forms) to complete the diagnostic process, define the prognosis and optimize the therapy. Advanced methods are available to express the gene variant in experimental model systems and test its effect on the properties of the affected protein, on neuronal excitability and on phenotypes in model organisms, and may help in identifying treatments with compatible action mechanisms. The influence of genetic studies on epilepsy taxonomy is now a matter of discussion: their impact on the international classification of the epilepsies will hopefully be defined soon.

Genetic basis of pediatric epilepsy syndromes

Childhood epilepsy affects ~0.5-1% in the general population worldwide. Early-onset epileptic encephalopathies are considered to be severe neurological disorders, which lead to impaired motor, cognitive, and sensory development due to recurrence of seizures. Many of the observed epilepsy phenotypes are associated with specific chromosomal imbalances and thus display gene dosage effects, and also specific mutations of a variety of genes ranging from ion channels to transcription factors. High throughput sequencing technologies and whole exome sequencing have led to the recognition of several new candidate genes with a possible role in the pathogenesis of epileptic encephalopathies. The mutations causing channelopathies can be either a gain or a loss of ion channel function and contribute to the pathogenesis of epilepsy syndrome. Nearly 300 mutations of SCN1A gene coding for the Nav1.1 channel protein have been identified that contribute to the pathology of epilepsy. Besides Na, potassium and calcium channels are also implicated in epileptic encephalopathies. Therapeutic management of epileptic encephalopathies has been challenging as the majority of the medications are not efficient and often have many undesirable side effects. A better understanding of the molecular nature of epilepsy in an individual is important to design a personalized medication, considering the number of possible genetic mutations that can contribute to epileptic encephalopathies.

Animal Models of Seizures and Epilepsy: Past, Present, and Future Role for the Discovery of Antiseizure Drugs

The identification of potential therapeutic agents for the treatment of epilepsy requires the use of seizure models. Except for some early treatments, including bromides and phenobarbital, the antiseizure activity of all clinically used drugs was, for the most part, defined by acute seizure models in rodents using the maximal electroshock and subcutaneous pentylenetetrazole seizure tests and the electrically kindled rat. Unfortunately, the clinical evidence to date would suggest that none of these models, albeit useful, are likely to identify those therapeutics that will effectively manage patients with drug resistant seizures. Over the last 30 years, a number of animal models have been developed that display varying degrees of pharmacoresistance, such as the phenytoin- or lamotrigine-resistant kindled rat, the 6-Hz mouse model of partial seizures, the intrahippocampal kainate model in mice, or rats in which spontaneous recurrent seizures develops after inducing status epilepticus by chemical or electrical stimulation. As such, these models can be used to study mechanisms of drug resistance and may provide a unique opportunity for identifying a truly novel antiseizure drug (ASD), but thus far clinical evidence for this hope is lacking. Although animal models of drug resistant seizures are now included in ASD discovery approaches such as the ETSP (epilepsy therapy screening program), it is important to note that no single model has been validated for use to identify potential compounds for as yet drug resistant seizures, but rather a battery of such models should be employed, thus enhancing the sensitivity to discover novel, highly effective ASDs. The present review describes the previous and current approaches used in the search for new ASDs and offers some insight into future directions incorporating new and emerging animal models of therapy resistance.

Clinical and genetic factors predicting Dravet syndrome in infants with SCN1A mutations

OBJECTIVE

To explore the prognostic value of initial clinical and mutational findings in infants with SCN1A mutations.

METHODS

Combining sex, age/fever at first seizure, family history of epilepsy, EEG, and mutation type, we analyzed the accuracy of significant associations in predicting Dravet syndrome vs milder outcomes in 182 mutation carriers ascertained after seizure onset. To assess the diagnostic accuracy of all parameters, we calculated sensitivity, specificity, receiver operating characteristic (ROC) curves, diagnostic odds ratios, and positive and negative predictive values and the accuracy of combined information. We also included in the study demographic and mutational data of the healthy relatives of mutation carrier patients.

RESULTS

Ninety-seven individuals (48.5%) had Dravet syndrome, 49 (23.8%) had generalized/genetic epilepsy with febrile seizures plus, 30 (14.8%) had febrile seizures, 6 (3.5%) had focal epilepsy, and 18 (8.9%) were healthy relatives. The association study indicated that age at first seizure and frameshift mutations were associated with Dravet syndrome. The risk of Dravet syndrome was 85% in the 0- to 6-month group, 51% in the 6- to 12-month range, and 0% after the 12th month. ROC analysis identified onset within the sixth month as the diagnostic cutoff for progression to Dravet syndrome (sensitivity = 83.3%, specificity = 76.6%).

CONCLUSIONS

In individuals with SCN1A mutations, age at seizure onset appears to predict outcome better than mutation type. Because outcome is not predetermined by genetic factors only, early recognition and treatment that mitigates prolonged/repeated seizures in the first year of life might also limit the progression to epileptic encephalopathy.

The genetic relationship between epilepsy and hemiplegic migraine

Epilepsy and migraine are common diseases of the nervous system and share genetic and pathophysiological mechanisms. Familial hemiplegic migraine is an autosomal dominant disease. It is often used as a model of migraine. Four genes often contain one or more mutations in both epilepsy and hemiplegic migraine patients (ie, CACNA1A, ATP1A2, SCN1A, and PRRT2). A better understanding of the shared genetics of epilepsy and hemiplegic migraine may reveal new strategic directions for research and treatment of both the disorders.

Fit for purpose application of currently existing animal models in the discovery of novel epilepsy therapies

Animal seizure and epilepsy models continue to play an important role in the early discovery of new therapies for the symptomatic treatment of epilepsy. Since 1937, with the discovery of phenytoin, almost all anti-seizure drugs (ASDs) have been identified by their effects in animal models, and millions of patients world-wide have benefited from the successful translation of animal data into the clinic. However, several unmet clinical needs remain, including resistance to ASDs in about 30% of patients with epilepsy, adverse effects of ASDs that can reduce quality of life, and the lack of treatments that can prevent development of epilepsy in patients at risk following brain injury. The aim of this review is to critically discuss the translational value of currently used animal models of seizures and epilepsy, particularly what animal models can tell us about epilepsy therapies in patients and which limitations exist. Principles of translational medicine will be used for this discussion. An essential requirement for translational medicine to improve success in drug development is the availability of animal models with high predictive validity for a therapeutic drug response. For this requirement, the model, by definition, does not need to be a perfect replication of the clinical condition, but it is important that the validation provided for a given model is fit for purpose. The present review should guide researchers in both academia and industry what can and cannot be expected from animal models in preclinical development of epilepsy therapies, which models are best suited for which purpose, and for which aspects suitable models are as yet not available. Overall further development is needed to improve and validate animal models for the diverse areas in epilepsy research where suitable fit for purpose models are urgently needed in the search for more effective treatments.

Ranolazine vs phenytoin: greater effect of ranolazine on the transient Na(+) current than on the persistent Na(+) current in central neurons

Voltage-gated Na(+) channels (NaV) are involved in pathologies and are important targets of drugs (NaV-blockers), e.g. some anti-epileptic drugs (AEDs). Besides the fast inactivating transient Na(+) current (INaT), they generate a slowly inactivating "persistent" current (INaP). Ranolazine, a NaV-blocker approved for treatment of angina pectoris, is considered a preferential inhibitor of INaP and has been proposed as a novel AED. Although it is thought that classic NaV-blockers used as AEDs target mainly INaT, they can also reduce INaP. It is important to disclose specific features of novel NaV-blockers, which could be necessary for their effect as AEDs in drug resistant patients. We have compared the action of ranolazine and of the classic AED phenytoin in transfected cells expressing the neuronal NaV1.1 Na(+) channel and in neurons of neocortical slices. Our results show that the relative block of INaT versus INaP of ranolazine and phenytoin is variable and depends on Na(+) current activation conditions. Strikingly, ranolazine blocks with less efficacy INaP and more efficacy INaT than phenytoin in conditions mimicking pathological states (i.e. high frequency firing and long lasting depolarizations). The effects are consistent with binding of ranolazine to both open/pre-open and inactivated states; larger INaT block at high stimulation frequencies is caused by the induction of a slow inactivated state. Thus, contrary than expected, ranolazine is not a better INaP blocker than phenytoin in central neurons, and phenytoin is not a better INaT blocker than ranolazine. Nevertheless, they show a complementary action and could differentially target specific pathological dysfunctions.

Opportunities for improving animal welfare in rodent models of epilepsy and seizures

Animal models of epilepsy and seizures, mostly involving mice and rats, are used to understand the pathophysiology of the different forms of epilepsy and their comorbidities, to identify biomarkers, and to discover new antiepileptic drugs and treatments for comorbidities. Such models represent an important area for application of the 3Rs (replacement, reduction and refinement of animal use). This report provides background information and recommendations aimed at minimising pain, suffering and distress in rodent models of epilepsy and seizures in order to improve animal welfare and optimise the quality of studies in this area. The report includes practical guidance on principles of choosing a model, induction procedures, in vivo recordings, perioperative care, welfare assessment, humane endpoints, social housing, environmental enrichment, reporting of studies and data sharing. In addition, some model-specific welfare considerations are discussed, and data gaps and areas for further research are identified. The guidance is based upon a systematic review of the scientific literature, survey of the international epilepsy research community, consultation with veterinarians and animal care and welfare officers, and the expert opinion and practical experience of the members of a Working Group convened by the United Kingdom's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs).

Rescuable folding defective NaV1.1 (SCN1A) mutants in epilepsy: properties, occurrence, and novel rescuing strategy with peptides targeted to the endoplasmic reticulum

Mutations of the voltage gated Na(+) channel Na(V)1.1 (SCN1A) are important causes of different genetic epilepsies and can also cause familial hemiplegic migraine (FHM-III). In previous studies, some rescuable epileptogenic folding defective mutants located in domain IV of Na(V)1.1 have been identified, showing partial loss of function also with maximal rescue. Variable rescue may be one of the causes of phenotypic variability, and rescue might be exploited for therapeutic approaches. Recently, we have identified a folding defective FHM-III Na(V)1.1 mutant that showed overall gain of function when rescued, consistent with a differential pathomechanism. Here, we have evaluated functional properties and cell surface expression of six Na(V)1.1 epileptogenic missense mutations in different rescuing conditions, including a novel one that we have developed expressing a selective sodium channel toxin (CsEI) targeted to the endoplasmic reticulum (ER). All the mutants showed loss of function and reduced cell surface expression, consistently with possibility of rescue. Four of them were rescuable by incubation at low temperature and interactions with different co-expressed proteins or a pharmacological chaperone (phenytoin). Notably, CsEI was able to rescue four mutants. Thus, Na(V)1.1 folding defective mutants can be relatively common and mutations inducing rescuable folding defects are spread in all Na(V)1.1 domains. Importantly, epileptogenic mutants showed overall loss of function even upon rescue, differently than FHM-III ones. The effectiveness of CsEI demonstrates that interactions in the ER are sufficient for inducing rescue, and provides a proof of concept for developing possible therapeutic approaches that may overcome some limitations of pharmacological chaperones.

Action potential initiation in neocortical inhibitory interneurons

Sodium channels add variety to inhibitory interneurons Different populations of inhibitory interneurons in the cerebral cortex express distinct subtypes of sodium channels, resulting in diverse action potential thresholds and network excitability.

Action potential (AP) generation in inhibitory interneurons is critical for cortical excitation-inhibition balance and information processing. However, it remains unclear what determines AP initiation in different interneurons. We focused on two predominant interneuron types in neocortex: parvalbumin (PV)- and somatostatin (SST)-expressing neurons. Patch-clamp recording from mouse prefrontal cortical slices showed that axonal but not somatic Na⁺ channels exhibit different voltage-dependent properties. The minimal activation voltage of axonal channels in SST was substantially higher (∼7 mV) than in PV cells, consistent with differences in AP thresholds. A more mixed distribution of high- and low-threshold channel subtypes at the axon initial segment (AIS) of SST cells may lead to these differences. Surprisingly, Na_V1.2 was found accumulated at AIS of SST but not PV cells; reducing Na_V1.2-mediated currents in interneurons promoted recurrent network activity. Together, our results reveal the molecular identity of axonal Na⁺ channels in interneurons and their contribution to AP generation and regulation of network activity.

Inhibitory interneurons in the cerebral cortex are diverse in many respects. Here, we examine whether this diversity extends to the composition of ion channels along the axon, which might determine the neurons' excitability. We performed patch-clamp recordings from cortical interneuron axons in brain slices obtained from two transgenic mouse lines. In each mouse line, distinct populations of inhibitory interneurons—those that express parvalbumin (PV) or those that express somatostatin (SST)—were labeled with green fluorescent protein to allow visualization. We show that action potentials initiate at the axon initial segment (a specialized region of the axon closest to the cell body) in both cell types, but SST neurons have a higher action potential threshold than PV neurons because their sodium channels require a greater degree of depolarization to be fully activated. At the molecular level, we found that the population of sodium channels in SST neurons requires a larger depolarization because it has a more mixed composition of high- and low-threshold sodium channel subtypes. In summary, this study reveals diversity in the molecular identity and voltage dependence of sodium channels that are responsible for initiating action potentials in different populations of interneurons. In addition, the presence of a particular subtype of sodium channel—Na_V1.2—in inhibitory interneurons might explain why loss-of-function mutations in this channel result in epilepsy.