Channelopathies in idiopathic epilepsy

The Use of Compounds Derived from Cannabis sativa in the Treatment of Epilepsy, Painful Conditions, and Neuropsychiatric and Neurodegenerative Disorders

Neurological disorders present a wide range of symptoms and challenges in diagnosis and treatment. Cannabis sativa, with its diverse chemical composition, offers potential therapeutic benefits due to its anticonvulsive, analgesic, anti-inflammatory, and neuroprotective properties. Beyond cannabinoids, cannabis contains terpenes and polyphenols, which synergistically enhance its pharmacological effects. Various administration routes, including vaporization, oral ingestion, sublingual, and rectal, provide flexibility in treatment delivery. This review shows the therapeutic efficacy of cannabis in managing neurological disorders such as epilepsy, neurodegenerative diseases, neurodevelopmental disorders, psychiatric disorders, and painful pathologies. Drawing from surveys, patient studies, and clinical trials, it highlights the potential of cannabis in alleviating symptoms, slowing disease progression, and improving overall quality of life for patients. Understanding the diverse therapeutic mechanisms of cannabis can open up possibilities for using this plant for individual patient needs.

Antiseizure medication and SUDEP - a need for unifying methodology in research

The risk of sudden unexpected death in epilepsy (SUDEP) increases with the frequency of generalized tonic-clonic seizures. Carbamazepine (CBZ) and lamotrigine (LTG) have been suggested to increase the risk. However, the prevailing viewpoint is that the choice of antiseizure medication (ASM) does not influence the occurrence. We have explored the approach to addressing this question in relevant studies to evaluate the validity of the conclusions reached. A systematic search was performed in PubMed to identify all controlled studies on SUDEP risk in individuals on CBZ or LTG. Studies were categorized according to whether idiopathic generalized epilepsy (IGE) or females were considered separately, and whether data were adjusted for seizure frequency. Eight studies on CBZ and six studies on LTG were identified. For CBZ, one study showed a significantly increased risk of SUDEP without adjustment for seizure frequency. Another study found significantly increased risk after statistical adjustment for seizure frequency and one study found increased risk with high blood levels. Five other studies found no increase in risk. For LTG, one study showed a significantly increased risk in patients with IGE as opposed to focal epilepsy, and another study showed a significantly increased risk in females. None of the subsequent studies on LTG and none of the studies on CBZ considered females with IGE separately. Taken together the available studies suggest that LTG, and possibly CBZ, may increase occurrence of SUDEP when used in females with IGE. Additional studies with sub-group analysis of females with IGE are needed.

Case Report: A developmental and epileptic encephalopathy 45 due to de novo variant of GABRB1

Background

The gamma-aminobutyric acid (GABA) variant causes developmental and epileptic encephalopathy 45 (DEE45), an autosomal dominant disorder that results in oculocortical visual impairment, reduced muscle tone, psychomotor retardation, and epilepsy. Analysis of the clinical features and genetics of DEE45 may be helpful in complementing genotype-phenotype studies.

Case presentation

We collected peripheral blood samples from the affected children and parents and extracted genomic DNA. Whole exome sequencing (WES) was utilized to identify the underlying disease-causing variant. WES showed that the prior carried a heterozygous variant c.686C > T p.(Ala229Val) in exon 7 of the GABRB1 (NM_000812.4), and no variant was detected in either parental sample. The child has DEE45.

Conclusion

The variant c.686C > T of the GABRB1 is a possible cause of DEE45. Gene variant analysis of the relevant family lines using WES provides effective genetic counseling for developing and regressing such patients in the clinic. However, further studies are needed to verify the pathogenic mechanism.

The role of molecular chaperones in the mechanisms of epileptogenesis

Epilepsy is a group of neurological diseases which requires significant economic costs for the treatment and care of patients. The central point of epileptogenesis stems from the failure of synaptic signal transmission mechanisms, leading to excessive synchronous excitation of neurons and characteristic epileptic electroencephalogram activity, in typical cases being manifested as seizures and loss of consciousness. The causes of epilepsy are extremely diverse, which is one of the reasons for the complexity of selecting a treatment regimen for each individual case and the high frequency of pharmacoresistant cases. Therefore, the search for new drugs and methods of epilepsy treatment requires an advanced study of the molecular mechanisms of epileptogenesis. In this regard, the investigation of molecular chaperones as potential mediators of epileptogenesis seems promising because the chaperones are involved in the processing and regulation of the activity of many key proteins directly responsible for the generation of abnormal neuronal excitation in epilepsy. In this review, we try to systematize current data on the role of molecular chaperones in epileptogenesis and discuss the prospects for the use of chemical modulators of various chaperone groups' activity as promising antiepileptic drugs.

Small Molecules as Modulators of Voltage-Gated Calcium Channels in Neurological Disorders: State of the Art and Perspectives

Voltage-gated calcium channels (VGCCs) are widely expressed in the brain, heart and vessels, smooth and skeletal muscle, as well as in endocrine cells. VGCCs mediate gene transcription, synaptic and neuronal structural plasticity, muscle contraction, the release of hormones and neurotransmitters, and membrane excitability. Therefore, it is not surprising that VGCC dysfunction results in severe pathologies, such as cardiovascular conditions, neurological and psychiatric disorders, altered glycemic levels, and abnormal smooth muscle tone. The latest research findings and clinical evidence increasingly show the critical role played by VGCCs in autism spectrum disorders, Parkinson's disease, drug addiction, pain, and epilepsy. These findings outline the importance of developing selective calcium channel inhibitors and modulators to treat such prevailing conditions of the central nervous system. Several small molecules inhibiting calcium channels are currently used in clinical practice to successfully treat pain and cardiovascular conditions. However, the limited palette of molecules available and the emerging extent of VGCC pathophysiology require the development of additional drugs targeting these channels. Here, we provide an overview of the role of calcium channels in neurological disorders and discuss possible strategies to generate novel therapeutics.

Characterization of Seizure Induction Methods in Drosophila

Epilepsy is one of the most common neurologic disorders. Around one third of patients do not respond to current medications. This lack of treatment indicates a need for better understanding of the underlying mechanisms and, importantly, the identification of novel targets for drug manipulation. The fruit fly Drosophila melanogaster has a fast reproduction time, powerful genetics, and facilitates large sample sizes, making it a strong model of seizure mechanisms. To better understand behavioral and physiological phenotypes across major fly seizure genotypes we systematically measured seizure severity and secondary behavioral phenotypes at both the larval and adult stage. Comparison of several seizure-induction methods; specifically electrical, mechanical and heat induction, show that larval electroshock is the most effective at inducing seizures across a wide range of seizure-prone mutants tested. Locomotion in adults and larvae was found to be non-predictive of seizure susceptibility. Recording activity in identified larval motor neurons revealed variations in action potential (AP) patterns, across different genotypes, but these patterns did not correlate with seizure susceptibility. To conclude, while there is wide variation in mechanical induction, heat induction, and secondary phenotypes, electroshock is the most consistent method of seizure induction across known major seizure genotypes in Drosophila.

Aberrant energy metabolism and redox balance in seizure onset zones of epileptic patients

Epilepsy is a disorder that affects around 1% of the population. Approximately one third of patients do not respond to anti-convulsant drugs treatment. To understand the underlying biological processes involved in drug resistant epilepsy (DRE), a combination of proteomics strategies was used to compare molecular differences and enzymatic activities in tissue implicated in seizure onset to tissue with no abnormal activity within patients. Label free quantitation identified 17 proteins with altered abundance in the seizure onset zone as compared to tissue with normal activity. Assessment of oxidative protein damage by protein carbonylation identified additional 11 proteins with potentially altered function in the seizure onset zone. Pathway analysis revealed that most of the affected proteins are involved in energy metabolism and redox balance. Further, enzymatic assays showed significantly decreased activity of transketolase indicating a disruption of the Pentose Phosphate Pathway and diversion of intermediates into purine metabolic pathway, resulting in the generation of the potentially pro-convulsant metabolites. Altogether, these findings suggest that imbalance in energy metabolism and redox balance, pathways critical to proper neuronal function, play important roles in neuronal network hyperexcitability and can be used as a primary target for potential therapeutic strategies to combat DRE. SIGNIFICANCE: Epileptic seizures are some of the most difficult to treat neurological disorders. Up to 40% of patients with epilepsy are resistant to first- and second-line anticonvulsant therapy, a condition that has been classified as refractory epilepsy. One potential therapy for this patient population is the ketogenic diet (KD), which has been proven effective against multiple refractory seizure types However, compliance with the KD is extremely difficult, and carries severe risks, including ketoacidosis, renal failure, and dangerous electrolyte imbalances. Therefore, identification of pathways disruptions or shortages can potentially uncover cellular targets for anticonvulsants, leading to a personalized treatment approach depending on a patient's individual metabolic signature.

Sleep Related Epilepsy and Pharmacotherapy: An Insight

In the last several decades, sleep-related epilepsy has drawn considerable attention among epileptologists and neuroscientists in the interest of new paradigms of the disease etiology, pathogenesis and management. Sleep-related epilepsy is nocturnal seizures that manifest solely during the sleep state. Sleep comprises two distinct stages i.e., non-rapid eye movement (NREM) and rapid eye movement (REM) that alternate every 90 min with NREM preceding REM. Current findings indicate that the sleep-related epilepsy manifests predominantly during the synchronized stages of sleep; NREM over REM stage. Sleep related hypermotor epilepsy (SHE), benign partial epilepsy with centrotemporal spikes or benign rolandic epilepsy (BECTS), and Panayiotopoulos Syndrome (PS) are three of the most frequently implicated epilepsies occurring during the sleep state. Although some familial types are described, others are seemingly sporadic occurrences. In the present review, we aim to discuss the predominance of sleep-related epilepsy during NREM, established familial links to the pathogenesis of SHE, BECTS and PS, and highlight the present available pharmacotherapy options.

Insight into tetrodotoxin blockade and resistance mechanisms of Nav 1.2 sodium channel by theoretical approaches

Na_v 1.2, a member of voltage-gated sodium channels (Na_v s) that are responsible for the generation and propagation of action potentials along the cell membrane, and play a vital role in the process of information transmission within the nervous system and muscle contraction, is preferentially expressed in the central nervous system. As a potent and selective blocker of Na_v s, tetrodotoxin (TTX) has been extensively studied in biological and chemical sciences, whereas the detailed mechanism by which it blocks nine Na_v 1 channel subtypes remain elusive. Despite the high structural similarity, the TTX metabolite 4,9-anhydro-TTX is 161 times less effective toward the mammalian Na_v 1.2, which puzzled us to ask a question why such a subtle structural variation results in the largely binding affinity difference. In the current work, an integrated computational strategy, including homology modeling, induced fit docking, explicit-solvent MD simulations, and free energy calculations, was employed to investigate the binding mechanism and conformational determinants of TTX analogs. Based on the computational results, the H-bond interactions between C4-OH and C9-OH of TTX and the outer ring carboxylates of the selectivity-filter residues, and the cation-π interaction between the primary amine of guanidinium of TTX and Phe385 determine the difference of their binding affinities. Moreover, the computationally simulations were carried out for the D384N and E945K mutants of hNa_v 1.2-TTX, and the rank of the predicted binding free energies is in accordance with the experimental data. These observations provide a valuable model to design potent and selective neurotoxins of Na_v 1.2 and shed light on the blocking mechanism of TTX to sodium channels.

High-throughput behavioral assay to investigate seizure sensitivity in zebrafish implicates ZFHX3 in epilepsy

Epilepsy, which affects ∼1% of the population, is caused by abnormal synchronous neural activity in the central nervous system (CNS). While there is a significant genetic contribution to epilepsy, the underlying causes for the majority of genetic cases remain unknown. The NIH Undiagnosed Diseases Project (UDP) utilized exome sequencing to identify genetic variants in patients affected by various conditions with undefined etiology, including epilepsy. Confirming the functional relevance of the candidate genes identified by exome sequencing in a timely manner is crucial to translating exome data into clinically useful information. To this end, we developed a high throughput version of a seizure-sensitivity assay in zebrafish (Danio rerio) to rapidly evaluate candidate genes found by exome sequencing. We developed open access software, Studying Epilepsy In Zebrafish using R (SEIZR), to efficiently analyze the data. SEIZR was validated by disrupting function of a known epilepsy gene, prickle 1. Next, using SEIZR, we analyzed a candidate gene from the UDP screen (Zinc Finger Homeobox 3, ZFHX3), and showed that reduced ZFHX3 function in zebrafish results in a significant hyperactive response to the convulsant drug pentylenetetrazol (PTZ). We find that ZFHX3 shows strong expression in the CNS during neurogenesis including in the pallium, thalamus, tegmentum, reticular formation, and medulla oblongata - all regions which have roles in motor control and coordination. Our findings in the zebrafish confirm human ZFHX3 is a strong candidate for further neurological studies. We offer SEIZR to other researchers as a tool to rapidly and efficiently analyze large behavioral data sets.

A Subset of Dogs with Presumptive Idiopathic Epilepsy Show Hippocampal Asymmetry: A Volumetric Comparison with Non-Epileptic Dogs Using MRI

MRI-acquired volumetric measurements from 100 dogs with presumptive idiopathic epilepsy (IE) and 41 non-epileptic (non-IE) dogs were used to determine if hippocampal asymmetry exists in the IE as compared to the non-IE dogs. MRI databases from three institutions were searched for dogs that underwent MRI of the brain and were determined to have IE and those that were considered non-IE dogs. Volumes of the right and left hippocampi were measured using Mimics^® software. Median hippocampal volumes of IE and non-IE dogs were 0.47 and 0.53 cm³, respectively. There was no significant difference in overall hippocampal volume between IE and non-IE dogs; however, IE dogs had greater hippocampal asymmetry than non-IE dogs (P < 0.012). A threshold value of 1.16 from the hippocampal ratio had an 85% specificity for identifying IE-associated asymmetry. Thirty five percent of IE dogs had a hippocampal ratio >1.16. Asymmetry was not associated with any particular hemisphere (P = 0.67). Our study indicates that hippocampal asymmetry occurs in a subset of dogs with presumptive idiopathic/genetic epilepsy, suggesting a structural etiology to some cases of IE.

The role of antiepileptic drugs in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) primarily affects young adults and is the leading cause of death related directly to seizures. High frequency of generalized tonic-clonic seizures is the most important risk factor, and effective seizure protection is probably the most important measure to prevent these tragic deaths. For several years a potential role of antiepileptic drugs (AEDs) has been discussed, but at present there is wide agreement that choice of AED therapy does not influence the risk. However, although it is well known that the efficacy and safety profiles of AEDs may differ significantly when used in the treatment of genetic epilepsy compared to symptomatic or cryptogenic epilepsy, this has generally been overlooked in epidemiologic studies of possible relationships between AEDs and SUDEP. Consequently important information about drug safety may have been lost. This review challenges the current view that no AED can increase the risk of SUDEP.

Comorbid Epilepsy and Developmental Disorders in Congenital Long QT Syndrome With Life-Threatening Perinatal Arrhythmias

OBJECTIVES

Given the association of long QT syndrome (LQTS) and neurological disorders, we speculated that the more severe LQTS phenotype, perinatal LQTS, would exhibit more frequent comorbid neurodevelopmental anomalies than LQTS without perinatal arrhythmias (nonperinatal LQTS).

BACKGROUND

Congenital LQTS with life-threatening perinatal arrhythmias (perinatal LQTS) has a poor life prognosis.

METHODS

Twenty-one consecutive LQTS patients diagnosed before 1 year of age at our institution and 3 previously reported perinatal LQTS patients with neurological seizures were enrolled. In total, the clinical course was evaluated in 24 patients.

RESULTS

Among 21 infantile LQTS patients, 5 of 6 with perinatal LQTS (83%) were diagnosed with epilepsy and 4 (67%) with developmental disorders, but none with nonperinatal LQTS were. The total development quotient by Kinder Infant Development Scale scores was 17 to 72 (median 67) in 5 epileptic perinatal LQTS. In the 8 perinatal LQTS patients with neurological disorders, including 3 previously reported cases, epileptic seizures occurred at 2 days to 2.5 years of age and 5 had developmental disorders. Mutations in these 8 patients were located in the transmembrane loop of KCNH2, and D3/S4-S5 linker, D4/S4, or the D4/S6 segment of SCN5A.

CONCLUSIONS

A high comorbidity of neurodevelopmental anomalies was observed in perinatal LQTS. Mutations in patients with neurological comorbidities were in loci linked to LQTS with a severe cardiac phenotype. These observations indicate the possibility that neurological disorders in perinatal LQTS are manifested as neurological phenotypes associated with severe cardiac phenotypes, while we could not completely exclude another possibility that those were caused by a brain perfusion injury.

Effect of chronic fluoxetine treatment on audiogenic epilepsy, symptoms of anxiety and depression in rats of four lines

Anxiety (Anx) and depression (Dp) levels were evaluated in rats of 4 lines: 2 of them (KM and "4") exhibited audiogenic seizures (AS), and 2 (Wistar and "0") had no AS. In KM rats (with AS), Anx and Dp levels were higher than in Wistars (without AS), while in "4" and "0" rats with the related genetic background but contrasting in AS severity, Anx and Dp indices were not different. Fluoxetine treatment exerted antidepressant effect in all rat lines irrespective of its effect on AS. Thus, phenotypic expression of AS is not directly associated with the mechanisms of Anx and Dp development.

Model systems for studying cellular mechanisms of SCN1A-related epilepsy

Mutations in SCN1A, the gene encoding voltage-gated sodium channel NaV1.1, cause a spectrum of epilepsy disorders that range from genetic epilepsy with febrile seizures plus to catastrophic disorders such as Dravet syndrome. To date, more than 1,250 mutations in SCN1A have been linked to epilepsy. Distinct effects of individual SCN1A mutations on neuronal function are likely to contribute to variation in disease severity and response to treatment in patients. Several model systems have been used to explore seizure genesis in SCN1A epilepsies. In this article we review what has been learned about cellular mechanisms and potential new therapies from these model systems, with a particular emphasis on the novel model system of knock in Drosophila and a look toward the future with expanded use of patient-specific induced pluripotent stem cell-derived neurons.

No relation between EFHC2 gene polymorphism and Idiopathic generalized epilepsy

BACKGROUND

Idiopathic generalized epilepsy (IGE) is an epilepsy form without an underlying brain lesion or neurological indication or symptom. Recent investigations on the genetic origins of IGE and its subtypes report that certain mutations of various ion and non-ion channels genes in the central nervous system may be associated with IGE.

PURPOSE

In this study we evaluated the relation between IGE and S430Y polymorphism in EFHC2 gene in a Turkish population.

MATERIAL/METHODS

The study enrolled 96 healthy volunteers (47 male, 49 female), served as controls, and 96 IGE patients (41 male, 55 female), IGE diagnosis was confirmed in the neurology department. DNA extractions were performed. The presence of S430Y polymorphism in the exon 9 of EFHC2 gene were analyzed by Real-Time PCR. The findings obtained from the control and patient groups were compared.

RESULTS

In the patient group there was one heterozygous male with 685 T>C mutation. In the control group, there were two objects with 685 T>C mutation; one heterozygous male, one heterozygous female. 662 G>A mutation was determined in neither controls nor patients.

CONCLUSION

In our series of 96 IGE patients and 96 healthy controls, there was no relation between S430Y polymorphism in EFHC2 gene and IGE presence.

Idiopathic generalized epilepsy and hypokalemic periodic paralysis in a family of South Indian descent

Inherited channelopathies are a heterogeneous group of disorders resulting from dysfunction of ion channels in cellular membranes. They may manifest as diseases affecting skeletal muscle contraction, the conduction system of the heart, nervous system function, and vision syndromes. We describe a family of South Indian descent with hypokalemic periodic paralysis in which four members also have idiopathic generalized epilepsy. Hypokalemic periodic paralysis is a genetically heterogeneous channelopathy that has been linked to mutations in genes encoding three ion channels CACNIAS, SCN4A, and KCNJ2 predominantly. Although data on specific gene in idiopathic generalized epilepsy is relatively scarce, mutations of voltage gated sodium channel subunit genes (CACNB4) and nonsense mutations in voltage gated calcium channels (CACNA1A) have been linked to idiopathic generalized epilepsy in two families. We speculate that gene mutations altering the ability of the beta subunit to interact with the alpha subunit of the CaV1.1 channel and mutations in the pore-forming potassium channel subunit may be possible explanations for the combined manifestation of both diseases. Functional analysis of voltage gated calcium channel and other ion channels mutations may provide additional support and insight for the causal role of these mutations. The understanding of mutations in ion-channel genes will lead to improved diagnosis and treatment of such inherited channelopathies.

Nocturnal frontal lobe epilepsy with paroxysmal arousals due to CHRNA2 loss of function

OBJECTIVE

We assessed the mutation frequency in nicotinic acetylcholine receptor (nAChR) subunits CHRNA4, CHRNB2, and CHRNA2 in a cohort including autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and sporadic nocturnal frontal lobe epilepsy (NFLE). Upon finding a novel mutation in CHRNA2 in a large family, we tested in vitro its functional effects.

METHODS

We sequenced all the coding exons and their flanking intronic regions in 150 probands (73 NFLE, 77 ADNFLE), in most of whom diagnosis had been validated by EEG recording of seizures. Upon finding a missense mutation in CHRNA2, we measured whole-cell currents in human embryonic kidney cells in both wild-type and mutant α2β4 and α2β2 nAChR subtypes stimulated with nicotine.

RESULTS

We found a c.889A>T (p.Ile297Phe) mutation in the proband (≈0.6% of the whole cohort) of a large ADNFLE family (1.2% of familial cases) and confirmed its segregation in all 6 living affected individuals. Video-EEG studies demonstrated sleep-related paroxysmal epileptic arousals in all mutation carriers. Oxcarbazepine treatment was effective in all. Whole-cell current density was reduced to about 40% in heterozygosity and to 0% in homozygosity, with minor effects on channel permeability and sensitivity to nicotine.

CONCLUSION

ADNFLE had previously been associated with CHRNA2 dysfunction in one family, in which a gain of function mutation was demonstrated. We confirm the causative role of CHRNA2 mutations in ADNFLE and demonstrate that also loss of function of α2 nAChRs may have pathogenic effects. CHRNA2 mutations are a rare cause of ADNFLE but this gene should be included in mutation screening.

Genetics of epilepsy: The testimony of twins in the molecular era

OBJECTIVE

Analysis of twins with epilepsy to explore the genetic architecture of specific epilepsies, to evaluate the applicability of the 2010 International League Against Epilepsy (ILAE) organization of epilepsy syndromes, and to integrate molecular genetics with phenotypic analyses.

METHODS

A total of 558 twin pairs suspected to have epilepsy were ascertained from twin registries (69%) or referral (31%). Casewise concordance estimates were calculated for epilepsy syndromes. Epilepsies were then grouped according to the 2010 ILAE organizational scheme. Molecular genetic information was utilized where applicable.

RESULTS

Of 558 twin pairs, 418 had confirmed seizures. A total of 534 twin individuals were affected. There were higher twin concordance estimates for monozygotic (MZ) than for dizygotic (DZ) twins for idiopathic generalized epilepsies (MZ = 0.77; DZ = 0.35), genetic epilepsy with febrile seizures plus (MZ = 0.85; DZ = 0.25), and focal epilepsies (MZ = 0.40; DZ = 0.03). Utilizing the 2010 ILAE scheme, the twin data clearly demonstrated genetic influences in the syndromes designated as genetic. Of the 384 tested twin individuals, 10.9% had mutations of large effect in known epilepsy genes or carried validated susceptibility alleles.

CONCLUSIONS

Twin studies confirm clear genetic influences for specific epilepsies. Analysis of the twin sample using the 2010 ILAE scheme strongly supported the validity of grouping the "genetic" syndromes together and shows this organizational scheme to be a more flexible and biologically meaningful system than previous classifications. Successful selected molecular testing applied to this cohort is the prelude to future large-scale next-generation sequencing of epilepsy research cohorts. Insights into genetic architecture provided by twin studies provide essential data for optimizing such approaches.

GABAA receptor biogenesis is impaired by the γ2 subunit febrile seizure-associated mutation, GABRG2(R177G)

A missense mutation in the GABAA receptor γ2L subunit, R177G, was reported in a family with complex febrile seizures (FS). To gain insight into the mechanistic basis for these genetic seizures, we explored how the R177G mutation altered the properties of recombinant α1β2γ2L GABAA receptors expressed in HEK293T cells. Using a combination of electrophysiology, flow cytometry, and immunoblotting, we found that the R177G mutation decreased GABA-evoked whole-cell current amplitudes by decreasing cell surface expression of α1β2γ2L receptors. This loss of receptor surface expression resulted from endoplasmic reticulum (ER) retention of mutant γ2L(R177G) subunits, which unlike wild-type γ2L subunits, were degraded by ER-associated degradation (ERAD). Interestingly, when compared to the condition of homozygous γ2L(R177G) subunit expression, disproportionately low levels of γ2L(R177G) subunits reached the cell surface with heterozygous expression, indicating that wild-type γ2L subunits possessed a competitive advantage over mutant γ2L(R177G) subunits for receptor assembly and/or forward trafficking. Inhibiting protein synthesis with cycloheximide demonstrated that the R177G mutation primarily decreased the stability of an intracellular pool of unassembled γ2L subunits, suggesting that the mutant γ2L(R177G) subunits competed poorly with wild-type γ2L subunits due to impaired subunit folding and/or oligomerization. Molecular modeling confirmed that the R177G mutation could disrupt intrasubunit salt bridges, thereby destabilizing secondary and tertiary structure of γ2L(R177G) subunits. These findings support an emerging body of literature implicating defects in GABAA receptor biogenesis in the pathogenesis of genetic epilepsies (GEs) and FS.

Phenotype, inheritance characteristics, and risk factors for idiopathic epilepsy in Finnish Spitz dogs

OBJECTIVE

To determine the phenotype, inheritance characteristics, and risk factors for idiopathic epilepsy (IE) in Finnish Spitz dogs (FSDs).

DESIGN

Prospective epidemiological study.

ANIMALS

2,141 FSDs.

PROCEDURES

From 2003 to 2004, questionnaires (n = 5,960) were sent to all owners of 1-to 10-year-old FSDs in Finland. Phone interviews were performed 1 to 2 years later.

RESULTS

Estimated prevalence of IE was 5.36% (111/2,069 of FSDs that were still alive). Males were predisposed to IE. The median age of onset was 3 years (range, 0.6 to 10 years). The median seizure frequency was 2 seizures/y (range, 0.5 to 48 seizures/y), and the median duration of the seizure episode was 11.75 minutes (range, 1.5 to 90 minutes). The majority (85%) of the seizures had a focal onset, and 54% were characterized as generalized secondary. A generalized seizure phase was determined to be a risk factor for development of progressive disease. Factors associated with the occurrence of a generalized phase were the age of onset, duration of the seizure, number of feeding times per day, and whether the dog was used for hunting. The seizures were not progressing in 678% of the dogs and were easily controlled by antiepileptic treatment in 78.9% of the dogs. The heritability estimate of IE in FSDs was 0.22; IE was best explained as a polygenic trait.

CONCLUSIONS AND CLINICAL RELEVANCE

In the present study conducted in Finland, complex focal seizures were the most common seizure type for FSDs with IE, and a generalized seizure phase was a risk factor for progression of the disease. Results suggested a benign course of epilepsy in FSDs.

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

Research in genetics of epilepsy represents an area of great interest both for clinical purposes and for understanding the basic mechanisms of epilepsy. Most mutations in epilepsies without structural brain abnormalities have been identified in ion channel genes, but an increasing number of genes involved in a diversity of functional and developmental processes are being recognized through whole exome or genome sequencing. Targeted molecular diagnosis is now available for different forms of epilepsy. The identification of epileptogenic mutations in patients before epilepsy onset and the possibility of developing therapeutic strategies tested in experimental models may facilitate experimental approaches that prevent epilepsy or decrease its severity. Functional analysis is essential for better understanding pathogenic mechanisms and gene interactions. In vitro experimental systems are either cells that usually do not express the protein of interest or neurons in primary cultures. In vivo/ex vivo systems are organisms or preparations obtained from them (e.g., brain slices), which should better model the complexity of brain circuits and actual pathophysiological conditions. Neurons differentiated from induced pluripotent stem cells generated from the skin fibroblasts of patients have recently allowed the study of mutations in human neurons having the genetic background of a given patient. However, there is remarkable complexity underlying epileptogenesis in the clinical dimension, as reflected by the fact that experimental models have not provided yet results having clinical translation and that, with a few exceptions concerning rare conditions, no new curative treatment has emerged from any genetic finding in epilepsy.

A novel GABRG2 mutation, p.R136*, in a family with GEFS+ and extended phenotypes

Genetic mutations in voltage-gated and ligand-gated ion channel genes have been identified in a small number of Mendelian families with genetic generalised epilepsies (GGEs). They are commonly associated with febrile seizures (FS), childhood absence epilepsy (CAE) and particularly with generalised or genetic epilepsy with febrile seizures plus (GEFS+). In clinical practice, despite efforts to categorise epilepsy and epilepsy families into syndromic diagnoses, many generalised epilepsies remain unclassified with a presumed genetic basis. During the systematic collection of epilepsy families, we assembled a cohort of families with evidence of GEFS+ and screened for variations in the γ2 subunit of the γ-aminobutyric acid (GABA) type A receptor gene (GABRG2). We detected a novel GABRG2(p.R136*) premature translation termination codon in one index-case from a two-generation nuclear family, presenting with an unclassified GGE, a borderline GEFS+ phenotype with learning difficulties and extended behavioural presentation. The GABRG2(p.R136*) mutation segregates with the febrile seizure component of this family's GGE and is absent in 190 healthy control samples. In vitro expression assays demonstrated that γ2(p.R136*) subunits were produced, but had reduced cell-surface and total expression. When γ2(p.R136*) subunits were co-expressed with α1 and β2 subunits in HEK 293T cells, GABA-evoked currents were reduced. Furthermore, γ2(p.R136*) subunits were highly-expressed in intracellular aggregations surrounding the nucleus and endoplasmic reticulum (ER), suggesting compromised receptor trafficking. A novel GABRG2(p.R136*) mutation extends the spectrum of GABRG2 mutations identified in GEFS+ and GGE phenotypes, causes GABAA receptor dysfunction, and represents a putative epilepsy mechanism.

A review of potassium channels in bipolar disorder

Although bipolar disorder (BP) is one of the most heritable psychiatric conditions, susceptibility genes for the disorder have yet to be conclusively identified. It is likely that variants in multiple genes across multiple pathways contribute to the genotype–phenotype relationship in the affected population. Recent evidence from genome-wide association studies implicates an entire class of genes related to the structure and regulation of ion channels, suggesting that the etiology of BP may arise from channelopathies. In this review, we examine the evidence for this hypothesis, with a focus on the potential role of voltage-gated potassium channels. We consider evidence from genetic and expression studies, and discuss the potential underlying biology. We consider animal models and treatment implications of the involvement of potassium ion channelopathy in BP. Finally, we explore intriguing parallels between BP and epilepsy, the signature channelopathy of the central nervous system.

Cation-chloride cotransporters NKCC1 and KCC2 as potential targets for novel antiepileptic and antiepileptogenic treatments

In cortical and hippocampal neurons, cation-chloride cotransporters (CCCs) control the reversal potential (EGABA) of GABAA receptor-mediated current and voltage responses and, consequently, they modulate the efficacy of GABAergic inhibition. Two members of the CCC family, KCC2 (the major neuron-specific K-Cl cotransporter; KCC isoform 2) and NKCC1 (the Na-K-2Cl cotransporter isoform 1 which is expressed in both neurons and glial cells) have attracted much interest in studies on GABAergic signaling under both normal and pathophysiological conditions, such as epilepsy. There is tentative evidence that loop diuretic compounds such as furosemide and bumetanide may have clinically relevant antiepileptic actions, especially when administered in combination with conventional GABA-mimetic drugs such as phenobarbital. Furosemide is a non-selective inhibitor of CCCs while at low concentrations bumetanide is selective for NKCCs. Search for novel antiepileptic drugs (AEDs) is highly motivated especially for the treatment of neonatal seizures which are often resistant to, or even aggravated by conventional AEDs. This review shows that the antiepileptic effects of loop diuretics described in the pertinent literature are based on widely heterogeneous mechanisms ranging from actions on both neuronal NKCC1 and KCC2 to modulation of the brain extracellular volume fraction. A promising strategy for the development of novel CCC-blocking AEDs is based on prodrugs that are activated following their passage across the blood-brain barrier. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.

Mutations in DEPDC5 cause familial focal epilepsy with variable foci

The majority of epilepsies are focal in origin, with seizures emanating from one brain region. Although focal epilepsies often arise from structural brain lesions, many affected individuals have normal brain imaging. The etiology is unknown in the majority of individuals, although genetic factors are increasingly recognized. Autosomal dominant familial focal epilepsy with variable foci (FFEVF) is notable because family members have seizures originating from different cortical regions. Using exome sequencing, we detected DEPDC5 mutations in two affected families. We subsequently identified mutations in five of six additional published large families with FFEVF. Study of families with focal epilepsy that were too small for conventional clinical diagnosis with FFEVF identified DEPDC5 mutations in approximately 12% of families (10/82). This high frequency establishes DEPDC5 mutations as a common cause of familial focal epilepsies. Shared homology with G protein signaling molecules and localization in human neurons suggest a role of DEPDC5 in neuronal signal transduction.

Missense mutations in the sodium-gated potassium channel gene KCNT1 cause severe autosomal dominant nocturnal frontal lobe epilepsy

We performed genomic mapping of a family with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and intellectual and psychiatric problems, identifying a disease-associated region on chromosome 9q34.3. Whole-exome sequencing identified a mutation in KCNT1, encoding a sodium-gated potassium channel subunit. KCNT1 mutations were identified in two additional families and a sporadic case with severe ADNFLE and psychiatric features. These findings implicate the sodium-gated potassium channel complex in ADNFLE and, more broadly, in the pathogenesis of focal epilepsies.

Emerging genetic influences in benign epilepsy with centro-temporal spikes - BECTS

BECTS is considered to be the most common childhood epileptic syndrome. Multifactorial inheritance is the most important model accounting for the genetic behavior of the common epilepsies. In recent years, different mutations in genes that control the excitability of neurons have been described. Recent reports on the involvement of the BDNF and ELP4 genes with possible roles in cell motility, migration, and adhesion have provided first insights into the complex molecular bases of childhood focal epilepsies. However, in the most common idiopathic benign childhood epilepsies (BECTS and occipital epilepsies), major breakthroughs are still awaited.

The patient with infantile seizures

Great strides in the identification, etiologic understanding, and treatment of metabolic and genetic disorders associated with infantile seizures have occurred in recent years. We explain the cause, pathogenesis, diagnosis, presentation, and treatment of certain metabolic disorders that now have defined interventions that improve and optimize neurologic outcome. A systematic approach to infantile seizures will allow the primary practitioner to more effectively create a differential diagnosis with close attention to the disorders that have specific treatment applications.

Genetic variations and associated pathophysiology in the management of epilepsy

The genomic era has enabled the application of molecular tools to the solution of many of the genetic epilepsies, with and without comorbidities. Massively parallel sequencing has recently reinvigorated gene discovery for the monogenic epilepsies. Recurrent and novel copy number variants have given much-needed impetus to the advancement of our understanding of epilepsies with complex inheritance. Superimposed upon that is the phenotypic blurring by presumed genetic modifiers scattering the effects of the primary mutation. The genotype-first approach has uncovered associated syndrome constellations, of which epilepsy is only one of the syndromes. As the molecular genetic basis for the epilepsies unravels, it will increasingly influence the classification and diagnosis of the epilepsies. The ultimate goal of the molecular revolution has to be the design of treatment protocols based on genetic profiles, and cracking the 30% of epilepsies refractory to current medications, but that still lies well into the future. The current focus is on the scientific basis for epilepsy. Understanding its genetic causes and biophysical mechanisms is where we are currently positioned: prizing the causes of epilepsy "out of the shadows" and exposing its underlying mechanisms beyond even the ion-channels.

Osteopenia due to enhanced cathepsin K release by BK channel ablation in osteoclasts

Background

The process of bone resorption by osteoclasts is regulated by Cathepsin K, the lysosomal collagenase responsible for the degradation of the organic bone matrix during bone remodeling. Recently, Cathepsin K was regarded as a potential target for therapeutic intervention of osteoporosis. However, mechanisms leading to osteopenia, which is much more common in young female population and often appears to be the clinical pre-stage of idiopathic osteoporosis, still remain to be elucidated, and molecular targets need to be identified.

Methodology/Principal Findings

We found, that in juvenile bone the large conductance, voltage and Ca²⁺-activated (BK) K⁺ channel, which links membrane depolarization and local increases in cytosolic calcium to hyperpolarizing K⁺ outward currents, is exclusively expressed in osteoclasts. In juvenile BK-deficient (BK^−/−) female mice, plasma Cathepsin K levels were elevated two-fold when compared to wild-type littermates. This increase was linked to an osteopenic phenotype with reduced bone mineral density in long bones and enhanced porosity of trabecular meshwork in BK^−/− vertebrae as demonstrated by high-resolution flat-panel volume computed tomography and micro-CT. However, plasma levels of sRANKL, osteoprotegerin, estrogene, Ca²⁺ and triiodthyronine as well as osteoclastogenesis were not altered in BK^−/− females.

Conclusion/Significance

Our findings suggest that the BK channel controls resorptive osteoclast activity by regulating Cathepsin K release. Targeted deletion of BK channel in mice resulted in an osteoclast-autonomous osteopenia, becoming apparent in juvenile females. Thus, the BK^−/− mouse-line represents a new model for juvenile osteopenia, and revealed the BK channel as putative new target for therapeutic controlling of osteoclast activity.

Candidate genes for idiopathic epilepsy in four dog breeds

Background

Idiopathic epilepsy (IE) is a naturally occurring and significant seizure disorder affecting all dog breeds. Because dog breeds are genetically isolated populations, it is possible that IE is attributable to common founders and is genetically homogenous within breeds. In humans, a number of mutations, the majority of which are genes encoding ion channels, neurotransmitters, or their regulatory subunits, have been discovered to cause rare, specific types of IE. It was hypothesized that there are simple genetic bases for IE in some purebred dog breeds, specifically in Vizslas, English Springer Spaniels (ESS), Greater Swiss Mountain Dogs (GSMD), and Beagles, and that the gene(s) responsible may, in some cases, be the same as those already discovered in humans.

Results

Candidate genes known to be involved in human epilepsy, along with selected additional genes in the same gene families that are involved in murine epilepsy or are expressed in neural tissue, were examined in populations of affected and unaffected dogs. Microsatellite markers in close proximity to each candidate gene were genotyped and subjected to two-point linkage in Vizslas, and association analysis in ESS, GSMD and Beagles.

Conclusions

Most of these candidate genes were not significantly associated with IE in these four dog breeds, while a few genes remained inconclusive. Other genes not included in this study may still be causing monogenic IE in these breeds or, like many cases of human IE, the disease in dogs may be likewise polygenic.

Neuronal voltage-gated ion channels are genetic modifiers of generalized epilepsy with febrile seizures plus

Mutations in the neuronal voltage-gated sodium channel genes SCN1A and SCN2A are associated with inherited epilepsies, including genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (severe myoclonic epilepsy of infancy). The clinical presentation and severity of these epilepsies vary widely, even in people with the same mutation, suggesting the action of environmental or genetic modifiers. To gain support for the hypothesis that genetic modifiers can influence clinical presentation in patients with SCN1A-derived GEFS+, we used mouse models to study the effect of combining the human GEFS+ mutation SCN1A-R1648H with SCN2A, KCNQ2, and SCN8A mutations. Knock-in mice heterozygous for the R1648H mutation (Scn1a(RH/+)) have decreased thresholds to induced seizures and infrequent spontaneous seizures, whereas homozygotes display spontaneous seizures and premature lethality. Scn2a(Q54) transgenic mice have a mutation in Scn2a that results in spontaneous, adult-onset partial motor seizures, and mice carrying the Kcnq2-V182M mutation exhibit increased susceptibility to induced seizures, and rare spontaneous seizures as adults. Combining the Scn1a-R1648H allele with either Scn2a(Q54) or Kcnq2(V182M/+) results in early-onset, generalized tonic-clonic seizures and juvenile lethality in double heterozygous mice. In contrast, Scn8a mutants exhibit increased resistance to induced seizures. Combining the Scn1a-R1648H and Scn8a-med-jo alleles restores normal thresholds to flurothyl-induced seizures in Scn1a(RH/+) heterozygotes and improved survival of Scn1a(RH/RH) homozygotes. Our results demonstrate that variants in Scn2a, Kcnq2, and Scn8a can dramatically influence the phenotype of mice carrying the Scn1a-R1648H mutation and suggest that ion channel variants may contribute to the clinical variation seen in patients with monogenic epilepsy.

Genetically complex epilepsies, copy number variants and syndrome constellations

Epilepsy is one of the most common neurological disorders, with a prevalence of 1% and lifetime incidence of 3%. There are numerous epilepsy syndromes, most of which are considered to be genetic epilepsies. Despite the discovery of more than 20 genes for epilepsy to date, much of the genetic contribution to epilepsy is not yet known. Copy number variants have been established as an important source of mutation in other complex brain disorders, including intellectual disability, autism and schizophrenia. Recent advances in technology now facilitate genome-wide searches for copy number variants and are beginning to be applied to epilepsy. Here, we discuss what is currently known about the contribution of copy number variants to epilepsy, and how that knowledge is redefining classification of clinical and genetic syndromes.

Prevalence of Epilepsy among Cataract Patients

PURPOSE

To evaluate the prevalence of epilepsy among patients undergoing cataract surgery.

DESIGN

A retrospective observational case control study.

METHODS

We calculated the prevalence of epilepsy among all the patients older than 50 years who underwent cataract surgery (years 2000-2007, n = 12,984) in a district of the largest health maintenance organization in Israel (the Central District of Clalit Health Services) and among 25,968 age and gender matched controls. The database was screened for epilepsy by integrating the clinical and ancillary work-up as well as the drug regimen. The use of anti-epileptic drugs (AEDs) was evaluated among the cataract patients and the controls. The main outcome measure was the prevalence of epilepsy and antiepileptic medical treatment among patients undergoing cataract surgery versus controls.

RESULTS

No difference was found in demographics among the groups including age, gender, marriage status, socioeconomic class and living place between the study and control groups (except for patients origin). Epilepsy was found to be significantly more prevalent in patients undergoing cataract surgery. The odds ratio (OR) was 1.3 (95% confidence interval (CI): 1.1-1.6): 1.4 in men (95% CI: 1.1-1.9) and 1.2 in women (95% CI: 1.0-1.6). AEDs, particularly clonazepam (OR = 1.5, 95% CI: 1.1-2.1) and carbamazepine (OR = 1.4, 95% CI: 1.05-1.8), were also used more by cataract patients. Multivariate logistic regression analysis revealed a significant association between cataract surgery and epilepsy (OR 1.26, p < 0.001) as well as diabetes (OR 1.38, p < 0.001), arterial hypertension (OR 1.26, p < 0.001), smoking (OR 1.22, p < 0.001), hyperlipidemia (OR 1.12, p < 0.001), and Ashkenazi origin (OR 0.85, p < 0.001).

CONCLUSIONS

Epilepsy is associated with the presence of cataract. Various hypotheses may explain this finding, including a cataractogenic role of AEDs.

Epilepsy as a dynamic disease: a tutorial of the past with an eye to the future

How can clinical epileptologists and computational neuroscientists learn to function together within the confines of interdisciplinary teams to develop new and more effective treatment strategies for epilepsy? Here we introduce epileptologists to the way modelers think about epilepsy as a dynamic disease. Not only is there terminology to be learned, but also it is necessary to identify those areas where clinical input might be expected to have the greatest impact. It is concluded that both groups have major roles to play in educating, evaluating, and shaping the direction of the efforts of each other.