KCNH2 gene mutation: a potential link between epilepsy and long QT-2 syndrome

Neurocardiac pathologies associated with potassium channelopathies

Voltage-gated potassium channels are expressed throughout the human body and are essential for physiological functions. These include delayed rectifiers, A-type channels, outward rectifiers, and inward rectifiers. They impact electrical function in the heart (repolarization) and brain (repolarization and stabilization of the resting membrane potential). KCNQx and KCNHx encode Kv7.x and Kv11.x proteins, which form delayed rectifier potassium channels. KCNQx and KCNHx channelopathies are associated with both cardiac and neuronal pathologies. These include electrocardiographic abnormalities, cardiac arrhythmias, sudden cardiac death (SCD), epileptiform discharges, seizures, bipolar disorder, and sudden unexpected death in epilepsy (SUDEP). Due to the ubiquitous expression of KCNQx and KCNHx channels, abnormalities in their function can be particularly harmful, increasing the risk of sudden death. For example, KCNH2 variants have a dual role in both cardiac and neuronal pathologies, whereas KCNQ2 and KCNQ3 variants are associated with severe and refractory epilepsy. Recurrent and uncontrolled seizures lead to secondary abnormalities, which include autonomics, cardiac electrical function, respiratory drive, and neuronal electrical activity. Even with a wide array of anti-seizure therapies available on the market, one-third of the more than 70 million people worldwide with epilepsy have uncontrolled seizures (i.e., intractable/drug-resistant epilepsy), which negatively impact neurodevelopment and quality of life. To capture the current state of the field, this review examines KCNQx and KCNHx expression patterns and electrical function in the brain and heart. In addition, it discusses several KCNQx and KCNHx variants that have been clinically and electrophysiologically characterized. Because these channel variants are associated with multi-system pathologies, such as epileptogenesis, Kv7 channel modulators provide a potential anti-seizure therapy, particularly for people with intractable epilepsy. Ultimately an increased understanding of the role of Kv channels throughout the body will fuel the development of innovative, safe, and effective therapies for people at a high risk of sudden death (SCD and SUDEP).

An intracellular hydrophobic nexus critical for hERG1 channel slow deactivation

Slow deactivation is a critical property of voltage-gated K+ channels encoded by the human Ether-à-go-go-Related Gene 1 (hERG). hERG1 channel deactivation is modulated by interactions between intracellular N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBh) domains. The PAS domain is multipartite, comprising a globular domain (gPAS; residues 26-135) and an N-terminal PAS-cap that is further subdivided into an initial unstructured "tip" (residues 1-12) and an amphipathic α-helical region (residues 13-25). Although the PAS-cap tip has long been considered the effector of slow deactivation, how its position near the gating machinery is controlled has not been elucidated. Here, we show that a triad of hydrophobic interactions among the gPAS, PAS-cap α helix, and the CNBh domains is required to support slow deactivation in hERG1. The primary sequence of this "hydrophobic nexus" is highly conserved among mammalian ERG channels but shows key differences to fast-deactivating Ether-à-go-go 1 (EAG1) channels. Combining sequence analysis, structure-directed mutagenesis, electrophysiology, and molecular dynamics simulations, we demonstrate that polar serine substitutions uncover an intermediate deactivation mode that is also mimicked by deletion of the PAS-cap α helix. Molecular dynamics simulation analyses of the serine-substituted channels show an increase in distance among the residues of the hydrophobic nexus, a rotation of the intracellular gating ring, and a retraction of the PAS-cap tip from its receptor site near the voltage sensor domain and channel gate. These findings provide compelling evidence that the hydrophobic nexus coordinates the respective components of the intracellular gating ring and positions the PAS-cap tip to control hERG1 deactivation gating.

Generation of KCNH2 heterozygous knockout induced pluripotent stem cell (iPSC) line (Long and Short QT Syndrome)

KCNH2 (Potassium Voltage-Gated Channel Subfamily H Member) encodes a voltage-activated potassium channel role as rapidly activating-delayed rectifier potassium channel that plays an essential role in the final repolarization of the ventricular action potential. Mutations in this gene can cause long QT syndrome and short QT syndrome. Transcript variants encoding distinct isoforms were also identified. In this study, we generated induced pluripotent stem cells (iPSC) from a healthy individual by electroporation of peripheral blood mononuclear cells and generated a KCNH2 heterozygous knockout human iPSC line via CRISPR/Cas9 gene editing. The resulting iPSCs had a normal karyotype, were free of genomically integrated epitomal plasmids, expressed pluripotency markers, and maintained trilineage differentiation potential.

Identification and characterization of two novel KCNH2 mutations contributing to long QT syndrome

We identified two different inherited mutations in KCNH2 gene, or human ether-a-go-go related gene (hERG), which are linked to Long QT Syndrome. The first mutation was in a 1-day-old infant, whereas the second was in a 14-year-old girl. The two KCNH2 mutations were transiently transfected into either human embryonic kidney (HEK) cells or human induced pluripotent stem-cell derived cardiomyocytes. We performed associated multiscale computer simulations to elucidate the arrhythmogenic potentials of the KCNH2 mutations. Genetic screening of the first and second index patients revealed a heterozygous missense mutation in KCNH2, resulting in an amino acid change (P632L) in the outer loop of the channel and substitution at position 428 from serine to proline (S428P), respectively. Heterologous expression of P632L and S428P into HEK cells produced no hERG current compared to the wild type (WT). Moreover, the co-transfection of WT and P632L yielded no hERG current; however, the co-transfection of WT and S428P yielded partial hERG current. Action potentials were prolonged in a complete or partial blockade of hERG current from computer simulations which was more severe in Purkinje than ventricular myocytes. Three dimensional simulations revealed a higher susceptibility to reentry in the presence of hERG current blockade. Our experimental findings suggest that both P632L and S428P mutations may impair the KCNH2 gene. The Purkinje cells exhibit a more severe phenotype than ventricular myocytes, and the hERG current blockade renders the ventricles an arrhythmogenic substrate from computer modeling.

Sudden unexpected death in epilepsy: A critical view of the literature

Sudden unexpected death in epilepsy (SUDEP) is a sudden, unexpected, witnessed or unwitnessed, non-traumatic and non-drowning death, occurring in benign circumstances, in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus in which postmortem examination does not reveal other causes of death. Lower diagnostic levels are assigned when cases met most or all of these criteria, but data suggested more than one possible cause of death. The incidence of SUDEP ranged from 0.09 to 2.4 per 1000 person-years. Differences can be attributed to the age of the study populations (with peaks in the 20-40-year age group) and the severity of the disease. Young age, disease severity (in particular, a history of generalized TCS), having symptomatic epilepsy, and the response to antiseizure medications (ASMs) are possible independent predictors of SUDEP. The pathophysiological mechanisms are not fully known due to the limited data available and because SUDEP is not always witnessed and has been electrophysiologically monitored only in a few cases with simultaneous assessment of respiratory, cardiac, and brain activity. The pathophysiological basis of SUDEP may vary according to different circumstances that make that particular seizure, in that specific moment and in that patient, a fatal event. The main hypothesized mechanisms, which could contribute to a cascade of events, are cardiac dysfunction (included potential effects of ASMs, genetically determined channelopathies, acquired heart diseases), respiratory dysfunction (included postictal arousal deficit for the respiratory mechanism, acquired respiratory diseases), neuromodulator dysfunction, postictal EEG depression and genetic factors.

ILAE Genetic Literacy Series: Postmortem Genetic Testing in Sudden Unexpected Death in Epilepsy

A 24-year-old man with non-lesional bitemporal lobe epilepsy since age 16 years was found dead in bed around midday. He was last seen the previous night when he was witnessed to have a tonic-clonic seizure. Before his death, he was experiencing weekly focal impaired awareness seizures and up to two focal-to-bilateral tonic-clonic seizures each year. He had trialed several antiseizure medications and was on levetiracetam 1500 mg/day, lamotrigine 400 mg/day, and clobazam 10 mg/day at the time of death. Other than epilepsy, his medical history was unremarkable. Of note, he had an older brother with a history of febrile seizures and a paternal first cousin with epilepsy. No cause of death was identified following a comprehensive postmortem investigation. The coroner classified the death as "sudden unexpected death in epilepsy" (SUDEP), and it would qualify as "definite SUDEP" using the current definitions.1 This left the family with many questions unanswered; in particular, they wish to know what caused the death and whether it could happen to other family members. Could postmortem genetic testing identify a cause of death, provide closure to the family, and facilitate cascade genetic testing of first-degree family members who may be at risk of sudden death? While grieving family members struggle with uncertainty about the cause of death, we as clinicians also face similar uncertainties about genetic contributions to SUDEP, especially when the literature is sparse, and the utility of genetic testing is still being worked out. We aim to shed some light on this topic, highlighting areas where data is emerging but also areas where uncertainty remains, keeping our case in mind as we examine this clinically important area.

KCNH2 variants in a family with epilepsy and long QT syndrome: A case report and literature review

OBJECTIVE

Genes associated with Long QT syndromes (LQTS), such as KCNQ1, KCNH2, and SCN5A, are common causes of epilepsy. The Arg 744* variant of KCNH2 has been previously reported in people with epilepsy or LQTS, but none of these patients were reported to simultaneously suffer from epilepsy and LQTS. Herein, we report the case of a family with epilepsy and cardiac disorders.

METHOD

The proband, a 25-year-old woman, with a family history of epilepsy and LQTS was followed at West China Hospital. The proband experienced her first seizure at the age of seven. Video electroencephalograms (vEEGs) showed epileptic discharges. Her 24-h dynamic electrocardiograms 2 (ECGs) showed QTc prolongation. The proband's mother, who is 50 years old, had her first generalized tonic-clonic seizure (GTCS) at the age of 18 years old. After she gave birth at the age of 25, the frequency of seizures increased, so antiepileptic therapy was initiated. When she was 28 years old, she complained of palpitations and syncope for the first time, and QTc prolongation was detected on her 24-h dynamic ECGs. The proband's grandmother also had complaints of palpitations and syncope at the age of 73. Her 24-h dynamic ECGs indicated supraventricular arrhythmia, with the lowest heart rate being 41 bpm, so she agreed to a pacemaker. Considering the young patient's family history, blood samples of the patient and her parents were collected for genetic analysis.

RESULTS

A heterozygous variant of KCNH2 [c.2230 (exon9) C>T, p. Arg744Ter, 416, NM_000238, rs189014161] was found in the proband and her mother. According to the guidelines of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology, we classified the KCNH2 variant as pathogenic.

SIGNIFICANCE

This study expands the clinical phenotype of the Arg 744* KCNH2 pathogenic variant. In the context of channelopathies, because of the genetic susceptibility of the brain and the heart, the risk of comorbidity should be considered. This also indicates the importance of precise antiepileptic drug (AED) management and regular ECG monitoring for patients with channelopathies.

Gene mutations in comorbidity of epilepsy and arrhythmia

Epilepsy is one of the most common neurological disorders, and sudden unexpected death in epilepsy (SUDEP) is the most severe outcome of refractory epilepsy. Arrhythmia is one of the heterogeneous factors in the pathophysiological mechanism of SUDEP with a high incidence in patients with refractory epilepsy, increasing the risk of premature death. The gene co-expressed in the brain and heart is supposed to be the genetic basis between epilepsy and arrhythmia, among which the gene encoding ion channel contributes to the prevalence of "cardiocerebral channelopathy" theory. Nevertheless, this theory could only explain the molecular mechanism of comorbid arrhythmia in part of patients with epilepsy (PWE). Therefore, we summarized the mutant genes that can induce comorbidity of epilepsy and arrhythmia and the possible corresponding treatments. These variants involved the genes encoding sodium, potassium, calcium and HCN channels, as well as some non-ion channel coding genes such as CHD4, PKP2, FHF1, GNB5, and mitochondrial genes. The relationship between genotype and clinical phenotype was not simple linear. Indeed, genes co-expressed in the brain and heart could independently induce epilepsy and/or arrhythmia. Mutant genes in brain could affect cardiac rhythm through central or peripheral regulation, while in the heart it could also affect cerebral electrical activity by changing the hemodynamics or internal environment. Analysis of mutations in comorbidity of epilepsy and arrhythmia could refine and expand the theory of "cardiocerebral channelopathy" and provide new insights for risk stratification of premature death and corresponding precision therapy in PWE.

Autonomic dysfunction in epilepsy mouse models with implications for SUDEP research

Epilepsy has a high prevalence and can severely impair quality of life and increase the risk of premature death. Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in drug-resistant epilepsy and most often results from respiratory and cardiac impairments due to brainstem dysfunction. Epileptic activity can spread widely, influencing neuronal activity in regions outside the epileptic network. The brainstem controls cardiorespiratory activity and arousal and reciprocally connects to cortical, diencephalic, and spinal cord areas. Epileptic activity can propagate trans-synaptically or via spreading depression (SD) to alter brainstem functions and cause cardiorespiratory dysfunction. The mechanisms by which seizures propagate to or otherwise impair brainstem function and trigger the cascading effects that cause SUDEP are poorly understood. We review insights from mouse models combined with new techniques to understand the pathophysiology of epilepsy and SUDEP. These techniques include in vivo, ex vivo, invasive and non-invasive methods in anesthetized and awake mice. Optogenetics combined with electrophysiological and optical manipulation and recording methods offer unique opportunities to study neuronal mechanisms under normal conditions, during and after non-fatal seizures, and in SUDEP. These combined approaches can advance our understanding of brainstem pathophysiology associated with seizures and SUDEP and may suggest strategies to prevent SUDEP.

The ERG1 K+ Channel and Its Role in Neuronal Health and Disease

The ERG1 potassium channel, encoded by KCNH2, has long been associated with cardiac electrical excitability. Yet, a growing body of work suggests that ERG1 mediates physiology throughout the human body, including the brain. ERG1 is a regulator of neuronal excitability, ERG1 variants are associated with neuronal diseases (e.g., epilepsy and schizophrenia), and ERG1 serves as a potential therapeutic target for neuronal pathophysiology. This review summarizes the current state-of-the-field regarding the ERG1 channel structure and function, ERG1’s relationship to the mammalian brain and highlights key questions that have yet to be answered.

Effects of Antiarrhythmic Drugs on Antiepileptic Drug Action-A Critical Review of Experimental Findings

Severe cardiac arrhythmias developing in the course of seizures increase the risk of SUDEP (sudden unexpected death in epilepsy). Hence, epilepsy patients with pre-existing arrhythmias should receive appropriate pharmacotherapy. Concomitant treatment with antiarrhythmic and antiseizure medications creates, however, the possibility of drug–drug interactions. This is due, among other reasons, to a similar mechanism of action. Both groups of drugs inhibit the conduction of electrical impulses in excitable tissues. The aim of this review was the analysis of such interactions in animal seizure models, including the maximal electroshock (MES) test in mice, a widely accepted screening test for antiepileptic drugs.

Clinical Genetics of Inherited Arrhythmogenic Disease in the Pediatric Population

Sudden death is a rare event in the pediatric population but with a social shock due to its presentation as the first symptom in previously healthy children. Comprehensive autopsy in pediatric cases identify an inconclusive cause in 40-50% of cases. In such cases, a diagnosis of sudden arrhythmic death syndrome is suggested as the main potential cause of death. Molecular autopsy identifies nearly 30% of cases under 16 years of age carrying a pathogenic/potentially pathogenic alteration in genes associated with any inherited arrhythmogenic disease. In the last few years, despite the increasing rate of post-mortem genetic diagnosis, many families still remain without a conclusive genetic cause of the unexpected death. Current challenges in genetic diagnosis are the establishment of a correct genotype-phenotype association between genes and inherited arrhythmogenic disease, as well as the classification of variants of uncertain significance. In this review, we provide an update on the state of the art in the genetic diagnosis of inherited arrhythmogenic disease in the pediatric population. We focus on emerging publications on gene curation for genotype-phenotype associations, cases of genetic overlap and advances in the classification of variants of uncertain significance. Our goal is to facilitate the translation of genetic diagnosis to the clinical area, helping risk stratification, treatment and the genetic counselling of families.

Anesthetic Care of a Child Harboring the KCNH2 Gene

Epilepsy is a heterogeneous group of disorders characterized by recurrent and generally unprovoked seizures. Genetic mutations may play an important role in the etiology of epilepsy. Over the past few years, genetic mutations in various genes have been identified in patients with epilepsy. One of the more common mutations responsible for seizures involves the KCNH2 gene. The KCNH2 gene encodes the Kv11.1 protein, which involves the pore-forming subunit of a rapidly activating-delayed rectifier potassium channel. This channel plays an essential role in phases 2 and 3 of the cardiac action potential involving cardiac repolarization as well as being expressed in various parts of the central nervous system where it regulates neuronal function. As such, patients presenting with this gene mutation may be at risk not only for seizures, but also abnormalities in cardiac repolarization leading to lethal arrhythmias. We present an 11-year-old girl who required general anesthesia for magnetic resonance imaging as part of her evaluation for non-convulsive status epilepticus. An epilepsy gene panel evaluated revealed a KCNH2 gene mutation. End-organ involvement of KCNH2 gene mutations is presented, previous reports of anesthetic care for these patients are reviewed, and options for anesthetic care are discussed.

Louis EK, Reichard RR, Edwards WD, Ackerman MJ, Somers VK. Confirmation of Cause of Death Via Comprehensive Autopsy and Whole Exome Molecular Sequencing in People With Epilepsy and Sudden Unexpected Death

Background Sudden cardiac arrest is the leading mode of death in the United States. Epilepsy affects 1% of Americans; yet epidemiological data show a prevalence of 4% in cases of sudden cardiac arrest. Sudden unexpected death in epilepsy (SUDEP) may share features with sudden cardiac arrest. The objective of this study was to report autopsy and genomic findings in a large cohort of SUDEP cases. Methods and Results Mayo Clinic Sudden Death Registry containing cases (ages 0-90 years) of sudden unexpected and unexplained deaths 1960 to present was queried. Exome sequencing performed on decedent cases. From 13 687 cases of sudden death, 656 (4.8%) had a history of seizures, including 368 confirmed by electroencephalography, 96 classified as SUDEP, 58 as non-SUDEP, and 214 as unknown (insufficient records). Mean age of death in SUDEP was 37 (±19.7) years; 56 (58.3%) were male; 65% of deaths occurred at night; 54% were found in bed; and 80.6% were prone. Autopsies were obtained in 83 cases; bystander coronary artery disease was frequently reported as cause of death; nonspecific fibrosis was seen in 32.6% of cases, in structurally normal hearts. There were 4 cases of Dravet syndrome with pathogenic variants in SCN1A gene. Using whole exome sequencing in 11 cases, 18 ultrarare nonsynonymous variants were identified in 6 cases including CACNB2, RYR2, CLNB, CACNA1H, and CLCN2. Conclusions This study examined one of the largest single-center US series of SUDEP cases. Several cases were reclassified as SUDEP, 15% had an ECG when alive, and 11 (11.4%) had blood for whole exome sequencing analysis. The most frequent antemortem genetic finding was pathogenic variants in SCN1A; postmortem whole exome sequencing identified 18 ultrarare variants.

Electrocardiographic Abnormalities and Mortality in Epilepsy Patients

Background and Objectives: People with epilepsy (PWE) have a 2–3 times higher mortality rate than the general population. Sudden unexpected death in epilepsy (SUDEP) comprises a significant proportion of premature deaths, whereas sudden cardiac death (SCD) is among the leading causes of sudden death in the general population. Cardiac pathologies are significantly more prevalent in PWE. Whether electrocardiographic (ECG) parameters are associated with remote death in PWE has yet to be elucidated. The study objective was to assess whether interictal ECG parameters are associated with mortality in the long-term. Materials and Methods: The study involved 471 epilepsy patients who were hospitalized after a bilateral tonic-clonic seizure(s). ECG parameters were obtained on the day of hospitalization (heart rate, PQ interval, QRS complex, QT interval, heart rate corrected QT interval (QTc), ST segment and T wave changes), as well as reported ECG abnormalities. Mortality data were obtained from the Latvian National Cause-of-Death database 3–11, mean 7.0 years after hospitalization. The association between the ECG parameters and the long-term clinical outcome were examined. Results: At the time of assessment, 75.4% of patients were alive and 24.6% were deceased. Short QTc interval (odds ratio (OR) 4.780; 95% confidence interval (CI) 1.668–13.698; p = 0.004) was associated with a remote death. After the exclusion of known comorbidities with high mortality rates, short QTc (OR 4.631) and ECG signs of left ventricular hypertrophy (OR 5.009) were associated with a remote death. Conclusions: The association between routine 12-lead rest ECG parameters—short QTc interval and a pattern of left ventricular hypertrophy—and remote death in epilepsy patients was found. To the best of our knowledge, this is the first study to associate rest ECG parameters with remote death in an epileptic population.

Potassium channels as prominent targets and tools for the treatment of epilepsy

INTRODUCTION

K⁺ channels are of great interest to epilepsy research as mutations in their genes are found in humans with inherited epilepsy. At the level of cellular physiology, K+ channels control neuronal intrinsic excitability and are the main contributors to membrane repolarization of active neurons. Recently, a genetically modified voltage-dependent K⁺ channel has been patented as a remedy for epileptic seizures.

AREAS COVERED

We review the role of potassium channels in excitability, clinical and experimental evidence for the association of potassium channelopathies with epilepsy, the targeting of K+ channels by drugs, and perspectives of gene therapy in epilepsy with the expression of extra K+ channels in the brain.

EXPERT OPINION

Control over K+ conductance is of great potential benefit for the treatment of epilepsy. Nowadays, gene therapy affecting K+ channels is one of the most promising approaches to treat pharmacoresistant focal epilepsy.

Sotalol does not interfere with the antielectroshock action of selected second-generation antiepileptic drugs in mice

Background

Due to blocking β-receptors, and potassium KCNH2 channels, sotalol may influence seizure phenomena. In the previous study, we have shown that sotalol potentiated the antielectroshock action of phenytoin and valproate in mice.

Materials and methods

As a continuation of previous experiments, we examined the effect of sotalol on the action of four chosen second-generation antiepileptic drugs (oxcarbazepine, lamotrigine, pregabalin, and topiramate) against the maximal electroshock in mice. Undesired effects were evaluated in the chimney test (motor impairment) and step-through passive-avoidance task (long-term memory deficits). Finally, brain concentrations of antiepileptics were determined by fluorescence polarization immunoassay, while those of sotalol by liquid chromatography–mass spectrometry.

Results

Sotalol at doses of up to 100 mg/kg did not affect the electroconvulsive threshold. Applied at doses of 80–100 mg/kg, sotalol did not affect the antielectroshock action of oxcarbazepine, lamotrigine, pregabalin, or topiramate. Sotalol alone and in combinations with antiepileptics impaired neither motor performance nor long-term memory. Finally, sotalol significantly decreased the brain concentrations of lamotrigine and increased those of oxcarbazepine and topiramate. Pharmacokinetic interactions, however, did not influence the final antielectroshock effects of above-mentioned drug combinations. On the other hand, the brain concentrations of sotalol were not changed by second-generation antiepileptics used in this study.

Conclusion

Sotalol did not reduce the antielectroshock action of four second-generation antiepileptic drugs examined in this study. Therefore, this antidepressant drug should not interfere with antiseizure effects of lamotrigine, oxcarbazepine, pregabalin, and topiramate in patients with epilepsy. To draw final conclusions, our preclinical data should still be confirmed in other experimental models and clinical conditions.

Neuro-arrhythmology: a challenging field of action and research: a review from the Task Force of Neuro-arrhythmology of Italian Association of Arrhythmias and Cardiac Pacing

: There is a growing interest in the study of the mechanisms of heart and brain interactions with the aim to improve the management of high-impact cardiac rhythm disorders, first of all atrial fibrillation. However, there are several topics to which the scientific interests of cardiologists and neurologists converge constituting the basis for enhancing the development of neuro-arrhythmology. This multidisciplinary field should cover a wide spectrum of diseases, even beyond the classical framework corresponding to stroke and atrial fibrillation and include the complex issues of seizures as well as loss of consciousness and syncope. The implications of a more focused interaction between neurologists and cardiologists in the field of neuro-arrhythmology should include in perspective the institution of research networks specifically devoted to investigate 'from bench to bedside' the complex pathophysiological links of the abovementioned diseases, with involvement of scientists in the field of biochemistry, genetics, molecular medicine, physiology, pathology and bioengineering. An investment in the field could have important implications in the perspectives of a more personalized approach to patients and diseases, in the context of 'precision'medicine. Large datasets and electronic medical records, with the approach typical of 'big data' could enhance the possibility of new findings with potentially important clinical implications. Finally, the interaction between neurologists and cardiologists involved in arrythmia management should have some organizational implications, with new models of healthcare delivery based on multidisciplinary assistance, similarly to that applied in the case of syncope units.

Variant frequencies of KCNQ1, KCNH2, and SCN5A in a Chinese inherited arrhythmia cohort and other disease cohorts undergoing genetic testing

KCNQ1, KCNH2, and SCN5A are the most common genes responsible for long QT syndrome and Brugada syndrome. However, the genetic variant frequencies of the three genes in different Chinese disease cohorts are largely unknown. In this study, we analyzed the genetic variants of KCNQ1, KCNH2, and SCN5A in patients from seven cohorts (total N = 11945, including patients clinically suspected to have inherited arrhythmia [n = 122], other cardiovascular diseases [n = 1045], epilepsy [n = 4797], or other diseases [n = 5841], and healthy controls [n = 140]) who had undergone genetic testing. All of these variants were identified via genetic testing by two Chinese companies using the Hi-Seq 2000 platform. A total of 1018 variants (minor allele frequency <0.01) were identified, with 186 (18%), 374 (37%), and 458 (46%) variants in the coding exons of KCNQ1, KCNH2, and SCN5A, respectively. Of these variants, 84% had unknown or uncertain clinical significance. The frequency of identified ClinVar pathological/likely pathological variants was higher for KCNQ1 (13/186, 7.0%) than for KCNH2 (6/374, 1.6%) or SCN5A (10/458, 2.2%), and KCNH2 held the highest number and proportion of radical mutations (30/374, 8%). The prevalence of variants was highest in the inherited arrhythmia cohort (35%) and lowest in the healthy controls (<4%), as expected. Noticeably, the variant prevalence was relatively high in the epilepsy cohort (27%). Finally, only 22 of the 82 variants (26%) identified by both companies had consistent interpretations of pathogenicity between the two companies. Our study demonstrated a comprehensive spectrum of variants in KCNQ1, KCNH2, and SCN5A in a large number of Chinese individuals, including inherited arrhythmia, cardiovascular diseases, and epilepsy. The detailed variant frequency data of each cohort could serve as a valuable reference to facilitate further variant classification by others. We also found that the interpretations of pathogenicity differed greatly among the companies.

The Drosophila ERG channel seizure plays a role in the neuronal homeostatic stress response

Neuronal physiology is particularly sensitive to acute stressors that affect excitability, many of which can trigger seizures and epilepsies. Although intrinsic neuronal homeostasis plays an important role in maintaining overall nervous system robustness and its resistance to stressors, the specific genetic and molecular mechanisms that underlie these processes are not well understood. Here we used a reverse genetic approach in Drosophila to test the hypothesis that specific voltage-gated ion channels contribute to neuronal homeostasis, robustness, and stress resistance. We found that the activity of the voltage-gated potassium channel seizure (sei), an ortholog of the mammalian ERG channel family, is essential for protecting flies from acute heat-induced seizures. Although sei is broadly expressed in the nervous system, our data indicate that its impact on the organismal robustness to acute environmental stress is primarily mediated via its action in excitatory neurons, the octopaminergic system, as well as neuropile ensheathing and perineurial glia. Furthermore, our studies suggest that human mutations in the human ERG channel (hERG), which have been primarily implicated in the cardiac Long QT Syndrome (LQTS), may also contribute to the high incidence of seizures in LQTS patients via a cardiovascular-independent neurogenic pathway.

Truncating biallelic variant in DNAJA1, encoding the co-chaperone Hsp40, is associated with intellectual disability and seizures

Intellectual disability poses a huge burden on the health care system, and it is one of the most common referral reasons to the genetic and child neurology clinic. Intellectual disability (ID) is genetically heterogeneous, and it is associated with several other neurological conditions. Exome sequencing is a robust genetic tool and has revolutionized the process of molecular diagnosis and novel gene discovery. Besides its diagnostic clinical value, novel gene discovery is prime in reverse genetics, when human mutations help to understand the function of a gene and may aid in better understanding of the human brain and nervous system. Using WES, we identified a biallelic truncating variant in DNAJA1 gene (c.511C>T p.(Gln171*) in a multiplex Saudi consanguineous family. The main phenotype shared between the siblings was intellectual disability and seizure disorder.

Sotalol enhances the anticonvulsant action of valproate and diphenylhydantoin in the mouse maximal electroshock model

BACKGROUND

Sotalol as a drug blocking β-receptors and potassium KCNH2 channels may interact with different substances that affect seizures. Herein, we present interactions between sotalol and four conventional antiepileptic drugs: carbamazepine, valproate, phenytoin and phenobarbital.

METHODS

Effects of sotalol and antiepileptics alone on seizures were determined in the electroconvulsive threshold test, while interactions between sotalol and antiepileptic drugs were estimated in the maximal electroshock test in mice. Motor coordination and long-term memory were evaluated, respectively, in the chimney test and passive-avoidance task. Brain concentrations of antiepileptics were determined by fluorescence polarization immunoassay.

RESULTS

Sotalol at doses up to 100mg/kg did not affect the electroconvulsive threshold. Applied at doses 60-100mg/kg, sotalol potentiated the antielectroshock action of valproate, while at doses 80-100mg/kg that of phenytoin. Sotalol (up to 100mg/kg) did not affect the action of carbamazepine or phenobarbital in the maximal electroshock. Sotalol alone and in combinations with antiepileptics impaired neither motor performance nor long-term memory in mice. Finally, sotalol did not change brain concentration of valproate and phenytoin, so pharmacokinetic interactions between the drugs are not probable.

CONCLUSIONS

As far as obtained data may be extrapolated into clinical conditions, sotalol may be considered as an arrhythmic drug that does not reduce the action of classical antiepileptic drugs and thereby can be used in epileptic patients with cardiac arrhythmias.

Ion Channel Genes and Epilepsy: Functional Alteration, Pathogenic Potential, and Mechanism of Epilepsy

Ion channels are crucial in the generation and modulation of excitability in the nervous system and have been implicated in human epilepsy. Forty-one epilepsy-associated ion channel genes and their mutations are systematically reviewed. In this paper, we analyzed the genotypes, functional alterations (funotypes), and phenotypes of these mutations. Eleven genes featured loss-of-function mutations and six had gain-of-function mutations. Nine genes displayed diversified funotypes, among which a distinct funotype-phenotype correlation was found in SCN1A. These data suggest that the funotype is an essential consideration in evaluating the pathogenicity of mutations and a distinct funotype or funotype-phenotype correlation helps to define the pathogenic potential of a gene.

Beyond the Electrocardiogram: Mutations in Cardiac Ion Channel Genes Underlie Nonarrhythmic Phenotypes

Cardiac ion channelopathies are an important cause of sudden death in the young and include long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, and short QT syndrome. Genes that encode ion channels have been implicated in all of these conditions, leading to the widespread implementation of genetic testing for suspected channelopathies. Over the past half-century, researchers have also identified systemic pathologies that extend beyond the arrhythmic phenotype in patients with ion channel gene mutations, including deafness, epilepsy, cardiomyopathy, periodic paralysis, and congenital heart disease. A coexisting phenotype, such as cardiomyopathy, can influence evaluation and management. However, prior to recent molecular advances, our understanding and recognition of these overlapping phenotypes were poor. This review highlights the systemic and structural heart manifestations of the cardiac ion channelopathies, including their phenotypic spectrum and molecular basis.

Cardiac arrhythmia in a mouse model of sodium channel SCN8A epileptic encephalopathy

Patients with early infantile epileptic encephalopathy (EIEE) are at increased risk for sudden unexpected death in epilepsy (SUDEP). De novo mutations of the sodium channel gene SCN8A, encoding the sodium channel Na_v1.6, result in EIEE13 (OMIM 614558), which has a 10% risk of SUDEP. Here, we investigated the cardiac phenotype of a mouse model expressing the gain of function EIEE13 patient mutation p.Asn1768Asp in Scn8a (Na_v1.6-N1768D). We tested Scn8a^N1768D/+ mice for alterations in cardiac excitability. We observed prolongation of the early stages of action potential (AP) repolarization in mutant myocytes vs. controls. Scn8a^N1768D/+ myocytes were hyperexcitable, with a lowered threshold for AP firing, increased incidence of delayed afterdepolarizations, increased calcium transient duration, increased incidence of diastolic calcium release, and ectopic contractility. Calcium transient duration and diastolic calcium release in the mutant myocytes were tetrodotoxin-sensitive. A selective inhibitor of reverse mode Na/Ca exchange blocked the increased incidence of diastolic calcium release in mutant cells. Scn8a^N1768D/+ mice exhibited bradycardia compared with controls. This difference in heart rate dissipated after administration of norepinephrine, and there were no differences in heart rate in denervated ex vivo hearts, implicating parasympathetic hyperexcitability in the Scn8a^N1768D/+ animals. When challenged with norepinephrine and caffeine to simulate a catecholaminergic surge, Scn8a^N1768D/+ mice showed ventricular arrhythmias. Two of three mutant mice under continuous ECG telemetry recording experienced death, with severe bradycardia preceding asystole. Thus, in addition to central neuron hyperexcitability, Scn8a^N1768D/+ mice have cardiac myoycte and parasympathetic neuron hyperexcitability. Simultaneous dysfunction in these systems may contribute to SUDEP associated with mutations of Scn8a.

The pathophysiology of cardiac dysfunction in epilepsy

Alterations in cardiac electrophysiology are an established consequence of long-standing drug resistant epilepsy. Patients with chronic epilepsy display abnormalities in both sinoatrial node pacemaker current as well as ventricular repolarizing current that places them at a greater risk of developing life-threatening cardiac arrhythmias. The development of cardiac arrhythmias secondary to drug resistant epilepsy is believed to be a key mechanism underlying the phenomenon of Sudden Unexpected Death in EPilepsy (SUDEP). Though an increasing amount of studies examining both animal models and human patients have provided evidence that chronic epilepsy can detrimentally affect cardiac function, the underlying pathophysiology remains unclear. Recent work has shown the expression of several key cardiac ion channels to be altered in animal models of genetic and acquired epilepsies. This has led to the currently held paradigm that cardiac ion channel expression may be secondarily altered as a consequence of seizure activity-resulting in electrophysiological cardiac dysfunction. Furthermore, cortical autonomic dysfunction - resulting from seizure activity-has also been suggested to play a role, whereby seizure activity may indirectly influence cardiac function via altering centrally-mediated autonomic output to the heart. In this review, we discuss various cardiac dysrhythmias associated with seizure events-including tachycardia, bradycardia and QT prolongation, both ictally and inter-ictally, as well as the role of the autonomic nervous system. We further discuss key ion channels expressed in both the heart and the brain that have been shown to be altered in epilepsy and may be responsible for the development of cardiac dysrhythmias secondary to chronic epilepsy.

Potassium Channels in Epilepsy

This review attempts to give a concise and up-to-date overview on the role of potassium channels in epilepsies. Their role can be defined from a genetic perspective, focusing on variants and de novo mutations identified in genetic studies or animal models with targeted, specific mutations in genes coding for a member of the large potassium channel family. In these genetic studies, a demonstrated functional link to hyperexcitability often remains elusive. However, their role can also be defined from a functional perspective, based on dynamic, aggravating, or adaptive transcriptional and posttranslational alterations. In these cases, it often remains elusive whether the alteration is causal or merely incidental. With ∼80 potassium channel types, of which ∼10% are known to be associated with epilepsies (in humans) or a seizure phenotype (in animals), if genetically mutated, a comprehensive review is a challenging endeavor. This goal may seem all the more ambitious once the data on posttranslational alterations, found both in human tissue from epilepsy patients and in chronic or acute animal models, are included. We therefore summarize the literature, and expand only on key findings, particularly regarding functional alterations found in patient brain tissue and chronic animal models.

Potassium Channels and Human Epileptic Phenotypes: An Updated Overview

Potassium (K⁺) channels are expressed in almost every cells and are ubiquitous in neuronal and glial cell membranes. These channels have been implicated in different disorders, in particular in epilepsy. K⁺ channel diversity depends on the presence in the human genome of a large number of genes either encoding pore-forming or accessory subunits. More than 80 genes encoding the K⁺ channels were cloned and they represent the largest group of ion channels regulating the electrical activity of cells in different tissues, including the brain. It is therefore not surprising that mutations in these genes lead to K⁺ channels dysfunctions linked to inherited epilepsy in humans and non-human model animals. This article reviews genetic and molecular progresses in exploring the pathogenesis of different human epilepsies, with special emphasis on the role of K⁺ channels in monogenic forms.

Neuronal and Cardiovascular Potassium Channels as Therapeutic Drug Targets: Promise and Pitfalls

Potassium (K(+)) channels, with their diversity, often tissue-defined distribution, and critical role in controlling cellular excitability, have long held promise of being important drug targets for the treatment of dysrhythmias in the heart and abnormal neuronal activity within the brain. With the exception of drugs that target one particular class, ATP-sensitive K(+) (KATP) channels, very few selective K(+) channel activators or inhibitors are currently licensed for clinical use in cardiovascular and neurological disease. Here we review what a range of human genetic disorders have told us about the role of specific K(+) channel subunits, explore the potential of activators and inhibitors of specific channel populations as a therapeutic strategy, and discuss possible reasons for the difficulty in designing clinically relevant K(+) channel modulators.

Faulty cardiac repolarization reserve in alternating hemiplegia of childhood broadens the phenotype

Alternating hemiplegia of childhood is a rare disorder caused by de novo mutations in the ATP1A3 gene, expressed in neurons and cardiomyocytes. As affected individuals may survive into adulthood, we use the term 'alternating hemiplegia'. The disorder is characterized by early-onset, recurrent, often alternating, hemiplegic episodes; seizures and non-paroxysmal neurological features also occur. Dysautonomia may occur during hemiplegia or in isolation. Premature mortality can occur in this patient group and is not fully explained. Preventable cardiorespiratory arrest from underlying cardiac dysrhythmia may be a cause. We analysed ECG recordings of 52 patients with alternating hemiplegia from nine countries: all had whole-exome, whole-genome, or direct Sanger sequencing of ATP1A3. Data on autonomic dysfunction, cardiac symptoms, medication, and family history of cardiac disease or sudden death were collected. All had 12-lead electrocardiogram recordings available for cardiac axis, cardiac interval, repolarization pattern, and J-point analysis. Where available, historical and prolonged single-lead electrocardiogram recordings during electrocardiogram-videotelemetry were analysed. Half the cohort (26/52) had resting 12-lead electrocardiogram abnormalities: 25/26 had repolarization (T wave) abnormalities. These abnormalities were significantly more common in people with alternating hemiplegia than in an age-matched disease control group of 52 people with epilepsy. The average corrected QT interval was significantly shorter in people with alternating hemiplegia than in the disease control group. J wave or J-point changes were seen in six people with alternating hemiplegia. Over half the affected cohort (28/52) had intraventricular conduction delay, or incomplete right bundle branch block, a much higher proportion than in the normal population or disease control cohort (P = 0.0164). Abnormalities in alternating hemiplegia were more common in those ≥16 years old, compared with those <16 (P = 0.0095), even with a specific mutation (p.D801N; P = 0.045). Dynamic, beat-to-beat or electrocardiogram-to-electrocardiogram, changes were noted, suggesting the prevalence of abnormalities was underestimated. Electrocardiogram changes occurred independently of seizures or plegic episodes. Electrocardiogram abnormalities are common in alternating hemiplegia, have characteristics reflecting those of inherited cardiac channelopathies and most likely amount to impaired repolarization reserve. The dynamic electrocardiogram and neurological features point to periodic systemic decompensation in ATP1A3-expressing organs. Cardiac dysfunction may account for some of the unexplained premature mortality of alternating hemiplegia. Systematic cardiac investigation is warranted in alternating hemiplegia of childhood, as cardiac arrhythmic morbidity and mortality are potentially preventable.

Functional Loss of Bmsei Causes Thermosensitive Epilepsy in Contractile Mutant Silkworm, Bombyx mori

The thermoprotective mechanisms of insects remain largely unknown. We reported the Bombyx mori contractile (cot) behavioral mutant with thermo-sensitive seizures phenotype. At elevated temperatures, the cot mutant exhibit seizures associated with strong contractions, rolling, vomiting, and a temporary lack of movement. We narrowed a region containing cot to ~268 kb by positional cloning and identified the mutant gene as Bmsei which encoded a potassium channel protein. Bmsei was present in both the cell membrane and cytoplasm in wild-type ganglia but faint in cot. Furthermore, Bmsei was markedly decreased upon high temperature treatment in cot mutant. With the RNAi method and injecting potassium channel blockers, the wild type silkworm was induced the cot phenotype. These results demonstrated that Bmsei was responsible for the cot mutant phenotype and played an important role in thermoprotection in silkworm. Meanwhile, comparative proteomic approach was used to investigate the proteomic differences. The results showed that the protein of Hsp-1 and Tn1 were significantly decreased and increased on protein level in cot mutant after thermo-stimulus, respectively. Our data provide insights into the mechanism of thermoprotection in insect. As cot phenotype closely resembles human epilepsy, cot might be a potential model for the mechanism of epilepsy in future.

Short-term variability in QT interval and ventricular arrhythmias induced by dofetilide are dependent on high-frequency autonomic oscillations

Background and Purpose

The present study was undertaken to investigate an effect of dofetilide, a potent arrhythmic blocker of the voltage-gated K⁺ channel, hERG, on cardiac autonomic control. Combined with effects on ardiomyocytes, these properties could influence its arrhythmic potency.

Experimental Approach

The short-term variability of beat-to-beat QT interval (STV_QT), induced by dofetilide is a strong surrogate of Torsades de pointes liability. Involvement of autonomic modulation in STV_QT was investigated in healthy cynomolgus monkeys and beagle dogs by power spectral analysis under conditions of autonomic blockade with hexamethonium.

Key Results

Increase in STV_QT induced by dofetilide in monkeys and dogs was closely associated with an enhancement of endogenous heart rate and QT interval high-frequency (HF) oscillations. These effects were fully suppressed under conditions of autonomic blockade with hexamethonium. Ventricular arrhythmias, including Torsades de pointes in monkeys, were prevented in both species when HF oscillations were suppressed by autonomic blockade. Similar enhancements of heart rate HF oscillations were found in dogs with other hERG blockers described as causing Torsades de pointes in humans.

Conclusions and Implications

These results demonstrate for the first time that beat-to-beat ventricular repolarization variability and ventricular arrhythmias induced by dofetilide are dependent on endogenous HF autonomic oscillations in heart rate. When combined with evidence of hERG-blocking properties, enhancement of endogenous HF oscillations in heart rate could constitute an earlier and more sensitive biomarker than STV_QT for Torsades de pointes liability, applicable to preclinical regulatory studies conducted in healthy animals.

Endocrinopathies in a boy with cryptic copy-number variations on 4q, 7q and Xp

We report a male patient with three copy-number variations (CNVs) and unique phenotype. He carried ~11.2 Mb terminal duplication on 4q, ~13.4 Mb terminal deletion on 7q and ~1.7 Mb interstitial duplication on Xp22.31, which were identified by array-based comparative genomic hybridization. He manifested mental retardation, mild brain anomalies and skeletal deformities ascribable to these CNVs, together with central precocious puberty and mild adrenocorticotropic hormone overproduction of unknown etiologies.

The human ether-a-go-go-related gene activator NS1643 enhances epilepsy-associated KCNQ channels

Human ether-a-go-go-related gene (hERG) and KCNQ channels are two classes of voltage-gated potassium channels. Specific mutations have been identified that are causal for type II long QT (LQT2) syndrome, neonatal epilepsy, and benign familial neonatal convulsions. Increasing evidence from clinical studies suggests that LQT2 and epilepsy coexist in some patients. Therefore, an integral approach to investigating and treating the two diseases is likely more effective. In the current study, we found that NS1643 [1,3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea], a previously reported hERG activator, is also an activator of KCNQ channels. It potentiates the neuronal KCNQ2, KCNQ4, and KCNQ2/Q3 channels, but not the cardiac KCNQ1. The effects of NS1643 on the KCNQ2 channel include left shifting of voltage for reaching 50% of the maximum conductance and slowing of deactivation. Analysis of the dose-response curve of NS1643 revealed an EC50 value of 2.44 ± 0.25 μM. A hydrophobic phenylalanine (F137) located at the middle region of the voltage-sensing domain was identified as critical for NS1643 activity on KCNQ2. When testing NS1643 effects in rescuing LQT2 hERG mutants and the KCNQ2 BFNC mutants, we found it is particularly efficacious in some cases. Considering the substantial relationship between LQT2 and epilepsy, these findings reveal that NS1643 is a useful compound to elucidate the causal connection of LQT2 and epilepsy. More generally, this may provide a strategy in the development of therapeutics for LQT2 and epilepsy.

Genomic biomarkers of SUDEP in brain and heart

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related mortality, but how to predict which patients are at risk and how to prevent it remain uncertain. The underlying pathomechanisms of SUDEP are still largely unknown, but the general consensus is that seizures somehow disrupt normal cardiac or respiratory physiology leading to death. However, the proportion of SUDEP cases exhibiting cardiac or respiratory dysfunction as a critical factor in the terminal cascade of events remains unresolved. Although many general risk factors for SUDEP have been identified, the development of reliable patient-specific biomarkers for SUDEP is needed to provide more accurate risk prediction and personalized patient management strategies. Studies in animal models and patient groups have revealed at least nine different brain-heart genes that may contribute to a genetic susceptibility for SUDEP, making them potentially useful as genomic biomarkers. This review summarizes data on the relationship between these neurocardiac genes and SUDEP, discussing their brain-heart expression patterns and genotype-phenotype correlations in mouse models and people with epilepsy. These neurocardiac genes represent good first candidates for evaluation as genomic biomarkers of SUDEP in future studies. The development of validated reliable genomic biomarkers for SUDEP has the potential to transform the clinical treatment of epilepsy by pinpointing patients at risk of SUDEP and allowing optimized, genotype-guided therapeutic and prevention strategies.

Genetic and forensic implications in epilepsy and cardiac arrhythmias: a case series

Epilepsy affects approximately 3% of the world's population, and sudden death is a significant cause of death in this population. Sudden unexpected death in epilepsy (SUDEP) accounts for up to 17% of all these cases, which increases the rate of sudden death by 24-fold as compared to the general population. The underlying mechanisms are still not elucidated, but recent studies suggest the possibility that a common genetic channelopathy might contribute to both epilepsy and cardiac disease to increase the incidence of death via a lethal cardiac arrhythmia. We performed genetic testing in a large cohort of individuals with epilepsy and cardiac conduction disorders in order to identify genetic mutations that could play a role in the mechanism of sudden death. Putative pathogenic disease-causing mutations in genes encoding cardiac ion channel were detected in 24% of unrelated individuals with epilepsy. Segregation analysis through genetic screening of the available family members and functional studies are crucial tasks to understand and to prove the possible pathogenicity of the variant, but in our cohort, only two families were available. Despite further research should be performed to clarify the mechanism of coexistence of both clinical conditions, genetic analysis, applied also in post-mortem setting, could be very useful to identify genetic factors that predispose epileptic patients to sudden death, helping to prevent sudden death in patients with epilepsy.

The effects of sleep deprivation on microRNA expression in rats submitted to pilocarpine-induced status epilepticus

Epilepsy is a neurological disorder with significant prevalence and the individuals affected by this disease have a great probability of occurrence of a lethal phenomenon known as Sudden Unexpected Death in Epilepsy (SUDEP). SUDEP occurs mainly during the night and probably during sleep. The pathophysiological mechanisms involved in this lethal phenomenon are still obscure and new evidences that could corroborate in this area are warranted. Thus, the aim of the present study was to evaluate the effect of sleep deprivation in the expression of microRNA (miRNA) in the frontal cortex and heart tissues of adult male rats after 50days of saline (SAL) or pilocarpine-induced status epilepticus (PILO). Initially 389 miRNA expressions were evaluated between SAL and PILO groups by microarray. Subsequently, 3 differentially expressed miRNAs of each tissue were investigated after total sleep deprivation (TSD 6h) and paradoxical sleep deprivation (PSD 24h). Still, it was analyzed that the effects of sleep rebound with equivalent duration of PSD and TSD. There was a significant increase of miR-146a expression, an important inflammatory modulator in the frontal cortex of PILO rats when compared to SAL animals. Animals treated with pilocarpine were affected by TSD (through overexpression of miRNAs related to inflammatory process) and these changes were maintained even after a sleep window of 6h. In contrast, miRNAs associated with heart diseases were down-regulated in PSD rebound, suggesting a possible restoration of homeostasis in cardiovascular system of SAL and PILO groups.

The WAVE regulatory complex links diverse receptors to the actin cytoskeleton

The WAVE regulatory complex (WRC) controls actin cytoskeletal dynamics throughout the cell by stimulating the actin-nucleating activity of the Arp2/3 complex at distinct membrane sites. However, the factors that recruit the WRC to specific locations remain poorly understood. Here, we have identified a large family of potential WRC ligands, consisting of ∼120 diverse membrane proteins, including protocadherins, ROBOs, netrin receptors, neuroligins, GPCRs, and channels. Structural, biochemical, and cellular studies reveal that a sequence motif that defines these ligands binds to a highly conserved interaction surface of the WRC formed by the Sra and Abi subunits. Mutating this binding surface in flies resulted in defects in actin cytoskeletal organization and egg morphology during oogenesis, leading to female sterility. Our findings directly link diverse membrane proteins to the WRC and actin cytoskeleton and have broad physiological and pathological ramifications in metazoans.

Stoichiometry of altered hERG1 channel gating by small molecule activators

Agonists bind to sites on all four subunits to activate human ether-a-go-go–related gene 1 (hERG1) K⁺ channels.

Voltage-gated K⁺ channels are tetramers formed by coassembly of four identical or highly related subunits. All four subunits contribute to formation of the selectivity filter, the narrowest region of the channel pore which determines K⁺ selective conductance. In some K⁺ channels, the selectivity filter can undergo a conformational change to reduce K⁺ flux by a mechanism called C-type inactivation. In human ether-a-go-go–related gene 1 (hERG1) K⁺ channels, C-type inactivation is allosterically inhibited by ICA-105574, a substituted benzamide. PD-118057, a 2-(phenylamino) benzoic acid, alters selectivity filter gating to enhance open probability of channels. Both compounds bind to a hydrophobic pocket located between adjacent hERG1 subunits. Accordingly, a homotetrameric channel contains four identical activator binding sites. Here we determine the number of binding sites required for maximal drug effect and determine the role of subunit interactions in the modulation of hERG1 gating by these compounds. Concatenated tetramers were constructed to contain a variable number (zero to four) of wild-type and mutant hERG1 subunits, either L646E to inhibit PD-118057 binding or F557L to inhibit ICA-105574 binding. Enhancement of hERG1 channel current magnitude by PD-118057 and attenuated inactivation by ICA-105574 were mediated by cooperative subunit interactions. Maximal effects of the both compounds required the presence of all four binding sites. Understanding how hERG1 agonists allosterically modify channel gating may facilitate mechanism-based drug design of novel agents for treatment of long QT syndrome.

Evolutionary analysis of voltage-gated potassium channels by Bayes method

Voltage-gated potassium channels (VGPCs) are among the most complex families of ion channels. VGPCs are distributed widely among species but their biological roles remain unclear. In this study, the evolution of VGPCs and the functions of ancestral families are determined according to phylogenetic studies. We downloaded 127 genomic data of alpha subunits and 38 genomic data of beta subunits including those from human, rat, mice, Drosophila and Puccinellia tenuiflora. The genetic neighborhood of subfamily genes was determined by neighbor-joining, minimum evolution, maximum parsimony, and Bayes methods. Data was presented as phylogenetic trees. We also detected positive selection sites by site model. New insights into the evolutionary history of the VGPC family are provided. Our assumptions are as follows: (a) KCNH subfamily is likely the most original subfamily in alpha subunit; (b) VGPCs are related to neural and cardiac systems at the earliest time; (c) KCNA4 and KCNF1 may be as ancestors; (d) abnormality in one gene may cause both cardiac and neural diseases; and (e) abnormalities in KCNH6 and KCNQ7 are more likely to cause cardiac diseases.

Loss-of-function KCNH2 mutation in a family with long QT syndrome, epilepsy, and sudden death

There has been increased interest in a possible association between epilepsy channelopathies and cardiac arrhythmias, such as long QT syndrome (LQTS). We report a kindred that features LQTS, idiopathic epilepsy, and increased risk of sudden death. Genetic study showed a previously unreported heterozygous point mutation (c.246T>C) in the KCNH2 gene. Functional studies showed that the mutation induces severe loss of function. This observation provides further evidence for a possible link between idiopathic epilepsy and LQTS.

K(+) channelepsy: progress in the neurobiology of potassium channels and epilepsy

K(+) channels are important determinants of seizure susceptibility. These membrane proteins, encoded by more than 70 genes, make the largest group of ion channels that fine-tune the electrical activity of neuronal and non-neuronal cells in the brain. Their ubiquity and extremely high genetic and functional diversity, unmatched by any other ion channel type, place K(+) channels as primary targets of genetic variations or perturbations in K(+)-dependent homeostasis, even in the absence of a primary channel defect. It is therefore not surprising that numerous inherited or acquired K(+) channels dysfunctions have been associated with several neurologic syndromes, including epilepsy, which often generate confusion in the classification of the associated diseases. Therefore, we propose to name the K(+) channels defects underlying distinct epilepsies as "K(+) channelepsies," and introduce a new nomenclature (e.g., Kx.y-channelepsy), following the widely used K(+) channel classification, which could be also adopted to easily identify other channelopathies involving Na(+) (e.g., Nav x.y-phenotype), Ca(2+) (e.g., Cav x.y-phenotype), and Cl(-) channels. Furthermore, we discuss novel genetic defects in K(+) channels and associated proteins that underlie distinct epileptic phenotypes in humans, and analyze critically the recent progress in the neurobiology of this disease that has also been provided by investigations on valuable animal models of epilepsy. The abundant and varied lines of evidence discussed here strongly foster assessments for variations in genes encoding for K(+) channels and associated proteins in patients with idiopathic epilepsy, provide new avenues for future investigations, and highlight these proteins as critical pharmacological targets.

Epilepsy misdiagnosed as long QT syndrome: it can go both ways

Cardiogenic seizures are common and could be the sentinel event heralding the presence of congenital long QT syndrome (LQTS). Distinguishing a cardiogenic seizure from a neurogenic one is of the utmost importance. Herein, we present the case of a 12-year-old boy with recurrent episodes of syncope and seizures. Despite absence of QT prolongation on electrocardiogram, absence of documented arrhythmias, a negative LQTS genetic test, and recurrent episodes while on nadolol beta-blocker therapy, he was diagnosed with LQTS and implanted with an implantable cardioverter defibrillator (ICD). When syncope and seizure occurred with normal sinus rhythm documented on the ICD, he was referred to neurology, and an electroencephalogram was positive for numerous bursts of bilaterally synchronous generalized discharges. He was started on antiepileptic treatment after which his seizures resolved. His LQTS diagnosis was removed, beta-blocker therapy discontinued, and his ICD was explanted. He has been seizure-free for over 2 years.