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BACKGROUND: The characteristics of electrocardiogram (ECG) abnormalities related to cardiac channelopathies potentially linked to sudden cardiac death (SCD) are not widely recognized in Iran. We examined the prevalence of such ECG patterns and their related factors among adult residents of Tehran, Iran. METHODS: The clinical characteristics and 12-lead ECGs of Tehran Cohort Study participants were examined. Long QT intervals, short QT intervals, Brugada syndrome (BrS) patterns, and early repolarization (ER) were evaluated using computer-based assessment software validated by cardiologists. Logistic regression models were employed to identify the factors associated with the prevalence of different ECG patterns. RESULTS: Out of 7678 available ECGs, 7350 were included in this analysis. Long QT interval, ER pattern, BrS patterns, and short QT interval were found in 3.08%, 1.43%, 0.31%, and 0.03% of participants, respectively. The prevalence of long QT interval increased with age, opium consumption, and presence of hypertension. Younger age, lower body mass index (BMI), alcohol use and male sex were independently linked to an elevated prevalence of ER pattern. Most individuals with BrS patterns were men (95%) and had lower BMI, high- and low-density lipoprotein, and total cholesterol compared to those without the BrS pattern. At a mean follow-up of 30.2 ± 5.5 months, all-cause mortality in the group exhibiting abnormal ECG patterns (6.3%) was approximately twice as high as that in the group without such patterns (2.96%). CONCLUSION: Abnormal ECG patterns corresponding to channelopathies were relatively rare among adult residents of the Tehran population, and their prevalence was influenced by various factors. CLINICAL TRIAL NUMBER: Not applicable.

Inherited cardiac channelopathies are major causes of sudden cardiac death (SCD) in young people. Genetic testing is focused on the identification of single-nucleotide variants (SNVs) by Next-Generation Sequencing (NGS). However, genetically elusive cases can carry copy number variants (CNVs), which need specific detection tools. We underlie the utility of identifying CNVs by investigating the literature data and internally analyzing cohorts with CNVs in KCNQ1, KCNH2, SCN5A, and RYR2. CNVs were reported in 119 patients from the literature and 21 from our cohort. Young patients with CNVs in KCNQ1 show a Long QT (LQT) phenotype > 480 ms and a higher frequency of syncope. None of them had SCD. All patients with CNV in KCNH2 had a positive phenotype for QT > 480 ms. CNVs in SCN5A were represented by the Brugada pattern, with major cardiac events mainly in males. Conversely, adult females show more supraventricular arrhythmias. RYR2-exon3 deletion showed a broader phenotype, including left ventricular non-compaction (LVNC) and catecholaminergic polymorphic ventricular tachycardia (CPVT). Pediatric patients showed atrial arrhythmias and paroxysmal atrial fibrillation. Relatively higher syncope and SCA were observed in young females. The detection of CNVs can be of greater yield in two groups: familial channelopathies and patients with suspected Jervell and Lange-Nielsen syndrome or CPVT. The limited number of reported individuals makes it mandatory for multicentric studies to give future conclusive results. [ABSTRACT FROM AUTHOR]

Background and Purpose Experimental Approach Key Results Conclusions and Implications Pathogenic gain‐of‐function mutations in Cav1.3 L‐type voltage‐gated Ca2+‐channels (CACNA1D) cause neurodevelopmental disorders with or without endocrine symptoms. We aimed to confirm a pathogenic gain‐of function phenotype of CACNA1D de novo missense mutations A749T and L271H, and investigated the molecular mechanism causing their enhanced sensitivity for the Ca2+‐channel blocker isradipine, a potential therapeutic for affected patients.Wildtype and mutant channels were expressed in tsA‐201 cells and their gating analysed using whole‐cell and single‐channel patch‐clamp recordings. The voltage‐dependence of isradipine action was quantified using protocols inducing variable fractions of inactivated channels. The molecular basis for altered channel gating in the mutants was investigated using in silico modelling and molecular dynamics simulations.Both mutations were confirmed pathogenic due to characteristic shifts of voltage‐dependent activation and inactivation towards negative potentials (~20 mV). At negative holding potentials both mutations showed significantly higher isradipine sensitivity compared to wildtype. The affinity for wildtype and mutant channels increased with channel inactivation as predicted by the modulated receptor hypothesis (30‐ to 40‐fold). The IC50 was indistinguishable for wildtype and mutants when >50% of channels were inactivated.Mutations A749T and L271H induce pathogenic gating changes. Like wildtype, isradipine inhibition is strongly voltage‐dependent. Our data explains their apparent higher drug sensitivity at a given negative voltage by the availability of more inactivated channels due to their more negative inactivation voltage range. Low nanomolar isradipine concentrations will only inhibit Cav1.3 channels in neurons during prolonged depolarized states without selectivity for mutant channels. [ABSTRACT FROM AUTHOR]

Background and objectives: Sudden cardiac death (SCD) is a natural and unexpected death of cardiac origin that occurs within 1 h from the onset of acute symptoms. The major leading causes of SCD are cardiomyopathies and channelopathies. In this review, we focus on channelopathies, inherited diseases caused by mutations affecting genes encoding membrane ion channels (sodium, potassium or calcium channels) or cellular structures that affect Ca2+ availability. The diagnosis of diseases such as long QT, Brugada syndrome, short QT and catecholaminergic polymorphic ventricular tachycardia (CPVT) is still challenging. Currently, genetic testing and next-generation sequencing allow us to identify many rare alterations. However, some non-coding variants, e.g., splicesite variants, are usually difficult to interpret and to classify. Methods: In our review, we searched for splice-site variants of genes involved in channelopathies, focusing on variants of unknown significance (VUSs) registered on ClinVar up to now. Results: The research led to a high number of splice-site VUSs of genes involved in channelopathies, suggesting the performance of deeper studies. Conclusions: In order to interpret the correlation between variants and pathologies, we discuss experimental studies, such as RNA sequencing and functional analysis of proteins. Unfortunately, as these in vitro analyses cannot always be performed, we draw attention to in silico studies as future perspectives in genetics. This review has the aim of discussing the potential methods of detection and interpretation of VUSs, bringing out the need for a future reclassification of variants with currently unknown significance. [ABSTRACT FROM AUTHOR]

Objectives: This study aims to analyze the results of comprehensive genetic testing in patients presenting to a dedicated multidisciplinary inherited heart disease clinic in India. Methods: All patients presenting to our clinic from August 2017 to October 2023 with a suspected inherited heart disease and consenting for genetic testing were included. The probands were grouped into familial cardiomyopathies namely hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), arrhythmogenic cardiomyopathy (ACM) and peripartum cardiomyopathy (PPCM), channelopathies namely congenital long QT syndrome (LQTS) and Brugada syndrome (BrS), and heritable connective tissue disorder namely Marfan Syndrome (MFS). Next generation sequencing (NGS) was used, and pre-test and post-test counseling were provided to probands and cascade screening offered to relatives. Results: Mean age of the subjects (n = 77; 48 probands, 29 relatives) was 43 ± 18 years, 68 % male and 44 % symptomatic, with 36 HCM, 3 DCM, 3 ACM, 1 PPCM, 3 LQTS, 1 BrS and 1 MFS probands. The diagnostic yield of NGS-based genetic testing was 31 %; variants of uncertain significance (VUS) were identified in 54 %; and 15 % were genotype-negative. Twenty-nine relatives from 18 families with HCM (n = 12), DCM (n = 3), ACM (n = 2) and MFS (n = 1) underwent genetic testing. The genotype positive probands/relatives and VUS carriers with strong disease phenotype and/or high risk variant were advised periodic follow-up; the remaining probands/relatives were discharged from further clinical surveillance. Conclusions: Genetic testing guides treatment and follow-up of patients with inherited heart diseases and should be carried out in dedicated multidisciplinary clinics with expertise for counseling and cascade screening of family members.

Abstract Background Ion channels, vital transmembrane protein complexes, regulate ion movement within cells. Germline variants in channel-encoding genes lead to channelopathies. The sodium channels in cardiac cells exhibit a structure of an alpha subunit and one to two beta subunits. The alpha subunit, encoded by the SCN5A gene, comprises four domains. Case presentation A fifteen-year-old Ecuadorian female with atrial flutter and abnormal sinus rhythm with no familial history of cardiovascular disease underwent NGS with the TruSight Cardio kit (Illumina). A likely pathogenic SCN5A gene variant (NM_188056.2:c.2677 C > Tp. Arg893Cys) was identified, associated with arrhythmias, long QT, atrial fibrillation, and Brugada syndrome. Ancestral analysis revealed a predominant European component (43.9%), followed by Native American (35.7%) and African (20.4%) components. Conclusions The participant presents atrial flutter and conduction disorders, despite lacking typical cardiovascular risk factors. The proband carries a SCN5A variant that has not been previously reported in Latin America and may be associated to her phenotype. The documented arginine-to-cysteine substitution at position 893 in the protein is crucial for various cellular functions. The subject’s mixed genetic composition highlights potential genetic contributors to atrial flutter, emphasizing the need for comprehensive genetic studies, particularly in mixed populations like Ecuadorians. This case underscores the importance of genetic analysis for personalized treatment and the significance of studying diverse genetic backgrounds in understanding cardiovascular diseases.

Understanding the molecular mechanisms underlying the generation of absence seizures is crucial for developing effective, patient-specific treatments for childhood absence epilepsy (CAE). Currently, one-third of patients remain refractive to the antiseizure medications (ASMs), previously called antiepileptic drugs (AEDs), available to treat CAE. Additionally, these ASMs often produce serious side effects and can even exacerbate symptoms in some patients. Determining the precise cellular and molecular mechanisms directly responsible for causing this type of epilepsy has proven challenging as they appear to be complex and multifactorial in patients with different genetic backgrounds. Aberrant neuronal activity in CAE may be caused by several mechanisms that are not fully understood. Thus, dissecting the causal factors that could be targeted in the development of precision medicines without side effects remains a high priority and the ultimate goal in this field of epilepsy research. The aim of this review is to highlight our current understanding of potential causative mechanisms for absence seizure generation, based on the latest research using cutting-edge technologies. This information will be important for identifying potential targets for future therapeutic intervention. [ABSTRACT FROM AUTHOR]

Polycystic kidney disease (PKD), a disease characterized by the enlargement of the kidney through cystic growth is the fourth leading cause of end-stage kidney disease world-wide. Transient receptor potential Vanilloid 4 (TRPV4), a calcium-permeable TRP, channel participates in kidney cell physiology and since TRPV4 forms complexes with another channel whose malfunction is associated to PKD, TRPP2 (or PKD2), we sought to determine whether patients with PKD, exhibit previously unknown mutations in TRPV4. Here, we report the presence of mutations in the TRPV4 gene in patients diagnosed with PKD and determine that they produce gain-of-function (GOF). Mutations in the sequence of the TRPV4 gene have been associated to a broad spectrum of neuropathies and skeletal dysplasias but not PKD, and their biophysical effects on channel function have not been elucidated. We identified and examined the functional behavior of a novel E6K mutant and of the previously known S94L and A217S mutant TRVP4 channels. The A217S mutation has been associated to mixed neuropathy and/or skeletal dysplasia phenotypes, however, the PKD carriers of these variants had not been diagnosed with these reported clinical manifestations. The presence of certain mutations in TRPV4 may influence the progression and severity of PKD through GOF mechanisms. PKD patients carrying TRVP4 mutations are putatively more likely to require dialysis or renal transplant as compared to those without these mutations. Graphical Abstract Abstract graph showing a schematic representation of a wild-type TRPV4 channel compared to the increased activity of a mutant TRPV4 channel carrying one of the two TRPV4 mutations located in the amino-terminal domain and found in a patient cohort diagnosed with polycystic kidney disease.Abstract graph showing a schematic representation of a wild-type TRPV4 channel compared to the increased activity of a mutant TRPV4 channel carrying one of the two TRPV4 mutations located in the amino-terminal domain and found in a patient cohort diagnosed with polycystic kidney disease. [ABSTRACT FROM AUTHOR]

Mental illnesses are one of the biggest contributors to the global disease burden. Despite the increased recognition, diagnosis and ongoing research of mental health disorders, the etiology and underlying molecular mechanisms of these disorders are yet to be fully elucidated. Moreover, despite many treatment options available, a large subset of the psychiatric patient population is nonresponsive to standard medications and therapies. There has not been a comprehensive study to date examining the burden and impact of treatable genetic disorders (TGDs) that can present with neuropsychiatric features in psychiatric patient populations. In this study, we test the hypothesis that TGDs that present with psychiatric symptoms are more prevalent within psychiatric patient populations compared to the general population by performing targeted next‐generation sequencing of 129 genes associated with 108 TGDs in a cohort of 2301 psychiatric patients. In total, 48 putative affected and 180 putative carriers for TGDs were identified, with known or likely pathogenic variants in 79 genes. Despite screening for only 108 genetic disorders, this study showed a two‐fold (2.09%) enrichment for genetic disorders within the psychiatric population relative to the estimated 1% cumulative prevalence of all single gene disorders globally. This strongly suggests that the prevalence of these, and most likely all, genetic diseases is greatly underestimated in psychiatric populations. Increasing awareness and ensuring accurate diagnosis of TGDs will open new avenues to targeted treatment for a subset of psychiatric patients. [ABSTRACT FROM AUTHOR]

Background and Aims Risk scores are proposed for genetic arrhythmias. Having proposed in 2010 one such score (M-FACT) for the long QT syndrome (LQTS), this study aims to test whether adherence to its suggestions would be appropriate. Methods LQT1/2/3 and genotype-negative patients without aborted cardiac arrest (ACA) before diagnosis or cardiac events (CEs) below age 1 were included in the study, focusing on an M-FACT score ≥2 (intermediate/high risk), either at presentation (static) or during follow-up (dynamic), previously associated with 40% risk of implantable cardioverter defibrillator (ICD) shocks within 4 years. Results Overall, 946 patients (26 ± 19 years at diagnosis, 51% female) were included. Beta-blocker (βB) therapy in 94% of them reduced the rate of those with a QTc ≥500 ms from 18% to 12% (P <.001). During 7 ± 6 years of follow-up, none died; 4% had CEs, including 0.4% with ACA. A static M-FACT ≥2 was present in 110 patients, of whom 106 received βBs. In 49/106 patients with persistent dynamic M-FACT ≥2, further therapeutic optimization (left cardiac sympathetic denervation in 55%, mexiletine in 31%, and ICD at 27%) resulted in just 7 (14%) patients with CEs (no ACA), with no CEs in the remaining 57. Additionally, 32 patients developed a dynamic M-FACT ≥2 but, after therapeutic optimization, only 3 (9%) had C Es. According to an M-FACT score ≥2, a total of 142 patients should have received an ICD, but only 22/142 (15%) were implanted, with shocks reported in 3. Conclusions Beta-blockers often shorten QTc, thus changing risk scores and ICD indications for primary prevention. Yearly risk reassessment with therapy optimization leads to fewer ICD implants (3%) without increasing life-threatening events. [ABSTRACT FROM AUTHOR]

Background: Ion channels, vital transmembrane protein complexes, regulate ion movement within cells. Germline variants in channel-encoding genes lead to channelopathies. The sodium channels in cardiac cells exhibit a structure of an alpha subunit and one to two beta subunits. The alpha subunit, encoded by the SCN5A gene, comprises four domains. Case presentation: A fifteen-year-old Ecuadorian female with atrial flutter and abnormal sinus rhythm with no familial history of cardiovascular disease underwent NGS with the TruSight Cardio kit (Illumina). A likely pathogenic SCN5A gene variant (NM_188056.2:c.2677 C > Tp. Arg893Cys) was identified, associated with arrhythmias, long QT, atrial fibrillation, and Brugada syndrome. Ancestral analysis revealed a predominant European component (43.9%), followed by Native American (35.7%) and African (20.4%) components. Conclusions: The participant presents atrial flutter and conduction disorders, despite lacking typical cardiovascular risk factors. The proband carries a SCN5A variant that has not been previously reported in Latin America and may be associated to her phenotype. The documented arginine-to-cysteine substitution at position 893 in the protein is crucial for various cellular functions. The subject's mixed genetic composition highlights potential genetic contributors to atrial flutter, emphasizing the need for comprehensive genetic studies, particularly in mixed populations like Ecuadorians. This case underscores the importance of genetic analysis for personalized treatment and the significance of studying diverse genetic backgrounds in understanding cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Vascular smooth muscle ATP-sensitive potassium (KATP) channels play critical roles in modulating vascular tone and thus represent important drug targets for diverse cardiovascular pathologies. Despite extensive research efforts spanning several decades, the search for selective inhibitors that can discriminate between vascular KATP (i.e. Kir6.1/SUR2B) and pancreatic and brain KATP (i.e. Kir6.2/SUR1) channels has, until recently, been unsuccessful. Our group therefore carried out a high-throughput screen of chemically diverse compounds with the goal of discovering specific Kir6.1/SUR2B inhibitors. This screen identified several novel classes of Kir6.1/SUR2B inhibitors, including the first potent (IC50 ~100 nM) and selective inhibitor published to date, termed VU0542270. Here, we expand on this work by disclosing the identity and pharmacological properties of four additional Kir6.1/SUR2B inhibitors that are structurally unrelated to Kir to VU0542270. These inhibitors, named VU0212387, VU0543336, VU0605768, and VU0544086, inhibit Kir6.1/SUR2B with IC50 values ranging from approximately 100 nM to 1 µM and exhibit no apparent inhibitory activity toward Kir6.2/SUR1. Functional analysis of heterologously expressed subunit combinations of Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B and demonstrated that all four inhibitors act on SUR2 to induce channel inhibition. Interestingly, VU0543336 and VU0212387 exhibit paradoxical stimulatory effects on Kir6.2/SUR1 at higher doses. This study broadens our understanding of KATP channel pharmacology, generally, and reveals novel chemical matter for the development of Kir6.1/SUR2-selective drugs, specifically.

The periodic paralyses are a rare group of muscle channel opathies characterized by intermittent attacks of episodic muscle weakness of variable duration. Typically, symptoms begin in the first or second decade of life. This case describes a 13 year-old girl with generalized epilepsy who presented with a 9- year history of recurrent attacks of inability to walk. Attacks which occurred at a frequency of 2-3 times a year with spontaneous resolution were often triggered by exposure to cold, strenuous exercise and occasionally by convulsions. At presentation, the index episode had been on -going for 2 days. Management of the acute paralytic episode and prophylaxis were accomplished with oral acetazolamide administration. This report underscores the ease with which effective prevention of paralytic episodes in periodic paralyses could be achieved in a resource- poor setting.

Pathogenic variants in genes encoding ion channels are causal for various pediatric and adult neurological conditions. In particular, several epilepsy syndromes have been identified to be caused by specific channelopathies. These encompass a spectrum from self-limited epilepsies to developmental and epileptic encephalopathies spanning genetic and acquired causes. Several of these channelopathies have exquisite responses to specific antiseizure medications (ASMs), while others ASMs may prove ineffective or even worsen seizures. Some channelopathies demonstrate phenotypic pleiotropy and can cause other neurological conditions outside of epilepsy. This review aims to provide a comprehensive exploration of the pathophysiology of seizure generation, ion channels implicated in epilepsy, and several genetic epilepsies due to ion channel dysfunction. We outline the clinical presentation, pathogenesis, and the current state of basic science and clinical research for these channelopathies. In addition, we briefly look at potential precision therapy approaches emerging for these disorders. [ABSTRACT FROM AUTHOR]

Potassium ion transport across myocardial cell membrane is essential for type 2 long QT syndrome (LQT2). However, the dysfunction of potassium ion transport due to genetic mutations limits the therapeutic effect in treating LQT2. Biomimetic ion channels that selectively and efficiently transport potassium ions across the cellular membranes are promising for the treatment of LQT2. To corroborate this, we synthesized a series of foldamer-based ion channels with different side chains, and found a biomimetic ion channel of K+ (BIC K) with the highest transport activity among them. The selected BIC K can restore potassium ion transport and increase transmembrane potassium ion current, thus shortening phase 3 of action potential (AP) repolarization and QT interval in LQT2. Moreover, BIC K does not affect heart rate and cardiac rhythm in treating LQT2 model induced by E4031 in isolated heart as well as in guinea pigs. By restoring ion transmembrane transport tactic, biomimetic ion channels, such as BIC K , will show great potential in treating diseases related to ion transport blockade. Type 2 long QT syndrome (LQT2) is a disease caused by K+ transport disorder, which can cause malignant arrhythmia and even death. There is currently no radical cure, so it is critical to explore ways to improve K+ transmembrane transport. In this study, we report that a small-molecule biomimetic ion channel BIC K can efficiently simulate natural K+ channel proteins on the cardiomyocyte and cure E4031-induced LQT2 in guinea pig by restoring K+ transport function for the first time. This study found that the potassium transmembrane transport by BIC K significantly reduced the QT interval, which provides a conceptually new strategy for the treatment of LQT2 disease. [Display omitted] [ABSTRACT FROM AUTHOR]

Voltage-gated ion channels are essential for membrane potential maintenance, homeostasis, electrical signal production and controlling the Ca2+ flow through the membrane. Among all ion channels, the key regulators of neuronal excitability are the voltage-gated potassium channels (KV), the largest family of K+ channels. Due to the ROS high levels in the aging brain, K+ channels might be affected by oxidative agents and be key in aging and neurodegeneration processes. This review provides new insight about channelopathies in the most studied neurodegenerative disorders, such as Alzheimer Disease, Parkinson's Disease, Huntington Disease or Spinocerebellar Ataxia. The main affected KV channels in these neurodegenerative diseases are the KV1, KV2.1, KV3, KV4 and KV7. Moreover, in order to prevent or repair the development of these neurodegenerative diseases, previous KV channel modulators have been proposed as therapeutic targets. [ABSTRACT FROM AUTHOR]

Sudden cardiac death in children and young adults is a relatively rare but tragic event whose pathophysiology is unknown at the molecular level. Evidence indicates that the main cardiac sodium channel (Na V 1.5) and the strong inward rectifier potassium channel (Kir2.1) physically interact and form macromolecular complexes (channelosomes) with common partners, including adapter, scaffolding, and regulatory proteins that help them traffic together to their eventual membrane microdomains. Most important, dysfunction of either or both ion channels has direct links to hereditary human diseases. For example, certain mutations in the KCNJ2 gene encoding the Kir2.1 protein result in Andersen-Tawil syndrome type 1 and alter both inward rectifier potassium and sodium inward currents. Similarly, trafficking-deficient mutations in the gene encoding the Na V 1.5 protein (SCN5A) result in Brugada syndrome and may also disturb both inward rectifier potassium and sodium inward currents. Moreover, gain-of-function mutations in KCNJ2 result in short QT syndrome type 3, which is extremely rare but highly arrhythmogenic, and can modify Kir2.1-Na V 1.5 interactions in a mutation-specific way, further highlighting the relevance of channelosomes in ion channel diseases. By expressing mutant proteins that interrupt or modify Kir2.1 or Na V 1.5 function in animal models and patient-specific pluripotent stem cell–derived cardiomyocytes, investigators are defining for the first time the mechanistic framework of how mutation-induced dysregulation of the Kir2.1-Na V 1.5 channelosome affects cardiac excitability, resulting in arrhythmias and sudden death in different cardiac diseases. [ABSTRACT FROM AUTHOR]

Ventricular fibrillation (VF) is a common cause of sudden cardiac death in patients with channelopathies, particularly in the young population. Although pharmacological treatment, cardiac sympathectomy, and implantable cardioverter defibrillators (ICD) have been the mainstay in the management of VF in patients with channelopathies, they are associated with significant adverse effects and complications, leading to poor quality of life. Given these drawbacks, catheter ablation has been proposed as a therapeutic option for patients with channelopathies. Advances in imaging techniques and modern mapping technologies have enabled increased precision in identifying arrhythmia triggers and substrate modification. This has aided our understanding of the underlying pathophysiology of ventricular arrhythmias in channelopathies, highlighting the roles of the Purkinje network and the epicardial right ventricular outflow tract in arrhythmogenesis. This review explores the role of catheter ablation in managing the most common channelopathies (Brugada syndrome, congenital long QT syndrome, short QT syndrome, and catecholaminergic polymorphic ventricular tachycardia). While the initial results for ablation in Brugada syndrome are promising, the long-term efficacy and durability of ablation in different channelopathies require further investigation. Given the genetic and phenotypic heterogeneity of channelopathies, future studies are needed to show whether catheter ablation in patients with channelopathies is associated with a reduction in VF, and psychological distress stemming from recurrent ICD shocks, particularly relative to other available therapeutic options (e.g., quinidine in high-risk Brugada patients). [ABSTRACT FROM AUTHOR]

Andersen–Tawil syndrome (ATS) is a multisystem channelopathy characterized by periodic paralysis, ventricular arrhythmias, prolonged QT interval, and facial dysmorphisms occurring in the first/second decade of life. High phenotypic variability and incomplete penetrance of the genes causing the disease make its diagnosis still a challenge. We describe a three-generation family with six living individuals affected by ATS. The proband is a 37-year-old woman presenting since age 16, with episodes of muscle weakness and cramps in the pre-menstrual period. The father, two brothers, one paternal uncle and one cousin also complained of cramps, muscle stiffness, and weakness. Despite normal serum potassium concentration, treatment with potassium, magnesium, and acetazolamide alleviated paralysis attacks suggesting a dyskalemic syndrome. Dysmorphic features were noted in the proband, only later. On the ECG, all but one had normal QT intervals. The affected males developed metabolic syndrome or obesity. The father had two myocardial infarctions and was implanted with an intracardiac cardioverter defibrillator (ICD). A genetic investigation by WES analysis detected the heterozygous pathogenic variant (NM_000891.2: c.652C>T, p. Arg218Trp) in the KCNJ2 gene related to ATS, confirmed by segregation studies in all affected members. Furthermore, we performed a review of cases with the same mutation in the literature, looking for similarities and divergences with our family case. [ABSTRACT FROM AUTHOR]

Objectives: This study aimed to determine the usefulness of electrophysiological exercise tests. The significance of slightly abnormal exercise tests was also examined. Methods: We identified all the patients who had undergone exercise testing between February 2007 to June 2022 in Tampere University Hospital, Finland. Their medical records after diagnostic workup and exercise test reports were reviewed. A binary logistic regression was performed to evaluate the association between positive test result in short exercise test, long exercise test, or short exercise test with cooling and genetically confirmed skeletal muscle channelopathy or myotonic disorder. Results: We identified 256 patients. 27 patients were diagnosed with nondystrophic myotonia, periodic paralysis, myotonic dystrophy type 1, myotonic dystrophy type 2, or other specified myopathy. 14 patients were suspected to have a skeletal muscle channelopathy, but pathogenic variants could not be identified. The remaining 215 patients were diagnosed with other conditions than skeletal muscle channelopathy or myotonic disorder. The combined sensitivity of exercise tests was 59.3% and specificity 99.1%. Abnormal exercise test result was associated with increased risk of skeletal muscle channelopathy or myotonic disorder (OR 164.3, 95% CI 28.3–954.6, p < 0.001). Conclusions: Electrophysiological exercise test is not optimal to exclude skeletal muscle channelopathy. It may be useful if a skeletal muscle channelopathy is suspected and genetic testing is negative or indeterminate and further evidence is required. Slightly abnormal exercise test results are possible in various conditions and result from different aetiologies. There is a demand for neurophysiological studies with higher sensitivity to detect skeletal muscle channelopathies. [ABSTRACT FROM AUTHOR]

Large Conductance Voltage- and Calcium-activated K+ (BK) channels are transmembrane pore-forming proteins that regulate cell excitability and are also expressed in non-excitable cells. They play a role in regulating vascular tone, neuronal excitability, neurotransmitter release, and muscle contraction. Dysfunction of the BK channel can lead to arterial hypertension, hearing disorders, epilepsy, and ataxia. Here, we provide an overview of BK channel functioning and the implications of its abnormal functioning in various diseases. Understanding the function of BK channels is crucial for comprehending the mechanisms involved in regulating vital physiological processes, both in normal and pathological conditions, controlled by BK. This understanding may lead to the development of therapeutic interventions to address BK channelopathies. [ABSTRACT FROM AUTHOR]

Inherited cardiac channelopathies are major causes of sudden cardiac death (SCD) in young people. Genetic testing is focused on the identification of single-nucleotide variants (SNVs) by Next-Generation Sequencing (NGS). However, genetically elusive cases can carry copy number variants (CNVs), which need specific detection tools. We underlie the utility of identifying CNVs by investigating the literature data and internally analyzing cohorts with CNVs in KCNQ1, KCNH2, SCN5A, and RYR2. CNVs were reported in 119 patients from the literature and 21 from our cohort. Young patients with CNVs in KCNQ1 show a Long QT (LQT) phenotype > 480 ms and a higher frequency of syncope. None of them had SCD. All patients with CNV in KCNH2 had a positive phenotype for QT > 480 ms. CNVs in SCN5A were represented by the Brugada pattern, with major cardiac events mainly in males. Conversely, adult females show more supraventricular arrhythmias. RYR2-exon3 deletion showed a broader phenotype, including left ventricular non-compaction (LVNC) and catecholaminergic polymorphic ventricular tachycardia (CPVT). Pediatric patients showed atrial arrhythmias and paroxysmal atrial fibrillation. Relatively higher syncope and SCA were observed in young females. The detection of CNVs can be of greater yield in two groups: familial channelopathies and patients with suspected Jervell and Lange-Nielsen syndrome or CPVT. The limited number of reported individuals makes it mandatory for multicentric studies to give future conclusive results.

Novel KCNMA1 variants, encoding the BK K+ channel, are associated with a debilitating dyskinesia and epilepsy syndrome. Neurodevelopmental delay, cognitive disability, and brain and structural malformations are also diagnosed at lower incidence. More than half of affected individuals present with a rare negative episodic motor disorder, paroxysmal nonkinesigenic dyskinesia (PNKD3). The mechanistic relationship of PNKD3 to epilepsy and the broader spectrum of KCNMA1-associated symptomology is unknown. This review summarizes patient-associated KCNMA1 variants within the BK channel structure, functional classifications, genotype-phenotype associations, disease models, and treatment. Patient and transgenic animal data suggest delineation of gain-of-function (GOF) and loss-of-function KCNMA1 neurogenetic disease, validating two heterozygous alleles encoding GOF BK channels (D434G and N999S) as causing seizure and PNKD3. This discovery led to a variant-defined therapeutic approach for PNKD3, providing initial insight into the neurological basis. A comprehensive clinical definition of monogenic KCNMA1-linked disease and the neuronal mechanisms currently remain priorities for continued investigation. [ABSTRACT FROM AUTHOR]

Introduction: Sudden cardiac death (SCD) and ventricular fibrillation are rare but severe complications of many cardiovascular diseases and represent a major health issue worldwide. Although the primary causes are often acute or chronic coronary diseases, genetic conditions, such as inherited channelopathies or non-ischemic cardiomyopathies are leading causes of SCD among the young. However, relevant experimental models to study the underlying mechanisms of arrhythmias and develop new therapies are still needed. The number of genetically engineered mouse models with cardiac phenotype is growing, making electrophysiological studies in mice essential tools to study arrhythmogenicity and arrhythmia mechanisms and to test novel treatments. Recently, intracardiac catheterization via the jugular vein was described to induce and record ventricular arrhythmias in living anesthetized mice. Several strategies have been reported, developed in healthy wild-type animals and based on aggressive right ventricular stimulation. Methods: Here, we report a protocol based on programmed electrical stimulation (PES) performed in clinical practice in patients with cardiac rhythm disorders, adapted to two transgenic mice models of arrhythmia - Brugada syndrome and cardiolaminopathy. Results: We show that this progressive protocol, based on a limited number of right ventricular extrastimuli, enables to reveal different rhythmic phenotypes between control and diseased mice. In this study, we provide detailed information on PES in mice, including catheter positioning, stimulation protocols, intracardiac and surface ECG interpretation and we reveal a higher susceptibility of two mouse lines to experience triggered ventricular arrhythmias, when compared to control mice. Discussion: Overall, this technique allows to characterize arrhythmias and provides results in phenotyping 2 arrhythmogenic-disease murine models. [ABSTRACT FROM AUTHOR]

Long QT syndrome (LQTS) is a congenital ion channel disorder causing prolonged ventricular repolarization and presents on surface ECG with a prolonged QTc interval. This condition predisposes to ventricular arrhythmias and also sudden cardiac death. LQTS without appropriate therapy during pregnancy and the postnatal phase poses an additionally increased risk of sudden cardiac death due to physiological changes associated with gestation. We present a case report of a 30-year-old pregnant woman with known long QT syndrome Type 2 (LQT2) and discuss the management in cardiological practice. [ABSTRACT FROM AUTHOR]

Congenital insensitivity to pain (CIP) is a rare phenotype characterized by the inability to perceive pain stimuli with subsequent self‐injuries, whereas CIP associated with anhidrosis (CIPA) is an overlapping phenotype mainly characterized by insensitivity to noxious stimuli and anhidrosis. CIP is primarily associated with pathogenetic variants in the SCN9A gene while CIPA is associated with pathogenetic variants in NGF and NRTK genes. However, in recent years, a significant overlap between these two disorders has been observed highlighting the presence of anhidrosis in SCN9A variants. We report the cases of two siblings (age 4 and 6 years) born from consanguineous parents presenting with a previously undescribed phenotype due to a novel pathogenic variant in SCN9A clinically characterized by congenital insensitivity to pain, anhidrosis, and mild cognitive impairment. [ABSTRACT FROM AUTHOR]

Voltage-gated ion channels are essential for membrane potential maintenance, homeostasis, electrical signal production and controlling the Ca2+ flow through the membrane. Among all ion channels, the key regulators of neuronal excitability are the voltage-gated potassium channels (KV), the largest family of K+ channels. Due to the ROS high levels in the aging brain, K+ channels might be affected by oxidative agents and be key in aging and neurodegeneration processes. This review provides new insight about channelopathies in the most studied neurodegenerative disorders, such as Alzheimer Disease, Parkinson’s Disease, Huntington Disease or Spinocerebellar Ataxia. The main affected KV channels in these neurodegenerative diseases are the KV1, KV2.1, KV3, KV4 and KV7. Moreover, in order to prevent or repair the development of these neurodegenerative diseases, previous KV channel modulators have been proposed as therapeutic targets.

Abstract Background Muscle channelopathies are a rare and heterogeneous group of disorders that can be clinically challenging and functionally disabling. These disorders can present in both adult and pediatric age groups. These disorders have been known since the turn of the 20th century, with a steady evolution in terms of understanding the pathophysiology, phenotype, diagnostic, and treatment modalities over the last three decades. Methods We present a comprehensive review of muscle channelopathies that includes nondystrophic myotonias and periodic paralyses. The disorders in this review have been classified based on the presence or absence of myotonia on either the clinical exam or on electrophysiological testing. The historical background, genetics, pathophysiology, phenotypic presentations, and treatment modalities of each disorder reveal similarities as well as specific nuances in the disease phenotypes. Neurophysiologic testing shows differences in responses on routine and exercise testing and can narrow the differential within subsets of nondystrophic myotonias and periodic paralyses. The advances in genetics further aid in specifying which of the putative channels are at fault. Management can then be guided by knowledge of the causative gene and involves either avoidance of triggers or channel‐based therapeutics. Conclusion Muscle channelopathies are rare, but a high index of suspicion along with a knowledge of the phenotype will help guide neurophysiological and genetic testing. A muscle channelopathy diagnosis, subsequently, can assist in avoiding triggers and directing treatments.

Small- and intermediate-conductance Ca2+-activated potassium (KCa2.x and KCa3.1, also called SK and IK) channels are activated exclusively by a Ca2+-calmodulin gating mechanism. Wild-type KCa2.3 channels have a Ca2+ EC50 value of ∼0.3 μM, while the apparent Ca2+ sensitivity of wild-type KCa3.1 channels is ∼0.27 μM. Heterozygous genetic mutations of KCa2.3 channels have been associated with Zimmermann-Laband syndrome and idiopathic noncirrhotic portal hypertension, while KCa3.1 channel mutations were reported in hereditary xerocytosis patients. KCa2.3_S436C and KCa2.3_V450L channels with mutations in the S45A/S45B helices exhibited hypersensitivity to Ca2+. The corresponding mutations in KCa3.1 channels also elevated the apparent Ca2+ sensitivity. KCa3.1_S314P, KCa3.1_A322V and KCa3.1_R352H channels with mutations in the HA/HB helices are hypersensitive to Ca2+, whereas KCa2.3 channels with the equivalent mutations are not. The different effects of the equivalent mutations in the HA/HB helices on the apparent Ca2+ sensitivity of KCa2.3 and KCa3.1 channels may imply distinct modulation of the two channel subtypes by the HA/HB helices. AP14145 reduced the apparent Ca2+ sensitivity of the hypersensitive mutant KCa2.3 channels, suggesting the potential therapeutic usefulness of negative gating modulators.

Calcium is a key ion involved in cardiac and skeletal muscle contractility, nerve function, and skeletal structure. Global calcium balance is affected by parathyroid hormone and vitamin D, and calcium is shuttled between the extracellular space and the bone matrix compartment dynamically. The kidney plays an important role in whole-body calcium balance. Abnormalities in the kidney transport proteins alter the renal excretion of calcium. Various hormonal and regulatory pathways have evolved that regulate the renal handling of calcium to maintain the serum calcium within defined limits despite dynamic changes in dietary calcium intake. Dysregulation of renal calcium transport can occur pharmacologically, hormonally, and via genetic mutations in key proteins in various nephron segments resulting in several disease processes. This review focuses on the regulation transport of calcium in the nephron. Genetic diseases affecting the renal handling of calcium that can potentially lead to changes in the serum calcium concentration are reviewed.

Abstract Benign idiopathic neonatal seizures (BINS), colloquially referred to as the “fifth‐day fits,” is a clinical neonatal epilepsy syndrome associated with early, spontaneous resolution of seizures and favorable developmental outcome. Although this disease entity was first described over four decades ago, the etiopathogenesis remains unknown, and it is unclear if the syndrome represents a single, cohesive disorder or a common manifestation of various unrelated neonatal neurological disturbances. As such, there are no standardized approaches to diagnostic workup and management. Benign familial neonatal seizures (BFNS) is a well‐characterized genetic syndrome associated with KCNQ2 and KCNQ3 pathogenic variants, which also manifests clinically with self‐resolving seizures in the neonatal period. While it remains unclear if there is any shared pathogenesis between these two disorders, the exceedingly similar phenotypic presentations and natural history raise the question of whether consensus management approaches used in genetic BFNS can also be applied to BINS. Here, we present a topical and historical review of BINS and BFNS literature and propose specific treatment recommendations based on extrapolation of limited existing clinical data.

Large Conductance Voltage- and Calcium-activated K+ (BK) channels are transmembrane pore-forming proteins that regulate cell excitability and are also expressed in non-excitable cells. They play a role in regulating vascular tone, neuronal excitability, neurotransmitter release, and muscle contraction. Dysfunction of the BK channel can lead to arterial hypertension, hearing disorders, epilepsy, and ataxia. Here, we provide an overview of BK channel functioning and the implications of its abnormal functioning in various diseases. Understanding the function of BK channels is crucial for comprehending the mechanisms involved in regulating vital physiological processes, both in normal and pathological conditions, controlled by BK. This understanding may lead to the development of therapeutic interventions to address BK channelopathies.

Functional investigation of genetic variants found in long QT syndrome can provide evidence that is needed to confirm the genetic diagnosis and establish the cause of the condition. We performed functional assessment to determine the z-score, using a clinically calibrated automated patch clamp assay, for 2 missense KCNH2 variants found in 2 families that have been diagnosed with long QT syndrome. These variants are currently classified as variant of uncertain significance in ClinVar. The z-scores for homozygous and heterozygous NM_000238.4:c.1819A>T p.(Ile607Phe) from family 1 were –5.16 and –3.97, respectively, and for heterozygous NM_000238.4:c.1832A>G p.(Tyr611Cys) from family 2 was –6.63. The z-scores for these variants are consistent with severe loss-of-function phenotypes. We have established the genetic cause of the long QT syndrome in these 2 families by providing validated functional evidence that supports the pathogenicity of p.(Ile607Phe) and p.(Tyr611Cys). Clinical diagnosis of long QT syndrome has been very successful in providing adequate clinical management for patients. However, functional assessment of variants found in these patients by using variant-specific z-scores can further enhance the current clinical management of patients with long QT syndrome through shared decision making based on validated experimental evidence.

Introduction: Sudden cardiac death (SCD) and ventricular fibrillation are rare but severe complications of many cardiovascular diseases and represent a major health issue worldwide. Although the primary causes are often acute or chronic coronary diseases, genetic conditions, such as inherited channelopathies or non-ischemic cardiomyopathies are leading causes of SCD among the young. However, relevant experimental models to study the underlying mechanisms of arrhythmias and develop new therapies are still needed. The number of genetically engineered mouse models with cardiac phenotype is growing, making electrophysiological studies in mice essential tools to study arrhythmogenicity and arrhythmia mechanisms and to test novel treatments. Recently, intracardiac catheterization via the jugular vein was described to induce and record ventricular arrhythmias in living anesthetized mice. Several strategies have been reported, developed in healthy wild-type animals and based on aggressive right ventricular stimulation.Methods: Here, we report a protocol based on programmed electrical stimulation (PES) performed in clinical practice in patients with cardiac rhythm disorders, adapted to two transgenic mice models of arrhythmia - Brugada syndrome and cardiolaminopathy.Results: We show that this progressive protocol, based on a limited number of right ventricular extrastimuli, enables to reveal different rhythmic phenotypes between control and diseased mice. In this study, we provide detailed information on PES in mice, including catheter positioning, stimulation protocols, intracardiac and surface ECG interpretation and we reveal a higher susceptibility of two mouse lines to experience triggered ventricular arrhythmias, when compared to control mice.Discussion: Overall, this technique allows to characterize arrhythmias and provides results in phenotyping 2 arrhythmogenic-disease murine models.

SCN4A mutations have been shown to be associated with myotonia, paramyotonia congenita, and periodic paralyses. More recently, loss-of-function variants in the SCN4A gene were also noted to be associated with rarer, autosomal recessive forms of congenital myasthenic syndrome and congenital myopathy. Diagnosis is challenging as the initial clinical presentation and histological features on muscle biopsies are non-specific. We report a Han Chinese patient presented with congenital myopathy with two missense SCN4A variants. The patient had an antenatal history of reduced fetal movements, polyhydramnios and a very preterm birth. At birth, she was noted to have low Apgar score, respiratory distress syndrome and hypotonia. Delayed motor development was noted in early childhood. Dysmorphic features such as an elongated face, dolichocephaly and high arched palate were present. At 16 years of age, the patient developed progressive muscle weakness and was wheelchair-bound by age 20. Muscle biopsy revealed non-specific changes only. Targeted hereditary myopathy panel testing by next generation sequencing revealed two previously unreported missense variants c.1841A > T p.(Asn614Ile) and c.4420G > A p.(Ala1474Thr) in the SCN4A gene. The clinical features of SCN4A-related congenital myopathy and myasthenic syndrome were reviewed. This case exemplifies the utility of next generation sequencing in the diagnosis of undifferentiated muscle disease.

The membrane potential of a cell (Vm) regulates several physiological processes. The voltage sensor domain (VSD) is a region that confers voltage sensitivity to different types of transmembrane proteins such as the following: voltage-gated ion channels, the voltage-sensing phosphatase (Ci-VSP), and the sperm-specific Na+/H+ exchanger (sNHE). VSDs contain four transmembrane segments (S1–S4) and several positively charged amino acids in S4, which are essential for the voltage sensitivity of the protein. Generally, in response to changes of the Vm, the positive residues of S4 displace along the plasma membrane without generating ionic currents through this domain. However, some native (e.g., Hv1 channel) and mutants of VSDs produce ionic currents. These gating pore currents are usually observed in VSDs that lack one or more of the conserved positively charged amino acids in S4. The gating pore currents can also be induced by the isolation of a VSD from the rest of the protein domains. In this review, we summarize gating pore currents from all families of proteins with VSDs with classification into three cases: (1) pathological, (2) physiological, and (3) artificial currents. We reinforce the model in which the position of S4 that lacks the positively charged amino acid determines the voltage dependency of the gating pore current of all VSDs independent of protein families. [ABSTRACT FROM AUTHOR]