SCN5A Research Articles

Concise Review: Stem Cell Models of SCN1A-Related Encephalopathies-Current Perspective and Future Therapies.

Mutations in the SCN1A gene can cause a variety of phenotypes, ranging from mild forms, such as febrile seizures and generalized epilepsy with febrile seizures plus, to severe, such as Dravet and non-Dravet developmental epileptic encephalopathies. Until now, more than two thousand pathogenic variants of the SCN1A gene have been identified and different pathogenic mechanisms (loss vs. gain of function) described, but the precise molecular mechanisms responsible for the deficits exhibited by patients are not fully elucidated. Additionally, the phenotypic variability proves the involvement of other genetic factors in its final expression. This is the reason why animal models and cell line models used to explore the molecular pathology of SCN1A-related disorders are only of limited use. The results of studies based on such models cannot be directly translated to affected individuals because they do not address each patient’s unique genetic background. The generation of functional neurons and glia for patient-derived iPSCs, together with the generation of isogenic controls using CRISPR/Cas technology, and finally, the 3D brain organoid models, seem to be a good way to solve this problem. Here, we review SCN1A-related encephalopathies, as well as the stem cell models used to explore their molecular basis.

SCN2A and arrhythmia: A potential correlation? A case report and literature review

Variants in SCN2A, encoding the voltage-gated sodium channel Nav1.2, are commonly associated with developmental and epileptic encephalopathy. Although animal studies demonstrated a role for Nav1.2 in intraventricular conduction, heart anomalies have been only occasionally described in patients with SCN2A variants. In this report we trace the prenatal and neonatal history of a fetus/newborn with a de novo pathogenic variant in the SCN2A gene identified by prenatal trio whole-exome sequencing (WES). In addition to more typically SCN2A-associated neurological manifestations, the patient showed sustained tachyarrhythmia, potentially expanding the phenotypic spectrum associated with SCN2A variants and raising the question of whether cardiological assessment and prompt pharmacological intervention in SCN2A channelopathies to avoid heart complications might be beneficial. To the best of our knowledge, this represents the first clinical description of a SCN2A phenotype in a prenatal setting, as well as the first SCN2A diagnosis achieved by prenatal trio-WES approach.

Genetic variation rs6795970 of the SCN10A gene is associated with PR interval in young population of Republic of Moldova

Abstract Background/Objectives The electrocardiographic PR interval reflects atrial and atrioventricular nodal conduction time. Prolongation of the PR interval increase risk of atrial fibrillation (AF) and heart block. Genome-wide association studies (GWAS) have identified association of a nonsynonymous single nucleotide polymorphism (SNP), rs6795970, in the SCN10A gene with PR interval in individuals of European and Asian ancestry. The aim of the study was to determine distribution of the genetic variants of rs6795970, associated with PR interval in young population of Republic of Moldova. Methods 1380 young participants from Republic of Moldova aged between 19–25 years, were genotyped for rs6795970 in the SCN10A gene, using TaqMan SNP Genotyping Assay. Results The genotype G/G, A/G, A/A distributions of rs6795970 among participants were 37%, 48%, 15%, respectively (χ2=0.086, p=0.770). The allele frequencies for G and A, in young participants were 61% and 39%, respectively. We observed association between rs6795970_A and a prolongation of the PR interval (p=0.003). Conclusions In our study, we determined that distribution of the genetic variants of rs6795970, associated with PR interval in young population of Republic of Moldova was consistent with 1000 Genomes data in the European population. Therefore, our data demonstrate that the A allele is associated with prolongation of the PR interval and at least 15% of all participants (the A/A genotype), may have an increased risk of conduction abnormalities. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National project “Study of molecular genetic polymorphism of metabolic risk factors in young population of the Republic of Moldova National project “Identification and validation of genetic and epigenetic biomarkers in chronic non-communicable diseases with major impact on public health”

Brugada syndrome in Portugal: a cohort characterization

Abstract Introduction Brugada syndrome (BrS) is an inherited cardiac arrhythmic disorder that can lead to sudden death. Although SCN5A was the first pathogenic associated gene, other potential genes have been described. The relationship between SCN5A, spontaneous type 1 pattern and the predisposition to ventricular arrhythmias is not totally understood. Purpose To characterize mutations in a Portuguese cohort with BrS and explore the genotype-phenotype association in terms of electrocardiographic pattern and arrhythmic risk. Methods Prospective single-center study of patients (pts) with BrS. Genetic test included SCN5A direct sequencing from 2003 a broad panel of 120 genes associated with cardiomyopathies and arrhythmic disorders from 2018. Genetic test results were classified according to pathogenicity: mutations of unknown significance (MUS), mutations potentially pathogenic (MPP) and known pathogenic mutations (KPM). Kaplan-Meyer survival analysis was used to explore the association between genetic test results and the risk of arrhythmic events. Results A total of 94 pts [46±12 years, 67% male,64.9% with type 1 spontaneous pattern] were submitted to genetic testing. No relevant mutations were identified in 68pts and suspicious or pathogenic mutations were recognized in 26pts. The most frequent mutations occurred in SCN5A (N=20,76.9%), and included 8 KPM: 4 in exon 23 (3 of them had the same mutation,c.4018G>A), 2 in exon 26 (c.4534C>T), 1 in exon 28 and 1 in exon 16. All MPP in SCN5A occurred either in exon 23 or 28. Considering MUS, different mutations were described in 6 different exons (8,15,18,23,25 and two in 28). Additionally, 6 pts presented MUS in other genes: SCN10A (N=2), ANK2 (N=2), SFM13A, CAV2 (associated with long QT), CACNA1D and PXDNL. We found no differences in the prevalence of spontaneous type 1 pattern considering gene mutation or mutation pathogenicity. A non-significant trend to higher arrhythmic risk was observed in pts presenting genetic mutations (either KPM, MPP or MUS), Long-Rank: 1.743, p=0.187. Conclusion Gene mutations are identified in a minority of BrS pts, mostly at SCN5A gene. No association was noticed between genetic test results and the ECG pattern. However, pts with identified mutation presented a tendency to higher arrhythmic risk. At present time, genetic tests in BrS are only relevant for familial screening, but long-term collection of data is crucial to elucidate the genotype-phenotype relation and arrhythmic risk. Funding Acknowledgement Type of funding sources: None.

Characterization and long-term follow-up of children with brugada syndrome: experience from a tertiary paediatric referral centre

Abstract Introduction Brugada syndrome (BrS) is an autosomal dominant channelopathy, which typically presents in young adults. It can also be diagnosed in children, but data in this age group is scarce. Purpose To describe the clinical features, management and long-term follow-up of children with BrS history followed-up in a tertiary paediatric referral centre. Methods Single centre retrospective study of consecutive patients with history of BrS, defined as having a BrS positive phenotype (BrS(+)), or a negative phenotype-positive genotype (BrS(−)). They were all followed up in a paediatric heart rhythm clinic. Clinical and demographical data were collected and analysed according to the phenotype. Results 30 patients were included, with a median age at diagnosis of 7 years (IQR 1–13) and a mean follow-up time of 7±3 years. Sixteen patients were BrS(+), predominantly male (n=13, 81%). 88% (n=14) performed a genetic test, which was positive in 57% (n=8); the most frequent mutation was SCN5A (n=5). Family history of BrS was present in 56% (n=9) and almost one third had family history of sudden cardiac death (SCD). Most of the patients had a type 1 Brugada ECG pattern (n=14) and 2 patients presented a fever and drug induced pattern, respectively. Fourteen patients were BrS(−), mostly female (n=11, 79%) with a loss-of-function mutation in the SCN5A gene (n=10). They all had family members with BrS, mainly from the paternal side, and 43% (n=6) mentioned SCD history. Although most of the patients were asymptomatic, the prevalence of rhythm or conduction disturbances was not infrequent, particularly in BrS(+) patients (n=12, 75%). Also, in this group and during follow-up, 3 patients had documented supraventricular tachyarrhythmias, and 2 patients had syncope episodes, one of which required an implantable cardioverter-defibrillator. No events were reported in the BrS(−) patients. Nine patients (n=9/30, 30%) were hospitalized, 3 due to an arrhythmic event (all in the BrS(+) group). Overall, no sudden cardiac death event was reported during follow-up. Conclusion In our study, although the majority of the patients were asymptomatic, the occurrence of arrhythmic events was not negligible, especially in the BrS(+) patients. Despite the significant family history, patients with BrS(−) had no events reported during follow-up. Nevertheless, the management of these patients is not clear cut, and a personalized therapeutic strategy with close follow-up is essential. Funding Acknowledgement Type of funding sources: None.

Genome-wide analyses identify SCN5A as a susceptibility locus for premature atrial contraction frequency

SummaryPremature atrial contractions (PACs) are frequently observed on electrocardiograms and are associated with increased risks of atrial fibrillation (AF), stroke, and mortality. In this study, we aimed to identify genetic susceptibility loci for PAC frequency. We performed a genome-wide association study meta-analysis with PAC frequency obtained from ambulatory cardiac monitoring in 4,831 individuals of European ancestry. We identified a genome-wide significant locus at the SCN5A gene. The lead variant, rs7373862, located in an intron of SCN5A, was associated with an increase of 0.12 [95% CI 0.08–0.16] standard deviations of the normalized PAC frequency per risk allele. Among genetic variants previously associated with AF, there was a significant enrichment in concordance of effect for PAC frequency (n = 73/106, p = 5.1 × 10−5). However, several AF risk loci, including PITX2, were not associated with PAC frequency. These findings suggest the existence of both shared and distinct genetic mechanisms for PAC frequency and AF.

SCN1A polymorphisms influence the antiepileptic drugs responsiveness in Jordanian epileptic patients.

The aim of this study was to evaluate whether the voltage-gated sodium channel alpha subunit 1 (SCN1A) gene polymorphisms influence the responsiveness of Jordanian epileptic patients to antiepileptic drugs (AEDs). A total of 72 AEDs-treated epileptics were polymerase chain reaction (PCR)-genotyped for six single nucleotide polymorphisms (SNPs), including SCN1A rs2298771, rs3812718, rs3812719, rs2217199, rs2195144 and rs1972445. Genotype and allele distributions in drug-responsive and drug-resistant patients were compared. The six SNPs haplotypes were examined, and the linkage disequilibrium (LD) was assessed. The genotypes of drug-resistant and drug-responsive groups were in Hardy-Weinberg equilibrium. Three genetic polymorphisms of the SCN1A gene seemed to influence the resistance to AEDs, on the level of alleles and genotypes. Data revealed that rs2298771 G allele, rs3812719 C allele, and rs2195144 T allele increased the risk of developing AEDs-resistance (OR=2.9; 95%CI= 1.4-5.9, p=0.003; OR=2.4; 95%CI=1.2-4.7, p=0.01; OR=2.3; 95%CI=1.2-4.7, p=0.01), respectively. Haplo type analysis of SCN1A polymorphisms revealed high-degree LD associated with resistance to AEDs. A synergetic effect appears with highly significant association in GCCATG haplotype of rs2298771, rs3812718, rs3812719, rs2217199, rs2195144, and rs1972445 respectively (OR=2.8; 95%CI=1.5-6.2, p=0.002). Data suggests that SCN1A polymorphisms could influence the resistance to AEDs in Jordanian epileptics at three SNPs (rs2298771; rs3812719; rs2195144). Additionally, haplotype analysis indicated a substantial degree of LD between the six SCN1A polymorphisms. Further investigation with larger sample size is needed to confirm the results of the current study.

Exploring the genetic etiology of drug-resistant epilepsy: incorporation of exome sequencing into practice.

By affecting about 50 million people worldwide, epilepsy is considered a global concern in neurology. Intolerable enough, up to ¼ of all patients do not respond to antiepileptic drugs and have recurring seizures. Therefore, revealing the underlying etiology is quite demanding in a clinical context to improve diagnosis and disease management. Initially, 85 patients suspected of epilepsy underwent thorough clinical and paraclinical evaluation and 24 individuals with drug-resistant epilepsy entered the study. Using whole-exome sequencing, the genetic etiology of drug-resistant epilepsy was investigated and discerned whether this method could facilitate the management of drug-resistant epilepsy through personalized medicine. Eventually, functional annotation was performed and drug-gene interaction networks were constructed to find potential therapeutic targets. We found eleven novel variants in various genes including IRF2BPL, ST3GAL3, and GPAA1, for which a few epilepsy-related variants are available in public databases. The overall diagnostic yield for likely pathogenic and pathogenic variants and the detection rate of novel variants were 25% and 84.6%, respectively. Based on the results, two patients were considered potential candidates for personalized medicine. The highest number of interaction with drugs was demonstrated for SCN1A, SCN2A, and GRIN2A genes. This study highlighted the importance of consanguineous marriage in drug-resistant epilepsy and suggested the possibility of reduced penetrance and variable expressivity in some of the autosomal dominant cases. We also suggest that whole-exome sequencing could facilitate personalized management of drug-resistant epilepsy. Regarding drug-gene interactions, some genes such as SCN1A and SCN2A might serve as therapeutic targets in drug-resistant epilepsy.

Ocular manifestations among patients with congenital insensitivity to pain due to variants in PRDM12 and SCN9A genes.

Congenital insensitivity to pain (CIP) is a group of rare genetic disorders with a common characteristic of absent sensation to nociceptive pain. Here we present a series of six patients; three had a novel variant in the PRDM12 gene (group A), and three had a missense variant in the SCN9A gene (group B). We compared the ocular manifestations between the two groups. Records of these patients from 2009 through 2018 were reviewed. The retrieved data included demographics, genetic analysis results, ocular history and ophthalmic findings including visual acuity, corneal sensitivity, tear production, ocular surface findings, cycloplegic refraction, and fundoscopy. We found that patients with PRDM12 variant had more severe manifestations of ocular surface disease, with more prevalent corneal opacities and worse visual acuity, compared to patients with SCN9A variant.

Human macrophages directly modulate iPSC-derived cardiomyocytes at healthy state and congenital arrhythmia model in vitro.

The electrophysiological regulation of cardiomyocytes (CMs) by the cardiac macrophages (MΦs) has been recently described as an unconventional role of MΦs in the murine heart. Investigating the molecular and physiological modulation of CM by MΦ is critical to understand the novel mechanisms behind cardiac disorders from the systems perspective and to develop new therapeutic approaches. Here, we developed an in vitro direct coculture system to investigate the cellular and functional interaction between human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and monocyte-derived MΦs both in healthy-state and congenital arrhythmia disease model associated with SCN5A ion channel mutations. Congenital arrhythmia patient-derived (P) and healthy individual-derived control (C) monocytes and derived MΦs exhibited distinct M1- and M2-like polarization-related gene expression pattern. The iPSC-CMs and MΦs formed direct membrane contacts in cocultures demonstrated by time-lapse imaging, scanning electron microscopy, and immunolabeling. The intracellular Ca2+ transients were observed in iPSC-CMs and MΦs when in contact with each other. Interestingly, the C-MΦs in direct contact with C-CMs significantly accelerated the contraction rates, demonstrating the positive chronotropic effect of MΦs on healthy cardiac cultures. Furthermore, the MΦs carrying the SCN5A gene mutation significantly enhanced the arrhythmic events in both C-CMs and P-CMs, implying that the sodium channel mutation in the MΦ is important for the CM function. Importantly, when C-MΦs were coupled to tachycardic P-CMs, the contraction frequency drastically decreased, and rhythmicity enhanced implicating the amelioration of the disease phenotype in vitro. Consequently, our results indicated the functional regulatory role of MΦs on human iPSC-CM contractility by membrane contacts in a physiologically relevant in vitro coculture model of both steady-state and arrhythmia. Our findings could serve as a valuable source for the development of effective immunoregulatory therapies for cardiac arrhythmia in the future.

Biallelic Loss of Function Mutation in Sodium Channel Gene SCN10A in an Autism Spectrum Disorder Trio from Pakistan.

The genetic dissection of autism spectrum disorders (ASD) has uncovered the contribution of de novo mutations in many single genes as well as de novo copy number variants. More recent work also suggests a strong contribution from recessively inherited variants, particularly in populations in which consanguineous marriages are common. What is also becoming more apparent is the degree of pleiotropy, whereby mutations in the same gene may have quite different phenotypic and clinical consequences. We performed whole exome sequencing in a group of 115 trios from countries with a high level of consanguineous marriages. In this paper we report genetic and clinical findings on a proband with ASD, who inherited a biallelic truncating pathogenic/likely pathogenic variant in the gene encoding voltage-gated sodium channel X alpha subunit, SCN10A (NM_006514.2:c.937G>T:(p.Gly313*)). The biallelic pathogenic/likely pathogenic variant in this study have different clinical features than heterozygous mutations in the same gene. The study of consanguineous families for autism spectrum disorder is highly valuable.

A case of Dravet syndrome with focal cortical myoclonus

BackgroundDravet syndrome (DS) is a severe epileptic encephalopathy in children dominated by polymorphic seizures. Focal cortical myoclonus indicated on conventional electroencephalogram (EEG) was rarely observed in DS.Case presentationThe child, boy, thirteen months old, suffered from clonic seizures during bathing at two months old. Later he suffered from recurrent afebrile or febrile generalized tonic–clonic seizures often developing into status epilepticus. A genetic analysis of the SCN1A gene revealed a de novo heterozygous frame shift mutation in exon 21(c.3836_c.3837del AT).His myoclonic jerks of unilateral arm occurred spontaneously in response to movement. A spike wave from right central-parietal cortex immediately preceded a left myoclonic muscle activity, while a spike wave from left immediately preceded a right myoclonic muscle activity. The onset of the detected spike preceded the onset of myoclonic muscle activity by 42 ms using jerk-locked back-averaging of electroencephalogram data. The focal cortical myoclonus was not noted when one year old.ConclusionsFocal cortical myoclonus could be a form of seizures during the first year of life in DS, which may broaden the types of seizures of DS and may provide some diagnostic clues for DS.

Investigation of MicroRNA-134 as a Target against Seizures and SUDEP in a Mouse Model of Dravet Syndrome.

Dravet syndrome (DS) is a catastrophic form of pediatric epilepsy mainly caused by noninherited mutations in the SCN1A gene. DS patients suffer severe and life-threatening focal and generalized seizures which are often refractory to available anti-seizure medication. Antisense oligonucleotides (ASOs) based approaches may offer treatment opportunities in DS. MicroRNAs are short noncoding RNAs that play a key role in brain structure and function by post-transcriptionally regulating gene expression, including ion channels. Inhibiting miRNA-134 (miR-134) using an antimiR ASO (Ant-134) has been shown to reduce evoked seizures in juvenile and adult mice and reduce epilepsy development in models of focal epilepsy. The present study investigated the levels of miR-134 and whether Ant-134 could protect against hyperthermia-induced seizures, spontaneous seizures and mortality (SUDEP) in F1.Scn1a(+/-)tm1kea mice. At P17, animals were intracerebroventricular injected with 0.1-1 nmol of Ant-134 and subject to a hyperthermia challenge at postnatal day (P)18. A second cohort of P21 F1.Scn1a(+/-)tm1kea mice received Ant-134 and were followed by video and EEG monitoring until P28 to track the incidence of spontaneous seizures and SUDEP. Hippocampal and cortical levels of miR-134 were similar between wild-type (WT) and F1.Scn1a(+/-)tm1kea mice. Moreover, Ant-134 had no effect on hyperthermia-induced seizures, spontaneous seizures and SUDEP incidence were unchanged in Ant-134-treated DS mice. These findings suggest that targeting miR-134 does not have therapeutic applications in DS.

Study of the diagnostic yield of gene panels in long QT syndrome in pediatrics

Long QT syndrome (LQTS) is an inherited heart disease responsible for serious arrhythmias. Identification of the mutation is essential for diagnosis, initiation of preventive treatment and family screening. The purpose is to evaluate the diagnostic yield of a panel of 21 genes in the pediatric revelation SQTL and secondarily to describe its clinical, paraclinical and therapeutic characteristics. Descriptive, retrospective and multicenter French study, conducted between 2015 and 2020, using genetic and clinical data from proband children analyzed with the same panel of genes in search of a LQTS. We included 366 patients, aged 11 [7] years, of which 47.5% had a causal mutation resulting mainly from the KCNQ1 (35.6%), KCNH2 (33.9%), SCN5A (14.9%) and including 37 unpublished variants. The genes in the level 2 panel represented 13.2% and the syndromic forms 8.6% of the mutations. Among the 151 patients with an available Schwartz score, 23.5% of patients with mutations had a low clinical probability. Finally, 69% of patients with clinical data collected ( n = 42) had symptoms and the main circumstances of discovery were syncope (45.2%), accidental discovery (28.6%) and cardio-respiratory arrest (9.5%). The genetic yield in the pediatric revealing LQTS is 47.5%. We describe a higher rate of mutations in the SCN5A gene, minor genes in the level 2 panel and syndromic forms, compared to data from the current literature. The poor performance of genetic diagnosis calls for further research, particularly with the growth of the whole genom sequencing.

Identifying novel genetic loci associated with polycystic ovary syndrome based on its shared genetic architecture with type 2 diabetes.

Genome-wide association studies (GWAS) have identified several common variants associated with polycystic ovary syndrome (PCOS). However, the etiology behind PCOS remains incomplete. Available evidence suggests a potential genetic correlation between PCOS and type 2 diabetes (T2D). The publicly available data may provide an opportunity to enhance the understanding of the PCOS etiology. Here, we quantified the polygenic overlap between PCOS and T2D using summary statistics of PCOS and T2D and then identified the novel genetic variants associated with PCOS behind this phenotypic association. A bivariate causal mixture model (MiXeR model) found a moderate genetic overlap between PCOS and T2D (Dice coefficient = 44.1% and after adjusting for body mass index, 32.1%). The conditional/conjunctional false discovery rate method identified 11 potential risk variants of PCOS conditional on associations with T2D, 9 of which were novel and 6 of which were jointly associated with two phenotypes. The functional annotation of these genetic variants supports a significant role for genes involved in lipid metabolism, immune response, and the insulin signaling pathway. An expression quantitative trait locus functionality analysis successfully repeated that 5 loci were significantly associated with the expression of candidate genes in many tissues, including the whole blood, subcutaneous adipose, adrenal gland, and cerebellum. We found that SCN2A gene is co-localized with PCOS in subcutaneous adipose using GWAS-eQTL co-localization analyses. A total of 11 candidate genes were differentially expressed in multiple tissues of the PCOS samples. These findings provide a new understanding of the shared genetic architecture between PCOS and T2D and the underlying molecular genetic mechanism of PCOS.

Complex interactions between p.His558Arg and linked variants in the sodium voltage-gated channel alpha subunit 5 (Na V 1.5).

Common genetic polymorphisms may modify the phenotypic outcome when co-occurring with a disease-causing variant, and therefore understanding their modulating role in health and disease is of great importance. The polymorphic p.His558Arg variant of the sodium voltage-gated channel alpha subunit 5 (NaV1.5) encoded by the SCN5A gene is a case in point, as several studies have shown it can modify the clinical phenotype in a number of cardiac diseases. To evaluate the genetic backgrounds associated with this modulating effect, we reanalysed previous electrophysiological findings regarding the p.His558Arg variant and further assessed its patterns of genetic diversity in human populations. The NaV1.5 p.His558Arg variant was found to be in linkage disequilibrium with six other polymorphic variants that previously were also associated with cardiac traits in GWAS analyses. On account of this, incongruent reports that Arg558 allele can compensate, aggravate or have no effect on NaV1.5, likely might have arose due to a role of p.His558Arg depending on the additional linked variants. Altogether, these results indicate a major influence of the epistatic interactions between SCN5A variants, revealing also that phenotypic severity may depend on the polymorphic background associated to each individual genome.

Primary erythromelalgia mainly manifested by hypertensive crisis: A case report and literature review.

BackgroundPrimary erythrocytic (PEM) is a rare autosomal dominant single gene disease. Most of the changes of gene loci can be found by whole exon gene sequencing, and the clinical symptoms and patient survival can be improved by specific site-to-site drug treatment. The other manifestations of this patient population are not remarkable. After the application of common drugs, the toxicity and side effects can be limiting. In addition to other common clinical manifestations, we found that the only unique manifestation of this patient was hypertensive crisis. Following multidisciplinary diagnosis and treatment (MDT), we decided to first control hypertension to alleviate the acute and critical patients. However, after controlling the hypertensive crisis, we unexpectedly found that the clinical symptoms of the patients had been significantly improved. Therefore, we concluded that the use of antihypertensive drugs can treat erythematous limb pain with the clinical manifestation of hypertensive crisis. Here, we describe a typical PEM disease, primary clinical features, diagnosis and treatment.MethodsMedical records of an 8-year-old boy with PEM were analyzed retrospectively, which included clinical characteristics, follow-up information, and SCN9A (Sodium Voltage-Gated Channel Alpha Subunit 9) gene analysis.ResultsThe 8-year-old boy had complained of abnormal paresthesia in his feet and ankles with burning sensation and pain for 2 years. The skin of both lower legs was red and underwent ichthyosis and lichenification. Genetic analysis confirmed the existence of a SCN9A gene mutation. The symptoms were gradually improved by treating with intravenous drip and oral administration of nitroglycerin to slow his heart rhythm.ConclusionPrimary erythrocytic is characterized by skin ulceration, redness, elevated temperature, and severe burning pain primarily in both lower extremities. PEM can be diagnosed by genetic analysis. As this case demonstrates, treating with nitroglycerin as the drug of choice to control the hypertensive crisis significantly improved the symptoms of PEM and hypertension in this patient.

“Virtual patch clamp analysis” for predicting the functional significance of pathogenic variants in sodium channels

ObjectiveOpening of voltage-gated sodium channels is crucial for neuronal depolarization. Proper channel opening and influx of Na+ through the ion pore, is dependent upon binding of Na+ ion to a specific amino-acid motif (DEKA) within the pore. In this study we used molecular dynamic simulations, an advanced bioinformatic tool, to research the dysfunction caused by pathogenic variants in SCN1a, SCN2a and SCN8a genes. MethodMolecular dynamic simulations were performed in six patients: three patients with Dravet syndrome (p.Gly177Ala,p.Ser259Arg and p.Met1267Ile, SCN1a), two patients with early onset drug resistant epilepsy(p.Ala263Val, SCN2a and p.Ile251Arg, SCN8a), and a patient with autism (p.Thr155Ala, SCN2a). After predicting the 3D-structure of mutated proteins by homology modeling, time dependent molecular dynamic simulations were performed, using the Schrödinger algorithm. The opening of the sodium channel, including the detachment of the sodium ion to the DEKA motif and pore diameter were assessed. Results were compared to the existent patch clamp analysis in four patients, and consistency with clinical phenotype was noted. ResultsThe Na+ ion remained attached to DEKA filter longer when compared to wild type in the p.Gly177Ala, p.Ser259Arg,SCN1a, and p.Thr155Ala, SCN2a variants, consistent with loss-of-function. In contrast, it detached quicker from DEKA than wild type in the p.Ala263Val,SCN2a variant, consistent with gain-of-function. In the p.Met1267Ile,SCN1a variant, detachment from DEKA was quicker, but pore diameter decreased, suggesting partial loss-of-function. In the p.Leu251Arg,SCN8a variant, the pore remained opened longer when compared to wild type, consistent with a gain-of-function. The molecular dynamic simulation results were consistent with the existing patch-clamp analysis studies, as well as the clinical phenotype. SignificanceMolecular dynamic simulation can be useful in predicting pathogenicity of variants and the disease phenotype, and selecting targeted treatment based on channel dysfunction. Further development of these bioinformatic tools may lead to “virtual patch-clamp analysis”.

Functional evaluation of the tachycardia patient-derived iPSC cardiomyocytes carrying a novel pathogenic SCN5A variant.

Tachycardia is characterized by high beating rates that can lead to life-threatening fibrillations. Mutations in several ion-channel genes were implicated with tachycardia; however, the complex genetic contributors and their modes of action are still unclear. Here, we investigated the influence of an SCN5A gene variant on tachycardia phenotype by deriving patient-specific iPSCs and cardiomyocytes (iPSC-CM). Two tachycardia patients were genetically analyzed and revealed to inherit a heterozygous p.F1465L variant in the SCN5A gene. Gene expression and immunocytochemical analysis in iPSC-CMs generated from patients did not show any significant changes in mRNA levels of SCN5A or gross NaV1.5 cellular mislocalization, compared to healthy-derived iPSC-CMs. Electrophysiological and contraction imaging analysis in patient iPSC-CMs revealed intermittent fibrillation-like states, occasional arrhythmic events, and sustained high-paced contractions that could be selectively reduced by flecainide treatment. The patch-clamp analysis demonstrated a negative shift in the voltage-dependent activation at the patient-derived iPSC-CMs compared to the healthy control line, suggestive of a gain-of-function activity associated with the SCN5A+/p.F1465L variant. Our patient-derived iPSC-CM model recapitulated the clinically relevant characteristics of tachycardia associated with a novel pathogenic SCN5A+/p.F1465L variant leading to altered Na+ channel kinetics as the likely mechanism underlying high excitability and tachycardia phenotype.

Improving The Management of Non-dystrophic Myotonia to Benefit Care Delivery and Improve Patient Outcomes

Non-dystrophic myotonias (NDM) are rare muscle disorders caused by mutations in skeletal voltage-gated muscle channels leading to delayed muscle relaxation after voluntary contraction. They are subdivided into sodium channelopathies, when the mutation is in the SCN4A gene, and chloride channelopathies, when the mutation is in the CLCN1 gene. Symptoms, which may differ according to subtype, exacerbating factors, and over disease course, can include muscle stiffness, pain, fatigue, muscle hypertrophy, myalgia, and weakness. The severity of NDM symptoms varies widely, from being barely noticeable to causing considerable disability that impacts health-related quality of life. People with NDM may remain undiagnosed for several years, potentially due to a lack of awareness of NDM among many healthcare professionals. The symptomatic treatment for NDM predominantly involves sodium channel blockers, such as mexiletine. Randomised, placebo-controlled trials have shown mexiletine can reduce muscle stiffness and pain, and improve health-related quality of life. Patient and clinician surveys, as well as national guidelines, place this medication as one of the first choices for pharmaceutical treatment of myotonia. Other choices include lamotrigine, carbamazepine, acetazolamide, ranolazine, and flecainide, though clinical evidence is limited, and all are used on an off-label basis. Herein, the challenges in recognising and treating myotonia symptoms in people with NDM are reviewed, along with strategies to increase awareness of the disease and its potential treatment.