Circulating Autoantibodies Targeting TREK-1 in Patients With Short-Coupled Ventricular Fibrillation.

BACKGROUND: Short-coupled ventricular fibrillation (SCVF) is increasingly being recognized as a distinct primary electrical disorder and cause of otherwise unexplained cardiac arrest. However, the pathophysiology of SCVF remains largely elusive. Despite extensive genetic screening, there is no convincing evidence of a robust monogenic disease gene, thus raising the speculations for alternative pathogeneses. The role of autoimmune mechanisms in SCVF has not been investigated so far. The objective of this study was to screen for circulating autoantibodies in patients with SCVF and assess their role in arrhythmogenesis. METHODS: This is a prospective, single-center, case-control study enrolling cardiac arrest survivors diagnosed with SCVF or idiopathic ventricular fibrillation (IVF) between 2019 and 2023 at the Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval Inherited Arrhythmia Clinic in Canada. Plasma samples were screened for autoantibodies targeting cardiac ion channels using peptide microarray technology. Identified target autoantibodies were then purified from pooled plasma samples for subsequent cellular electrophysiological studies. RESULTS: Fourteen patients with SCVF (n=4 [29% of patients] female patients; median age, 45 years [interquartile range: 36, 59]; n=14 [100% of patients] non-Hispanic White) and 19 patients with idiopathic ventricular fibrillation (n=8 [42%] female patients; median age, 49 years [38, 57]; n=19 [100%] non-Hispanic White) were enrolled in the study and compared with 38 (n=20 [53%] female subjects; median age, 45 years [29, 66]; n=36 [95%] non-Hispanic White) sex-, age- and ethnicity-matched healthy controls. During the study period, 11 (79%) SCVF probands experienced ventricular fibrillation recurrence after a median of 4.3 months (interquartile range, 0.3-20.7). Autoantibodies targeting cardiac TREK-1 (TWIK [tandem of pore-domains in a weakly inward rectifying potassium channel]-related potassium channel 1 were identified in 7 (50%) patients with SCVF (P=0.049). Patch clamp experiments demonstrated channel-activating properties of anti-TREK-1 autoantibodies that are antagonized by quinidine in both HEK293 cells and human induced pluripotent stem cell-derived cardiomyocytes. CONCLUSIONS: Patients with SCVF harbor circulating autoantibodies against the cardiac TREK-1 channel. Anti-TREK-1 autoantibodies not only present the first reported biomarker for SCVF, but our functional studies also suggest a direct implication in the arrhythmogenesis of SCVF.

Prevalence and phenotypes associated with ALPK3 null variants in a large French multicentric cohort: Confirming its involvement in hypertrophic cardiomyopathy.

Biallelic disease-causing variants in the ALPK3 gene were first identified in children presenting with a severe cardiomyopathy. More recently, it was shown that carriers of heterozygous ALPK3 null variants are at risk of developing hypertrophic cardiomyopathy (HCM) with an adult onset. Since the number of reported ALPK3 patients is small, the mutational spectrum and clinical data are not fully described. In this multi-centric study, we described the molecular and clinical spectrum of a large cohort of ALPK3 patients. Genetic testing using targeted next generation sequencing was performed in 16 183 cardiomyopathy index cases. Thirty-six patients carried at least one null ALPK3 variant. The five paediatric patients carried two ALPK3 variants, all presented an HCM phenotype with severe outcomes (one transplantation, one heart failure and one cardiac arrest). The 31 adult patients carried heterozygous variants and the main phenotype was HCM (n = 26/31); including 15% (n = 4) presented with an apical or a concentric form of hypertrophy. Reporting a large cohort of ALPK3 patients, this collaborative work confirmed a strong association with HCM and suggesting his screening in the context of idiopathic HCM.

DNASE1L3 deficiency, new phenotypes, and evidence for a transient type I IFN signaling.

BACKGROUND: Deoxyribonuclease 1 like 3 (DNASE1L3) is a secreted enzyme that has been shown to digest the extracellular chromatin derived from apoptotic bodies, and DNASE1L3 pathogenic variants have been associated with a lupus phenotype. It is unclear whether interferon signaling is sustained in DNASE1L3 deficiency in humans. OBJECTIVES: To explore interferon signaling in DNASE1L3 deficient patients. To depict the characteristic features of DNASE1L3 deficiencies in human. METHODS: We identified, characterized, and analyzed five new patients carrying biallelic DNASE1L3 variations. Whole or targeted exome and/or Sanger sequencing was performed to detect pathogenic variations in five juvenile systemic erythematosus lupus (jSLE) patients. We measured interferon-stimulated gene (ISG) expression in all patients. We performed a systematic review of all published cases available from its first description in 2011 to March 24th 2022. RESULTS: We identified five new patients carrying biallelic DNASE1L3 pathogenic variations, including three previously unreported mutations. Contrary to canonical type I interferonopathies, we noticed a transient increase of ISGs in blood, which returned to normal with disease remission. Disease in one patient was characterized by lupus nephritis and skin lesions, while four others exhibited hypocomplementemic urticarial vasculitis syndrome. The fourth patient presented also with early-onset inflammatory bowel disease. Reviewing previous reports, we identified 35 additional patients with DNASE1L3 deficiency which was associated with a significant risk of lupus nephritis and a poor outcome together with the presence of anti-neutrophil cytoplasmic antibodies (ANCA). Lung lesions were reported in 6/35 patients. CONCLUSIONS: DNASE1L3 deficiencies are associated with a broad phenotype including frequently lupus nephritis and hypocomplementemic urticarial vasculitis with positive ANCA and rarely, alveolar hemorrhages and inflammatory bowel disease. This report shows that interferon production is transient contrary to anomalies of intracellular DNA sensing and signaling observed in Aicardi-Goutières syndrome or STING-associated vasculitis in infancy (SAVI).

APOB CRISPR-Cas9 Engineering in Hypobetalipoproteinemia: A Promising Tool for Functional Studies of Novel Variants.

Hypobetalipoproteinemia is characterized by LDL-cholesterol and apolipoprotein B (apoB) plasma levels below the fifth percentile for age and sex. Familial hypobetalipoproteinemia (FHBL) is mostly caused by premature termination codons in the APOB gene, a condition associated with fatty liver and steatohepatitis. Nevertheless, many families with a FHBL phenotype carry APOB missense variants of uncertain significance (VUS). We here aimed to develop a proof-of-principle experiment to assess the pathogenicity of VUS using the genome editing of human liver cells. We identified a novel heterozygous APOB-VUS (p.Leu351Arg), in a FHBL family. We generated APOB knock-out (KO) and APOB-p.Leu351Arg knock-in Huh7 cells using CRISPR-Cas9 technology and studied the APOB expression, synthesis and secretion by digital droplet PCR and ELISA quantification. The APOB expression was decreased by 70% in the heterozygous APOB-KO cells and almost abolished in the homozygous-KO cells, with a consistent decrease in apoB production and secretion. The APOB-p.Leu351Arg homozygous cells presented with a 40% decreased APOB expression and undetectable apoB levels in cellular extracts and supernatant. Thus, the p.Leu351Arg affected the apoB secretion, which led us to classify this new variant as likely pathogenic and to set up a hepatic follow-up in this family. Therefore, the functional assessment of APOB-missense variants, using gene-editing technologies, will lead to improvements in the molecular diagnosis of FHBL and the personalized follow-up of these patients.

Reccurrent F8 Intronic Deletion Found in Mild Hemophilia A Causes Alu Exonization.

Incorporation of distant intronic sequences in mature mRNA is an underappreciated cause of genetic disease. Several disease-causing pseudoexons have been found to contain repetitive elements such as Alu elements. This study describes an original pathological mechanism by which a small intronic deletion leads to Alu exonization. We identified an intronic deletion, c.2113+461_2113+473del, in the F8 intron 13, in two individuals with mild hemophilia A. In vivo and in vitro transcript analysis found an aberrant transcript, with an insertion of a 122-bp intronic fragment (c.2113_2114ins2113+477_2113+598) at the exon 13-14 junction. This out-of-frame insertion is predicted to lead to truncated protein (p.Gly705Aspfs∗37). DNA sequencing analysis found that the pseudoexon corresponds to antisense AluY element and the deletion removed a part of the poly(T)-tail from the right arm of these AluY. The heterogenous nuclear riboprotein C1/C2 (hnRNP C) is an important antisense Alu-derived cryptic exon silencer and binds to poly(T)-tracts. Disruption of the hnRNP C binding site in AluY T-tract by mutagenesis or hnRNP C knockdown using siRNA in HeLa cells reproduced the effect of c.2113+461_2113+473del. The screening of 114 unrelated families with mild hemophilia A in whom no genetic event was previously identified found a deletion in the poly(T)-tail of AluY in intron 13 in 54% of case subjects (n = 61/114). In conclusion, this study describes a deletion leading to Alu exonization found in 6.1% of families with mild hemophila A in France.

PPA2-associated sudden cardiac death: extending the clinical and allelic spectrum in 20 new families.

PURPOSE: Biallelic hypomorphic variants in PPA2, encoding the mitochondrial inorganic pyrophosphatase 2 protein, have been recently identified in individuals presenting with sudden cardiac death, occasionally triggered by alcohol intake or a viral infection. Here we report 20 new families harboring PPA2 variants. METHODS: Synthesis of clinical and molecular data concerning 34 individuals harboring five previously reported PPA2 variants and 12 novel variants, 11 of which were functionally characterized. RESULTS: Among the 34 individuals, only 6 remain alive. Twenty-three died before the age of 2 years while five died between 14 and 16 years. Within these 28 cases, 15 died of sudden cardiac arrest and 13 of acute heart failure. One case was diagnosed prenatally with cardiomyopathy. Four teenagers drank alcohol before sudden cardiac arrest. Progressive neurological signs were observed in 2/6 surviving individuals. For 11 variants, recombinant PPA2 enzyme activities were significantly decreased and sensitive to temperature, compared to wild-type PPA2 enzyme activity. CONCLUSION: We expand the clinical and mutational spectrum associated with PPA2 dysfunction. Heart failure and sudden cardiac arrest occur at various ages with inter- and intrafamilial phenotypic variability, and presentation can include progressive neurological disease. Alcohol intake can trigger cardiac arrest and should be strictly avoided.

Whole MYBPC3 NGS sequencing as a molecular strategy to improve the efficiency of molecular diagnosis of patients with hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiomyopathy, historically believed to affect 1 of 500 people. MYBPC3 pathogenic variations are the most frequent cause of familial HCM and more than 90% of them introduce a premature termination codon. The current study aims to determine the prevalence of deep intronic MYBPC3 pathogenic variations that could lead to splice mutations. To improve molecular diagnosis, a next-generation sequencing (NGS) workflow based on whole MYBPC3 sequencing of a cohort of 93 HCM patients, for whom no putatively causative point mutations were identified after NGS sequencing of a panel of 48 cardiomyopathy-causing genes, was performed. Our approach led us to reconsider the molecular diagnosis of six patients of the cohort (6.5%). These HCM probands were carriers of either a new large MYBPC3 rearrangement or splice intronic variations (five cases). Four pathogenic intronic variations, including three novel ones, were detected. Among them, the prevalence of one of them (NM_000256.3:c.1927+ 600 C>T) was estimated at about 0.35% by the screening of 1,040 unrelated HCM individuals. This study suggests that deep MYBPC3 splice mutations account for a significant proportion of HCM cases (6.5% of this cohort). Consequently, NGS sequencing of MYBPC3 intronic sequences have to be performed systematically.

Development of a new expanded next-generation sequencing panel for genetic diseases involved in dyslipidemia.

The aim of this study was to provide an efficient tool: reliable, able to increase the molecular diagnosis performance, to facilitate the detection of copy number variants (CNV), to assess genetic risk scores (wGRS) and to offer the opportunity to explore candidate genes. Custom SeqCap EZ libraries, NextSeq500 sequencing and a homemade pipeline enable the analysis of 311 dyslipidemia-related genes. In the training group (48 DNA from patients with a well-established molecular diagnosis), this next-generation sequencing (NGS) workflow showed an analytical sensitivity >99% (n = 532 variants) without any false negative including a partial deletion of one exon. In the prospective group, from 25 DNA from patients without prior molecular analyses, 18 rare variants were identified in the first intention panel genes, allowing the diagnosis of monogenic dyslipidemia in 11 patients. In six other patients, the analysis of minor genes and wGRS determination provided a hypothesis to explain the dyslipidemia. Remaining data from the whole NGS workflow identified four patients with potentially deleterious variants. This NGS process gives a major opportunity to accede to an enhanced understanding of the genetic of dyslipidemia by simultaneous assessment of multiple genetic determinants.

Cardiac voltage-gated sodium channel mutations associated with left atrial dysfunction and stroke in children.

Aims: Cardiac atrial arrhythmias are the most common type of heart rhythm disorders. Its genetic elucidation remains challenging with poor understanding of cellular and molecular processes. These arrhythmias usually affect elderly population but in rare cases, young children may also suffer from such electrical diseases. Severe complications, including stroke, are commonly age related. This study aims to identify a genetic link between electro-mechanic atrial dysfunction and stroke in children. Methods and results: In two unrelated boys of 11 and 14 years with both stroke and atrial arrhythmias, the clinical phenotype was determined through a complete physical examination, electrocardiogram (ECG), Holter ECG, and computed tomography. The genetic testing was performed on a large 95 genes panel implicated in myocardial electrical imbalance, using the next generation sequencing method. The panel also includes the genes usually associated with the development of cardiomyopathies. In one child, a left atrial dilation was observed. The 2nd boy suffered from atrial standstill. Both suffered from atrial bradycardia, flutter, and fibrillation. The complete genetic testing revealed the SCN5A c.3823G>A (p.D1275N) mutation in the first family, c.1141-2A>G and c.3157G>A (p.E1053K) mutations in the second family. Conclusion: Our results strengthen the association between Nav1.5 mutations and the occurrence of stroke in young patients. It emphasizes the need to look for atrial myopathy in the decision process for anticoagulation in young patients with atrial arrhythmic events.

Functional and clinical characterization of a novel homozygous KCNH2 missense variant in the pore region of Kv11.1 leading to a viable but severe long-QT syndrome.

BACKGROUND: Among KCNH2 missense loss of function (LOF) variants, homozygosity -at any position in the Kv11.1/hERG channel - is very rare and generally leads to intrauterine death, while heterozygous variants in the pore are responsible for severe Type 2 long-QT syndrome (LQTS). We report a novel homozygous p.Gly603Ser missense variant in the pore of Kv11.1/hERG (KCNH2 c.1807G > A) discovered in the context of a severe LQTS. METHODS: We carried out a phenotypic family study combined with a functional analysis of mutated and wild-type (WT) Kv11.1 by two-electrode voltage-clamp using the Xenopus laevis oocyte heterologous expression system. RESULTS: The variant resulted in a severe LQTS phenotype (very prolonged corrected QT interval, T-wave alternans, multiple Torsades de pointes) with a delayed clinical expression in later childhood in the homozygous state, and in a Type 2 LQTS phenotype in the heterozygous state. Expression of KCNH2 p.Gly603Ser cRNA alone elicited detectable current in Xenopus oocytes. Inactivation kinetics and voltage dependence of activation were not significantly affected by the variant. The macroscopic slope conductance of the variant was three-fold less compared to the WT (18.5 ± 9.01 vs 54.7 ± 17.2 µS, p < 0.001). CONCLUSIONS: We characterized the novel p.Gly603Ser KCNH2 missense LOF variant in the pore region of Kv11.1/hERG leading to a severe but viable LQTS in the homozygous state and an attenuated Type 2 LQTS in heterozygous carriers. To our knowledge we provide the first description of a homozygous variant in the pore-forming region of Kv11.1 with a functional impact but a delayed clinical expression.

Relevance of Extending FGFR3 Gene Analysis in Osteochondrodysplasia to Non-Coding Sequences: A Case Report.

Skeletal dysplasia, also called osteochondrodysplasia, is a category of disorders affecting bone development and children's growth. Up to 552 genes, including fibroblast growth factor receptor 3 (FGFR3), have been implicated by pathogenic variations in its genesis. Frequently identified causal mutations in osteochondrodysplasia arise in the coding sequences of the FGFR3 gene: c.1138G>A and c.1138G>C in achondroplasia and c.1620C>A and c.1620C>G in hypochondroplasia. However, in some cases, the diagnostic investigations undertaken thus far have failed to identify the causal anomaly, which strengthens the relevance of the diagnostic strategies being further refined. We observed a Caucasian adult with clinical and radiographic features of achondroplasia, with no common pathogenic variant. Exome sequencing detected an FGFR3(NM_000142.4):c.1075+95C>G heterozygous intronic variation. In vitro studies showed that this variant results in the aberrant exonization of a 90-nucleotide 5' segment of intron 8, resulting in the substitution of the alanine (Ala359) for a glycine (Gly) and the in-frame insertion of 30 amino acids. This change may alter FGFR3's function. Our report provides the first clinical description of an adult carrying this variant, which completes the phenotype description previously provided in children and confirms the recurrence, the autosomal-dominant pathogenicity, and the diagnostic relevance of this FGFR3 intronic variant. We support its inclusion in routinely used diagnostic tests for osteochondrodysplasia. This may increase the detection rate of causal variants and therefore could have a positive impact on patient management. Finally, FGFR3 alteration via non-coding sequence exonization should be considered a recurrent disease mechanism to be taken into account for new drug design and clinical trial strategies.

NEXN Gene in Cardiomyopathies and Sudden Cardiac Deaths: Prevalence, Phenotypic Expression, and Prognosis.

BACKGROUND: Few clinical data are available on NEXN mutation carriers, and the gene's involvement in cardiomyopathies or sudden death has not been fully established. Our objectives were to assess the prevalence of putative pathogenic variants in NEXN and to describe the phenotype and prognosis of patients carrying the variants. METHODS: DNA samples from consecutive patients with cardiomyopathy or sudden cardiac death/sudden infant death syndrome/idiopathic ventricular fibrillation were sequenced with a custom panel of genes. Index cases carrying at least one putative pathogenic variant in the NEXN gene were selected. RESULTS: Of the 9516 index patients sequenced, 31 were carriers of a putative pathogenic variant in NEXN only, including 2 with double variants and 29 with a single variant. Of the 29 unrelated probands with a single variant (16 males; median age at diagnosis, 32.0 [26.0-49.0] years), 21 presented with dilated cardiomyopathy (prevalence, 0.33%), and 3 presented with hypertrophic cardiomyopathy (prevalence, 0.14%). Three patients had idiopathic ventricular fibrillation, and there were 2 cases of sudden infant death syndrome (prevalence, 0.46%). For patients with dilated cardiomyopathy, the median left ventricle ejection fraction was 37.5% (26.25-50.0) at diagnosis and improved with treatment in 13 (61.9%). Over a median follow-up period of 6.0 years, we recorded 3 severe arrhythmic events and 2 severe hemodynamic events. CONCLUSIONS: Putative pathogenic NEXN variants were mainly associated with dilated cardiomyopathy; in these individuals, the prognosis appeared to be relatively good. However, severe and early onset phenotypes were also observed-especially in patients with double NEXN variants. We also detected NEXN variants in patients with hypertrophic cardiomyopathy and sudden infant death syndrome/idiopathic ventricular fibrillation, although a causal link could not be established.

Molecular Diagnosis of Primary Cardiomyopathy in 231 Unrelated Pediatric Cases by Panel-Based Next-Generation Sequencing: A Major Focus on Five Carriers of Biallelic TNNI3 Pathogenic Variants.

BACKGROUND AND OBJECTIVE: Pediatric cardiomyopathies are clinically heterogeneous heart muscle disorders associated with significant morbidity and mortality for which substantial evidence for a genetic contribution was previously reported. We present a detailed molecular investigation of a cohort of 231 patients presenting with primary cardiomyopathy below the age of 18 years. METHODS: Cases with pediatric cardiomyopathies were analyzed using a next-generation sequencing (NGS) workflow based on a virtual panel including 57 cardiomyopathy-related genes. RESULTS: This molecular approach led to the identification of 69 cases (29.9% of the cohort) genotyped as a carrier of at least one pathogenic or likely pathogenic variant. Fourteen patients were carriers of two mutated alleles (homozygous or compound heterozygous) on the same cardiomyopathy-related gene, explaining the severe clinical disease with early-onset cardiomyopathy. Homozygous TNNI3 pathogenic variants were detected for five unrelated neonates (2.2% of the cohort), with four of them carrying the same truncating variant, i.e. p.Arg69Alafs*8. CONCLUSIONS: Our study confirmed the importance of genetic testing in pediatric cardiomyopathies. Discovery of novel pathogenic variations is crucial for clinical management of affected families, as a positive genetic result might be used by a prospective parent for prenatal genetic testing or in the process of pre-implantation genetic diagnosis.

Molecular Diagnosis of Inherited Cardiac Diseases in the Era of Next-Generation Sequencing: A Single Center's Experience Over 5 Years.

BACKGROUND AND OBJECTIVE: Molecular diagnosis in inherited cardiac diseases is challenging because of the significant genetic and clinical heterogeneity. We present a detailed molecular investigation of a cohort of 4185 patients with referrals for inherited cardiac diseases. METHODS: Patients suffering from cardiomyopathies (3235 probands), arrhythmia syndromes (760 probands), or unexplained sudden cardiac arrest (190 cases) were analyzed using a next-generation sequencing (NGS) workflow based on a panel of 105 genes involved in sudden cardiac death. RESULTS: (Likely) pathogenic variations were identified for approximately 30% of the cohort. Pathogenic copy number variations (CNVs) were detected in approximately 3.1% of patients for whom a (likely) pathogenic variation were identified. A (likely) pathogenic variation was also detected for 21.1% of patients who died from sudden cardiac death. Unexpected variants, including incidental findings, were present for 28 cases. Pathogenic variations were mainly observed in genes with definitive evidence of disease causation. CONCLUSIONS: Our study, which comprises over than 4000 probands, is one of most important cohorts reported in inherited cardiac diseases. The global mutation detection rate would be significantly increased by determining the putative pathogenicity of the large number of variants of uncertain significance. Identification of "unexpected" variants also showed the clinical utility of genetic testing in inherited cardiac diseases as they can redirect clinical management and medical resources toward a meaningful precision medicine. In cases with negative result, a WGS approach could be considered, but would probably have a limited impact on mutation detection rate as (likely) pathogenic variations were essentially clustered in genes with strong evidence of disease causation.

Whole Sequencing of Most Prevalent Dilated Cardiomyopathy-Causing Genes as a Molecular Strategy to Improve Molecular Diagnosis Efficiency?

Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy and one of the most common causes of heart failure. TTN-truncating variants represent the most common cause of DCM. Similarly, among other prevalent DCM-causing genes, truncating variants were also frequently detected in BAG3, DSP, FLNC, and LMNA. For these four genes, the current study aims to determine the prevalence of deep intronic pathogenic variants that could lead to splice defects. A next-generation sequencing (NGS) workflow based on whole gene sequencing of BAG3, DSP, FLNC, and LMNA of a cohort of 95 DCM patients, for whom no putatively causative point mutations were identified after NGS of a panel of 48 cardiomyopathy-causing genes, was thus performed. Our approach did not lead us to reconsider the molecular diagnosis of any patient of the cohort. This study suggests that deep splice mutations do not account for a significant proportion of DCM cases. In contrast with MYBPC3 in hypertrophic cardiomyopathy cases, NGS of BAG3, DSP, FLNC, and LMNA whole intronic sequences would not significantly improve the efficiency of molecular diagnosis of DCM probands.

Characterization of Loss-Of-Function KCNJ2 Mutations in Atypical Andersen Tawil Syndrome.

Andersen-Tawil Syndrome (ATS) is a rare disease defined by the association of cardiac arrhythmias, periodic paralysis and dysmorphic features, and is caused by KCNJ2 loss-of-function mutations. However, when extracardiac symptoms are atypical or absent, the patient can be diagnosed with Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT), a rare arrhythmia at high risk of sudden death, mostly due to RYR2 mutations. The identification of KCNJ2 variants in CPVT suspicion is very rare but important because beta blockers, the cornerstone of CPVT therapy, could be less efficient. We report here the cases of two patients addressed for CPVT-like phenotypes. Genetic investigations led to the identification of p. Arg82Trp and p. Pro186Gln de novo variants in the KCNJ2 gene. Functional studies showed that both variants forms of Kir2.1 monomers act as dominant negative and drastically reduced the activity of the tetrameric channel. We characterize here a new pathogenic variant (p.Pro186Gln) of KCNJ2 gene and highlight the interest of accurate cardiologic evaluation and of attention to extracardiac signs to distinguish CPVT from atypical ATS, and guide therapeutic decisions. We also confirm that the KCNJ2 gene must be investigated during CPVT molecular analysis.

Deciphering DSC2 arrhythmogenic cardiomyopathy electrical instability: From ion channels to ECG and tailored drug therapy.

BACKGROUND: Severe ventricular rhythm disturbances are the hallmark of arrhythmogenic cardiomyopathy (ACM), and are often explained by structural conduction abnormalities. However, comprehensive investigations of ACM cell electrical instability are lacking. This study aimed to elucidate early electrical myogenic signature of ACM. METHODS: We investigated a 41-year-old ACM patient with a missense mutation (c.394C>T) in the DSC2 gene, which encodes desmocollin 2. Pathogenicity of this variant was confirmed using a zebrafish DSC2 model system. Control and DSC2 patient-derived pluripotent stem cells were reprogrammed and differentiated into cardiomyocytes (hiPSC-CM) to examine the specific electromechanical phenotype and its modulation by antiarrhythmic drugs (AADs). Samples of the patient's heart and hiPSC-CM were examined to identify molecular and cellular alterations. RESULTS: A shortened action potential duration was associated with reduced Ca2+ current density and increased K+ current density. This finding led to the elucidation of previously unknown abnormal repolarization dynamics in ACM patients. Moreover, the Ca2+ mobilised during transients was decreased, and the Ca2+ sparks frequency was increased. AAD testing revealed the following: (1) flecainide normalised Ca2+ transients and significantly decreased Ca2+ spark occurrence and (2) sotalol significantly lengthened the action potential and normalised the cells' contractile properties. CONCLUSIONS: Thorough analysis of hiPSC-CM derived from the DSC2 patient revealed abnormal repolarization dynamics, prompting the discovery of a short QT interval in some ACM patients. Overall, these results confirm a myogenic origin of ACM electrical instability and provide a rationale for prescribing class 1 and 3 AADs in ACM patients with increased ventricular repolarization reserve.