TAD boundary deletion causes PITX2-related cardiac electrical and structural defects

While 3D chromatin organization in topologically associating domains (TADs) and loops mediating regulatory element-promoter interactions is crucial for tissue-specific gene regulation, the extent of their involvement in human Mendelian disease is largely unknown. Here, we identify 7 families presenting a new cardiac entity associated with a heterozygous deletion of 2 CTCF binding sites on 4q25, inducing TAD fusion and chromatin conformation remodeling. The CTCF binding sites are located in a gene desert at 1 Mb from the Paired-like homeodomain transcription factor 2 gene (PITX2). By introducing the ortholog of the human deletion in the mouse genome, we recapitulate the patient phenotype and characterize an opposite dysregulation of PITX2 expression in the sinoatrial node (ectopic activation) and ventricle (reduction), respectively. Chromatin conformation assay performed in human induced pluripotent stem cell-derived cardiomyocytes harboring the minimal deletion identified in family#1 reveals a conformation remodeling and fusion of TADs. We conclude that TAD remodeling mediated by deletion of CTCF binding sites causes a new autosomal dominant Mendelian cardiac disorder.

Clinical characterization of type 1 long QT syndrome caused by C-terminus Kv7.1 variants

BACKGROUND

Variants in the KCNQ1 gene, encoding the α-subunit of the slow component of delayed rectifier K+ channel Kv7.1, cause long QT syndrome (LQTS) type 1. The location of variants may be one of the factors in determining prognosis. However, detailed genotype-phenotype relationships associated with C-terminus variants remain unelucidated.

OBJECTIVE

We investigated the clinical characteristics and variant-specific arrhythmic risks in patients with LQTS carrying Kv7.1 C-terminus variants.

METHODS

The study comprises 202 consecutive patients with LQTS (98 probands and 104 family members) who carry a rare heterozygous variant in the Kv7.1 C-terminus. Their clinical characteristics and arrhythmic events were investigated.

RESULTS

We identified 36 unique C-terminus variants (25 missense and 11 non-missense). The p.R366W variant was identified in 8 families, and p.T587M was identified in 21 families in large numbers from northwestern Japan. As for the location of the variant, we found that the variants in highly conserved regions and nonhelical domains were associated with longer QTc intervals compared with the variants in other regions. Both p.R366W and p.T587M variants are located in the highly conserved and functionally pivotal regions close to helices A and D, which are associated with calmodulin binding and channel assembly (tetramerization), respectively. The probands carrying p.T587M and p.R366W variants had worse arrhythmia outcomes compared with those with other C-terminus variants. The haplotype analysis of p.T587M families was suggestive of a founder effect.

CONCLUSION

The arrhythmic risk of C-terminus variants in Kv7.1 in LQTS is not homogeneous, and locations of variants can be a determining factor for prognosis.

KUS121, a VCP modulator, has an ameliorating effect on acute and chronic heart failure without calcium loading via maintenance of intracellular ATP levels

AIMS

As heart failure (HF) progresses, ATP levels in myocardial cells decrease, and myocardial contractility also decreases. Inotropic drugs improve myocardial contractility but increase ATP consumption, leading to poor prognosis. Kyoto University Substance 121 (KUS121) is known to selectively inhibit the ATPase activity of valosin-containing protein, maintain cellular ATP levels, and manifest cytoprotective effects in several pathological conditions. The aim of this study is to determine the therapeutic effect of KUS121 on HF models.

METHODS AND RESULTS

Cultured cell, mouse, and canine models of HF were used to examine the therapeutic effects of KUS121. The mechanism of action of KUS121 was also examined. Administration of KUS121 to a transverse aortic constriction (TAC)-induced mouse model of HF rapidly improved the left ventricular ejection fraction and improved the creatine phosphate/ATP ratio. In a canine model of high frequency-paced HF, administration of KUS121 also improved left ventricular contractility and decreased left ventricular end-diastolic pressure without increasing the heart rate. Long-term administration of KUS121 to a TAC-induced mouse model of HF suppressed cardiac hypertrophy and fibrosis. In H9C2 cells, KUS121 reduced ER stress. Finally, in experiments using primary cultured cardiomyocytes, KUS121 improved contractility and diastolic capacity without changing peak Ca2+ levels or contraction time. These effects were not accompanied by an increase in cyclic adenosine monophosphate or phosphorylation of phospholamban and ryanodine receptors.

CONCLUSIONS

KUS121 ameliorated HF by a mechanism totally different from that of conventional catecholamines. We propose that KUS121 is a promising new option for the treatment of HF.

Calmodulinopathy in Japanese Children - Their Cardiac Phenotypes Are Severe and Show Early Onset in Fetal Life and Infancy

BACKGROUND

Cardiac calmodulinopathy, characterized by a life-threatening arrhythmia and sudden death in the young, is extremely rare and caused by genes encoding calmodulin, namely calmodulin 1 (CALM1), CALM2, and CALM3.Methods and Results: We screened 195 symptomatic children (age 0-12 years) who were suspected of inherited arrhythmias for 48 candidate genes, using a next-generation sequencer. Ten probands were identified as carrying variants in any of CALM1-3 (5%; median age 5 years), who were initially diagnosed with long QT syndrome (LQTS; n=5), catecholaminergic polymorphic ventricular tachycardia (CPVT; n=3), and overlap syndrome (n=2). Two probands harbored a CALM1 variant and 8 probands harbored 6 CALM2 variants. There were 4 clinical phenotypes: (1) documented lethal arrhythmic events (LAEs): 4 carriers of N98S in CALM1 or CALM2; (2) suspected LAEs: CALM2 p.D96G and D132G carriers experienced syncope and transient cardiopulmonary arrest under emotional stimulation; (3) critical cardiac complication: CALM2 p.D96V and p.E141K carriers showed severe cardiac dysfunction with QTc prolongation; and (4) neurological and developmental disorders: 2 carriers of CALM2 p.E46K showed cardiac phenotypes of CPVT. Beta-blocker therapy was effective in all cases except cardiac dysfunction, especially in combination with flecainide (CPVT-like phenotype) and mexiletine (LQTS-like).

CONCLUSIONS

Calmodulinopathy patients presented severe cardiac features, and their onset of LAEs was earlier in life, requiring diagnosis and treatment at the earliest age possible.

Non-missense variants of KCNH2 show better outcomes in type 2 long QT syndrome

AIMS

More than one-third of type 2 long QT syndrome (LQT2) patients carry KCNH2 non-missense variants that can result in haploinsufficiency (HI), leading to mechanistic loss-of-function. However, their clinical phenotypes have not been fully investigated. The remaining two-thirds of patients harbour missense variants, and past studies uncovered that most of these variants cause trafficking deficiency, resulting in different functional changes: either HI or dominant-negative (DN) effects. In this study, we examined the impact of altered molecular mechanisms on clinical outcomes in LQT2 patients.

METHODS AND RESULTS

We included 429 LQT2 patients (234 probands) carrying a rare KCNH2 variant from our patient cohort undergoing genetic testing. Non-missense variants showed shorter corrected QT (QTc) and less arrhythmic events (AEs) than missense variants. We found that 40% of missense variants in this study were previously reported as HI or DN. Non-missense and HI-groups had similar phenotypes, while both exhibited shorter QTc and less AEs than the DN-group. Based on previous work, we predicted the functional change of the unreported variants-whether they cause HI or DN via altered functional domains-and stratified them as predicted HI (pHI)- or pDN-group. The pHI-group including non-missense variants exhibited milder phenotypes compared to the pDN-group. Multivariable Cox model showed that the functional change was an independent risk of AEs (P = 0.005).

CONCLUSION

Stratification based on molecular biological studies enables us to better predict clinical outcomes in the patients with LQT2.

Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

BACKGROUND

CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca²⁺ sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear. In this study, we sought to investigate the arrhythmogenic mechanism of CPVT caused by a novel variant using human induced pluripotent stem cell (iPSC) models and biochemical assays.

METHODS

We generated iPSCs from a patient with CPVT bearing CALM2 p.E46K. As comparisons, we used 2 control lines including an isogenic line, and another iPSC line from a patient with long QT syndrome bearing CALM2 p.N98S (also reported in CPVT). Electrophysiological properties were investigated using iPSC-cardiomyocytes. We further examined the RyR2 (ryanodine receptor 2) and Ca²⁺ affinities of CaM using recombinant proteins.

RESULTS

We identified a novel de novo heterozygous variant, CALM2 p.E46K, in 2 unrelated patients with CPVT accompanied by neurodevelopmental disorders. The E46K-cardiomyocytes exhibited more frequent abnormal electrical excitations and Ca²⁺ waves than the other lines in association with increased Ca²⁺ leakage from the sarcoplasmic reticulum via RyR2. Furthermore, the [³H]ryanodine binding assay revealed that E46K-CaM facilitated RyR2 function especially by activating at low [Ca²⁺] levels. The real-time CaM-RyR2 binding analysis demonstrated that E46K-CaM had a 10-fold increased RyR2 binding affinity compared with wild-type CaM which may account for the dominant effect of the mutant CaM. Additionally, the E46K-CaM did not affect CaM-Ca²⁺ binding or L-type calcium channel function. Finally, antiarrhythmic agents, nadolol and flecainide, suppressed abnormal Ca²⁺ waves in E46K-cardiomyocytes.

CONCLUSIONS

We, for the first time, established a CaM-related CPVT iPSC-CM model which recapitulated severe arrhythmogenic features resulting from E46K-CaM dominantly binding and facilitating RyR2. In addition, the findings in iPSC-based drug testing will contribute to precision medicine.

Disrupted CaV1.2 selectivity causes overlapping long QT and Brugada syndrome phenotypes in the CACNA1C-E1115K iPS cell model

BACKGROUND

A missense mutation in the α1c subunit of voltage-gated L-type Ca²⁺ channel-coding CACNA1C-E1115K, located in the Ca²⁺ selectivity site, causes a variety of arrhythmogenic phenotypes.

OBJECTIVE

We aimed to investigate the electrophysiological features and pathophysiological mechanisms of CACNA1C-E1115K in patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs).

METHODS

We generated iPSCs from a patient carrying heterozygous CACNA1C-E1115K with overlapping phenotypes of long QT syndrome, Brugada syndrome, and mild cardiac dysfunction. Electrophysiological properties were investigated using iPSC-CMs. We used iPSCs from a healthy individual and an isogenic iPSC line corrected using CRISPR-Cas9-mediated gene editing as controls. A mathematical E1115K-CM model was developed using a human ventricular cell model.

RESULTS

Patch-clamp analysis revealed that E1115K-iPSC-CMs exhibited reduced peak Ca²⁺ current density and impaired Ca²⁺ selectivity with an increased permeability to monovalent cations. Consequently, E1115K-iPSC-CMs showed decreased action potential plateau amplitude, longer action potential duration (APD), and a higher frequency of early afterdepolarization compared with controls. In optical recordings examining the antiarrhythmic drug effect, late Na⁺ channel current (I_NaL) inhibitors (mexiletine and GS-458967) shortened APDs specifically in E1115K-iPSC-CMs. The AP-clamp using a voltage command obtained from E1115K-iPSC-CMs with lower action potential plateau amplitude and longer APD confirmed the upregulation of I_NaL. An in silico study recapitulated the in vitro electrophysiological properties.

CONCLUSION

Our iPSC-based analysis in CACNA1C-E1115K with disrupted Ca_V1.2 selectivity demonstrated that the aberrant currents through the mutant channels carried by monovalent cations resulted in specific action potential changes, which increased endogenous I_NaL, thereby synergistically contributing to the arrhythmogenic phenotype.

Targeted deep sequencing analyses of long QT syndrome in a Japanese population

Long QT syndrome (LQTS) is one of the most common inherited arrhythmias and multiple genes have been reported as causative. Presently, genetic diagnosis for LQTS patients is becoming widespread and contributing to implementation of therapies. However, causative genetic mutations cannot be detected in about 20% of patients. To elucidate additional genetic mutations in LQTS, we performed deep-sequencing of previously reported 15 causative and 85 candidate genes for this disorder in 556 Japanese LQTS patients. We performed in-silico filtering of the sequencing data and found 48 novel variants in 33 genes of 53 cases. These variants were predicted to be damaging to coding proteins or to alter the binding affinity of several transcription factors. Notably, we found that most of the LQTS-related variants in the RYR2 gene were in the large cytoplasmic domain of the N-terminus side. They might be useful for screening of LQTS patients who had no known genetic factors. In addition, when the mechanisms of these variants in the development of LQTS are revealed, it will be useful for early diagnosis, risk stratification, and selection of treatment.

Gradient-based parameter optimization method to determine membrane ionic current composition in human induced pluripotent stem cell-derived cardiomyocytes

Premature cardiac myocytes derived from human induced pluripotent stem cells (hiPSC-CMs) show heterogeneous action potentials (APs), probably due to different expression patterns of membrane ionic currents. We developed a method for determining expression patterns of functional channels in terms of whole-cell ionic conductance (G_x) using individual spontaneous AP configurations. It has been suggested that apparently identical AP configurations can be obtained using different sets of ionic currents in mathematical models of cardiac membrane excitation. If so, the inverse problem of G_x estimation might not be solved. We computationally tested the feasibility of the gradient-based optimization method. For a realistic examination, conventional 'cell-specific models' were prepared by superimposing the model output of AP on each experimental AP recorded by conventional manual adjustment of G_xs of the baseline model. G_xs of 4-6 major ionic currents of the 'cell-specific models' were randomized within a range of ± 5-15% and used as an initial parameter set for the gradient-based automatic G_xs recovery by decreasing the mean square error (MSE) between the target and model output. Plotting all data points of the MSE-G_x relationship during optimization revealed progressive convergence of the randomized population of G_xs to the original value of the cell-specific model with decreasing MSE. The absence of any other local minimum in the global search space was confirmed by mapping the MSE by randomizing G_xs over a range of 0.1-10 times the control. No additional local minimum MSE was obvious in the whole parameter space, in addition to the global minimum of MSE at the default model parameter.

Syndromic cardiac disorder is associated with a non-coding deletion that induces a 3D chromatin remodeling and PITX2 expression dysregulation

 

In a first family (family#1), we identified 53 members of whom 17 present a syndromic cardiac disorder characterized by electrical disorders (sinus node dysfunction, atrial fibrillation...) and developmental defects (atrial septal defect, valvopathy, left ventricle non-compaction...) following an autosomal dominant model. Among the affected family members, 6 are implanted with a pacemaker and one experienced a sudden death at 43yo. Despite a strong linkage pointing to the 4q25 region, exome sequencing failed to identify causal variant. Interestingly, 6 additional non-related families presenting the same phenotype have been also identified.

Our aims are to identity the causal mutation and the molecular mechanism underlying this complex cardiac syndrome.

Genetic study has been performed using whole genome sequencing (WGS). Based on transgenic mouse strains, we assessed the impact of Family#1 mutation on the phenotype and on gene expression. Then, we generated human cardiomyocytes derived iPS cells (CM-iPS) isogenic models to evaluate the epigenome (CUT&RUN and ATAC-seq), transcriptome (RNA-seq) and topological associated domain (TAD) remodelling (Hi-C).

By WGS we uncovered a deletion of 15kb in a gene desert area on 4q25, segregating in all affected relatives of Family#1. The 6 other families present overlapping deletions. Mouse model recapitulates the cardiac phenotype and exhibit a dysregulation of Pitx2 expression in cardiac specific compartments. Based on human CM-iPS models, epigenetic data highlight among the 15kb deletion a unique open region containing a CTCF binding site, crucial for delimiting TAD boundaries. Hi-C assay reveals the fusion of 2 TADs and highlights new interactions between PITX2 and atrial specific regulatory elements.

We identified a deletion located within a gene desert area associated with a complex cardiac disorder. The CTCF binding site contained in the deletion seems key in the TAD border. The TAD remodelling leads to new (regulatory) interactions and expression dysregulation of PITX2. We describe a new molecular mechanism implying a yet unidentified non-coding regulatory element of PITX2 and responsible for a complex electrical and developmental cardiac syndrome.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Nantes UniversitéFrench national reserch agency (ANR)

Calmodulinopathy is a common cause of critical cardiac phenotypes in fetus and infancy

Background

Cardiac calmodulinopathy is a life-threatening arrhythmia syndrome which presents several phenotypes of inherited primary arrhythmia syndrome (IPAS), and caused by mutations in calmodulin-encoded genes (CALM1–3). We aimed clarify the frequency and their clinical characteristics of calmodulinopathy in our IPAS cohort.

Methods

By using next generation sequencing, we screened arrhythmia related genes including calmodulin-encoding genes in 322 unrelated symptomatic children (0–12 years) who were suspected as IPAS; they included 40 cases with lethal arrhythmic attacks (LAE) under 6-year-old. After gene screening, we investigated their physiological and clinical characteristics about mutation carriers.

Results

Among 322 children, we identified 6 mutations of calmodulin-encoded genes in 9 probands (2.8%); one CALM1 in 2 probands (N98S), and 5 CALM2 in 7 probands (E46K, D96V, D96G, N98S, E141K). Their clinical diagnoses were long QT syndrome (LQTS, n=4), catecholaminergic polymorphic ventricular tachycardia (CPVT, n=3) and both (n=2). Their age of diagnosis ranges at 0–9 with the median of 5 years. There were three major clinical phenotypes; 1) CALM2-D96V, and E141K: two infants with advanced atrio-ventricular block, significant QTc prolongation, severe heart failure from their fetal period – both of them deceased within 1.5-year-old. Their clinical phenotypes resembled classical Timothy syndrome caused by CACNA1C mutations. 2) CALM1-N98S (n=2), CALM2-N98S (n=2), and CALM2-D96G: four preschoolers with LAEs and one syncope: all of them were 3–5 years old. In addition, a T wave morphology of CALM2-D96G carrier was very similar to LQT1. 3) CALM2-E46K (n=2): two were first diagnosed with neurological and developmental disorders, and showed phenotype of CPVT: their cardiac phenotypes were milder compared with that of 1) or 2). Overall, these phenotypes seemed to be mutation specific (indicated in figure). Their cardiac features were severer, and the onset of LAEs was earlier compared with other genotypes of LQTS/CPVT. As the treatment, β-blocker was effective for control of LAEs.

Conclusion

Cardiac calmodulinopathy presented serious and potentially lethal phenotypes in fetus or infancy. To prevent cardiac death in them, we must correctly diagnose and start the treatment as earlier as possible.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): MEXT KAKENHI from the Ministry of Education, Culture, Sports, Science, and Technology of Japan

Exacerbation of ventricular arrhythmias by continuous positive airway pressure treatment in idiopathic dilated cardiomyopathy

Continuous positive airway pressure (CPAP) therapy can be beneficial in patients with obstructive sleep apnea (OSA) and cardiovascular diseases, reducing arrhythmia frequency and improving cardiac function. We describe a case of moderate OSA with idiopathic dilated cardiomyopathy, in which the frequency of premature ventricular contraction (PVC) and non-sustained ventricular tachycardia (NSVT) increased immediately after initiating CPAP therapy. Although PVC and NSVT are benign cardiac arrhythmias, they are associated with an increased risk of sustained lethal ventricular tachyarrhythmias. Therefore, when initiating CPAP therapy, the possibility of increased arrhythmia should be considered.

Oral Adrenergic Agents Produced Ventricular Fibrillation and QT Prolongation in an Elderly Patient Carrying an RYR2 Variant

Mutant cardiac ryanodine receptor channels (RyR2) are "leaky," and spontaneous Ca²⁺ release through these channels causes delayed afterdepolarizations that can deteriorate into ventricular fibrillation. Some patients carrying RYR2 mutations in type 1 catecholaminergic polymorphic ventricular tachycardia exhibit QT prolongation and are initially diagnosed with long QT syndrome. However, none have been reported to cause drug-induced ventricular fibrillation in patients with RYR2 variants. We describe the first case of an elderly woman with drug-induced QT prolongation and ventricular fibrillation who carried a novel RYR2 variant but no other mutations related to long QT syndrome. Oral adrenergic agents might induce QT prolongation and subsequent ventricular fibrillation in patients carrying an RYR2 variant. Screening for RYR2 could be valuable in patients with suspected drug-induced long QT syndrome.

Association Between Deleterious SCN5A Variants and Ventricular Septal Defect in Young Patients With Brugada Syndrome

OBJECTIVES

This study aimed to investigate the clinical characteristics of young patients with Brugada syndrome (BrS) with ventricular septal defect (VSD) and explore their genetic backgrounds.

BACKGROUND

VSD is the most frequently occurring congenital heart disease among children. In contrast, BrS is a rare hereditary disease that is responsible for ventricular fibrillation and sudden cardiac death. Owing to their low incidence, the genetic background and clinical characteristics of patients with BrS with VSD have not been elucidated yet.

METHODS

This study enrolled 36 individuals who were diagnosed with BrS when they were <20 years of age and performed genetic screening for SCN5A. The functional alteration in mutant Na⁺ channels was confirmed by patch clamp technique.

RESULTS

Among the 36 patients with BrS, 5 had been diagnosed with VSD. This study found 14 heterozygous SCN5A variants in 15 unrelated patients. The 5 patients with VSD carried SCN5A variants, including R367S, R535∗, R893C, W1345C, and G1743R. The 3 missense variants (R893C, W1345C, and G1743R) have been proved to reduce peak Na⁺ current to <10%. A functional analysis of SCN5A R367S was performed and the variant was found to be nonfunctional.

CONCLUSIONS

This study identified 5 loss-of-function SCN5A variants in 5 young patients with BrS with VSD. The study hypothesizes that altered blood flow in the right ventricular outflow tract leads to fibrosis and electrophysiological changes, predisposing the patients to earlier clinical presentation of BrS. In patients with VSD and ST-segment elevation in the right precordial leads, BrS should be considered and appropriate screening should be pursued accordingly.

Impact of cascade screening for catecholaminergic polymorphic ventricular tachycardia type 1

Objective

Human cardiac ryanodine receptor 2 (RYR2) shows autosomal-dominant inheritance in catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1); however, de novo variants have been observed in sporadic cases. Here, we investigated CPVT1-related RYR2 variant inheritance and its clinical significance between familial and de novo cases.

Methods

We enrolled 82 independent CPVT1 probands (median age: 10.0 (7.0–13.0) years; 45 male) carrying the RYR2 variants and whose biological origin could be confirmed by parental genetic analysis: assured familial inheritance (familial group: n=24) and de novo variants (de novo group: n=58). We examined the clinical characteristics of the probands and their family members carrying the RYR2 variants.

Results

In the de novo group, the RYR2 variants were more likely located in the C-terminus domain and less likely in the N-terminus domain than those in the familial group. The cumulative incidence of the first cardiac events (syncope and cardiac arrest (CA) or CA only) of the probands at the age of 5 and 10 years was higher in the de novo group than in the familial group. Nearly half of the probands in both groups experienced CA events before diagnosis. Only 37.5% of their genotype-positive parents had symptoms; however, at least 66.7% of the genotype-positive siblings were symptomatic.

Conclusions

CPVT1 probands harbouring de novo RYR2 variants showed an earlier onset of symptoms than those with assured familial inheritance. Cascade screening may enable early diagnosis, risk stratification and prophylactic therapeutic intervention to prevent sudden cardiac death of probands and potential genotype-positive family members.

School-based routine screenings of electrocardiograms for the diagnosis of long QT syndrome

Aims

School-based routine screenings of electrocardiograms (ECGs) have been performed upon admission to primary school (PS), junior high school (JHS), and high school (HS) in Japan. Though ECGs with prolonged QT intervals are occasionally found, the role of regular ECG screening tests in identifying long QT syndrome (LQTS) remains to be determined. We investigated the usefulness of the ECG screenings by comparing the results of genetic tests between students who showed QT-prolongation in the screenings and patients with LQTS.

Methods and results

We genetically screened 341 students (106 PS, 173 JHS, and 62 HS). Of these, 230 subjects showed QT-prolongation during regular screenings (S-S group), and the other 111 patients were clinically consulted with suspected LQTS by paediatricians (C-C group). Genotype–phenotype relationships were compared between the two groups. The positive rates in the genetic tests were comparable among the two groups; however, symptomatic subjects were significantly fewer in the S-S group than the C-C group (3% vs. 70%). Compared to the genotype-negative subjects, the positive subjects showed significantly longer QTc (P &lt; 0.0001) and more frequently presented LQTS risk scores with ≥3.5 points (P &lt; 0.0001). Lethal arrhythmic events (LAE) occurred only in the C-C group; 18 subjects experienced LAE and 83% of them were found to carry variant(s) in the LQTS-related genes.

Conclusion

The school-based ECG screenings are effective in identifying young patients with LQTS who require genetic analysis. If individuals are screened at a younger age, we can identify patients at risk earlier and provide preventative treatments.

Loss-of-function mutations in cardiac ryanodine receptor channel cause various types of arrhythmias including long QT syndrome

AIMS

Gain-of-function mutations in RYR2, encoding the cardiac ryanodine receptor channel (RyR2), cause catecholaminergic polymorphic ventricular tachycardia (CPVT). Whereas, genotype-phenotype correlations of loss-of-function mutations remains unknown, due to a small number of analysed mutations. In this study, we aimed to investigate their genotype-phenotype correlations in patients with loss-of-function RYR2 mutations.

METHODS AND RESULTS

We performed targeted gene sequencing for 710 probands younger than 16-year-old with inherited primary arrhythmia syndromes (IPAS). RYR2 mutations were identified in 63 probands, and 3 probands displayed clinical features different from CPVT. A proband with p.E4146D developed ventricular fibrillation (VF) and QT prolongation whereas that with p.S4168P showed QT prolongation and bradycardia. Another proband with p.S4938F showed short-coupled variant of torsade de pointes (scTdP). To evaluate the functional alterations in these three mutant RyR2s and p.K4594Q previously reported in a long QT syndrome (LQTS), we measured Ca2+ signals in HEK293 cells and HL-1 cardiomyocytes as well as Ca2+-dependent [3H]ryanodine binding. All mutant RyR2s demonstrated a reduced Ca2+ release, an increased endoplasmic reticulum Ca2+, and a reduced [3H]ryanodine binding, indicating loss-of-functions. In HL-1 cells, the exogenous expression of S4168P and K4594Q reduced amplitude of Ca2+ transients without inducing Ca2+ waves, whereas that of E4146D and S4938F evoked frequent localized Ca2+ waves.

CONCLUSION

Loss-of-function RYR2 mutations may be implicated in various types of arrhythmias including LQTS, VF, and scTdP, depending on alteration of the channel activity. Search of RYR2 mutations in IPAS patients clinically different from CPVT will be a useful strategy to effectively discover loss-of-function RYR2 mutations.

Electrophysiological Analysis of hiPSC-Derived Cardiomyocytes Using a Patch-Clamp Technique

Electrophysiological analysis of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) using a patch-clamp technique enables the most precise evaluation of electrophysiological properties in single cells. Compared to multielectrode array (MEA) and membrane voltage imaging, patch-clamp recordings offer quantitative measurements of action potentials, and the relevant ionic currents which are essential for the research of disease modeling of inherited arrhythmias, safety pharmacology, and drug discovery using hiPSC-CMs. In this chapter, we describe the detail flow of patch-clamp recordings in hiPSC-CMs.

Pueraria mirifica, an estrogenic tropical herb, unveiled the severity of Type 1 LQTS caused by KCNQ1-T587M

After taking an estrogen-containing supplement derived from a tropical plant Pueraria mirifica, a 24-year-old woman presented marked QT prolongation and repetitive torsade de pointes. The patient was found to carry a heterozygous KCNQ1-T587M mutation. This is the first report on Pueraria mirifica-related acquired long QT syndrome.

Overview of the 84th Annual Scientific Meeting of the Japanese Circulation Society - Change Practice!

Due to the COVID-19 pandemic, the 84^thAnnual Meeting of the Japanese Circulation Society (JCS) was held in a web-based format for the first time in its history as "The Week for JCS 2020" from Monday, July 27 to Sunday, August 2, 2020. All sessions, including general abstracts, were streamed live or on-demand. The main theme of the meeting was "Change Practice!" and the aim was to organize the latest findings in the field of cardiovascular medicine and discuss how to change practice. The total number of registered attendees was over 16,800, far exceeding our expectations, and many of the sessions were viewed by far more people than at conventional face-to-face scientific meetings. At this conference, the power of online information dissemination was fully demonstrated, and the evolution of online academic meetings will be a direction that cannot be reversed in the future. The meeting was completed with great success, and we express our heartfelt gratitude to all affiliates for their enormous amount of work, cooperation, and support.

D-dimer levels at diagnosis and long-term clinical outcomes in venous thromboembolism: from the COMMAND VTE Registry

The relationship between D-dimer level at diagnosis and long-term clinical outcomes has not been fully evaluated in venous thromboembolism (VTE). The COMMAND VTE Registry is a multicenter registry enrolling consecutive acute symptomatic VTE patients in Japan. Patients with available D-dimer levels at diagnosis (N = 2852) were divided into 4 groups according to the D-dimer levels; Quartile 1 (0.0-4.9 µg/mL): N = 682, Quartile 2 (5.0-9.9 µg/mL) N = 694, Quartile 3 (10.0-19.9 µg/mL) N = 710, and Quartile 4 (≥ 20.0 µg/mL): N = 766. The cumulative incidence of all-cause death was higher in Quartile 4 throughout the entire follow-up period (19.9%, 24.9%, 28.8%, and 41.5% at 5-year, P < 0.0001), as well as both within and beyond 30-day. After adjustment, the excess risk of Quartile 4 relative to Quartile 1 for all-cause death remained significant (HR 1.60, 95% CI 1.29-2.03). Similarly, the excess risk of Quartile 4 relative to Quartile 1 for recurrent VTE was significant (HR 1.57, 95% CI 1.02-2.41), which was more prominent in the cancer subgroup. The dominant causes of death in Quartile 4 were pulmonary embolism within 30-day, and cancer beyond 30-day. In conclusions, in VTE patients, elevated D-dimer levels at diagnosis were associated with the increased risk for both short-term and long-term mortality. The higher mortality risk of patients with highest D-dimer levels was driven by the higher risk for fatal PE within 30-day, and by the higher risk for cancer death beyond 30-day. Elevated D-dimer levels were also associated with the increased risk for long-term recurrent VTE, which was more prominent in patients with active cancer.

Impact of no, distal, and proximal deep vein thrombosis on clinical outcomes in patients with acute pulmonary embolism: From the COMMAND VTE registry

BACKGROUND

The majority of acute pulmonary embolism (PE) is caused by thrombus developed from leg veins. However, impact of concomitant deep venous thrombosis (DVT) on clinical outcomes has not been fully evaluated in patients with acute PE.

METHODS

The COMMAND VTE Registry is a multicenter registry enrolling consecutive 3027 patients with acute symptomatic venous thromboembolism (VTE) in Japan. The current study population consisted of 655 acute PE patients who underwent lower extremities ultrasound examination at diagnosis for the assessment of concomitant DVT status.

RESULTS

There were 424 patients with proximal DVT (64.7%), 162 patients with distal DVT (24.7%), and 69 patients with no DVT (10.5%). The cumulative 90-day incidence of all-cause death was higher in proximal DVT patients than in distal DVT and no DVT patients (7.9%, 2.5%, and 1.4%, p = 0.01). Regarding the causes of death, the cumulative 90-day incidence of PE-related death was low, and not significantly different across the 3 groups (1.4%, 0.6%, and 1.7%, p = 0.62). The most frequent cause of death was cancer in proximal and distal DVT patients. There were no significant differences in 90-day rates of recurrent VTE and major bleeding, regardless of the status of concomitant DVT (2.9%, 3.2%, and 2.2%, p = 0.79, and 1.5%, 4.4%, and 4.9%, p = 0.46, respectively).

CONCLUSIONS

Acute PE with proximal DVT at diagnosis was associated with a higher risk for short-term mortality than in patients without DVT, while the risk for short-term mortality was not significantly different between distal DVT patients and patients without DVT.

Preclinical proof-of-concept study: antisense-mediated knockdown of CALM as a therapeutic strategy for calmodulinopathy

Background

Calmodulin (CaM) is a ubiquitous Ca2+ sensor molecule encoded by three distinct calmodulin genes, CALM1–3, and has an important role for cardiac ion channel function. Recently, heterozygous missense mutations in CALM genes were reported to cause a new category of life-threatening genetic arrhythmias such as long-QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT), which is called as “calmodulinopathy”. The patients with calmodulinopathy show poor prognosis and there is no effective treatment for them.

Purpose

Considering the dominant-negative effect of mutant calmodulin proteins produced by heterozygous missense mutations in CALMs, we aimed to prove the concept of antisense-based therapy to treat calmodulinopathy using human iPS cell-derived cardiomyocyte (hiPSC-CM) model.

Methods

We designed multiple locked nucleic acid (LNA) gapmer-antisense oligonucleotides (ASOs) targeting CALM2 and analyzed the silencing efficiency and toxicity in cultured cells to select the most potent ASO. Using CMs differentiated from hiPSCs which were generated form a 12-year-old boy with LQTS carrying a heterozygous CALM2-N98S mutation, CALM2 expression and action potentials (APs) were analyzed to evaluate the efficacy of ASOs.

Results

We identified several ASOs which reduced CALM2 expression without affecting cell viability in human cultured cells (HepG2) (ASO 50 nM, n=2; Figure 1A). Considering further experiments in vivo mouse model, we investigated the CALM2 silencing activity in mouse cultured cells (3T3-L1) without transfection (free-uptake) (ASO 1 μM, n=2; †ASOs have homologous sequence between human and mouse; Figure B). After free-uptake CALM2 silencing analysis in 3T3-L1 cells, we identified that ASO #2 has the most potent CALM2 silencing activity and low cytotoxicity (Figure 1B). ASO #2 effectively reduced CALM2 expression even in hiPSC-CMs (ASO(−): n=3, lipofection: n=4, free-uptake: n=3; P&lt;0.05; Figure 1C). In action potential recordings, we demonstrated that ASO #2 ameliorated prolonged AP durations (APD90) in N98S-hiPSC-CMs at 0.5 Hz pacing (ASO(−): 666±123 ms (n=7), lipofection: 329±21 ms (n=8), free-uptake: 388±34 ms (n=12); P&lt;0.05; Figure 1D).

Conclusion

Our results using patient-derived hiPSC-CM model suggest that ASO-based therapy might be a promising strategy for the treatment of calmodulinopathy.

Figure 1

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): Nissan Chemical Corporation

Molecular mechanism of a new cardiac syndrome associated with a regulatory element deletion of chromosome 4q25

Introduction

We identified a large family of 53 members of whom 22 present a new cardiac syndrome characterized by electrical disorders and developmental defects following an autosomal dominant model. Among the affected family members 6 are implanted with a pacemaker, 2 experienced syncope and one a sudden death at 43yo. Linkage analysis points, with high confidence, to the chromosome 4q25 region. This region is associated with the Ankyrin syndrome (mutation in ANK2) sharing partly the electrical defects observed in the affected family members. No mutation was found in the coding region of the 4q25 region as well as in the coding and non-coding part of the ANK2.

Objective

Our aims are first to identity the responsible mutation present in this family and understand the molecular mechanisms leading to this new syndrome.

Method

Whole genome sequencing (WGS) has been employed to identify genetic variants responsible for this syndrome. ChIP-seq and ATAC-seq were used for functional annotation and genome editing (CRISPR-Cas9) to generate iPS cellular models.

Results

By WGS we uncovered a deleted region of 15kb in a gene desert area on 4q25, segregating in all affected relatives. Five other families (3 French and 2 Japanese) presenting the same phenotype show overlapping deletions. We generated human cardiac epigenetic data and identified among the 15kb deleted region a unique active enhancer region within the presence of a transcript factor CTCF binding site. Isogenic cell lines where the 15kb and the CTCF binding have been deleted are under investigation.

Conclusion

We identified a new cardiac syndrome and for the first time a mutation located within a gene desert area leading to severe and complex cardiac disorders. We demonstrated the presence of a likely gene regulatory element. Experiments are ongoing to characterize the molecular mechanisms and consequence of the deletion on gene expression.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Pays de la loire - Etoiles montantes

Clinical aspects of pediatric Brugada syndrome

Introduction

Brugada syndrome (BrS) is an inherited arrhythmia characterized by a coved-type ST elevation and sudden death, especially in middle-aged males and more common in Asia. Mutations in SCN5A are detected in 15–20% and reported to be associated with poor prognosis. Among children, BrS is rare and the risk factors in pediatric BrS are unknown, especially in Asian population.

Purpose

The purpose of this study is to elucidate the risk factors for fatal arrhythmic events in Japanese pediatric patients with BrS.

Methods

We enrolled 52 Japanese children with BrS younger than 20 years, and performed genetic analysis and collected the clinical information.

Results

The mean age of initial symptoms was 10.7±5.5 years, and the mean follow-up period was 3.9±5.5 years. Ninety percent of patients were probands. No subjective symptom was confirmed in 28 of the patients, but aborted cardiac arrest (ACA) in 4, ventricular tachycardia in 4, ventricular fibrillation in 1, and syncope in 11. We identified mutations in SCN5A in 63%. There was no significant gender difference in ≤10 years, but a significant male predominance appeared in &gt;10 years. And no gender difference was confirmed in the incidence of severe cardiac events in ≤10 years.

Conclusion

No gender difference was confirmed in ≤10 years in this study about Asian children. And being girls did not reduce the risk in ≤10 years. The frequency of SCN5A mutations was higher than adults, but decreased from childhood (68%) to adolescence (59%). In BrS, genetical and environmental factors may be more effective in childhood and adulthood, respectively.

Funding Acknowledgement

Type of funding source: None

Clinical characteristics and outcomes of patients with venous thromboembolism according to diagnosis on weekends versus weekdays: from the COMMAND VTE Registry

Background/Introduction

The medical systems of hospitals often differs between on weekends and weekdays. These differences could lead different clinical outcomes for patients with acute medical conditions that require complex treatment strategies. However, the effect of the time of diagnosis on clinical outcomes in patients with acute venous thromboembolism (VTE), including pulmonary embolism (PE) and deep vein thrombosis (DVT), is still controversial.

Purpose

We sought to evaluate the clinical characteristics and outcomes of patients with VTE comparing on weekends and weekdays in a large observational database of VTE in Japan.

Methods

The COMMAND VTE Registry is a multicenter registry enrolling 3027 consecutive patients with acute symptomatic VTE objectively confirmed by imaging examination or by autopsy among 29 centers in Japan between January 2010 and August 2014. In the current analysis, diagnosis on weekends was defined as diagnosis during the period from 00:00 hours on Saturday to 24:00 on Sunday. All other times were defined as weekdays. We divided the entire cohort into 2 groups; diagnosis on weekends and diagnosis on weekdays groups, and we compared the clinical characteristics, management strategies and 30-day outcomes between the 2 groups.

Results

The current study population consisted of 337 patients diagnosed on weekends and 2690 patients diagnosed on weekdays. The median days from onset to diagnosis were shorter in the patients diagnosed on weekends than in those diagnosed on weekdays (2 days vs. 4 days, P&lt;0.001). The patients diagnosed on weekends presented with PE more frequently (72% vs. 55%, P&lt;0.001), and they showed more severe condition for PE with a higher simplified pulmonary embolism severity index score. The vast majority of PE patients were diagnosed by contrast-enhanced computed tomography in both groups (97% vs. 97%, P=0.67). The patients diagnosed on weekends more often received initial parenteral anticoagulation therapy and thrombolysis than those diagnosed on weekdays. The cumulative 30-day incidence of all-cause death was not significantly different between the 2 groups among PE patients (diagnosis on weekends: 6.2% vs. diagnosis on weekdays: 6.5%, P=0.87), as well as among DVT patients (0.0% vs. 1.5%, P=0.24) (Figure). After adjusting the confounders, the risk of diagnosis on weekends relative to diagnosis on weekdays for all-cause death among PE patients was still insignificant (adjusted HR: 0.76; 95% CI: 0.42–1.28). The most frequent cause of deaths was fatal PE in both groups among PE patients. The risks for recurrent VTE and major bleeding at 30 days were not significantly different between the 2 groups among PE patients nor DVT patients.

Conclusions

The VTE patients diagnosed on weekends presented with PE more frequently, and they showed more severe condition for PE, although the risks for short-term mortality were not significantly different between patients diagnosed on weekends and weekdays.

Kaplan-Meier curves for all-cause death

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Research Institute for Production Development, Mitsubishi Tanabe Pharma Corporation

Systematic Evaluation of KCNQ1 variant using ACMG/AMP Guidelines and Risk Stratification in Long QT Syndrome Type 1

Background

Mutation/variant-site specific risk stratification in long-QT syndrome type 1 (LQT1) has been well investigated, but it is still challenging to adopt current enormous genomic information to clinical aspects caused by each mutation/variant. We assessed a novel variant-specific risk stratification in LQT1 patients.

Methods

We classified a pathogenicity of 142 KCNQ1 variants among 927 LQT1 patients (536 probands and 391 family members) based on the American College of Medical Genetics and Genomics (ACMG) and Association for Molecular Pathology (AMP) guidelines and evaluated whether the ACMG/AMP-based classification was associated with arrhythmic risk in LQT1 patients.

Results

Among 142 KCNQ1 variants, 60 (42.3%), 58 (40.8%), and 24 (16.9%) variants were classified into pathogenic (P), likely pathogenic (LP), and variant of unknown significance (VUS), respectively. The ACMG/AMP guideline-based classification was significantly associated with syncopal events (particularly those during exercise) and LQT risk score (Schwartz score) in overall population. On the other hand, arrhythmic risk was completely different between probands and families even in the same variants. The baseline QTc interval and variant location could stratify the risk in family members but not in probands, however, the ACMG/AMP-based KCNQ1 variant classification stratified the risk in LQT1 probands as well as family members. Multivariate analysis showed that proband (HR=2.52; 95% CI: 1.93–3.30; p&lt;0.0001), longer QTc interval (≥500ms) (HR=1.41; 95% CI: 1.11–1.79; p&lt;0.0001), variants at membrane spanning (MS) (vs. those at N/C terminus) (HR=1.40; 95% CI: 1.07–1.85; p=0.02), C-loop (vs. N/C terminus) (HR=1.58; 95% CI: 1.11–2.24; p=0.01), and P variants [(vs. LP) (HR=1.71; 95% CI: 1.33–2.23; p&lt;0.0001), (vs. VUS) (HR=1.96; 95% CI: 1.19–3.46; p=0.007)] were significantly associated with syncopal events. A clinical score (0–4) based on the proband, QTc (≥500ms), variant location (MS or C-loop) and P variant by the ACMG/AMP guidelines allowed identification of patients more likely to have arrhythmic events (Figure A and B).

Conclusion

Comprehensive evaluation of clinical findings and pathogenicity of KCNQ1 variants based on the ACMG/AMP-based evaluation may stratify arrhythmic risk of congenital long-QT syndrome type 1.

Figure 1

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Health Science Research Grant from the Ministry of Health,Labor and Welfare of Japan for Clinical Research on Measures for Intractable Diseases (H24-033, H26-040, H27-032) and a research grant from the Japan Agency for Medical Research and Development (AMED) (15km0305015h0101, 16ek0210073h0001)

Splice site mutation of LMNA causes severe dilated cardiomyopathy via strong dominant reduction of total lamin expression

Objective

LMNA is a known causative gene of dilated cardiomyopathy (DCM) and familial cardiac conduction disturbance (CCD). Genetic variants affecting the pre-mRNA splicing process often lead to premature stop codons and result in nonsense-mediated mRNA decay (NMD), followed by degradation of mutated alleles. The misssense variant LMNA c. 936G&gt;C was previously reported in a French family affected by muscular dystrophy, CCD, and DCM, but no detailed analysis has been performed. We so far identified the same variant in two Japanese families affected by CCD and DCM. In this study, we investigated the molecular consequences of the variant located at the last codon of LMNA exon5 to demonstrate its pathogenicity.

Methods

Genomic DNA and total RNA were isolated from patients' peripheral blood lymphocytes or cardiac tissue. LMNA-coding exons were screened by direct sequencing. Complementary DNAs (cDNAs) were generated by reverse transcription PCR from RNA. Quantitative PCR (qPCR) was performed to quantify the LMNA cDNA amount by using specific primers for lamins A and C. The protein expressions of both isoforms were analyzed by western blotting.

Results

We detected the heterozygous LMNA c.936 G&gt;C (p. Q312H) variant at the end of exon 5 by genomic DNA sequencing in two unrelated Japanese families (figure. pedigree) affected by DCM and CCD. In a genomic database survey, we did not find the variant in either gnomAD, TogoVar, or the Human Genetic Variation Database. The two commonly used splice site predictor tools, NetGene2 and FSPLICE, estimated that this site was a splice donor site. Sequencing of cDNA demonstrated that the mutated allele was absent. By qPCR assay, we confirmed a 90% reduction in LMNA cDNA. Western blot analysis revealed that lamin A and C expression was reduced far more than 50% (figure. western blot).

Conclusions

We report a LMNA missense mutation found in two families, which disrupts a normal splicing site, leads to NMD, and resulted in severe cardiac laminopathy. The drastic reductions of lamin expression at the cDNA and protein levels suggested that other co-existing mechanisms may also have suppressed the expression of the healthy wild type allele.

Pedigree and western blot assay

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science KAKENHI

Usefulness of collaboration between mathematical models and cell engineering for elucidating complex disease mechanisms and discover effective drugs

Background

A missense mutation, CACNA1C-E1115K, located in the cardiac L-type calcium channel (LTCC), was recently reported to be associated with diverse arrhythmias. Several studies reported in-vivo and in-vitro modeling of this mutation, but actual mechanism and target drug of this disease has not been clarified due to its complex ion-mechanisms.

Objective

To reveal the mechanism of this diverse arrhythmogenic phenotype using combination of in-vitro and in-silico model.

Methods and results

Cell-Engineering Phase: We generated human induced pluripotent stem cell (hiPSC) from a patient carrying heterozygous CACNA1C-E1115K and differentiated into cardiomyocytes. Spontaneous APs were recorded from spontaneously beating single cardiomyocytes by using the perforated patch-clamp technique.

Mathematical-Modeling Phase: We newly developed ICaL-mutation mathematical model, fitted into experimental data, including its impaired ion selectivity. Furthermore, we installed this mathematical model into hiPSC-CM simulation model.

Collaboration Phase: Mutant in-silico model showed APD prolongation and frequent early afterdepolarization (EAD), which are same as in-vitro model. In-silico model revealed this EAD was mostly related to robust late-mode of sodium current occurred by Na+ overload and suggested that mexiletine is capable of reducing arrhythmia. Afterward, we applicated mexiletine onto hiPSC-CMs mutant model and found mexiletine suppress EADs.

Conclusions

Precise in-silico disease model can elucidate complicated ion currents and contribute predicting result of drug-testing.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists

Risk Factors for Major Bleeding During Anticoagulation Therapy in Cancer-Associated Venous Thromboembolism - From the COMMAND VTE Registry

BACKGROUND

Patients with cancer-associated venous thromboembolism (VTE) are at high risk for recurrent VTE and are recommended to receive prolonged anticoagulation therapy if they are at a low risk for bleeding. However, there are no established risk factors for bleeding during anticoagulation therapy.Methods and Results:The COMMAND VTE Registry is a multicenter retrospective registry enrolling 3,027 consecutive patients with acute symptomatic VTE among 29 Japanese centers. The present study population consisted of 592 cancer-associated VTE patients with anticoagulation therapy. We constructed a multivariable Cox proportional hazard model to estimate the hazard ratio (HR) and 95% confidence interval (CI) of the potential risk factors for major bleeding. During a median follow-up period of 199 days, major bleeding occurred in 72 patients. The cumulative incidence of major bleeding was 5.8% at 3 months, 13.8% at 1 year, 17.5% at 2 years, and 28.1% at 5 years. The most frequent major bleeding site was gastrointestinal tract (47%). Terminal cancer (adjusted HR, 4.17; 95% CI, 2.22-7.85, P<0.001), chronic kidney disease (adjusted HR, 1.89; 95% CI 1.06-3.37, P=0.031), and gastrointestinal cancer (adjusted HR, 1.78; 95% CI, 1.04-3.04, P=0.037) were independently associated with an increased risk of major bleeding.

CONCLUSIONS

Major bleeding events were common during anticoagulation therapy in real-world cancer-associated VTE patients. Terminal cancer, chronic kidney disease, and gastrointestinal cancer were the independent risk factors for major bleeding.

Systematic Evaluation of KCNQ1 Variant Using ACMG/AMP Guidelines and Risk Stratification in Long QT Syndrome Type 1

Background - Mutation/variant-site specific risk stratification in long-QT syndrome type 1 (LQT1) has been well investigated, but it is still challenging to adapt current enormous genomic information to clinical aspects caused by each mutation/variant. We assessed a novel variant-specific risk stratification in LQT1 patients. Methods - We classified a pathogenicity of 141 KCNQ1 variants among 927 LQT1 patients (536 probands) based on the American College of Medical Genetics and Genomics (ACMG) and Association for Molecular Pathology (AMP) guidelines and evaluated whether the ACMG/AMP-based classification was associated with arrhythmic risk in LQT1 patients. Results - Among 141 KCNQ1 variants, 61 (43.3%), 55 (39.0%), and 25 (17.7%) variants were classified into pathogenic (P), likely pathogenic (LP), and variant of unknown significance (VUS), respectively. Multivariable analysis showed that proband (HR = 2.53; 95%CI = 1.94-3.32; p <0.0001), longer QTc (≥500ms) (HR = 1.44; 95%CI = 1.13-1.83; p = 0.004), variants at membrane spanning (MS) (vs. those at N/C terminus) (HR = 1.42; 95%CI = 1.08-1.88; p = 0.01), C-loop (vs. N/C terminus) (HR = 1.52; 95%CI = 1.06-2.16; p = 0.02), and P variants [(vs. LP) (HR = 1.72; 95%CI = 1.32-2.26; p <0.0001), (vs. VUS) (HR = 1.81; 95%CI = 1.15-2.99; p = 0.009)] were significantly associated with syncopal events. The ACMG/AMP-based KCNQ1 evaluation was useful for risk stratification not only in family members but also in probands. A clinical score (0~4) based on proband, QTc (≥500ms), variant location (MS or C-loop) and P variant by ACMG/AMP guidelines allowed identification of patients more likely to have arrhythmic events. Conclusions - Comprehensive evaluation of clinical findings and pathogenicity of KCNQ1 variants based on the ACMG/AMP-based evaluation may stratify arrhythmic risk of congenital long-QT syndrome type 1.

Impact of the T-wave characteristics on distinguishing arrhythmogenic right ventricular cardiomyopathy from healthy children

BACKGROUND

T-wave inversion (TWI) is not considered useful for diagnosing pediatric arrhythmogenic right ventricular cardiomyopathy (ARVC), because right precordial TWI in ARVC resembles a normal juvenile pattern.

OBJECTIVES

The aims of this study were to clarify the electrocardiographic (ECG) characteristics of pediatric ARVC to distinguish those patients from healthy children.

METHODS

Between 1979 and 2017, 11 ARVC patients under 18 years old were registered and compared with school screening ECGs from 48,401 healthy children.

RESULTS

The mean age at the first arrhythmic event or diagnosis was 13.3 ± 4.7 years. Nine patients were asymptomatic initially and were found by ECG screening, but 6 developed severe symptoms during the follow-up. Healthy children had a normal juvenile pattern, while ARVC children, especially symptomatic patients, had a significant tendency to have inferior and anterior TWI. The phenomenon of T-wave discontinuity (TWD) in which the TWI became deeper from V1 to V3 and suddenly turned positive in V5 was significantly more frequent in ARVC (60%) than healthy children (0.55%). Anterior TWI and TWD were also significantly more frequent in those who developed severe symptoms. The sensitivity and specificity of TWD were 60% (95% CI, 31-83%), and 99% (95% CI, 99-99%) to distinguish ARVC from healthy children, as well as 100% (95% CI, 71-100%) and 80% (95% CI, 51-80%), respectively, to predict severe symptoms in the future.

CONCLUSIONS

The ECG is useful to distinguish ARVC children, even in the early phase. Anterior TWI and TWD could detect ARVC children and to predict the possible serious conditions.

LMNA Missense Mutation Causes Nonsense-Mediated mRNA Decay and Severe Dilated Cardiomyopathy

BACKGROUND

LMNA is a known causative gene of dilated cardiomyopathy and familial conduction disturbance. Nonsense-mediated mRNA decay, normally caused by nonsense mutations, is a safeguard process to protect cells from deleterious effects of inappropriate proteins from mutated genes. Nonsense-mediated mRNA decay induced by nonstop codon mutations is rare. We investigated the effect of an LMNA missense mutation identified in 2 families affected by cardiac laminopathy.

METHODS

Genomic DNA and total RNA were isolated from patients' peripheral blood lymphocytes or cardiac tissue. LMNA-coding exons were screened by direct sequencing. Complementary DNAs were generated by a reverse transcription-polymerase chain reaction from total RNA. Quantitative polymerase chain reaction was performed to quantify the LMNA complementary DNA amount by using specific primers for lamins A and C. A minigene splicing reporter experiment was performed to assess the effect of detected variants on RNA splicing. The protein expressions of both isoforms were analyzed by Western blotting.

RESULTS

We detected a missense variant c.936 G>C (p. Q312H) at the end of exon 5 of LMNA by genomic DNA sequencing in 2 unrelated families affected by dilated cardiomyopathy and cardiac conduction disturbance. This variant was previously reported in a French family suffering from muscular dystrophy and cardiac conduction disturbance. Sequencing of complementary DNA demonstrated that the mutated allele was absent. By quantitative polymerase chain reaction assay, we confirmed a 90% reduction in LMNA complementary DNA. The minigene splicing reporter assay demonstrated a splicing error by the variant. Western blot analysis revealed that lamin A and C expressions were reduced far >50%.

CONCLUSIONS

We report an LMNA missense mutation found in 2 families, which disrupted a normal splicing site, led to nonsense-mediated mRNA decay, and resulted in severe cardiac laminopathy.

Propranolol Attenuates Late Sodium Current in a Long QT Syndrome Type 3-Human Induced Pluripotent Stem Cell Model

Background

Long QT syndrome type 3 (LQT3) is caused by gain-of-function mutations in the SCN5A gene, which encodes the α subunit of the cardiac voltage-gated sodium channel. LQT3 patients present bradycardia and lethal arrhythmias during rest or sleep. Further, the efficacy of β-blockers, the drug used for their treatment, is uncertain. Recently, a large multicenter LQT3 cohort study demonstrated that β-blocker therapy reduced the risk of life-threatening cardiac events in female patients; however, the detailed mechanism of action remains unclear.

Objectives

This study aimed to establish LQT3-human induced pluripotent stem cells (hiPSCs) and to investigate the effect of propranolol in this model.

Method

An hiPSCs cell line was established from peripheral blood mononuclear cells of a boy with LQT3 carrying the SCN5A-N1774D mutation. He had suffered from repetitive torsades de pointes (TdPs) with QT prolongation since birth (QTc 680 ms), which were effectively treated with propranolol, as it suppressed lethal arrhythmias. Furthermore, hiPSCs were differentiated into cardiomyocytes (CMs), on which electrophysiological functional assays were performed using the patch-clamp method.

Results

N1774D-hiPSC-CMs exhibited significantly prolonged action potential durations (APDs) in comparison to those of the control cells (N1774D: 440 ± 37 ms vs. control: 272 ± 22 ms; at 1 Hz pacing; p < 0.01). Furthermore, N1774D-hiPSC-CMs presented gain-of-function features: a hyperpolarized shift of steady-state activation and increased late sodium current compared to those of the control cells. 5 μM propranolol shortened APDs and inhibited late sodium current in N1774D-hiPSC-CMs, but did not significantly affect in the control cells. In addition, even in the presence of intrapipette guanosine diphosphate βs (GDPβs), an inhibitor of G proteins, propranolol reduced late sodium current in N1774D cells. Therefore, these results suggested a unique inhibitory effect of propranolol on late sodium current unrelated to β-adrenergic receptor block in N1774D-hiPSC-CMs.

Conclusion

We successfully recapitulated the clinical phenotype of LQT3 using patient-derived hiPSC-CMs and determined that the mechanism, by which propranolol inhibited the late sodium current, was independent of β-adrenergic receptor signaling pathway.

An NGS-based genotyping in LQTS; minor genes are no longer minor

Mutations in KCNQ1, KCNH2, and SCN5A are the major cause of long QT syndrome (LQTS). More than 90% of the genotyped patients have been reported to carry mutations in any of these three genes. Thanks to increasing popularity of next generation sequencer (NGS), novel CACNA1C mutations have been identified among LQTS patients without extra-cardiac phenotypes. We aimed to clarify the frequency of genotypes in LQTS patients in the era of NGS. The study comprised 160 congenital LQTS patients (71 males) registered from November 2015 to September 2018. Inclusion criteria was QTc > 460 ms and Schwartz score ≥ 3. We performed genetic analysis using target gene method by NGS and confirmed the mutations by Sanger method. The median age for genetic screening was 13 (0-68) years. Sixteen patients suffered cardiac arrest, 47 syncope, and 97 were asymptomatic. We identified genetic mutations in 111 (69.4%) patients including 6 CACNA1C (5.4% of the genotyped patients) with 4 asymptomatic patients. Five (3.1%) patients carried double mutations; three out of them with RYR2 and KCNQ1 or KCNH2. In conclusion, CACNA1C screening would be recommended even if the patient is asymptomatic to elucidate the genetic background of the LQTS patients.

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome

Supplemental Digital Content is available in the text.

Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility.