Search

LMNA-related dilated cardiomyopathy is an inherited heart disease caused by mutations in the LMNA gene encoding for lamin A/C. The disease is characterized by left ventricular enlargement and impaired systolic function associated with conduction defects and ventricular arrhythmias. We hypothesized that LMNA-mutated patients’ induced Pluripotent Stem Cell-derived cardiomyocytes (iPSC-CMs) display electrophysiological abnormalities, thus constituting a suitable tool for deciphering the arrhythmogenic mechanisms of the disease, and possibly for developing novel therapeutic modalities. iPSC-CMs were generated from two related patients (father and son) carrying the same E342K mutation in the LMNA gene. Compared to control iPSC-CMs, LMNA-mutated iPSC-CMs exhibited the following electrophysiological abnormalities: (1) decreased spontaneous action potential beat rate and decreased pacemaker current (If) density, (2) prolonged action potential duration and increased L-type Ca2+ current (ICa,L) density, (3) delayed afterdepolarizations (DADs), arrhythmias and increased beat rate variability, (4) DADs, arrhythmias and cessation of spontaneous firing in response to β-adrenergic stimulation and rapid pacing. Additionally, compared to healthy control, LMNA-mutated iPSC-CMs displayed nuclear morphological irregularities and gene expression alterations. Notably, KB-R7943, a selective inhibitor of the reverse-mode of the Na+/Ca2+ exchanger, blocked the DADs in LMNA-mutated iPSC-CMs. Our findings demonstrate cellular electrophysiological mechanisms underlying the arrhythmias in LMNA-related dilated cardiomyopathy.

Visual Abstract, Highlights • The homozygous c.38T>G mutation in the LEMD2 gene causes arrhythmic cardiomyopathy with bilateral juvenile cataract in the Hutterite population. • The cardiac phenotype is characterized by localized inferior and inferolateral fibrosis of the left ventricle and mild impairment of left ventricular systolic function but severe ventricular arrhythmias leading to sudden cardiac death. • Affected heart tissue and fibroblasts exhibit abnormally shaped nuclei with condensed peripheral heterochromatin. • Functional assays on affected fibroblasts show decreased proliferation capacity, cellular senescence, and a prolonged G1 phase, suggesting premature aging and cellular senescence in proliferating cells., Summary Nuclear envelope proteins have been shown to play an important role in the pathogenesis of inherited dilated cardiomyopathy. Here, we present a remarkable cardiac phenotype caused by a homozygous LEMD2 mutation in patients of the Hutterite population with juvenile cataract. Mutation carriers develop arrhythmic cardiomyopathy with mild impairment of left ventricular systolic function but severe ventricular arrhythmias leading to sudden cardiac death. Affected cardiac tissue from a deceased patient and fibroblasts exhibit elongated nuclei with abnormal condensed heterochromatin at the periphery. The patient fibroblasts demonstrate cellular senescence and reduced proliferation capacity, which may suggest an involvement of LEM domain containing protein 2 in chromatin remodeling processes and premature aging.

Purpose of Review Arrhythmogenic cardiomyopathy (ACM) is a genetic disease characterized by life-threatening ventricular arrhythmias and sudden cardiac death (SCD) in apparently healthy young adults. Mutations in genes encoding for cellular junctions can be found in about half of the patients. However, disease onset and severity, risk of arrhythmias, and outcome are highly variable and drug-targeted treatment is currently unavailable. Recent Findings This review focuses on advances in clinical risk stratification, genetic etiology, and pathophysiological concepts. The desmosome is the central part of the disease, but other intercalated disc and associated structural proteins not only broaden the genetic spectrum but also provide novel molecular and cellular insights into the pathogenesis of ACM. Signaling pathways and the role of inflammation will be discussed and targets for novel therapeutic approaches outlined. Summary Genetic discoveries and experimental-driven preclinical research contributed significantly to the understanding of ACM towards mutation- and pathway-specific personalized medicine.

The interplay between the cardiovascular system, metabolism, and inflammation plays a central role in the pathophysiology of a wide spectrum of cardiovascular diseases, including heart failure. Here, we provide an overview of the fundamental aspects of the interrelation between inflammation and metabolism, ranging from the role of metabolism in immune cell function to the processes how inflammation modulates systemic and cardiac metabolism. Furthermore, we discuss how disruption of this immuno-metabolic interface is involved in the development and progression of cardiovascular disease, with a special focus on heart failure. Finally, we present new technologies and therapeutic approaches that have recently emerged and hold promise for the future of cardiovascular medicine.

Arrhythmogenic cardiomyopathy has been clinically defined since the 1980s and causes right or biventricular cardiomyopathy associated with ventricular arrhythmia. Although it is a rare cardiac disease, it is responsible for a significant proportion of sudden cardiac deaths, especially in athletes. The majority of patients with arrhythmogenic cardiomyopathy carry one or more genetic variants in desmosomal genes. In the 1990s, several knockout mouse models of genes encoding for desmosomal proteins involved in cell-cell adhesion revealed for the first time embryonic lethality due to cardiac defects. Influenced by these initial discoveries in mice, arrhythmogenic cardiomyopathy received an increasing interest in human cardiovascular genetics, leading to the discovery of mutations initially in desmosomal genes and later on in more than 25 different genes. Of note, even in the clinic, routine genetic diagnostics are important for risk prediction of patients and their relatives with arrhythmogenic cardiomyopathy. Based on improvements in genetic animal engineering, different transgenic, knock-in, or cardiac-specific knockout animal models for desmosomal and nondesmosomal proteins have been generated, leading to important discoveries in this field. Here, we present an overview about the existing animal models of arrhythmogenic cardiomyopathy with a focus on the underlying pathomechanism and its importance for understanding of this disease. Prospectively, novel mechanistic insights gained from the whole animal, organ, tissue, cellular, and molecular levels will lead to the development of efficient personalized therapies for treatment of arrhythmogenic cardiomyopathy.

Vasovagal syncope may have a genetic predisposition. It has a high prevalence in some families, and children of a fainting parent are more likely to faint than those without a parent who faints. Having two fainting parents or a fainting twin increases the likelihood even further. Several genotypes appear to associate with the phenotype of positive tilt tests, but the control subjects are usually those who faint and have negative tilt tests. Twin studies, highly focused genome-wide association studies, and copy number variation studies all suggest there are loci in the genome that associate with vasovagal syncope, although the specific genes, pathways, and proteins are unknown. A recent multigenerational kindred candidate gene study identified 3 genes that associate with vasovagal syncope. The best evidence to date is for central signaling genes involving serotonin and dopamine. Genome-wide association studies to date have not yet been helpful. Our understanding of the genetic correlates of vasovagal syncope leaves ample opportunity for future work.

The underlying genetic mechanisms and early pathological events of children with primary cardiomyopathy (CMP) are insufficiently characterized. In this study, we aimed to characterize the mutational spectrum of primary CMP in a large cohort of patients ���18 years referred to a tertiary center. Eighty unrelated index patients with pediatric primary CMP underwent genetic testing with a panel-based next-generation sequencing approach of 89 genes. At least one pathogenic or probably pathogenic variant was identified in 30/80 (38%) index patients. In all CMP subgroups, patients carried most frequently variants of interest in sarcomere genes suggesting them as a major contributor in pediatric primary CMP. In MYH7, MYBPC3, and TNNI3, we identified 18 pathogenic/probably pathogenic variants (MYH7 n = 7, MYBPC3 n = 6, TNNI3 n = 5, including one homozygous (TNNI3 c.24+2T>A) truncating variant. Protein and transcript level analysis on heart biopsies from individuals with homozygous mutation of TNNI3 revealed that the TNNI3 protein is absent and associated with upregulation of the fetal isoform TNNI1. The present study further supports the clinical importance of sarcomeric mutation-not only in adult-but also in pediatric primary CMP. TNNI3 is the third most important disease gene in this cohort and complete loss of TNNI3 leads to severe pediatric CMP.

Background: Several studies suggest that vasovagal syncope has a genetic origin, but this is unclear. We assessed whether plausible gene variants associate with vasovagal syncope. Methods: We studied 160 subjects in 9 kindreds comprising 82 fainters and 78 controls. The diagnosis was ascertained with the Calgary Syncope Score. Common genetic variants were genotyped for 12 genes for vascular signaling, potassium channels, the HTR1A (serotonin 5-HT1A receptor), SLC6A4 (serotonin reuptake transporter), and COMT (catecholamine O-methyltransferase). Sex-specific associations between genotypes and phenotypes were tested. Results: In 9 out of 12 variants, there was no significant association between genotype and phenotype. However, the HTR1A (−1019) G alleles associated with syncope in males, but not in females ( P =0.005). CC and GG males had 9% versus 77% likelihoods of syncope. The SLC6A4 promoter L alleles associated with decreased syncope in males but increased in females ( P =0.059). The LL and SS males had 25% and 47% syncope likelihoods, whereas females had 75% and 50% syncope likelihoods. The COMT c.472 A alleles associated with decreased syncope in males but increased in females ( P =0.017). The GG and AA males had 50% and 15% syncope likelihoods, whereas females had 52% and 73% syncope likelihoods. Conclusions: There is a sex-dependent effect of alleles of serotonin signaling and vasovagal syncope, supporting the serotonin hypothesis of the physiology of vasovagal syncope.

About 50% of patients with arrhythmogenic cardiomyopathy (ACM) carry a pathogenic or likely pathogenic mutation in the desmosomal genes. However, there is a significant number of patients without positive familial anamnesis. Therefore, the molecular reasons for ACM in these patients are frequently unknown and a genetic contribution might be underestimated. Here, we used a next-generation sequencing (NGS) approach and in addition single nucleotide polymor-phism (SNP) arrays for the genetic analysis of two independent index patients without familial medical history. Of note, this genetic strategy revealed a homozygous splice site mutation (DSG2–c.378+1G&gt, T) in the first patient and a nonsense mutation (DSG2–p.L772X) in combination with a large deletion in DSG2 in the second one. In conclusion, a recessive inheritance pattern is likely for both cases, which might contribute to the hidden medical history in both families. This is the first report about these novel loss-of-function mutations in DSG2 that have not been previously identi-fied. Therefore, we suggest performing deep genetic analyses using NGS in combination with SNP arrays also for ACM index patients without obvious familial medical history. In the future, this finding might has relevance for the genetic counseling of similar cases.

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole-exome sequencing (WES), are identifying the genetic basis of disease for 25-40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation-wide effort to identify mutations for childhood-onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

Background— Unexplained cardiac arrest may be because of an inherited arrhythmia syndrome. The role of genetic testing in cardiac arrest survivors without a definite clinical phenotype is unclear. Methods and Results— The CASPER (Cardiac Arrest Survivors with Preserved Ejection Fraction Registry) is a large registry of cardiac arrest survivors where initial assessment reveals normal coronary arteries, left ventricular function, and resting ECG. Of 375 cardiac arrest survivors in CASPER from 2006 to 2015, 174 underwent genetic testing. Patients were classified as phenotype-positive (n=72) or phenotype-negative (n=102). Genetic testing was performed at treating physicians’ discretion in line with contemporary guidelines and availability. All genetic variants identified from original laboratory reports were reassessed by the investigators in line with modern criteria. Pathogenic variants were identified in 29 (17%) patients (60% channelopathy-associated and 40% cardiomyopathy-associated genes) and 70 variants of unknown significance were identified in 32 (18%) patients. Prior syncope (odds ratio, 4.0; 95% confidence interval, 1.6–9.7) and a family history of sudden death (odds ratio, 3.2; 95% confidence interval, 1.1–9.4) were independently associated with the presence of a pathogenic variant. In phenotype-negative patients, broad multiphenotype genetic testing led to higher yields (21% versus 8%; P =0.04) but was associated with more variants of unknown significance (55% versus 5%; P Conclusions— Genetic testing identifies a pathogenic variant in a significant proportion of unexplained cardiac arrest survivors. Prior syncope and family history of sudden death are predictors of a positive genetic test. Both arrhythmia and cardiomyopathy genes are implicated. Broad, multiphenotype testing revealed the highest frequency of pathogenic variants in phenotype-negative patients. Clinical Trial Registration— https://www.clinicaltrials.gov . Unique Identifier: NCT00292032

Background Arrhythmogenic cardiomyopathy is an inherited heart muscle disorder leading to ventricular arrhythmias and heart failure, mainly as a result of mutations in cardiac desmosomal genes. Desmosomes are cell-cell junctions mediating adhesion of cardiomyocytes; however, the molecular and cellular mechanisms underlying the disease remain widely unknown. Desmocollin-2 is a desmosomal cadherin serving as an anchor molecule required to reconstitute homeostatic intercellular adhesion with desmoglein-2. Cardiac specific lack of desmoglein-2 leads to severe cardiomyopathy, whereas overexpression does not. In contrast, the corresponding data for desmocollin-2 are incomplete, in particular from the view of protein overexpression. Therefore, we developed a mouse model overexpressing desmocollin-2 to determine its potential contribution to cardiomyopathy and intercellular adhesion pathology. Methods and results We generated transgenic mice overexpressing DSC2 in cardiac myocytes. Transgenic mice developed a severe cardiac dysfunction over 5 to 13 weeks as indicated by 2D-echocardiography measurements. Corresponding histology and immunohistochemistry demonstrated fibrosis, necrosis and calcification which were mainly localized in patches near the epi- and endocardium of both ventricles. Expressions of endogenous desmosomal proteins were markedly reduced in fibrotic areas but appear to be unchanged in non-fibrotic areas. Furthermore, gene expression data indicate an early up-regulation of inflammatory and fibrotic remodeling pathways between 2 to 3.5 weeks of age. Conclusion Cardiac specific overexpression of desmocollin-2 induces necrosis, acute inflammation and patchy cardiac fibrotic remodeling leading to fulminant biventricular cardiomyopathy.

Congenital Long QT Syndrome (LQTS) is a potentially lethal cardiac channelopathy characterized by prolongation of the corrected QT (QTc) interval on the surface electrocardiogram. The hallmark phenotypic features are syncope, seizure or sudden death, however most of the mutation carriers are asymptomatic and their risk for arrhythmias such as Torsade de pointes (TdP) are low. We report a case of Long QT syndrome with a corrected QT of 520 ms. For symptom – arrhythmia correlation a loop recorder was implanted with no documented arrhythmias. Epinephrine testing was performed for clinical risk stratification leading to Torsades de pointes during recovery phase which required defibrillation. Genetic testing discovered two pathogenic heterozygous mutations in two different LQT genes ( SCN5A and KCNQ1 ). We propose a calcium homeostasis mechanism for the interaction of both mutations that exaggerated the phenotype, while each mutation by itself is causing a relatively modest phenotype.

Background A systematic evaluation of patients with unexplained cardiac arrest (UCA) yields a diagnosis in 50% of the cases. However, evolution of clinical phenotype, identification of new disease-causing mutations, and description of new syndromes may revise the diagnosis. Objective To assess the evolution in diagnosis among patients with initially UCA. Methods Diagnoses were reviewed for all patients with UCA recruited from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry with at least 1 year of follow-up. Results After comprehensive investigation of 68 patients (age 45.2 ± 14.9 years; 63% men), the initial diagnosis was as follows: idiopathic ventricular fibrillation (n = 34 [50%]), a primary arrhythmic disorder (n = 21 [31%]), and an occult structural cause (n = 13 [19%]). Patients were followed for 30 ± 17 months, during which time the diagnosis changed in 12 (18%) patients. A specific diagnosis emerged for 7 patients (21%) with an initial diagnosis of idiopathic ventricular fibrillation. A structural cardiomyopathy evolved in 2 patients with an initial diagnosis of primary electrical disorder, while the specific structural cardiomyopathy was revised for 1 patient. Two patients with an initial diagnosis of a primary arrhythmic disorder were subsequently considered to have a different primary arrhythmic disorder. A follow-up resting electrocardiogram was the test that most frequently changed the diagnosis (67% of the cases), followed by genetic testing (17%). Conclusions The reevaluation of patients presenting with UCA may lead to a change in diagnosis in up to 20%. This emphasizes the need to actively monitor the phenotype and also has implications for the treatment of these patients and the screening of their relatives.

Background— Unexplained cardiac arrest (UCA) may be explained by inherited arrhythmia syndromes. The Cardiac Arrest Survivors With Preserved Ejection Fraction Registry prospectively assessed first-degree relatives of UCA or sudden unexplained death victims to screen for cardiac abnormalities. Methods and Results— Around 398 first-degree family members (186 UCA, 212 sudden unexplained death victims’ relatives; mean age, 44±17 years) underwent extensive cardiac workup, including ECG, signal averaged ECG, exercise testing, cardiac imaging, Holter-monitoring, and selective provocative drug testing with epinephrine or procainamide. Genetic testing was performed when a mutation was identified in the UCA survivor or when the diagnostic workup revealed a phenotype suggestive of a specific inherited arrhythmia syndrome. The diagnostic strength was classified as definite, probable, or possible based on previously published definitions. Cardiac abnormalities were detected in 120 of 398 patients (30.2%) with 67 of 398 having a definite or probable diagnosis (17%), including Long-QT syndrome (13%), catecholaminergic polymorphic ventricular tachycardia (4%), arrhythmogenic right ventricular cardiomyopathy (4%), and Brugada syndrome (3%). The detection yield was similar for family members of UCA and sudden unexplained death victims (31% versus 27%; P =0.59). Genetic testing was performed more often in family members of UCA patients (29% versus 20%; P =0.03). Disease-causing mutations were identified in 20 of 398 relatives (5%). The most common pathogenic mutations were RyR2 (2%), SCN5A (1%), and KNCQ1 (0.8%). Conclusions— Cardiac screening revealed abnormalities in 30% of first-degree relatives of UCA or sudden unexplained death victims, with a clear working diagnosis in 17%. Long-QT, arrhythmogenic right ventricular cardiomyopathy, and catecholaminergic polymorphic ventricular tachycardia were the most common diagnoses. Systematic cascade screening and genetic testing in asymptomatic individuals will lead to preventive lifestyle and medical interventions with potential to prevent sudden cardiac death. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00292032.

We would like to thank Professors Jaimez and Sanchez for their letter of response commenting on our recent summary of evaluation and outcome of our first 200 unexplained cardiac arrest probands.1 We would first like to point out that we excluded patients with a manifest diagnosis, so none of these patients had overt evidence of an ion channelopathy or cardiomyopathy that are typically both readily diagnosed and treated. This is reflected in our empirical strength of diagnosis framework, which is necessary when a classic diagnosis is not forthcoming.2 In addition, registries do not mandate care but rather capture it, and reflect the reality of practice with the vagaries of contextual clinical decision making. In response to the concerns about the incidence of shocks and the inefficacy of medical therapy, it is important to point out the difference between efficacy and effectiveness. Without …

Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a complex and clinically heterogeneous arrhythmic condition. Incomplete penetrance and variable expressivity are particularly evident in ARVC, making clinical decision-making challenging. Methods Pediatric and adult cardiologists, geneticists, genetic counsellors, ethicists, nurses, and qualitative researchers are collaborating to create the Canadian ARVC registry using a web-based clinical database. Biological samples will be banked and systematic analysis will be performed to examine potentially causative mutations, variants, and biomarkers. Outcomes will include syncope, ventricular arrhythmias, defibrillator therapies, heart failure, and mortality. Results Preliminary recruitment has enrolled 365 participants (aged 42.7 ± 17.1 years; 50% women), including 129 probands and 236 family members. Previous cardiac arrest occurred in 28 (8%) participants, syncope occurred in 43 (12%) participants, and 46% of probands had a family history of sudden death. Overall yield of genetic testing was 36% for a disease-causing mutation and 20% for a variant of unknown significance. Target enrollment is 1000 affected patients and 500 unaffected family member controls over 7 years. The cross-sectional and longitudinal data collected in this manner will allow a robust assessment of the natural history and clinical course of genetic subtypes. Conclusions The Canadian ARVC Registry will create a population-based cohort of patients and their families to inform clinical decisions regarding patients with ARVC.

Background— The Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) enrolls patients with apparently unexplained cardiac arrest and no evident cardiac disease to identify the pathogenesis of cardiac arrest through systematic clinical testing. Exercise testing, drug provocation, advanced cardiac imaging, and genetic testing may be useful when a cause is not apparent. Methods and Results— The first 200 survivors of unexplained cardiac arrest from 14 centers across Canada were evaluated to determine the results of investigation and follow-up (age, 48.6±14.7 years, 41% female). Patients were free of evidence of coronary artery disease, left ventricular dysfunction, or evident repolarization syndromes. Advanced testing determined a diagnosis in 34% of patients at baseline, with a diagnosis emerging during follow-up in 7% of patients. Of those who were diagnosed, 28 (35%) had an underlying structural condition and 53 (65%) had a primary electric disease. During a mean follow-up of 3.15±2.34 years, 23% of patients had either a shock or an appropriate antitachycardia pacing from their implantable cardioverter defibrillator, or both. The implantable cardioverter defibrillator appropriate intervention rate was 8.4% at 1 year and 18.1% at 3 years, with no clear difference between diagnosed and undiagnosed subjects, or between those diagnosed with a primary electric versus structural pathogenesis. Conclusions— Obtaining a diagnosis in previously unexplained cardiac arrest patients requires systematic clinical testing and regular follow-up to unmask the cause. Nearly half of apparently unexplained cardiac arrest patients ultimately received a diagnosis, allowing for improved treatment and family screening. A substantial proportion of patients received appropriate implantable cardioverter defibrillator therapy during medium-term follow-up. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00292032.

Objective The 3-bp deletion in exon 2 of the Lamin A/C (LMNA) gene has not been described in association with dilated cardiomyopathy, which is characterized by progressive heart failure, atrioventricular (AV) block, tachyarrhythmias, and variable skeletal muscle involvement. Case Report In a 43-year-old woman with a long-term history of palpitations and newly diagnosed AV blocks I and II, ventricular ectopic beats, inducible nonsustained ventricular tachycardias (VTs), cardiac arrest, and successful resuscitation, an implantable cardioverter defibrillator was successfully implanted. Her family history was positive for sudden cardiac death (her father and sister), dyspnea and heart failure (her grandmother and sister), palpitations (her brother), and elevated levels of creatine-kinase (CK) (her sister). Two cousins had died of nonspecific muscular dystrophy at ages 10 years and 11 years. Upon neurological investigations revealing sore neck muscles, reduced tendon reflexes, and detached, spot-like white matter lesions bilaterally, a neuromuscular disorder was suspected. The direct sequencing of all exons and flanking intronic regions of the LMNA gene detected the heterozygote 3-bp deletion (AAG) c.367_369del in exon 2 of the gene. This mutation resulted in the deletion of a lysine at position 123 (p.lys123del) in the lamin A/C protein. Conclusions The novel 3-bp deletion in exon 2 of the LMNA gene may phenotypically manifest as dilated cardiomyopathy, heart failure, severe tachyarrhythmias, and muscular dystrophy. Sudden cardiac death from ventricular fibrillation may be prevented in LMNA mutation carriers if the diagnosis is established early enough to implant a cardioverter defibrillator.

Familial dilated cardiomyopathy is a major cause of advanced heart failure and heart transplantation. In most families, the disease-causing mutation is unknown, and relatives should therefore undergo periodic screening to facilitate early diagnosis and therapy. In the present study, we describe a novel titin truncation mutation causing adult-onset familial dilated cardiomyopathy in an Israeli Arab family. The family members underwent physical examination, electrocardiography, and Doppler echocardiography. Linkage to candidate loci was performed, followed by gene sequencing. We identified 13 clinically affected family members (8 men and 5 women, mean age 47 ± 12 years). Compared with their healthy first-degree relatives, the affected relatives had a larger end-diastolic left ventricular dimension (60 ± 10 vs 49 ± 4 mm, p

The giant muscle filament protein titin is encoded by a single gene consisting of 364 exons. In the past, because of its enormous size and complexity, only few titin mutations were discovered causing different cardiac and skeletal muscle conditions; however, the overall role for heritable diseases, in particular dilated cardiomyopathy (DCM), has been significantly underestimated. Recently performed systematic studies using next-generation sequencing (NGS) recognized TTN as the major human disease gene for DCM, but at the same time those data sets revealed that unique genetic variations are also more common in the general population than previously expected. Truncating variants in TTN have been reported in about 25% of patients with DCM and in 2%-3% of controls; however, most of the disease-associated truncation variants were found in constitutively expressed exons across the gene and in A-band titin, which is abundant in both major cardiac isoforms N2B and N2BA. Titin isoform composition and switch is an important factor for determination and modulation of titin-based stiffness in health and heart disease. Moreover, other factors, including post-translational modification resulting from phosphorylation and oxidative modifications of titin spring elements contribute at the cellular level to titin's stiffness. A better understanding of titin's role in cardiac (patho)physiology will achieve further insights into the molecular mechanisms leading to heart failure and arrhythmias in patients with DCM caused by titin truncation mutations and may provide potential targets for future therapeutic interventions.

Background The p.Gln554X mutation in desmocollin‐2 ( DSC 2) is prevalent in ≈10% of the Hutterite population. While the homozygous mutation causes severe biventricular arrhythmogenic right ventricular cardiomyopathy, the phenotypic features and prognosis of heterozygotes remain incompletely understood. Methods and Results Eleven homozygotes (mean age 32±8 years, 45% female), 28 heterozygotes (mean age 40±15 years, 50% female), and 22 mutation‐negatives (mean age 43±17 years, 41% female) were examined. Diagnostic testing was performed as per the arrhythmogenic right ventricular cardiomyopathy modified Task Force Criteria. Inverted T waves in the right precordial leads on ECG were seen in all homozygotes but not in their counterparts ( P premature ventricular complex burden than did heterozygotes or mutation‐negatives (1407 [ IQR 1080 to 2936] versus 2 [ IQR 0 to 6] versus 6 [ IQR 0 to 214], P =0.0002). Ventricular tachycardia was observed in 60% of homozygotes but in none of the remaining individuals ( P 2 , P 2 , P =0.0124) and lower ejection fraction values compared with heterozygotes and mutation‐negatives (right ventricular ejection fraction: 41±9% versus 59±9% versus 61±6%, P P Conclusions The ECG reliably identifies homozygous p.Gln554X carriers and may be useful as an initial step in the screening of high‐risk Hutterites. The cardiac phenotype of heterozygotes appears benign, but further prospective follow‐up of their arrhythmic risk is needed.

In this issue of Circulation: Cardiovascular Genetics , Barsheshet et al shed novel and unexpected light on the genetics of syncope, defined as a transient loss of consciousness caused by cerebral hypoperfusion with spontaneous recovery. Syncope is very common, with a cumulative incidence of 37% by age 60 years.1,2 In “young” patients, by far the most common cause of syncope is vasovagal syncope, with a well-characterized symptom complex and a benign natural history.3,4 Hidden in the forest of vasovagal syncope are rare but more worrisome sentinel events that reflect more life-threatening arrhythmic disorders, particularly inherited arrhythmia syndromes such as long-QT syndrome (LQTS).5 The genetics of these syndromes are now relatively clear. Article see p 491 In contrast to the LQTS, relatively little is known about the genetics of vasovagal syncope, though there are numerous reports of fainting in families, and a parental history of syncope greatly increases the likelihood that offspring will have fainting.3,6 Despite these findings, the role of genetic factors and the model of inheritance of vasovagal syncope are unknown. In this issue, Barsheshet et al present data that inadvertently shed tantalizing light on the possible genetics of vasovagal syncope. The purpose of their study was to examine the role of clinical factors and genetic polymorphisms in syncope in family members of subjects with known culprit mutations causing LQTS. To remove the influence of the culprit mutation, the authors focused on family members who did not have those particular mutations. Barsheshet et al …

Andersen-Tawil syndrome (ATS) is caused by mutations in KCNJ2 (Kir2.1). It remains unclear whether dilated cardiomyopathy (DCM) is a primary feature of ATS. We studied a proband with typical physical features of ATS plus DCM and moderate to severe left ventricular dysfunction (left ventricular ejection fraction = 30.5%). Genetic screening revealed a novel mutation in Kir2.1 (c.665T>C, p.L222S). Functional studies showed that this mutation reduced ionic currents in a dominant-negative manner. Suppression of ventricular arrhythmias with bisoprolol led to normalization of left ventricular size and function. We conclude that DCM is likely a secondary phenotype in ATS and is caused by high ventricular arrhythmia burden.

Background The genetics of congenital heart disease (CHD) remain incompletely understood. Exome sequencing has been successfully used to identify disease-causing mutations in familial disorders in which candidate gene analyses and linkage mapping have failed. Methods We studied a large family characterized by autosomal dominant isolated secundum atrial septal defect (ASD) (MIM No. 612794). Candidate gene resequencing and linkage analysis were uninformative. Results Whole-exome sequencing of 2 affected family members identified 44 rare shared variants, including a nonsynonymous mutation (c.532A>T, p.M178L, NM_005159.4) in alpha-cardiac actin ( ACTC1 ). This mutation was absent from 1834 internal controls as well as from the 1000 Genomes and the Exome Sequencing Project (ESP) databases, but predictions regarding its effect on protein function were divergent. However, p.M178L was the only rare mutation segregating with disease in our family. Conclusions Our results provide further evidence supporting a causative role for ACTC1 mutations in ASD. Massively parallel sequencing of the exome allows for the detection of novel rare variants causing CHD without the limitations of a candidate gene approach. When mutation prediction algorithms are not helpful, studies of familial disease can help distinguish rare pathologic mutations from benign variants. Consideration of the family history can lead to genetic insights into CHD.

Background Provocative testing with sodium channel blockers is advocated for the evaluation of unexplained cardiac arrest (UCA) with the primary purpose of unmasking the typical ECG features of Brugada syndrome. The Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) systematically assesses subjects with UCA or a family history of sudden death (FHSD). Objective The purpose of this study was to determine the clinical yield of procainamide infusion in a national registry of subjects with either UCA or a FHSD. Methods Subjects with either UCA or a FHSD without evidence of a Brugada pattern at baseline underwent procainamide testing (15 mg/kg to a maximum of 1 g at 50 mg/min). A test was considered positive for Brugada pattern if there was an increase in ST elevation >1 mm or if there was >1 mm of new ST elevation in leads V1 and/or V2. Genetic testing was performed on the basis of phenotype detection. Results Procainamide testing was performed in 174 subjects (age 46.8 ± 15.4 years, 47% female). Testing provoked a Brugada pattern in 12 subjects (6.9%), 5 of whom had no ST abnormalities at baseline. No subjects with a negative procainamide challenge were subsequently diagnosed with Brugada syndrome. Genetic testing was conducted in 10 of the 12 subjects with a provoked Brugada pattern and was positive for a mutation in the SCN5A gene in 1. Conclusion Irrespective of the baseline ECG, procainamide testing provoked a Brugada pattern in a significant proportion of subjects with UCA or a FHSD, thereby facilitating a diagnosis of Brugada syndrome, and is recommended in the workup of UCA.

Background— Epinephrine infusion may unmask latent genetic conditions associated with cardiac arrest, including long-QT syndrome and catecholaminergic polymorphic ventricular tachycardia (VT). Methods and Results— Patients with unexplained cardiac arrest (normal left ventricular function and QT interval) and selected family members from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) registry underwent epinephrine challenge at doses of 0.05, 0.10, and 0.20 μg/kg per minute. A test was considered positive for long-QT syndrome if the absolute QT interval prolonged by ≥30 ms at 0.10 μg/kg per minute and borderline if QT prolongation was 1 to 29 ms. Catecholaminergic polymorphic VT was diagnosed if epinephrine provoked ≥3 beats of polymorphic or bidirectional VT and borderline if polymorphic couplets, premature ventricular contractions, or nonsustained monomorphic VT was induced. Epinephrine infusion was performed in 170 patients (age, 42±16 years; 49% men), including 98 patients with unexplained cardiac arrest. Testing was positive for long-QT syndrome in 31 patients (18%) and borderline in 24 patients (14%). Exercise testing provoked an abnormal QT response in 42% of tested patients with a positive epinephrine response. Testing for catecholaminergic polymorphic VT was positive in 7% and borderline in 5%. Targeted genetic testing of abnormal patients was positive in 17% of long-QT syndrome patients and 13% of catecholaminergic polymorphic VT patients. Conclusions— Epinephrine challenge provoked abnormalities in a substantial proportion of patients, most commonly a prolonged QT interval. Exercise and genetic testing replicated the diagnosis suggested by the epinephrine response in a small proportion of patients. Epinephrine infusion combined with exercise testing and targeted genetic testing is recommended in the workup of suspected familial sudden death syndromes. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00292032.

BACKGROUND: Arrhythmogenic cardiomyopathy (AC) is an inherited heart disease associated with arrhythmias and right or biventricular dilation often leading to sudden cardiac death or heart failure. AC is mainly caused by mutations in five genes encoding cardiac desmosomal proteins (JUP, DSP, PKP2, DSG2 and DSC2). The cardiac desmosomes are cellcell junctions coupling the cardiomyocytes. Desmocollin-2 (DSC2) and desmoglein-2 (DSG2) are members of the cadherin family and mediate the Ca2+-dependent cardiomyocyte adhesion. Plakophilin-2 (PKP2), plakoglobin (JUP) and desmoplakin (DSP) are linker proteins connecting the cytoplasmic domains of these cadherins to the intermediate filament system. However, the molecular and cellular pathomechanisms induced by mutations in these genes are widely unknown limiting the efficient development of therapeutic therapies. PURPOSE: So far, no Dsc2 mouse model mimicking an AC is described. The aim of this project was therefore to establish and characterize an adequate mouse model to understand the underlying pathomechanisms in vivo and ex vivo. METHODS: We developed and characterized a transgenic mouse model with a cardiac-specific overexpression of DSC2. Echocardiography was used to characterize the heart function and (immuno)histology was used to characterize the structural defects the transgenic mice. Western-blot analysis and qRTPCR was used to characterize the molecular expression changes of the desmosomal genes. RESULTS: Transgenic mice with a cardiac specific overexpression of DSC2 developed a severe cardiomyopathy shortly after birth with significantly reduced fractional shortening and ejection fractions. Time-dependent functional analysis revealed that the phenotype is deteriorating leading to heart failure and cardiac death after 12 weeks. The myocardial tissue of the septum as well as of both ventricular walls was significantly replaced by fibrosis and was associated with calcification and necrosis in these areas. CONCLUSION: The established cardiac specific overexpressing DSC2 mice are viable but develop a progressive biventricular cardiomyopathy mimicking the clinical phenotype of patients with arrhythmogenic cardiomyopathy. In the future this novel mouse model could contribute to further understanding of the molecular and cellular pathomechanisms leading to AC. 129 INCREASED CARDIAC MITOCHONDRIAL-DERIVED VESICLE FORMATION IN RESPONSE TO ACUTE STRESS AND DOXORUBICIN-INDUCED CARDIOTOXICITY

OBJECTIVES We sought to identify the genetic locus for an inherited form of dilated cardiomyopathy (DCM) that is characterized by diffuse myocardial fibrosis and sudden death. BACKGROUND Genetic studies have mapped multiple loci for DCM, which is a major cause of nonischemic heart failure; however, the genes responsible for the majority of cases have yet to be identified. METHODS Sixty-six family members were evaluated by 12-lead electrocardiogram (ECG), echocardiogram, and laboratory studies. Individuals with echocardiographically documented DCM were defined as affected. Subjects were considered unaffected if they were older than 20 years of age, had a normal ECG and echocardiogram, no personal history of heart failure, and had no affected offspring. Genotyping was performed using polymorphic markers. RESULTS Genome-wide linkage analysis identified a novel locus for this inherited phenotype on chromosome 10q25.3-q26.13. Peak two-point logarithm of the odds scores >3.0 were obtained independently with each family using the markers D10S1773 and D10S1483, respectively. Haplotype analyses defined a critical interval of 14.0 centiMorgans between D10S1237 and D10S1723, corresponding to a physical distance of 9.5 megabases. Multipoint linkage analyses confirmed this interval and generated a peak logarithm of the odds score of 8.2 indicating odds of >100,000,000:1 in favor of this interval as the location of the gene defect responsible for DCM in these families. CONCLUSIONS We have mapped a novel locus for cardiomyopathy, diffuse myocardial fibrosis, and sudden death to chromosome 10q25-q26. The identification of the causative gene in this interval will be an important step in understanding the fundamental mechanisms of heart failure and sudden death.

Isolated noncompaction of the ventricular myocardium (INVM, MIM 300183 and 604169) is a congenital unclassified cardiomyopathy with numerous prominent trabeculations and deep intertrabecular recesses in a hypertrophied and hypokinetic myocardium. Mutations in the G4.5 gene result in a wide spectrum of severe infantile X-linked cardiomyopathic phenotypes including Barth syndrome with dilated cardiomyopathy and INVM. Molecular genetic analysis of INVM has only been performed in pediatric patients. Although adult INVM patients show similar cardiac abnormalities, the influence of genetic factors, especially of mutations in G4.5, is unknown. We analyzed 25 adult INVM patients for the presence of mutations in the G4.5 gene and performed a pedigree analysis of probands. Mutations were not found in the coding sequence or splice sites of G4.5. Systematic analysis of relatives from seven of nine probands showed multiple affected members consistent with an autosomal dominant pattern of inheritance in the majority of cases. We conclude that INVM in the adult is an autosomal dominant disorder rarely caused by mutations in G4.5 and therefore genetically distinct from infantile X-linked cases.

cardiac FDG uptake, including 2 that had received prior steroid therapy. Five out of 8 patients with negative cardiac biopsy had abnormal cardiac FDG uptake. While 13 (65%) patients had confirmed or high suspicion of CS after multimodality testing and biopsy, only 2 (10%) met the JMHW diagnostic criteria. FDG-PET influenced management in 14 (70%) patients: by helping initiate, continue, or change steroid dosage in 3 (15%) patients, and by allowing discontinuation or lack of initiation of treatment in 11 (55%) patients on the basis of negative FDG-PET. Of the remaining 6 (30%) patients, either no treatment was given despite an abnormal FDG uptake in 2 patients due to clinically silent disease, or treatment decisions were not yet finalized. CONCLUSION: In our series, FDG-PET aided in treatment decisions in patients suspected of CS. Due to its ability to assess disease activity and monitor response to therapy, FDG-PET adds value beyond conventional testing, and its use is advocated in cases with high suspicion of CS.

Left Ventricular Noncompaction Cardiomyopathy (LVNC) is a very rare congenital heart disease. LVNC is a form of cardiomyopathy in which the fetal myocardium fails to "compact" during cardiac development and it may be associated with impairment of LV function and LV dilatation. Mutations in several sarcomere genes have been described in LVNC. Nexilin, encoded by NEXN, is a cardiac Z-disc protein that stabilizes the sarcomere. We evaluated nexilin as a disease gene for LVNC.