Hypertrophic cardiomyopathy: from genetics to treatment

Phospholamban p.Leu39* Cardiomyopathy Compared with Other Sarcomeric Cardiomyopathies: Age-Matched Patient Cohorts and Literature Review

Hypertrophic cardiomyopathy (HCM) is a heterogeneous genetic disorder, most often caused by sarcomeric gene mutations, with a small proportion due to variants in non-sarcomeric loci. Phospholamban (PLN) is a phosphoprotein associated with the cardiac sarcoplasmic reticulum, a major determinant of cardiac contractility and relaxation. We conducted a retrospective study to determine the prevalence, phenotypical spectrum and clinical course of patients carrying the PLN p.Leu39* variant. A cohort including 11 PLN patients was identified among all patients with HCM (9/189, 4.8%) and DCM (2/62, 3.2%) who underwent genetic testing from two tertiary centers and five more were detected through cascade screening. Complete phenotyping was performed. PLN p.Leu39* variant-driven cardiomyopathy presented mostly as hypertrophic, with frequent progression to end-stage dilated HCM. We proceeded to compare these results to a similar analysis of a control cohort consisting of age-matched individuals that inherited pathogenic or likely pathogenic variants in common sarcomeric genes (MYBPC3/MYH7). Overall, the clinical characteristics and examination findings of patients carrying PLN p.Leu39* were not different from patients with cardiomyopathy related to sarcomeric mutations except for the presence of pathological Q waves and the incidence of non-sustained ventricular arrhythmias, which were higher in PLN patients than in those with MYBPC3/MYH7-related diseases.

Inherited Arrhythmias in the Pediatric Population: An Updated Overview

Pediatric cardiomyopathies (CMs) and electrical diseases constitute a heterogeneous spectrum of disorders distinguished by structural and electrical abnormalities in the heart muscle, attributed to a genetic variant. They rank among the main causes of morbidity and mortality in the pediatric population, with an annual incidence of 1.1-1.5 per 100,000 in children under the age of 18. The most common conditions are dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Despite great enthusiasm for research in this field, studies in this population are still limited, and the management and treatment often follow adult recommendations, which have significantly more data on treatment benefits. Although adult and pediatric cardiac diseases share similar morphological and clinical manifestations, their outcomes significantly differ. This review summarizes the latest evidence on genetics, clinical characteristics, management, and updated outcomes of primary pediatric CMs and electrical diseases, including DCM, HCM, arrhythmogenic right ventricular cardiomyopathy (ARVC), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome (LQTS), and short QT syndrome (SQTS).

Exploring Health Care Disparities in Genetic Testing and Research for Hereditary Cardiomyopathy: Current State and Future Perspectives

Background  Hereditary cardiomyopathies are commonly occurring myocardial conditions affecting heart structure and function with a genetic or familial association, but the etiology is often unknown. Cardiomyopathies are linked to significant mortality, requiring robust risk stratification with genetic testing and early diagnosis. Hypothesis  We hypothesized that health care disparities exist in genetic testing for hereditary cardiomyopathies within clinical practice and research studies. Methods  In a narrative fashion, we conducted a literature search with online databases such as PubMed/MEDLINE, Google Scholar, EMBASE, and Science Direct on papers related to hereditary cardiomyopathies. A comprehensive analysis of findings from articles in English on disparities in diagnostics and treatment was grouped into four categories. Results  Racial and ethnic disparities in research study enrollment and health care delivery favor White populations and higher socioeconomic status, resulting in differences in the development and implementation of effective genetic screening. Such disparities have shown to be detrimental, as minorities often suffer from disease progression to heart failure and sudden cardiac death. Barriers related to clinical genetic testing included insurance-related issues and health illiteracy. The underrepresentation of minority populations extends to research methodologies, as testing in ethnic minorities resulted in a significantly lower detection rate and diagnostic yield, as well as a higher likelihood of misclassification of variants. Conclusions  Prioritizing minority-based participatory research programs and screening protocols can address systemic disparities. Diversifying research studies can improve risk stratification strategies and impact clinical practice.

Model for classification of heart failure severity in patients with hypertrophic cardiomyopathy using a deep neural network algorithm with a 12-lead electrocardiogram

OBJECTIVES

In hypertrophic cardiomyopathy (HCM), specific ECG abnormalities are observed. Therefore, ECG is a valuable screening tool. Although several studies have reported on estimating the risk of developing fatal arrhythmias from ECG findings, the use of ECG to identify the severity of heart failure (HF) by applying deep learning (DL) methods has not been established.

METHODS

We assessed whether data-driven machine-learning methods could effectively identify the severity of HF in patients with HCM. A residual neural network-based model was developed using 12-lead ECG data from 218 patients with HCM and 245 patients with non-HCM, categorised them into two (mild-to-moderate and severe) or three (mild, moderate and severe) severities of HF. These severities were defined according to the New York Heart Association functional class and levels of the N-terminal prohormone of brain natriuretic peptide. In addition, the patients were divided into groups according to Kansas City Cardiomyopathy Questionnaire (KCCQ)-12. A transfer learning method was applied to resolve the issue of the low number of target samples. The model was trained in advance using PTB-XL, which is an open ECG dataset.

RESULTS

The model trained with our dataset achieved a weighted average F1 score of 0.745 and precision of 0.750 for the mild-to-moderate class samples. Similar results were obtained for grouping based on KCCQ-12. Through data analyses using the Guided Gradient Weighted-Class Activation Map and Integrated Gradients, QRS waves were intensively highlighted among true-positive mild-to-moderate class cases, while the highlighted part was highly variable among true-positive severe class cases.

CONCLUSIONS

We developed a model for classifying HF severity in patients with HCM using a deep neural network algorithm with 12-lead ECG data. Our findings suggest that applications of this DL algorithm for using 12-lead ECG data may be useful to classify the HF status in patients with HCM.

Cardiac proteomic profiling suggests that hypertrophic and dilated cardiomyopathy share a common pathogenetic pathway of the calcium signalling pathway

OBJECTIVE

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are classified as different diseases but have many similar pathogenic genes and clinical symptoms. Previous research has focused on mutated genes. This study was conducted to identify key molecular mechanisms and explore effective therapeutic targets.

METHODS

Myocardial tissue was harvested from patients with HCM (n = 3) or DCM (n = 4) during surgery. Hearts donated by healthy traffic accident victims were treated as controls (n = 4). Total proteins were extracted for liquid chromatography-tandem mass spectrometry. Differentially expressed proteins (DEPs) were annotated via GO and KEGG analyses. Selected distinguishing protein abundance was confirmed by western blotting.

RESULTS

Compared with the control group, there were 121 and 76 DEPs in the HCM and DCM groups, respectively. GO terms for these two comparisons are associated with contraction-related components and actin binding. Additionally, the most significantly upregulated and downregulated proteins were periostin and tropomyosin alpha-3 chain in both comparisons. Moreover, when comparing the HCM and DCM groups, we found 60 significant DEPs, and the GO and KEGG terms are related to the calcium signalling pathway. Expression of the calcium regulation-related protein peptidyl-prolyl cis-trans isomerase (FKBP1A) was significantly upregulated in multiple samples.

CONCLUSION

HCM and DCM have many mutual pathogenetic pathways. Calcium ion-related processes are among the most significant factors affecting disease development. For HCM and DCM, research on regulating linchpin protein expression or interfering with key calcium-related pathways may be more beneficial than genetic research.

Echocardiography and MALDI-TOF Identification of Myosin-Binding Protein C3 A74T Gene Mutations Involved Healthy and Mutated Bengal Cats

This study aimed to identify the potential peptide candidates and expected proteins associated with MYBPC3-A74T gene mutations in Bengal cats and determine if peptidome profiles differ between healthy controls and cats with MYBPC3-A74T gene mutations. All animals were evaluated using echocardiography. DNA was isolated and followed by the screening test of MYBPC3 gene mutation. The MALDI-TOF mass spectrometry was conducted for analyzing the targeted peptide and protein patterns. The expected protein candidates were searched for within the NCBI database. Our results demonstrated that the MYBPC3-A74T gene mutation was dominant in Bengal cats but not in domestic shorthair cats. Correlations between baseline characteristics and echocardiographic parameters were discovered in Bengal cats. Mass spectrometry profiles of the candidate proteins were suspected to accompany the cat with the MYBPC3-A74T gene mutation, involving integral protein–membrane, organization of nucleus, DNA replication, and ATP-binding protein. Therefore, MYBPC3-A74T gene mutations occur frequently in Bengal cat populations. The high incidence of homozygotes for the mutation supports the causal nature of the MYBPC3-A74T mutation. In addition, peptidomics analysis was established for the first time under this condition to promise a complementary technique for the future clinical diagnosis of the MYBPC3-A74T mutation associated with physiological variables and cardiac morphology in cats.

Single-cell transcriptomics provides insights into hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic heart disease that is characterized by unexplained segmental hypertrophy that is usually most pronounced in the septum. While sarcomeric gene mutations are often the genetic basis for HCM, the mechanistic origin for the heterogeneous remodeling remains largely unknown. A better understanding of the gene networks driving the cardiomyocyte (CM) hypertrophy is required to improve therapeutic strategies. Patients suffering from HCM often receive a septal myectomy surgery to relieve outflow tract obstruction due to hypertrophy. Using single-cell RNA sequencing (scRNA-seq) on septal myectomy samples from patients with HCM, we identify functional links between genes, transcription factors, and cell size relevant for HCM. The data show the utility of using scRNA-seq on the human hypertrophic heart, highlight CM heterogeneity, and provide a wealth of insights into molecular events involved in HCM that can eventually contribute to the development of enhanced therapies.

The genetic basis of sudden death in young people - Cardiac and non-cardiac

Sudden death is one of the major causes of death in young adults. Sudden death could be a result from both genetic and environmental or acquired factors. Understanding the genetic etiology is crucial to prevent preventable sudden death for those who are not aware of their genetic condition. In fact, the spectrum of causes of sudden death is complex and varied. In this study, we reviewed the genes that are associated with multiple causes of sudden death in terms of both sudden cardiac death and sudden noncardiac death. A summary of genetic risk factors of the major causes of genetic relevant sudden death is also provided. We believe this review could benefit the researchers who are interested in sudden death genetic studies or the young people who are concerning about their own risk on sudden death.

Sudden cardiac death in sports: could we save Pheidippides?

Hereditary diseases under the age of 35 are the most common underlying heart disease, leading to sudden cardiac death (SCD) in competitive sports, while in older people, atherosclerotic coronary artery disease (CAD) is the main cause. The following preventive measures are recommended: (a) The pre-participation cardiovascular screening, (b) the genetic testing, (c) the use of implantable cardioverter-defibrillator (ICD), (d) the prohibition of doping in sports, (e) the prevention of 'exercise-induced' cardiac complications, (f) the reduction of high-risk factors for CAD, and (g) the use of cardiopulmonary resuscitation. The cost-effectiveness of the electrocardiograms in the pre-participation screening programs remains questionable. Genetic testing is recommended in borderline cases and positive family history. Athletes with ICD can, under certain conditions, participate in competitive sports. Excessive endurance exercise appears to harm the endothelium, promotes inflammatory processes and leads to fibrosis in the myocardium, and calcium deposition in the coronary vessels. Cardiac arrest may be reversed if cardiopulmonary resuscitation is performed and a defibrillator is immediately used. Thus, equipping all fields with automatic external defibrillators are recommended.

Genetic evaluation of cardiomyopathies in Qatar identifies enrichment of pathogenic sarcomere gene variants and possible founder disease mutations in the Arabs

Background

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are serious inherited heart diseases with various causative mutations identified. The full spectrum of causative mutations remains to be discovered, especially in understudied populations.

Methods

Here, we established the DOHA Registry and Biobank for cardiomyopathies in Qatar, followed by sequencing of 174 genes on 51 HCM and 53 DCM patients, and 31 relatives.

Results

In HCM, the analysis of 25 HCM‐associated genes showed that 20% of HCM cases had putative pathogenic variants for cardiomyopathy, mainly in sarcomere genes. Additional 49% of HCM cases had variants of uncertain significance, while 31% of HCM cases had likely benign variant(s) or had no variants identified within the analyzed HCM genes. In DCM, 56 putative DCM genes were analyzed. Eight percent of DCM cases had putative pathogenic variants for DCM, in the TTN gene while 70% of cases had variants of uncertain significance, in the analyzed DCM genes, that will need further pathogenicity assessment. Moreover, 22% of DCM cases remain unexplained, by having likely benign variant(s) or having no variants detected in any of the analyzed DCM genes.

Conclusion

We identified or replicated at least four recurrent variants among cardiomyopathy patients, which could be founder disease mutations in the Arabic population, including a frameshift variant (c.1371_1381dupTATCCAGTTAT) of unknown significance in the FKTN gene which seems to cause DCM in homozygosity, and HCM in heterozygosity. In vivo and/or in vitro functional validation need to be pursued in order to assess the pathogenicity of the identified variants.

The Indices of Cardiovascular Magnetic Resonance Derived Atrial Dynamics May Improve the Contemporary Risk Stratification Algorithms in Children with Hypertrophic Cardiomyopathy

Introduction: The most efficient risk stratification algorithms are expected to deliver robust and indefectible identification of high-risk children with hypertrophic cardiomyopathy (HCM). Here we compare algorithms for risk stratification in primary prevention in HCM children and investigate whether novel indices of biatrial performance improve these algorithms. Methods and Results: The endpoints were defined as sudden cardiac death, resuscitated cardiac arrest, or appropriate implantable cardioverter-defibrillator discharge. We examined the prognostic utility of classic American College of Cardiology/American Heart Association (ACC/AHA) risk factors, the novel HCM Risk-Kids score and the combination of these with indices of biatrial dynamics. The study consisted of 55 HCM children (mean age 12.5 ± 4.6 years, 69.1% males); seven had endpoints (four deaths, three appropriate ICD discharges). A strong trend (DeLong p = 0.08) was observed towards better endpoint identification performance of the HCM Risk-Kids Model compared to the ACC/AHA strategy. Adding the atrial conduit function component significantly improved the prediction capabilities of the AHA/ACC Model (DeLong p = 0.01) and HCM Risk-Kids algorithm (DeLong p = 0.04). Conclusions: The new HCM Risk-Kids individualised algorithm and score was capable of identifying high-risk children with very good accuracy. The inclusion of one of the atrial dynamic indices improved both risk stratification strategies.

Hypertrophic Cardiomyopathy: A Review

A cardiomiopatia hipertrófica (CMH) é a doença cardíaca de origem genética mais comum, cuja principal característica consiste na hipertrofia ventricular esquerda que acontece na ausência de outras patologias que desencadeiam tal alteração. A CMH pode se apresentar desde formas assintomáticas até manifestações de morte cardíaca súbita e de insuficiência cardíaca refratária. Métodos de imagem contemporâneos de alta resolução e escores clínicos mais acurados vêm sendo utilizados e desenvolvidos no sentido de propiciar uma avaliação prognóstica e funcional mais adequada, bem como possibilitar a estratificação dos casos de maior gravidade. Nesta revisão, serão abordados esses aspectos, entre outros tópicos clássicos inerentes ao estudo dessa doença.

Tyrosyl phosphorylation of PZR promotes hypertrophic cardiomyopathy in PTPN11-associated Noonan syndrome with multiple lentigines

Noonan syndrome with multiple lentigines (NSML) is a rare autosomal dominant disorder that presents with cardio-cutaneous-craniofacial defects. Hypertrophic cardiomyopathy (HCM) represents the major life-threatening presentation in NSML. Mutations in the PTPN11 gene that encodes for the protein tyrosine phosphatase (PTP), SHP2, represents the predominant cause of HCM in NSML. NSML-associated PTPN11 mutations render SHP2 catalytically inactive with an "open" conformation. NSML-associated PTPN11 mutations cause hypertyrosyl phosphorylation of the transmembrane glycoprotein, protein zero-related (PZR), resulting in increased SHP2 binding. Here we show that NSML mice harboring a tyrosyl phosphorylation-defective mutant of PZR (NSML/PZRY242F) that is defective for SHP2 binding fail to develop HCM. Enhanced AKT/S6 kinase signaling in heart lysates of NSML mice was reversed in NSML/PZRY242F mice, demonstrating that PZR/SHP2 interactions promote aberrant AKT/S6 kinase activity in NSML. Enhanced PZR tyrosyl phosphorylation in the hearts of NSML mice was found to drive myocardial fibrosis by engaging an Src/NF-κB pathway, resulting in increased activation of IL-6. Increased expression of IL-6 in the hearts of NSML mice was reversed in NSML/PZRY242F mice, and PZRY242F mutant fibroblasts were defective for IL-6 secretion and STAT3-mediated fibrogenesis. These results demonstrate that NSML-associated PTPN11 mutations that induce PZR hypertyrosyl phosphorylation trigger pathophysiological signaling that promotes HCM and cardiac fibrosis.

Sexual dimorphism in cardiac transcriptome associated with a troponin C murine model of hypertrophic cardiomyopathy

Heart disease remains the number one killer of women in the US. Nonetheless, studies in women and female animal models continue to be underrepresented in cardiac research. Hypertrophic cardiomyopathy (HCM), the most commonly inherited cardiac disorder, has been tied to sarcomeric protein variants in both sexes. Among the susceptible genes, TNNC1-encoding cardiac troponin C (cTnC)-causes a substantial HCM phenotype in mice. Mice bearing an HCM-associated cTnC-A8V point mutation exhibited a significant decrease in stroke volume and left ventricular diameter and volume. Importantly, isovolumetric contraction time was significantly higher for female HCM mice. We utilized a transcriptomic approach to investigate the basis underlying the sexual dimorphism observed in the cardiac physiology of adult male and female HCM mice. RNA sequencing revealed several altered canonical pathways within the HCM mice versus WT groups including an increase in eukaryotic initiation factor 2 signaling, integrin-linked kinase signaling, actin nucleation by actin-related protein-Wiskott-Aldrich syndrome family protein complex, regulation of actin-based motility by Rho kinase, vitamin D receptor/retinoid X receptor activation, and glutathione redox reaction pathways. In contrast, valine degradation, tricarboxylic acid cycle II, methionine degradation, and inositol phosphate compound pathways were notably down-regulated in HCM mice. These down-regulated pathways may be reduced in response to altered energetics in the hypertrophied hearts and may represent conservation of energy as the heart is compensating to meet increased contractile demands. HCM male versus female mice followed similar trends of the canonical pathways altered between HCM and WT. In addition, seven of the differentially expressed genes in both WT and HCM male versus female comparisons swapped directions in fold-change between the sexes. These findings suggest a sexually-dimorphic HCM phenotype due to a sarcomeric mutation and pinpoint several key targetable pathways and genes that may provide the means to alleviate the more severe decline in female cardiac function.

Hypertrophic Cardiomyopathy: An Overview of Genetics and Management

Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous cardiac muscle disorder with a diverse natural history, characterized by unexplained left ventricular hypertrophy (LVH), with histopathological hallmarks including myocyte enlargement, myocyte disarray and myocardial fibrosis. Although these features can cause significant cardiac symptoms, many young individuals with HCM are asymptomatic or mildly symptomatic. Sudden cardiac death (SCD) may occur as the initial clinical manifestation. Over the past few decades, HCM has been considered a disease of sarcomere, and typically as an autosomal dominant disease with variable expressivity and incomplete penetrance. Important insights into the genetic landscape of HCM have enhanced our understanding of the molecular pathogenesis, empowered gene-based diagnostic testing to identify at-risk individuals, and offered potential targets for the development of therapeutic agents. This article reviews the current knowledge on the clinical genetics and management of HCM.

Sex Differences at the Time of Myectomy in Hypertrophic Cardiomyopathy

BACKGROUND

One of the first clinically detectable alterations in heart function in hypertrophic cardiomyopathy (HCM) is a decline in diastolic function. Diastolic dysfunction is caused by changes in intrinsic properties of cardiomyocytes or an increase in fibrosis. We investigated whether clinical and cellular parameters of diastolic function are different between male and female patients with HCM at the time of myectomy.

METHODS AND RESULTS

Cardiac tissue from the interventricular septum of patients with HCM (27 women and 44 men) was obtained during myectomy preceded by echocardiography. At myectomy, female patients were 7 years older than male patients and showed more advanced diastolic dysfunction than men evident from significantly higher values for E/e' ratio, left ventricular filling pattern, tricuspid regurgitation velocity, and left atrial diameter indexed for body surface. Whereas most male patients (56%) showed mild (grade I) diastolic dysfunction, 50% of female patients showed grade III diastolic dysfunction. Passive tension in HCM cardiomyocytes was comparable with controls, and myofilament calcium sensitivity was higher in HCM compared with controls, but no sex differences were observed in myofilament function. In female patients with HCM, titin was more compliant, and more fibrosis was present compared with men. Differences between female and male patients with HCM remained significant after correction for age.

CONCLUSIONS

Female patients with HCM are older at the time of myectomy and show greater impairment of diastolic function. Furthermore, left ventricular and left atrial remodeling is increased in women when corrected for body surface area. At a cellular level, HCM women showed increased compliant titin and a larger degree of interstitial fibrosis.

Changes in Biological Pathways During 6,000 Years of Civilization in Europe

The beginning of civilization was a turning point in human evolution. With increasing separation from the natural environment, mankind stimulated new adaptive reactions in response to new environmental factors. In this paper, we describe direct signs of these reactions in the European population during the past 6,000 years. By comparing whole-genome data between Late Neolithic/Bronze Age individuals and modern Europeans, we revealed biological pathways that are significantly differently enriched in nonsynonymous single nucleotide polymorphisms in these two groups and which therefore could be shaped by cultural practices during the past six millennia. They include metabolic transformations, immune response, signal transduction, physical activity, sensory perception, reproduction, and cognitive functions. We demonstrated that these processes were influenced by different types of natural selection. We believe that our study opens new perspectives for more detailed investigations about when and how civilization has been modifying human genomes.

Defining genotype-phenotype relationships in patients with hypertrophic cardiomyopathy using cardiovascular magnetic resonance imaging

PURPOSE

HCM is the most common inherited cardiomyopathy. Historically, there has been poor correlation between genotype and phenotype. However, CMR has the potential to more accurately assess disease phenotype. We characterized phenotype with CMR in a cohort of patients with confirmed HCM and high prevalence of genetic testing.

METHODS

Patients with a diagnosis of HCM, who had undergone contrast-enhanced CMR were identified. Left ventricular mass index (LVMI) and volumes were measured from steady-state free precession sequences. Late gadolinium enhancement (LGE) was quantified using the full width, half maximum method. All patients were prospectively followed for the development of septal reduction therapy, arrhythmia or death.

RESULTS

We included 273 patients, mean age 51.2 ± 15.5, 62.9% male. Of those patients 202 (74.0%) underwent genetic testing with 90 pathogenic, likely pathogenic, or rare variants and 13 variants of uncertain significance identified. Median follow-up was 1138 days. Mean LVMI was 82.7 ± 30.6 and 145 patients had late gadolinium enhancement (LGE). Patients with beta-myosin heavy chain (MYH7) mutations had higher LV ejection fraction (68.8 vs 59.1, p<0.001) than those with cardiac myosin binding protein C (MYBPC3) mutations. Patients with MYBPC3 mutations were more likely to have LVEF < 55% (29.7% vs 4.9%, p = 0.005) or receive a defibrillator than those with MYH7 mutations (54.1% vs 26.8%, p = 0.020).

CONCLUSIONS

We found that patients with MYBPC3 mutations were more likely to have impaired ventricular function and may be more prone to arrhythmic events. Larger studies using CMR phenotyping may be capable of identifying additional characteristics associated with less frequent genetic causes of HCM.

From cell to heart: the impact of the cell organelles dysfunction on heart disease

: Cellular morphology reflects biologic behavior and activity of the tissue and of the organ also reflects the genetic and molecular biology of the cells themselves. This intermediary position places examination of the cell in a key role to our understanding of the innumerable processes that affect this closely knit chain, from molecules to host. A large volume of the cell is occupied by organelles that come in a variety of shapes and sizes. Organelles are dynamic to maintain homeostasis and adjust to the various functions of the cell. The cardiovascular system is metabolically very active and is therefore particularly vulnerable to defects of the cellular substructures, such as the mitochondrial respiratory chain. Given the functional complexity of the cardiovascular system, it is not surprising that defects in cell organelles produce diverse clinical manifestations. Organelle dysfunction is being recognized as the basis of a wide variety of heart diseases. In this review, the authors discuss the relationship between organelle structure and function in myocardial cells and how these organelles have been linked to the cardiovascular diseases.

Hypertrophic Cardiomyopathy: Genetics, Pathogenesis, Clinical Manifestations, Diagnosis, and Therapy

Hypertrophic cardiomyopathy (HCM) is a genetic disorder that is characterized by left ventricular hypertrophy unexplained by secondary causes and a nondilated left ventricle with preserved or increased ejection fraction. It is commonly asymmetrical with the most severe hypertrophy involving the basal interventricular septum. Left ventricular outflow tract obstruction is present at rest in about one third of the patients and can be provoked in another third. The histological features of HCM include myocyte hypertrophy and disarray, as well as interstitial fibrosis. The hypertrophy is also frequently associated with left ventricular diastolic dysfunction. In the majority of patients, HCM has a relatively benign course. However, HCM is also an important cause of sudden cardiac death, particularly in adolescents and young adults. Nonsustained ventricular tachycardia, syncope, a family history of sudden cardiac death, and severe cardiac hypertrophy are major risk factors for sudden cardiac death. This complication can usually be averted by implantation of a cardioverter-defibrillator in appropriate high-risk patients. Atrial fibrillation is also a common complication and is not well tolerated. Mutations in over a dozen genes encoding sarcomere-associated proteins cause HCM. MYH7 and MYBPC3, encoding β-myosin heavy chain and myosin-binding protein C, respectively, are the 2 most common genes involved, together accounting for ≈50% of the HCM families. In ≈40% of HCM patients, the causal genes remain to be identified. Mutations in genes responsible for storage diseases also cause a phenotype resembling HCM (genocopy or phenocopy). The routine applications of genetic testing and preclinical identification of family members represents an important advance. The genetic discoveries have enhanced understanding of the molecular pathogenesis of HCM and have stimulated efforts designed to identify new therapeutic agents.

Myosin Rod Hypophosphorylation and CB Kinetics in Papillary Muscles from a TnC-A8V KI Mouse Model

The cardiac troponin C (TnC)-A8V mutation is associated with hypertrophic and restrictive cardiomyopathy (HCM and RCM) in human and mice. The residue affected lies in the N-helix, a region known to affect Ca²⁺-binding affinity to the N-terminal domain. Here we report on the functional effects of this mutation in skinned papillary muscle fibers from homozygous knock-in TnC-A8V mice. Muscle fibers from left ventricle were activated at 25°C under the ionic conditions of working cardiomyocytes. The pCa-tension relationship showed a 3× increase in Ca²⁺-sensitivity and a decrease (0.8×) in cooperativity (n_H) in mutant fibers. The elementary steps of the cross-bridge (CB) cycle were investigated by sinusoidal analysis. The ATP study revealed that there is no significant change in the affinity of ATP (K₁) for the myosin head. In TnC-A8V mutant fibers, the CB detachment rate (k₂) and its equilibrium constant (K₂) increased (1.5×). The phosphate study revealed that rate constant of the force-generation step (k₄) decreased (0.5×), reversal step (k_-4) increased (2×), and the phosphate-release step (1/K₅) increased (2×). Pro-Q Diamond staining of the skinned fibers samples revealed no significant changes in total phosphorylation of multiple sarcomeric proteins. Further investigation using liquid chromatography-tandem mass spectrometry revealed hypophosphorylation of the rod domain of myosin heavy chain in TnC-A8V mutant fibers compared to wild-type. Immunoblotting confirmed the results observed in the mass spectrometry analysis. The results suggest perturbed CB kinetics-possibly caused by changes in the α-myosin heavy chain phosphorylation profile-as a novel mechanism, to our knowledge, by which a mutation in TnC can have rippling effects in the myofilament and contribute to the pathogenesis of HCM/RCM.

Genetics and Genomics of Single-Gene Cardiovascular Diseases: Common Hereditary Cardiomyopathies as Prototypes of Single-Gene Disorders

This is the first of 2 review papers on genetics and genomics appearing as part of the series on "omics." Genomics pertains to all components of an organism's genes, whereas genetics involves analysis of a specific gene or genes in the context of heredity. The paper provides introductory comments, describes the basis of human genetic diversity, and addresses the phenotypic consequences of genetic variants. Rare variants with large effect sizes are responsible for single-gene disorders, whereas complex polygenic diseases are typically due to multiple genetic variants, each exerting a modest effect size. To illustrate the clinical implications of genetic variants with large effect sizes, 3 common forms of hereditary cardiomyopathies are discussed as prototypic examples of single-gene disorders, including their genetics, clinical manifestations, pathogenesis, and treatment. The genetic basis of complex traits is discussed in a separate paper.

Hypertrophic Cardiomyopathy Cardiac Troponin C Mutations Differentially Affect Slow Skeletal and Cardiac Muscle Regulation

Mutations in TNNC1—the gene encoding cardiac troponin C (cTnC)—that have been associated with hypertrophic cardiomyopathy (HCM) and cardiac dysfunction may also affect Ca²⁺-regulation and function of slow skeletal muscle since the same gene is expressed in both cardiac and slow skeletal muscle. Therefore, we reconstituted rabbit soleus fibers and bovine masseter myofibrils with mutant cTnCs (A8V, C84Y, E134D, and D145E) associated with HCM to investigate their effects on contractile force and ATPase rates, respectively. Previously, we showed that these HCM cTnC mutants, except for E134D, increased the Ca²⁺ sensitivity of force development in cardiac preparations. In the current study, an increase in Ca²⁺ sensitivity of isometric force was only observed for the C84Y mutant when reconstituted in soleus fibers. Incorporation of cTnC C84Y in bovine masseter myofibrils reduced the ATPase activity at saturating [Ca²⁺], whereas, incorporation of cTnC D145E increased the ATPase activity at inhibiting and saturating [Ca²⁺]. We also tested whether reconstitution of cardiac fibers with troponin complexes containing the cTnC mutants and slow skeletal troponin I (ssTnI) could emulate the slow skeletal functional phenotype. Reconstitution of cardiac fibers with troponin complexes containing ssTnI attenuated the Ca²⁺ sensitization of isometric force when cTnC A8V and D145E were present; however, it was enhanced for C84Y. In summary, although the A8V and D145E mutants are present in both muscle types, their functional phenotype is more prominent in cardiac muscle than in slow skeletal muscle, which has implications for the protein-protein interactions within the troponin complex. The C84Y mutant warrants further investigation since it drastically alters the properties of both muscle types and may account for the earlier clinical onset in the proband.

Vps34 regulates myofibril proteostasis to prevent hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common heart disease with a prevalence of 1 in 500 in the general population. Several mutations in genes encoding cardiac proteins have been found in HCM patients, but these changes do not predict occurrence or prognosis and the molecular mechanisms underlying HCM remain largely elusive. Here we show that cardiac expression of vacuolar protein sorting 34 (Vps34) is reduced in a subset of HCM patients. In a mouse model, muscle-specific loss of Vps34 led to HCM-like manifestations and sudden death. Vps34-deficient hearts exhibited abnormal histopathologies, including myofibrillar disarray and aggregates containing αB-crystallin (CryAB). These features result from a block in the ESCRT-mediated proteolysis that normally degrades K63-polyubiquitinated CryAB. CryAB deposition was also found in myocardial specimens from a subset of HCM patients whose hearts showed decreased Vps34. Our results identify disruption of the previously unknown Vps34-CryAB axis as a potentially novel etiology of HCM.

Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype

Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the β-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the “disease of the sarcomere.” The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca²⁺ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.

miR-155 functions downstream of angiotensin II receptor subtype 1 and calcineurin to regulate cardiac hypertrophy

Cardiac hypertrophy is characterized by maladaptive tissue remodeling that may lead to heart failure or sudden death. MicroRNAs (miRs) are negative regulators of angiotensin II and the angiotensin II receptor subtype 1 (AGTR₁), which are two components involved in cardiac hypertrophy. In the present study, the interaction between angiotensin II receptor subtype 1 (AGTR₁) signaling and miR-155 was investigated. Rat H9C2 (2-1) cardiomyocytes were transfected with miR-155 analogues or inhibitors, then stimulated with angiotensin II to induce cardiac hypertrophy. miR-155 expression was revealed to be altered following transfection with chemically-modified miR-155 analogues and inhibitors in rat cardiomyocytes. In cell cardiac hypertrophy models, the cell surface area, AGTR₁, atrial natriuretic peptide and myosin heavy chain-β mRNA expression levels were revealed to be lower in cells stimulated with miR-155 analogue-transfected cells treated with angiotensin II compared with cells stimulated with angiotensin alone (P<0.05), as determined using reverse transcription-polymerase chain reaction (PCR), quantitative PCR and western blot analyses. Furthermore, calcineurin mRNA and protein, intracellular free calcium and nuclear factor of activated T-cells-4 proteins were downregulated in miR-155 analogue-transfected cells treated with angiotensin II, as compared with cells stimulated with angiotensin II alone (P<0.05). In conclusion, the current study indicates that miR-155 may improve cardiac hypertrophy by downregulating AGTR₁ and suppressing the calcium signaling pathways activated by AGTR₁.

Enhanced troponin I binding explains the functional changes produced by the hypertrophic cardiomyopathy mutation A8V of cardiac troponin C

Higher affinity for TnI explains how troponin C (TnC) carrying a causative hypertrophic cardiomyopathy mutation, TnC(A8V), sensitizes muscle cells to Ca(2+). Muscle fibers reconstituted with TnC(A8V) require ∼2.3-fold less [Ca(2+)] to achieve 50% maximum-tension compared to fibers reconstituted with wild-type TnC (TnC(WT)). Binding measurements rule out a significant change in N-terminus Ca(2+)-affinity of isolated TnC(A8V), and TnC(A8V) binds the switch-peptide of troponin-I (TnI(sp)) ∼1.6-fold more strongly than TnC(WT); thus we model the TnC-TnI(sp) interaction as competing with the TnI-actin interaction. Tension data are well-fit by a model constrained to conditions in which the affinity of TnC(A8V) for TnI(sp) is 1.5-1.7-fold higher than that of TnC(WT) at all [Ca(2+)]. Mean ATPase rates of reconstituted cardiac myofibrils is greater for TnC(A8V) than TnC(WT) at all [Ca(2+)], with statistically significant differences in the means at higher [Ca(2+)]. To probe TnC-TnI interaction in low Ca(2+), displacement of bis-ANS from TnI was monitored as a function of TnC. Whereas Ca(2+)-TnC(WT) displaces significantly more bis-ANS than Mg(2+)-TnC(WT), Ca(2+)-TnC(A8V) displaces probe equivalently to Mg(2+)-TnC(A8V) and Ca(2+)-TnC(WT), consistent with stronger Ca(2+)-independent TnC(A8V)-TnI(sp). A Matlab program for computing theoretical activation is reported. Our work suggests that contractility is constantly above normal in hearts made hypertrophic by TnC(A8V).

Cardiac concentric hypertrophy promoted by activated Met receptor is mitigated in vivo by inhibition of Erk1,2 signalling with Pimasertib

Cardiac hypertrophy is a major risk factor for heart failure. Hence, its attenuation represents an important clinical goal. Erk1,2 signalling is pivotal in the cardiac response to stress, suggesting that its inhibition may be a good strategy to revert heart hypertrophy. In this work, we unveiled the events associated with cardiac hypertrophy by means of a transgenic model expressing activated Met receptor. c-Met proto-oncogene encodes for the tyrosine kinase receptor of Hepatocyte growth factor and is a strong inducer of Ras-Raf-Mek-Erk1,2 pathway. We showed that three weeks after the induction of activated Met, the heart presents a remarkable concentric hypertrophy, with no signs of congestive failure and preserved contractility. Cardiac enlargement is accompanied by upregulation of growth-regulating transcription factors, natriuretic peptides, cytoskeletal proteins, and Extracellular Matrix remodelling factors (Timp1 and Pai1). At a later stage, cardiac hypertrophic remodelling results into heart failure with preserved systolic function. Prevention trial by suppressing activated Met showed that cardiac hypertrophy is reversible, and progression to heart failure is prevented. Notably, treatment with Pimasertib, Mek1 inhibitor, attenuates cardiac hypertrophy and remodelling. Our results suggest that modulation of Erk1.2 signalling may constitute a new therapeutic approach for treating cardiac hypertrophies.

Drosophila in the Heart of Understanding Cardiac Diseases: Modeling Channelopathies and Cardiomyopathies in the Fruitfly

Cardiovascular diseases and, among them, channelopathies and cardiomyopathies are a major cause of death worldwide. The molecular and genetic defects underlying these cardiac disorders are complex, leading to a large range of structural and functional heart phenotypes. Identification of molecular and functional mechanisms disrupted by mutations causing channelopathies and cardiomyopathies is essential to understanding the link between an altered gene and clinical phenotype. The development of animal models has been proven to be efficient for functional studies in channelopathies and cardiomyopathies. In particular, the Drosophila model has been largely applied for deciphering the molecular and cellular pathways affected in these inherited cardiac disorders and for identifying their genetic modifiers. Here we review the utility and the main contributions of the fruitfly models for the better understanding of channelopathies and cardiomyopathies. We also discuss the investigated pathological mechanisms and the discoveries of evolutionarily conserved pathways which reinforce the value of Drosophila in modeling human cardiac diseases.

Hypertrophic Cardiomyopathy in Children, Adolescents, and Young Adults Associated With Low Cardiovascular Mortality With Contemporary Management Strategies

Background—

Youthful age has been considered the time of greatest risk for patients with hypertrophic cardiomyopathy (HCM), largely because of the possibility of sudden death. The last 2 decades have witnessed more reliable identification of at-risk patients and utilization of implantable cardioverter-defibrillators for prevention of sudden death, and other contemporary treatment options. Whether such management advances have significantly altered the considerable mortality rate for young HCM patients remains unresolved.

Methods and Results—

We studied long-term outcome in 474 consecutive HCM patients between 7 and 29 years of age presenting at 2 referral institutions. Over 7.1±5.1 years of follow-up (6.0 [3.0, 10.0]), 452 patients (95%) survived, with 95% experiencing no or mild symptoms. HCM-related death occurred in 18 patients (3%; 0.54%/y): arrhythmic sudden death (n=12), progressive heart failure and heart transplant complications (n=5), or postoperatively (n=1). In contrast, aborted life-threatening events occurred in 63 other high-risk patients (13%) with implantable cardioverter-defibrillator interventions for ventricular tachyarrhythmias (n=31), resuscitated out-of-hospital cardiac arrest (n=20), or heart transplant for advanced heart failure (n=12), 1.8%/y, 3-fold higher than HCM mortality. Five- and 10-year survival (considering only HCM deaths) was high (97% and 94%, respectively), virtually identical to that reported in middle-aged adult HCM patients (98% and 94%, P =0.23).

Conclusions—

In a large hospital-based cohort of young HCM patients, representing an age group considered at greatest risk, low mortality rates can be achieved with the application of contemporary cardiovascular treatment strategies, largely because of reliable identification of high-risk patients who benefited from implantable cardioverter-defibrillators for sudden death prevention, thereby creating the opportunity for extended longevity and good quality of life.

Contemporary strategies for risk stratification and prevention of sudden death with the implantable defibrillator in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is regarded as the most common nontraumatic cause of sudden death (SD) in young people (including trained athletes). Introduction of implantable cardioverter-defibrillators (ICD) to HCM 15 years ago represented a new paradigm for clinical practice and probably the most significant advance in management of this disease. ICDs offer protection against SD by terminating potentially lethal ventricular tachyarrhythmias (11%/year secondary and 4%/year primary prevention), although implant decisions are weighed against the possibility of device-related complications (5%/year). ICDs have altered the natural history of HCM, creating the opportunity for extended or normal longevity for many patients. However, assessing SD risk and targeting appropriate candidates for prophylactic device therapy can be compounded by unpredictability of the underlying arrhythmogenic substrate, evident by delays ≥10 years between implant and first ICD intervention. Multiple or a single strong risk marker within the clinical profile of an individual HCM patient can justify consideration for a primary-prevention ICD when combined with physician judgment and shared decision making. The role of the mathematical SD risk score proposed by the European Society of Cardiology to identify patients who benefit from ICD therapy is incompletely resolved. Contemporary treatment interventions and advanced risk stratification using ≥1 conventional markers have served the HCM patient population well, with reduced disease-related mortality rates across all age groups to <1%/year, due largely to the penetration of ICDs into HCM practice. Prevention of SD has now become an integral, albeit challenging, component of HCM management, contributing importantly to its emergence as a contemporary treatable cardiac disease.

Sex-dependent pathophysiological mechanisms in hypertrophic cardiomyopathy: implications for rhythm disorders

Differences in cardiac physiology are seen between men and women in terms of health and disease. Sex differences start to develop at puberty and are maintained during aging. The prevalence of almost all cardiovascular diseases is found to be higher in men than in women, and disease progression tends to be more rapid in male than in female patients. In cohorts of patients with hypertrophic cardiomyopathy (HCM), the most common autosomal inherited cardiac disease, men are overrepresented, suggesting increased penetrance of HCM-causing mutations in male patients. Cardiac remodeling in patients with HCM is higher in men than in women, the same is seen in HCM animal models. Patients with HCM are at increased risk of sudden cardiac death (SCD) and developing rhythm disorders. There seems to be no sex effect on the risk of SCD or arrhythmias in patients with HCM; however, animal studies suggest that certain mutations predispose men to SCD.

Familial cardiomyopathy in Norwegian Forest cats

Norwegian Forest cats (NFCs) are often listed as a breed predisposed to cardiomyopathy, but the characteristics of cardiomyopathy in this breed have not been described. The aim of this preliminary study was to report the features of NFC cardiomyopathy based on prospective echocardiographic screening of affected family groups; necropsy findings; and open-source breed screening databases. Prospective examination of 53 NFCs revealed no murmur or left ventricular (LV) outflow tract obstruction in any screened cat, though mild LV hypertrophy (defined as diastolic LV wall thickness ≥5.5mm) was present in 13/53 cats (25%). Gross pathology results and histopathological sections were analysed in eight NFCs, six of which had died of a cardiac cause. Myocyte hypertrophy, myofibre disarray and interstitial fibrosis typical of hypertrophic cardiomyopathy were present in 7/8 cats, but endomyocardial fibrosis suggestive of restrictive cardiomyopathy was also present in the same cats. Pedigree data analysis from 871 NFCs was supportive of a familial cardiomyopathy in this breed.

Genetics of hypertrophic cardiomyopathy: advances and pitfalls in molecular diagnosis and therapy

Hypertrophic cardiomyopathy (HCM) is a primary disease of the cardiac muscle that occurs mainly due to mutations (>1,400 variants) in genes encoding for the cardiac sarcomere. HCM, the most common familial form of cardiomyopathy, affecting one in every 500 people in the general population, is typically inherited in an autosomal dominant pattern, and presents variable expressivity and age-related penetrance. Due to the morphological and pathological heterogeneity of the disease, the appearance and progression of symptoms is not straightforward. Most HCM patients are asymptomatic, but up to 25% develop significant symptoms, including chest pain and sudden cardiac death. Sudden cardiac death is a dramatic event, since it occurs without warning and mainly in younger people, including trained athletes. Molecular diagnosis of HCM is of the outmost importance, since it may allow detection of subjects carrying mutations on HCM-associated genes before development of clinical symptoms of HCM. However, due to the genetic heterogeneity of HCM, molecular diagnosis is difficult. Currently, there are mainly four techniques used for molecular diagnosis of HCM, including Sanger sequencing, high resolution melting, mutation detection using DNA arrays, and next-generation sequencing techniques. Application of these methods has proven successful for identification of mutations on HCM-related genes. This review summarizes the features of these technologies, highlighting their strengths and weaknesses. Furthermore, current therapeutics for HCM patients are correlated with clinically observed phenotypes and are based on the alleviation of symptoms. This is mainly due to insufficient knowledge on the mechanisms involved in the onset of HCM. Tissue engineering alongside regenerative medicine coupled with nanotherapeutics may allow fulfillment of those gaps, together with screening of novel therapeutic drugs and target delivery systems.

Hypertrophic cardiomyopathy: Can the noninvasive diagnostic testing identify high risk patients?

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death (SCD) in the young, particularly among athletes. Identifying high risk individuals is very important for SCD prevention. The purpose of this review is to stress that noninvasive diagnostic testing is important for risk assessment. Extreme left ventricular hypertrophy and documented ventricular tachycardia and fibrillation increase the risk of SCD. Fragmented QRS and T wave inversion in multiple leads are more common in high risk patients. Cardiac magnetic resonance imaging provides complete visualization of the left ventricular chamber, allowing precise localization of the distribution of hypertrophy and measurement of wall thickness and cardiac mass. Moreover, with late gadolinium enhancement, patchy myocardial fibrosis within the area of hypertrophy can be detected, which is also helpful in risk stratification. Genetic testing is encouraged in all cases, especially in those with a family history of HCM and SCD.

Cardiomyopathies: Evolution of pathogenesis concepts and potential for new therapies

Cardiomyopathies are defined as diseases of the myocardium with associated structural and functional abnormalities. Knowledge of these pathologies for a long period was not clear in clinical practice due to uncertainties regarding definition, classification and clinical diagnosis. In recent decades, major advances have been made in the understanding of the molecular and genetic issues, pathophysiology, and clinical and radiological assessment of the diseases. Progress has been made also in management of several types of cardiomyopathy. Advances in the understanding of these diseases show that cardiomyopathies represent complex entities. Here, special attention is given to evolution of classification of cardiomyopathies, with the aim of assisting clinicians to look beyond schematic diagnostic labels in order to achieve more specific diagnosis. Knowledge of the genotype of cardiomyopathies has changed the pathophysiological understanding of their etiology and clinical course, and has become more important in clinical practice for diagnosis and prevention of cardiomyopathies. New approaches for clinical and prognostic assessment are provided based on contemporary molecular mechanisms of contribution in the pathogenesis of cardiomyopathies. The genotype-phenotype complex approach for assessment improves the clinical evaluation and management strategies of these pathologies. The review covers also the important role of imaging methods, particularly echocardiography, and cardiac magnetic resonance imaging in the evaluation of different types of cardiomyopathies. In summary, this review provides complex presentation of current state of cardiomyopathies from genetics to management aspects for cardiovascular specialists.

Rapid molecular genetic diagnosis of hypertrophic cardiomyopathy by semiconductor sequencing

Background

Rapidly determining the complex genetic basis of Hypertrophic cardiomyopathy (HCM) is vital to better understanding and optimally managing this common polygenetic cardiovascular disease.

Methods

A rapid custom Ion-amplicon-resequencing assay, covering 30 commonly affected genes of HCM, was developed and validated in 120 unrelated patients with HCM to facilitate genetic diagnosis of this disease. With this HCM-specific panel and only 20 ng of input genomic DNA, physicians can, for the first time, go from blood samples to variants within a single day.

Results

On average, this approach gained 595628 mapped reads per sample, 95.51% reads on target (64.06 kb), 490-fold base coverage depth and 93.24% uniformity of base coverage in CDS regions of the 30 HCM genes. After validation, we detected underlying pathogenic variants in 87% (104 of 120) samples. Tested seven randomly selected HCM genes in eight samples by Sanger sequencing, the sensitivity and false-positive-rate of this HCM panel was 100% and 5%, respectively.

Conclusions

This Ion amplicon HCM resequencing assay provides a currently most rapid, comprehensive, cost-effective and reliable measure for genetic diagnosis of HCM in routinely obtained samples.

MYBPC3 in hypertrophic cardiomyopathy: from mutation identification to RNA-based correction

Mutations in MYBPC3 gene, encoding cardiac myosin-binding protein C (cMyBP-C), frequently cause hypertrophic cardiomyopathy (HCM), which affects 0.2 % of the general population. This myocardial autosomal-dominant disorder is the leading cause of sudden cardiac death particularly in young athletes. The current pharmacological and surgical treatments of HCM focus on symptoms relief, but do not address the cause of the disease. With the development of novel strategies targeting the endogenous mutation, causal HCM therapy is now possible. This review will discuss the current knowledge on HCM from the identification of MYBPC3 gene mutations to potential RNA-based correction.

Mitochondrial DNA variations associated with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a primary disorder, characterized by unexplained hypertrophy of the left ventricle that frequently involved in the inter-ventricular septum. Mitochondrial DNA (mtDNA) mutations and haplogroups have been found to be associated with several diseases. Therefore, in the present study, we have sequenced the complete mtDNA of 114 clinically well-characterized HCM patients to look for the role of mtDNA variations and haplogroups in HCM phenotype among Indian patients. Complete mtDNA analysis revealed 28 novel variations, 25 disease-associated and 50 private mutations. We found 13 (11.40%) HCM patients having novel non-synonymous and/or MT-tRNA variations, of which two (m.4797C>M and m.8728T>Y) were in heteroplasmic condition. In silico prediction showed that a few mutations are pathogenic, which may affect the energy production in the heart. Unlike some of the other studies, we did not find association of mitochondrial haplogroup with HCM.

Genetics and sudden death

PURPOSE OF REVIEW

Sudden cardiac death (SCD) affects a significant percentage of young individuals. SCDs are due to genetic heart disorders, such as cardiomyopathies and channelopathies. In the present review, we will describe the recent advancements in understanding the genetic and molecular basis of hereditary cardiac diseases.

RECENT FINDINGS

Considerable progress has been made in identification of new genes associated with monogenic familial arrhythmogenic syndromes, giving the opportunity to delineate their molecular pathogenesis and identify potential targets for therapeutic intervention. Research discoveries and rapidly dropping costs of DNA sequencing technologies have resulted in availability of genetic testing panels.

SUMMARY

Advances in genetic sequencing technology are expected to significantly impact the clinical practice in the near future. Genetic testing represents a powerful tool for cause determination of arrhythmogenic cardiac diseases, efficient screening of family members, possible risk stratification and treatment choices. However, specific expertise is required for rational ordering and correct interpretation of the genetic screening results.

Implanted defibrillators in young hypertrophic cardiomyopathy patients: a multicenter study

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease, with an annual risk of sudden cardiac death (SCD) estimated at 1 %. Limited data are available regarding both the risk of SCD in the young HCM population and the use of implantable cardioverter-defibrillators (ICDs). This retrospective study included all patients with HCM who underwent ICD implantation for primary or secondary prevention of SCD before the age of 30 years at five institutions between 1995 and 2009. There were 99 devices implanted in 73 patients. Appropriate shocks occurred for 11 % of all the patients. None of the previously identified conventional risk factors for SCD in HCM patients were associated with increased risk of appropriate shocks in the young study cohort. During a median follow-up period of 2.4 years, inappropriate shocks occurred for 22 % of the patients. Older age at implant was associated with a decreased risk of inappropriate shock. Those who underwent implantation in the earlier decade had a higher incidence of inappropriate shocks. Late complications including lead fracture or dislodgement, generator malfunction, and infection occurred for 32 % of the patients. Three patients died (4 %), one of whom had an arrhythmic sudden death. A greater proportion of primary prevention implantations was performed for patients from the latter decade. Over time, ICD use in young HCM patients has become increasingly primary prevention oriented. Shock rates mirror those reported in adult series, and there is a substantial incidence of device complications.

Contractile abnormalities and altered drug response in engineered heart tissue from Mybpc3-targeted knock-in mice

Myosin-binding protein C (Mybpc3)-targeted knock-in mice (KI) recapitulate typical aspects of human hypertrophic cardiomyopathy. We evaluated whether these functional alterations can be reproduced in engineered heart tissue (EHT) and yield novel mechanistic information on the function of cMyBP-C. EHTs were generated from cardiac cells of neonatal KI, heterozygous (HET) or wild-type controls (WT) and developed without apparent morphological differences. KI had 70% and HET 20% lower total cMyBP-C levels than WT, accompanied by elevated fetal gene expression. Under standard culture conditions and spontaneous beating, KI EHTs showed more frequent burst beating than WT and occasional tetanic contractions (14/96). Under electrical stimulation (6Hz, 37°C) KI EHTs exhibited shorter contraction and relaxation times and a twofold higher sensitivity to external [Ca(2+)]. Accordingly, the sensitivity to verapamil was 4-fold lower and the response to isoprenaline or the Ca(2+) sensitizer EMD 57033 2- to 4-fold smaller. The loss of EMD effect was verified in 6-week-old KI mice in vivo. HET EHTs were apparently normal under basal conditions, but showed similarly altered contractile responses to [Ca(2+)], verapamil, isoprenaline and EMD. In contrast, drug-induced changes in intracellular Ca(2+) transients (Fura-2) were essentially normal. In conclusion, the present findings in auxotonically contracting EHTs support the idea that cMyBP-C's normal role is to suppress force generation at low intracellular Ca(2+) and stabilize the power-stroke step of the cross bridge cycle. Pharmacological testing in EHT unmasked a disease phenotype in HET. The altered drug response may be clinically relevant.