Hypertrophic cardiomyopathy: genetics and clinical perspectives

Characteristics and pharmacological responsiveness in hiPSC models of inherited cardiomyopathy

Inherited cardiomyopathies are a major cause of heart failure in all age groups, often with an onset in adolescence or early adult life. More than a thousand variants in approximately one hundred genes are associated with cardiomyopathies. Interestingly, many genetic cardiomyopathies display overlapping phenotypical defects in patients, despite the diversity of the initial pathogenic variants. Understanding how the underlying pathophysiology of genetic cardiomyopathies leads to these phenotypes, will improve insights into a patient's disease course and creates the opportunity for conceiving treatment strategies. Moreover, therapeutic strategies can be used to treat multiple cardiomyopathies based on shared phenotypes. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer reliable, high-throughput models for studying molecular and cellular characteristics of hereditary cardiomyopathies. hiPSC-CMs are produced relatively easily, either by directly originating them from patients, or by introducing patient-specific genetic variants in healthy lines. This review evaluates 90 studies on 24 cardiomyopathy-associated genes and systematically summarises the morphological and functional phenotypes observed in hiPSC-CMs. Additionally, treatment strategies applied in cardiomyopathic hiPSC-CMs are compiled and scored for effectiveness. Multiple overlapping phenotypic defects were identified in cardiomyocytes with different variants, whereas certain characteristics were only associated with specific genetic variants. Based on these findings, common mechanisms, therapeutic prospects, and considerations for future research are discussed with the aim to improve clinical translation from hiPSC-CMs to patients.

Spatial QRS-T angle can indicate presence of myocardial fibrosis in pediatric and young adult patients with hypertrophic cardiomyopathy

BACKGROUND

Myocardial fibrosis, expressed as late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMR), is an important risk factor for malignant cardiac events in hypertrophic cardiomyopathy (HCM). However, CMR is not easily available, expensive, also needing intravenous access and contrast.

OBJECTIVE

To determine if derived vectorcardiographic spatial QRS-T angles, an aspect of advanced ECG (A-ECG), can indicate LGE to appropriately prioritize young HCM-patients for CMR.

METHODS

Young patients (age 7-31 years) with clinical HCM (N = 19) or genotype-positive but phenotype-negative (G+ P-) results (N = 6) and nine healthy volunteers were evaluated for LGE by CMR at a single centre between 2011 and 2018. A-ECG was performed within 4 months before and 6 months after CMR and evaluated for spatial mean and peaks QRS-T angles. ECG Risk-score and frontal, two-dimensional QRS-T angle were also calculated from the 12‑lead ECG.

RESULTS

All QRS-T angles were significantly higher in the HCM group with LGE as compared to the HCM group without LGE, and the G+ P- and Healthy groups. Only HCM-patients showed LGE (11/19). The optimal cut-offs for indicating LGE were > 50° for the spatial peaks (AUC = 0.98 [95 %CI 0.95-1.00], sensitivity 100 %, specificity 93 %; p < 0.001), >80° for the spatial mean (AUC = 0.91; p < 0.001), and > 60° for the frontal QRS-T angles (AUC = 0.85; p < 0.001), and > 2 points for an established ECG risk-score (AUC = 0.90, p < 0.001).

CONCLUSION

A spatial peaks QRS-T angle >50° has excellent sensitivity and specificity as a marker of myocardial fibrosis in a young patients with HCM, and can be useful for management and follow-up of such patients.

Myocardial dysfunction caused by MyBPC3 P459fs mutation in hypertrophic cardiomyopathy: evidence from multi-omics approaches and super-resolution imaging

Introduction

Mutations in the sarcomere protein, particularly in cardiac myosin binding protein C gene (MyBPC3), were the most frequent genetic cause of hypertrophic cardiomyopathy (HCM). The pathogenic MyBPC3 P459fs mutation has been reported in HCM patients. However, there was limited knowledge of the structure-function relationships and potential pathways in clinical HCM with MyBPC3 P459fs mutation.

Methods

We used multi-omics approaches and super-resolution imaging to explore the effects of MyBPC3 P459fs mutation on humans and cells. HCM patients carrying MyBPC3 P459fs mutation (MyBPC3-P459fs HCMs) and healthy controls (HCs) were evaluated for myocardial function using both conventional and advanced echocardiography. In parallel, H9C2 myocardial cells infected with either MyBPC3 P459fs mutation (P459fs cells) or its wild type (WT cells) were investigated for myocardial fiber formation and the potential pathways behind this using super-resolution imaging and metabolomics and proteomics.

Results

First, conventional and advanced echocardiography showed that MyBPC3-P459fs HCMs exhibited left ventricular diastolic and systolic dysfunction. Subsequently, super-resolution imaging indicated that P459fs cells formed fewer and shorter myocardial fibers in the cytoplasm compared to WT cells. Moreover, our metabolomic and proteomic data suggested several key components of mitochondrial membrane integrity, myocardial remodeling, myocardial energy metabolism, oxidative stress, inflammation, and actin binding capacity were significantly altered in response to P459fs mutation.

Conclusions

This investigation indicated myocardial dysfunction and myocardial fiber disarray in clinical HCMs with MyBPC3 P459fs mutation and added potential pathways underlying this. These findings provided a link between the observed structural and functional disorders in MyBPC3 P459fs mutation and its onset of HCM pathogenesis and might have a significant translational contribution to effective treatment in HCM patients with MyBPC3 P459fs mutation.

Reassessment and reclassification of variants of unknown significance in patients with cardiomyopathy in a specialist department

BACKGROUND

The utility of diagnostic genetic testing in cardiomyopathy has grown significantly, due to the discovery of novel genes and greater awareness among healthcare professionals. However, a substantial proportion of cases (around 50%) yield no causative genetic variants or have variants of unknown significance (VUS), limiting their use in clinical management and familial screening. The increase in data quantity and quality in reference databases, coupled with variant interpretation guidelines, allows for periodic reanalysis of VUS, potentially reducing diagnostic gaps.

METHODS

This study presents a review of VUS results identified in hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and arrhythmogenic cardiomyopathy (ACM) probands over a 5-year period, using American College of Medical Genetics and Genomics criteria. A total of 248 VUS from 233 reports were reviewed, with the majority of patients with a diagnosis of HCM (n=112), followed by DCM (n=99) and ACM (n=22).

RESULTS

Four (1.6%) VUS showed sufficient evidence to upgrade to likely pathogenic/pathogenic status, while 8 (3.2%) were downgraded to benign. The majority 236 (95.2%) remained VUS after reanalysis, of which 12 (4.7%) had potential to reclassification to benign or likely pathogenic/pathogenic depending on further data.

CONCLUSION

The study emphasises the importance of periodic re-evaluation of VUS results for clinical management of probands as well as cascade testing. We show feasibility of conducting reclassification analysis in a referral centre, but highlight the need for ongoing collaboration between clinical and laboratory experts. Our work supports the current recommendation of reclassification every 3-5 years to keep pace with evolving evidence.

The Future of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 Gene Therapy in Cardiomyopathies: A Review of Its Therapeutic Potential and Emerging Applications

Cardiomyopathies, among the leading causes of heart failure and sudden cardiac death, are often driven by genetic mutations affecting the heart's structural proteins. Despite significant advancements in understanding the genetic basis of hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and arrhythmogenic right ventricular cardiomyopathy (ARVC), effective long-term therapies remain limited. The advent of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) gene editing offers a promising therapeutic strategy to address these genetic disorders at their root. CRISPR-Cas9 enables precise modification of pathogenic variants (PVs) in genes encoding sarcomeric and desmosomal proteins, which are frequently implicated in cardiomyopathies. By inducing site-specific double-stranded breaks in DNA, followed by repair through nonhomologous end joining (NHEJ) or homology-directed repair (HDR), this system allows for targeted correction of mutations. In preclinical models, CRISPR-Cas9 has shown promise in correcting HCM-associated mutations in β-myosin heavy chain 7 (MYH7), preventing disease phenotypes such as ventricular hypertrophy and myocardial fibrosis. Similarly, gene editing has successfully rectified DCM-linked mutations in Titin (TTN) and LMNA, resulting in improved heart function and reduced pathological remodeling. For ARVC, CRISPR-Cas9 has demonstrated the ability to repair mutations in desmosomal genes such as plakophilin 2 (PKP2), thereby restoring normal cardiac function and cellular adhesion. Despite these successes, challenges remain, including mosaicism, delivery efficiency, and off-target effects. Nevertheless, CRISPR-Cas9 represents a transformative approach to treating genetic cardiomyopathies, potentially offering long-lasting cures by directly addressing their underlying genetic causes.

Understanding Genetic Screening: Harnessing Health Information to Prevent Disease Risks

Genetic screening analyzes an individual's genetic information to assess disease risk and provide personalized health recommendations. This article introduces the public to genetic screening, explaining its definition, principles, history, and common types, including prenatal, newborn, adult disease risk, cancer, and pharmacogenetic screening. It elaborates on the benefits of genetic screening, such as early risk detection, personalized prevention, family risk assessment, and reproductive decision-making. The article also notes limitations, including result interpretation uncertainty, psychological and ethical issues, and privacy and discrimination risks. It provides advice on selecting suitable screening, consulting professionals, choosing reliable institutions, and understanding screening purposes and limitations. Finally, it discusses applying screening results through lifestyle adjustments, regular check-ups, and preventive treatments. By comprehensively introducing genetic screening, the article aims to raise public awareness and encourage utilizing this technology to prevent disease and maintain health.

Electrocardiographic Findings in Genotype-Positive and Non-sarcomeric Children with Definite Hypertrophic Cardiomyopathy and Subclinical Variant Carriers

In children with hypertrophic cardiomyopathy (HCM), the genotype-phenotype association of abnormal electrocardiographic (ECG) features in the backdrop of gene positivity has not been well described. This study aimed to describe the abnormal ECG findings in children with HCM harboring who have genetic variants and determine the association with major adverse cardiac events (MACE). We retrospectively analyzed 81 variants-positive, phenotype-positive (V+P+), 66 variant-positive, phenotype-negative (V+P-), and 85 non-sarcomeric subjects. We analyzed ECG findings and clinical outcomes in the three groups of subjects. Repolarization abnormalities (ST and T wave changes) and pathologic Q waves were the most common abnormalities in variant and non-sarcomeric subjects. The V+P+ group showed higher occurrence of ST segment changes and T wave abnormalities compared to V+P- group. Independent predictors of MACE included ST segment changes (OR 3.54, CI 1.20-10.47, p = 0.022). T wave changes alone did not predict outcome (OR 2.13, CI 0.75-6.07, p = 0.157), but combined repolarization abnormalities (ST+T changes) were strong predictors of MACE (OR 5.84, CI 1.43-23.7, p = 0.014) than ST segment changes alone. Maximal wall z score by echocardiography was a predictor of MACE (OR 1.21, CI 1.07-1.37, p = 0.002). Despite the presence of significant myocardial hypertrophy (z score > 4.7), voltage criteria for LVH were much less predictive. In the non-sarcomeric group, RVH was significantly associated with MACE (OR 3.85, CI 1.08-13.73, p = 0.038). These abnormal ECG findings described on the platform of known genetic status and known myocardial hypertrophy may add incremental value to the diagnosis and surveillance of disease progression in children with HCM. Select ECG findings, particularly repolarization abnormalities, may serve as predictors of MACE in children.

MYBPC3 D389V Variant Induces Hypercontractility in Cardiac Organoids

MYBPC3, encoding cardiac myosin binding protein-C (cMyBP-C), is the most mutated gene known to cause hypertrophic cardiomyopathy (HCM). However, since little is known about the underlying etiology, additional in vitro studies are crucial to defining the underlying molecular mechanisms. Accordingly, this study aimed to investigate the molecular mechanisms underlying the pathogenesis of HCM associated with a polymorphic variant (D389V) in MYBPC3 by using isogenic human-induced pluripotent stem cell (hiPSC)-derived cardiac organoids (hCOs). The hiPSC-derived cardiomyocytes (hiPSC-CMs) and hCOs were generated from human subjects to define the molecular, cellular, functional, and energetic changes caused by the MYBPC3D389V variant, which is associated with increased fractional shortening and highly prevalent in South Asian descendants. Recombinant C0-C2, N' region of cMyBP-C (wild-type and D389V), and myosin S2 proteins were also utilized to perform binding and motility assays in vitro. Confocal and electron microscopic analyses of hCOs generated from noncarriers (NC) and carriers of the MYBPC3D389V variant revealed the presence of highly organized sarcomeres. Furthermore, functional experiments showed hypercontractility, faster calcium cycling, and faster contractile kinetics in hCOs expressing MYBPC3D389V than NC hCOs. Interestingly, significantly increased cMyBP-C phosphorylation in MYBPC3D389V hCOs was observed, but without changes in total protein levels, in addition to higher oxidative stress and lower mitochondrial membrane potential (ΔΨm). Next, spatial mapping revealed the presence of endothelial cells, fibroblasts, macrophages, immune cells, and cardiomyocytes in the hCOs. The hypercontractile function was significantly improved after the treatment of the myosin inhibitor mavacamten (CAMZYOS®) in MYBPC3D389V hCOs. Lastly, various vitro binding assays revealed a significant loss of affinity in the presence of MYBPC3D389V with myosin S2 region as a likely mechanism for hypercontraction. Conceptually, we showed the feasibility of assessing the functional and molecular mechanisms of HCM using highly translatable hCOs through pragmatic experiments that led to determining the MYBPC3D389V hypercontractile phenotype, which was rescued by the administration of a myosin inhibitor.

The synergistic protective effects of paeoniflorin and β-ecdysterone against cardiac hypertrophy through suppressing oxidative stress and ferroptosis

Exploring feasible drugs for the treatment of pathological cardiac hypertrophy has always been a focus of cardiovascular disease research. Paeoniflorin (PF) and β-Ecdysterone (β-Ecd) are the main active components of Paeonia lactiflora and Achyranthes bidentata, which can be used for the treatment of cardiovascular diseases, but their mechanism of action remains unclear. This study focused on oxidative stress and ferroptosis to investigate the protective effects of PF and β-Ecd on cardiac hypertrophy in primary cardiomyocytes and C57BL/6 mice, utilizing the integration of CCK8 assays, ROS detection, molecular docking, real-time quantitative PCR, western blot, immunofluorescence, etc. The result of combination indices demonstrated a significant synergistic protective effect of PF and β-Ecd on cardiac hypertrophy. Furthermore, in vitro and in vivo studies further showed that the combination of PF and β-Ecd could improve the abnormalities of cell surface area, ANP, β-MHC, MDA, SOD, calcium ion, mitochondrial membrane potential and so on induced by cardiac hypertrophy through the inhibition effects of oxidative stress and iron metabolism, which might be closely related to the impact on the Nrf2/HO-1 and SLC7A11/GPX4 pathways. Altogether, this work revealed the mechanism of the combination of PF and β-Ecd in the treatment of cardiac hypertrophy from the aspects of suppressing oxidative stress and ferroptosis, aiming to promote effective treatment of the disease and the clinical application of PF and β-Ecd.

A Machine Learning Approach to Gene Expression in Hypertrophic Cardiomyopathy

BACKGROUND/OBJECTIVES

Hypertrophic cardiomyopathy (HCM) is a common heart disorder characterized by the thickening of the heart muscle, particularly in the left ventricle, which increases the risk of cardiac complications. This study aims to analyze the expression of apoptosis-regulating genes (CASP8, CASP9, CASP3, BAX, and BCL2) in blood samples from HCM patients, to better understand their potential as biomarkers for disease progression.

METHODS

Quantitative real-time PCR (qPCR) was used to evaluate gene expression in blood samples from 93 HCM patients. The correlation between apoptosis-regulating genes was conducted and clinical parameters were integrated for feature importance and clustering analysis.

RESULTS

Most patients exhibited significant downregulation of CASP8, CASP9, and CASP3. In contrast, BAX expression was elevated in 71 out of 93 patients, while BCL2 was increased in 55 out of 93 patients. Correlation analysis revealed weak negative correlations between the BAX/BCL2 ratio and CASP gene expression.

CONCLUSIONS

These findings suggest that reduced expression of apoptotic genes may indicate a protective cellular mechanism, which could serve as a biomarker for disease progression. Further studies are needed to investigate the potential for therapeutic modulation of these pathways to improve patient outcomes.

Toward the latest advancements in cardiac regeneration using induced pluripotent stem cells (iPSCs) technology: approaches and challenges

A novel approach to treating heart failures was developed with the introduction of iPSC technology. Knowledge in regenerative medicine, developmental biology, and the identification of illnesses at the cellular level has exploded since the discovery of iPSCs. One of the most frequent causes of mortality associated with cardiovascular disease is the loss of cardiomyocytes (CMs), followed by heart failure. A possible treatment for heart failure involves restoring cardiac function and replacing damaged tissue with healthy, regenerated CMs. Significant strides in stem cell biology during the last ten years have transformed the in vitro study of human illness and enhanced our knowledge of the molecular pathways underlying human disease, regenerative medicine, and drug development. We seek to examine iPSC advancements in disease modeling, drug discovery, iPSC-Based cell treatments, and purification methods in this article.

The Role of S-Glutathionylation in Health and Disease: A Bird's Eye View

Protein glutathionylation is a reversible post-translational modification that involves the attachment of glutathione to cysteine residues. It plays a role in the regulation of several cellular processes and protection against oxidative damage. Glutathionylation (GS-ylation) modulates protein function, inhibits or enhances enzymatic activity, maintains redox homeostasis, and shields several proteins from irreversible oxidative stress. Aberrant GS-ylation patterns are thus implicated in various diseases, particularly those associated with oxidative stress and inflammation, such as cardiovascular diseases, neurodegenerative disorders, cancer, and many others. Research in the recent years has highlighted the potential to manipulate protein GS-ylation for therapeutic purposes with strategies that imply both its enhancement and inhibition according to different cases. Moreover, it has become increasingly evident that monitoring the GS-ylation status of selected proteins offers diagnostic potential in different diseases. In this review, we try to summarize recent research in the field with a focus on our current understanding of the molecular mechanisms related to aberrant protein GS-ylation.

Hypertrophic Cardiomyopathy

PURPOSE OF REVIEW

Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac condition with potential for severe complications including sudden cardiac death. Early diagnosis allows appropriate risk stratification and prompt intervention to minimise the potential for adverse outcomes. The implications of poorly coordinated screening are significant, either missing relatives at high-risk or burdening low-risk individuals with a diagnosis associated with reduced life expectancy. We aim to guide clinicians through the diagnostic pathway through to novel treatment options. Several conditions mimic the condition, and we discuss the phenocopies and how to differentiate from HCM.

RECENT FINDINGS

We summarise the latest developments informing clinical decision making in the modern era of myosin inhibitors and future gene editing therapies. Early identification will enable prompt referral to specialist centres. A diagnostic flowchart is included, to guide the general cardiology and heart failure clinician in important decision making regarding the care of the HCM patient and importantly their relatives at risk. We have highlighted the importance of screening because genotype-positive/phenotype-negative patients are likely to have the most to gain from novel therapies.

Modeling cardiomyocyte signaling and metabolism predicts genotype-to-phenotype mechanisms in hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (HCM) is a significant precursor of heart failure and sudden cardiac death, primarily caused by mutations in sarcomeric and structural proteins. Despite the extensive research on the HCM genotype, the complex and context-specific nature of many signaling and metabolic pathways linking the HCM genotype to phenotype has hindered therapeutic advancements for patients. Here, we have developed a computational model of HCM encompassing cardiomyocyte signaling and metabolic networks and their associated interactions. Utilizing a stochastic logic-based ODE approach, we linked cardiomyocyte signaling to the metabolic network through a gene regulatory network and post-translational modifications. We validated the model against published data on activities of signaling species in the HCM context and transcriptomes of two HCM mouse models (i.e., R403Q-αMyHC and R92W-TnT). Our model predicts that HCM mutation induces changes in metabolic functions such as ATP synthase deficiency and a transition from fatty acids to carbohydrate metabolism. The model indicated major shifts in glutamine-related metabolism and increased apoptosis after HCM-induced ATP synthase deficiency. We predicted that the transcription factors STAT, SRF, GATA4, TP53, and FoxO are the key regulators of cardiomyocyte hypertrophy and apoptosis in HCM in alignment with experiments. Moreover, we identified shared (e.g., activation of PGC1α by AMPK, and FHL1 by titin) and context-specific mechanisms (e.g., regulation of Ca2+ sensitivity by titin in HCM patients) that may control genotype-to-phenotype transition in HCM across different species or mutations. We also predicted potential combination drug targets for HCM (e.g., mavacamten plus ROS inhibitors) preventing or reversing HCM phenotype (i.e., hypertrophic growth, apoptosis, and metabolic remodeling) in cardiomyocytes. This study provides new insights into mechanisms linking genotype to phenotype in familial hypertrophic cardiomyopathy and offers a framework for assessing new treatments and exploring variations in HCM experimental models.

MYBPC3 D389V Variant Induces Hypercontractility in Cardiac Organoids

BACKGROUND

MYBPC3 , encoding cardiac myosin binding protein-C (cMyBP-C), is the most mutated gene known to cause hypertrophic cardiomyopathy (HCM). However, since little is known about the underlying etiology, additional in vitro studies are crucial to defining the underlying molecular mechanisms. Accordingly, this study aimed to investigate the molecular mechanisms underlying the pathogenesis of HCM associated with a polymorphic variant (D389V) in MYBPC3 by using human-induced pluripotent stem cell (hiPSC)-derived cardiac organoids (hCOs).

METHODS

The hiPSC-derived cardiomyocytes (hiPSC-CMs) and hCOs were generated from human subjects to define the molecular, cellular, and functional changes caused by the MYBPC3 D389V variant. This variant is associated with increased fractional shortening and is highly prevalent in South Asian descendants. Recombinant C0-C2, N'-region of cMyBP-C (wildtype and D389V), and myosin S2 proteins were also utilized to perform binding and motility assays in vitro .

RESULTS

Confocal and electron microscopic analyses of hCOs generated from noncarriers (NC) and carriers of the MYBPC3 D389V variant revealed the presence of highly organized sarcomeres. Furthermore, functional experiments showed hypercontractility with increased contraction velocity, faster calcium cycling, and faster contractile kinetics in hCOs expressing MYBPC3 D389V than NC hCOs. Interestingly, significantly increased cMyBP-C phosphorylation in MYBPC3 D389V hCOs was observed, but without changes in total protein levels, in addition to higher oxidative stress and lower mitochondrial membrane potential (ΔΨm). Next, spatial mapping revealed the presence of endothelial cells, fibroblasts, macrophages, immune cells, and cardiomyocytes in the hCOs. The hypercontractile function was significantly improved after treatment with the myosin inhibitor mavacamten (CAMZYOS®) in MYBPC3 D389V hCOs. Lastly, various in vitro binding assays revealed a significant loss of affinity in the presence of MYBPC3 D389V with myosin S2 region as a likely mechanism for hypercontraction.

CONCLUSIONS

Conceptually, we showed the feasibility of assessing the functional and molecular mechanisms of HCM using highly translatable hCOs through pragmatic experiments that led to determining the MYBPC3 D389V hypercontractile phenotype, which was rescued by administration of a myosin inhibitor. Novelty and Significance: What Is Known?: MYBPC3 mutations have been implicated in hypertrophic cardiomyopathy. D389V is a polymorphic variant of MYBPC3 predicted to be present in 53000 US South Asians owing to the founder effect. D389V carriers have shown evidence of hyperdynamic heart, and human-induced pluripotent stem cells (hiPSC)-derived cardiomyocytes with D389V show cellular hypertrophy and irregular calcium transients. The molecular mechanism by which the D389V variant develops pathological cardiac dysfunction remains to be conclusively determined.What New Information Does This Article Contribute ?: The authors leveraged a highly translational cardiac organoid model to explore the role of altered cardiac calcium handling and cardiac contractility as a common pathway leading to pathophysiological phenotypes in patients with early HCM. The MYBPC3 D389V -mediated pathological pathway is first studied here by comparing functional properties using three-dimensional cardiac organoids differentiated from hiPSC and determining the presence of hypercontraction. Our data demonstrate that faster sarcomere kinetics resulting from lower binding affinity between D389V-mutated cMyBP-C protein and myosin S2, as evidenced by in vitro studies, could cause hypercontractility which was rescued by administration of mavacamten (CAMZYOS®), a myosin inhibitor. In addition, hypercontractility causes secondary mitochondrial defects such as higher oxidative stress and lower mitochondrial membrane potential (ΔΨm), highlighting a possible early adaptive response to primary sarcomeric changes. Early treatment of MYBPC3 D389V carriers with mavacamten may prevent or reduce early HCM-related pathology. GRAPHICAL ABSTRACT: A graphical abstract is available for this article.

Genetic Mutations and Mitochondrial Redox Signaling as Modulating Factors in Hypertrophic Cardiomyopathy: A Scoping Review

Hypertrophic cardiomyopathy (HCM) is a heart condition characterized by cellular and metabolic dysfunction, with mitochondrial dysfunction playing a crucial role. Although the direct relationship between genetic mutations and mitochondrial dysfunction remains unclear, targeting mitochondrial dysfunction presents promising opportunities for treatment, as there are currently no effective treatments available for HCM. This review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extension for Scoping Reviews guidelines. Searches were conducted in databases such as PubMed, Embase, and Scopus up to September 2023 using "MESH terms". Bibliographic references from pertinent articles were also included. Hypertrophic cardiomyopathy (HCM) is influenced by ionic homeostasis, cardiac tissue remodeling, metabolic balance, genetic mutations, reactive oxygen species regulation, and mitochondrial dysfunction. The latter is a common factor regardless of the cause and is linked to intracellular calcium handling, energetic and oxidative stress, and HCM-induced hypertrophy. Hypertrophic cardiomyopathy treatments focus on symptom management and complication prevention. Targeted therapeutic approaches, such as improving mitochondrial bioenergetics, are being explored. This includes coenzyme Q and elamipretide therapies and metabolic strategies like therapeutic ketosis. Understanding the biomolecular, genetic, and mitochondrial mechanisms underlying HCM is crucial for developing new therapeutic modalities.

Advances in Hypertrophic Cardiomyopathy Disease Modelling Using hiPSC-Derived Cardiomyocytes

The advent of human induced pluripotent stem cells (hiPSCs) and their capacity to be differentiated into beating human cardiomyocytes (CMs) in vitro has revolutionized human disease modelling, genotype-phenotype predictions, and therapeutic testing. Hypertrophic cardiomyopathy (HCM) is a common inherited cardiomyopathy and the leading known cause of sudden cardiac arrest in young adults and athletes. On a molecular level, HCM is often driven by single pathogenic genetic variants, usually in sarcomeric proteins, that can alter the mechanical, electrical, signalling, and transcriptional properties of the cell. A deeper knowledge of these alterations is critical to better understanding HCM manifestation, progression, and treatment. Leveraging hiPSC-CMs to investigate the molecular mechanisms driving HCM presents a unique opportunity to dissect the consequences of genetic variants in a sophisticated and controlled manner. In this review, we summarize the molecular underpinnings of HCM and the role of hiPSC-CM studies in advancing our understanding, and we highlight the advances in hiPSC-CM-based modelling of HCM, including maturation, contractility, multiomics, and genome editing, with the notable exception of electrophysiology, which has been previously covered.

Biomarkers and Proteomics in Sarcomeric Hypertrophic Cardiomyopathy in the Young-FGF-21 Highly Associated with Overt Disease

Background: Any difference in biomarkers between genotype-positive individuals with overt hypertrophic cardiomyopathy (HCM), and genotype-positive but phenotype-negative individuals (G+P-) in HCM-associated pathways might shed light on pathophysiological mechanisms. We studied this in young HCM patients. Methods: 29 HCM patients, 17 G+P--individuals, and age- and sex-matched controls were prospectively included. We analyzed 184 cardiovascular disease-associated proteins by two proximity extension assays, categorized into biological pathways, and analyzed with multivariate logistic regression analysis. Significant proteins were dichotomized into groups above/below median concentration in control group. Results: Dichotomized values of significant proteins showed high odds ratio (OR) in overt HCMphenotype for Fibroblast growth factor-21 (FGF-21) 10 (p = 0.001), P-selectin glycoprotein ligand-1 (PSGL-1) OR 8.6 (p = 0.005), and Galectin-9 (Gal-9) OR 5.91 (p = 0.004). For G+P-, however, angiopoietin-1 receptor (TIE2) was notably raised, OR 65.5 (p = 0.004), whereas metalloproteinase inhibitor 4 (TIMP4) involved in proteolysis, in contrast, had reduced OR 0.06 (p = 0.013). Conclusions: This study is one of the first in young HCM patients and G+P- individuals. We found significantly increased OR for HCM in FGF-21 involved in RAS-MAPK pathway, associated with cardiomyocyte hypertrophy. Upregulation of FGF-21 indicates involvement of the RAS-MAPK pathway in HCM regardless of genetic background, which is a novel finding.

Myosin folding boosts solubility in cardiac muscle sarcomeres

The polymerization of myosin molecules into thick filaments in muscle sarcomeres is essential for cardiac contractility, with the attenuation of interactions between the heads of myosin molecules within the filaments being proposed to result in hypercontractility, as observed in hypertrophic cardiomyopathy (HCM). However, experimental evidence demonstrates that the structure of these giant macromolecular complexes is highly dynamic, with molecules exchanging between the filaments and a pool of soluble molecules on the minute timescale. Therefore, we sought to test the hypothesis that the enhancement of interactions between the heads of myosin molecules within thick filaments limits the mobility of myosin by taking advantage of mavacamten, a small molecule approved for the treatment of HCM. Myosin molecules were labeled in vivo with a green fluorescent protein (GFP) and imaged in intact hearts using multiphoton microscopy. Treatment of the intact hearts with mavacamten resulted in an unexpected > 5-fold enhancement in GFP-myosin mobility within the sarcomere. In vitro biochemical assays suggested that mavacamten enhanced the mobility of GFP-myosin by increasing the solubility of myosin molecules, through the stabilization of a compact/folded conformation of the molecules, once disassociated from the thick filaments. These findings provide alternative insight into the mechanisms by which molecules exchange into and out of thick filaments and have implications for how mavacamten may affect cardiac contractility.

Fever Unveiling a Hidden Cardiac Condition: A Case of Pediatric Hypertrophic Obstructive Cardiomyopathy

This case report presents the clinical management of a 18-month-old female child who presented with fever, cough, and cold symptoms for eight days. Despite initial treatment with antipyretic syrup, the persistence of symptoms prompted further evaluation, revealing signs of hypertrophic obstructive cardiomyopathy (HOCM) on echocardiography. The patient was subsequently initiated on beta-blocker therapy and supportive care, leading to clinical improvement and eventual discharge. This case underscores the importance of considering cardiac etiologies in pediatric patients presenting with nonspecific symptoms. It highlights the role of timely diagnosis and multidisciplinary management in optimizing outcomes for affected individuals. Further research and awareness efforts are warranted to enhance diagnostic capabilities and refine treatment strategies for pediatric cardiac conditions like HOCM.

A Case Report of a Clinically Suspected Diagnosis of Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS) Syndrome With Cardiac Impairment

This case report presents a description of a hypertrophic left ventricle with reduced ejection fraction in a man in his mid-twenties with clinical, radiologic, and biochemical features of a rare syndrome called mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). A literature review of this uncommon syndrome and MELAS cardiomyopathy has been conducted.

Hypertrophic cardiomyopathy in MYBPC3 carriers in aging

Hypertrophic cardiomyopathy (HCM) is characterized by abnormal thickening of the myocardium, leading to arrhythmias, heart failure, and elevated risk of sudden cardiac death, particularly among the young. This inherited disease is predominantly caused by mutations in sarcomeric genes, among which those in the cardiac myosin binding protein-C3 (MYBPC3) gene are major contributors. HCM associated with MYBPC3 mutations usually presents in the elderly and ranges from asymptomatic to symptomatic forms, affecting numerous cardiac functions and presenting significant health risks with a spectrum of clinical manifestations. Regulation of MYBPC3 expression involves various transcriptional and translational mechanisms, yet the destiny of mutant MYBPC3 mRNA and protein in late-onset HCM remains unclear. Pathogenesis related to MYBPC3 mutations includes nonsense-mediated decay, alternative splicing, and ubiquitin-proteasome system events, leading to allelic imbalance and haploinsufficiency. Aging further exacerbates the severity of HCM in carriers of MYBPC3 mutations. Advancements in high-throughput omics techniques have identified crucial molecular events and regulatory disruptions in cardiomyocytes expressing MYBPC3 variants. This review assesses the pathogenic mechanisms that promote late-onset HCM through the lens of transcriptional, post-transcriptional, and post-translational modulation of MYBPC3, underscoring its significance in HCM across carriers. The review also evaluates the influence of aging on these processes and MYBPC3 levels during HCM pathogenesis in the elderly. While pinpointing targets for novel medical interventions to conserve cardiac function remains challenging, the emergence of personalized omics offers promising avenues for future HCM treatments, particularly for late-onset cases.

The Definition of Sarcomeric and Non-Sarcomeric Gene Mutations in Hypertrophic Cardiomyopathy Patients: A Multicenter Diagnostic Study Across Türkiye

BACKGROUND

Hypertrophic cardiomyopathy is a common genetic heart disease and up to 40%-60% of patients have mutations in cardiac sarcomere protein genes. This genetic diagnosis study aimed to detect pathogenic or likely pathogenic sarcomeric and non-sarcomeric gene mutations and to confirm a final molecular diagnosis in patients diagnosed with hypertrophic cardiomyopathy.

METHODS

A total of 392 patients with hypertrophic cardiomyopathy were included in this nationwide multicenter study conducted at 23 centers across Türkiye. All samples were analyzed with a 17-gene hypertrophic cardiomyopathy panel using next-generation sequencing technology. The gene panel includes ACTC1, DES, FLNC, GLA, LAMP2, MYBPC3, MYH7, MYL2, MYL3, PLN, PRKAG2, PTPN11, TNNC1, TNNI3, TNNT2, TPM1, and TTR genes.

RESULTS

The next-generation sequencing panel identified positive genetic variants (variants of unknown significance, likely pathogenic or pathogenic) in 12 genes for 121 of 392 samples, including sarcomeric gene mutations in 30.4% (119/392) of samples tested, galactosidase alpha variants in 0.5% (2/392) of samples and TTR variant in 0.025% (1/392). The likely pathogenic or pathogenic variants identified in 69 (57.0%) of 121 positive samples yielded a confirmed molecular diagnosis. The diagnostic yield was 17.1% (15.8% for hypertrophic cardiomyopathy variants) for hypertrophic cardiomyopathy and hypertrophic cardiomyopathy phenocopies and 0.5% for Fabry disease.

CONCLUSIONS

Our study showed that the distribution of genetic mutations, the prevalence of Fabry disease, and TTR amyloidosis in the Turkish population diagnosed with hypertrophic cardiomyopathy were similar to the other populations, but the percentage of sarcomeric gene mutations was slightly lower.

Myocardial Fibrosis in Hypertrophic Cardiomyopathy: A Perspective from Fibroblasts

Hypertrophic cardiomyopathy (HCM) is the most common inherited heart disease and the leading cause of sudden cardiac death in young people. Mutations in genes that encode structural proteins of the cardiac sarcomere are the more frequent genetic cause of HCM. The disease is characterized by cardiomyocyte hypertrophy and myocardial fibrosis, which is defined as the excessive deposition of extracellular matrix proteins, mainly collagen I and III, in the myocardium. The development of fibrotic tissue in the heart adversely affects cardiac function. In this review, we discuss the latest evidence on how cardiac fibrosis is promoted, the role of cardiac fibroblasts, their interaction with cardiomyocytes, and their activation via the TGF-β pathway, the primary intracellular signalling pathway regulating extracellular matrix turnover. Finally, we summarize new findings on profibrotic genes as well as genetic and non-genetic factors involved in the pathophysiology of HCM.

Medical Therapies to Improve Left Ventricular Outflow Obstruction and Diastolic Function in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy-both obstructive hypertrophic cardiomyopathy (oHCM) and nonobstructive hypertrophic cardiomyopathy (nHCM) subtypes-is the most common monogenic cardiomyopathy. Its structural hallmarks are abnormal thickening of the myocardium and hyperdynamic contractility, while its hemodynamic consequences are left ventricular outflow tract or intracavitary obstruction (in oHCM) and diastolic dysfunction (in both oHCM and nHCM). Several medical therapies are routinely used to improve these abnormalities with the goal to decrease symptom burden in patients with HCM. Current guidelines recommend nonvasodilating beta blockers as first-line and nondihydropyridine calcium channel blockers followed by disopyramide as second- and third-line medical therapies for symptomatic oHCM and give weaker recommendations for beta blockers and calcium channel blockers in nHCM. These recommendations are based on small studies-mostly nonrandomized-and expert opinion. Our review will summarize the available data on the effectiveness of commonly prescribed medications used in oHCM and nHCM to uncover knowledge gaps, but also new data on cardiac myosin inhibitors.

Cardiac Remodeling and Functional Changes in Patients With Hypertrophic Cardiomyopathy: A Longitudinal Observational Study

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a hereditary cardiac disorder characterized by abnormal thickening of the left ventricular myocardium. This can lead to various clinical manifestations, including sudden death.

AIM

To investigate the cardiac remodeling and functional changes in patients with HCM over a specific time period and explore the impact of different treatment regimens on disease progression.

METHODS

We conducted a prospective longitudinal observational study involving 100 patients diagnosed with HCM. Baseline clinical data, including demographics, medical history, and echocardiographic measurements, were collected. Follow-up assessments were performed at regular intervals over 24 months to track changes in cardiac structure, function, and clinical status. Statistical analysis, including paired t-tests and subgroup analysis, was conducted to identify significant associations and differences between treatment groups.

RESULTS

A total of 100 patients (mean age = 55 years, 50% male) were enrolled in the study. At baseline, echocardiography revealed increased left ventricular wall thickness (mean = 18.5 mm), left atrial dimensions (mean = 39 mm), and ventricular mass (mean = 230 g). During the follow-up period, there was a progressive increase in left ventricular wall thickness (mean change = 1.0 mm/year, p < 0.001), left atrial dimensions (mean change = 3.0 mm/year, p < 0.001), and ventricular mass (mean change = 8 g/year, p = 0.003). Additionally, alterations in diastolic and systolic function parameters were noted, with a decline in E/A ratio (mean change = -0.1 units/year, p = 0.008) and a reduction in ejection fraction (mean change = -2.0% per year, p = 0.001).

CONCLUSION

Our longitudinal observational study provides important insights into the cardiac remodeling and functional changes in patients with HCM over time. The progressive increase in cardiac parameters indicates ongoing disease progression. Additionally, beta-blocker therapy was associated with a slower rate of left ventricular wall thickening. These findings contribute to a better understanding of HCM's natural history and may guide targeted therapeutic approaches to improve patient outcomes.

Hypertrophic Cardiomyopathy: Genetic Foundations, Outcomes, Interconnections, and Their Modifiers

Hypertrophic cardiomyopathy (HCM) is the most prevalent heritable cardiomyopathy. HCM is considered to be caused by mutations in cardiac sarcomeric protein genes. Recent research suggests that the genetic foundation of HCM is much more complex than originally postulated. The clinical presentations of HCM are very variable. Some mutation carriers remain asymptomatic, while others develop severe HCM, terminal heart failure, or sudden cardiac death. Heterogeneity regarding both genetic mutations and the clinical course of HCM hinders the establishment of universal genotype-phenotype correlations. However, some trends have been identified. The presence of a mutation in some genes encoding sarcomeric proteins is associated with earlier HCM onset, more severe left ventricular hypertrophy, and worse clinical outcomes. There is a diversity in the mechanisms implicated in the pathogenesis of HCM. They may be classified into groups, but they are interrelated. The lack of known supplementary elements that control the progression of HCM indicates that molecular mechanisms that exist between genotype and clinical presentations may be crucial. Secondary molecular changes in pathways implicated in HCM pathogenesis, post-translational protein modifications, and epigenetic factors affect HCM phenotypes. Cardiac loading conditions, exercise, hypertension, diet, alcohol consumption, microbial infection, obstructive sleep apnea, obesity, and environmental factors are non-molecular aspects that change the HCM phenotype. Many mechanisms are implicated in the course of HCM. They are mostly interconnected and contribute to some extent to final outcomes.

Sarcomeric gene variants among Indians with hypertrophic cardiomyopathy: A scoping review

Hypertrophic cardiomyopathy (HCM) is a genetic heart muscle disease that frequently causes sudden cardiac death (SCD) among young adults. Several pathogenic mutations in genes encoding the cardiac sarcomere have been identified as diagnostic factors for HCM and proposed as prognostic markers for SCD. The objective of this review was to determine the scope of available literature on the variants encoding sarcomere proteins associated with SCD reported among Indian patients with HCM. The eligibility criteria for the scoping review included full text articles that reported the results of genetic screening for sarcomeric gene mutations in HCM patients of Indian south Asian ancestry. We systematically reviewed studies from the databases of Medline, Scopus, Web of Science core collection and Google Scholar. The electronic search strategy included a combination of generic terms related to genetics, disease and population. The protocol of the study was registered with Open Science Framework (https://osf.io/53gde/). A total of 19 articles were identified that reported pathogenic or likely pathogenic (P/LP) variants within MYH7, MYBPC3, TNNT2, TNNI3 and TPM1 genes, that included 16 singletons, one de novo and one digenic mutation (MYH7/ TPM1) associated with SCD among Indian patients. Evidence from functional studies and familial segregation implied a plausible mechanistic role of these P/LP variants in HCM pathology. This scoping review has compiled all the P/LP variants reported to-date among Indian patients and summarized their association with SCD. Single homozygous, de novo and digenic mutations were observed to be associated with severe phenotypes compared to single heterozygous mutations. The abstracted genetic information was updated with reference sequence ID (rsIDs) and compiled into freely accessible HCMvar database, available at https://hcmvar.heartfailure.org.in/. This can be used as a population specific genetic database for reference by clinicians and researchers involved in the identification of diagnostic and prognostic markers for HCM.

Case report: Diagnosis of apical hypertrophic cardiomyopathy that escaped clinical and echocardiographic investigations for twenty years: Reasons and clinical implications

BACKGROUND

Apical hypertrophic cardiomyopathy (ApHCM) is a rare form of hypertrophic cardiomyopathy which predominantly affects the apex of the left ventricle. The diagnosis can be challenging due to several factors, ranging from no typical clinical and electrocardiogram (EKG) findings to potential difficulties in executing and interpreting the echocardiographic examination.

CASE PRESENTATION

We report the case of an 84-year-old woman who came to our echo-lab to undergo a routine echocardiogram. She had a history of permanent atrial fibrillation, paced rhythm and previous episodes of heart failure (HF), allegedly explained by a diagnosis of hypertensive heart disease that had been confirmed many times over the previous 20 years. The clinical examination and the EKG were unremarkable. The echocardiographic images were poor quality. But a senior cardiologist, expert in imaging and echocardiography, noted the lack of delineation of the endocardial border of the left ventricular (LV) apex region. Contrast echocardiography was performed and severe apical hypertrophy discovered.

CONCLUSION

ApHCM can be a challenging diagnosis. Contrast echocardiography must always be applied in cases of poor delineation of the LV apical endocardial border at baseline echocardiography. Timely detection and appropriate lifestyle intervention might slow the development of LV hypertrophy, and possibly minimize and delay heart failure (HF) related symptoms and arrhythmias. The prognosis remains relatively benign during long term follow-up.

CRISPR gene-editing therapies for hypertrophic cardiomyopathy

Pre-symptomatic gene editing in preclinical models of hypertrophic cardiomyopathy show therapeutic promise; clinical studies are now needed to assess safety and efficacy in humans.

Lineage-specific regulatory changes in hypertrophic cardiomyopathy unraveled by single-nucleus RNA-seq and spatial transcriptomics

Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder characterized by cardiomyocyte hypertrophy and cardiac fibrosis. Pathological cardiac remodeling in the myocardium of HCM patients may progress to heart failure. An in-depth elucidation of the lineage-specific changes in pathological cardiac remodeling of HCM is pivotal for the development of therapies to mitigate the progression. Here, we performed single-nucleus RNA-seq of the cardiac tissues from HCM patients or healthy donors and conducted spatial transcriptomic assays on tissue sections from patients. Unbiased clustering of 55,122 nuclei from HCM and healthy conditions revealed 9 cell lineages and 28 clusters. Lineage-specific changes in gene expression, subpopulation composition, and intercellular communication in HCM were discovered through comparative analyses. According to the results of pseudotime ordering, differential expression analysis, and differential regulatory network analysis, potential key genes during the transition towards a failing state of cardiomyocytes such as FGF12, IL31RA, and CREB5 were identified. Transcriptomic dynamics underlying cardiac fibroblast activation were also uncovered, and potential key genes involved in cardiac fibrosis were obtained such as AEBP1, RUNX1, MEOX1, LEF1, and NRXN3. Using the spatial transcriptomic data, spatial activity patterns of the candidate genes, pathways, and subpopulations were confirmed on patient tissue sections. Moreover, we showed experimental evidence that in vitro knockdown of AEBP1 could promote the activation of human cardiac fibroblasts, and overexpression of AEBP1 could attenuate the TGFβ-induced activation. Our study provided a comprehensive analysis of the lineage-specific regulatory changes in HCM, which laid the foundation for targeted drug development in HCM.

Assisted Da Vinci robotic surgery combined with 3D printing technology applied in septal myectomy

Generally, the standard surgical route of Morrow begins with the incision of median sternal, which leads to more trauma, pains and discomforts to patients with hypertrophic obstructive cardiomyopathy (HOCM). It is more difficult and rough to perform the competed resection of hypertrophic myocardium due to complicated anatomical morphology of left ventricular outflow tract and limited visual field of left ventricle during surgery. As the novel surgical strategy, firstly, under the guiding of 3D printing technology, the platform of effective preoperative evaluation focusing on how to resect the hypertrophic myocardium is established. Then, combined with assisted Da Vinci robotic surgery system, the outcome of patient with HOCM is positive and promised.

A Case Report on the Atypical Presentation of Hypertrophic Cardiomyopathy (HOCM) in a 19-Year-Old Female

Atypical hypertrophic cardiomyopathy (HOCM) is a relatively rare genetic disorder that can affect the left ventricular system. HOCM can lead to various cardiac issues such as sudden cardiac death (SCD). We report a case of a 19-year-old female who was referred to a cardiology clinic after presenting with bi-ventricular hypertrophy on an echocardiogram (ECHO). Results from screening tests for infiltrative diseases and an iron panel came negative. The patient was asymptomatic, with no functional limitations and no family history of any cardiac disease or sudden death. In conclusion, HOCM can present with an atypical pattern, such as biventricular hypertrophy, and has been linked to SCD; therefore, it is important to be aware of this condition and take the necessary precautions to prevent it.

Mavacamten: A First-in-class Oral Modulator of Cardiac Myosin for the Treatment of Symptomatic Hypertrophic Obstructive Cardiomyopathy

Hypertrophic cardiomyopathy is the most common monogenic cardiovascular disease that is caused by sarcomeric protein gene mutations. A hallmark of the most common form of the disease is outflow obstruction secondary to systolic narrowing of the left ventricular outflow tract from septal hypertrophy, mitral valve abnormalities and, most importantly, hyperdynamic contractility. Recent mechanistic studies have identified excessive myosin adenosine triphosphatase activation and actin-myosin cross-bridging as major underlying causes. These studies have led to the development of mavacamten, a first-in-class myosin adenosine triphosphatase inhibitor and the first specific therapy for hypertrophic obstructive cardiomyopathy. Preclinical and subsequent pivotal clinical studies have demonstrated the efficacy and safety of mavacamten. A remarkable improvement among treated patients in peak oxygen consumption, functional capacity, symptom relief and post-exercise left ventricular outflow tract gradient, along with dramatic reductions in heart failure biomarkers, suggests that this new medication will be transformative for the symptom management of hypertrophic obstructive cardiomyopathy. There is also hope and early evidence that mavacamten may delay or obviate the need for invasive septal reduction therapies. In this article, we review the current evidence for the efficacy and safety of mavacamten and highlight important considerations for its clinical use.

Left ventricular remodeling following septal myectomy in hypertrophic obstructive cardiomyopathy

Objectives

The purpose of this study is to determine whether or not left ventricular remodeling can be induced after septal myectomy in patients with obstructive hypertrophic cardiomyopathy, and if so, how it occurs, using gated cardiac computed tomography.

Methods

Fifty patients with hypertrophic obstructive cardiomyopathy who underwent septal myectomy along the septal band between March 2016 and July 2020 were retrospectively reviewed. Recent consecutive 19 patients underwent postoperative cardiac computed tomography. In these patients, volumes of the septal band and thickness of 17 left ventricular myocardial segments were measured to determine the changes after surgery.

Results

The resection volume predicted by preoperative computed tomography and the actual resection volume were 6.7 ± 3.3 mL and 6.4 ± 2.7 mL. In-hospital mortality was 0%. Moderate or greater mitral valve regurgitation and systolic anterior motion decreased from 56% to 6% and 86% to 6%, respectively. Median preoperative ventricular septal thickness and left ventricular outflow tract pressure gradient at rest decreased from 20.0 mm (interquartile range, 17.0-24.0 mm) and 74.0 mm Hg (interquartile range, 42.5-92.5 mm Hg) to 14.0 mm (interquartile range, 11.5-16.0 mm) and 15.5 mm Hg (interquartile range, 12.1-21.5 mm Hg), respectively. Postoperative computed tomography confirmed a reduction in septal band volume of 5.7 ± 2.8 mL. Total left ventricular myocardial volume was reduced by 12.9 ± 8.8 mL, which exceeded the volume reduction of the resected septal band. All segments except the basal inferior and basal inferolateral regions showed a significant decrease in wall thickness by a median of 6.4%.

Conclusions

Properly performed septal myectomy may induce remodeling of the entire left ventricle, not just the resected area.

Clinical significance of genetic variation in hypertrophic cardiomyopathy: comparison of computational tools to prioritize missense variants

Hypertrophic cardiomyopathy (HCM) is a common heart disease associated with sudden cardiac death. Early diagnosis is critical to identify patients who may benefit from implantable cardioverter defibrillator therapy. Although genetic testing is an integral part of the clinical evaluation and management of patients with HCM and their families, in many cases the genetic analysis fails to identify a disease-causing mutation. This is in part due to difficulties in classifying newly detected rare genetic variants as well as variants-of-unknown-significance (VUS). Multiple computational algorithms have been developed to predict the potential pathogenicity of genetic variants, but their relative performance in HCM has not been comprehensively assessed. Here, we compared the performance of 39 currently available prediction tools in distinguishing between high-confidence HCM-causing missense variants and benign variants, and we developed an easy-to-use-tool to perform variant prediction benchmarks based on annotated VCF files (VETA). Our results show that tool performance increases after HCM-specific calibration of thresholds. After excluding potential biases due to circularity type I issues, we identified ClinPred, MISTIC, FATHMM, MPC and MetaLR as the five best performer tools in discriminating HCM-associated variants. We propose combining these tools in order to prioritize unknown HCM missense variants that should be closely followed-up in the clinic.

Ventricular arrhythmia and sudden cardiac death in hypertrophic cardiomyopathy: From bench to bedside

Patients with hypertrophic cardiomyopathy (HCM) mostly experience minimal symptoms throughout their lifetime, and some individuals have an increased risk of ventricular arrhythmias and sudden cardiac death (SCD). How to identify patients with a higher risk of ventricular arrythmias and SCD is the priority in HCM research. The American College of Cardiology/American Heart Association (ACC/AHA) and the European Society of Cardiology (ESC) both recommend the use of risk algorithms to identify patients at high risk of ventricular arrhythmias, to be selected for implantation of implantable cardioverters/defibrillators (ICDs) for primary prevention of SCD, although major discrepancies exist. The present SCD risk scoring systems cannot accurately identify early-stage HCM patients with modest structural remodeling and mild disease manifestations. Unfortunately, SCD events could occur in young asymptomatic HCM patients and even as initial symptoms, prompting the determination of new risk factors for SCD. This review summarizes the studies based on patients' surgical specimens, transgenic animals, and patient-derived induced pluripotent stem cells (hiPSCs) to explore the possible molecular mechanism of ventricular arrhythmia and SCD. Ion channel remodeling, Ca2+ homeostasis abnormalities, and increased myofilament Ca2+ sensitivity may contribute to changes in action potential duration (APD), reentry circuit formation, and trigger activities, such as early aferdepolarization (EAD) or delayed afterdepolarization (DAD), leading to ventricular arrhythmia in HCM. Besides the ICD implantation, novel drugs represented by the late sodium current channel inhibitor and myosin inhibitor also shed light on the prevention of HCM-related arrhythmias. The ideal prevention strategy of SCD in early-stage HCM patients needs to be combined with gene screening, hiPSC-CM testing, machine learning, and advanced ECG studies, thus achieving individualized SCD prevention.

Cardiac myosin binding protein-C variants in paediatric-onset hypertrophic cardiomyopathy: natural history and clinical outcomes

BACKGROUND

Variants in the cardiac myosin-binding protein C gene (MYBPC3) are a common cause of hypertrophic cardiomyopathy (HCM) in adults and have been associated with late-onset disease, but there are limited data on their role in paediatric-onset HCM. The objective of this study was to describe natural history and clinical outcomes in a large cohort of children with HCM and pathogenic/likely pathogenic (P/LP) MYBPC3 variants.

METHODS AND RESULTS

Longitudinal data from 62 consecutive patients diagnosed with HCM under 18 years of age and carrying at least one P/LP MYBPC3 variant were collected from a single specialist referral centre. The primary patient outcome was a major adverse cardiac event (MACE). Median age at diagnosis was 10 (IQR: 2-14) years, with 12 patients (19.4%) diagnosed in infancy. Forty-seven (75%) were boy and 31 (50%) were probands. Median length of follow-up was 3.1 (IQR: 1.6-6.9) years. Nine patients (14.5%) experienced an MACE during follow-up and five (8%) died. Twenty patients (32.3%) had evidence of ventricular arrhythmia, including 6 patients (9.7%) presenting with out-of-hospital cardiac arrest. Five-year freedom from MACE for those with a single or two MYBPC3 variants was 95.2% (95% CI: 78.6% to 98.5%) and 68.4% (95% CI: 40.6% to 88.9%), respectively (HR 4.65, 95% CI: 1.16 to 18.66, p=0.03).

CONCLUSIONS

MYBPC3 variants can cause childhood-onset disease, which is frequently associated with life-threatening ventricular arrhythmia. Clinical outcomes in this cohort vary substantially from aetiologically and genetically mixed paediatric HCM cohorts described previously, highlighting the importance of identifying specific genetic subtypes for clinical management of childhood HCM.

SUMO2-mediated SUMOylation of SH3GLB1 promotes ionizing radiation-induced hypertrophic cardiomyopathy through mitophagy activation

Hypertrophic cardiomyopathy (HC) is characterized by the enlargement of individual cardiomyocytes, which is a typical pathophysiological process that occurs in various cardiovascular diseases. Ionizing radiation (IR) is an important independent risk factor for hypertrophic cardiomyopathy, but the underlying molecular mechanism is still unclear. In the present study, we aimed to clarify the role of IR in promoting cardiac hypertrophy and investigate the mechanism by which the SUMO2-mediated SUMOylation of SH3GLB1 affects mitophagy in IR-induced cardiac hypertrophy. In vivo, IR promoted cardiac hypertrophy by activating mitophagy. In vitro, IR upregulated PINK1 and Parkin protein expression and damaged mitochondrial morphological structure. We further demonstrated that SH3GLB1 deficiency inhibited mitophagy activation and restored mitochondrial cristae, revealing a regulatory role of SH3GLB1 in cardiac hypertrophy. IR promoted interactions between SH3GLB1 and mitochondrial membrane proteins, such as MFN1/2, TOM20 and Drp1, further indicating that the mechanism by which SH3GLB1 functions in cardiac hypertrophy might involve mitophagy. A bioinformatics prediction found that SUMO2 could SUMOylate SH3GLB1 at position K82. Consistent with this finding, both co-IP assays and laser confocal microscopy showed that IR promoted the interaction and colocalization of SUMO2 and SH3GLB1. In summary, our study identifies IR as an important factor that promotes hypertrophic cardiomyopathy by accelerating the activation of mitophagy through the SUMO2-mediated SUMOylation of SH3GLB1; thus, IR exerts dual therapeutic effects in the treatment of thoracic tumours with long-term radiotherapy. Additionally, this study provides novel treatment strategies and targets for preventing the hypertrophic cardiomyopathy caused by thoracic tumour radiotherapy. Furthermore, SH3GLB1 may be a promising experimental target for the development of strategies for treating cardiovascular diseases caused by IR.

Metabolite Signature in the Carriers of Pathogenic Genetic Variants for Cardiomyopathy: A Population-Based METSIM Study

Hypertrophic (HCM) and dilated (DCM) cardiomyopathies are among the leading causes of sudden cardiac death. We identified 38 pathogenic or likely pathogenic variant carriers for HCM in three sarcomere genes (MYH7, MYBPC3, TPMI) among 9.928 participants of the METSIM Study having whole exome sequencing data available. Eight of them had a clinical diagnosis of HCM. We also identified 20 pathogenic or likely pathogenic variant carriers for DCM in the TTN gene, and six of them had a clinical diagnosis of DCM. The aim of our study was to investigate the metabolite signature in the carriers of the pathogenic or likely pathogenic genetic variants for HCM and DCM, compared to age- and body-mass-index-matched controls. Our novel findings were that the carriers of pathogenic or likely pathogenic variants for HCM had significantly increased concentrations of bradykinin (des-arg 9), vanillactate, and dimethylglycine and decreased concentrations of polysaturated fatty acids (PUFAs) and lysophosphatidylcholines compared with the controls without HCM. Additionally, our novel findings were that the carriers of pathogenic or likely pathogenic variants for DCM had significantly decreased concentrations of 1,5-anhydrogluticol, histidine betaine, N-acetyltryptophan, and methylsuccinate and increased concentrations of trans-4-hydroxyproline compared to the controls without DCM. Our population-based study shows that the metabolite signature of the genetic variants for HCM and DCM includes several novel metabolic pathways not previously described.

Case Report: Two New Cases of Autosomal-Recessive Hypertrophic Cardiomyopathy Associated With TRIM63-Compound Heterozygous Variant

Hypertrophic cardiomyopathy (HCM) is one of the most common hereditary diseases, and it is associated with fatal complications. The clinical heterogeneity of HCM requires risk prediction models to identify patients at a high risk of adverse events. Most HCM cases are caused by mutations in genes encoding sarcomere proteins. However, HCM is associated with rare genetic variants with limited data about its clinical course and prognosis, and existing risk prediction models are not validated for such patients' cohorts. TRIM63 is one of the rare genes recently described as a cause of HCM with autosomal-recessive inheritance. Herein, we present two cases of HCM associated with TRIM63-compound heterozygous variants in young male sportsmen. They demonstrated progressively marked hypertrophy, advanced diastolic dysfunction, a significant degree of fibrosis detected by magnetic resonance imaging, and clear indications for implantable cardioverter-defibrillator. One of the cases includes the first description of TRIM63-HCM with extreme hypertrophy. The presented cases are discussed in light of molecular consequences that might underlie cardiac and muscle phenotype in patients with mutations of TRIM63, the master regulator of striated muscle mass.

Myofibril orientation as a metric for characterizing heart disease

Myocyte disarray is a hallmark of many cardiac disorders. However, the relationship between alterations in the orientation of individual myofibrils and myofilaments to disease progression has been largely underexplored. This oversight has predominantly been because of a paucity of methods for objective and quantitative analysis. Here, we introduce a novel, less-biased approach to quantify myofibrillar and myofilament orientation in cardiac muscle under near-physiological conditions and demonstrate its superiority as compared with conventional histological assessments. Using small-angle x-ray diffraction, we first investigated changes in myofibrillar orientation at increasing sarcomere lengths in permeabilized, relaxed, wild-type mouse myocardium from the left ventricle by assessing the angular spread of the 1,0 equatorial reflection (angle σ). At a sarcomere length of 1.9 μm, the angle σ was 0.23 ± 0.01 rad, decreased to 0.19 ± 0.01 rad at a sarcomere length of 2.1 μm, and further decreased to 0.15 ± 0.01 rad at a sarcomere length of 2.3 μm (p < 0.0001). Angle σ was significantly larger in R403Q, a MYH7 hypertrophic cardiomyopathy model, porcine myocardium (0.24 ± 0.01 rad) compared with wild-type myocardium (0.14 ± 0.005 rad; p < 0.0001), as well as in human heart failure tissue (0.19 ± 0.006 rad) when compared with nonfailing samples (0.17 ± 0.007 rad; p = 0.01). These data indicate that diseased myocardium suffers from greater myofibrillar disorientation compared with healthy controls. Finally, we showed that conventional, histology-based analysis of disarray can be subject to user bias and/or sampling error and lead to false positives. Our method for directly assessing myofibrillar orientation avoids the artifacts introduced by conventional histological approaches that assess myocyte orientation and only indirectly evaluate myofibrillar orientation, and provides a precise and objective metric for phenotypically characterizing myocardium. The ability to obtain excellent x-ray diffraction patterns from frozen human myocardium provides a new tool for investigating structural anomalies associated with cardiac diseases.

Correlation between markers of fibrosis and myocardial remodeling in patients with various course of hypertrophic cardiomyopathy

Aim. To assess the relationship between fibrosis markers and structural and functional parameters in patients with various types of hypertrophic cardiomyopathy (HCM).

Material and methods. This prospective comparative non-randomized study included 49 patients with HCM. Patients were divided into 3 groups according to the disease course: group 1  — stable course (n=12; men, 8 (67%), mean age ‒ 41±12 years); group 2 — progressive course (n=26; men, men, 16 (61%). mean age — 57±11 years); group 3 — patients with atrial fibrillation (AF) (n=11; men, 4 (36%), mean age — 63±6 years). Patients underwent standard clinical and paraclinical investigations. The levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinases-1 (TIMP-1) were determined in all patients using enzyme-linked immunosorbent assay in blood serum.

Results. In all patients with HCM, elevated levels of MMP-9 and TIMP-1 are noted compared to the reference values. In group 1, the MMP-9 level [Me (Q1; Q3)] was 226 (201;271) ng/ml; TIMP-1 — 410 (267;488) ng/ml; in group 2, the MMP-9 level was 236 (187;285) ng/ml; TIMP-1 — 421 (321;499) ng/ml. In the course with AF, the MMP-9 level was 260 (228;296) ng/ml, while TIMP-1 — 381,5 (305;466) ng/ml; no significant difference was revealed (p=0,59; p=0,90, respectively). A correlation was found between age and MMP-9 levels, as well as between MMP-9 levels and left atrial volume (p=0,034; p=0,035, respectively).

Conclusion. The high activity of matrix metalloproteinases and their tissue inhibitors reflects enhanced fibrosis and myocardial remodeling in HCM, which is especially characteristic of patients with AF.

 

Hypertrophic Cardiomyopathy in the Elderly: A Case Identified With Genetic Screening

Hypertrophic cardiomyopathy (HCM) is a hereditary disease with an autosomal dominant pattern of inheritance, that is caused by a mutation in one of several sarcomere genes that encodes components of the contractile system of the heart. Hypertrophic cardiomyopathy has been described as a disease that is more heavily diagnosed in the second decade of life, that may present with abnormal syncopal episodes or sudden cardiac death. However, with a better understanding of the genetic changes that occur in HCM and with improved imaging techniques, there has now been an increased recognition of a late-onset disease that can occur in the elderly population. We report a case of a 73-year-old woman who was found to have HCM after various clinical events took place.

Identification of atrial-enriched lncRNA Walras linked to cardiomyocyte cytoarchitecture and atrial fibrillation

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in humans. Genetic and genomic analyses have recently demonstrated that the homeobox transcription factor Pitx2 plays a fundamental role regulating expression of distinct growth factors, microRNAs and ion channels leading to morphological and molecular alterations that promote the onset of AF. Here we address the plausible contribution of long non-coding (lnc)RNAs within the Pitx2>Wnt>miRNA signaling pathway. In silico analyses of annotated lncRNAs in the vicinity of the Pitx2, Wnt8 and Wnt11 chromosomal loci identified five novel lncRNAs with differential expression during cardiac development. Importantly, three of them, Walaa, Walras, and Wallrd, are evolutionarily conserved in humans and displayed preferential atrial expression during embryogenesis. In addition, Walrad displayed moderate expression during embryogenesis but was more abundant in the right atrium. Walaa, Walras and Wallrd were distinctly regulated by Pitx2, Wnt8, and Wnt11, and Wallrd was severely elevated in conditional atrium-specific Pitx2-deficient mice. Furthermore, pro-arrhythmogenic and pro-hypertrophic substrate administration to primary cardiomyocyte cell cultures consistently modulate expression of these lncRNAs, supporting distinct modulatory roles of the AF cardiovascular risk factors in the regulation of these lncRNAs. Walras affinity pulldown assays revealed its association with distinct cytoplasmic and nuclear proteins previously involved in cardiac pathophysiology, while loss-of-function assays further support a pivotal role of this lncRNA in cytoskeletal organization. We propose that lncRNAs Walaa, Walras and Wallrd, distinctly regulated by Pitx2>Wnt>miRNA signaling and pro-arrhythmogenic and pro-hypertrophic factors, are implicated in atrial arrhythmogenesis, and Walras additionally in cardiomyocyte cytoarchitecture.

Identification and verification of promising diagnostic biomarkers in patients with hypertrophic cardiomyopathy associate with immune cell infiltration characteristics

AIMS

To explore immune cell infiltration characteristics of, and hub genes associated with, hypertrophic cardiomyopathy (HCM).

MATERIALS AND METHODS

The GSE130036 dataset was downloaded and the differentially expressed genes (DEGs) were identified. The DEGs were analyzed via the CIBERSORT algorithm to understand the composition of 22 immune cell types between the HCM and normal myocardial tissue specimens. Weighted gene co-expression network analysis (WGCNA) was performed to segregate the DEGs into several modules and explore correlation between the key modules and specific immune cells enriched in the myocardial tissues of HCM patients. The biofunctional and disease enrichment of the genes among the modules was explored, and hub genes serving as potential biomarkers of HCM were identified. These genes were validated by GSE36961 dataset, and the discrimination ability was assessed by receiver operating characteristic curve analysis.

KEY FINDINGS

CIBERSORT analysis showed that neutrophils and B-cells (naive and memory B-cells) were highly abundant in HCM samples, while macrophages (M0, M1, M2) were highly abundant in normal samples. WGCNA analysis of the DEGs yielded seven modules, and the gray and yellow modules were strongly associated with neutrophils and B-cells, and with macrophages, respectively. Yellow module genes were mainly functional in immune and inflammation processes. Gray module genes were mainly functional in the transportation of intercellular substances. SLITRK4 and CD163 showed a notably high area under the curve values in both datasets and may serve as potential biomarkers for HCM.

SIGNIFICANCE

SLITRK4 and CD163 may be promising Diagnostic Biomarkers of Hypertrophic Cardiomyopathy.

Identification and Verification of Feature Immune-Related Genes in Patients With Hypertrophic Cardiomyopathy Based on Bioinformatics Analyses

Objective: To identify feature immune-related genes (IRGs) in patients with hypertrophic cardiomyopathy (HCM) and verify their ability to diagnose HCM.

Methods: The GSE160997 dataset on cardiac tissue from 18 HCM patients and 5 controls was downloaded from the Gene Expression Omnibus database. A false discovery rate <0.05 and |log2 fold change| >1 were the filters applied to identify the differentially expressed genes (DEGs). The differentially expressed IRGs were the intersection results between the DEGs and an IRG dataset from the IMMPORT database. The protein-protein interaction network of differentially expressed IRGs was constructed, and the top 20 hub genes with the most adjacent nodes in the network were selected. The least absolute shrinkage and selection operator regression algorithm and a random forest algorithm were used to identify the feature IRGs as biomarkers that were then verified against GSE36961.

Results: A total of 1079 DEGs were identified in GSE160997. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses indicated that immune-related mechanisms play an important role in the pathogenesis of HCM. A total of 121 differentially expressed IRGs were identified, and 5 feature IRGs were selected, 4 of which were confirmed as potential biomarkers of HCM by external verification with excellent discrimination ability. A diagnosis model of HCM based on the four feature IRGs was developed and visualized as a nomogram with a C-index of 0.925 (95% confidence interval 0.869–0.981).

Conclusion: Our study identified four feature IRGs as biomarkers for the diagnosis of HCM, offering an innovative perspective of the underlying immune-related pathological molecular mechanisms.

Compound Mutation in Cardiac Sarcomere Proteins Is Associated with Increased Risk for Major Arrhythmic Events in Pediatric Onset Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is associated with adverse left ventricular (LV) remodeling causing dysfunction and malignant arrhythmias. Severely affected patients present with disease onset during childhood and sudden cardiac death risk (SCD) stratification is of the highest importance in this cohort. This study aimed to investigate genotype–phenotype association regarding clinical outcome and disease progression in pediatric onset HCM. Medical charts from forty-nine patients with pediatric HCM who had undergone genetic testing were reviewed for retrospective analysis. Demographic, clinical, transthoracic echocardiographic, electrocardiographic, long-term electrocardiogram, cardiopulmonary exercise test, cardiac magnetic resonance, and medication data were recorded. Childhood onset HCM was diagnosed in 29 males and 20 females. Median age at last follow-up was 18.7 years (range 2.6–51.7 years) with a median follow-up time since diagnosis of 8.5 years (range 0.2–38.0 years). Comparison of patients carrying mutations in distinct genes and comparison of genotype-negative with genotype-positive individuals, revealed no differences in functional classification, LV morphology, hypertrophy, systolic and diastolic function, fibrosis and cardiac medication. Patients with compound mutations had a significantly higher risk for major arrhythmic events than a single-mutation carrier. No association between affected genes and disease severity or progression was identified in this cohort.

Hypertrophic Cardiomyopathy: From Phenotype and Pathogenesis to Treatment

Hypertrophic cardiomyopathy (HCM) is a very common inherited cardiovascular disease (CAD) and the incidence is about 1/500 of the common population. It is caused by more than 1,400 mutations in 11 or more genes encoding the proteins of the cardiac sarcomere. HCM presents a heterogeneous clinical profile and complex pathophysiology and HCM is the most important cause of sudden cardiac death (SCD) in young people. HCM also contributes to functional disability from heart failure and stroke (caused by atrial fibrillation). Current treatments for HCM (medication, myectomy, and alcohol septal ablation) are geared toward slowing down the disease progression and symptom relief and implanted cardiac defibrillator (ICD) to prevent SCD. HCM is, however, entering a period of tight translational research that holds promise for the major advances in disease-specific therapy. Main insights into the genetic landscape of HCM have improved our understanding of molecular pathogenesis and pointed the potential targets for the development of therapeutic agents. We reviewed the critical discoveries about the treatments, mechanism of HCM, and their implications for future research.