Gene therapy strategies in the treatment of hypertrophic cardiomyopathy

Current perspectives of sudden cardiac death management in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder characterized by left ventricular hypertrophy. Sudden cardiac death (SCD) is a rare but the most catastrophic complication in patients with HCM. Implantable cardioverter-defibrillators (ICDs) are widely recognized as effective preventive measures for SCD. Individualized risk stratification and early intervention in HCM can significantly improve patient prognosis. In this study, we review the latest findings regarding pathogenesis, risk stratification, and prevention of SCD in HCM patients, highlighting the clinic practice of cardiovascular magnetic resonance imaging for SCD management.

Deficiency of Transcription Factor Sp1 Contributes to Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most prevalent monogenic heart disorder. However, the pathogenesis of HCM, especially its nongenetic mechanisms, remains largely unclear. Transcription factors are known to be involved in various biological processes including cell growth. We hypothesized that SP1 (specificity protein 1), the first purified TF in mammals, plays a role in the cardiomyocyte growth and cardiac hypertrophy of HCM.

METHODS

Cardiac-specific conditional knockout of Sp1 mice were constructed to investigate the role of SP1 in the heart. The echocardiography, histochemical experiment, and transmission electron microscope were performed to analyze the cardiac phenotypes of cardiac-specific conditional knockout of Sp1 mice. RNA sequencing, chromatin immunoprecipitation sequencing, and adeno-associated virus experiments in vivo were performed to explore the downstream molecules of SP1. To examine the therapeutic effect of SP1 on HCM, an SP1 overexpression vector was constructed and injected into the mutant allele of Myh6 R404Q/+ (Myh6 c. 1211C>T) HCM mice. The human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a patient with HCM were used to detect the potential therapeutic effects of SP1 in human HCM.

RESULTS

The cardiac-specific conditional knockout of Sp1 mice developed a typical HCM phenotype, displaying overt myocardial hypertrophy, interstitial fibrosis, and disordered myofilament. In addition, Sp1 knockdown dramatically increased the cell area of hiPSC-CMs and caused intracellular myofibrillar disorganization, which was similar to the hypertrophic cardiomyocytes of HCM. Mechanistically, Tuft1 was identified as the key target gene of SP1. The hypertrophic phenotypes induced by Sp1 knockdown in both hiPSC-CMs and mice could be rescued by TUFT1 (tuftelin 1) overexpression. Furthermore, SP1 overexpression suppressed the development of HCM in the mutant allele of Myh6 R404Q/+ mice and also reversed the hypertrophic phenotype of HCM hiPSC-CMs.

CONCLUSIONS

Our study demonstrates that SP1 deficiency leads to HCM. SP1 overexpression exhibits significant therapeutic effects on both HCM mice and HCM hiPSC-CMs, suggesting that SP1 could be a potential intervention target for HCM.

Advancing Treatments for Feline Hypertrophic Cardiomyopathy: The Role of Animal Models and Targeted Therapeutics

Feline HCM is the most common cardiovascular disease in cats, leading to devastating outcomes, including congestive heart failure (CHF), arterial thromboembolism (ATE), and sudden death. Evidence demonstrating long-term survival benefit with currently available therapies is lacking. Therefore, it is imperative to explore intricate genetic and molecular pathways that drive HCM pathophysiology to inspire the development of novel therapeutics. Several clinical trials exploring new drug therapies are currently underway, including those investigating small molecule inhibitors and rapamycin. This article outlines the key work performed using cellular and animal models that has led to and continues to guide the development of new innovative therapeutic strategies.

International Consensus on Differential Diagnosis and Management of Patients With Danon Disease: JACC State-of-the-Art Review

Danon disease is a rare X-linked autophagic vacuolar cardioskeletal myopathy associated with severe heart failure that can be accompanied with extracardiac neurologic, skeletal, and ophthalmologic manifestations. It is caused by loss of function variants in the LAMP2 gene and is among the most severe and penetrant of the genetic cardiomyopathies. Most patients with Danon disease will experience symptomatic heart failure. Male individuals generally present earlier than women and die of either heart failure or arrhythmia or receive a heart transplant by the third decade of life. Herein, the authors review the differential diagnosis of Danon disease, diagnostic criteria, natural history, management recommendations, and recent advances in treatment of this increasingly recognized and extremely morbid cardiomyopathy.

Unmet needs and future directions in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a highly treatable monogenetic disorder affecting nearly 0.2% of the population. The high burden of this disease demands suitable measures for early diagnosis and preventing as well as tackling misdiagnosis. While conventionally available therapies have been efficacious in reducing symptoms, they have not been able to change the natural history of the disease. The landscape of medical treatment is rapidly changing with advent of novel pharmacotherapies such as cardiac myosin inhibitors. Ongoing investigations in gene editing have demonstrated benefits in correcting underlying genetic mutations and this is where the future of treatment lies. Contemporary procedural techniques as alternatives to available septal reduction therapies independent of coronary vascular anatomy are also emerging. This review details the recent developments, unmet needs and future directions in diagnosis, medical and invasive treatment of HCM.

An Unbiased Screen Identified the Hsp70-BAG3 Complex as a Regulator of Myosin-Binding Protein C3

Variants in the gene myosin-binding protein C3 (MYBPC3) account for approximately 50% of familial hypertrophic cardiomyopathy (HCM), leading to reduced levels of myosin-binding protein C3 (MyBP-C), the protein product made by gene MYBPC3. Elucidation of the pathways that regulate MyBP-C protein homeostasis could uncover new therapeutic strategies. Toward this goal, we screened a library of 2,426 bioactive compounds and identified JG98, an allosteric modulator of heat shock protein 70 that inhibits interaction with Bcl-2-associated athanogene (BAG) domain co-chaperones. JG98 reduces MyBP-C protein levels. Furthermore, genetic reduction of BAG3 phenocopies treatment with JG-98 by reducing MYBP-C protein levels.. Thus, an unbiased compound screen identified the heat shock protein 70-BAG3 complex as a regulator of MyBP-C stability.

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.

Homology-directed repair of an MYBPC3 gene mutation in a rat model of hypertrophic cardiomyopathy

Variants in myosin-binding protein C3 (MYBPC3) gene are a main cause of hypertrophic cardiomyopathy (HCM), accounting for 30% to 40% of the total number of HCM mutations. Gene editing represents a potential permanent cure for HCM. The aim of this study was to investigate whether genome editing of MYBPC3 using the CRISPR/Cas9 system in vivo could rescue the phenotype of rats with HCM. We generated a rat model of HCM ("1098hom") that carried an Mybpc3 premature termination codon mutation (p.W1098x) discovered in a human HCM pedigree. On postnatal day 3, the CRISPR/Cas9 system was introduced into rat pups by a single dose of AAV9 particles to correct the variant using homology-directed repair (HDR). Analysis was performed 6 months after AAV9 injection. The 1098hom rats didn't express MYBPC3 protein and developed an HCM phenotype with increased ventricular wall thickness and diminished cardiac function. Importantly, CRISPR HDR genome editing corrected 3.56% of total mutations, restored MYBPC3 protein expression by 2.12%, and normalized the HCM phenotype of 1098hom rats. Our work demonstrates that the HDR strategy is a promising approach for treating HCM associated with MYBPC3 mutation, and that CRISPR technology has great potential for treating hereditary heart diseases.

A Narrative Review of Emerging Therapies for Hypertrophic Obstructive Cardiomyopathy

Hypertrophic obstructive cardiomyopathy is a hereditary condition that affects myocardial contraction. In case of failure of pharmacological treatment, alternative approaches might be used that include surgical myectomy, percutaneous transluminal septal myocardial ablation, and radiofrequency ablation. In respect of long-term advantages, surgical septal myectomy remains the therapy of choice for symptomatic hypertrophic obstructive cardiomyopathy. Alcohol septal ablation has been considered an alternative to surgical myectomy, which confers the benefits of a shorter hospital stay, less discomfort, and fewer complications. However, only expert operators should perform it on carefully chosen patients. Further, radiofrequency septal ablation reduces the left ventricular outflow tract gradient and improves the NYHA functional class of patients with hypertrophic obstructive cardiomyopathy, despite complications like cardiac tamponade and atrioventricular block. Further research with a larger sample size is required to compare the radiofrequency approach with established invasive treatment methods for hypertrophic obstructive cardiomyopathy. Septal myectomy has low morbidity and mortality rates, making it the preferred procedure; however, the efficacy and morbidity remain debatable. Advances in invasive techniques, including percutaneous septal radiofrequency ablation and transcatheter myotomy, have provided alternative approaches for reducing left ventricular outflow tract (LVOT) obstruction in patients who are not candidates for traditional surgical septal myectomy. Candidates for alcohol and radiofrequency septal ablation include patients with symptomatic hypertrophic obstructive cardiomyopathy, older adults, and those with multiple comorbidities.

Gene Therapy of Extracellular Vesicles in Cardiovascular and Metabolic Diseases

The ultimate and most complex form of treating human diseases is embodied by gene therapy. For an effective gene therapeutic product we need to hack the cellular plasma membrane entry-system, then escaping degradation in the cytosol and in most cases, we need an efficient hacking of the nuclear membrane-system, achieving the delivery of genetic construct into the central stage of the target cells: nucleoplasm or chromosomal DNA found in this highly controlled space. These steps need to be performed in a targeted, ordered, and efficient way. Possessing intrinsic ability of nucleic acid and protein delivery, extracellular vesicles can bypass biological barriers and may be able to deliver a next-generation platform for gene therapy. Fine-tuned genetic constructs included in (synthetic) extracellular vesicles may provide an upgraded approach to the current gene therapeutical technologies by significantly upgrading and improving biosafety, versatility, and delivery, thus evoking the desired therapeutic response. This chapter addresses the main types, vectors, challenges, and safety issues of gene therapy. Afterwards, a brief introduction and beneficial roles of extracellular vesicles are given. The concept of engineering vesicles for gene therapy is also discussed. A snapshot of most relevant clinical trials in the field of cardiovascular and metabolic diseases is shown. Finally, a wrap-up and outlook about gene therapy are presented.

Review of Contemporary Invasive Treatment Approaches and Critical Appraisal of Guidelines on Hypertrophic Obstructive Cardiomyopathy: State-of-the-Art Review

BACKGROUND

Hypertrophic obstructive cardiomyopathy (HOCM) is a heterogeneous disease with different clinical presentations, albeit producing similar dismal long-term outcomes if left untreated. Several approaches are available for the treatment of HOCM; e.g., alcohol septal ablation (ASA) and surgical myectomy (SM). The objectives of the current review were to (1) discuss the place of the standard invasive treatment modalities (ASA and SM) for HOCM; (2) summarize and compare novel techniques for the management of HOCM; (3) analyze current guidelines addressing HOCM management; and (4) offer suggestions for the treatment of complex HOCM presentations.

METHODS

We searched the literature and attempted to gather the most relevant and impactful available evidence on ASA, SM, and other invasive means of treatment of HOCM. The literature search yielded thousands of results, and 103 significant publications were ultimately included.

RESULTS

We critically analyzed available guidelines and provided context in the setting of patient selection for standard and novel treatment modalities. This review offers the most comprehensive analysis to-date of available invasive treatments for HOCM. These include the standard treatments, SM and ASA, as well as novel treatments such as dual-chamber pacing and radiofrequency catheter ablation. We also account for complex pathoanatomic presentations and current guidelines to offer suggestions for tailored care of patients with HOCM. Finally, we consider promising future therapies for HOCM.

CONCLUSIONS

HOCM is a heterogeneous disease associated with poor outcomes if left untreated. Several strategies for treatment of HOCM are available but patient selection for the procedure is crucial.

Clinical Features and Natural History of Preadolescent Nonsyndromic Hypertrophic Cardiomyopathy

BACKGROUND

Up to one-half of childhood sarcomeric hypertrophic cardiomyopathy (HCM) presents before the age of 12 years, but this patient group has not been systematically characterized.

OBJECTIVES

The aim of this study was to describe the clinical presentation and natural history of patients presenting with nonsyndromic HCM before the age of 12 years.

METHODS

Data from the International Paediatric Hypertrophic Cardiomyopathy Consortium on 639 children diagnosed with HCM younger than 12 years were collected and compared with those from 568 children diagnosed between 12 and 16 years.

RESULTS

At baseline, 339 patients (53.6%) had family histories of HCM, 132 (20.9%) had heart failure symptoms, and 250 (39.2%) were prescribed cardiac medications. The median maximal left ventricular wall thickness z-score was 8.7 (IQR: 5.3-14.4), and 145 patients (27.2%) had left ventricular outflow tract obstruction. Over a median follow-up period of 5.6 years (IQR: 2.3-10.0 years), 42 patients (6.6%) died, 21 (3.3%) underwent cardiac transplantation, and 69 (10.8%) had life-threatening arrhythmic events. Compared with those presenting after 12 years, a higher proportion of younger patients underwent myectomy (10.5% vs 7.2%; P = 0.045), but fewer received primary prevention implantable cardioverter-defibrillators (18.9% vs 30.1%; P = 0.041). The incidence of mortality or life-threatening arrhythmic events did not differ, but events occurred at a younger age.

CONCLUSIONS

Early-onset childhood HCM is associated with a comparable symptom burden and cardiac phenotype as in patients presenting later in childhood. Long-term outcomes including mortality did not differ by age of presentation, but patients presenting at younger than 12 years experienced adverse events at younger ages.

Non-pharmaceutical Interventions for Hypertrophic Cardiomyopathy: A Mini Review

Hypertrophic cardiomyopathy is an inherited cardiovascular disease, and 70% of patients have left ventricular outflow tract obstruction. Ventricular septal myectomy has been the gold standard treatment for most patients with refractory symptoms. Due to higher mortality associated with medical facilities with less experience, alcohol septal ablation has been accepted as an alternative to conventional surgical myectomy. It offers lower all-cause in-hospital complications and mortality, which could be potentially more preferable for patients with serious comorbidities. In recent years, radiofrequency ablation, providing another option with reproducibility and a low risk of permanent atrioventricular block, has become an effective invasive treatment to relieve left ventricular outflow tract obstruction. Moreover, substantial progress has been made in gene therapy for hypertrophic cardiomyopathy. The principal objective of this review is to present recent advances in non-pharmaceutical interventions in hypertrophic cardiomyopathy.

Understanding the Genetic and Molecular Basis of Familial Hypertrophic Cardiomyopathy and the Current Trends in Gene Therapy for Its Management

Hypertrophic cardiomyopathy (HCM) is a genetically acquired disease of cardiac myocytes. Studies show that 70% of this disease is a result of different mutations in various sarcomere genes. This review aims to discuss several genetic mutations, epigenetic factors, and signal transduction pathways leading to the development of HCM. In addition, this article elaborates on recent advances in gene therapies and their implications for managing this condition. We start by discussing the founding mutations in HCM and their effect on power stroke generation. The less explored field of epigenetics including methylation, acetylation, and the role of different micro RNAs in the development of cardiac muscle hypertrophy has been highlighted in this article. The signal transduction pathways that lead to gene transcription, which in turn lead to increased protein synthesis of cardiac muscle fibers are elaborated. Finally, the microscopic events leading to the pathophysiologic macro events of cardiac failure, and the current experimental trials of gene therapy models, and the clustered regularly interspaced short palindromic repeats (CRISPR) type 2 system proteins, are discussed. We have concluded our discussion by emphasizing the need for more studies on epigenomics and experimental designs for gene therapy in HCM patients. This review focuses on the process of HCM from initial mutation to the development of phenotypic expression and various points of intervention in cardiac myocardial hypertrophy development.

Genetic Testing in Patients with Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common inherited heart disease with an estimated prevalence of up to 1 in 200 individuals. In the majority of cases, HCM is considered a Mendelian disease, with mainly autosomal dominant inheritance. Most pathogenic variants are usually detected in genes for sarcomeric proteins. Nowadays, the genetic basis of HCM is believed to be rather complex. Thousands of mutations in more than 60 genes have been described in association with HCM. Nevertheless, screening large numbers of genes results in the identification of many genetic variants of uncertain significance and makes the interpretation of the results difficult. Patients lacking a pathogenic variant are now believed to have non-Mendelian HCM and probably have a better prognosis than patients with sarcomeric pathogenic mutations. Identifying the genetic basis of HCM creates remarkable opportunities to understand how the disease develops, and by extension, how to disrupt the disease progression in the future. The aim of this review is to discuss the brief history and recent advances in the genetics of HCM and the application of molecular genetic testing into common clinical practice.

Gene therapy for inherited arrhythmias

Inherited arrhythmias are disorders caused by one or more genetic mutations that increase the risk of arrhythmia, which result in life-long risk of sudden death. These mutations either primarily perturb electrophysiological homeostasis (e.g. long QT syndrome and catecholaminergic polymorphic ventricular tachycardia), cause structural disease that is closely associated with severe arrhythmias (e.g. hypertrophic cardiomyopathy), or cause a high propensity for arrhythmia in combination with altered myocardial structure and function (e.g. arrhythmogenic cardiomyopathy). Currently available therapies offer incomplete protection from arrhythmia and fail to alter disease progression. Recent studies suggest that gene therapies may provide potent, molecularly targeted options for at least a subset of inherited arrhythmias. Here, we provide an overview of gene therapy strategies, and review recent studies on gene therapies for catecholaminergic polymorphic ventricular tachycardia and hypertrophic cardiomyopathy caused by MYBPC3 mutations.

Shared Molecular Mechanisms of Hypertrophic Cardiomyopathy and Its Clinical Presentations: Automated Molecular Mechanisms Extraction Approach

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease with a prevalence of 1 in 500 people and varying clinical presentations. Although there is much research on HCM, underlying molecular mechanisms are poorly understood, and research on the molecular mechanisms of its specific clinical presentations is scarce. Our aim was to explore the molecular mechanisms shared by HCM and its clinical presentations through the automated extraction of molecular mechanisms. Molecular mechanisms were congregated by a query of the INDRA database, which aggregates knowledge from pathway databases and combines it with molecular mechanisms extracted from abstracts and open-access full articles by multiple machine-reading systems. The molecular mechanisms were extracted from 230,072 articles on HCM and 19 HCM clinical presentations, and their intersections were found. Shared molecular mechanisms of HCM and its clinical presentations were represented as networks; the most important elements in the intersections’ networks were found, centrality scores for each element of each network calculated, networks with reduced level of noise generated, and cooperatively working elements detected in each intersection network. The identified shared molecular mechanisms represent possible mechanisms underlying different HCM clinical presentations. Applied methodology produced results consistent with the information in the scientific literature.

Understanding the genetics of adult-onset dilated cardiomyopathy: what a clinician needs to know

There is increasing understanding of the genetic basis to dilated cardiomyopathy and in this review, we offer a practical primer for the practising clinician. We aim to help all clinicians involved in the care of patients with dilated cardiomyopathy to understand the clinical relevance of the genetic basis of dilated cardiomyopathy, introduce key genetic concepts, explain which patients and families may benefit from genetic testing, which genetic tests are commonly performed, how to interpret genetic results, and the clinical applications of results. We conclude by reviewing areas for future research in this dynamic field.

Hypertrophic Cardiomyopathy: Genetic Testing and Risk Stratification

PURPOSE OF REVIEW

Our knowledge of the genetic basis and molecular pathogenesis of hypertrophic cardiomyopathy (HCM) continues to evolve. We describe the genetic basis of HCM, recent advances in genetic testing and the role of genetics in guiding risk stratification and management, both now and in the future.

RECENT FINDINGS

While initially thought to be an exclusively Mendelian disease, we now know there are important HCM sub-groups. A proportion will have sarcomere variants as the cause of their disease, while others will have genetic variants in genes that can give rise to conditions that can mimic HCM. The role of genetics is primarily for cascade genetic testing, though there is emerging evidence of a role for prognosis and patient management. Genetic testing is a useful addition to management. Genotype may play a greater role in risk stratification, management, treatment and prognosis in future, offering improved outcomes for patients and their families with HCM.

Machine learning based CRISPR gRNA design for therapeutic exon skipping

Restoring gene function by the induced skipping of deleterious exons has been shown to be effective for treating genetic disorders. However, many of the clinically successful therapies for exon skipping are transient oligonucleotide-based treatments that require frequent dosing. CRISPR-Cas9 based genome editing that causes exon skipping is a promising therapeutic modality that may offer permanent alleviation of genetic disease. We show that machine learning can select Cas9 guide RNAs that disrupt splice acceptors and cause the skipping of targeted exons. We experimentally measured the exon skipping frequencies of a diverse genome-integrated library of 791 splice sequences targeted by 1,063 guide RNAs in mouse embryonic stem cells. We found that our method, SkipGuide, is able to identify effective guide RNAs with a precision of 0.68 (50% threshold predicted exon skipping frequency) and 0.93 (70% threshold predicted exon skipping frequency). We anticipate that SkipGuide will be useful for selecting guide RNA candidates for evaluation of CRISPR-Cas9-mediated exon skipping therapy.

Therapeutic applications of trans-splicing

BACKGROUND

RNA trans-splicing joins exons from different pre-mRNA transcripts to generate a chimeric product. Trans-splicing can also occur at the protein level, with split inteins mediating the ligation of separate gene products to generate a mature protein.

SOURCES OF DATA

Comprehensive literature search of published research papers and reviews using Pubmed.

AREAS OF AGREEMENT

Trans-splicing techniques have been used to target a wide range of diseases in both in vitro and in vivo models, resulting in RNA, protein and functional correction.

AREAS OF CONTROVERSY

Off-target effects can lead to therapeutically undesirable consequences. In vivo efficacy is typically low, and delivery issues remain a challenge.

GROWING POINTS

Trans-splicing provides a promising avenue for developing novel therapeutic approaches. However, much more research needs to be done before developing towards preclinical studies.

AREAS TIMELY FOR DEVELOPING RESEARCH

Increasing trans-splicing efficacy and specificity by rational design, screening and competitive inhibition of endogenous cis-splicing.

Mixed Hypertrophic and Dilated Phenotype of Cardiomyopathy in a Patient With Homozygous In-Frame Deletion in the MyBPC3 Gene Treated as Myocarditis for a Long Time

Hypertrophic cardiomyopathy (HCM) is the most common inherited disease, with a prevalence of 1:200 worldwide. The cause of HCM usually presents with an autosomal dominant mutation in the genes encoding one of more than 20 sarcomeric proteins, incomplete penetrance, and variable expressivity. HCM classically manifests as an unexplained thickness of the interventricular septum (IVS) and left ventricular (LV) walls, with or without the obstruction of the LV outflow tract (LVOT), and variable cardiac arrhythmias. Here, we present a rare case of mixed cardiomyopathy (cardiac hypertrophy and dilation) and erythrocytosis in a young patient. A 27-year-old man was admitted to the clinic due to biventricular heart failure (HF) NYHA class III. Personal medical records included a diagnosis of dilated cardiomyopathy (DCM) since the age of 4 years and were, at the time, considered an outcome of myocarditis. Severe respiratory infection led to circulatory decompensation and acute femoral thrombosis. The combination of non-obstructive LV hypertrophy (LV walls up to 15 mm), LV dilatation, decreased contractility (LV EF 24%), and LV apical thrombosis were seen. Cardiac MRI showed a complex pattern of late gadolinium enhancement (LGE). Endomyocardial biopsy (EMB) revealed primary cardiomyopathy with intravascular coagulation and an inflammatory response. No viral genome was detected in the plasma or EMB samples. Whole exome sequencing (WES) revealed a homozygous in-frame deletion p.2711_2737del in the MyBPC3 gene. The clinically unaffected mother was a heterozygous carrier of this deletion, and the father was unavailable for clinical and genetic testing. Essential erythrocytosis remains unexplained. No significant improvement was achieved by conventional treatment, including prednisolone 40 mg therapy. ICD was implanted due to sustained VT and high risk of SCD. Orthotopic heart transplantation (HTx) was considered optimal. Early manifestation combined hypertrophic and dilated phenotype, and progression may reflect a complex genotype with more than one pathogenic allele and/or a combination of genetic diseases in one patient.

Targeting the population for gene therapy with MYBPC3

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited myocardial disease characterized by unexplained left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. Clinical heterogeneity is wide, ranging from asymptomatic individuals to heart failure, arrhythmias and sudden death. HCM is often caused by mutations in genes encoding components of the sarcomere. Among them, MYBPC3, encoding cardiac myosin-myosin binding protein C is the most frequently mutated gene. Three quarter of pathogenic or likely pathogenic mutations in MYBPC3 are truncating and the resulting protein was not detected in HCM myectomy samples. The overall prognosis of the patients is excellent if managed with contemporary therapy, but still remains a significant disease-related health burden, and carriers with double heterozygous, compound heterozygous and homozygous mutations often display a more severe clinical phenotype than single heterozygotes. We propose these individuals as a good target population for MYBPC3 gene therapy.

Genetic, clinical, molecular, and pathogenic aspects of the South Asian-specific polymorphic MYBPC3Δ25bp variant

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by ventricular enlargement, diastolic dysfunction, and increased risk for sudden cardiac death. Sarcomeric genetic defects are the predominant known cause of HCM. In particular, mutations in the myosin-binding protein C gene (MYBPC3) are associated with ~ 40% of all HCM cases in which a genetic basis has been established. A decade ago, our group reported a 25-base pair deletion in intron 32 of MYBPC3 (MYBPC3Δ25bp) that is uniquely prevalent in South Asians and is associated with autosomal dominant cardiomyopathy. Although our studies suggest that this deletion results in left ventricular dysfunction, cardiomyopathies, and heart failure, the precise mechanism by which this variant predisposes to heart disease remains unclear. Increasingly appreciated, however, is the contribution of secondary risk factors, additional mutations, and lifestyle choices in augmenting or modifying the HCM phenotype in MYBPC3Δ25bp carriers. Therefore, the goal of this review article is to summarize the current research dedicated to understanding the molecular pathophysiology of HCM in South Asians with the MYBPC3Δ25bp variant. An emphasis is to review the latest techniques currently applied to explore the MYBPC3Δ25bp pathogenesis and to provide a foundation for developing new diagnostic strategies and advances in therapeutics.

New perspectives in the pharmacological treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is an inherited cardiac disease and a major cause of heart failure and sudden death. Even though it was described more than 50 years ago, sarcomeric hypertrophic cardiomyopathy still lacks a disease-specific treatment. The drugs routinely used alleviate symptoms but do not prevent or revert the phenotype. With recent advances in the knowledge about the genetics and pathophysiology of hypertrophic cardiomyopathy, new genetic and pharmacological approaches have been recently discovered and studied that, by influencing different pathways involved in this disease, have the potential to function as disease-modifying therapies. These promising new pharmacological and genetic therapies will be the focus of this review.

Genetics of feline hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by an abnormal increase in myocardial mass that affects cardiac structure and function. HCM is the most common inherited cardiovascular disease in humans (0.2%) and the most common cardiovascular disease in cats (14.7%). Feline HCM phenotype is very similar to the phenotype found in humans, but the time frame for the development of the disease is significantly shorter. Similar therapeutic agents are used in its treatment and it has the same complications, such as heart failure, thromboembolism and sudden cardiac death. In contrast to humans, in whom thousands of genetic variants have been identified, genetic studies in cats have been limited to fragment analysis of two sarcomeric genes identifying two variants in MYBPC3 and one in MYH7. Two of these variants have also been associated with human disease. The high prevalence of the reported variants in non-affected cats hinders the assumption of their pathogenicity in heterozygotes. An in-depth review of the literature about genetic studies on feline HCM in comparison with the same disease in humans is presented here. The close similarity in the phenotype and genotype between cats and humans makes the cat an excellent model for the pathophysiological study of the disease and future therapeutic agents.

Phenotypes of hypertrophic cardiomyopathy: genetics, clinics, and modular imaging

Hypertrophic cardiomyopathy (HCM) is the most common cardiovascular disease with genetic transmission, characterized by the hypertrophy of any segment of the left ventricle (LV), not totally explained by improper loading conditions, with LV systolic function preserved, increased, or reduced. The histopathological mechanism involved in HCM refers to the primary injury of the myocardium, as follows: disorganized array of myocytes, extracellular matrix modification, microvascular dysfunction, with subsequent appearance of myocardial fibrosis. Multiple sarcomere proteins mutations are responsible for HCM, but two of them are involved in 70% of the cases of HCM: β-myosin heavy chain (MYH7) and myosin-binding protein C (MYBPC3). The development of new genetic techniques involving genome editing is promising to discover a gene therapy for patients with HCM. Clinical presentation may differ from asymptomatic to sudden cardiac death (SCD), the last one targeting younger adults. In this case, the diagnosis and evaluation of SCD risk factors is extremely important. The common method of diagnosis is transthoracic echocardiography, but cardiac magnetic resonance (CMR) imaging represents "gold standard" in the evaluation of HCM patients. Treatment includes pharmacological therapy, surgery, alcohol ablation, and not least SCD prevention.

A novel MYBPC3 c.2737+1 (IVS26) G>T mutation responsible for high-risk hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy is an autosomal dominant hereditary disease characterised by left ventricular asymmetry hypertrophy. However, our knowledge of the genetic background in hypertrophic cardiomyopathy cases is limited. Here, we aimed to evaluate pathogenic gene mutations in a family with high-risk hypertrophic cardiomyopathy and analyse the genotype/phenotype relationships in this family.

METHODS

The proband, her parents, and her niece underwent whole-exome sequencing, and the genotypes of family members were identified using Sanger sequencing. mRNA expression was detected using reverse transcription sequencing. Structural impairments were predicted by homologous modelling. A family survey was conducted for patients with positive results to obtain information on general clinical symptoms, electrocardiography, ambulatory electrocardiography, echocardiography, and 3.0T cardiac magnetic resonance findings. Regular follow-up was performed for up to 6 months.

RESULTS

Five family members, including the proband, carried a cleavage site mutation in the MYBPC3 gene (c.2737+1 (IVS26) G>T), causing exon 26 of the MYBPC3 gene transcript to be skipped and leading to truncation of cardiac myosin-binding protein C. Family survey showed that the earliest onset age was 13 years old, and three people had died suddenly at less than 40 years old. Three pathogenic gene carriers were diagnosed with hypertrophic cardiomyopathy, and all showed severe ventricular septal hypertrophy.

CONCLUSION

The c.2737+1 (IVS26) G>T mutation in the MYBPC3 gene led to exon 26 skipping, thereby affecting the structure and function of cardiac myosin-binding protein C and leading to severe ventricular hypertrophy and sudden death.

Combinatorial genetic replenishments in myocardial and outflow tract tissues restore heart function in tnnt2 mutant zebrafish

Cardiac muscle troponin T (Tnnt2) mediates muscle contraction in response to calcium ion dynamics, and Tnnt2 mutations are associated with multiple types of cardiomyopathy. Here, we employed a zebrafish model to investigate the genetic replenishment strategies of using conditional and inducible promoters to rescue the deficiencies in the heart. tnnt2a mutations were induced in zebrafish via the CRISPR/Cas9 technique, and the mutants displayed heart arrest and dilated cardiomyopathy-like phenotypes. We first utilized the classic myocardial promoter of the myl7 and TetOn inducible system to restore tnnt2a expression in myocardial tissue in tnnt2a mutant zebrafish. However, this attempt failed to recover normal heart function and circulation, although heart pumping was partially restored. Further analyses via both RNA-seq and immunofluorescence indicated that Tnnt2a, which was also expressed in a novel group of myl7-negative smooth muscle cells on the outflow tract (OFT), was indispensably responsible for the normal mechanical dynamics of OFT. Lastly, tnnt2 expression induced by OFT cells in addition to the myocardial cells successfully rescued heart function and circulation in tnnt2a mutant zebrafish. Together, our results reveal the significance of OFT expression of Tnnt2 for cardiac function and demonstrate zebrafish larva as a powerful and convenient in vivo platform for studying cardiomyopathy and the relevant therapeutic strategies.

Inducing Pluripotency in the Domestic Cat (Felis catus)

Domestic cats suffer from a range of inherited genetic diseases, many of which display similarities with equivalent human conditions. Developing cellular models for these inherited diseases would enable drug discovery, benefiting feline health and welfare as well as enhancing the potential of cats as relevant animal models for translation to human medicine. Advances in our understanding of these diseases at the cellular level have come from the use of induced pluripotent stem cells (iPSCs). iPSCs can differentiate into virtually any cell type and can be derived from adult somatic cells, therefore overcoming the ethical implications of destroying embryos to obtain embryonic stem cells. No studies, however, report the generation of iPSCs from domestic cats [feline iPSCs (fiPSCs)]. Feline adipose-derived fibroblasts were infected with amphotropic retrovirus containing the coding sequences for human Oct4, Sox2, Klf4, cMyc, and Nanog. Isolated iPSC clones were expanded on inactivated mouse embryonic fibroblasts in the presence of feline leukemia inhibitory factor (fLIF). Retroviral delivery of human pluripotent genes gave rise to putative fiPSC colonies within 5-7 days. These iPS-like cells required fetal bovine serum and fLIF for maintenance. Colonies were domed with refractile edges, similar to mouse iPSCs. Immunocytochemistry demonstrated positive staining for stem cell markers: alkaline phosphatase, Oct4, Sox2, Nanog, and SSEA1. Cells were negative for SSEA4. Expression of endogenous feline Nanog was confirmed by quantitative polymerase chain reaction. The cells were able to differentiate in vitro into cells representative of the three germ layers. These results confirm the first generation of induced pluripotent stem cells from domestic cats. These cells will provide valuable models to study genetic diseases and explore novel therapeutic strategies.

Myoarchitectural disarray of hypertrophic cardiomyopathy begins pre-birth

Myoarchitectural disarray – the multiscalar disorganisation of myocytes, is a recognised histopathological hallmark of adult human hypertrophic cardiomyopathy (HCM). It occurs before the establishment of left ventricular hypertrophy (LVH) but its early origins and evolution around the time of birth are unknown. Our aim is to investigate whether myoarchitectural abnormalities in HCM are present in the fetal heart. We used wild‐type, heterozygous and homozygous hearts (n = 56) from a Mybpc3‐targeted knock‐out HCM mouse model and imaged the 3D micro‐structure by high‐resolution episcopic microscopy. We developed a novel structure tensor approach to extract, display and quantify myocyte orientation and its local angular uniformity by helical angle, angle of intrusion and myoarchitectural disarray index, respectively, immediately before and after birth. In wild‐type, we demonstrate uniformity of orientation of cardiomyocytes with smooth transitions of helical angle transmurally both before and after birth but with traces of disarray at the septal insertion points of the right ventricle. In comparison, heterozygous mice free of LVH, and homozygous mice showed not only loss of the normal linear helical angulation transmural profiles observed in wild‐type but also fewer circumferentially arranged myocytes at birth. Heterozygous and homozygous showed more disarray with a wider distribution than in wild‐type before birth. In heterozygous mice, disarray was seen in the anterior, septal and inferior walls irrespective of stage, whereas in homozygous mice it extended to the whole LV circumference including the lateral wall. In conclusion, myoarchitectural disarray is detectable in the fetal heart of an HCM mouse model before the development of LVH.

Gene Therapy Leaves a Vicious Cycle

The human genetic code encrypted in thousands of genes holds the secret for synthesis of proteins that drive all biological processes necessary for normal life and death. Though the genetic ciphering remains unchanged through generations, some genes get disrupted, deleted and or mutated, manifesting diseases, and or disorders. Current treatment options—chemotherapy, protein therapy, radiotherapy, and surgery available for no more than 500 diseases—neither cure nor prevent genetic errors but often cause many side effects. However, gene therapy, colloquially called “living drug,” provides a one-time treatment option by rewriting or fixing errors in the natural genetic ciphering. Since gene therapy is predominantly a viral vector-based medicine, it has met with a fair bit of skepticism from both the science fraternity and patients. Now, thanks to advancements in gene editing and recombinant viral vector development, the interest of clinicians and pharmaceutical industries has been rekindled. With the advent of more than 12 different gene therapy drugs for curing cancer, blindness, immune, and neuronal disorders, this emerging experimental medicine has yet again come in the limelight. The present review article delves into the popular viral vectors used in gene therapy, advances, challenges, and perspectives.