Genetic Insights into Primary Restrictive Cardiomyopathy

Structural and functional insights into α-actinin isoforms and their implications in cardiovascular disease

α-actinin (ACTN) is a pivotal member of the actin-binding protein family, crucial for the anchoring and organization of actin filaments within the cytoskeleton. Four isoforms of α-actinin exist: two non-muscle isoforms (ACTN1 and ACTN4) primarily associated with actin stress fibers and focal adhesions, and two muscle-specific isoforms (ACTN2 and ACTN3) localized to the Z-disk of the striated muscle. Although these isoforms share structural similarities, they exhibit distinct functional characteristics that reflect their specialized roles in various tissues. Genetic variants in α-actinin isoforms have been implicated in a range of pathologies, including cardiomyopathies, thrombocytopenia, and non-cardiovascular diseases, such as nephropathy. However, the precise impact of these genetic variants on the α-actinin structure and their contribution to disease pathogenesis remains poorly understood. This review provides a comprehensive overview of the structural and functional attributes of the four α-actinin isoforms, emphasizing their roles in actin crosslinking and sarcomere stabilization. Furthermore, we present detailed structural modeling of select ACTN1 and ACTN2 variants to elucidate mechanisms underlying disease pathogenesis, with a particular focus on macrothrombocytopenia and hypertrophic cardiomyopathy. By advancing our understanding of α-actinin's role in both normal cellular function and disease states, this review lays the groundwork for future research and the development of targeted therapeutic interventions.

Cardiac Amyloidosis Versus Other Restrictive Cardiomyopathies: A Retrospective Analysis of Cardiovascular Outcomes and Arrhythmic Burden

Background

The arrhythmic burden and cardiovascular risks of cardiac amyloidosis compared with other types of restrictive cardiomyopathies (RCM), such as hemochromatosis and cardiac sarcoid, have not been well characterized in the literature. An increase in emphasis on screening has resulted in more diagnoses of cardiac amyloidosis and a larger data pool to analyze the cardiovascular outcomes of this cardiomyopathy.

Methods and results

We queried the National Inpatient Sample (NIS) database to identify all adult patients diagnosed with cardiac amyloidosis or other RCM between the years 2016 and 2019. Discharge-weighted analysis using survey regressions accounts for discharge weights and characteristics found to be significantly different between groups. A total sample size of 13 345 patients was obtained, including cardiac amyloidosis (N = 8365; 62.7%) and other RCM (N = 4980; 37.3%). Cardiac amyloidosis was associated with a significantly increased risk of stroke (Odds ratio = 3.91: 95% confidence interval = [2.15, 7.11], P < .001) and ventricular tachycardia (1.98 [1.35-2.91], P < .001). Cardiac amyloidosis had a decreased risk of atrial fibrillation (0.56 [0.47-0.68], P < .001). Significant differences in risk were not observed among the different types of heart block and supraventricular arrhythmias. In-hospital mortality was similar between the 2 groups (P = .72).

Conclusions

Cardiac amyloidosis was associated with an increased risk of stroke and ventricular tachycardia compared to other types of RCM. Significant differences in in-hospital mortality, bundle branch blocks, and supraventricular arrhythmias were not appreciated. A subgroup analysis comparing light chain (AL) and wild-type transthyretin (ATTR) amyloidosis outcomes would further delineate the cardiovascular risks of cardiac amyloidosis.

Identification of a Missense Mutation in the FLNC Gene from a Chinese Family with Restrictive Cardiomyopathy

Objective

Restrictive cardiomyopathy (RCM) is a heterogenous cardiomyopathy with various causes, and genetic variants take an important part of the pathogenesis. Whole-exome sequencing (WES) is effective to discover genes that cause genetic diseases. By using WES, we attempted to identify the genetic cause of an RCM family and clarify the clinical diagnosis of the patient and then provide a personalized treatment plan.

Materials and Methods

Blood samples were obtained from the proband and his healthy parents. WES and Sanger sequencing were performed to identify the possible pathogenic gene. Co-segregation analysis was conducted for candidate variants, and the allele frequency was checked in databases including Ensembl, Exome Aggregation Consortium (ExAC) and Human Gene Mutation Database (HGMD). Furthermore, the potential effect of variant was predicted using various-free software such as SIFT, Polyphen-2 and Mutation Taster and the conservation was tested using multiple sequence alignments by ClustalX.

Results

The proband was a 20 years old boy with severe heart failure symptoms including dyspnea, massive ascites, edema of both lower limbs and chest congestion. Echocardiography showed significant biatrial enlargement, normal left ventricular wall thickness and preserved systolic function of both ventricles. A missense mutation in FLNC (c.6451G>A, p.G2151S), encoded filamin-C was detected in proband by WES and Sanger sequencing, while it was not be found in his parents, we supposed that the FLNC mutation (c.6451G>A, p.G2151S) may be a de-novo mutation. Through multiple functional predictions, we found that it is a deleterious mutation and the mutation in filamin-C could alter its structure and normal function, contributing to RCM.

Conclusion

Here, an FLNC missense mutation (c.6451G>A, p.G2151S) known to be pathogenic in hypertrophic cardiomyopathy, was found to be associated with RCM, indicating the genetic overlap among cardiomyopathies. This study provides insights into Phenotype-Genotype Correlations of RCM in patients with FLNC mutations.

Exploring the role of exosomes in the pathogenesis and treatment of cardiomyopathies: A comprehensive literature review

Exosomes, a subset of small extracellular vesicles that play a crucial role in intercellular communication, have garnered significant attention for their potential applications in the diagnosis and treatment of cardiomyopathies. Cardiomyopathies, which encompass a spectrum of heart muscle disorders, present complex challenges in diagnosis and management. Understanding the role of exosomes in the etiology of cardiomyopathies such as dilated cardiomyopathy (DCM), restrictive cardiomyopathy (RCM), arrhythmogenic cardiomyopathy (AC), and hypertrophic cardiomyopathy (HCM) may open new possibilities for therapeutic intervention and diagnosis. Exosomes have indeed demonstrated promise as diagnostic biomarkers, particularly in identifying cardiac conditions such as atrial fibrillation (AF) and in the timely classification of high-risk patients with different forms of cardiomyopathy. In DCM, exosomes have been implicated in mediating pathological responses in cardiomyocytes, potentially exacerbating disease progression. Moreover, in RCM, AC, and HCM, exosomes present significant potential as diagnostic biomarkers and therapeutic targets, offering insights into disease pathogenesis and potential avenues for intervention. Understanding the influence of exosomes on disease progression and identifying the specific molecular pathways involved in cardiomyopathy pathogenesis may significantly advance diagnostic and treatment strategies. While key findings highlight the multifaceted role of exosomes in cardiomyopathy, they also emphasize the need for further research to elucidate molecular mechanisms and translate findings into clinical practice. This review highlights the evolving landscape of exosome research in cardiomyopathies and underscores the importance of ongoing investigations to harness the full potential of exosomes in improving patient outcomes.

Biallelic potential disease-causing missense variants in TAF1A in two siblings with infantile restrictive cardiomyopathy

TAF1A, a gene encoding a TATA-box binding protein involved in ribosomal RNA synthesis, is a candidate gene for pediatric cardiomyopathy as biallelic TAF1A variants were reported in two families with affected individuals. Here, we report a third family with two siblings who presented with infantile restrictive cardiomyopathy and carried biallelic missense variants in TAF1A (NM_001201536.1:c.1021G>A p.(Gly341Arg) and c.781A>C p.(Thr261Pro)). Additional shared clinical features in the siblings included feeding intolerance, congenital leukoencephalopathy, ventriculomegaly and concern for primary immunodeficiency. The first-born sibling passed away at 6 months of age due to complications of hemophagocytic lymphohistiocytosis (HLH) whereas the second sibling underwent cardiac transplantation at 1 year of age and is currently well. We compare the clinical and molecular features of all the TAF1A associated cardiomyopathy cases. Our study adds evidence for the gene-disease association of TAF1A with autosomal recessive pediatric cardiomyopathy.

Role of Filamin C in Muscle Cells

Filamin C (FLNC) is a member of a high-molecular weight protein family, which bind actin filaments in the cytoskeleton of various cells. In human genome FLNC is encoded by the FLNC gene located on chromosome 7 and is expressed predominantly in striated skeletal and cardiac muscle cells. Filamin C is involved in organization and stabilization of thin actin filaments three-dimensional network in sarcomeres, and is supposed to play a role of mechanosensor transferring mechanical signals to different protein targets. Under mechanical stress FLNC can undergo unfolding that increases the risk of its aggregation. FLNC molecules with an impaired native structure could be eliminated by the BAG3-mediated chaperone-assisted selective autophagy. Mutations in the FLNC gene could be accompanied by the changes in FLNC interaction with its protein partners and could lead to formation of aggregates, which overload the autophagy and proteasome protein degradation systems, thus facilitating development of various pathological processes. Molecular mechanisms of the FLNC-associated congenital disorders, called filaminopathies, remain poorly understood. This review is devoted to analysis of the structure and mechanisms of filamin C function in muscle and heart cells in normal state and in the FLNC-associated pathologies. The presented data summarize the results of research at the molecular, cellular, and tissue levels and allow us to outline promising ways for further investigation of pathogenetic mechanisms in filaminopathies.

Sudden Cardiac Death in the Young: State-of-the-Art Review in Molecular Autopsy

Sudden cardiac death (SCD) is defined as unexpected death due to a cardiac cause that occurs rapidly. Despite the identification of prevention strategies, SCD remains a serious public health problem worldwide, accounting for 15-20% of all deaths, and is therefore a challenge for modern medicine, especially when it affects young people. Sudden cardiac death in young people affects the population aged ≤ 35 years, including athletes and non-athletes, and it is due to various hereditary and non-hereditary causes. After an autopsy, if the cause remains unknown, it is called sudden unexplained death, often attributable to genetic causes. In these cases, molecular autopsy-post-mortem genetic testing-is essential to facilitate diagnostic and therapeutic pathways and/or the monitoring of family members of the cases. This review aims to elaborate on cardiac disorders marked by genetic mutations, necessitating the post-mortem genetic investigation of the deceased for an accurate diagnosis in order to facilitate informed genetic counseling and to implement preventive strategies for family members of the cases.

Generation of human induced pluripotent stem cell line from a patient with restrictive cardiomyopathy

Restrictive cardiomyopathy (RCM) is a rare cardiomyopathy characterized by diastolic dysfunction, which affects cardiac systolic function. We successfully established human induced pluripotent stem cells (hiPSCs) from peripheral blood mononuclear cells of 24-year-old male with restrictive cardiomyopathy (RCM). The patient-derived hiPSCs carried heterozygous mutation of CRYAB gene (c.326A > G, p.D109G), which was consistent with clinical whole exon sequencing results. We confirmed the pluripotency, multipotential differentiation and karyotype of hiPSCs. The hiPSCs will be useful for studying the pathogenesis of RCM caused by CRYAB (c.326A > G) mutation.

Heart transplant outcomes in restrictive cardiomyopathy: UNOS registry analysis of the last three decades

Background

Restrictive cardiomyopathy (RCM) comprises diverse etiologies with overall poor prognosis. Emerging therapies have significantly impacted some of these entities. However, these therapies may have limited impact in the end-stages and have only recently become available. We sought to assess outcomes before and after transplant in the RCM population stratified into 3 distinct time periods from the recent era.

Methods

Retrospective analysis of the United Network of Organ Sharing registry (n = 62,709) for all patients transplanted between 1987 and March 1, 2022, were stratified by RCM status with 1157 patients with RCM. Populations were grouped temporally into classic (1987-2000), contemporary (2000-2013), and current (2014-2022) eras. Multiorgan and repeat transplants were excluded from the analysis. Baseline demographics, listing status, hemodynamics, donor information, and life support methods were compared using Kruskal-Wallis and Pearson's tests. Longitudinal survival was assessed via Kaplan-Meier survival analysis. Univariate and multivariate analyses using Cox modeling and competing outcomes analyses were performed.

Results

RCM patients were older, female, with older donors and longer ischemic times (p < 0.001). There were no significant differences in overall survival compared to the non-RCM population, however, with increased transplant rates. Amyloidosis and chemotherapy/radiation portend the worst prognosis but have shorter waitlist times and up-trending survival in the current era.

Conclusions

RCM represents a small but significant population of those requiring heart transplant. RCM transplant outcomes appear to be improving across all subsets with shorter wait times and better survival. Early recognition is important to help mitigate adverse outcomes.

Application of next generation sequencing in cardiology: current and future precision medicine implications

Inherited cardiovascular diseases are highly heterogeneous conditions with multiple genetic loci involved. The application of advanced molecular tools, such as Next Generation Sequencing, has facilitated the genetic analysis of these disorders. Accurate analysis and variant identification are required to maximize the quality of the sequencing data. Therefore, the application of NGS for clinical purposes should be limited to laboratories with a high level of technological expertise and resources. In addition, appropriate gene selection and variant interpretation can result in the highest possible diagnostic yield. Implementation of genetics in cardiology is imperative for the accurate diagnosis, prognosis and management of several inherited disorders and could eventually lead to the realization of precision medicine in this field. However, genetic testing should also be accompanied by an appropriate genetic counseling procedure that clarifies the significance of the genetic analysis results for the proband and his family. In this regard, a multidisciplinary collaboration among physicians, geneticists, and bioinformaticians is imperative. In the present review, we address the current state of knowledge regarding genetic analysis strategies employed in the field of cardiogenetics. Variant interpretation and reporting guidelines are explored. Additionally, gene selection procedures are accessed, with a particular emphasis on information concerning gene-disease associations collected from international alliances such as the Gene Curation Coalition (GenCC). In this context, a novel approach to gene categorization is proposed. Moreover, a sub-analysis is conducted on the 1,502,769 variation records with submitted interpretations in the Clinical Variation (ClinVar) database, focusing on cardiology-related genes. Finally, the most recent information on genetic analysis's clinical utility is reviewed.

The role of noncoding genetic variants in cardiomyopathy

Cardiomyopathies remain one of the leading causes of morbidity and mortality worldwide. Environmental risk factors and genetic predisposition account for most cardiomyopathy cases. As with all complex diseases, there are significant challenges in the interpretation of the molecular mechanisms underlying cardiomyopathy-associated genetic variants. Given the technical improvements and reduced costs of DNA sequence technologies, an increasing number of patients are now undergoing genetic testing, resulting in a continuously expanding list of novel mutations. However, many patients carry noncoding genetic variants, and although emerging evidence supports their contribution to cardiac disease, their role in cardiomyopathies remains largely understudied. In this review, we summarize published studies reporting on the association of different types of noncoding variants with various types of cardiomyopathies. We focus on variants within transcriptional enhancers, promoters, intronic sites, and untranslated regions that are likely associated with cardiac disease. Given the broad nature of this topic, we provide an overview of studies that are relatively recent and have sufficient evidence to support a significant degree of causality. We believe that more research with additional validation of noncoding genetic variants will provide further mechanistic insights on the development of cardiac disease, and noncoding variants will be increasingly incorporated in future genetic screening tests.

The N-Terminal Part of the 1A Domain of Desmin Is a Hot Spot Region for Putative Pathogenic DES Mutations Affecting Filament Assembly

Desmin is the major intermediate filament protein of all three muscle cell types, and connects different cell organelles and multi-protein complexes such as the cardiac desmosomes. Several pathogenic mutations in the DES gene cause different skeletal and cardiac myopathies. However, the significance of the majority of DES missense variants is currently unknown, since functional data are lacking. To determine whether desmin missense mutations within the highly conserved 1A coil domain cause a filament assembly defect, we generated a set of variants with unknown significance and systematically analyzed the filament assembly using confocal microscopy in transfected SW-13, H9c2 cells and cardiomyocytes derived from induced pluripotent stem cells. We found that mutations in the N-terminal part of the 1A coil domain affect filament assembly, leading to cytoplasmic desmin aggregation. In contrast, mutant desmin in the C-terminal part of the 1A coil domain forms filamentous structures comparable to wild-type desmin. Our findings suggest that the N-terminal part of the 1A coil domain is a hot spot for pathogenic desmin mutations, which affect desmin filament assembly. This study may have relevance for the genetic counselling of patients carrying variants in the 1A coil domain of the DES gene.

Case report: Rare restrictive cardiomyopathy with ventricular fibrillation as initial symptom rescued by automatic external defibrillator in a pediatric patient

Restrictive cardiomyopathy (RCM) is a rare form of heart muscle disease with poor prognosis. Its primary manifestations were caused by systemic or pulmonary circulation congestion. Here, we reported a case of RCM with ventricular fibrillation as initial symptom in a 7-year-old boy. The child suffered cardiac and respiratory arrest suddenly while exercising at school and immediately was given external chest compression and defibrillation by the school’s equipped automatic external defibrillator (AED). The rescue was successful. At the time of the AED discharge, his electrocardiogram (ECG) indicated ventricular fibrillation. Upon further examination, the echocardiogram revealed enlarged bilateral atria, decreased diastolic function and normal ventricular thickness. Genetic analysis identified a heterozygous missense mutation [c.611(exon8)G&gt;A,p.R204H] of TNNI3 in the proband boy. This case contributes to our understanding of RCM in children and emphasizes the importance of having AEDs available in public places.

Clinical Exome Sequencing Revealed a De Novo FLNC Mutation in a Child with Restrictive Cardiomyopathy

Restrictive cardiomyopathy (RCM) is a rare disease of the myocardium caused by mutations in several genes including TNNT2, DES, TNNI3, MYPN and FLNC. Individuals affected by RCM often develop heart failure at a young age, requiring early heart transplantation. A 7-year-old patient was referred for genetic testing following a diagnosis of restrictive cardiomyopathy. Clinical exome sequencing analysis identified a likely pathogenic mutation in the FLNC gene [(NM_001458.5 c.6527_6547dup p.(Arg2176_2182dup)]. Its clinical relevance was augmented by the fact that this variant was absent in the parents and was thus interpreted as de novo. Genetic testing is a powerful tool to clarify the diagnosis, guide intervention strategies and enable cascade testing in patients with pediatric-onset RCM.