Cadherin 2-Related Arrhythmogenic Cardiomyopathy: Prevalence and Clinical Features

A Comprehensive Analysis of Non-Desmosomal Rare Genetic Variants in Arrhythmogenic Cardiomyopathy: Integrating in Padua Cohort Literature-Derived Data

Arrhythmogenic cardiomyopathy (ACM) is an inherited myocardial disease at risk of sudden death. Genetic testing impacts greatly in ACM diagnosis, but gene-disease associations have yet to be determined for the increasing number of genes included in clinical panels. Genetic variants evaluation was undertaken for the most relevant non-desmosomal disease genes. We retrospectively studied 320 unrelated Italian ACM patients, including 243 cases with predominant right-ventricular (ARVC) and 77 cases with predominant left-ventricular (ALVC) involvement, who did not carry pathogenic/likely pathogenic (P/LP) variants in desmosome-coding genes. The aim was to assess rare genetic variants in transmembrane protein 43 (TMEM43), desmin (DES), phospholamban (PLN), filamin c (FLNC), cadherin 2 (CDH2), and tight junction protein 1 (TJP1), based on current adjudication guidelines and reappraisal on reported literature data. Thirty-five rare genetic variants, including 23 (64%) P/LP, were identified in 39 patients (16/243 ARVC; 23/77 ALVC): 22 FLNC, 9 DES, 2 TMEM43, and 2 CDH2. No P/LP variants were found in PLN and TJP1 genes. Gene-based burden analysis, including P/LP variants reported in literature, showed significant enrichment for TMEM43 (3.79-fold), DES (10.31-fold), PLN (117.8-fold) and FLNC (107-fold). A non-desmosomal rare genetic variant is found in a minority of ARVC patients but in about one third of ALVC patients; as such, clinical decision-making should be driven by genes with robust evidence. More than two thirds of non-desmosomal P/LP variants occur in FLNC.

Accurate Classification of Non-ischemic Cardiomyopathy

PURPOSE OF REVIEW

This article aims to review the accurate classification of non-ischemic cardiomyopathy, including the methods, basis, subtype characteristics, and prognosis, especially the similarities and differences between different classifications.

RECENT FINDINGS

Non-ischemic cardiomyopathy refers to a myocardial disease that excludes coronary artery disease or ischemic injury and has a variety of etiologies and high incidence. Recent studies suggest that traditional classification methods based on primary/mixed/acquired or genetic/non-genetic cannot meet the precise needs of contemporary clinical management. This article systematically describes the history of classifications of cardiomyopathy and presents etiological and genetic differences between cardiomyopathies. The accurate classification is described from the perspective of morphology, function, and genomics in hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular noncompaction, and partially acquired cardiomyopathy. The different clinical characteristics and treatment needs of these cardiomyopathies are elaborated. Some single-gene mutant cardiomyopathies have unique phenotypes, and some cardiomyopathies have mixed phenotypes. These special classifications require personalized precision treatment, which is worthy of independent research. This article describes recent advances in the accurate classification of non-ischemic cardiomyopathy from clinical phenotypes and causative genes, discusses the advantages and usage scenarios of each classification, compares the differences in prognosis and patient management needs of different subtypes, and summarizes common methods and new exploration directions for accurate classification.

From gene-discovery to gene-tailored clinical management: 25 years of research in channelopathies and cardiomyopathies

In the early nineties, few years before the birth of Europace, the clinical and scientific world of familial arrhythmogenic conditions was revolutionized by the identification of the first disease-causing genes. The explosion of genetic studies over a 15-year period led to the discovery of major disease-causing genes in practically all channelopathies and cardiomyopathies, bringing insight into the pathophysiological mechanisms of these conditions. The birth of next generation sequencing allowed a further step forward and other significant genes, as CALM1-3 in channelopathies and FLN C and TTN in cardiomyopathies were identified. Genotype-phenotype studies allowed the implementation of the genetic results in diagnosis, risk stratification, and therapeutic management with a different level of evidence in different arrhythmogenic conditions. The influence of common genetic variants, i.e. SNPs, on disease manifestation was proved in mid-twenties, and in the last 10 years with the advent of genome-wide association studies performed in familial arrhythmogenic diseases, the concept of polygenic risk score has been consolidated. Now, we are at the start of another amazing phase, i.e. the initiation of first gene therapy clinical trials.

Maturation and Function of the Intercalated Disc: Report of Two Pediatric Cases Focusing on Cardiac Development and Myocardial Hyperplasia

The development of the normal human heart, ranging from gestational age to the mature adult heart, relies on a very delicate and timely orchestrated order of processes. One of the most striking alterations in time is the gradual extinction of the ability for cardiomyocytes to proliferate. Once passing this event, cardiomyocytes grow and increase in contractile strength by means of physiological hypertrophy. This process, importantly, seems to depend on an adequate development of electromechanical coupling that is achieved by the appropriate formation of the intercellular junction named the intercalated disc (ICD). In this report, we describe two sudden death cases of young and apparently healthy-born individuals without external abnormalities compared to an age-matched control. Histological examination, including the comparison with the age-matched and histology-matched controls, showed a disturbed formation of the protein machinery composing the electromechanical junctions at the ICD and an increased nuclei count for both patients. As a cause or consequence, cardiomyocytes in both sudden death cases showed signs of a delayed developmental stage, presumably resulting in an exaggerated degree of hyperplasia.

Desmosomal Arrhythmogenic Cardiomyopathy: The Story Telling of a Genetically Determined Heart Muscle Disease

The history of arrhythmogenic cardiomyopathy (AC) as a genetically determined desmosomal disease started since the original discovery by Lancisi in a four-generation family, published in 1728. Contemporary history at the University of Padua started with Dalla Volta, who haemodynamically investigated patients with "auricularization" of the right ventricle, and with Nava, who confirmed familiarity. The contemporary knowledge advances consisted of (a) AC as a heart muscle disease with peculiar electrical instability of the right ventricle; (b) the finding of pathological substrates, in keeping with a myocardial dystrophy; (c) the inclusion of AC in the cardiomyopathies classification; (d) AC as the main cause of sudden death in athletes; (e) the discovery of the culprit genes coding proteins of the intercalated disc (desmosome); (f) progression in clinical diagnosis with specific ECG abnormalities, angiocardiography, endomyocardial biopsy, 2D echocardiography, electron anatomic mapping and cardiac magnetic resonance; (g) the discovery of left ventricular AC; (h) prevention of SCD with the invention and application of the lifesaving implantable cardioverter defibrillator and external defibrillator scattered in public places and playgrounds as well as the ineligibility for competitive sport activity for AC patients; (i) genetic screening of the proband family to unmask asymptomatic carriers. Nondesmosomal ACs, with a phenotype overlapping desmosomal AC, are also treated, including genetics: Transmembrane protein 43, SCN5A, Desmin, Phospholamban, Lamin A/C, Filamin C, Cadherin 2, Tight junction protein 1.

Cheek-Pro-Heart: What Can the Buccal Mucosa Do for Arrhythmogenic Cardiomyopathy?

Arrhythmogenic cardiomyopathy (ACM) is a heart muscle disease associated with ventricular arrhythmias and a high risk of sudden cardiac death (SCD). Although the disease was described over 40 years ago, its diagnosis is still difficult. Several studies have identified a set of five proteins (plakoglobin, Cx43, Nav1.5, SAP97 and GSK3β), which are consistently re-distributed in myocardial samples from ACM patients. Not all protein shifts are specific to ACM, but their combination has provided us with a molecular signature for the disease, which has greatly aided post-mortem diagnosis of SCD victims. The use of this signature, however, was heretofore restricted in living patients, as the analysis requires a heart sample. Recent studies have shown that buccal cells behave similarly to the heart in terms of protein re-localization. Protein shifts are associated with disease onset, deterioration and favorable response to anti-arrhythmic therapy. Accordingly, buccal cells can be used as a surrogate for the myocardium to aid diagnosis, risk stratification and even monitor response to pharmaceutical interventions. Buccal cells can also be kept in culture, hence providing an ex vivo model from the patient, which can offer insights into the mechanisms of disease pathogenesis, including drug response. This review summarizes how the cheek can aid the heart in the battle against ACM.

Genomic and RNA-Seq profiling of patients with HFrEF unraveled OAS1 mutation and aggressive expression

BACKGROUND

Heart failure (HF) is a complex pathophysiological state characterized by inadequate delivery of blood and nutrients to the cardiac tissues. It is rarely curable and is commonly associated with a poor prognosis. In this study, we aimed to analyse exomic and RNA-Seq data from patients with HF to identify the key altered pathways in HF.

METHODS

Whole blood samples were collected from patients with HF and subjected to whole exome sequencing (WES) and RNA-Seq analysis. The gene expression and RNA-Seq data obtained were verified using gene chip analysis and RT-PCR.

RESULTS

Both exomic and RNA-Seq data confirmed the dysregulation of phosphorylation and immune signalling in patients with HF. Specifically, exomic analysis showed that TITIN, OBSCURIN, NOD2, CDH2, MAP3K5, and SLC17A4 mutations were associated with HF, and RNA-Seq revealed that S100A12, S100A8, S100A9, PFDN5, and TMCC2, were upregulated in patients with HF. Additionally, comparison between RNA-seq and WES data showed that OAS1 mutations are associated with HF.

CONLCUSION

Our findings indicated that patients with HF show an overall disruption of key phosphorylation and immune signalling pathways. Based on RNA-seq and WES, OAS1 mutations may be primarily responsible for these changes.

Subcellular diversity of Nav1.5 in cardiomyocytes: distinct functions, mechanisms and targets

In cardiomyocytes, the rapid depolarisation of the membrane potential is mediated by the α-subunit of the cardiac voltage-gated Na⁺ channel (Na_V 1.5), encoded by the gene SCN5A. This ion channel allows positively charged Na⁺ ions to enter the cardiomyocyte, resulting in the fast upstroke of the action potential and is therefore crucial for cardiac excitability and electrical propagation. This essential role is underscored by the fact that dysfunctional Na_V 1.5 is associated with high risk for arrhythmias and sudden cardiac death. However, development of therapeutic interventions regulating Na_V 1.5 has been limited due to the complexity of Na_V 1.5 structure and function and its diverse roles within the cardiomyocyte. In particular, research from the last decade has provided us with increased knowledge on the subcellular distribution of Na_V 1.5 as well as the proteins which it interacts with in distinct cardiomyocyte microdomains. We here review these insights, detailing the potential role of Na_V 1.5 within subcellular domains as well as its dysfunction in the setting of arrhythmia disorders. We furthermore provide an overview of current knowledge on the pathways involved in (microdomain-specific) trafficking of Na_V 1.5, and their potential as novel targets. Unravelling the complexity of Na_V 1.5 (dys)function may ultimately facilitate the development of therapeutic strategies aimed at preventing lethal arrhythmias. This is not only of importance for pathophysiological conditions where sodium current is specifically decreased within certain subcellular regions, such as in arrhythmogenic cardiomyopathy and Duchenne muscular dystrophy, but also for other acquired and inherited disorders associated with Na_V 1.5.

Modern genomic techniques in the identification of genetic causes of cardiomyopathy

Over the past three decades numerous disease-causing genes have been linked to the pathogenesis of heritable cardiomyopathies, but many causal genes are yet to be identified. Next-generation sequencing (NGS) platforms have revolutionised clinical testing capacity in familial cardiomyopathy. In this review, we summarise how NGS technologies have advanced our understanding of genetic non-syndromic cardiomyopathy over the last decade. First, 26 putative new disease-causing genes have been identified to date, mostly from whole-exome sequencing, and some of which (FLNC, MTO1, HCN4) have had a considerable clinical impact and are now included in routine diagnostic gene panels. Second, we consider challenges in variant interpretation and the importance of large-scale NGS population control cohorts for this purpose. Third, an emerging role of common variation in some forms of genetic cardiomyopathy is being elucidated through recent studies which have illustrated an additive effect of numerous polymorphic loci on cardiac parameters; this may explain phenotypic variability and low rates of genetic diagnosis from sequencing studies. Finally, we discuss the clinical utility of genetic testing in cardiomyopathy in Western settings, where NGS panel testing of core disease genes is currently recommended with possible implications for patient management. Given the findings of recent studies, whole-exome or whole-genome sequencing should be considered in patients of non-European ancestry with clearly familial disease, or severe paediatric disease, when no result is obtained on panel sequencing. The clinical utility of polygenic risk assessment needs to be investigated further in patients with unexplained dilated cardiomyopathy and hypertrophic cardiomyopathy in whom a pathogenic variant is not identified.

Arrhythmogenic Cardiomyopathy: Exercise Pitfalls, Role of Connexin-43, and Moving beyond Antiarrhythmics

Arrhythmogenic Cardiomyopathy (ACM), a Mendelian disorder that can affect both left and right ventricles, is most often associated with pathogenic desmosomal variants that can lead to fibrofatty replacement of the myocardium, a pathological hallmark of this disease. Current therapies are aimed to prevent the worsening of disease phenotypes and sudden cardiac death (SCD). Despite the use of implantable cardioverter defibrillators (ICDs) there is no present therapy that would mitigate the loss in electrical signal and propagation by these fibrofatty barriers. Recent studies have shown the influence of forced vs. voluntary exercise in a variety of healthy and diseased mice; more specifically, that exercised mice show increased Connexin-43 (Cx43) expression levels. Fascinatingly, increased Cx43 expression ameliorated the abnormal electrical signal conduction in the myocardium of diseased mice. These findings point to a major translational pitfall in current therapeutics for ACM patients, who are advised to completely cease exercising and already demonstrate reduced Cx43 levels at the myocyte intercalated disc. Considering cardiac dysfunction in ACM arises from the loss of cardiomyocytes and electrical signal conduction abnormalities, an increase in Cx43 expression-promoted by low to moderate intensity exercise and/or gene therapy-could very well improve cardiac function in ACM patients.

Histopathological Features and Protein Markers of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a heritable heart muscle disease characterized by syncope, palpitations, ventricular arrhythmias and sudden cardiac death (SCD) especially in young individuals. It is estimated to affect 1:5,000 individuals in the general population, with >60% of patients bearing one or more mutations in genes coding for desmosomal proteins. Desmosomes are intercellular adhesion junctions, which in cardiac myocytes reside within the intercalated disks (IDs), the areas of mechanical and electrical cell-cell coupling. Histologically, ACM is characterized by fibrofatty replacement of cardiac myocytes predominantly in the right ventricular free wall though left ventricular and biventricular forms have also been described. The disease is characterized by age-related progression, vast phenotypic manifestation and incomplete penetrance, making proband diagnosis and risk stratification of family members particularly challenging. Key protein redistribution at the IDs may represent a specific diagnostic marker but its applicability is still limited by the need for a myocardial sample. Specific markers of ACM in surrogate tissues, such as the blood and the buccal epithelium, may represent a non-invasive, safe and inexpensive alternative for diagnosis and cascade screening. In this review, we shall cover the most relevant biomarkers so far reported and discuss their potential impact on the diagnosis, prognosis and management of ACM.

Insights Into Genetics and Pathophysiology of Arrhythmogenic Cardiomyopathy

Purpose of Review

Arrhythmogenic cardiomyopathy (ACM) is a genetic disease characterized by life-threatening ventricular arrhythmias and sudden cardiac death (SCD) in apparently healthy young adults. Mutations in genes encoding for cellular junctions can be found in about half of the patients. However, disease onset and severity, risk of arrhythmias, and outcome are highly variable and drug-targeted treatment is currently unavailable.

Recent Findings

This review focuses on advances in clinical risk stratification, genetic etiology, and pathophysiological concepts. The desmosome is the central part of the disease, but other intercalated disc and associated structural proteins not only broaden the genetic spectrum but also provide novel molecular and cellular insights into the pathogenesis of ACM. Signaling pathways and the role of inflammation will be discussed and targets for novel therapeutic approaches outlined.

Summary

Genetic discoveries and experimental-driven preclinical research contributed significantly to the understanding of ACM towards mutation- and pathway-specific personalized medicine.

Identification of Hub Genes and MicroRNAs Associated With Idiopathic Pulmonary Arterial Hypertension by Integrated Bioinformatics Analyses

Objective

The aim of this study is the identification of hub genes associated with idiopathic pulmonary arterial hypertension (IPAH).

Materials and Methods

GSE15197 gene expression data was downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified by screening IPAH patients and controls. The 5,000 genes with the greatest variances were analyzed using a weighted gene co-expression network analysis (WGCNA). Modules with the strongest correlation with IPAH were chosen, followed by a functional enrichment analysis. Protein–protein interaction (PPI) networks were constructed to identify hub gene candidates using calculated degrees. Real hub genes were found from the overlap of DEGs and candidate hub genes. microRNAs (miRNAs) targeting real hub genes were found by screening miRNet 2.0. The most important IPAH miRNAs were identified.

Results

There were 4,395 DEGs identified. WGCNA indicated that green and brown modules associated most strongly with IPAH. Functional enrichment analysis showed that green and brown module genes were mainly involved in protein digestion and absorption and proteoglycans in cancer, respectively. The top ten candidate hub genes in green and brown modules were identified, respectively. After overlapping with DEGs, 11 real hub genes were identified: EP300, MMP2, CDH2, CDK2, GNG10, ALB, SMC2, DHX15, CUL3, BTBD1, and LTN1. These genes were expressed with significant differences in IPAH versus controls, indicating a high diagnostic ability. The miRNA–gene network showed that hsa-mir-1-3p could associate with IPAH.

Conclusion

EP300, MMP2, CDH2, CDK2, GNG10, ALB, SMC2, DHX15, CUL3, BTBD1, and LTN1 may play essential roles in IPAH. Predicted miRNA hsa-mir-1-3p could regulate gene expression in IPAH. Such hub genes may contribute to the pathology and progression in IPAH, providing potential diagnostic and therapeutic opportunities for IPAH patients.