Evolving molecular diagnostics for familial cardiomyopathies: at the heart of it all

Mendelian Randomization Study on the Associations Between Genetically Predicted Cardiovascular Disease Subtypes and the Risk of Developing Cardiomyopathies

Cardiomyopathies are commonly believed to have genetic origins; however, the connection between cardiomyopathies and cardiovascular diseases remains uncertain. Thus, we employed a Mendelian randomization (MR) approach to investigate the potential causal effects of specific cardiovascular disease subtypes on dilated and hypertrophic cardiomyopathies, focusing primarily on a European population. Summary-level data for cardiomyopathies and other cardiovascular diseases were obtained from public genome-wide association studies. Random-effects inverse-variance weighting was used as the primary analysis, whereas sensitivity analyses, including weighted median, MR-Egger, and multivariable MR methods, were also conducted. A genetic predisposition to atrial fibrillation [odds ratio (OR): 1.33; 95% confidence interval (CI): 1.18-1.50; P < 0.001], heart failure (OR: 3.22; 95% CI: 1.92-5.41; P < 0.001), and hypertension (OR: 1.50; 95% CI: 1.25-1.81; P < 0.001) were causally linked to an increased risk of developing dilated cardiomyopathy. However, there was no direct causal connection between genetically predicted coronary heart disease, pulmonary embolism, or ischemic stroke and the risk of developing dilated cardiomyopathy. In contrast, no significant associations were found between genetically predicted CVD subtypes and the risk of developing hypertrophic cardiomyopathy. Genetically predicted heart failure is significantly associated with the risk of developing dilated cardiomyopathy, underscoring the importance of effective heart failure management for risk prevention. Moreover, individuals with hypertension and atrial fibrillation might have an increased predisposition to dilated cardiomyopathy, highlighting crucial implications for management.

Association between cathepsins and cardiomyopathy: A Mendelian randomization study

Research suggests that cathepsins, due to their extensive mechanisms of action, may play a crucial role in cardiomyopathies. However, further studies are necessary to establish causality. This study aims to investigate the causal relationship between cathepsins and various types of cardiomyopathies. This study investigated causal associations between 9 cathepsins and cardiomyopathies, including their subtypes: hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy, and restrictive cardiomyopathy, using pooled data from genome-wide association studies. The analyses employed inverse variance weighted (IVW), Mendelian randomization (MR)-Egger, and weighted median methods for univariable MR, reverse MR, and multivariable MR to estimate causality. For sensitivity analyses, we applied Cochran Q test, MR-PRESSO, MR-Egger intercept test, and the leave-one-out method to ensure the robustness and reliability of our findings. Univariable MR analyses indicated that elevated levels of cathepsin E were associated with an increased risk of overall cardiomyopathy (IVW: P = .045, odds ratio [OR] = 1.078, 95% confidence interval [CI] = 1.002-1.160). Conversely, higher levels of cathepsin B were linked to a reduced risk of HCM (IVW: P = .037, OR = 0.856, 95% CI = 0.740-0.990), and higher cathepsin O levels were causally related to a reduced risk of HCM (IVW: P = .04, OR = 0.810, 95% CI = 0.662-0.991). Reverse MR analyses indicated that a higher risk of HCM was causally related to increased levels of cathepsin E (IVW: P = .038, OR = 1.024, 95% CI = 1.001-1.047). Multivariable MR analyses showed that increased cathepsin E levels still correlated with increased overall cardiomyopathy, even after the addition of other types of cathepsins (IVW: P = .0165, OR = 1.005, 95% CI = 1.0176-1.1901), while cathepsin O levels remained causally related to a reduced risk of HCM (IVW: P = .0053, OR = 0.7183, 95% CI = 0.5692-0.9065). Cathepsin L2 was also found to be associated with an increased risk of restrictive cardiomyopathy (IVW: P = .0374, OR = 2.1337, 95% CI = 1.0450-4.3565). This study demonstrates the causal relationship between cathepsins E, B, L2, O and the development of cardiomyopathy. The findings may be crucial for early diagnosis, prognosis prediction, molecular classification, and identifying potential therapeutic targets for cardiomyopathy.

Cardiomyopathy: pathogenesis and therapeutic interventions

Cardiomyopathy is a group of disease characterized by structural and functional damage to the myocardium. The etiologies of cardiomyopathies are diverse, spanning from genetic mutations impacting fundamental myocardial functions to systemic disorders that result in widespread cardiac damage. Many specific gene mutations cause primary cardiomyopathy. Environmental factors and metabolic disorders may also lead to the occurrence of cardiomyopathy. This review provides an in-depth analysis of the current understanding of the pathogenesis of various cardiomyopathies, highlighting the molecular and cellular mechanisms that contribute to their development and progression. The current therapeutic interventions for cardiomyopathies range from pharmacological interventions to mechanical support and heart transplantation. Gene therapy and cell therapy, propelled by ongoing advancements in overarching strategies and methodologies, has also emerged as a pivotal clinical intervention for a variety of diseases. The increasing number of causal gene of cardiomyopathies have been identified in recent studies. Therefore, gene therapy targeting causal genes holds promise in offering therapeutic advantages to individuals diagnosed with cardiomyopathies. Acting as a more precise approach to gene therapy, they are gradually emerging as a substitute for traditional gene therapy. This article reviews pathogenesis and therapeutic interventions for different cardiomyopathies.

Phenotyping heart failure by genetics and associated conditions

Heart failure is a highly heterogeneous disease, and genetic testing may allow phenotypic distinctions that are incremental to those obtainable from imaging. Advances in genetic testing have allowed for the identification of deleterious variants in patients with specific heart failure phenotypes (dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and hypertrophic cardiomyopathy), and many of these have specific treatment implications. The diagnostic yield of genetic testing in heart failure is modest, and many rare variants are associated with incomplete penetrance and variable expressivity. Environmental factors and co-morbidities have a large role in the heterogeneity of the heart failure phenotype. Future endeavours should concentrate on the cumulative impact of genetic polymorphisms in the development of heart failure.

Role of non-coding variants in cardiovascular disease

Cardiovascular diseases (CVDs) constitute one of the significant causes of death worldwide. Different pathological states are linked to CVDs, which despite interventions and treatments, still have poor prognoses. The genetic component, as a beneficial tool in the risk stratification of CVD development, plays a role in the pathogenesis of this group of diseases. The emergence of genome-wide association studies (GWAS) have led to the identification of non-coding parts associated with cardiovascular traits and disorders. Variants located in functional non-coding regions, including promoters/enhancers, introns, miRNAs and 5'/3' UTRs, account for 90% of all identified single-nucleotide polymorphisms associated with CVDs. Here, for the first time, we conducted a comprehensive review on the reported non-coding variants for different CVDs, including hypercholesterolemia, cardiomyopathies, congenital heart diseases, thoracic aortic aneurysms/dissections and coronary artery diseases. Additionally, we present the most commonly reported genes involved in each CVD. In total, 1469 non-coding variants constitute most reports on familial hypercholesterolemia, hypertrophic cardiomyopathy and dilated cardiomyopathy. The application and identification of non-coding variants are beneficial for the genetic diagnosis and better therapeutic management of CVDs.

Genomic findings of hypertrophic and dilated cardiomyopathy characterized in a Thai clinical genetics service

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are the most common referrals in the Inherited Cardiovascular Condition (ICC) Genetics Service. Several issues must be discussed with patients and their families during the genetic consultation session, including the options for genetic testing and cardiovascular surveillance in family members. We developed an ICC registry and performed next-generation-based DNA sequencing for all patients affected by non-syndromic HCM and idiopathic DCM in our joint specialist genetics service. The target gene sequencing panel relied on the Human Phenotype Ontology with 237 genes for HCM (HP:0001639) and 142 genes for DCM (HP:0001644). All subjects were asked to contact their asymptomatic first-degree relatives for genetic counseling regarding their risks and to initiate cardiovascular surveillance and cascade genetic testing. The study was performed from January 1, 2014, to December 31, 2020, and a total of 62 subjects (31-HCM and 31-DCM) were enrolled. The molecular detection frequency was 48.39% (32.26% pathogenic/likely pathogenic, 16.13% variant of uncertain significance or VUS for HCM, and 25.81% (16.13% pathogenic/likely pathogenic, 9.68% VUS) for DCM. The most prevalent gene associated with HCM was MYBPC3. The others identified in this study included ACTN2, MYL2, MYH7, TNNI3, TPM1, and VCL. Among the DCM subjects, variants were detected in two cases with the TTN nonsense variants, while the others were missense and identified in MYH7, DRSP3, MYBPC3, and SCN5A. Following the echocardiogram surveillance and cascade genetic testing in the asymptomatic first-degree relatives, the detection rate of new cases was 8.82% and 6.25% in relatives of HCM and DCM subjects, respectively. Additionally, a new pre-symptomatic relative belonging to an HCM family was identified, although the genomic finding in the affected case was absent. Thus, ICC service is promising for the national healthcare system, aiming to prevent morbidity and mortality in asymptomatic family members.

Restrictive cardiomyopathy: from genetics and clinical overview to animal modeling

Restrictive cardiomyopathy (RCM), a potentially devastating heart muscle disorder, is characterized by diastolic dysfunction due to abnormal muscle relaxation and myocardial stiffness resulting in restrictive filling of the ventricles. Diastolic dysfunction is often accompanied by left atrial or bi-atrial enlargement and normal ventricular size and systolic function. RCM is the rarest form of cardiomyopathy, accounting for 2-5% of pediatric cardiomyopathy cases, however, survival rates have been reported to be 82%, 80%, and 68% at 1-, 2-, and 5-years after diagnosis, respectively. RCM can be idiopathic, familial, or secondary to a systemic disorder, such as amyloidosis, sarcoidosis, and hereditary hemochromatosis. Approximately 30% of cases are familial RCM, and the genes that have been linked to RCM are cTnT, cTnI, MyBP-C, MYH7, MYL2, MYL3, DES, MYPN, TTN, BAG3, DCBLD2, LNMA, and FLNC. Increased Ca2+ sensitivity, sarcomere disruption, and protein aggregates are some of the few mechanisms of pathogenesis that have been revealed by studies utilizing cell lines and animal models. Additional exploration into the pathogenesis of RCM is necessary to create novel therapeutic strategies to reverse restrictive cardiomyopathic phenotypes.

Genetic predisposition study of heart failure and its association with cardiomyopathy

Heart failure (HF) is a clinical condition distinguished by structural and functional defects in the myocardium, which genetic and environmental factors can induce. HF is caused by various genetic factors that are both heterogeneous and complex. The incidence of HF varies depending on the definition and area, but it is calculated to be between 1 and 2% in developed countries. There are several factors associated with the progression of HF, ranging from coronary artery disease to hypertension, of which observed the most common genetic cause to be cardiomyopathy. The main objective of this study is to investigate heart failure and its association with cardiomyopathy with their genetic variants. The selected novel genes that have been linked to human inherited cardiomyopathy play a critical role in the pathogenesis and progression of HF. Research sources collected from the human gene mutation and several databases revealed that numerous genes are linked to cardiomyopathy and thus explained the hereditary influence of such a condition. Our findings support the understanding of the genetics aspect of HF and will provide more accurate evidence of the role of changing disease accuracy. Furthermore, a better knowledge of the molecular pathophysiology of genetically caused HF could contribute to the emergence of personalized therapeutics in future.

Genetics and pharmacogenetics in the diagnosis and therapy of cardiovascular diseases

Cardiovascular diseases are the main cause of death worldwide. The ability to accurately define individual susceptibility to these disorders is therefore of strategic importance. Linkage analysis and genome-wide association studies have been useful for the identification of genes related to cardiovascular diseases. The identification of variants predisposing to cardiovascular diseases contributes to the risk profile and the possibility of tailored preventive or therapeutic strategies. Molecular genetics and pharmacogenetics are playing an increasingly important role in the correct clinical management of patients. For instance, genetic testing can identify variants that influence how patients metabolize medications, making it possible to prescribe personalized, safer and more efficient treatments, reducing medical costs and improving clinical outcomes. In the near future we can expect a great increment in information and genetic testing, which should be acknowledged as a true branch of diagnostics in cardiology, like hemodynamics and electrophysiology. In this review we summarize the genetics and pharmacogenetics of the main cardiovascular diseases, showing the role played by genetic information in the identification of cardiovascular risk factors and in the diagnosis and therapy of these conditions. (www.actabiomedica.it)

Cardiomyopathies

The most common cardiomyopathies often present to primary care physicians with similar symptoms, despite the fact that they involve a variety of phenotypes and etiologies (1). Many have signs and symptoms common in heart failure, such as reduced ejection fraction, peripheral edema, fatigue, orthopnea, exertion dyspnea, paroxysmal nocturnal dyspnea, presyncope, syncope and cardiac ischemia (1). In all cardiomyopathies, the cardiac muscle (myocardium) may be structurally and/or functionally impaired. They can be classified as hypertrophic, dilated, left-ventricular non compaction, restrictive and arrhythmogenic right ventricular cardiomyopathies. (www.actabiomedica.it)

Biallelic mutation in MYH7 and MYBPC3 leads to severe cardiomyopathy with left ventricular noncompaction phenotype

Dominant mutations in the MYH7 and MYBPC3 genes are common causes of inherited cardiomyopathies, which often demonstrate variable phenotypic expression and incomplete penetrance across family members. Biallelic inheritance is rare but allows gaining insights into the genetic mode of action of single variants. Here, we present three cases carrying a loss-of-function (LoF) variant in a compound heterozygous state with a missense variant in either MYH7 or MYBPC3 leading to severe cardiomyopathy with left ventricular noncompaction. Most likely, MYH7 haploinsufficiency due to one LoF allele results in a clinical phenotype only in compound heterozygous form with a missense variant. In contrast, haploinsufficiency in MYBPC3 results in a severe early-onset ventricular noncompaction phenotype requiring heart transplantation when combined with a de novo missense variant on the second allele. In addition, the missense variant may lead to an unstable protein, as overall only 20% of the MYBPC3 protein remain detectable in affected cardiac tissue compared to control tissue. In conclusion, in patients with early disease onset and atypical clinical course, biallelic inheritance or more complex variants including copy number variations and de novo mutations should be considered. In addition, the pathogenic consequence of variants may differ in heterozygous versus compound heterozygous state.

Chronic Calmodulin-Kinase II Activation Drives Disease Progression in Mutation-Specific Hypertrophic Cardiomyopathy

BACKGROUND

Although the genetic causes of hypertrophic cardiomyopathy (HCM) are widely recognized, considerable lag in the development of targeted therapeutics has limited interventions to symptom palliation. This is in part attributable to an incomplete understanding of how point mutations trigger pathogenic remodeling. As a further complication, similar mutations within sarcomeric genes can result in differential disease severity, highlighting the need to understand the mechanism of progression at the molecular level. One pathway commonly linked to HCM progression is calcium homeostasis dysregulation, though how specific mutations disrupt calcium homeostasis remains unclear.

METHODS

To evaluate the effects of early intervention in calcium homeostasis, we used 2 mouse models of sarcomeric HCM (cardiac troponin T R92L and R92W) with differential myocellular calcium dysregulation and disease presentation. Two modes of intervention were tested: inhibition of the autoactivated calcium-dependent kinase (calmodulin kinase II [CaMKII]) via the AC3I peptide and diltiazem, an L-type calcium channel antagonist. Two-dimensional echocardiography was used to determine cardiac function and left ventricular remodeling, and atrial remodeling was monitored via atrial mass. Sarcoplasmic reticulum Ca2+ATPase activity was measured as an index of myocellular calcium handling and coupled to its regulation via the phosphorylation status of phospholamban.

RESULTS

We measured an increase in phosphorylation of CaMKII in R92W animals by 6 months of age, indicating increased autonomous activity of the kinase in these animals. Inhibition of CaMKII led to recovery of diastolic function and partially blunted atrial remodeling in R92W mice. This improved function was coupled to increased sarcoplasmic reticulum Ca2+ATPase activity in the R92W animals despite reduction of CaMKII activation, likely indicating improvement in myocellular calcium handling. In contrast, inhibition of CaMKII in R92L animals led to worsened myocellular calcium handling, remodeling, and function. Diltiazem-HCl arrested diastolic dysfunction progression in R92W animals only, with no improvement in cardiac remodeling in either genotype.

CONCLUSIONS

We propose a highly specific, mutation-dependent role of activated CaMKII in HCM progression and a precise therapeutic target for clinical management of HCM in selected cohorts. Moreover, the mutation-specific response elicited with diltiazem highlights the necessity to understand mutation-dependent progression at a molecular level to precisely intervene in disease progression.

Phenotypic diversity identified by cardiac magnetic resonance in a large hypertrophic cardiomyopathy family with a single MYH7 mutation

Limited data is available on phenotypic variations with the same genotype in hypertrophic cardiomyopathy (HCM). The present study aims to explore the relationship between genotype and phenotype characterized by cardiovascular magnetic resonance (CMR) in a large Chinese family. A proband diagnosed with HCM from a multigenerational family underwent next-generation sequencing based on a custom sureSelect panel, including 117 candidate pathogenic genes associated with cardiomyopathies. All genetic results were confirmed by the Sanger sequencing method. All confirmed mutation carriers underwent CMR exam and myocardial tissue characterization using T1 mapping and late gadolinium enhancement (LGE) on a 3T scanner (Siemens Trio, Gemany). After clinical and genetic screening of 36 (including the proband) members of a large Chinese family, nineteen family members are determined to carry the single p.T1377M (c.4130C>T) mutation in the MYH7 gene. Of these 19 mutation carriers, eight are diagnosed with HCM, one was considered as borderline affected and ten are not clinically or phenotypically affected. Different HCM phenotypes are present in the nine affected individuals in this family. In addition, we have found different tissue characteristics assessed by T1 mapping and LGE in these individuals. We describe a family that demonstrates the diverse HCM phenotypes associated with a single MYH7 mutation.

Autosomal Dominant Polycystic Kidney Patients May Be Predisposed to Various Cardiomyopathies

Introduction

Mutations in PKD1 and PKD2 cause autosomal dominant polycystic kidney disease (ADPKD). Experimental evidence suggests an important role of the polycystins in cardiac development and myocardial function. To determine whether ADPKD may predispose to the development of cardiomyopathy, we have evaluated the coexistence of diagnoses of ADPKD and primary cardiomyopathy in our patients.

Methods

Clinical data were retrieved from medical records for patients with a coexisting diagnosis of ADPKD and cardiomyopathies evaluated at the Mayo Clinic (1984-2015).

Results

Among the 58 of 667 patients with available echocardiography data, 39 (5.8%) had idiopathic dilated cardiomyopathy (IDCM), 17 (2.5%) had hypertrophic obstructive cardiomyopathy, and 2 (0.3%) had left ventricular noncompaction. Genetic data were available for 19, 8, and 2 cases of IDCM, hypertrophic obstructive cardiomyopathy, and left ventricular noncompaction, respectively. PKD1 mutations were detected in 42.1%, 62.5%, and 100% of IDCM, hypertrophic obstructive cardiomyopathy, and left ventricular noncompaction cases, respectively. PKD2 mutations were detected only in IDCM cases and were overrepresented (36.8%) relative to the expected frequency in ADPKD (15%). In at least 1 patient from 3 IDMC families and 1 patient from a hypertrophic obstructive cardiomyopathy family, the cardiomyopathy did not segregate with ADPKD, suggesting that the PKD mutations may be predisposing factors rather than solely responsible for the development of cardiomyopathy.

Discussion

Coexistence of ADPKD and cardiomyopathy in our tertiary referral center cohort appears to be higher than expected by chance. We suggest that PKD1 and PKD2 mutations may predispose to primary cardiomyopathies and that genetic interactions may account for the observed coexistence of ADPKD and cardiomyopathies.

Diverse Phenotypic Expression of Cardiomyopathies in a Family with TNNI3 p.Arg145Trp Mutation

Genetic diagnosis of cardiomyopathies is challenging, due to the marked genetic and allelic heterogeneity and the lack of knowledge of the mutations that lead to clinical phenotypes. Here, we present the case of a large family, in which a single TNNI3 mutation caused variable phenotypic expression, ranging from restrictive cardiomyopathy (RCMP) to hypertrophic cardiomyopathy (HCMP) to near-normal phenotype. The proband was a 57-year-old female with HCMP. Examining the family history revealed that her elder sister had expired due to severe RCMP. Using a next-generation sequencing-based gene panel to analyze the proband, we identified a known TNNI3 gene mutation, c.433C>T, which is predicted to cause an amino acid substitution (p.Arg145Trp) in the highly conserved inhibitory region of the cardiac troponin I protein. Sanger sequencing confirmed that six relatives with RCMP or near-normal phenotypes also carried this mutation. To our knowledge, this is the first genetically confirmed family with diverse phenotypic expression of cardiomyopathies in Korea. Our findings demonstrate familial implications, where a single mutation in a sarcomere protein can cause diverse phenotypic expression of cardiomyopathies.

Identification of novel mutations including a double mutation in patients with inherited cardiomyopathy by a targeted sequencing approach using the Ion Torrent PGM system

Inherited cardiomyopathy is the major cause of sudden cardiac death (SCD) and heart failure (HF). The disease is associated with extensive genetic heterogeneity; pathogenic mutations in cardiac sarcomere protein genes, cytoskeletal protein genes and nuclear envelope protein genes have been linked to its etiology. Early diagnosis is conducive to clinical monitoring and allows for presymptomatic interventions as needed. In the present study, the entire coding sequences and flanking regions of 12 major disease (cardiomyopathy)-related genes [namely myosin, heavy chain 7, cardiac muscle, β (MYH7); myosin binding protein C, cardiac (MYBPC3); lamin A/C (LMNA); troponin I type 3 (cardiac) (TNNI3); troponin T type 2 (cardiac) (TNNT2); actin, α, cardiac muscle 1 (ACTC1); tropomyosin 1 (α) (TPM1); sodium channel, voltage gated, type V alpha subunit (SCN5A); myosin, light chain 2, regulatory, cardiac, slow (MYL2); myosin, heavy chain 6, cardiac muscle, α (MYH6); myosin, light chain 3, alkali, ventricular, skeletal, slow (MYL3); and protein kinase, AMP-activated, gamma 2 non-catalytic subunit  (PRKAG2)] in 8 patients with dilated cardiomyopathy (DCM) and in 8 patients with hypertrophic cardiomyopathy (HCM) were amplified and then sequenced using the Ion Torrent Personal Genome Machine (PGM) system. As a result, a novel heterozygous mutation (MYH7, p.Asn885Thr) and a variant of uncertain significance (TNNT2, p.Arg296His) were identified in 2 patients with HCM. These 2 missense mutations, which were absent in the samples obtained from the 200 healthy control subjects, altered the amino acid that was evolutionarily conserved among a number of vertebrate species; this illustrates that these 2 non-synonymous mutations play a role in the pathogenesis of HCM. Moreover, a double heterozygous mutation (PRKAG2, p.Gly100Ser plus MYH7, p.Arg719Trp) was identified in a patient with severe familial HCM, for the first time to the best of our knowledge. This patient provided us with more information regarding the genotype-phenotype correlation between mutations of MYH7 and PRKAG2. Taken together, these findings provide insight into the molecular mechanisms underlying inherited cardiomyopathy. The mutations identified in this study may be further investigated in the future in order to improve the diagnosis and treatment of patients with inherited cardiomyopathy. Furthermore, our findings indicated that sequencing using the Ion Torrent PGM system is a useful approach for the identification of pathogenic mutations associated with inherited cardiomyopathy, and it may be used for the risk evaluation of individuals with a possible susceptibility to inherited cardiomyopathy.

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

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

Knock-out of nexilin in mice leads to dilated cardiomyopathy and endomyocardial fibroelastosis

Cardiomyopathy is one of the most common causes of chronic heart failure worldwide. Mutations in the gene encoding nexilin (NEXN) occur in patients with both hypertrophic and dilated cardiomyopathy (DCM); however, little is known about the pathophysiological mechanisms and relevance of NEXN to these disorders. Here, we evaluated the functional role of NEXN using a constitutive Nexn knock-out (KO) mouse model. Heterozygous (Het) mice were inter-crossed to produce wild-type (WT), Het, and homozygous KO mice. At birth, 32, 46, and 22 % of the mice were WT, Het, and KO, respectively, which is close to the expected Mendelian ratio. After postnatal day 6, the survival of the Nexn KO mice decreased dramatically and all of the animals died by day 8. Phenotypic characterizations of the WT and KO mice were performed at postnatal days 1, 2, 4, and 6. At birth, the relative heart weights of the WT and KO mice were similar; however, at day 4, the relative heart weight of the KO group was 2.3-fold higher than of the WT group. In addition, the KO mice developed rapidly progressive cardiomyopathy with left ventricular dilation and wall thinning and decreased cardiac function. At day 6, the KO mice developed a fulminant DCM phenotype characterized by dilated ventricular chambers and systolic dysfunction. At this stage, collagen deposits and some elastin deposits were observed within the left ventricle cavity, which resembles the features of endomyocardial fibroelastosis (EFE). Overall, these results further emphasize the role of NEXN in DCM and suggest a novel role in EFE.

Genetics and heart failure: a concise guide for the clinician

The pathogenesis of heart failure involves a complex interaction between genetic and environmental factors. Genetic factors may influence the susceptibility to the underlying etiology of heart failure, the rapidity of disease progression, or the response to pharmacologic therapy. The genetic contribution to heart failure is relatively minor in most multifactorial cases, but more direct and profound in the case of familial dilated cardiomyopathy. Early studies of genetic risk for heart failure focused on polymorphisms in genes integral to the adrenergic and renin-angiotensin-aldosterone system. Some of these variants were found to increase the risk of developing heart failure, and others appeared to affect the therapeutic response to neurohormonal antagonists. Regardless, each variant individually confers a relatively modest increase in risk and likely requires complex interaction with other variants and the environment for heart failure to develop. Dilated cardiomyopathy frequently leads to heart failure, and a genetic etiology increasingly has been recognized in cases previously considered to be "idiopathic". Up to 50% of dilated cardiomyopathy cases without other cause likely are due to a heritable genetic mutation. Such mutations typically are found in genes encoding sarcomeric proteins and are inherited in an autosomal dominant fashion. In recent years, rapid advances in sequencing technology have improved our ability to diagnose familial dilated cardiomyopathy and those diagnostic tests are available widely. Optimal care for the expanding population of patients with heritable heart failure involves counselors and physicians with specialized training in genetics, but numerous online genetics resources are available to practicing clinicians.

Experimental models of inherited cardiomyopathy and its therapeutics

Cardiomyopathy is a disease of myocardium categorized into three major forms, hypertrophic (HCM), dilated (DCM) and restrictive cardiomyopathy (RCM), which has recently been demonstrated to be a monogenic disease due to mutations in various proteins expressed in cardiomyocytes. Mutations in HCM and RCM typically increase the myofilament sensitivity to cytoplasmic Ca²⁺, leading to systolic hyperfunction and diastolic dysfunction. In contrast, mutations in DCM typically decrease the myofilament sensitivity to cytoplasmic Ca²⁺ and/or force generation/transmission, leading to systolic dysfunction. Creation of genetically-manipulated transgenic and knock-in animals expressing mutant proteins exogenously and endogenously, respectively, in their hearts provides valuable animal models to discover the molecular and cellular mechanisms for pathogenesis and promising therapeutic strategy in vivo. Recently, cardiomyocytes have been differentiated from patient’s induced pluripotent stem cells as a model of inherited cardiomyopathies in vitro. In this review, we provide overview of experimental models of cardiomyopathies with a focus on revealed molecular and cellular pathogenic mechanisms and potential therapeutics.

Importance of genetic evaluation and testing in pediatric cardiomyopathy

Pediatric cardiomyopathies are clinically heterogeneous heart muscle disorders that are responsible for significant morbidity and mortality. Phenotypes include hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, left ventricular noncompaction and arrhythmogenic right ventricular cardiomyopathy. There is substantial evidence for a genetic contribution to pediatric cardiomyopathy. To date, more than 100 genes have been implicated in cardiomyopathy, but comprehensive genetic diagnosis has been problematic because of the large number of genes, the private nature of mutations, and difficulties in interpreting novel rare variants. This review will focus on current knowledge on the genetic etiologies of pediatric cardiomyopathy and their diagnostic relevance in clinical settings. Recent developments in sequencing technologies are greatly impacting the pace of gene discovery and clinical diagnosis. Understanding the genetic basis for pediatric cardiomyopathy and establishing genotype-phenotype correlations may help delineate the molecular and cellular events necessary to identify potential novel therapeutic targets for heart muscle dysfunction in children.

Cardiovascular genomics

PURPOSE

This article provides an update on cardiovascular genomics using three clinically relevant exemplars, including myocardial infarction (MI) and coronary artery disease (CAD), stroke, and sudden cardiac death (SCD). ORGANIZATIONAL CONSTRUCT: Recent advances in cardiovascular genomic research, testing, and clinical implications are presented.

METHODS

Genomic nurse experts reviewed and summarized recent salient literature to provide updates on three selected cardiovascular genomic conditions.

FINDINGS

Research is ongoing to discover comprehensive genetic markers contributing to many common forms of cardiovascular disease (CVD), including MI and stroke. However, genomic technologies are increasingly being used clinically, particularly in patients with long QT syndrome (LQTS) or hypertrophic cardiomyopathy (HCM) who are at risk for SCD.

CONCLUSIONS

Currently, there are no clinically recommended genetic tests for many common forms of CVD even though direct-to-consumer genetic tests are being marketed to healthcare providers and the general public. On the other hand, genetic testing for patients with certain single gene conditions, including channelopathies (e.g., LQTS) and cardiomyopathies (e.g., HCM), is recommended clinically.

CLINICAL RELEVANCE

Nurses play a pivotal role in cardiogenetics and are actively engaged in direct clinical care of patients and families with a wide variety of heritable conditions. It is important for nurses to understand current development of cardiovascular genomics and be prepared to translate the new genomic knowledge into practice.

Inherited cardiomyopathies: molecular genetics and clinical genetic testing in the postgenomic era

Inherited cardiomyopathies include hypertrophic cardiomyopathy, dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, left ventricular noncompaction, and restrictive cardiomyopathy. These diseases have a substantial genetic component and predispose to sudden cardiac death, which provides a high incentive to identify and sequence disease genes in affected individuals to identify pathogenic variants. Clinical genetic testing, which is now widely available, can be a powerful tool for identifying presymptomatic individuals. However, locus and allelic heterogeneity are the rule, as are clinical variability and reduced penetrance of disease in carriers of pathogenic variants. These factors, combined with genetic and phenotypic overlap between different cardiomyopathies, have made clinical genetic testing a lengthy and costly process. Next-generation sequencing technologies have removed many limitations such that comprehensive testing is now feasible, shortening diagnostic odysseys for clinically complex cases. Remaining challenges include the incomplete understanding of the spectrum of benign and pathogenic variants in the cardiomyopathy genes, which is a source of inconclusive results. This review provides an overview of inherited cardiomyopathies with a focus on their genetic etiology and diagnostic testing in the postgenomic era.

[Isolated noncompaction cardiomyopathy with special emphasis on arrhythmia complications]

Isolated noncompaction cardiomyopathy (NCCM) is a rare genetically determined myocardial disease caused by abnormal fetal development of the myocardium resulting in a thin compacted and a thicker noncompacted layer of the affected left ventricular (LV) wall. The genetic basis of NCCM is heterogenous. Diagnosis can be made using echocardiography or magnetic resonance imaging. The diagnostic criteria for NCCM are still under discussion. Afflicted patients may present with various symptoms caused by arrhythmias, heart failure and cardioembolic events. Severely reduced LV function as well as left bundle branch block and atrial fibrillation were shown to be linked to worse outcomes. Treatment in patients with NCCM should be targeted at individual symptoms and clinical findings. Therapy includes pharmacological treatment, and in individual cases ablation or device therapy, as well as consideration for heart transplantation in selected cases. Aside from regular clinical follow-up of patients with NCCM screening of first degree family members with assessment of medical history, physical examination, ECG recording, and echocardiography are recommended.

Caenorhabditis elegans muscle: a genetic and molecular model for protein interactions in the heart

The nematode Caenorhabditis elegans has become established as a major experimental organism with applications to many biomedical research areas. The body wall muscle cells are a useful model for the study of human cardiomyocytes and their homologous structures and proteins. The ability to readily identify mutations affecting these proteins and structures in C elegans and to be able to rigorously characterize their genotypes and phenotypes at the cellular and molecular levels permits mechanistic studies of the responsible interactions relevant to the inherited human cardiomyopathies. Future work in C elegans muscle holds great promise in uncovering new mechanisms in the pathogenesis of these cardiac disorders.

Edge of the world: practical considerations and a clinical perspective of next-generation sequencing for hereditary cardiac disease

In the article by Jongbloed et al. in the current issue of Expert Opinion on Medical Diagnostics entitled 'New clinical molecular diagnostic methods for congenital and inherited heart disease', the authors introduce the application of next-generation sequencing technologies to a wide range of genetically based cardiac diseases. Although these technologies certainly are exciting and hold great diagnostic promise, their impact is limited at present by insufficient correlation between genotype and phenotype in cardiac disease. In the following discussion, the application of genetic testing in the evaluation of two important familial cardiac diseases, familial cardiomyopathy and long QT syndrome, is considered.