Search Results (63)

Myosin-binding protein C (MyBP-C) comprises a family of myofilament proteins that maintain sarcomeric structure and regulate actomyosin crossbridge cycling. Pathogenic variants in MYBPC1, the gene encoding the slow skeletal isoform (sMyBP-C), lead to a dominant congenital myopathy, termed Myotrem, characterized by muscle weakness, hypotonia, and a distinctive tremor of myogenic origin, in the absence of neuropathy. However, the molecular mechanism(s) of myogenic tremorgenesis is largely unknown. One potential mechanism is aberrant myofilament stretch activation, which is defined as a delayed increase in force after a rapid stretch. We utilized the Myotrem murine model harboring the pathogenic MYBPC1 E248K variant to test the hypothesis that stretch activation is augmented in permeabilized Myotrem E248K soleus fibers. We found that stretch activation was significantly increased in E248K soleus muscle fibers. Interestingly, once submaximally Ca²⁺ activated, a subpopulation of slow-twitch E248K fibers exhibited spontaneous pulsatile sarcomere oscillations. This pulsing behavior generated a sinusoidal waveform pattern in sarcomere length, which often persisted on a timescale of minutes. These results align with sMyBP-C as key regulator of the synchronous activation of myofilaments by dampening both spontaneous oscillatory activity and stretch-dependent activation. We propose that the presence of sMyBP-C-E248K disrupts this regulation, thereby driving pathogenic myogenic tremors. Full article

In hypertrophic cardiomyopathy (HCM), the presence of pathogenic/likely pathogenic (P/LP) disease-causing genetic variants may indicate a worse prognosis. Few data exist on the effects of these genetic variants on cardiopulmonary exercise test (CPET) performance in HCM patients. We analysed asymptomatic and slightly symptomatic HCM patients (NYHA I-II) whose genetic analysis and CPET were available; at baseline, left ventricular function was normal and severe left ventricular outflow trait obstruction was excluded. Out of 120 HCM patients, we excluded 13 carrying variants of uncertain significance; of the remaining 107 patients, 54 were genotype negative [gene (−)], and 53 had a P/LP variant in sarcomeric genes [gene (+)]. Patients in the two groups had similar NYHA class, cardiovascular risk factors and echocardiographic characteristics. Gene (+) patients showed a lower peak VO₂% and O₂ pulse % (p < 0.05). Moreover, among gene (+), patients with P/LP variants in the so called “thin-filament” genes (TNNT2, TPM1 and MYL3) had the poorest CPET results. In asymptomatic or slightly symptomatic HCM patients with similar echocardiographic characteristics, exercise tolerance is affected by the genetic background. Indeed, exercise capacity is poorer in gene (+) compared to gene (−) patients and those carrying P/LP variants in “thin-filament” genes show the worst performance. Full article

Background: Apical hypertrophic cardiomyopathy (ApHCM) is a distinct variant of hypertrophic cardiomyopathy (HCM). Few studies have focused on the genetic determinants of this subtype. We aimed to investigate the genetic basis of apical hypertrophy in a Swedish cohort. Methods–Results: Longitudinal data on 58 unrelated index patients with ApHCM from the Southeast healthcare region in Sweden from 2010 to 2024 were assessed retrospectively. Additionally, the original raw data from genetic testing were re-evaluated using AI-based Emedgene software. Patients were 47 ± 14 years old, and 60% males. A total of 72.4% had the pure apical type and the remaining had the mixed phenotype, dominant distal. In the cohort, 50/58 (86.2%) underwent genetic testing, of whom 7/50 (14%) were considered genotype positive for a pathogenic/likely pathogenic variant, mainly in MYH7 (43%) and in the non-sarcomeric ALPK3 gene (28.6%). A re-evaluation of the original data from genetic testing identified a previously unreported variant in the skeletal muscle α-actin (ACTA1) gene. Overall, 21 of 58 patients (36.2%) had HCM-related events during their disease course: 10% had a stroke, and 12% had heart failure. Atrial fibrillation was present in 41.4% and non-sustained ventricular tachycardia occurred in 29.3% of the patients. Apical aneurysm was observed in 17.2% of cases. Patients with a positive genotype were more likely to have a positive family history of HCM compared to those with a negative genotype (p = 0.020). Conclusions: In ApHCM, a positive genotype was found less frequently compared to classic HCM. Only 14% of patients with ApHCM were found to be genotype positive, indicating that apical hypertrophy represents a genetically unique population with low risk of mortality. Nevertheless, patients with ApHCM faced higher rates of atrial fibrillation, ventricular arrhythmias, and apical aneurysms. Full article

Cardiomyopathy represents the most important life-limiting condition of Duchenne muscular dystrophy (DMD) patients after the age of 20. Genetic alterations in the DMD gene result in the absence of functional dystrophin protein, leading to skeletal/cardiac muscle impairment. The DMD incidence is one in 5000 live male births. Identifying the genetic background, in addition to DMD disease-causing variants, is one of the unmet needs in understanding the cardiac disease’s pathogenetic mechanisms and its prognostic implications. The clinical scenario is made even more intricate by the difficulty in predicting the onset and progression of cardiomyopathy, as no clear genotype/phenotype correspondence has been found thus far. The evaluation of genes involved in the onset of primary cardiomyopathies could explore the hypothesis that changes in cytoskeletal and sarcomeric protein function are the modulators of ventricular dysfunction in DMD patients. In the last decade, with the advent of next-generation sequencing (NGS) technology, many disease-causing genes and modifiers have been identified. Assessing the genetic origin of the phenotypic variability of the disease in both the onset and progression of cardiomyopathy in DMD would be extremely helpful in managing these patients. This review article aims to spotlight the genetic background associated with Cardiomyopathy in DMD patients toward a more predictive personalized model of care. Full article

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

Genome-wide association studies have identified a locus on chromosome 10q22, where many co-inherited single nucleotide polymorphisms (SNPs) are associated with atrial fibrillation (AF). This study seeks to identify the impact of this locus on gene expression at the transcript isoform level in human left atria and to gain insight into potential causal variants. Bulk RNA sequencing was analyzed to identify myozenin 1 (MYOZ1) and synaptopodin 2-like (SYNPO2L) transcript isoforms and the association of common SNPs in this region with transcript isoform expression levels. Chromatin marks were used to suggest candidate regulatory SNPs in this region. Protein amino acid changes were examined for predicted functional consequences. Transfection of MYOZ1 and two SYNPO2L isoforms were performed to localize their encoded proteins in cardiomyocytes derived from stem cells. We identified one MYOZ1 transcript isoform and four SYNPO2L transcript isoforms, two of which encode proteins, while the other two encode long noncoding RNAs (lncRNAs). The risk allele of the strongest AF susceptibility SNP on chromosome 10q22 is associated with decreased MYOZ1 expression and increased expression of the two SNYPO2L lncRNA isoforms. There are many SNPs co-inherited with the top AF-associated SNP due to linkage disequilibrium (LD), including rs11000728, which we propose as the MYOZ1 regulatory SNP, confirmed by reporter gene transfection. In addition, this LD block includes three missense SNPs in the SYNPO2L gene, with the minor protective haplotype predicted to be detrimental to protein function. MYOZ1 and both protein isoforms of SYNPO2L were localized to the sarcomere. This is a complex locus with the potential for several SNPs in a haplotype to alter AF susceptibility by opposing effects on MYOZ1 and SYNPO2L lncRNA expression, along with effects on SYNPO2L protein function. Full article

Hypertrophic cardiomyopathy (HCM) is a common cardiovascular condition in cats, affecting yth males and females of all ages. Some breeds, such as Ragdolls and Maine Coons, can develop HCM at a young age. The disease has a wide range of progression and severity, characterized by various pathological changes in the heart, including arteritis, fibrous tissue deposition, and myocardial cell hypertrophy. Left ventricular hypertrophy, which can restrict blood flow, is a common feature of HCM. The disease may persist into old age and eventually lead to heart failure and increased diastolic pressure. The basis of HCM in cats is thought to be genetic, although the exact mechanisms are not fully understood. Mutations in sarcomeric proteins, in particular myosin-binding protein C (MYBPC3), have been identified in cats with HCM. Two specific mutations, MYBPC3 [R818W] and MYBPC3 [A31P], have been classified as ‘pathogenic’. Other variants in genes such as MYBPC3, TNNT2, ALMS1, and MYH7 are also associated with HCM. However, there are cases where cats without known genetic mutations still develop HCM, suggesting the presence of unknown genetic factors contributing to the disease. This work aims to summarise the new knowledge of HCM in cats and the alterations in cardiac tissue as a result of genetic variants. Full article

Hypertrophic cardiomyopathy (HCM) is a cardiovascular pathology that is caused by variants in genes encoding sarcomere-associated proteins. However, the clinical significance of numerous variants in HCM-associated genes is still unknown. CRISPR/Cas9 is a tool of nucleotide sequence editing that allows for the unraveling of different biological tasks. In this study, introducing a mutation with CRISPR/Cas9 into induced pluripotent stem cells (iPSCs) of a healthy donor and the directed differentiation of the isogenic iPSC lines into cardiomyocytes were used to assess the pathogenicity of a variant of unknown significance, p.M659I (c.1977G > A) in MYH7, which was found previously in an HCM patient. Using two single-stranded donor oligonucleotides with and without the p.M659I (c.1977G > A) mutation, together with CRISPR/Cas9, an iPSC line heterozygous at the p.M659I (c.1977G > A) variant in MYH7 was generated. No CRISPR/Cas9 off-target activity was observed. The iPSC line with the introduced p.M659I (c.1977G > A) mutation in MYH7 retained its pluripotent state and normal karyotype. Compared to the isogenic control, cardiomyocytes derived from the iPSCs with the introduced p.M659I (c.1977G > A) mutation in MYH7 recapitulated known HCM features: enlarged size, elevated diastolic calcium level, changes in the expression of HCM-related genes, and disrupted energy metabolism. These findings indicate the pathogenicity of the variant. Full article

Novel therapies for the treatment of familial dilated cardiomyopathy (DCM) are lacking. Shaping research directions to clinical needs is critical. Triggers for the progression of the disorder commonly occur due to specific gene variants that affect the production of sarcomeric/cytoskeletal proteins. Generally, these variants cause a decrease in tension by the myofilaments, resulting in signaling abnormalities within the micro-environment, which over time result in structural and functional maladaptations, leading to heart failure (HF). Current concepts support the hypothesis that the mutant sarcomere proteins induce a causal depression in the tension-time integral (TTI) of linear preparations of cardiac muscle. However, molecular mechanisms underlying tension generation particularly concerning mutant proteins and their impact on sarcomere molecular signaling are currently controversial. Thus, there is a need for clarification as to how mutant proteins affect sarcomere molecular signaling in the etiology and progression of DCM. A main topic in this controversy is the control of the number of tension-generating myosin heads reacting with the thin filament. One line of investigation proposes that this number is determined by changes in the ratio of myosin heads in a sequestered super-relaxed state (SRX) or in a disordered relaxed state (DRX) poised for force generation upon the Ca²⁺ activation of the thin filament. Contrasting evidence from nanometer–micrometer-scale X-ray diffraction in intact trabeculae indicates that the SRX/DRX states may have a lesser role. Instead, the proposal is that myosin heads are in a basal OFF state in relaxation then transfer to an ON state through a mechano-sensing mechanism induced during early thin filament activation and increasing thick filament strain. Recent evidence about the modulation of these mechanisms by protein phosphorylation has also introduced a need for reconsidering the control of tension. We discuss these mechanisms that lead to different ideas related to how tension is disturbed by levels of mutant sarcomere proteins linked to the expression of gene variants in the complex landscape of DCM. Resolving the various mechanisms and incorporating them into a unified concept is crucial for gaining a comprehensive understanding of DCM. This deeper understanding is not only important for diagnosis and treatment strategies with small molecules, but also for understanding the reciprocal signaling processes that occur between cardiac myocytes and their micro-environment. By unraveling these complexities, we can pave the way for improved therapeutic interventions for managing DCM. Full article

Mutations in the LMNA gene-encoding A-type lamins can cause Limb–Girdle muscular dystrophy Type 1B (LGMD1B). This disease presents with weakness and wasting of the proximal skeletal muscles and has a variable age of onset and disease severity. This variability has been attributed to genetic background differences among individuals; however, such variants have not been well characterized. To identify such variants, we investigated a multigeneration family in which affected individuals are diagnosed with LGMD1B. The primary genetic cause of LGMD1B in this family is a dominant mutation that activates a cryptic splice site, leading to a five-nucleotide deletion in the mature mRNA. This results in a frame shift and a premature stop in translation. Skeletal muscle biopsies from the family members showed dystrophic features of variable severity, with the muscle fibers of some family members possessing cores, regions of sarcomeric disruption, and a paucity of mitochondria, not commonly associated with LGMD1B. Using whole genome sequencing (WGS), we identified 21 DNA sequence variants that segregate with the family members possessing more profound dystrophic features and muscle cores. These include a relatively common variant in coiled-coil domain containing protein 78 (CCDC78). This variant was given priority because another mutation in CCDC78 causes autosomal dominant centronuclear myopathy-4, which causes cores in addition to centrally positioned nuclei. Therefore, we analyzed muscle biopsies from family members and discovered that those with both the LMNA mutation and the CCDC78 variant contain muscle cores that accumulated both CCDC78 and RyR1. Muscle cores containing mislocalized CCDC78 and RyR1 were absent in the less profoundly affected family members possessing only the LMNA mutation. Taken together, our findings suggest that a relatively common variant in CCDC78 can impart profound muscle pathology in combination with a LMNA mutation and accounts for variability in skeletal muscle disease phenotypes. Full article

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy. It follows an autosomal dominant inheritance pattern in most cases, with incomplete penetrance and heterogeneity. It is familial in 60% of cases and most of these are caused by pathogenic variants in the core sarcomeric genes (MYH7, MYBPC3, TNNT2, TNNI3, MYL2, MYL3, TPM1, ACTC1). Genetic testing using targeted disease-specific panels that utilize next-generation sequencing (NGS) and include sarcomeric genes with the strongest evidence of association and syndrome-associated genes is highly recommended for every HCM patient to confirm the diagnosis, identify the molecular etiology, and guide screening and management. The yield of genetic testing for a disease-causing variant is 30% in sporadic cases and up to 60% in familial cases and in younger patients with typical asymmetrical septal hypertrophy. Genetic testing remains challenging in the interpretation of results and classification of variants. Therefore, in 2015 the American College of Medical Genetics and Genomics (ACMG) established guidelines to classify and interpret the variants with an emphasis on the necessity of periodic reassessment of variant classification as genetic knowledge rapidly expands. The current guidelines recommend focused cascade genetic testing regardless of age in phenotype-negative first-degree relatives if a variant with decisive evidence of pathogenicity has been identified in the proband. Genetic test results in family members guide longitudinal clinical surveillance. At present, there is emerging evidence for genetic test application in risk stratification and management but its implementation into clinical practice needs further study. Promising fields such as gene therapy and implementation of artificial intelligence in the diagnosis of HCM are emerging and paving the way for more effective screening and management, but many challenges and obstacles need to be overcome before establishing the practical implications of these new methods. Full article

Filamin C-related disorders include myopathies and cardiomyopathies linked to variants in the FLNC gene. Filamin C belongs to a family of actin-binding proteins involved in sarcomere stability. This study investigates the pathogenic impact of the FLNC c.3557C > T (p.Ala1186Val) pathogenic variant associated with an early-onset cytoplasmic body myopathy and cardiomyopathy in three unrelated patients. We performed clinical imaging and myopathologic and genetic characterization of three patients with an early-onset myopathy and cardiomyopathy. Bioinformatics analysis, variant interpretation, and protein structure analysis were performed to validate and assess the effects of the filamin C variant. All patients presented with a homogeneous clinical phenotype marked by a severe contractural myopathy, leading to loss of gait. There was prominent respiratory involvement and restrictive or hypertrophic cardiomyopathies. The Ala1186Val variant is located in the interstrand loop involved in intradomain stabilization and/or interdomain interactions with neighbor Ig-like domains. 3D modeling highlights local structural changes involving nearby residues and probably impacts the protein stability, causing protein aggregation in the form of cytoplasmic bodies. Myopathologic studies have disclosed the prominent aggregation and upregulation of the aggrephagy-associated proteins LC3B and p62. As a whole, the Ala1186Val variant in the FLNC gene provokes a severe myopathy with contractures, respiratory involvement, and cardiomyopathy due to protein aggregation in patients’ muscles. Full article

Hypertrophic cardiomyopathy (HCM) is a heterogeneous genetic disorder, most often caused by sarcomeric gene mutations, with a small proportion due to variants in non-sarcomeric loci. Phospholamban (PLN) is a phosphoprotein associated with the cardiac sarcoplasmic reticulum, a major determinant of cardiac contractility and relaxation. We conducted a retrospective study to determine the prevalence, phenotypical spectrum and clinical course of patients carrying the PLN p.Leu39* variant. A cohort including 11 PLN patients was identified among all patients with HCM (9/189, 4.8%) and DCM (2/62, 3.2%) who underwent genetic testing from two tertiary centers and five more were detected through cascade screening. Complete phenotyping was performed. PLN p.Leu39* variant-driven cardiomyopathy presented mostly as hypertrophic, with frequent progression to end-stage dilated HCM. We proceeded to compare these results to a similar analysis of a control cohort consisting of age-matched individuals that inherited pathogenic or likely pathogenic variants in common sarcomeric genes (MYBPC3/MYH7). Overall, the clinical characteristics and examination findings of patients carrying PLN p.Leu39* were not different from patients with cardiomyopathy related to sarcomeric mutations except for the presence of pathological Q waves and the incidence of non-sustained ventricular arrhythmias, which were higher in PLN patients than in those with MYBPC3/MYH7-related diseases. Full article

Hypertrophic cardiomyopathy (HCM) is among the most common forms of cardiomyopathies, with a prevalence of 1:200 to 1:500 people. HCM is caused by variants in genes encoding cardiac sarcomeric proteins, of which a majority reside in MYH7, MYBPC3, and TNNT2. Up to 40% of the HCM cases do not have any known HCM variant. Genotype–phenotype associations in HCM remain incompletely understood. This study involved two visits of 46 adult patients with a confirmed diagnosis of HCM. In total, 174 genes were analyzed on the Next-Generation Sequencing platform, and transthoracic echocardiography was performed. Gene-specific discriminative echocardiogram findings were identified using the computer vision library Fast AI. This was accomplished with the generation of deep learning models for the classification of ultrasonic images based on the underlying genotype and a later analysis of the most decisive image regions. Gene-specific echocardiogram findings were identified: for variants in the MYH7 gene (vs. variant not detected), the most discriminative structures were the septum, left ventricular outflow tract (LVOT) segment, anterior wall, apex, right ventricle, and mitral apparatus; for variants in MYBPC3 gene (vs. variant not detected) these were the septum, left ventricle, and left ventricle/chamber; while for variants in the TNNT2 gene (vs. variant not detected), the most discriminative structures were the septum and right ventricle. Full article

Arrhythmogenic cardiomyopathy (ACM) may present with sudden cardiac arrest (SCA), and demonstration of a pathogenic variant in ACM-related genes is crucial for its definitive diagnosis. A 42-year-old female patient with family history of sudden cardiac death (SCD) was referred to the cardiomyopathy clinic after two episodes of aborted SCA. In the second episode, the patient was transported under cardiopulmonary resuscitation (downtime of 57 min) until extracorporeal membrane oxygenation was implanted. A thorough diagnostic work-up led to a diagnosis of biventricular ACM. Genetic testing revealed a previously undescribed variant in ACM patients in the MYH6 gene, c.3673G>T p.(Glu 1225*), which inserts a premature stop codon. This was considered a possible pathogenic variant originating a truncated protein, previously undescribed in ACM. The patient’s 23-year-old daughter was positive for the MYH6 variant and had ECG abnormalities suggestive of ACM. This case details the complex differential diagnosis of SCA and explores the current recommendations for the diagnosis of biventricular ACM. The identification of a MYH6 variant in a patient with ACM, recurrent SCA, and family history of SCD appears to support the hypothesis of the pathogenicity of MYH6 variants in ACM, in which the association of phenotype with sarcomere variants is still unclear. Full article