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To investigate the role of genetic testing in patients with idiopathic atrioventricular conduction disease requiring pacemaker (PM) implantation before the age of 50 years. All consecutive PM implantations in Southern Switzerland between 2010 and 2019 were evaluated. Inclusion criteria were: (i) age at the time of PM implantation: < 50 years; (ii) atrioventricular block (AVB) of unknown aetiology. Study population was investigated by ajmaline challenge and echocardiographic assessment over time. Genetic testing was performed using next-generation sequencing panel, containing 174 genes associated to inherited cardiac diseases, and Sanger sequencing confirmation of suspected variants with clinical implication. Of 2510 patients who underwent PM implantation, 15 (0.6%) were young adults (median age: 44 years, male predominance) presenting with advanced AVB of unknown origin. The average incidence of idiopathic AVB computed over the 2010-2019 time window was 0.7 per 100 000 persons per year (95% CI 0.4-1.2). Most of patients (67%) presented with specific genetic findings (pathogenic variant) or variants of uncertain significance (VUS). A pathogenic variant of PKP2 gene was found in one patient (6.7%) with no overt structural cardiac abnormalities. A VUS of TRPM4, MYBPC3, SCN5A, KCNE1, LMNA, GJA5 genes was found in other nine cases (60%). Of these, three unrelated patients (20%) presented the same heterozygous missense variant c.2531G > A p.(Gly844Asp) in TRPM4 gene. Diagnostic re-assessment over time led to a diagnosis of Brugada syndrome and long-QT syndrome in two patients (13%). No cardiac events occurred during a median follow-up of 72 months. Idiopathic AVB in adults younger than 50 years is a very rare condition with an incidence of 0.7 per 100 000 persons/year. Systematic investigations, including genetic testing and ajmaline challenge, can lead to the achievement of a specific diagnosis in up to 20% of patients. Heterozygous missense variant c.2531G > A p.(Gly844Asp) in TRPM4 gene was found in an additional 20% of unrelated patients, suggesting possible association of the variant with the disease. Show less

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited cardiac disease in humans and cats and lacks efficacious pharmacologic interventions in the preclinical phase of disease. LV outflow tract obstruction (LVOTO) is commonly observed in HCM-affected patients and is a primary driver of heart failure symptoms and reduced quality of life. Novel small-molecule cardiac myosin inhibitors target actin-myosin interactions to alleviate overactive protein interactions. A prospective, randomized, controlled cross-over study was performed to evaluate pharmacodynamic effects of two doses (0.3 and 1 mg/kg) of a next-in-class cardiac myosin inhibitor, aficamten (CK-3773274, CK-274), on cardiac function in cats with the A31P MYBPC3 mutation and oHCM. Dose-dependent reductions in LV systolic function, LVOT pressure gradient, and isovolumetric relaxation times compared to baseline were observed. Promising beneficial effects of reduced systolic function warrant further studies of this next-in-class therapeutic to evaluate the benefit of long-term administration in this patient population. Show less

Hypertrophic cardiomyopathy (HCM) is the most prevalent cardiac disease in cats and lacks efficacious preclinical pharmacologic intervention, prompting investigation of novel therapies. Genetic mutations encoding sarcomeric proteins are implicated in the development of HCM and small molecule myosin inhibitors are an emerging class of therapeutics designed to target the interaction of actin and myosin to alleviate the detrimental effects of inappropriate contractile protein interactions. The purpose of this study was to characterize the pharmacodynamic effects of a single oral dose of the novel cardiac myosin inhibitor aficamten (CK-274) on cardiac function in purpose bred cats with naturally occurring A31P MYBPC3 mutation and a clinical diagnosis of HCM with left ventricular outflow tract obstruction (LVOTO). Five purpose bred cats were treated with aficamten (2 mg/kg) or vehicle and echocardiographic evaluations were performed at 0, 6, 24, and 48 h post-dosing. High dose aficamten (2 mg/kg) reduced left ventricular fractional shortening (LVFS%) by increasing the LV systolic internal dimension (LVIDs) and reduced isovolumic relaxation time (IVRT) compared with baseline without significant adverse effects. The marked reduction in systolic function and reduced IVRT coupled with an increased heart rate in treated cats, suggest a lower dose may be optimal. Further studies to determine optimal dosing of aficamten are indicated. Show less

Hypertrophic cardiomyopathy (HCM) is the most common genetically inherited cardiomyopathy with an autosomal dominant inheritance pattern. A disease-causing gene is found between 34% and >60% of the times and the two most frequently mutated genes, which encode sarcomeric proteins, are MYBPC3 and MYH7. HCM is a diagnosis of exclusion since secondary causes of left ventricular hypertrophy should first be ruled out. These include hypertension, aortic stenosis, infiltrative disease, metabolic and endocrine disorders, mitochondrial cardiomyopathies, neuromuscular disorders, malformation syndromes and some chronic drug use. The disease is characterized by great heterogeneity of its clinical manifestations, however diastolic dysfunction and increased ventricular arrhythmogenesis are commonly seen. Current HCM therapies focus on symptom management and prevention of sudden cardiac death. Symptom management includes the use of pharmacological agents, elimination of medication promoting outflow track obstruction, control of comorbid conditions and invasive procedures, whereas in the prevention of sudden cardiac death, implantable cardiac defibrillators and antiarrhythmic drugs are used. A targeted therapy for LVOTO represented by allosteric cardiac myosin inhibitors has been developed. In terms of sport participation, a more liberal approach is recently recommended, after careful evaluation and common-shared decision. The application of the current therapies has lowered HCM mortality rates to <1.0%/year, however it appears to have shifted focus to heart failure and atrial fibrillation, as the predominant causes of disease-related morbidity and mortality and, therefore, unmet treatment need. With improved understanding of the genetic and molecular basis of HCM, the present decade will witness novel treatments for disease prevention and modification. Show less

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

Aim      To determine specific clinical characteristics caused by a combination of the rs397516037 pathogenic variant in the myosin-binding protein C (MTBPC3) and the rs749628307 polymorphic variant in the vinculin (VCL) gene in a Russian family of carriers and to evaluate the contribution of the rs749628307 polymorphic variant in the VCL gene to the development of hypertrophic cardiomyopathy (HCMP).Material and methods  The family under study included one healthy person and 3 patients with HCMP. A targeted analysis of proband's exome was performed. A structural alignment for both forms of the VCL protein, the canonical form and the form with p.Arg230His substitution, was performed.Results The pathogenic rs397516037 variant and the potentially pathogenic rs749628307 variant were detected in the proband and several family members. A possibly damaging variant rs749628307 was detected in the proband and several family members evaluated in this study. The structural alignment confirmed that the rs749628307 variant did not alter the protein structure significantly and could not cause an impairment or loss of the protein function.Conclusion      This study demonstrated that apparently the rs749628307 variant in the VCL gene does not affect the protein structure in a pathogenetically significant way, neither does it affect the severity and form of the clinical manifestations of HCMP; therefore, it cannot be considered as pathogenic. Show less

Background Sarcomere gene mutation and myocardial fibrosis are both associated with poorer clinical outcomes in patients with hypertrophic cardiomyopathy (HCM). The aim of this study was to determine the relationship between sarcomere gene mutation and myocardial fibrosis measured by both histopathology and cardiac magnetic resonance (CMR). Methods and Results Two hundred twenty-seven patients with HCM who underwent surgical treatment, genetic testing, and CMR were enrolled. We retrospectively analyzed basic characteristics, sarcomere gene mutation, and myocardial fibrosis measured by CMR and histopathology. In our study, the mean age was 43 years, and 152 patients (67.0%) were men. A total of 107 patients (47.1%) carried a positive sarcomere gene mutation. The myocardial fibrosis ratio was significantly higher in the late gadolinium enhancement (LGE)+ group (LGE+ 14.3±7.5% versus LGE- 9.0±4.3%; Show less

Application of next-generation sequencing may lead to the detection of secondary findings (SF) not related to the initially analyzed disease but to other severe medically actionable diseases. However, the analysis of SFs is not yet routinely performed. We mined whole-exome sequencing data of 231 pediatric cancer patients and their parents who had been treated in our center for the presence of SFs. By this approach, we identified in 6 children (2.6%) pathogenic germline variants in 5 of the noncancer-related genes on the American College of Medical Genetics and Genomics (ACMG) SF v3.0 list, of which the majority were related to cardiovascular diseases ( RYR2 , MYBPC3 , KCNQ1 ). Interestingly, only the patient harboring the KCNQ1 variant showed at the time point of the analysis signs of the related Long QT syndrome. Moreover, we report 3 variants of unknown significance which, although not classified as pathogenic, have been reported in the literature to occur in individuals with the respective disease. While the frequency of patients with SFs is low, the impact of such findings on the patients' life is enormous, with regard to the potential prevention of life-threatening diseases. Hence, we are convinced that such actionable SF should be routinely analyzed. Show less

Cardiomyopathies are a heterogeneous group of diseases predominantly affecting the heart muscle and often lead to progressive heart failure-related disability or cardiovascular death. Hypertrophic cardiomyopathy (HCM) is a cardiac muscle disorder mostly caused by the mutations in genes encoding cardiac sarcomere. Germ-line mutations in Show less

Currently, no standardized system exists for evaluating and testing at-risk family members of decedents with abnormal post-mortem genetic testing in cases of sudden unexpected death (SUD). The goal of this study was to evaluate the outcomes of referrals made by an urban medical examiner's office to a multi-disciplinary cardiogenetics clinic. Relatives of decedents with pathogenic/likely pathogenic (P/LP) variants or variants of unknown significance (VUS) in genes known to be associated with cardiomyopathies and/or arrhythmias were identified by the New York City Office of Chief Medical Examiner and referred to the Cardiogenetics Clinic at Montefiore Medical Center. Familial referrals of 15 decedents (median 15 years, range 2 days to 57 years) were evaluated. Variants in 13 genes were identified among decedents (9 arrhythmia, 5 cardiomyopathy). P/LP variants were identified in both arrhythmia (RYR2, SCN5A) and cardiomyopathy syndrome (MYBPC3 (2), MYH7) genes. Thirty-two family members were referred, and 14 variants were detected. One pathogenic (MYBPC3) and two likely pathogenic (RYR2, MYH7) mutations were identified. Referral of at-risk family members of decedents who experienced SUD based on informative post-mortem genetic testing for cardiac and genetic evaluation is warranted, as family studies help to reclassify variants and prevent additional sudden death. Show less

Hypertrophic cardiomyopathy (HCM) is the most common inherited heart disease often caused by sarcomeric gene mutations. MYBPC3 is one of the most common genes associated with HCM. In this study, we generated a human induced pluripotent stem cell line ZZUNEUi028-A from a 19-year-old male HCM patient with c. 1504C → T in MYBPC3 gene using non-integrative Sendai viral reprogramming technology. This cell line expresses pluripotency markers, exhibits a normal male karyotype (46, XY) and can differentiate into all three germ layers in vitro. ZZUNEUi028-A can serve as a cell disease model in the understanding of HCM pathogenesis. Show less

MYBPC3 is the most frequently mutated gene in hypertrophic cardiomyopathy (HCM). Several loss-of-function founder variants have been reported in MYBPC3 from various geographic regions, altogether suggestive of a modest or absent effect of these variants on reproductive fitness. One of them, a MYBPC3 splice variant, NM₀₀₀₂₅₆.3:c.3330+2T > G, was first described in homozygous state in newborns presenting with a severe, recessive form of HCM among the Amish population and was later associated with adult-onset dominant HCM in heterozygous carriers. We here report this splice variant in heterozygous state in eight unrelated Swiss families with HCM, making it the most prevalent cardiomyopathy variant in western Switzerland. This variant was identified in patients using targeted (n = 5) or full-genome sequencing (n = 3). Given the prevalence of this variant in the Old Order Amish, Mennonites and Swiss populations, and given that both Amish and Mennonites founders originated from the Bern Canton in Switzerland, the MYBPC3, NM₀₀₀₂₅₆.3:c.3330+2T > G variant appears to be of Swiss origin. Neighboring regions that hosted the first Amish settlements (Alsace, South Germany) should be on the lookout for that variant. The existence of MYBPC3 founder variants in different populations suggests that individuals with early-onset clinical disease may be the tip of the iceberg of a much larger number of asymptomatic carriers. Alternatively, reproductive fitness could even be slightly increased in some variant carriers to compensate for the reduction of fitness in the more severely affected ones, but this remains to be investigated. Show less

Hypertrophic cardiomyopathy (HCM) is a monogenic disease with autosomal dominant inheritance. Genotype−phenotype relationships are complex, with variable penetrance even within the same family. The involvement of other modulating genetic and environmental factors is unknown. We aimed to analyze the HCM in monozygotic twins, carriers of the same founder pathogenic variant MYBPC3 p.G263*. The relationship was verified using the PowerPlex 16 HS System kit. Phenotypic differences and environmental differences (overloading conditions, coexistence and location, lifestyle, sport, and intensity) were analyzed. Three pairs of twins genetically identical for all markers and carriers of MYBPC3 G263* were identified. No environmental differences were identified. One of the 89-year-old twins had symptomatic severe obstructive HCM that required septal ablation, while her twin has remained asymptomatic with mild phenotype >80 years. A 49-year-old twin had a severe phenotype of obstructive HCM and pending myectomy, while his twin had a mild asymptomatic phenotype. In the last pair of twins, one presented a much larger left ventricular hypertrophy than his identical twin. In summary, we present three pairs of HCM twin patients sharing not only the genetic cause of the inherited disease but the entire genetic background. Despite identical genetic information and the absence of other known clinical, environmental, or lifestyle differences, the severity of the HCM phenotype is strikingly different. These unexplained differences should prompt the study of other unknown modulating factors, either epigenetic or environmental. Show less

Modulation of sarcomere contractility represents a new therapeutic opportunity for the treatment of heart failure by directly targeting the thick and thin filament proteins of the sarcomere to increase cardiac muscle contraction. This study compared the effect of 2 small molecules (M and T) that selectively alter myosin thick filament (M) or troponin thin filament (T) activity on overall cardiac muscle mechanics. This study revealed key differences related to the mechanism utilized by M and T to increase contractile force generation and suggests that targeting different proteins within the sarcomere may result in differentiating therapeutic profiles. Show less

Transcriptional bursting is a common expression mode for most genes where independent transcription of alleles leads to different ratios of allelic mRNA from cell to cell. Here we investigated burst-like transcription and its consequences in cardiac tissue from Hypertrophic Cardiomyopathy (HCM) patients with heterozygous mutations in the sarcomeric proteins cardiac myosin binding protein C (cMyBP-C, Show less

Hypertrophic cardiomyopathy (HCM) is an inherited cardiovascular disease characterized by left ventricular hypertrophy and a high risk of sudden death. In this study, a skin biopsy was obtained from a HCM patient harboring a heterozygous missense mutation (c.3764C>A; p.A1225D) in the myosin binding protein C3 (MYBPC3) gene. The isolated fibroblasts were reprogrammed using non-integrated Sendai viral method to establish the patient-specific induced pluripotent stem cell (iPSC) line. The established iPSC line displayed normal morphology and karyotype, expressed pluripotency markers, and can differentiate into three germ layers in vivo. Show less

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. Show less

Genetic mutations in the MYBPC3 gene encoding cardiac myosin binding protein C (cMyBP-C) are the most common cause of hypertrophic cardiomyopathy (HCM). Myocardial fibrosis (MF) plays a critical role in the development of HCM. However, the mechanism for mutant MYBPC3-induced MF is not well defined. In this study, we developed a R495Q mutant pig model using cytosine base editing and observed an early-onset MF in these mutant pigs shortly after birth. Unexpectedly, we found that the "cardiac-specific" MYBPC3 gene was actually expressed in cardiac fibroblasts from different species as well as NIH3T3 fibroblasts at the transcription and protein levels. CRISPR-mediated disruption of Mybpc3 in NIH3T3 fibroblasts activated nuclear factor κB (NF-κB) signaling pathway, which increased the expression of transforming growth factor beta (TGF-β1) and other pro-inflammatory genes. The upregulation of TGF-β1 promoted the expression of hypoxia-inducible factor-1 subunit α (HIF-1α) and its downstream targets involved in glycolysis such as GLUT1, PFK, and LDHA. Consequently, the enhanced aerobic glycolysis with higher rate of ATP biosynthesis accelerated the activation of cardiac fibroblasts, contributing to the development of HCM. This work reveals an intrinsic role of MYBPC3 in maintaining cardiac fibroblast homeostasis and disruption of MYBPC3 in these cells contributes to the disease pathogenesis of HCM. Show less

RBPs (RNA-binding proteins) perform indispensable functions in the post-transcriptional regulation of gene expression. Numerous RBPs have been implicated in cardiac development or physiology based on gene knockout studies and the identification of pathogenic RBP gene mutations in monogenic heart disorders. The discovery and characterization of additional RBPs performing indispensable functions in the heart will advance basic and translational cardiovascular research. We performed a differential expression screen in zebrafish embryos to identify genes enriched in We identified 1848 genes enriched in the Our study identifies Show less

Myosin binding protein C3 (MYBPC3) is a thick filament contractile protein that interacts with myosin, titin and actin and regulates cardiac muscle contraction. Genetic variations in the MYBPC3 gene are known causal factors for cardiomyopathy and heart failure. Previously, we identified a recurrent MYBPC3 deletion (25 base pairs) among South Asians associated with cardiomyopathy and heart failure. Here, we generated an induced pluripotent stem cell (iPSC) line using peripheral blood mononuclear cells (PBMC) from an Indian harboring MYBPC3 deletion. This iPSC line displayed embryonic stem cell morphology, expressed pluripotency markers, differentiated into three germ layers and exhibited normal karyotype. Show less

The present study aimed to evaluate the diagnostic usefulness of selected novel parameters as biomarkers of hypertension: miR-145-5p, miR-1-3p, miR-423-5p, PCSK9, MyBPC3, NOX1, and CYBb, and NCF2, DNase 1, anti-MPO and anti-PR3 antibodies. We present the data of men with normal blood pressure, diagnosed hypertension, confirmed hypertension, and hypertension and coexisting coronary artery disease. Elevated levels of miR-145-5p, miR-1-3p, and miR-423-5p and high levels of PCSK9, MyBPC3, and DNase 1 were observed in all groups of hypertensive men. We showed decreased levels of NOX1 and CYBb, and an elevated level of NCF2. PCSK9 shows the greatest potential as an early biomarker of screening-detected hypertension. Show less

Increasing evidence suggests that both coding and non-coding regions of sarcomeric protein genes can contribute to hypertrophic cardiomyopathy (HCM). Here, we introduce an experimental workflow (tested on four patients) for complete sequencing of the most common HCM genes ( Show less

Hypertrophic cardiomyopathy (HCM) is an inherited myocardial disease with the presence of left ventricular hypertrophy (LVH). The disease is characterized by high locus, allelic and phenotypic heterogeneity, even among members of the same family. The list of confirmed and potentially relevant genes implicating the disease is constantly increasing, with novel genes frequently reported. Heterozygous alterations in the five main sarcomeric genes ( Show less

Inherited primary arrhythmia syndromes and arrhythmogenic cardiomyopathies can lead to sudden cardiac arrest in otherwise healthy individuals. The burden and expression of these diseases in a real-world, well-phenotyped cardiovascular population is not well understood. Whole exome sequencing was performed on 8574 individuals from the CATHGEN cohort (Catheterization Genetics). Variants in 55 arrhythmia-related genes (associated with 8 disorders) were identified and assessed for pathogenicity based on American College of Genetics and Genomics/Association for Molecular Pathology criteria. Individuals carrying pathogenic/likely pathogenic (P/LP) variants were grouped by arrhythmogenic disorder and matched 1:5 to noncarrier controls based on age, sex, and genetic ancestry. Long-term phenotypic data were annotated through deep electronic health record review. Fifty-eight P/LP variants were found in 79 individuals in 12 genes associated with 5 arrhythmogenic disorders (arrhythmogenic right ventricular cardiomyopathy, Brugada syndrome, hypertrophic cardiomyopathy, In a real-world cardiovascular cohort, P/LP variants in arrhythmia-related genes were relatively common (1:108 prevalence) and most penetrant in Show less

Considered as the representatives of neurodegenerative diseases, Alzheimer's disease (AD) and glaucoma are complex progressive neuropathies affected by both genetic and environmental risk factors and cause irreversible damages. Current research indicates that there are common features between AD and glaucoma in terms of epidemiology and pathophysiology. However, the understandings and explanations of their comorbidity and potential genetic overlaps are still limited and insufficient. Genetic pleiotropy analysis was performed using large genome-wide association studies summary statistics of AD and glaucoma, with an independent cohort of glaucoma for replication. Conditional and conjunctional false discovery rate methods were applied to identify the shared loci. Biological function and network analysis, as well as the expression level analysis were performed to investigate the significance of the shared genes. A significant positive genetic correlation between AD and glaucoma was identified, indicating that there were significant polygenetic overlaps. Forty-nine shared loci were identified and mapped to 11 shared protein-coding genes. Functional genomic analyses of the shared genes indicate their modulation of critical physiological processes in human cells, including those occurring in the mitochondria, nucleus, and cellular membranes. Most of the shared genes indicated a potential modulation of metabolic processes in human cells and tissues. Furthermore, human protein-protein interaction network analyses revealed that some of the shared genes, especially Our study identified a shared genetic architecture between AD and glaucoma, which may explain their shared features in epidemiology and pathophysiology. The potential involvement of these shared genes in molecular and cellular processes reflects the "inter-organ crosstalk" between AD and glaucoma. These results may serve as a genetic basis for the development of innovative and effective therapeutics for AD, glaucoma, and other neurodegenerative diseases. Show less

Variants in cardiac myosin-binding protein C (cMyBP-C) are the leading cause of inherited hypertrophic cardiomyopathy (HCM), demonstrating the key role that cMyBP-C plays in the heart's contractile machinery. To investigate the Show less