Modelling sarcomeric cardiomyopathies with human cardiomyocytes derived from induced pluripotent stem cells.

Cardiomyocytes derived from human induced pluripotent stem cells (iPSCs) provide a unique opportunity to understand the pathophysiological effects of genetic cardiomyopathy mutations. In particular, these cells hold the potential to unmask the effects of mutations on contractile behaviour in vitro, providing new insights into genotype-phenotype relationships. With this goal in mind, several groups have established iPSC lines that contain sarcomeric gene mutations linked to cardiomyopathy in patient populations. Their studies have employed diverse systems and methods for performing mechanical measurements of contractility, ranging from single cell techniques to multicellular tissue-like constructs. Here, we review published results to date within the growing field of iPSC-based sarcomeric cardiomyopathy disease models. We devote special attention to the methods of mechanical characterization selected in each case, and how these relate to the paradigms of classical muscle mechanics. An appreciation of these somewhat subtle paradigms can inform efforts to compare the results of different studies and possibly reconcile discrepancies. Although more work remains to be done to improve and possibly standardize methods for producing, maturing, and mechanically interrogating iPSC-derived cardiomyocytes, the initial results indicate that this approach to modelling cardiomyopathies will continue to provide critical insights into these devastating diseases.

Family screening for hypertrophic cardiomyopathy: Is it time to change practice guidelines?

AIMS: Current guidelines recommend initiating family screening for hypertrophic cardiomyopathy (HCM) after age 10 or 12 years unless early screening criteria are met. The aim was to evaluate if current screening guidelines miss early onset disease. METHODS AND RESULTS: Children who underwent family screening for HCM before age 18 years were analysed. Major cardiac events (MaCEs) were defined as death, sudden cardiac death (SCD), or need for major cardiac interventions (myectomy, implantable cardioverter-defibrillator insertion, transplantation). Of 524 children screened, 331 were under 10 years of age, 9.9% had echocardiographic evidence of HCM, and 1.1% were symptomatic at first screening. The median (interquartile range) age at HCM onset was 8.9 (4.7-13.4) years, and at MaCE was 10.9 (8.5-14.3) years with a median time to MaCE from HCM onset of 1.5 (0.5-4.1) years. About 52.5% phenotype-positive children and 41% with MaCEs were <10 years old. Only 69% children with early HCM met early screening criteria. Cox regression identified male gender, family history of SCD, and pathogenic variants in MYH7/MYBPC3 as a predictor of early onset HCM and MaCEs. CONCLUSION: A third of children not eligible for early screening by current guidelines had phenotype-positive HCM. MYH7 and MYBC3 mutation-positive patients were at highest risk for developing early HCM and experiencing an event or requiring a major intervention. Our findings suggest that younger family members should be considered for early clinical and genetic screening to identify the subset in need of closer monitoring and interventions.

Unraveling obscurins in heart disease.

Obscurins, expressed from the single OBSCN gene, are a family of giant, modular, cytoskeletal proteins that play key structural and regulatory roles in striated muscles. They were first implicated in the development of heart disease in 2007 when two missense mutations were found in a patient diagnosed with hypertrophic cardiomyopathy (HCM). Since then, the discovery of over a dozen missense, frameshift, and splicing mutations that are linked to various forms of cardiomyopathy, including HCM, dilated cardiomyopathy (DCM), and left ventricular non-compaction (LVNC), has highlighted OBSCN as a potential disease-causing gene. At this time, the functional consequences of the identified mutations remain largely elusive, and much work has yet to be done to characterize the disease mechanisms of pathological OBSCN variants. Herein, we describe the OBSCN mutations known to date, discuss their potential impact on disease development, and provide future directions in order to better understand the involvement of obscurins in heart disease.

Could two-dimensional radial strain be considered as a novel tool to identify pre-clinical hypertrophic cardiomyopathy mutation carriers?

Treatment of overt form of hypertrophic cardiomyopathy (HCM) is often unsuccessful. Efforts are focused on a possible early identification in order to prevent or delaying the development of hypertrophy. Our aim was to find an echocardiographic marker able to distinguish mutation carriers without left ventricular hypertrophy (LVH) from healthy subjects. We evaluated 28 patients, members of eight families. Three types of mutation were recognized: MYBPC3 (five families), MYH7 (two families) and TNNT2 (one family). According to genetic (G) and phenotypic (Ph) features, patients were divided in three groups: Group A (10 patients), mutation carriers with LVH (G+/Ph+); Group B (9 patients), mutation carriers without LVH (G+/Ph-); Group C (9 patients), healthy subjects (G-/Ph-). Echocardiography examination was performed acquiring standard 2D, DTI and 2D-strain imaging. Global longitudinal strain (GLS) and global radial strain (GRS) at basal and mid-level were measured. GRS was significantly different between group B and C at basal level (32.18% ± 9.6 vs. 44.59% ± 12.67 respectively; p-value < 0.0001). In basal posterior and basal inferior segments this difference was particularly evident. ROC curves showed for both the involved segments good AUCs (0.931 and 0.861 for basal posterior and inferior GRS respectively) with the best predictive cut-off for basal posterior GRS at 43.65%, while it was 38.4% for basal inferior GRS. Conversely, GLS values were similar in the three group. 2D longitudinal strain is a valid technique to study HCM. Radial strain and particularly basal posterior and inferior segmental reduction could be able to identify mutation carriers in a pre-clinical phase of disease.

Clinical outcomes associated with sarcomere mutations in hypertrophic cardiomyopathy: a meta-analysis on 7675 individuals.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease, which goes along with increased risk for sudden cardiac death (SCD). Despite the knowledge about the different causal genes, the relationship between individual genotypes and phenotypes is incomplete. METHODS AND RESULTS: We retrieved PubMed/Medline literatures on genotype-phenotype associations in patients with HCM and mutations in MYBPC3, MYH7, TNNT2, and TNNI3. Altogether, 51 studies with 7675 HCM patients were included in our meta-analysis. The average frequency of mutations in MYBPC3 (20%) and MYH7 (14%) was higher than TNNT2 and TNNI3 (2% each). The mean age of HCM onset for MYH7 mutation positive patients was the beginning of the fourth decade, significantly earlier than patients without sarcomeric mutations. A high male proportion was observed in TNNT2 (69%), MYBPC3 (62%) and mutation negative group (64%). Cardiac conduction disease, ventricular arrhythmia and heart transplantation (HTx) rate were higher in HCM patients with MYH7 mutations in comparison to MYBPC3 (p < 0.05). Furthermore, SCD was significantly higher in patients with sarcomeric mutations (p < 0.01). CONCLUSION: A pooled dataset and a comprehensive genotype-phenotype analysis show that the age at disease onset of HCM patients with MYH7 is earlier and leads to a more severe phenotype than in patient without such mutations. Furthermore, patients with sarcomeric mutations are more susceptible to SCD. The present study further supports the clinical interpretation of sarcomeric mutations in HCM patients.

Hypertrophic cardiomyopathy. / Miocardiopatía hipertrófica.

Hypertrophic cardiomyopathy is the most common inherited cardiovascular disease. It is characterized by increased ventricular wall thickness and is highly complex due to its heterogeneous clinical presentation, several phenotypes, large number of associated causal mutations and broad spectrum of complications. It is caused by mutations in sarcomeric proteins, which are identified in up to 60% of cases of the disease. Clinical manifestations of Hypertrophic Cardiomyopathy include shortness of breath, chest pain, palpitations and syncope, which are related to the onset of diastolic dysfunction, left ventricular outflow tract obstruction, ischemia, atrial fibrillation and abnormal vascular responses. It is associated with an increased risk of sudden cardiac death, heart failure and thromboembolic events. In this article, we discuss the diagnostic and therapeutic aspects of this disease.

Cardiac Troponin and Tropomyosin: Structural and Cellular Perspectives to Unveil the Hypertrophic Cardiomyopathy Phenotype.

Inherited myopathies affect both skeletal and cardiac muscle and are commonly associated with genetic dysfunctions, leading to the production of anomalous proteins. In cardiomyopathies, mutations frequently occur in sarcomeric genes, but the cause-effect scenario between genetic alterations and pathological processes remains elusive. Hypertrophic cardiomyopathy (HCM) was the first cardiac disease associated with a genetic background. Since the discovery of the first mutation in the ß-myosin heavy chain, more than 1400 new mutations in 11 sarcomeric genes have been reported, awarding HCM the title of the "disease of the sarcomere." The most common macroscopic phenotypes are left ventricle and interventricular septal thickening, but because the clinical profile of this disease is quite heterogeneous, these phenotypes are not suitable for an accurate diagnosis. The development of genomic approaches for clinical investigation allows for diagnostic progress and understanding at the molecular level. Meanwhile, the lack of accurate in vivo models to better comprehend the cellular events triggered by this pathology has become a challenge. Notwithstanding, the imbalance of Ca2+ concentrations, altered signaling pathways, induction of apoptotic factors, and heart remodeling leading to abnormal anatomy have already been reported. Of note, a misbalance of signaling biomolecules, such as kinases and tumor suppressors (e.g., Akt and p53), seems to participate in apoptotic and fibrotic events. In HCM, structural and cellular information about defective sarcomeric proteins and their altered interactome is emerging but still represents a bottleneck for developing new concepts in basic research and for future therapeutic interventions. This review focuses on the structural and cellular alterations triggered by HCM-causing mutations in troponin and tropomyosin proteins and how structural biology can aid in the discovery of new platforms for therapeutics. We highlight the importance of a better understanding of allosteric communications within these thin-filament proteins to decipher the HCM pathological state.

Mimics of Hypertrophic Cardiomyopathy - Diagnostic Clues to Aid Early Identification of Phenocopies.

Hypertrophic cardiomyopathy (HCM) is the most common genetic cause of cardiomyopathy worldwide. Significant advances and widespread availability of genetic testing have improved detection of the sarcomeric mutations that cause HCM, but have also highlighted the significance of inborn errors of metabolism (IEM) or metabolic storage disorders that can mimic HCM ('HCM phenocopies'). These conditions cannot always be reliably differentiated on the basis of imaging alone. Whilst HCM phenocopies are relatively rare, it is crucial to distinguish these conditions at an early stage as their natural history, management and prognosis vary significantly from that of HCM with sarcomeric mutations. This review illustrates the salient features of HCM phenocopies and stresses the need for a high level of suspicion for these conditions in the assessment of cardiac hypertrophy.