Mutation-specific pathology and treatment of hypertrophic cardiomyopathy in patients,mouse models and human engineered heart tissue

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy and is characterized by asymmetric left ventricular hypertrophy and diastolic dysfunction, and a frequent cause of sudden cardiac death at young age. Pharmacological treatment to prevent or reverse HCM is lacking. This may be partly explained by the variety of underlying disease causes. Over 1500 mutations have been associated with HCM, of which the majority reside in genes encoding sarcomere proteins, the cardiac contractile building blocks. Several mutation-mediated disease mechanisms have been identified, with proof for gene- and mutation-specific cellular perturbations. In line with mutation-specific changes in cellular pathology, the response to treatment may depend on the underlying sarcomere gene mutation. In this review, we will discuss evidence for mutation-specific pathology and treatment responses in HCM patients, mouse models and engineered heart tissue. The pros and cons of these experimental models for studying mutation-specific HCM pathology and therapies will be outlined.     

Identification and functional analysis of a caveolin-3 mutation associated with familial hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are caused by mutations in 14 and 15 different disease genes, respectively, in a part of the patients and the disease genes for cardiomyopathy overlap in part with that for limb-girdle muscular dystrophy (LGMD). In this study, we examined an LGMD gene encoding caveolin-3 (CAV3) for mutation in the patients with HCM or DCM. A Thr63Ser mutation was identified in a sibling case of HCM. Because the mutation was found at the residue that is involved in the LGMD-causing mutations, we investigate the functional change due to the Thr63Ser mutation as compared with the LGMD mutations by examining the distribution of GFP-tagged CAV3 proteins. It was observed that the Thr63Ser mutation reduced the cell surface expression of caveolin-3, albeit the change was mild as compared with the LGMD mutations. These observations suggest that HCM is a clinical spectrum of CAV3 mutations.     

Mitochondrial Haplogroups Modify the Risk of Developing Hypertrophic Cardiomyopathy in a Danish Population

Hypertrophic cardiomyopathy (HCM) is a genetic disorder caused by mutations in genes coding for proteins involved in sarcomere function. The disease is associated with mitochondrial dysfunction. Evolutionarily developed variation in mitochondrial DNA (mtDNA), defining mtDNA haplogroups and haplogroup clusters, is associated with functional differences in mitochondrial function and susceptibility to various diseases, including ischemic cardiomyopathy. We hypothesized that mtDNA haplogroups, in particular H, J and K, might modify disease susceptibility to HCM. Mitochondrial DNA, isolated from blood, was sequenced and haplogroups identified in 91 probands with HCM. The association with HCM was ascertained using two Danish control populations. Haplogroup H was more prevalent in HCM patients, 60% versus 46% (p = 0.006) and 41% (p = 0.003), in the two control populations. Haplogroup J was less prevalent, 3% vs. 12.4% (p = 0.017) and 9.1%, (p = 0.06). Likewise, the UK haplogroup cluster was less prevalent in HCM, 11% vs. 22.1% (p = 0.02) and 22.8% (p = 0.04). These results indicate that haplogroup H constitutes a susceptibility factor and that haplogroup J and haplogroup cluster UK are protective factors in the development of HCM. Thus, constitutive differences in mitochondrial function may influence the occurrence and clinical presentation of HCM. This could explain some of the phenotypic variability in HCM. The fact that haplogroup H and J are also modifying factors in ischemic cardiomyopathy suggests that mtDNA haplotypes may be of significance in determining whether a physiological hypertrophy develops into myopathy. mtDNA haplotypes may have the potential of becoming significant biomarkers in cardiomyopathy.     

A variant of unknown significance in the GLA gene causing diagnostic uncertainty in a young female with isolated hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is genetically heterogeneous, and largely caused by mutations in genes encoding sarcomere proteins. However, GLA mutations causing Fabry disease, an X-linked lysosomal storage disorder, may also present with isolated HCM. As HCM genetic testing panels are increasingly being used clinically, variants of unknown significance (VUS) are encountered, leading to challenges in interpretation. We present an illustrative case: a 10-year-old girl with isolated HCM who, on testing with a HCM multi-gene panel, was found to carry a maternally inherited p.W24R variant in GLA. Attempts to evaluate the significance of this variant, by direct biochemical testing of patient specimens, gave inconclusive results. Subsequent in vitro protein expression studies suggested that the variant is unlikely to be pathogenic. This case highlights diagnostic dilemmas that can be provoked by VUS in general, and specifically raises a question whether GLA sequencing should be included in first-line diagnostic testing for female children with isolated hypertrophic cardiomyopathy.     

Structural analysis of obscurin gene in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a cardiac disease characterized by left ventricular hypertrophy with diastolic dysfunction. Molecular genetic studies have revealed that HCM is caused by mutations in genes for sarcomere/Z-band components including titin/connectin and its associate proteins. However, disease-causing mutations can be found in about half of the patients, suggesting that other disease-causing genes remain to be identified. To explore a novel disease gene, we searched for obscurin gene (OBSCN) mutations in HCM patients, because obscurin interacts with titin/connectin. Two linked variants, Arg4344Gln and Ala4484Thr, were identified in a patient and functional analyses demonstrated that Arg4344Gln affected binding of obscurin to Z9-Z10 domains of titin/connectin, whereas Ala4484Thr did not. Myc-tagged obscurin showed that Arg4344Gln impaired obscurin localization to Z-band. These observations suggest that the obscurin abnormality may be involved in the pathogenesis of HCM.     

Phospholamban Gene Mutations Are Not Associated with Hypertrophic Cardiomyopathy in a Northern Greek Population

Hypertrophic cardiomyopathy (HCM) is a genetically transmitted cardiac disease characterized by unexplained myocardial hypertrophy and diverse clinical spectrum. Currently, more than 250 HCM-related mutations in 10 genes encoding contractile sarcomeric proteins have been identified. Phospholamban (PLN) is a modest modulator of intracellular Ca2+ homeostasis and may be a candidate gene responsible for cardiomyopathy. In this study 53 consecutive patients with HCM, coming from Northern Greece, were screened for mutations of PLN gene. The patients were evaluated by clinical history, physical examination, electrocardiogram and echocardiography. All PCR products were analyzed for mutation by both restriction analysis and sequencing. The systematic mutation screening did not reveal any mutation in exons 1 and 2 or in the promoter region of phospholamban gene. Additionally, no polymorphisms were detected in all patients. Therefore, PLN gene mutations were not found to be associated with HCM in a Northern Greece population.     

Hypertrophic cardiomyopathy: two homozygous cases with "typical" hypertrophic cardiomyopathy and three new mutations in cases with progression to dilated cardiomyopathy

About 10% of cases of hypertrophic cardiomyopathy (HCM) evolve into dilated cardiomyopathy (DCM) with unknown causes. We studied 11 unrelated patients (pts) with HCM who progressed to DCM (group A) and 11 who showed "typical" HCM (group B). Mutational analysis of the beta-myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), and cardiac troponin T (TNNT2) genes demonstrated eight mutations affecting MYH7 or MYBPC3 gene, five of which were new mutations. In group A-pts, the first new mutation occurred in the myosin head-rod junction and the second occurred in the light chain-binding site. The third new mutation leads to a MYBPC3 lacking titin and myosin binding sites. In group B, two pts with severe HCM carried two homozygous MYBPC3 mutations and one with moderate hypertrophy was a compound heterozygous for MYBPC3 gene. We identified five unreported mutations, potentially "malignant" defects as for the associated phenotypes, but no specific mutations of HCM/DCM.     

Evaluation of ultrasound lung comets by hand-held echocardiography

Background

Most patients with hypertrophic cardiomyopathy (HCM) have asymmetric septal hypertrophy and among them, 25% present dynamic subaortic obstruction. Apical HCM is unusual and mid-ventricular HCM is the most infrequent presentation, but both variants may be associated to an apical aneurysm. An even more rare presentation is the coexistece mid-ventricular and apical HCM. This case is a combination of obstructive HCM with mid-ventricular HCM and an apical aneurysm, which to date, has not been reported in the literature.

Case presentation

The patient is a 49 year-old lady who presents a combination of septal asymmetric hypertrophic cardiomyopathy (HCM) and midventricular HCM, a subaortic gradient of 65 mm Hg and a midventricular gradient of 20 mm Hg, plus an apical aneurysm. Her clinical presentation was an acute myocardial infarction in June 2005. One month after hospital discharge, the electrocardiogram (ECG) showed a right bundle branch block (RBBB) with no Q waves or ST segment elevation. Coronary angiography revealed normal coronary arteries, left ventricular hypertrophy and an apical aneurysm.

Conclusion

This case is a rare example of an asymptomatic patient with subaortic and mid-ventricular hypertrophic cardiomyopathy, who presents a myocardial infarction and normal coronary arteries, and during the course of her disease develops an apical aneurysm.     

肥厚型心肌病患者心肌mtDNA大片段缺失的探讨

应用Long PCR及Primer Shift Long PCR 技术对3例肥厚型心肌病(HCM）患者和10例正常引产胎儿的13份心肌标本予以线粒体 DNA缺失检测,结果在1例HCM患者心肌线粒体DNA中发现约5.0kb缺失,而在正常引产胎儿的标本未见该缺失,提示HCM的发生可能与mtDNA缺失相关。 Astract　Using long PCR and primer shift long PCR techniques, we analyzed the mitochondrial DNA (mtDNA) isolated from the heart muscles of 3 hypertrophic cardiomyopathy (HCM) patients and 10 normal abortive fetuses. Almost 5.0kb deletion was found in the heart mtDNA of one HCM patient, while no deletion was detected in that of 10 fetuses. It is concluded that HCM may correlate with mtDNA deletion.     

Image and DNA analysis of hypertrophic myocytes in hypertensive heart disease and hypertrophic cardiomyopathy

OBJECTIVE: To investigate differences in the pathophysiology of cardiac hypertrophy between patients with hypertensive heart disease (HHD) and hypertrophic cardiomyopathy (HCM). STUDY DESIGN: The study group consisted of 30 autopsied heart disease patients (10 HHD, 10 HCM and 10 noncardiac heart disease). DNA synthesis by hypertrophic cardiac myocytes was examined, and three-dimensional myocyte structure image was investigated. DNA synthesis and the cell cycle were investigated by flow cytometry using autopsy material. Three-dimensional myocyte structure image was visualized. RESULTS: The percentage of cells in G2M phase of the cell cycle was significantly decreased in the myocardium of autopsied hearts with HCM as compared with hearts with HHD (HCM:HHD = 1.2 +/- 1.1%: 7.7 +/- 2.6%, mean +/- SD). Hypertrophic myocytes of HCM characteristically possessed myocardial disarray and irregular side-to-side branch connections between myocytes. No myocyte disarray or irregular connections could be observed in HHD. CONCLUSION: These results suggest that the mechanism of cardiac hypertrophy differs between patients with HHD and HCM and also suggest dissimilar cell vitality and latent proliferative viability of hypertrophic myocytes in a hypertrophic process between HHD and HCM. That is, hypertrophic myocytes may be called "restricted" myocytes in a morphologic and biochemical sense.     

Hypertrophic cardiomyopathy in daily practice: an introduction on diagnosis,prognosis and treatment

Hypertrophic cardiomyopathy (HCM) is a complex, inherited cardiac disease that has been subject to intense investigation since it was first described in 1957. Over the past 40 years, understanding has evolved regarding the diagnosis, prognosis and treatment of HCM. Analyses of HCM populations from nonreferral centres have refined the insights into the natural history and the occurrence of sudden cardiac death, which is the most devastating component of its natural history. Therapeutic strategies are diverse and may vary during the course of the disease. Optimal therapy depends on symptoms, haemodynamic findings and the presence of risk factors for sudden cardiac death. At present, invasive therapy for patients with obstructive HCM and drug-refractory symptoms includes surgery or percutaneous transluminal septal myocardial ablation.This report summarises the diagnostic criteria, clinical course and therapeutic management of HCM. Attention is also paid to certain issues of special interest in this disease.     

ENerGetIcs in hypertrophic cardiomyopathy: traNslation between MRI, PET and cardiac myofilament function (ENGINE study)

Introduction

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant heart disease mostly due to mutations in genes encoding sarcomeric proteins. HCM is characterised by asymmetric hypertrophy of the left ventricle (LV) in the absence of another cardiac or systemic disease. At present it lacks specific treatment to prevent or reverse cardiac dysfunction and hypertrophy in mutation carriers and HCM patients. Previous studies have indicated that sarcomere mutations increase energetic costs of cardiac contraction and cause myocardial dysfunction and hypertrophy. By using a translational approach, we aim to determine to what extent disturbances of myocardial energy metabolism underlie disease progression in HCM.

Methods

Hypertrophic obstructive cardiomyopathy (HOCM) patients and aortic valve stenosis (AVS) patients will undergo a positron emission tomography (PET) with acetate and cardiovascular magnetic resonance imaging (CMR) with tissue tagging before and 4 months after myectomy surgery or aortic valve replacement + septal biopsy. Myectomy tissue or septal biopsy will be used to determine efficiency of sarcomere contraction in-vitro, and results will be compared with in-vivo cardiac performance. Healthy subjects and non-hypertrophic HCM mutation carriers will serve as a control group.

Endpoints

Our study will reveal whether perturbations in cardiac energetics deteriorate during disease progression in HCM and whether these changes are attributed to cardiac remodelling or the presence of a sarcomere mutation per se. In-vitro studies in hypertrophied cardiac muscle from HOCM and AVS patients will establish whether sarcomere mutations increase ATP consumption of sarcomeres in human myocardium. Our follow-up imaging study in HOCM and AVS patients will reveal whether impaired cardiac energetics are restored by cardiac surgery.     

Role of implantable cardioverter defibrillators in the treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an important cardiovascular disease with sudden cardiac death as the most devastating presentation. Implantable cardioverter defibrillators (ICD) are the optimal therapy for prevention of sudden death from ventricular tachycardia or fibrillation of any cause. While there is no controversy with implanting ICDs in patients who have already survived a cardiac arrest, identifying high-risk patients for primary prevention in this disease remains a challenge. Implanting ICDs in patients with HCM is an important clinical consideration since many individuals could achieve normal or near-normal lifespans with this protection.     

Genetic variation screening of TNNT2 gene in a cohort of patients with hypertrophic and dilated cardiomyopathy

Mutations in troponin T (TNNT2) gene represent the important part of currently identified disease-causing mutations in hypertrophic (HCM) and dilated (DCM) cardiomyopathy. The aim of this study was to analyze TNNT2 gene exons in patients with HCM and DCM diagnosis to improve diagnostic and genetic consultancy in affected families. All 15 exons and their flanking regions of the TNNT2 gene were analyzed by DNA sequence analysis in 174 patients with HCM and DCM diagnosis. We identified genetic variations in TNNT2 exon regions in 56 patients and genetic variations in TNNT2 intron regions in 164 patients. Two patients were found to carry unique mutations in the TNNT2 gene. Limited genetic screening analysis is not suitable for routine testing of disease-causing mutations in patients with HCM and DCM as only individual mutation-positive cases may be identified. Therefore, this approach cannot be recommended for daily clinical practice even though, due to financial constraints, it currently represents the only available strategy in a majority of cardio-centers.     

Structural analysis of the titin gene in hypertrophic cardiomyopathy: identification of a novel disease gene.

Hypertrophic cardiomyopathy (HCM) is characterized by ventricular hypertrophy accompanied by myofibrillar disarrays. Molecular genetic analyses have revealed that mutations in 8 different genes cause HCM. Mutations in these disease genes, however, could be found in about half of HCM patients, suggesting that there are other unknown disease gene(s). Because the known disease genes encode sarcomeric proteins expressed in the cardiac muscle, we searched for a disease-associated mutation in the titin gene in 82 HCM patients who had no mutation in the known disease genes. A G to T transversion in codon 740, from CGC to CTC, replacing Arginine with Leucine was found in a patient. This mutation was not found in more than 500 normal chromosomes and increased the binding affinity of titin to alpha-actitin in the yeast two-hybrid assay. These observations suggest that the titin mutation may cause HCM in this patient via altered affinity to alpha-actinin.     

A missense mutation in a ubiquitously expressed protein, vinculin, confers susceptibility to hypertrophic cardiomyopathy

The R975W mutation, in the alternatively spliced exon 19 of vinculin (VCL) which yields the isoform metavinculin, was associated previously with hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), and shown to alter in vivo organization of intercalated discs. We tested the hypothesis that alterations in the ubiquitously expressed, VCL-encoded protein, vinculin, may provide a pathogenic substrate for HCM. Comprehensive mutational analysis of VCL's 22 translated exons was performed in a cohort of 228 unrelated patients with genotype negative HCM, having no identifiable mutations in 12 HCM-associated myofilament/Z-disc-encoding genes. A novel missense mutation, L277M-VCL, involving a conserved residue was identified in a patient with severely obstructive, mid-ventricular hypertrophy. This mutation was not detected in 400 reference alleles. Immunohistochemical analysis of the proband's myectomy specimen demonstrated markedly reduced vinculin levels in the intercalated discs. We provide the first report of a cardiomyopathy associated mutation in vinculin. Despite its ubiquitous expression, the HCM-associated VCL mutation clinically yielded a cardiac-specific phenotype.     

Gender-Specific Clinical Characteristics of Deep Q Waves in Hypertrophic Cardiomyopathy

Background: Despite male predominance in the prevalence of hypertrophic cardiomyopathy (HCM), repeated diagnosis at our institute indicates a possible higher prevalence of deep Q waves with HCM in women.Objective: The current study examined gender similarities and differences in the prevalence of deep Q waves in HCM and in the morphologic and electrocardiographic features of HCM with deep Q waves.Methods: Patients with HCM underwent cardiac magnetic resonance (CMR) imaging to identify the prevalence of deep Q waves in electrocardiographic limb leads, and to analyze the relationship between distribution patterns of deep Q waves and those of the localization of maximum amplitude of left ventricular (LV) hypertrophy. Contiguous LV short-axis images were obtained from the base toward the apex.Results: Of the 200 consecutive patients (172 males, aged 20–78 years; 28 females, aged 16–79 years) with HCM who underwent CMR imaging, 10 male and 8 female patients had deep Q waves. Deep Q waves were more prevalent in females with HCM than in their male counterparts (28.6% vs 5.8%, respectively; P < 0.001). Of the 18 patients with deep Q waves, maximum wall thickness was localized at either the basal anterior wall or the midventricular septum in 9 (90%) of the 10 male patients and 6 (75%) of the 8 female patients. In both sexes, the Q wave distribution pattern of I and aVL and of II and aVF indicated localization of maximum hypertrophy at the midventricular septum in 6 (75%) of the 8 patients with the former pattern, and at the basal anterior wall in 9 (90%) of the 10 patients with the latter pattern.Conclusions: Diagnostic deep Q waves were detected more frequently in female patients with HCM than in their male counterparts. In HCM with deep Q waves in limb leads, morphologic and electrocardiographic analysis showed similar features in both sexes. (Gend Med.Keywords: deep Q wave, hypertrophic cardiomyopathy, gender, cardiac magnetic resonance.     

心肌肌钙蛋白T基因突变在心肌病发病机制中的研究进展

肥厚型和扩张型心肌病中,基因缺陷分别占发病的50％和35％,其病理生理机制,主要包括肌小节蛋白基因突变引起的收缩力产生缺陷,细胞骨架蛋白基因突变引起的收缩力传递缺陷等。心肌肌钙蛋白T将肌钙蛋白C和肌钙蛋白I连接到肌动蛋白和原肌球蛋白上,在心肌细胞收缩和舒张过程中发挥重要作用。在肥厚型和扩张型心肌病中发现了多种心肌肌钙蛋白T的基因突变,围绕心肌肌钙蛋白T的研究有助于阐明心肌病的发病机制。本文总结了心肌肌钙蛋白T基因突变在心肌病发病机制中的研究情况。     

Familial screening and genetic counselling in hypertrophic cardiomyopathy: the Rotterdam experience

Hypertrophic cardiomyopathy (HCM) is a disease characterised by unexplained left ventricular hypertrophy (LVH) (i.e. LVH in the absence of another cardiac or systemic disease that could produce a similar degree of hypertrophy), electrical instability and sudden death (SD). Germline mutations in genes encoding for sarcomere proteins are found in more than half of the cases of unexplained LVH. The autosomal dominant inherited forms of HCM are characterised by incomplete penetrance and variability in clinical and echocardiographic features, prognosis and therapeutic modalities. The identification of the genetic defect in one of the HCM genes allows accurate presymptomatic detection of mutation carriers in a family. Cardiac evaluation of at-risk relatives enables early diagnosis and identification of those patients at high risk for SD, which can be the first manifestation of the disease in asymptomatic persons. In this article we present our experience with genetic testing and cardiac screening in our HCM population and give an overview of the current literature available on this subject. (Neth Heart J 2007;15:184-9.)     

Blocking cardiac growth in hypertrophic cardiomyopathy induces cardiac dysfunction and decreased survival only in males

Mutations in myosin heavy chain (MyHC) can cause hypertrophic cardiomyopathy (HCM) that is characterized by hypertrophy, histopathology, contractile dysfunction, and sudden death. The signaling pathways involved in the pathology of HCM have not been elucidated, and an unresolved question is whether blocking hypertrophic growth in HCM may be maladaptive or beneficial. To address these questions, a mouse model of HCM was crossed with an antihypertrophic mouse model of constitutive activated glycogen synthase kinase-3beta (caGSK-3beta). Active GSK-3beta blocked cardiac hypertrophy in both male and female HCM mice. However, doubly transgenic males (HCM/GSK-3beta) demonstrated depressed contractile function, reduced sarcoplasmic (endo) reticulum Ca(2+)-ATPase (SERCA) expression, elevated atrial natriuretic factor (ANF) expression, and premature death. In contrast, female HCM/GSK-3beta double transgenic mice exhibited similar cardiac histology, function, and survival to their female HCM littermates. Remarkably, dietary modification from a soy-based diet to a casein-based diet significantly improved survival in HCM/GSK-3beta males. These findings indicate that activation of GSK-3beta is sufficient to limit cardiac growth in this HCM model and the consequence of caGSK-3beta was sexually dimorphic. Furthermore, these results show that blocking hypertrophy by active GSK-3beta in this HCM model is not therapeutic.