Recent advances in the molecular genetics of hypertrophic cardiomyopathy

Identification of variants in genes associated with hypertrophic cardiomyopathy in Mexican patients

The objective of this work was to identify genetic variants in Mexican patients diagnosed with hypertrophic cardiomyopathy (HCM). According to world literature, the genes mainly involved are MHY7 and MYBPC3, although variants have been found in more than 50 genes related to heart disease and sudden death, and to our knowledge there are no studies in the Mexican population. These variants are reported and classified in the ClinVar (PubMed) database and only some of them are recognized in the Online Mendelian Information in Men (OMIM). The present study included 37 patients, with 14 sporadic cases and 6 familial cases, with a total of 21 index cases. Next-generation sequencing was performed on a predesigned panel of 168 genes associated with heart disease and sudden death. The sequencing analysis revealed twelve (57%) pathogenic or probably pathogenic variants, 9 of them were familial cases, managing to identify pathogenic variants in relatives without symptoms of the disease. At the molecular level, nine of the 12 variants (75%) were single nucleotide changes, 2 (17%) deletions, and 1 (8%) splice site alteration. The genes involved were MYH7 (25%), MYBPC3 (25%) and ACADVL, KCNE1, TNNI3, TPM1, SLC22A5, TNNT2 (8%). In conclusion; we found five variants that were not previously reported in public databases. It is important to follow up on the reclassification of variants, especially those of uncertain significance in patients with symptoms of the condition. All patients included in the study and their relatives received family genetic counseling.

Emergency department utilization in patients with hypertrophic cardiomyopathy: a nationwide population-based study

Despite the increasing burden of hypertrophic cardiomyopathy (HCM) on healthcare resources, data on emergency department (ED) utilization in HCM are lacking. This nationwide population-based study extracted 14,542 HCM patients from the National Health Insurance Service database between 2015–2016, and investigated their ED utilization during a one-year period. The reason for ED utilization was defined as the primary diagnosis upon discharge from EDs. The clinical outcome was defined as hospitalization or all-cause mortality within 90 days after the ED visits. A total of 3209 (22.1%) HCM patients visited EDs within a one-year period (mean age, 66.8 ± 13.8 years; male, 57.4%). The majority (71.1%) of HCM patients who visited the EDs were aged ≥ 60 years. The ED utilization rate was higher in women than in men (26.3% versus 19.7%, P < 0.001). Cardiovascular diseases were the most common reason for ED visits (n = 1333, 41.5%). Among HCM patients who visited EDs, 1195 (37.2%) were hospitalized, and 231 (7.2%) died within 90 days. ED visits for cardiovascular disease was associated with a higher 90-day all-cause mortality (adjusted odds ratio, 2.72; 95% confidence interval 1.79–4.12). These findings would serve as a basis for future research to establish medical policies on ED utilization in HCM.

Effect of rs4646994 polymorphism of angiotensin converting enzyme on the risk of nonischemic cardiomyopathy

Background: Angiotensin-converting enzyme (ACE) gene polymorphisms have recently been shown to be associated with risk of developing left ventricular hypertrophy (LVH). However, the results were controversial. We aimed to conduct this meta-analysis to further confirm the association between ACE rs4646994 polymorphism and hypertrophic cardiomyopathy (HCM)/dilated cardiomyopathy (DCM).

Methods: PubMed, Embase, the Chinese National Knowledge Information, and Wanfang databases were searched for eligible studies. The Newcastle–Ottawa Scale (NOS) was used to evaluate the quality of included studies. Then we evaluated the association between ACE gene mutation and HCM/DCM by calculating odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analysis was further performed to explore situations in specialized subjects. Sensitivity analysis and publication bias was assessed to confirm the study reliability.

Results: There were 13 studies on DCM (2004 cases and 1376 controls) and 16 studies on HCM (2161 controls and 1192 patients). ACE rs4646994 polymorphism was significantly associated with DCM in all genetic models. However, in HCM, four genetic models (allele model, homozygous model, heterozygous model, and dominant model) showed significant association between ACE rs4646994 polymorphism and DCM. In subgroup analysis, we found that ACE rs4646994 polymorphism was significantly associated with DCM/HCM in Asian population. Finally, we also conducted a cumulative meta-analysis, which indicates that the results of our meta-analysis are highly reliable.

Conclusion: ACE rs4646994 polymorphism increases the risk of DCM/HCM in Asians, but not in Caucasians. More case–control studies are needed to strengthen our conclusions and to assess the gene–gene and gene–environment interactions between ACE rs4646994 polymorphism and DCM/HCM.

Transgenic rabbit models for cardiac disease research

To study the pathophysiology of human cardiac diseases and to develop novel treatment strategies, complex interactions of cardiac cells on cellular, tissue and on level of the whole heart need to be considered. As in vitro cell-based models do not depict the complexity of the human heart, animal models are used to obtain insights that can be translated to human diseases. Mice are the most commonly used animals in cardiac research. However, differences in electrophysiological and mechanical cardiac function and a different composition of electrical and contractile proteins limit the transferability of the knowledge gained. Moreover, the small heart size and fast heart rate are major disadvantages. In contrast to rodents, electrophysiological, mechanical and structural cardiac characteristics of rabbits resemble the human heart more closely, making them particularly suitable as an animal model for cardiac disease research. In this review, various methodological approaches for the generation of transgenic rabbits for cardiac disease research, such as pronuclear microinjection, the sleeping beauty transposon system and novel genome-editing methods (ZFN and CRISPR/Cas9)will be discussed. In the second section, we will introduce the different currently available transgenic rabbit models for monogenic cardiac diseases (such as long QT syndrome, short-QT syndrome and hypertrophic cardiomyopathy) in detail, especially in regard to their utility to increase the understanding of pathophysiological disease mechanisms and novel treatment options.

Screening of MYH7 gene mutation sites in hypertrophic cardiomyopathy and its significance

BACKGROUND

There have been few reports of mutations in the beta-myosin heavy chain (MYH7) gene in hypertrophic cardiomyopathy (HCM), which is associated with sudden cardiac death caused by HCM. This study aimed to screen the mutation sites in the sarcomeric gene MYH7 in Chinese patients with HCM. We also planned to analyze the pathogenicity of the mutation site as well as its significance in clinical and forensic medicine.

METHODS

From January 2006 to June 2017, autopsy cases were collected from the Department of Pathology, the Affiliated Hospital of Qingdao University. The experiment was to detect MYH7 gene status in formalin-fixed paraffin-embedded tissues from 18 independent autopsy cases who suffered HCM related sudden death (fatal HCM) and 20 cases without cardiomyopathy. Common mutation exon fragments of MYH7 gene were amplified by polymerase chain reaction. The end-of-deoxygenation method and gene cloning method were further performed to analyze the mutation sites. Homologous comparison among mutant sites was conducted using BLAST online database.

RESULTS

The 1336th nucleotide of MYH7 gene at exon 14 was converted from T to G in one HCM case, resulting in the conversion of threonine (Thr) at position 446 to proline (Pro). In another case, the 1402th nucleotide at exon 14 was converted from T to C, resulting in the conversion of phenylalanine (Phe) at position 468 to leucine (Leu). Homologous comparison results showed that the two amino acid residues of Thr446 and Phe468 are highly conserved among different species.

CONCLUSIONS

Our results showed fatal HCM harbored mutations of Thr446Pro and Phe468Leu in the MYH7 gene. It is significant for clinical and forensic medicine to further explore the functions and detailed mechanisms of these mutations.

Phenotypic variation and targeted therapy of hypertrophic cardiomyopathy using genetic animal models

Hypertrophic cardiomyopathy (HCM) has a variable clinical presentation due to the diversity of causative genetic mutations. Animal models allow in vivo study of genotypic expression through non-invasive imaging, pathologic sampling, and force analysis. This review focuses on the spontaneous and induced mutations in various animal models affecting mainly sarcomere proteins. The sarcomere is comprised of thick (myosin) filaments and related proteins including myosin heavy chain and myosin binding protein-C; thin (actin) filament proteins and their associated regulators including tropomyosin, troponin I, troponin C, and troponin T. The regulatory milieu including transcription factors and cell signaling also play a significant role. Animal models provide a layered approach of understanding beginning with the causative mutation as a foundation. The functional consequences of protein energy utilization and calcium sensitivity in vivo and ex vivo can be studied. Beyond pathophysiologic disruption of sarcomere function, these models demonstrate the clinical sequalae of diastolic dysfunction, heart failure, and arrhythmogenic death. Through this cascade of understanding the mutation followed by their functional significance, targeted therapies have been developed and are briefly discussed.

GABA tea attenuates cardiac apoptosis in spontaneously hypertensive rats (SHR) by enhancing PI3K/Akt-mediated survival pathway and suppressing Bax/Bak dependent apoptotic pathway

Cardiomyocyte apoptosis is the major risk factor for the development of heart failure (HF). The purpose of this study was to evaluate the effects of Gamma-aminobutyric acid (GABA) tea on hypertension-induced cardiac apoptotic pathways in spontaneously hypertensive rats (SHR). In order to reveal the mechanisms, 36 male SHR at eight weeks of age, 200 g were divided into six groups. One group was fed water as a control group. Other rats were administered one of the following treatments: GABA tea at dose 150 and 300 mg/kg/day as low GABA tea (LGT) and high GABA tea (HGT) groups, respectively, pure GABA at dose 150 and 300 mg/kg/day as LG and HG groups, respectively, green tea (GT) as control of LGT and HGT groups. After 12 weeks, cardiac tissues were analyzed by histological analysis, western blotting, and TUNEL assays. GABA tea, GT, and pure GABA decreased hypertension-induced cardiac abnormalities, including abnormal myocardial architecture. In addition, GABA tea, GT, and pure GABA dramatically increased anti-apoptotic protein, Bcl2. Furthermore, GABA tea, GT, and pure GABA also decreased activated-caspase 9 and activated-caspase 3. Additionally, the survival associated protein IGF-I and PI3K/Akt were enhanced in cardiac tissues upon treatment. Our results showed an optimistic anti-apoptotic and pro-survival effects of GABA tea treatment against hypertensive rat hearts.

Genetic polymorphism of angiotensin-converting enzyme and hypertrophic cardiomyopathy risk: A systematic review and meta-analysis

BACKGROUND

Genetic factors in the pathogenesis of cardiomyopathies have received a lot of attention during the past 2 decades. Some studies have reported that angiotensin-converting enzyme (ACE) gene has been associated with hypertrophic cardiomyopathy (HCM). However, there have been inconsonant results among different studies. To clarify the influence of ACE on HCM, a systemic review and meta-analysis of case-control studies were performed.

METHODS

The following databases were searched to indentify related studies: PubMed database, the Embase database, the Cochrane Central Register of Controlled Trials database, China National Knowledge Information database, and Chinese Scientific and Technological Journal database. Search terms included "hypertrophic cardiomyopathy," "angiotensin converting enzyme" or "ACE," and "polymorphism or mutation."

RESULTS

Fifteen separate studies were suitable for the inclusion criterion. The selected studies contained 2972 participants, including 1047 in HCM group and 1925 controls. Pooled odds ratios (ORs) were calculated to assess the association between ACE insertion/deletion (I/D) polymorphism and HCM. Our case-control data indicated that D allele carrier is a risk allele in all genetic models: allele contrast (D vs I: OR = 1.35, 95% confidence interval [CI]: 1.10-1.65, P = .004), homozygous comparison (DD vs II: OR = 1.69; 95% CI: 1.12-2.54; P = .01), dominant model (DD + ID vs II: OR = 1.52, 95% CI: 1.15-2.02, P = .003), and recessive model (DD vs ID + II: OR = 1.34, 95% CI: 0.99-1.81, P = .03).

CONCLUSION

In summary, the current meta-analysis provided solid evidence suggesting that ACE gene I/D polymorphism was probably a genetic risk factor for HCM.

Enhanced Expression of FRA16B using AT-Rich DNA Binding Chemicals in a Woman with Secondary Amenorrhoea

Fragile sites represent regions of chromatin that fail to compact during mitosis. Based on the prevalence and pattern of inheritance they are classified as rare fragile sites or common fragile sites. Rare fragile sites either occur spontaneously or can be induced by certain AT-specific binding chemicals namely distamycin, Hoechst 33258, Berenil and others. The most common of all rare autosomal fragile sites is fra(16)(q22) with a heterozygote frequency of ~5%. FRA16B results from an expansion of a 33 bp AT-rich Minisatellite repeat. These rare forms are usually heritable and segregate in a Mendelian fashion. The proband who was referred for secondary amenorrhoea, revealed 46,XX,fra(16)(q22.1)pat karyotype. Her father and younger sibling were also found to be carriers. This study aimed to delineate the genotypic and phenotypic features exhibited by these carriers and to evaluate FRA16B expression using AT-specific binding chemicals. The additives employed were Berenil, BrdU and Hoechst 33258. Berenil at a concentration of 150 µg/ml showed the highest expression of FRA16B. Although the recent breakthrough in molecular characterization of fragile sites plays a critical role in comprehending their association with various diseases, the physiological link between them and amenorrhoea is not clearly understood.

The association between brain natriuretic peptide and tissue Doppler parameters in children with hypertrophic cardiomyopathy

In this study, we investigated the association between brain natriuretic peptide (BNP) levels and tissue Doppler imaging measurements and also screening for deadly mutations in patients with hypertrophic cardiomyopathy (HCM). We enrolled 20 patients diagnosed with HCM (age:10.7±5 years (1-17), 85% male, weight:42.25±23.10 kg, height:141.80±32.45 cm) and 20 age, gender and body weight-matched control subjects. We performed electrocardiography, transthoracic echocardiography, and tissue Doppler echocardiography in each group, as well as genetic tests (for Arg403Gln, Arg453Cys, Arg719Trp and Arg719Gln mutations in MYH7 Exons 13, 14, 19) and BNP in the patients. The patients were divided into two groups according to the presence (Group 1) or absence (Group 2) of left ventricular (LV) outflow tract obstruction. QTc dispersion and the LV ejection fraction and left atrial (LA) volume index were increased in Group 1. The LA volume index and the mitral and septal E/Ea ratio and septum Z-score were increased while the mitral lateral annulus and septal annulus Ea wave velocities and the mitral and tricuspid E/A ratio were decreased in patients with high levels of BNP compared to those with normal BNP levels. There were no mutations that are associated with increased risk of sudden death found in patients included in this study. In the light of our data, we conclude that such parameters BNP levels above the 98 pg/mL, septal thickness Z-score ˃6, and higher mitral and septal E/Ea ratios can be used for management of patients with HCM according to life-threatening conditions.

ZAK induces cardiomyocyte hypertrophy and brain natriuretic peptide expression via p38/JNK signaling and GATA4/c-Jun transcriptional factor activation

Cardiomyocyte hypertrophy is an adaptive response of heart to various stress conditions. During the period of stress accumulation, transition from physiological hypertrophy to pathological hypertrophy results in the promotion of heart failure. Our previous studies found that ZAK, a sterile alpha motif and leucine zipper containing kinase, was highly expressed in infarcted human hearts and demonstrated that overexpression of ZAK induced cardiac hypertrophy. This study evaluates, cellular events associated with the expression of two doxycycline (Dox) inducible Tet-on ZAK expression systems, a Tet-on ZAK WT (wild-type), and a Tet-on ZAK DN (mutant, Dominant-negative form) in H9c2 myoblast cells; Tet-on ZAK WT was found to increase cell size and hypertrophic marker BNP in a dose-dependent manner. To ascertain the mechanism of ZAK-mediated hypertrophy, expression analysis with various inhibitors of the related upstream and downstream proteins was performed. Tet-on ZAK WT expression triggered the p38 and JNK pathway and also activated the expression and nuclear translocation of p-GATA4 and p-c-Jun transcription factors, without the involvement of p-ERK or NFATc3. However, Tet-on ZAK DN showed no effect on the p38 and JNK signaling cascade. The results showed that the inhibitors of JNK1/2 and p38 significantly suppressed ZAK-induced BNP expression. The results show the role of ZAK and/or the ZAK downstream events such as JNK and p38 phosphorylation, c-Jun, and GATA-4 nuclear translocation in cardiac hypertrophy. ZAK and/or the ZAK downstream p38, and JNK pathway could therefore be potential targets to ameliorate cardiac hypertrophy symptoms in ZAK-overexpressed patients.

Biventricular reverse remodeling after successful alcohol septal ablation for obstructive hypertrophic cardiomyopathy

The aim of the present study was to investigate the long-term effects of alcohol septal ablation (ASA) on left ventricular (LV) and right ventricular (RV) remodeling in patients with obstructive hypertrophic cardiomyopathy (HC) using cardiovascular magnetic resonance (CMR). CMR was performed at baseline and 16 months after ASA in 38 patients with obstructive HC (mean age 48 ± 9 years) despite optimal medical treatment. ASA resulted in significant reductions of LV outflow tract gradient (mean 89 ± 22 vs 24 ± 12 mm Hg, p <0.001) and improvements in New York Heart Association functional class (p <0.001) during the follow-up period. LV remote mass and septal mass decreased from 98.34 ± 37.02 to 84.23 ± 34.71 g and from 77.56 ± 16.40 to 68.43 ± 14.02 g, respectively (p <0.001 for both) at 16-month follow-up. There were significant reductions of RV mass (mean 53.69 ± 7.12 vs 47.49 ± 6.17 g, p <0.001) and improvements in RV end-diastolic volume (mean 110.58 ± 22.47 vs 124.22 ± 24.17 ml, p <0.001) and the RV ejection fraction (p <0.001) during 16-month follow-up. Linear regression analysis showed that LV outflow tract gradient reduction was correlated significantly with LV remote mass reduction (r = 0.475, p = 0.003) and RV mass reduction (r = 0.535, p = 0.001) at 16-month follow-up. In conclusion, successful ASA can lead to positive biventricular reverse remodeling, showing significant reductions of RV and LV mass as well as increased RV and LV end-diastolic volumes during follow-up.

Mitochondrial fission is required for cardiomyocyte hypertrophy mediated by a Ca2+-calcineurin signaling pathway

Cardiomyocyte hypertrophy has been associated with diminished mitochondrial metabolism. Mitochondria are crucial organelles for the production of ATP, and their morphology and function are regulated by the dynamic processes of fusion and fission. The relationship between mitochondrial dynamics and cardiomyocyte hypertrophy is still poorly understood. Here, we show that treatment of cultured neonatal rat cardiomyocytes with the hypertrophic agonist norepinephrine promotes mitochondrial fission (characterized by a decrease in mitochondrial mean volume and an increase in the relative number of mitochondria per cell) and a decrease in mitochondrial function. We demonstrate that norepinephrine acts through α1-adrenergic receptors to increase cytoplasmic Ca(2+), activating calcineurin and promoting migration of the fission protein Drp1 (encoded by Dnml1) to mitochondria. Dominant-negative Drp1 (K38A) not only prevented mitochondrial fission, it also blocked hypertrophic growth of cardiomyocytes in response to norepinephrine. Remarkably, an antisense adenovirus against the fusion protein Mfn2 (AsMfn2) was sufficient to increase mitochondrial fission and stimulate a hypertrophic response without agonist treatment. Collectively, these results demonstrate the importance of mitochondrial dynamics in the development of cardiomyocyte hypertrophy and metabolic remodeling.

Clinical significance of left ventricular apical aneurysms in hypertrophic cardiomyopathy patients: the role of diagnostic electrocardiography

OBJECTIVES

Some patients with hypertrophic cardiomyopathy (HCM) develop left ventricular apical aneurysm, leading to serious cardiovascular complications. The aims of this study were to identify the incidence and clinical course of HCM patients with apical aneurysms in Japan, and to evaluate the role of electrocardiography (ECG) as a screening test to detect apical aneurysms in HCM patients.

METHODS AND RESULTS

In a retrospective, single center analysis of a population of 247 HCM patients, 21 patients (8.5%) had left ventricular apical aneurysms. Their mean age was 60 ± 14 years (range: 23-77 years) at study entry. Over 4.7 ± 3.3 years of follow-up, 10 patients (47.6%) experienced an adverse clinical event (annual event rate: 10.1%/y), including five implantable cardioverter-defibrillator (ICD) implantations for ventricular tachycardia/ventricular fibrillation (VT/VF), an appropriate discharge of ICD for VT/VF, and four nonfatal thromboembolic strokes. Two patients developed systolic dysfunction (ejection fraction <50%). No sudden cardiac death or progressive heart failure was detected. Fourteen patients showed ST-segment elevation (≥ 1 mm) in V3 through V5 of ECG. In four patients, progression of the ST-segment elevation was recognized. When the ST-segment elevation was used to identify apical aneurysms in HCM patients, the sensitivity was 66.7%, and the specificity was 98.7%.

CONCLUSION

Apical aneurysms in HCM patients in Japan are not rare, and are associated with serious cardiovascular complications. The early diagnosis of apical aneurysms can be achieved by serial ECG.

Hypertrophic cardiomyopathy with right ventricular outflow tract and left ventricular intracavitary obstruction

Obstruction of the right ventricular outflow tract (RVOT) is a rare finding in hypertrophic cardiomyopathy (HCM) patients unlike left ventricular outflow tract (LVOT) obstruction. Although there are guidelines that aid in clinical decision making in patients with LVOT obstruction, there are none addressing RVOT obstruction. As RVOT obstruction may pose serious clinical implications similar to LVOT obstruction, appropriate medical and surgical management is very important. A unique phenotype of HCM with RVOT obstruction in conjunction with left ventricle (LV) intracavitary obstruction is discussed.

The influence of Angiotensin converting enzyme and angiotensinogen gene polymorphisms on hypertrophic cardiomyopathy

Some studies have reported that angiotensin converting enzyme (ACE) and angiotensinogen (AGT) genes have been associated with hypertrophic cardiomyopathy (HCM). However, there have been inconsonant results among different studies. To clarify the influence of ACE and AGT on HCM, a systemic review and meta-analysis of case-control studies were performed. The following databases were searched to indentify related studies: PubMed database, the Embase database, the Cochrane Central Register of Controlled Trials database, China National Knowledge Information database, and Chinese Scientific and Technological Journal database. Search terms included "hypertrophic cardiomyopathy", "angiotensin converting enzyme" (ACE) or "ACE" and "polymorphism or mutation". For the association of AGT M235T polymorphism and HCM, "angiotensin converting enzyme" or "ACE" was replaced with "angiotensinogen". A total of seventeen studies were included in our review. For the association of ACE I/D polymorphism and HCM, eleven literatures were included in the meta-analysis on association of penetrance and genotype. Similarly, six case-control studies were included in the meta-analysis for AGT M235T. For ACE I/D polymorphism, the comparison of DI/II genotype vs DD genotype was performed in the present meta-analysis. The OR was 0.73 (95% CI: 0.527, 0.998, P = 0.049, power = 94%, alpha = 0.05) after the study which deviated from Hardy-Weinberg Equilibrium was excluded, indicating that the ACE I/D gene polymorphism might be associated with HCM. The AGT M235T polymorphism did not significantly affect the risk of HCM. In addition, ACE I/D gene polymorphism did not significantly influence the interventricular septal thickness in HCM patients. In conclusion, the ACE I/D polymorphism might be associated with the risk of HCM.

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.

Rapamycin reverses hypertrophic cardiomyopathy in a mouse model of LEOPARD syndrome-associated PTPN11 mutation

LEOPARD syndrome (LS) is an autosomal dominant "RASopathy" that manifests with congenital heart disease. Nearly all cases of LS are caused by catalytically inactivating mutations in the protein tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11) gene that encodes the SH2 domain-containing PTP-2 (SHP2). RASopathies typically affect components of the RAS/MAPK pathway, yet it remains unclear how PTPN11 mutations alter cellular signaling to produce LS phenotypes. We therefore generated knockin mice harboring the Ptpn11 mutation Y279C, one of the most common LS alleles. Ptpn11(Y279C/+) (LS/+) mice recapitulated the human disorder, with short stature, craniofacial dysmorphia, and morphologic, histologic, echocardiographic, and molecular evidence of hypertrophic cardiomyopathy (HCM). Heart and/or cardiomyocyte lysates from LS/+ mice showed enhanced binding of Shp2 to Irs1, decreased Shp2 catalytic activity, and abrogated agonist-evoked Erk/Mapk signaling. LS/+ mice also exhibited increased basal and agonist-induced Akt and mTor activity. The cardiac defects in LS/+ mice were completely reversed by treatment with rapamycin, an inhibitor of mTOR. Our results demonstrate that LS mutations have dominant-negative effects in vivo, identify enhanced mTOR activity as critical for causing LS-associated HCM, and suggest that TOR inhibitors be considered for treatment of HCM in LS patients.

MEK-ERK pathway modulation ameliorates disease phenotypes in a mouse model of Noonan syndrome associated with the Raf1(L613V) mutation

Hypertrophic cardiomyopathy (HCM) is a leading cause of sudden death in children and young adults. Abnormalities in several signaling pathways are implicated in the pathogenesis of HCM, but the role of the RAS-RAF-MEK-ERK MAPK pathway has been controversial. Noonan syndrome (NS) is one of several autosomal-dominant conditions known as RASopathies, which are caused by mutations in different components of this pathway. Germline mutations in RAF1 (which encodes the serine-threonine kinase RAF1) account for approximately 3%-5% of cases of NS. Unlike other NS alleles, RAF1 mutations that confer increased kinase activity are highly associated with HCM. To explore the pathogenesis of such mutations, we generated knockin mice expressing the NS-associated Raf1(L613V) mutation. Like NS patients, mice heterozygous for this mutation (referred to herein as L613V/+ mice) had short stature, craniofacial dysmorphia, and hematologic abnormalities. Valvuloseptal development was normal, but L613V/+ mice exhibited eccentric cardiac hypertrophy and aberrant cardiac fetal gene expression, and decompensated following pressure overload. Agonist-evoked MEK-ERK activation was enhanced in multiple cell types, and postnatal MEK inhibition normalized the growth, facial, and cardiac defects in L613V/+ mice. These data show that different NS genes have intrinsically distinct pathological effects, demonstrate that enhanced MEK-ERK activity is critical for causing HCM and other RAF1-mutant NS phenotypes, and suggest a mutation-specific approach to the treatment of RASopathies.

Heat shock protein 90 regulates IκB kinase complex and NF-κB activation in angiotensin II-induced cardiac cell hypertrophy

Heat shock protein 90 (HSP90), one of the most abundant proteins in the cardiac cells is essential for cell survival. Previous studies have shown that angiotensin II induces cardiac cell hypertrophy. However, the role of HSP90 in the angiotensin II-induced cardiac hypertrophy is unclear. In this study, we showed that HSP90 regulated angiotensin II-induced hypertrophy via maintenance of the IκB kinase (IKK) complex stability in cardiac cells. An HSP90 inhibitor, geldanamycin (GA), significantly suppressed angiotensin II-induced [³H]leucine incorporation and atrial natriuretic factor expression in cardiac cells. GA also inhibited the NF-κB activation induced by angiotensin II. Importantly, treatment with GA caused a degradation of IKKα/β; on the other hand, a proteasome-specific inhibitor restored the level of IKKα/β. We also found that GA prevented HSP90-IKKs complex induced by angiotensin II in cardiac cells. The small interfering RNA (siRNA)-mediated knockdown of HSP90 expression significantly inhibited angiotensin II-induced cell hypertrophy and NF-κB activation. These results suggest that angiotensin II-induced cardiac hypertrophy requires HSP90 that regulates the stability and complex of IKK.

Hypertrophic cardiomyopathy: assessment with MR imaging and multidetector CT

Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease. Its early detection is important because it is the most common cause of sudden cardiac death among young people. However, HCM is often a dilemma for clinicians because it manifests with diverse phenotypic expressions and clinical courses. With the advances in imaging technology, magnetic resonance (MR) imaging and multidetector computed tomography (CT) serve as suitable modalities for detecting and characterizing HCM and obtaining information for appropriate management of cases of HCM, although echocardiography is currently the most widely used modality. This article is an overview of the definition of HCM, its various phenotypes, risk stratification of HCM, and the potential application of cardiac MR imaging and multidetector CT for the assessment of HCM.

Imaging spectrum of sudden athlete cardiac death

Sudden athlete death (SAD) is a widely publicized and increasingly reported phenomenon. For many, the athlete population epitomize human physical endeavour and achievement and their unexpected death comes with a significant emotional impact on the public. Sudden deaths within this group are often without prior warning. Preceding symptoms of exertional syncope and chest pain do, however, occur and warrant investigation. Similarly, a positive family history of sudden death in a young person or a known family history of a condition associated with SAD necessitates further tests. Screening programmes aimed at detecting those at risk individuals also exist with the aim of reducing fatalities. In this paper we review the topic of SAD and discuss the epidemiology, aetiology, and clinical presentations. We then proceed to discuss each underlying cause, in turn discussing the pathophysiology of each condition. This is followed by a discussion of useful imaging methods with an emphasis on cardiac magnetic resonance and cardiac computed tomography and how these address the various issues raised by the pathophysiology of each entity. We conclude by proposing imaging algorithms for the investigation of patients considered at risk for these conditions and discuss the various issues raised in screening.

Comparative transcriptomics implicates mechanisms of evolved pollution tolerance in a killifish population

Wild populations of the killifish Fundulus heteroclitus resident in heavily contaminated North American Atlantic coast estuaries have recently and independently evolved dramatic, heritable, and adaptive pollution tolerance. We compared physiological and transcriptome responses to embryonic polychlorinated biphenyl (PCB) exposures between one tolerant population and a nearby sensitive population to gain insight into genomic, physiological and biochemical mechanisms of evolved tolerance in killifish, which are currently unknown. The PCB exposure concentrations at which developmental toxicity emerged, the range of developmental abnormalities exhibited, and global as well as specific gene expression patterns were profoundly different between populations. In the sensitive population, PCB exposures produced dramatic, dose-dependent toxic effects, concurrent with the alterations in the expression of many genes. For example, PCB-mediated cardiovascular system failure was associated with the altered expression of cardiomyocyte genes, consistent with sarcomere mis-assembly. In contrast, genome-wide expression was comparatively refractory to PCB induction in the tolerant population. Tolerance was associated with the global blockade of the aryl hydrocarbon receptor (AHR) signalling pathway, the key mediator of PCB toxicity, in contrast to the strong dose-dependent up-regulation of AHR pathway elements observed in the sensitive population. Altered regulation of signalling pathways that cross-talk with AHR was implicated as one candidate mechanism for the adaptive AHR signalling repression and the pollution tolerance that it affords. In addition to revealing mechanisms of PCB toxicity and tolerance, this study demonstrates the value of comparative transcriptomics to explore molecular mechanisms of stress response and evolved adaptive differences among wild populations.

Midregional pro-atrial natriuretic peptide: a novel marker of myocardial fibrosis in patients with hypertrophic cardiomyopathy

We aimed to determine the diagnostic performance of biomarkers in predicting myocardial fibrosis assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) in patients with hypertrophic cardiomyopathy (HCM). LGE CMR was performed in 40 consecutive patients with HCM. Left and right ventricular parameters, as well as the extent of LGE were determined and correlated to the plasma levels of midregional pro-atrial natriuretic peptide (MR-proANP), midregional pro-adrenomedullin (MR-proADM), carboxy-terminal pro-endothelin-1 (CT-proET-1), carboxy-terminal pro-vasopressin (CT-proAVP), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-8 (IL-8). Myocardial fibrosis was assumed positive, if CMR indicated LGE. LGE was present in 26 of 40 patients with HCM (65%) with variable extent (mean: 14%, range: 1.3-42%). The extent of LGE was positively associated with MR-proANP (r = 0.4; P = 0.01). No correlations were found between LGE and MR-proADM (r = 0.1; P = 0.5), CT-proET-1 (r = 0.07; P = 0.66), CT-proAVP (r = 0.16; P = 0.3), MMP-9 (r = 0.01; P = 0.9), TIMP-1 (r = 0.02; P = 0.85), and IL-8 (r = 0.02; P = 0.89). After adjustment for confounding factors, MR-proANP was the only independent predictor associated with the presence of LGE (P = 0.007) in multivariate analysis. The area under the ROC curve (AUC) indicated good predictive performance (AUC = 0.882) of MR-proANP with respect to LGE. The odds ratio was 1.268 (95% confidence interval 1.066-1.508). The sensitivity of MR-proANP at a cut-off value of 207 pmol/L was 69%, the specificity 94%, the positive predictive value 90% and the negative predictive value 80%. The results imply that MR-proANP serves as a novel marker of myocardial fibrosis assessed by LGE CMR in patients with HCM.

Sudden cardiac death in a 20-year-old male swimmer

In young adults, hypertrophic obstructive cardiomyopathy (HOCM) is an acknowledged risk factor for sudden cardiac death (SCD) in an otherwise healthy and active patient. While the incidence of SCD in young people is not high enough for extensive, wide-scale examinations, the potential for prevention of some deaths via pre-exercise imaging may be beneficial in certain patient populations, such as those with a family history of SCD or professional athletes. We present the case of a healthy 20-year-old man with no past medical history who died while swimming in a river, likely secondary to cardiac arrest in the setting of HOCM.

Genomics of heart failure

Cardiovascular disease is the leading cause of death in men and women, and heart failure (HF) is associated with high rates of morbidity and mortality. Most common forms of HF are non-mendelian and the evidence for heritability is modest. Study of the genetic susceptibility to HF has been limited to patients with rare familial forms of HF and candidate gene association studies in patients with distinct subtypes of HF. However, with the completion of the human genome project and the development of the HapMap template, new large-scale genome-wide association studies are possible. This article reviews the status of these and other important developments in genomics, in particular genome-wide sequencing, and other "omics".

Cardiovascular translational medicine (IV): The genetic basis of malignant arrhythmias and cardiomyopathies

The remarkable advances that have taken place in biomedicine over the past 50 years have resulted in dramatic improvements in the prevention, diagnosis and treatment of many diseases. Although cardiology has adopted these advances at a relatively slow pace, today it is fully immersed in this revolution and has become one of the most innovative medical specialties. Research is continuing to give rise to new developments in genetics and molecular biology that lead, almost daily, to innovative ways of preventing, diagnosing and treating the most severe forms of heart disease. Consequently, it is essential that clinical cardiologists have some basic knowledge of genetics and molecular biology as these disciplines are having an increasing influence on clinical practice.

Association of angiotensin-converting enzyme activity and polymorphism with echocardiographic measures in familial and nonfamilial hypertrophic cardiomyopathy

Angiotensin-converting enzyme (ACE) activity and polymorphism contribute significantly to the prognosis of patients with cardiomyopathy. The aim of this study was to determine the activity and type of ACE polymorphism in patients with familial and nonfamilial hypertrophic cardiomyopathy (HCM) and to correlate these with echocardiographic measurements (echo-Doppler). We studied 136 patients (76 males) with HCM (69 familial and 67 nonfamilial cases). Mean age was 41 +/- 17 years. DNA was extracted from blood samples for the polymerase chain reaction and the determination of plasma ACE levels. Left ventricular mass, interventricular septum, and wall thickness were measured. Mean left ventricular mass index, interventricular septum and wall thickness in familial and nonfamilial forms were 154 +/- 63 and 174 +/- 57 g/m(2) (P = 0.008), 19 +/- 5 and 21 +/- 5 mm (P = 0.02), and 10 +/- 2 and 12 +/- 3 mm (P = 0.0001), respectively. ACE genotype frequencies were DD = 35%, ID = 52%, and II = 13%. A positive association was observed between serum ACE activity and left ventricular mass index (P = 0.04). Logistic regression showed that ACE activity was twice as high in patients with familial HCM and left ventricular mass index >or=190 g/m(2) compared with the nonfamilial form (P = 0.02). No other correlation was observed between ACE polymorphisms and the degree of myocardial hypertrophy. In conclusion, ACE activity, but not ACE polymorphisms, was associated with the degree of myocardial hypertrophy in the patients with HCM.

Cardiovascular translational medicine (IV): The genetic basis of malignant arrhythmias and cardiomyopathies

The remarkable advances that have taken place in biomedicine over the past 50 years have resulted in dramatic improvements in the prevention, diagnosis and treatment of many diseases. Although cardiology has adopted these advances at a relatively slow pace, today it is fully immersed in this revolution and has become one of the most innovative medical specialties. Research is continuing to give rise to new developments in genetics and molecular biology that lead, almost daily, to innovative ways of preventing, diagnosing and treating the most severe forms of heart disease. Consequently, it is essential that clinical cardiologists have some basic knowledge of genetics and molecular biology as these disciplines are having an increasing influence on clinical practice.

The molecular genetics of arrhythmias and sudden death

The current status of the research in genetics of cardiac diseases causing sudden death is reviewed. Few techniques will impact medicine as will those of molecular biology. The identification of the gene-causing diseases will allow the use of better preventive, diagnostic, and therapeutic options. From genetic counseling at present to gene therapy in the future, the new challenge for the clinician will be to acquire the new information provided by molecular biology and apply it at the bedside to improve the quality of life for the patient.

Sudden death in competitive athletes

Sudden death in athletes is an extremely rare event yet no less tragic for its infrequency. Up to 90% of these deaths are due to underlying cardiovascular diseases and therefore categorized as sudden cardiac death (SCD). The causes of SCD among athletes are strongly correlated with age. In young athletes (<35 years), the leading causes are congenital cardiac diseases, particularly hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and congenital coronary artery anomalies. By contrast, most of deaths in older athletes (<35 years) are due to coronary artery disease. This review focuses on the cardiac causes of SCD and provides a brief summary of the principal noncardiac causes. Current pre-participation screening strategies are also discussed, with particular emphasis on the Italian experience.

Right ventricular involvement in hypertrophic cardiomyopathy

The aim of this study was to assess, using cardiovascular magnetic resonance (CMR), whether morphologic right ventricular (RV) abnormalities are present in patients with hypertrophic cardiomyopathy (HC). Left ventricular hypertrophy has been considered the predominant phenotypic expression of HC. Whether structural abnormalities of the right ventricle are also present in HC is unknown. CMR provides complete coverage of both ventricles with high spatial resolution. CMR was applied to study RV morphology in HC. CMR was performed on 46 subjects with HC (mean age 39 +/- 16 years; 70% men) free of pulmonary hypertension and 22 healthy subjects (mean age 44 +/- 16 years; 50% men). Mass, wall thickness, chamber volume, the ejection fraction, and fibrosis were assessed for both ventricles. Maximum RV wall thickness was increased in patients with HC compared with referent controls (7 +/- 2 vs 5 +/- 1 mm, p <0.001), including 15 (33%) with maximum wall thicknesses > or =8 mm (> or =2 SDs higher than the mean for controls) and 4 (9%) with extreme hypertrophy (> or =10 mm). RV hypertrophy was predominantly a diffuse process involving the entire or a significant proportion of the RV wall in most patients (n = 8 [53%]). The RV wall mass index was also increased in patients with HC (28 +/- 9 vs 22 +/- 4 g, p <0.001). A significant correlation was found between maximum RV and left ventricular wall thickness (R(2) = 0.4, p <0.001) and between RV and left ventricular mass (R(2) = 0.4, p <0.001). Only 1 (2%) patient with HC had evidence of RV wall fibrosis. In conclusion, morphologic RV abnormalities are present in a substantial proportion of patients with HC.

Use of cardiovascular magnetic resonance for diagnosis and management in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited cardiac disorder characterized by unexplained myocardial hypertrophy. The condition is associated with sudden cardiac death and is therefore often diagnosed postmortem, especially in the young and in competitive athletes. For this reason, intense research focuses on developing strategies to minimize this tragic consequence. Cardiovascular magnetic resonance (CMR) is a novel imaging modality that provides high-resolution images in an infinite number of planes with additional sequences that allows for tissue characterization and quantification of flow. The most exciting development is the application of late gadolinium-enhanced (LGE) imaging, which allows for in vivo detection of myocardial fibrosis. This review summarizes the current applications of CMR in HCM and also speculates on future applications, particularly the potential for risk stratification using LGE-CMR.

Screening of the endothelin1 gene (EDN1) in a cohort of patients with essential left ventricular hypertrophy

Our objective was to analyse the role of endothelin1 gene (EDN1) variation in essential left ventricular hypertrophy (LVH). We searched for EDN1 variants in 145 Spanish patients with an essential form of LVH (not secondary to hypertension, aortic stenosis, or any other disease that could explain the hypertrophy). The five EDN1 coding exons and 1.5 kilobases of the promoter region were analysed through single strand conformation analysis and direct sequencing. We found four nucleotide changes: -1224 C/A (promoter), -131 ins/del A (exon 1, 5'-non-translated sequence), A/G in codon 106 (exon 3, silent), and G/T in codon 198 (exon 5, lys198asn). To determine the association between these polymorphisms and cardiac hypertrophy, we compared the genotype frequencies from these 145 patients with 250 healthy controls. We found a higher frequency of patients homozygous for 198 lys (198 KK) (65% vs. 52%; p = 0.01; OR = 1.76) and for -1224 AA (73% vs. 66%; p = 0.19). Homozygotes for -1224 A + 198 K (AA+KK) were significantly more frequent in patients (62% vs. 45%; p = 0.0007; OR = 2.10; 95% CI = 1.35-3.25). The expression of the -1224 C/A and exon 5 K198N variants was analysed with cells in culture. These in vitro studies showed that these variations did not differ in their expression levels. In conclusion, our work has shown that EDN1 variation, and in particular homozygosity for the -1224A/198K haplotype, is associated with the risk of developing cardiac hypertrophy. However, these EDN1 variants do not affect in vitro gene expression.

[Beta-myosin heavy-chain gene mutations in patients with hypertrophic cardiomyopathy]

INTRODUCTION AND OBJECTIVES

To determine the frequency of mutations in the beta-myosin heavy-chain gene (MYH7) in a cohort of patients with hypertrophic cardiomyopathy (HCM) and their families, and to investigate correlations between genotype and phenotype.

METHODS

Single-strand conformation polymorphism analysis and sequencing of fragments with abnormal MYH7 gene mobility were carried out in 128 consecutive index patients with HCM. The phenotypes of patients with and without mutations were compared and the phenotypes of identified families were recorded.

RESULTS

A total of 11 mutations were found in 13 families (10%); 7/11 had been previously described. The I736T mutation was found in three families and the A797T in two. One patient had two mutations (i.e., I736T and R787H). Mutations were more frequent in patients with a family history of sudden death (31%) and in those with severe hypertrophy (39% had a thickness > or = 30 mm). Mutations were found in 29 of 42 members of the 13 families, including six family members (20%) who were healthy carriers and aged < or = 36 years. Sudden death had occurred in eight members of four families: four in two families with the I736T mutation, one in a family with A797T, one in a family with R870H, and two in a family with A901P.

CONCLUSIONS

MYH7 mutations were present in 10% of our families. Mutations were more frequent in patients with a family history of sudden death and in those with severe hypertrophy. Most mutations had been described previously. Some appeared in several families. For some mutations, the correlation between genotype and phenotype was stable, while for others, there were marked differences between the phenotypes of the index patients and their relatives, suggesting the presence of additional genetic factors that have yet to be identified.

Hypertrophic cardiomyopathy complicated by severe bradycardias: a pedigree report

We describe four patients with nonobstructive hypertrophic cardiomyopathy (HCM) from an extended Chinese family. The patients had remarkably similar physical and echocardiographic findings including a harsh localized systolic murmur and apical left ventricular hypertrophy. All four had severe sinus bradycardia and atrial-ventricular conduction block (AVB) manifest by recurrent syncope. Two died suddenly due to bradycardia. Holter monitoring showed no tachycardias. Late potentials were not present. We conclude that this unusual form of HCM may be caused by a new and as yet unknown gene mutation.

Proposal for contemporary screening strategies in families with hypertrophic cardiomyopathy

Screening families with hypertrophic cardiomyopathy (HCM) presents a common clinical problem to practicing cardiologists, internists, and pediatricians. The traditional recommended strategy for screening relatives in most HCM families calls for such evaluations with echocardiography (and electrocardiogram [ECG]) on a 12- to 18-month basis, usually beginning at about age 12 years. If such tests show no evidence of left ventricular hypertrophy, i.e., without one or more segments of abnormally increased wall thickness by the time full growth and maturation is achieved (at the age of about 18 to 21 years), it has been customary practice to conclude that HCM is probably absent and reassure family members accordingly that further echocardiographic testing is unnecessary. However, novel developments in the definition of the genetic causes of HCM have defined both substantial molecular diversity and heterogeneity of the disease expression including (in some relatives) incomplete phenotypic penetrance and delayed, late-onset left ventricular hypertrophy well into adulthood. These observations have unavoidably reshaped the customary practice of genetic counseling and established a new proposed paradigm for clinical family screening of HCM families. Therefore, in the absence of genetic testing, strong consideration should be given to extending diagnostic serial echocardiography past adolescence and into mid-life for those family members with a normal echocardiogram and ECG. Of note, recent developments in laboratory DNA-based diagnosis for HCM could potentially avoid the necessity for serial echocardiography in many such relatives.

Identification of a new missense mutation in the mtDNA of hereditary hypertrophic, but not dilated cardiomyopathic hamsters

The cardiomyopathic hamster is characterized by a naturally occurring deletion in the delta-sarcoglycan gene generating either the hypertrophic or the dilatative phenotype of cardiomyopathy. This evidence suggests that other genetic or environmental factors might concur to the pathogenesis of cardiomyopathy. The aim of the present study was to investigate on the possibility that other genes are involved in the pathogenesis of hamster cardiomyopathy. For this purpose, a series of genes of cardiomyopathic and healthy hamsters were compared by the differential display technique. The hamster cytochrome c oxidase mitochondrial subunit III (COIII) gene has been sequenced and identified as the gene upregulated in brain and skeletal muscle. The gene sequencing and restriction analysis demonstrated that a missense mutation is present in the COIII gene of hamsters exhibiting hypertrophic cardiomyopathy while no mutations were present in dilatative cardiomyopathic hamsters. The mutation was heteroplasmic and the heteroplasmy level was increased with age in skeletal muscle and heart. The ultrastructural analysis of cardiac tissue showed severe damage in the mitochondrial structure of hypertrophic but not dilatative hamster hearts. These results suggest that the pathogenesis of the cardiac damage in hypertrophic cardiomyopathic hamster may be sustained by multiple mutations exerting a cumulative effect on both structure and function of cardiac muscle.