Genetic polymorphisms in the renin-angiotensin-aldosterone system associated with expression of left ventricular hypertrophy in hypertrophic cardiomyopathy: a study of five polymorphic genes in a family with a disease causing mutation in the myosin binding protein C gene

The effects of candesartan on left ventricular hypertrophy and function in nonobstructive hypertrophic cardiomyopathy: a pilot, randomized study

Hypertrophic cardiomyopathy is caused by mutations in the genes that encode sarcomeric proteins and is primarily characterized by unexplained left ventricular hypertrophy, impaired cardiac function, reduced exercise tolerance, and a relatively high incidence of sudden cardiac death, especially in the young. The extent of left ventricular hypertrophy is one of the major determinants of disease prognosis. Angiotensin II has trophic effects on the heart and plays an important role in the development of myocardial hypertrophy. Here in a double-blind, placebo-controlled, randomized study, we show that the long-term administration of the angiotensin II type 1 receptor antagonist candesartan in patients with hypertrophic cardiomyopathy was associated with the significant regression of left ventricular hypertrophy, improvement of left ventricular function, and exercise tolerance. The magnitude of the treatment effect was dependent on specific sarcomeric protein gene mutations that had the greatest responses on the carriers of ss-myosin heavy chain and cardiac myosin binding protein C gene mutations. These data indicate that modulating the role of angiotensin II in the development of hypertrophy is specific with respect to both the affected sarcomeric protein gene and the affected codon within that gene. Thus, angiotensin II type 1 receptor blockade has the potential to attenuate myocardial hypertrophy and may, therefore, provide a new treatment option to prevent sudden cardiac death in patients with hypertrophic cardiomyopathy.

Myocardial fibrosis in patients with symptomatic obstructive hypertrophic cardiomyopathy: correlation with echocardiographic measurements, sarcomeric genotypes, and pro-left ventricular hypertrophy polymorphisms involving the renin-angiotensin-aldosterone system

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disorder of the cardiac sarcomere, resulting in myocyte hypertrophy and disarray, interstitial fibrosis, and cardiac dysfunction. Our aim was to determine whether the amount of fibrosis in HCM correlates with echocardiographic measures of diastolic dysfunction, presence of HCM-susceptibility mutations, or polymorphisms in the renin-angiotensin-aldosterone system (RAAS).

METHODS

Surgical specimens from patients with obstructive HCM undergoing septal myectomy at the Mayo Clinic (2001-2004) were examined and compared with autopsy-derived tissues from age- and sex-matched normal controls. Digital image analysis was used to quantitate the fibrosis in representative microscopic sections. Genotyping was performed for myofilament-HCM using polymerase chain reaction, high-performance liquid chromatography, and direct DNA sequencing. RAAS polymorphism status was similarly established.

RESULTS

The study included 59 HCM cases and 44 controls. Patients with HCM exhibited more fibrosis (mean 17%, range 3-45%) than controls (mean 8%, range 3-17%) (P<.0001). A significant relationship existed between amount of fibrosis and maximum wall thickness (P=.02), left ventricular ejection fraction (P=.02), and peak early/late diastolic mitral annulus velocity (E/A ratio) (P=.002). Although there was no association between amount of fibrosis and myofilament-HCM genotype status or polymorphisms in the RAAS cascade, there was a trend toward more fibrosis in patients with > or =1 C-encoding allele in CYP11B2-encoded aldosterone synthase.

CONCLUSIONS

Patients with HCM undergoing septal myectomy had significantly more myocardial interstitial fibrosis than controls. The amount of fibrosis in HCM patients correlated with degree of septal hypertrophy and left ventricular systolic and diastolic function. Notably, neither mutations in cardiac myofilament proteins or polymorphisms in RAAS exhibited strong associations with severity of myocardial fibrosis.

Genetic variation in angiotensin-converting enzyme 2 gene is associated with extent of left ventricular hypertrophy in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy, a common, inherited cardiac muscle disease, is primarily caused by mutations in sarcomeric protein-encoding genes and is characterized by overgrowth of ventricular muscle that is highly variable in extent and location. This variability has been partially attributed to locus and allelic heterogeneity of the disease-causing gene, but other factors, including unknown genetic factors, also modulate the extent of hypertrophy that develops in response to the defective sarcomeric functioning. Components of the renin-angiotensin-aldosterone system are plausible candidate hypertrophy modifiers because of their role in controlling blood pressure and biological effects on cardiomyocyte hypertrophy.

MYBPC3 gene variations in hypertrophic cardiomyopathy patients in India

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a complex cardiac muscular disorder, inherited as an autosomal dominant disease with variable penetrance. Cardiac myosin-binding protein C (MyBPC) is the predominant myosin-binding protein isoform in the heart muscle. One hundred forty-seven mutations have been detected in MYBPC3, accounting for 15% of all HCM cases.

OBJECTIVE

To screen exons 16, 18, 19, 22, 24, 28, 30, 31 and 34 in the MYBPC3 gene in Indian HCM patients.

METHODS

Sixty control and 95 HCM samples were collected from cardiology units of the CARE Hospital (Nampally, Banjara Hills, Secunderabad, India) for genomic DNA isolation followed by polymerase chain reaction and single-stranded conformational polymorphism analysis.

RESULTS

Screening of the exons revealed two variations - one novel frame shift mutation in exon 19 at the nucleotide position 11577-11578 and one novel single nucleotide polymorphism (SNP) in codon 1093 of exon 31, coding for glycine with a C>T transition (GGC/GGT), in addition to the seven known SNPs mainly in the intronic region and one known missense mutation D770N in this population.

CONCLUSION

The novel frame shift mutation identified in exon 19, D570fs, with the insertion of an adenine residue in codon 570 coding for aspartate, results in a premature termination codon that produces a truncated protein lacking myosin- and titin-binding sites, explaining the role of the nonsense-mediated decay pathway. A novel SNP identified in codon 1093 of exon 31 was found to be a synonymous codon, which may have a regulatory effect at the translational level, attributing to affinity differences between codon-anticodon interactions. The screening of this gene may be relevant in the Indian context.

Hypertrophic cardiomyopathy: the genetic determinants of clinical disease expression

Hypertrophic cardiomyopathy (HCM), defined clinically by the presence of unexplained left ventricular hypertrophy, is the most common inherited cardiac disorder. This condition is the major cause of sudden death in the young (<30 years of age) and in athletes. The clinical phenotype is heterogeneous, and mutations in a number of sarcomeric contractile-protein genes are responsible for causing the disease in approximately 60% of individuals with HCM. Other inherited syndromes, as well as metabolic and mitochondrial disorders, can present as clinical phenocopies and can be distinguished by their associated cardiac and noncardiac features and on the basis of their unique molecular genetics. The mode of inheritance, natural history and treatment of phenocopies can differ from those of HCM caused by mutations in sarcomere genes. Detailed clinical evaluation and mutation analysis are, therefore, important in providing an accurate diagnosis in order to enable genetic counseling, prognostic evaluation and appropriate clinical management. This Review summarizes current knowledge on the genetics, disease mechanisms, and correlations between phenotype and genotype in patients with HCM, and discusses the implications of genetic testing in routine clinical practice.

ACE I/D polymorphism in Indian patients with hypertrophic cardiomyopathy and dilated cardiomyopathy

AIM

The study was carried to determine the association of angiotensin converting enzyme (ACE) insertion/deletion (I/D) polymorphism with the risk of hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and restrictive cardiomyopathy (RCM).

METHODS AND RESULTS

A total of 174 patients diagnosed with cardiomyopathy (118 with HCM, 51 with DCM, and 5 with RCM) and 164 ethnically, age- and gender-matched controls were included in the study. ACE I/D genotyping was performed by PCR. In total, 25.86% of the patients were in New York Heart Association (NYHA) class III and IV at presentation. A total of 67.24% patients had dyspnea, 56.89% had angina pectoris, and 25.28% of the patients had at least one event of syncope. Frequency of occurrence of the disease was more in male patients compared to female patients (P < 0.05). After adjustment for age, sex, body mass index (BMI), and smoking habit, the prevalence of ACE DD genotype, and ACE 'D' allele was significantly higher in patients as compared to controls and was associated with increased risk (DD: OR 2.11, 95% CI 1.27-3.52, P < 0.05; 'D': OR 1.91, 95% CI 1.08-3.35, P < 0.05). The mean septal thickness was higher for DD and ID genotypes (20.40 +/- 3.73 mm and 21.82 +/- 5.35 mm, respectively) when compared with II genotype (18.63 +/- 6.69 mm) in HCM patients, however, the differences were not significant statistically (P > 0.05). The DCM patients with ID genotype showed significantly decreased left ventricular ejection fraction (LVEF) at enrolment (26.50 +/- 8.04%) (P = 0.04).

CONCLUSION

Our results suggest that D allele of ACE I/D polymorphism significantly influences the HCM and DCM phenotypes.

RAAS gene polymorphisms influence progression of pediatric hypertrophic cardiomyopathy

Hypertrophic Cardiomyopathy (HCM) is a disease with variable rate of progression. Young age is an independent risk factor for poor outcome in HCM. The influence of renin-angiotensin-aldosterone (RAAS) genotype on the progression of HCM in children is unknown. Children with HCM (n = 65) were enrolled prospectively across two centers (2001-2005). All subjects were genotyped for five RAAS gene polymorphisms previously associated with LV hypertrophy (pro-LVH): AGT M235T, ACE DD, CMA-1903 A/G, AGTR1 1666 A/C and CYP11B2-344 C/T. Linear regression models, based on maximum likelihood estimates, were created to assess the independent effect of RAAS genotype on LV hypertrophy (LVH). Forty-six subjects were homozygous for <2 and 19 were homozygous for > or =2 pro-LVH RAAS polymorphisms. Mean age at presentation was 9.6 +/- 6 years. Forty children had follow-up echocardiograms after a median of 1.5 years. Indexed LV mass (LVMI) and LV mass z-scores were higher at presentation and follow-up in subjects with > or =2 pro-LVH genotypes compared to those with <2 (P < 0.05). Subjects with > or =2 pro-LVH genotypes also demonstrated a greater increase in septal thickness (IVST) and in LV outflow tract (LVOT) obstruction on follow-up (P < 0.05). On multivariate analysis, a higher number of pro-LVH genotypes was associated with a larger effect size (P < 0.05). Pro-LVH RAAS gene polymorphisms are associated with progressive septal hypertrophy and LVOT obstruction in children with HCM. Identification of RAAS modifier genes may help to risk-stratify patients with HCM.

Reviews of Translational Medicine and Genomics in Cardiovascular Disease: New Disease Taxonomy and Therapeutic Implications

The enduring subdivision of cardiomyopathies into hypertrophic (HCM), dilated (DCM), and restrictive (RCM) categories reflects the emphasis of traditional classifications on morphology. Rapid advances in the genetic interrogation of these disorders have redefined their taxonomy and revealed potential conflicts between the old and new classifications. Hypertrophic cardiomyopathy has been redefined as a disease of perturbed sarcomere function. Dilated cardiomyopathy is a disease that results from more varied perturbations, including, but not limited to, defects of the cytoskeleton. Positional cloning and candidate gene approaches have been successful in identifying >40 disease loci, many of which have led to disease genes in HCM, DCM, RCM, and arrhythmogenic right ventricular cardiomyopathy. These findings provide mechanistic insights, permit genetic screening, and to a limited extent, facilitate prognostication. Although single gene analyses rapidly focus down to the underlying mechanistic pathways, they do not take account of all relevant variation in the human genome. Correspondingly, advances in genomics, through microarrays, have facilitated characterization of these broader downstream elements. As well as refining the taxonomic reclassification of cardiomyopathies, these genomic approaches, coupled with functional studies, have identified novel potential therapeutic targets, such as cardiac energetics, calcium handling, and apoptosis. We review the successes and pitfalls of genetic and genomic approaches to cardiomyopathy and their impact on current and future clinical care.

The genetic basis for cardiac remodeling

Cardiomyopathies are primary disorders of cardiac muscle associated with abnormalities of cardiac wall thickness, chamber size, contraction, relaxation, conduction, and rhythm. They are a major cause of morbidity and mortality at all ages and, like acquired forms of cardiovascular disease, often result in heart failure. Over the past two decades, molecular genetic studies of humans and analyses of model organisms have made remarkable progress in defining the pathogenesis of cardiomyopathies. Hypertrophic cardiomyopathy can result from mutations in 11 genes that encode sarcomere proteins, and dilated cardiomyopathy is caused by mutations at 25 chromosome loci where genes encoding contractile, cytoskeletal, and calcium regulatory proteins have been identified. Causes of cardiomyopathies associated with clinically important cardiac arrhythmias have also been discovered: Mutations in cardiac metabolic genes cause hypertrophy in association with ventricular pre-excitation and mutations causing arrhythmogenic right ventricular dysplasia were recently discovered in protein constituents of desmosomes. This considerable genetic heterogeneity suggests that there are multiple pathways that lead to changes in heart structure and function. Defects in myocyte force generation, force transmission, and calcium homeostasis have emerged as particularly critical signals driving these pathologies. Delineation of the cell and molecular events triggered by cardiomyopathy gene mutations provide new fundamental knowledge about myocyte biology and organ physiology that accounts for cardiac remodeling and defines mechanistic pathways that lead to heart failure.

Cine MR Imaging of Myocardial Contractile Impairment in Patients with Hypertrophic Cardiomyopathy Attributable to Asp175Asn Mutation in the α-Tropomyosin Gene

PURPOSE

To prospectively investigate the relationship between myocardial contractile impairment and left ventricular (LV) hypertrophy measured at cardiac magnetic resonance (MR) imaging in patients with hypertrophic cardiomyopathy (HCM) caused by the substitution of aspartic acid 175 with asparagine (ie, Asp175Asn mutation) in the alpha-tropomyosin gene (TPM1).

MATERIALS AND METHODS

The study protocol was approved by the hospital ethics committee, and all subjects gave written informed consent. LV mass, maximal LV wall thickness, and myocardial fractional thickening during systole were measured at cine MR imaging in 24 subjects (11 male, 13 female; mean age, 42 years; age range, 17-68 years) with the Asp175Asn mutation in TPM1 and in 17 healthy volunteers (eight men, nine women; mean age, 38 years; age range, 23-60 years). The proportion of hypokinetic LV segments was calculated as the number of LV segments with fractional thickening of less than 30% divided by the total number of segments measured. Anthropometric and biochemical correlates of LV hypertrophy were determined. Univariate and multiple linear regression analyses were used to investigate the association of the proportion of hypokinetic segments and other correlates of LV hypertrophy with LV mass and maximal wall thickness.

RESULTS

The proportion of hypokinetic segments was higher in patients with HCM than in control subjects (37% +/- 20 [standard deviation] vs 12% +/- 12, P < .001). In stepwise multiple regression analysis, the proportion of hypokinetic segments accounted for 42% (P < .001); the LV end-diastolic volume, for 24% (P = .003); and male sex, for 10% (P = .014) of the variability in LV mass in patients with HCM. The proportion of hypokinetic LV segments, which accounted for 48% of the variability in LV maximal wall thickness (P < .001), was the only variable significantly associated with maximal wall thickness.

CONCLUSION

The extent of myocardial contractile impairment is strongly and independently related to LV mass and maximal wall thickness in patients with HCM attributable to the Asp175Asn mutation in TPM1.

Gene-specific modifying effects of pro-LVH polymorphisms involving the renin-angiotensin-aldosterone system among 389 unrelated patients with hypertrophic cardiomyopathy

AIMS

The purpose of this study was to determine whether the deletion/insertion (D/I) polymorphism in the ACE-encoded angiotensin-converting enzyme or the pooled gene effect of five renin-angiotensin-aldosterone system (RAAS) polymorphisms were disease modifiers in a large cohort of unrelated patients with genotyped hypertrophic cardiomyopathy (HCM).

METHODS AND RESULTS

Five different RAAS polymorphism genotypes were established by PCR amplification of the surrounding polymorphic regions of genomic DNA in a cohort of 389 unrelated patients comprehensively genotyped for HCM-causing mutations in eight sarcomeric/myofilament genes. Patient clinical data were archived in a database blinded both to the primary myofilament defect and the polymorphism genotype. Each patient was assessed with respect to ACE genotype as well as composite pro-left ventricular hypertrophy (LVH) RAAS polymorphism score (0-5). Overall, no clinical parameter correlated independently with ACE genotype. Subset analysis of the two most common genetic subtypes of HCM, MYBPC3 (myosin binding protein C) and MYH7 (beta myosin heavy chain), demonstrated a significant pro-LVH effect of DD-ACE only in patients with MYBPC3-HCM. In MYBPC3-HCM, left ventricular wall thickness was greater in patients with DD genotype (25.8+/-5 mm) compared with DI (21.8+/-4) or II genotype (20.8+/-5, P=0.01). Moreover, extreme hypertrophy (>30 mm) was only seen in MYBPC3-HCM patients who also hosted DD-ACE. An effect of RAAS pro-LVH score was evident only in the subgroup of patients with no previously identified myofilament mutation.

CONCLUSION

This study demonstrates that RAAS genotypes may modify the clinical phenotype of HCM in a disease gene-specific fashion rather than indiscriminately.

Genetic polymorphisms and heart failure

Heart failure is a complex clinical syndrome. There is evidence for a genetic contribution to the pathophysiology of heart failure. Considering the fundamental role of neurohormonal factors in the pathophysiology and progression of cardiac dysfunction and hypertrophy, variants of genes involved in this system are logical candidate genes in heart failure. In this report, genetic polymorphisms of the major neurohormonal systems in heart failure will be discussed. Studies on polymorphisms of the renin-angiotensin-aldosterone system (RAAS), adrenergic receptor polymorphisms, endothelin (receptor) polymorphisms, and a group of miscellaneous polymorphisms that may be involved in the development or phenotypic expression of heart failure will be reviewed. Research on left ventricular hypertrophy is also included. The majority of genetic association studies focused on the ACE I/D polymorphism. Initial genetic associations have often been difficult to replicate, mainly due to problems in study design and lack of power. Promising results have been obtained with genetic polymorphisms of the RAAS and sympathetic system. Considering the evidence so far, a modifying role for these polymorphisms seems more likely than a role of these variants as susceptibility genes. Besides the need for larger studies to examine the effects of single nucleotide polymorphisms and haplotypes, future studies also need to focus on the complexity of these systems and study gene-gene interactions and gene-environment interactions.

Consequences of pressure overload on sarcomere protein mutation-induced hypertrophic cardiomyopathy

BACKGROUND

Whether ventricular remodeling from hypertrophic cardiomyopathy (HCM), systemic hypertension, or other pathologies arises through a common signaling pathway or through independent molecular mechanisms is unknown. To study this, we assessed cardiac hypertrophy in a mouse model of HCM subjected to increased left ventricular (LV) load.

METHODS AND RESULTS

Transverse aortic banding of mice with or without an Arg403Gln cardiac myosin heavy chain mutation (alphaMHC403/+) produced similarly elevated LV pressures (120+/-30 versus 112+/-14 mm Hg; P=NS). No mice developed heart failure, and mortality (26% alphaMHC403/+, 35% wild-type) was comparable. Load-induced hypertrophy was identical in banded 129SvEv alphaMHC403/+ mice (LV anterior wall [LVAW]=1.28+/-0.11) and 129SvEv wild-type mice (LVAW=1.29+/-0.11 mm; P=NS). Genetically outbred Black Swiss (BS) alphaMHC403/+ mice showed only mildly exaggerated hypertrophy in response to aortic banding (BS alphaMHC403/+ LVAW=1.30+/-0.13 mm; BS wild-type LVAW=1.17+/-0.15 mm; P=0.03), suggesting some effect from a BS genetic locus that modifies hypertrophy induced by the cardiac MHC Arg403Gln mutation. Histopathology and molecular markers of hypertrophy were comparable in all banded 129SvEv or BS mice. Banded alphaMHC403/+ mice had potential for greater hypertrophy, because cyclosporin A treatment markedly augmented hypertrophy.

CONCLUSIONS

The uniform hypertrophic response to increased ventricular load in wild-type and alphaMHC403/+ mice indicates independent cardiac remodeling pathways and predicts that coexistent hypertension and HCM should not profoundly exacerbate cardiac hypertrophy. In contrast, sarcomere mutation and cyclosporin A-mediated calcineurin inhibition stimulate a shared hypertrophic signaling pathway. Defining distinct signaling pathways that trigger myocyte growth should help to tailor therapies for cardiac hypertrophy.

Polymorphisms in the RAS and cardiac function

Since the discovery of the polymorphism in the angiotensin converting enzyme (ACE) and the consequences of this polymorphism on the activity levels of the enzyme, numerous association studies have been performed. However, these investigations do not often adhere to the most stringent criteria for such studies. The initial study reporting a positive association of the ACE polymorphism and myocardial infarction showed an increased risk of the DD genotype. This initial association was eventually refuted by a large, well conducted association study, which found a risk ratio of 1.02 after combining their own data with all published data. Although such large, well conducted association studies have not been performed in left ventricular (LV) hypertrophy, the association between DD genotype and hypertrophy is more convincing with a 192% excess risk of LV hypertrophy in untreated hypertensives. The role of ACE genotype in LV growth is well established, especially in athletes. In heart failure, large studies or meta-analyses have not been performed, because most studies have selected different end-points. This hampers a proper meta-analysis of the results obtained in associations with heart failure. As most association studies do not fulfill the criteria for good association studies and use too small sample sizes, it remains important to perform a meta-analysis to add meaning to the results of such studies. Above all, it is important to obey the rules set for association studies, large sample size, small P values, report associations that make biological sense and alleles that affect the gene product in a physiologically meaningful way.