From malignant mutations to malignant domains: the continuing search for prognostic significance in the mutant genes causing hypertrophic cardiomyopathy

Risk stratification in hypertrophic cardiomyopathy

Sudden cardiac death (SCD) is the most devastating complication of hypertrophic cardiomyopathy (HCM). The greatest challenge in the management of HCM is identifying those at increased risk, since an implantable cardioverter-defibrillator (ICD) is a potentially life-saving therapy. We sought to summarize the available data on SCD in HCM and provide a clinical perspective on the current differing and somewhat conflicting data on risk stratification, with balanced guidance regarding rational clinical decision-making. Additionally, we sought to determine the status of the current implementation of guidelines compiled by HCM experts worldwide. The HCM Risk-SCD model helps improve the risk stratification of HCM patients for primary prevention of SCD by calculating an individual risk estimate that contributes to the clinical decision-making process. Improved risk stratification is important for decision-making before ICD implantation for the primary prevention of SCD.

The Natural History of Nonobstructive Hypertrophic Cardiomyopathy

OBJECTIVE

To describe the survival of a large nonobstructive hypertrophic cardiomyopathy (NO-HCM) cohort and to identify risk factors for increased mortality in this population.

PATIENTS AND METHODS

Patients were identified from the Mayo Clinic HCM database from January 1, 1975, through November 30, 2006, for this retrospective observational study. Patients with resting or provocable left ventricular outflow tract gradients were excluded. Echocardiographic, clinical, and genetic data were compared between subgroups, and survival data were compared with expected population rates.

RESULTS

A total of 706 patients with NO-HCM were identified. During median follow-up of 5 years (mean, 7 years), there were 208 deaths. Overall survival was no different than expected compared with age- and sex-matched white US population mortality rates (P=.77). Independent predictors of death were age at diagnosis, "burned out" HCM, and history of transient ischemic attack or stroke; use of an implantable cardioverter defibrillator (ICD) was inversely related to death. After exclusion of patients with an ICD, there was no difference in survival compared with age- and sex- matched individuals (P=.39); age, previous transient ischemic attack/stroke, and burned out HCM were predictors of death.

CONCLUSION

In this cohort, patients with NO-HCM had similar survival rates as age- and sex-matched white US population mortality rates. Although use of an ICD was inversely related to death, no differences in overall survival were seen after those patients were excluded. Burned out HCM was independently associated with an increased risk of death, identifying a subset of patients who may benefit from more aggressive therapies.

ICD Therapy for Primary Prevention in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common and heterogeneous disorder that increases an individual's risk of sudden cardiac death (SCD). This review article discusses the relevant factors that are involved in the challenge of preventing SCD in patients with HCM. The epidemiology of SCD in patients is reviewed as well as the structural and genetic basis behind ventricular arrhythmias in HCM. The primary prevention of SCD with implantable cardioverter-defibrillator (ICD) therapy is the cornerstone of modern treatment for individuals at high risk of SCD. The focus here is on the current and emerging predictors of SCD as well as risk stratification recommendations from both North American and European guidelines. Issues related to ICD implantation, such as programming, complications and inappropriate therapies, are discussed. The emerging role of the fully subcutaneous ICD and the data regarding its implantation are reviewed.

Phenotype and prognostic correlations of the converter region mutations affecting the β myosin heavy chain

Objectives

The prognostic value of genetic studies in cardiomyopathies is still controversial. Our objective was to evaluate the outcome of patients with cardiomyopathy with mutations in the converter domain of β myosin heavy chain (MYH7).

Methods

Clinical characteristics and survival of 117 affected members with mutations in the converter domain of MYH7 were compared with 409 patients described in the literature with mutations in the same region.

Results

Twenty-five mutations were evaluated (9 in our families including 3 novel (Ile730Asn, Asp717Gly and Arg719Pro)). Clinical diagnoses were hypertrophic (n=407), dilated (n=15), non-compaction (n=4) and restrictive (n=5) cardiomyopathies, unspecified cardiomyopathy (n=11), sudden death (n=50) and 35 healthy carriers. One hundred eighty-four had events (cardiovascular death or transplant). Median event-free survival was 50±2 years in our patients and 53±3 years in the literature (p=0.27). There were significant differences in the outcome between mutation: Ile736Thr had fewer events than other mutations in the region (p=0.01), while Arg719Gln (p<0.01) had reduced event-free survival.

Conclusions

Mutations in the converter region are generally associated with adverse prognosis although there are differences between mutations. The identification of a mutation in this particular region provides important prognostic information that should be considered in the clinical management of affected patients.

Genetic biomarkers in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a common inherited heart muscle disorder associated with sudden cardiac death, arrhythmias and heart failure. Genetic mutations can be identified in approximately 60% of patients; these are commonest in genes that encode proteins of the cardiac sarcomere. Similar to other Mendelian diseases these mutations are characterized by incomplete penetrance and variable clinical expression. Our knowledge of this genetic diversity is rapidly evolving as high-throughput DNA sequencing technology is now used to characterize an individual patient's disease. In addition, the genomic basis of several multisystem diseases associated with a hypertrophic cardiomyopathy phenotype has been elucidated. Genetic biomarkers can be helpful in making an accurate diagnosis and in identifying relatives at risk of developing the condition. In the clinical setting, genetic testing and genetic screening should be used pragmatically with appropriate counseling. Here we review the current role of genetic biomarkers in hypertrophic cardiomyopathy, highlight recent progress in the field and discuss future challenges.

Evolving molecular diagnostics for familial cardiomyopathies: at the heart of it all

Cardiomyopathies are an important and heterogeneous group of common cardiac diseases. An increasing number of cardiomyopathies are now recognized to have familial forms, which result from single-gene mutations that render a Mendelian inheritance pattern, including hypertrophic cardiomyopathy, dilated cardiomyopathy, restrictive cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy and left ventricular noncompaction cardiomyopathy. Recently, clinical genetic tests for familial cardiomyopathies have become available for clinicians evaluating and treating patients with these diseases, making it necessary to understand the current progress and challenges in cardiomyopathy genetics and diagnostics. In this review, we summarize the genetic basis of selected cardiomyopathies, describe the clinical utility of genetic testing for cardiomyopathies and outline the current challenges and emerging developments.

Diagnostic, prognostic, and therapeutic implications of genetic testing for hypertrophic cardiomyopathy

Over the last 2 decades, the pathogenic basis for the most common heritable cardiovascular disease, hypertrophic cardiomyopathy (HCM), has been investigated extensively. Affecting approximately 1 in 500 individuals, HCM is the most common cause of sudden death in young athletes. In recent years, genomic medicine has been moving from the bench to the bedside throughout all medical disciplines including cardiology. Now, genomic medicine has entered clinical practice as it pertains to the evaluation and management of patients with HCM. The continuous research and discoveries of new HCM susceptibility genes, the growing amount of data from genotype-phenotype correlation studies, and the introduction of commercially available genetic tests for HCM make it essential that the modern-day cardiologist understand the diagnostic, prognostic, and therapeutic implications of HCM genetic testing.

Mendelian-inherited heart disease: a gateway to understanding mechanisms in heart disease Update on work done at the University of Stellenbosch

The presence of founder effects in South Africa for many single-gene diseases, which include heart diseases such as progressive familial heart block types I and II, hypertrophic cardiomyopathy and the long QT syndromes, afforded us the opportunity to identify causal genes and associated mutations through genetic mapping and positional cloning. From finding the genes, the emphasis has shifted to elucidating how primary defects cause disease and recognising factors that could explain the often pronounced phenotypic variability seen in persons carrying the same inherited defect. In some of these diseases, sudden unexpected death has been a frequent occurrence in young, apparently healthy individuals who had not been aware that they had inherited an underlying risk. Herein, we review progress in identifying genes, mutations and risk factors associated with the diseases mentioned.

Molecular genetics of sudden cardiac death

Sudden cardiac death (SCD) is one of the most common causes of death. An important number of sudden deaths, especially in the young, are due to genetic heart disorders, both with structural and arrhythmogenic abnormalities. In recent years, significant advances have been made in understanding the genetic basis of SCD. Identification of the genetic causes of sudden death is important because close relatives are also at potential risk of having a fatal cardiac condition. A comprehensive post-mortem investigation is vital to determine the cause and manner of death and provides the opportunity to assess the potential risk to the family after appropriate genetic counselling. In this paper, we present an update of the different genetic causes of sudden death, emphasizing their importance for the forensic pathologist due to his relevant role in the diagnosis and prevention of SCD.

Troponin T and beta-myosin mutations have distinct cardiac functional effects in hypertrophic cardiomyopathy patients without hypertrophy

AIMS

The validity of genotype:phenotype correlation studies in human hypertrophic cardiomyopathy (HCM) has recently been questioned, yet animal models and in vitro studies suggest distinct effects for different mutations. The aims of this study were to investigate whether distinct HCM-mutations have different consequences for cardiac structure and function in the absence of the confounding effects of hypertrophy.

METHODS AND RESULTS

Individuals aged 20-65 belonging to 21 R92W(TNNT2), R403W(MYH7), or A797T(MYH7) mutation-bearing families were investigated with 2D, M-mode, and Doppler echocardiography. Cardiac structural and functional parameters were compared between prehypertrophic mutation-carriers and their non-carrier family members, with concomitant adjustment for appropriate covariates. Findings were evaluated against existing animal and in vitro functional data. The distinct functional effect of the R92W(TNNT) mutation was a relative increase in systolic functional parameters, that of the A797T(MYH7) mutation was reduced diastolic function, while the R403W(MYH7) mutation reduced both systolic and diastolic function. The observed early effects of the R92W(TNNT2) mutation mechanistically fit with prolonged force-transients precipitated by increased Ca(2+) sensitivity of the thin filament, and that of the MYH7 mutations with local ATP depletion.

CONCLUSION

Evaluation of the impact of the mutations on cardiac structure and function in prehypertrophic mutation-carriers, relative to the baseline norm provided by their non-carrier family members, best recapitulated existing animal and in vitro functional data, while inclusion of mutation-carriers with hypertrophy obscured such findings. The results prompt speculation that timely treatment aimed at ameliorating Ca(2+) sensitivity for R92W(TNNT2)-carriers, and energy depletion for MYH7 mutation-carriers, may offer a plausible approach for preventing progression from a preclinical into a decompensated state.

Genomics, haplotypes and cardiovascular disease

Cardiovascular disease has a complex genetic and environmental origin. Single-gene mutations have been identified for a variety of disorders, including several forms of sudden cardiac death, atrial fibrillation, hypertrophic cardiomyopathy and coronary artery disease. The recent availability of haplotype data has further enabled genomic approaches to mapping genetic variants associated with the more common polygenic forms of cardiovascular disease. Genome-wide association studies have identified single nucleotide polymorphisms associated with coronary artery disease and are being applied to a variety of clinical problems such as in-stent restenosis. The combination of high-throughput genomic tools such as high density microarrays, genomic information such as sequence and haplotype data, and the careful clinical definition of phenotypes provides the framework for realizing the goals of personalized medicine.

Genetics of hypertrophic cardiomyopathy: one, two, or more diseases?

PURPOSE OF REVIEW

Hypertrophic cardiomyopathy is the most common identifiable cause of sudden death in the young. This review details the history of hypertrophic cardiomyopathy, recent discoveries in its genetic underpinnings and important genotype-phenotype relationships described in recent studies.

RECENT FINDINGS

Since the discovery of the genetic underpinnings of hypertrophic cardiomyopathy in 1989 hundreds of mutations scattered among at least 10 sarcomeric genes confer the pathogenetic substrate for this 'disease of the sarcomere/myofilament'. More recently, the genetic spectrum of hypertrophic cardiomyopathy has expanded to encompass mutations in Z-disc-associated genes (Z-disc hypertrophic cardiomyopathy) and glycogen storage diseases mimicking hypertrophic cardiomyopathy (metabolic hypertrophic cardiomyopathy). Recent genotype-phenotype studies have discovered an important relationship between the morphology of the left ventricle, its underlying genetic substrate and the long-term outcome of this disease.

SUMMARY

Genomic medicine has entered clinical practice and the diagnostic utility of genetic testing for hypertrophic cardiomyopathy is clearly evident, but with the growing number of hypertrophic cardiomyopathy-associated genes strategic choices have to be made. With recent discoveries in genotype-phenotype relationships, especially pertaining to the echocardiographic septal shape and the underlying pathogenetic mutation, time has come to subdivide the one disease we call hypertrophic cardiomyopathy.

Genetic testing for risk stratification in hypertrophic cardiomyopathy and long QT syndrome: fact or fiction?

PURPOSE OF REVIEW

Hypertrophic cardiomyopathy, affecting 1 in 500 persons, is the most common identifiable cause of sudden cardiac death in the young, whereas congenital long QT syndrome, affecting 1 in 5000 persons, is perhaps one of the most common causes of autopsy negative sudden unexplained death. Since May 2004, genetic testing has been available as a clinical diagnostic test for both hypertrophic cardiomyopathy and long QT syndrome. It is now critical to carefully scrutinize the relationships between genotype and phenotype as they pertain to clinical practice.

RECENT FINDINGS

In 1990, the molecular underpinnings of hypertrophic cardiomyopathy were exposed with the identification of a mutation in the MYH7-encoded beta myosin heavy chain. Since then, hundreds of mutations scattered among at least 14 genes confer the pathogenetic substrate for this 'disease of the sarcomere'. In 1995, the discipline of cardiac channelopathies was born with the revelation that mutations in critical cardiac channel genes cause long QT syndrome. Today, hundreds of mutations involving several cardiac channel genes account for approximately 75% of long QT syndrome. Over the past decade, scores of genotype-phenotype correlation studies in both hypertrophic cardiomyopathy and long QT syndrome have been conducted.

SUMMARY

Genomic medicine has now entered the clinical practice as it pertains to the evaluation and management of both hypertrophic cardiomyopathy and long QT syndrome. The diagnostic utility of genetic testing for both diseases is clearly evident, as well as current limitations. While treatment decisions are certainly influenced by knowing the underlying genotype in long QT syndrome, there seems to be negligible prognostic value associated with particular hypertrophic cardiomyopathy-causing mutations at this time.