The cardiac troponin I gene is not associated with hypertrophic cardiomyopathy in patients from eastern Finland

Current perspectives in hypertrophic cardiomyopathy with the focus on patients in the Finnish population: a review

Hypertrophic cardiomyopathy (HCM) is the most common inherited heart disease, with the prevalence of about 1/500. During the last two decades, the knowledge of the etiology, pathogenesis, risk stratification and prevention of sudden death in HCM has substantially advanced. Most often, HCM is familial and caused by mutations in sarcomere genes, inherited in an autosomal dominant manner. In Finland, genetic background of HCM is unique, with a few founder mutations in cardiac sarcomere genes accounting for a considerable proportion of the disease. Pathogenic mechanisms induced by disease-causing mutations are still poorly understood, although alterations in intracellular calcium handling and inefficient generation of contractile force in myocytes are considered key features in triggering the hypertrophic response. Clinical features of the disease are highly variable from no symptoms to the spectrum of exertional dyspnea, angina, palpitations, syncope and sudden death. In the current patient care, implantable cardioverter defibrillators (ICDs) are successfully used to prevent sudden cardiac death in high risk subjects. Targeted genetic testing is recommended to confirm the diagnosis in patients with HCM and to identify family members with the disease. Future research is needed to elucidate key cellular mechanisms leading to HCM, which may allow specific prevention and treatment of the disease. Key messages Hypertrophic cardiomyopathy, most often caused by defects in sarcomere genes, is the most common inherited heart disease, and a common cause of sudden cardiac death (SCD) in athletes and young subjects. Cardiac imaging, ECG and genetic testing are pivotal in the diagnosis of the disease in patients and first-degree relatives. Implantable cardioverter defibrillators in patients with high risk for SCD and tailored pharmacotherapy are efficient tools in patient care, but so far, exact mechanisms leading to cardiac hypertrophy in HCM are only partially understood, and there is no curative treatment for the disease.

A new common mutation in the cardiac beta-myosin heavy chain gene in Finnish patients with hypertrophic cardiomyopathy

BACKGROUND

In the nationwide FinHCM Study including 306 Finnish patients with hypertrophic cardiomyopathy (HCM), we have previously identified two founder mutations in the alpha-tropomyosin (TPM1-D175N) and myosin-binding protein C (MYBPC3-Q1061X) genes, accounting for 18% of all cases. Objective. To screen additional mutations, previously identified in eastern Finnish cohorts with HCM, in the FinHCM Study population.

PATIENTS AND METHODS

Ten mutations in the beta-myosin heavy chain gene (MYH7), TPM1, and MYBPC3 were screened.

RESULTS

MYH7-R1053Q was found in 17 of 306 patients (5.6%). No carriers of MYH7-R719W or N696S were found. A novel TPM1-D175G mutation was found in a single patient. MYBPC3 mutations were found in 14 patients: IVS5-2A-C in two, IVS14-13G-A in two, K811del in six, and A851insT in four patients. Altogether, a HCM-causing mutation was identified in 32 patients, accounting for 10.5% of all cases. In addition, two MYBPC3 variants R326Q and V896M with uncertain pathogenicity were found in eight and in 10 patients, respectively.

CONCLUSION

Combining the present findings with our previous results, a causative mutation was identified in 28% of the FinHCM cohort. MYH7-R1053Q was the third most common mutation, and should be screened in all new cases of HCM in Finland.

Genetic basis of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) was the first cardiovascular disorder in which a genetic basis was identified. The disease is characterized by a marked thickening of the left ventricle and is the most common structural cause of sudden cardiac death in those aged under 35 years. HCM is primarily a disease of the sarcomere with over 250 mutations identified currently within 13 sarcomere-related genes. At present, genetic screening is available for the genes shown to cause HCM most frequently, with a mutation pick-up rate of up to 60%. Current research is focused on the identification of additional causative genes and elucidation into signaling mechanisms involved in HCM pathogenesis, as well as investigation of modifying factors that can alter the clinical phenotype in HCM. The unifying goal of these studies is to improve our understanding of disease pathogenesis in HCM, thereby facilitating the process of new diagnostic and therapeutic approaches in patients, ultimately leading to disease prevention and possible curative treatment.

Two novel mutations in the beta-myosin heavy chain gene associated with dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is familial in approximately 20-35% of cases of idiopathic DCM. Several mutations in the different sarcomere protein genes have been reported to cause DCM.

AIMS

We wanted to investigate the role of sarcomere protein gene variants in Finnish DCM patients.

METHODS AND RESULTS

We screened all coding exons of five sarcomere protein genes (beta-myosin heavy chain, alpha-tropomyosin, troponin C, troponin I and troponin T) in a well-characterized population of 52 DCM patients in Eastern Finland by the PCR-SSCP and sequencing method. Two novel mutations, Arg1053Gln and Arg1500Trp, in the beta-myosin heavy chain gene in two index patients were detected. The proband with the Arg1053Gln mutation had a dilated left ventricle and impaired systolic function, but other family members carrying this mutation presented with septal hypertrophy. It thus seems that the Arg1053Gln mutation is primarily a HCM mutation, which can also lead to DCM. The other mutation, Arg1500Trp, was associated with a typical DCM phenotype. The Arg1500Trp mutation carrier had only one family member alive, but she did not carry the mutation and, therefore, cosegregation of the mutation and the disease in this family could not be reliably verified. No disease-causing mutations were found in the other sarcomere protein genes.

CONCLUSIONS

Two novel mutations in the beta-myosin heavy chain gene were detected in patients with DCM. Overall, mutations in the beta-myosin heavy chain gene seem to be relatively uncommon in Finnish DCM patients.

Diastolic dysfunction without left ventricular hypertrophy is an early finding in children with hypertrophic cardiomyopathy-causing mutations in the beta-myosin heavy chain, alpha-tropomyosin, and myosin-binding protein C genes

OBJECTIVES

We investigated the presence of left ventricular hypertrophy (LVH) and features of diastolic dysfunction in genotype-confirmed children from families with hypertrophic cardiomyopathy (HCM) and healthy control children.

BACKGROUND

In subjects with HCM-causing mutations, LVH usually does not evolve until adolescence. Diastolic dysfunction has not been systematically evaluated in children carrying HCM-causing mutations.

METHODS

All children (aged 1.5-16.7 years) from 14 HCM families with identified disease-causing mutations (the Arg719Trp mutation in the beta-myosin heavy chain gene [MYH7], the Asp175Asn mutation in the alpha-tropomyosin gene [TPM1], the Gln1061X mutation in the myosin-binding protein C gene [MYBPC3], and the IVS5-2A-->C mutation in the MYBPC3 gene) and 53 matched control children were examined with electrocardiography and 2- and 3-dimensional echocardiography (2DE and 3DE). Natriuretic peptides were measured in children from HCM families and 67 control children.

RESULTS

Of 53 children from HCM families, 27 (51%) had a disease-causing mutation (G+). G+ children had slightly thicker septum on 2DE compared with the control children (P = .004), but only 3 (11%) of 27 G+ children exceeded the 95th percentile values of the body surface area-adjusted maximal LV thickness of healthy children (the major echocardiographic criterion for HCM). However, prolonged isovolumetric relaxation time, increased left atrial volume on 3DE, or increased levels of NT-proANP, all features suggestive of diastolic dysfunction, were found in 14 (52%) of 27 G+ children.

CONCLUSIONS

In children with HCM-causing mutations, signs of diastolic dysfunction are found in about half of the cases, as LVH is present only in small percentage of these children.

Yield of genetic testing in hypertrophic cardiomyopathy

OBJECTIVE

To determine the clinical parameters of hypertrophic cardiomyopathy (HCM) that correlated significantly with the presence of an identifiable sarcomeric mutation.

PATIENTS AND METHODS

Previous comprehensive mutational analyses of all protein-coding exons of 8 sarcomeric genes revealed pathogenic mutations in 147 (38%) of 389 unrelated patients seen at the HCM outpatient clinic at the Mayo Clinic in Rochester, Minn, between April 1997 and December 2001. Clinical data, extracted from patient records and blinded to patient genotype, were maintained in a custom database.

RESULTS

In 389 unrelated patients, younger age at diagnosis, family history of HCM, and Increasing left ventricular wall thickness were all associated with Increased likelihood of identifying an HCM-associated sarcomeric mutation. In contrast, family history of sudden cardiac death, myectomy status, and anatomical subtype did not correlate significantly with genotype-positive status. With use of a simple scoring system based on age at diagnosis, left ventricular wall thickness, and family history of HCM, the likelihood of a sarcomeric mutation could be estimated.

CONCLUSION

Clinical predictors of positive genotype, such as the presence of an implantable cardioverter-defibrillator, age at diagnosis, degree of left ventricular wall hypertrophy, and family history of HCM, may aid in patient selection for genetic testing and increase the yield of cardiac sarcomere gene screening.

Prevalence and spectrum of thin filament mutations in an outpatient referral population with hypertrophic cardiomyopathy

BACKGROUND

Thin filament mutations are reported to cause approximately 20% of cases of hypertrophic cardiomyopathy (HCM), and they have been associated with specific phenotypes. However, the frequency of these mutations and their associated phenotype(s) from a large tertiary referral center population are unknown.

METHODS AND RESULTS

DNA was obtained from 389 unrelated patients with HCM. A mutational analysis of all protein coding exons of cardiac troponin T, cardiac troponin I, alpha-tropomyosin, and cardiac actin was performed using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing. The clinical data were extracted from patient records and maintained independent of the patient genotype. Overall, only 18 patients (4.6%) harbored isolated thin filament mutations: 8 had troponin T mutations, 6 had troponin I mutations, 3 had alpha-tropomyosin mutations, and 1 had an actin mutation. Of the 12 unique missense mutations identified, 9 (75%) were novel mutations. As a group, patients with thin filament mutations were not significantly different from the rest of the cohort in age at diagnosis, left ventricular wall thickness, left ventricular outflow tract obstruction, or family history of HCM or sudden cardiac death.

CONCLUSIONS

Mutations in genes encoding thin filament proteins are less prevalent in HCM than previously estimated. Patients with mutations in troponin T, troponin I, alpha-tropomyosin, and actin do not invariably present with any distinct clinical feature, thus limiting the utility of gene status for risk stratification or of clinical phenotype in guiding individual genetic screening at this time.