No variants in the cardiac actin gene in Finnish patients with dilated or hypertrophic cardiomyopathy

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.

Characterization of familial and sporadic arrhythmogenic right ventricular cardiomyopathy in Finland

BACKGROUND

Autosomal dominant inheritance is reported in arrhythmogenic right ventricular cardiomyopathy (ARVC) but the prevalence of the familial and sporadic forms in the general population is unknown.

AIM

To evaluate the familial occurrence and clinical features of ARVC in the genetically homogenous Finnish population.

METHODS

The study included 29 Finnish ARVC index patients and 135 relatives from 21 families evaluated. They underwent echocardiography, 24-hour electrocardiographic monitoring, signal-averaged electrocardiography, and exercise stress test.

RESULTS

Twenty-two index patients had ventricular arrhythmias as first manifestation, and three developed arrhythmias later. The right ventricle (RV) was mildly affected in 22 and strongly dilated in 7 index patients. Patients with dilated RV manifested first symptoms at younger age (mean 28 years) than those without RV dilatation (mean 38 years). Of the 135 relatives, ARVC was present in 12 (9%) patients belonging to 5 of the 21 families studied, resulting in 24% familial involvement. In addition, 46 relatives (34%) had subtle cardiac abnormalities, suggesting subclinical presentation.

CONCLUSIONS

The ARVC in Finland presents with distinct arrhythmic and RV dilative subtypes. The sporadic disease is similar to the familial one which may reflect low penetration in relatives. The proportion of familial manifestation of ARVC in Finland seems comparable to that elsewhere in Europe.

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.

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.

Differences between human and mouse embryonic stem cells

We compared gene expression profiles of mouse and human ES cells by immunocytochemistry, RT-PCR, and membrane-based focused cDNA array analysis. Several markers that in concert could distinguish undifferentiated ES cells from their differentiated progeny were identified. These included known markers such as SSEA antigens, OCT3/4, SOX-2, REX-1 and TERT, as well as additional markers such as UTF-1, TRF1, TRF2, connexin43, and connexin45, FGFR-4, ABCG-2, and Glut-1. A set of negative markers that confirm the absence of differentiation was also developed. These include genes characteristic of trophoectoderm, markers of germ layers, and of more specialized progenitor cells. While the expression of many of the markers was similar in mouse and human cells, significant differences were found in the expression of vimentin, beta-III tubulin, alpha-fetoprotein, eomesodermin, HEB, ARNT, and FoxD3 as well as in the expression of the LIF receptor complex LIFR/IL6ST (gp130). Profound differences in cell cycle regulation, control of apoptosis, and cytokine expression were uncovered using focused microarrays. The profile of gene expression observed in H1 cells was similar to that of two other human ES cell lines tested (line I-6 and clonal line-H9.2) and to feeder-free subclones of H1, H7, and H9, indicating that the observed differences between human and mouse ES cells were species-specific rather than arising from differences in culture conditions.

A novel mutation, Arg71Thr, in the delta-sarcoglycan gene is associated with dilated cardiomyopathy

Approximately 20-35% of cases of idiopathic dilated cardiomyopathy are familial. DCM-associated mutations have been reported in 13 genes including the desmin, delta-sarcoglycan, and metavinculin genes. This study screened for variants in these genes in Finnish patients with DCM. All coding regions of the desmin and delta-sarcoglycan genes and the metavinculin-specific exon of the vinculin gene were screened in 52 DCM patients from eastern Finland by PCR-SSCP. We detected a novel mutation, Arg71Thr, in the delta-sarcoglycan gene in two members of a small DCM family. One of the mutation carriers fulfills diagnostic criteria for DCM and is also symptomatic. The other mutation carrier has slightly dilated left ventricle and well preserved systolic function. Therefore carriers of the Arg71Thr mutation had a relatively mild phenotype and a late onset of the disease. Disease-associated mutations were not found in the desmin gene or the metavinculin-specific exon of the vinculin gene. We conclude that the desmin and delta-sarcoglycan genes are not predominant disease-causing genes in patients with DCM in eastern Finland.