A new locus for autosomal dominant dilated cardiomyopathy identified on chromosome 6q12-q16

Cocaine Exposure Increases Blood Pressure and Aortic Stiffness via the miR-30c-5p-Malic Enzyme 1-Reactive Oxygen Species Pathway

Cocaine abuse increases the risk of cardiovascular mortality and morbidity; however, the underlying molecular mechanisms remain elusive. By using a mouse model for cocaine abuse/use, we found that repeated cocaine injection led to increased blood pressure and aortic stiffness in mice associated with elevated levels of reactive oxygen species (ROS) in the aortas, a phenomenon similar to that observed in hypertensive humans. This ROS elevation was correlated with downregulation of Me1 (malic enzyme 1), an important redox molecule that counteracts ROS generation, and upregulation of microRNA (miR)-30c-5p that targets Me1 expression by directly binding to its 3'UTR (untranslated region). Remarkably, lentivirus-mediated overexpression of miR-30c-5p in aortic smooth muscle cells recapitulated the effect of cocaine on Me1 suppression, which in turn led to ROS elevation. Moreover, in vivo silencing of miR-30c-5p in smooth muscle cells resulted in Me1 upregulation, ROS reduction, and significantly suppressed cocaine-induced increases in blood pressure and aortic stiffness-a similar effect to that produced by treatment with the antioxidant N-acetyl cysteine. Discovery of this novel cocaine-↑miR-30c-5p-↓Me1-↑ROS pathway provides a potential new therapeutic avenue for treatment of cocaine abuse-related cardiovascular disease.

Hearing Profile in Patients with Dilated and Hypertrophic Cardiomyopathies

INTRODUCTION

Cardiomyopathy may cause disruptions in the micro-vascular system of the stria vascularis in the cochlea, and, subsequently, may result in cochlear degeneration. Degeneration in the stria vascularis affects the physical and chemical processes in the organ of Corti, thereby causing a possible hearing impairment. The objective of this study was to assess the hearing profiles of patients with dilated and hypertrophic cardiomyopathies to determine the relationship between the degree of hearing loss and the degree and duration of the disease and to compare the dilated and hypertrophic cardiomyopathies as regards hearing profile.

METHODS

In this case control study, we studied 21 patients (cases/study group/group 1) and 15 healthy individuals (controls/group 2). Six patients (group 1a) had hypertrophic cardiomyopathy (HCM), and 15 patients (group 1b) had dilated cardiomyopathy (DCM). The data were analyzed using the t-test, chi-squared test, Kruskal-Wallis test, and the Multiple Mann-Whitney test.

RESULTS

The results of this study showed that 80% of those patients with DCM (group 1b) had bilateral sensorineural hearing loss (SNHL), and 100% of the patients with HCM (group 1a) had mild to severe bilateral sloping SNHL. Distortion Product Otoacoustic Emissions (DPOAEs) were present in 14% of the study group and in 100 % of the control group. The results of the measurements of auditory brainstem response (ABR) showed that 50% of the study group had abnormal latencies compared to the control group, and there was no correlation between the duration of the disease and the degree of hearing loss or DPOAE. Fifty percent of the patients with HCM and 35% of the patients with DCM had positive family histories of similar conditions, and 35% of those with HCM had a positive family history of sudden death.

CONCLUSION

The results of this study suggested that the link between heart disease and hearing loss and early identification of hearing loss in patients with cardiomyopathy may reduce morbidity since hearing deficits sometimes precede heart disease.

Genetic Counseling and Screening Issues in Familial Dilated Cardiomyopathy

Idiopathic dilated cardiomyopathy (IDC), a treatable condition characterized by left ventricular dilatation and systolic dysfunction of unknown cause, has only recently been recognized to have genetic etiologies. Although familial dilated cardiomyopathy (FDC) was thought to be infrequent, it is now believed that 30-50% of cases of IDC may be familial. Echocardiographic and electrocardiographic (ECG) screening of first-degree relatives of individuals with IDC and FDC is indicated because detection and treatment are possible prior to the onset of advanced, symptomatic disease. However, such screening often creates uncertainty and anxiety surrounding the significance of the results. Furthermore, FDC demonstrates incomplete penetrance, variable expression, and significant locus and allelic heterogeneity, making genetic counseling complex. The provision of genetic counseling for IDC and FDC will require collaboration between cardiologists and genetics professionals, and may also improve the recognition of FDC, the availability of support services, and overall outcomes for patients and families.

Mendelian forms of structural cardiovascular disease

Clinical and molecular genetics are inextricably linked. In the last two decades genetic studies have revealed the causes of several forms of structural heart disease. Recent work is extending the insights from inherited arrhythmias and cardiomyopathies to other forms of heart disease. In this review we outline the current state of the art for the genetics of adult structural heart disease, in particular the cardiomyopathies, valvular heart disease and aortic disease. The general approaches are described with a focus on clinical relevance, while potential areas for imminent innovation in diagnosis and therapeutics are highlighted.

Dilated cardiomyopathy: the complexity of a diverse genetic architecture

Remarkable progress has been made in understanding the genetic basis of dilated cardiomyopathy (DCM). Rare variants in >30 genes, some also involved in other cardiomyopathies, muscular dystrophy, or syndromic disease, perturb a diverse set of important myocardial proteins to produce a final DCM phenotype. Large, publicly available datasets have provided the opportunity to evaluate previously identified DCM-causing mutations, and to examine the population frequency of sequence variants similar to those that have been observed to cause DCM. The frequency of these variants, whether associated with dilated or hypertrophic cardiomyopathy, is greater than estimates of disease prevalence. This mismatch might be explained by one or more of the following possibilities: that the penetrance of DCM-causing mutations is lower than previously thought, that some variants are noncausal, that DCM prevalence is higher than previously estimated, or that other more-complex genomics underlie DCM. Reassessment of our assumptions about the complexity of the genomic and phenomic architecture of DCM is warranted. Much about the genomic basis of DCM remains to be investigated, which will require comprehensive genomic studies in much larger cohorts of rigorously phenotyped probands and family members than previously examined.

Cardiac structural and sarcomere genes associated with cardiomyopathy exhibit marked intolerance of genetic variation

BACKGROUND

The clinical significance of variants in genes associated with inherited cardiomyopathies can be difficult to determine because of uncertainty regarding population genetic variation and a surprising amount of tolerance of the genome even to loss-of-function variants. We hypothesized that genes associated with cardiomyopathy might be particularly resistant to the accumulation of genetic variation.

METHODS AND RESULTS

We analyzed the rates of single nucleotide genetic variation in all known genes from the exomes of >5000 individuals from the National Heart, Lung, and Blood Institute's Exome Sequencing Project, as well as the rates of structural variation from the Database of Genomic Variants. Most variants were rare, with over half unique to 1 individual. Cardiomyopathy-associated genes exhibited a rate of nonsense variants, about 96.1% lower than other Mendelian disease genes. We tested the ability of in silico algorithms to distinguish between a set of variants in MYBPC3, MYH7, and TNNT2 with strong evidence for pathogenicity and variants from the Exome Sequencing Project data. Algorithms based on conservation at the nucleotide level (genomic evolutionary rate profiling, PhastCons) did not perform as well as amino acid-level prediction algorithms (Polyphen-2, SIFT). Variants with strong evidence for disease causality were found in the Exome Sequencing Project data at prevalence higher than expected.

CONCLUSIONS

Genes associated with cardiomyopathy carry very low rates of population variation. The existence in population data of variants with strong evidence for pathogenicity suggests that even for Mendelian disease genetics, a probabilistic weighting of multiple variants may be preferred over the single gene causality model.

Clinical and genetic issues in dilated cardiomyopathy: a review for genetics professionals

Dilated cardiomyopathy (DCM), usually diagnosed as idiopathic dilated cardiomyopathy (IDC), has been shown to have a familial basis in 20-35% of cases. Genetic studies in familial dilated cardiomyopathy (FDC) have shown dramatic locus heterogeneity with mutations identified in >30 mostly autosomal genes showing primarily dominant transmission. Most mutations are private missense, nonsense or short insertion/deletions. Marked allelic heterogeneity is the rule. Although to date most DCM genetics fits into a Mendelian rare variant disease paradigm, this paradigm may be incomplete with only 30-35% of FDC genetic cause identified. Despite this incomplete knowledge, we predict that DCM genetics will become increasingly relevant for genetics and cardiovascular professionals. This is because DCM causes heart failure, a national epidemic, with considerable morbidity and mortality. The fact that early, even pre-symptomatic intervention can prevent or ameliorate DCM, coupled with more cost-effective genetic testing, will drive further progress in the field. Ongoing questions include: whether sporadic (IDC) disease has a genetic basis, and if so, how it differs from familial disease; which gene-specific or genetic pathways are most relevant; and whether other genetic mechanisms (e.g., DNA structural variants, epigenetics, mitochondrial mutations and others) are operative in DCM. We suggest that such new knowledge will lead to novel approaches to the prevention and treatment of DCM.

Monogenic atrial fibrillation as pathophysiological paradigms

Atrial fibrillation (AF) is the most common cardiac rhythm abnormality and represents a major burden, both to patients and to health-care systems. In recent years, increasing evidence from population-based studies has demonstrated that AF is a heritable condition. Although familial forms of AF have been recognized for many years, they represent a rare subtype of the arrhythmia. However, despite their limited prevalence, the identification of mutations in monogenic AF kindreds has provided valuable insights into the molecular pathways underlying the arrhythmia and a framework for investigating AF encountered in the general population. In contrast to these rare families, the typical forms of AF occurring in the community are likely to be multigenic and have significant environmental influences. Recently, genome-wide association studies have uncovered common sequence variants that confer increased susceptibility to the arrhythmia. In the future, the elucidation of the genetic substrate underlying both familial and more typical forms of AF will hopefully lead to the development of novel diagnostic tools as well as more targeted rhythm control strategies. In this article, we will focus on monogenic forms of AF and also provide an overview of case-control association studies for AF.

Genetic association study identifies HSPB7 as a risk gene for idiopathic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a structural heart disease with strong genetic background. Monogenic forms of DCM are observed in families with mutations located mostly in genes encoding structural and sarcomeric proteins. However, strong evidence suggests that genetic factors also affect the susceptibility to idiopathic DCM. To identify risk alleles for non-familial forms of DCM, we carried out a case-control association study, genotyping 664 DCM cases and 1,874 population-based healthy controls from Germany using a 50K human cardiovascular disease bead chip covering more than 2,000 genes pre-selected for cardiovascular relevance. After quality control, 30,920 single nucleotide polymorphisms (SNP) were tested for association with the disease by logistic regression adjusted for gender, and results were genomic-control corrected. The analysis revealed a significant association between a SNP in HSPB7 gene (rs1739843, minor allele frequency 39%) and idiopathic DCM (p = 1.06 × 10⁻⁶, OR  = 0.67 [95% CI 0.57-0.79] for the minor allele T). Three more SNPs showed p < 2.21 × 10⁻⁵. De novo genotyping of these four SNPs was done in three independent case-control studies of idiopathic DCM. Association between SNP rs1739843 and DCM was significant in all replication samples: Germany (n =564, n = 981 controls, p = 2.07 × 10⁻³, OR = 0.79 [95% CI 0.67-0.92]), France 1 (n = 433 cases, n = 395 controls, p =3.73 × 10⁻³, OR  = 0.74 [95% CI 0.60-0.91]), and France 2 (n = 249 cases, n = 380 controls, p = 2.26 × 10⁻⁴, OR  = 0.63 [95% CI 0.50-0.81]). The combined analysis of all four studies including a total of n = 1,910 cases and n = 3,630 controls showed highly significant evidence for association between rs1739843 and idiopathic DCM (p = 5.28 × 10⁻¹³, OR= 0.72 [95% CI 0.65-0.78]). None of the other three SNPs showed significant results in the replication stage.This finding of the HSPB7 gene from a genetic search for idiopathic DCM using a large SNP panel underscores the influence of common polymorphisms on DCM susceptibility.

Genetics of dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a myocardial disorder defined by ventricular chamber enlargement and systolic dysfunction. DCM can result in progressive heart failure, arrhythmias, thromboembolism, and premature death, and contributes significantly to health care costs. In many cases, DCM results from acquired factors that affect cardiomyocyte function or survival. Inherited genetic variants are also now recognized to have an important role in the etiology of DCM. Despite substantial progress over the past decade, our understanding of familial DCM remains incomplete. Current concepts of the molecular pathogenesis, clinical presentation, natural history, and management of familial DCM are outlined in this review.

An N-ethyl-N-nitrosourea mutagenesis recessive screen identifies two candidate regions for murine cardiomyopathy that map to chromosomes 1 and 15

N-ethyl-N-nitrosourea (ENU) mutagenesis screens have been successful for identifying genes that affect important biological processes and diseases. However, for heart-related phenotypes, these screens have been employed exclusively for developmental phenotypes, and to date no adult cardiomyopathy-causing genes have been discovered through a mutagenesis screen. To identify novel disease-causing and disease-modifying genes for cardiomyopathy, we performed an ENU recessive mutagenesis screen in adult mice. Using noninvasive echocardiography to screen for abnormalities in cardiac function, we identified a heritable cardiomyopathic phenotype in two families. To identify the chromosomal regions where the mutations are localized, we used a single nucleotide polymorphism (SNP) panel for genetic mapping of mouse mutations. This panel provided whole-genome linkage information and identified the mutagenized candidate regions at the proximal end of chromosome 1 (family EN1), and at the distal end of chromosome 15 (family EN25). We have identified 94 affected mice in family EN1 and have narrowed the candidate interval to 1 Mb. We have identified 20 affected mice in family EN25 and have narrowed the candidate interval to 12 Mb. The identification of the genes responsible for the observed phenotype in these families will be strong candidates for disease-causing or disease-modifying genes in patients with heart failure.

Prediction of human disease genes by human-mouse conserved coexpression analysis

BACKGROUND

Even in the post-genomic era, the identification of candidate genes within loci associated with human genetic diseases is a very demanding task, because the critical region may typically contain hundreds of positional candidates. Since genes implicated in similar phenotypes tend to share very similar expression profiles, high throughput gene expression data may represent a very important resource to identify the best candidates for sequencing. However, so far, gene coexpression has not been used very successfully to prioritize positional candidates.

METHODOLOGY/PRINCIPAL FINDINGS

We show that it is possible to reliably identify disease-relevant relationships among genes from massive microarray datasets by concentrating only on genes sharing similar expression profiles in both human and mouse. Moreover, we show systematically that the integration of human-mouse conserved coexpression with a phenotype similarity map allows the efficient identification of disease genes in large genomic regions. Finally, using this approach on 850 OMIM loci characterized by an unknown molecular basis, we propose high-probability candidates for 81 genetic diseases.

CONCLUSION

Our results demonstrate that conserved coexpression, even at the human-mouse phylogenetic distance, represents a very strong criterion to predict disease-relevant relationships among human genes.

Genetics of dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a myocardial disease characterized by dilatation and impaired systolic function of the left or both ventricles. The etiology of DCM is multifactorial, and many different clinical conditions can lead to the phenotype of DCM. During recent years it has become evident that genetic factors play an important role in the etiology and pathogenesis of idiopathic DCM. The genetics of DCM have been under intensive investigation lately, and thereby the knowledge on the genetic basis of DCM has increased rapidly. The genetic background of the disease seems to be relatively heterogeneous, and the disease-associated mutations concern mostly single families and only few affected patients. Disease-associated mutations have been detected e.g. in genes encoding sarcomere, cytoskeletal, and nuclear proteins, as well as proteins involved with regulation of Ca(2+) metabolism. The mechanisms, by which mutations eventually result in clinical heart failure, are complex and not yet totally resolved. DCM causes considerable morbidity and mortality. Better knowledge of the genetic background and disease-causing mechanisms would probably help us in focusing early treatment on right subjects and potentially also developing new treatment modalities and improving cardiac outcome in the affected patients. This review deals with DCM of genetic origin.

In vivo and in vitro examination of the functional significances of novel lamin gene mutations in heart failure patients

CONTEXT

Lamin A/C (LMNA) gene variations have been reported in more than one third of genotyped families with dilated cardiomyopathy (DCM). However, the relationship between LMNA mutation and the development of DCM is poorly understood.

METHODS AND RESULTS

We found that end stage DCM patients carrying LMNA mutations displayed either dramatic ultrastructural changes of the cardiomyocyte nucleus (D192G) or nonspecific changes (R541S). Overexpression of the D192G lamin C dramatically increased the size of intranuclear speckles and reduced their number. This phenotype was only partially reversed by coexpression of the D192G and wild type lamin C. Moreover, the D192G mutation precludes insertion of lamin C into the nuclear envelope when co-transfected with the D192G lamin A. By contrast, the R541S phenotype was entirely reversed by coexpression of the R541S and wild type lamin C. As lamin speckle size is known to be correlated with regulation of transcription, we assessed the SUMO1 distribution pattern in the presence of mutated lamin C and showed that D192G lamin C expression totally disrupts the SUMO1 pattern.

CONCLUSION

Our in vivo and in vitro results question the relationship of causality between LMNA mutations and the development of heart failure in some DCM patients and therefore, the reliability of genetic counselling. However, LMNA mutations producing speckles result not only in nuclear envelope structural damage, but may also lead to the dysregulation of cellular functions controlled by sumoylation, such as transcription, chromosome organisation, and nuclear trafficking.

[Genetics of atrial fibrillation: rare mutations, common variants and clinical relevance?]

Atrial fibrillation (AF) is considered the, by far, the most common arrhythmia of man, affecting millions of patients worldwide. The high socio-economic relevance is due to several severe complications and therefore requires profound scientific research in the field of etiology and treatment options. Atrial fibrillation typically occurs in the older patient who often suffers from a number of underlying diseases that act as predisposing factors. That genetics contribute strongly to this rhythm disorder is therefore not evident at a first glance. However, there are a number of investigations that prove familial accumulation for lone AF. Furthermore it is remarkable that many older patients suddenly develop atrial fibrillation without underlying disease, while others remain in sinus rhythm although suffering from a series of risk factors. Considering all this, genetic interference becomes most probable. Therefore in the recent past remarkable endeavours have been ventured to clarify the genetic basis of both lone AF and AF in the context of underlying diseases. For the former, until now four different genetic loci and three disease genes have been identified as causative. Concerning AF in the general population, mainly studies turning the spotlight on single-nucleotide polymorphisms (SNPs) have been applied. It is assumed that SNPs in disease-causing genes are distributed differentially among healthy and diseased individuals. These differences in frequency have been investigated with case-control studies. Up to now six different genes have been found to be associated with AF, including the genes for angiotensin-converting enzyme, angiotensinogen and several cardiac ion channels. Promising new technologies, especially high-throughput SNP genotyping and the genome wide scan for new candidate genes using chip arrays capable of genotyping up to 500 000 SNPs at a time, will multiply the speed to achieve new results. With that the possibility, approaches to optimize existing therapies and to open up new pathways to treat AF.

Festschrift for Dr. John M. Opitz: Pathogenesis of cardiac conduction disorders in children genetic and histopathologic aspects

Fetal dysrhythmias are usually transient. Abnormal fetal rates and rhythms during labor are "functional." Fetal dysrhythmias may be associated with congenital heart disease and fetal hydrops. Bradycardia is usually related to fetal distress; supraventricular tachycardia, atrial flutter, and atrial fibrillation may be associated with severe congestive heart failure. Ventricular fibrillation is rare in the fetus and infant and is usually associated with myocardial necrosis with perimembranous septal defect; the nonbranching atrioventricular (AV) bundle may have an aberrant position and result in cardiac arrhythmia. Wolff-Parkinson-White syndrome with conduction abnormalities and left ventricular hypertrophy (LVH) is due to an accessory pathway that bypasses the AV sulcus and results in faster conduction. Carnitine deficiency may be primary or secondary and may result in cardiac arrhythmia. Histiocytoid cardiomyopathy is characterized by cardiomegaly, incessant ventricular tachycardia, and frequently sudden death. Arrhythmogenic right ventricular dysplasia (ARVD) results in ventricular tachycardia and left bundle branch block. Noncompaction of the left ventricle predisposes to potentially fatal arrhythmias. Long Q-T syndromes (LQTS) are a heterogeneous group of disorders with many genetic mutations. Brugada syndrome is an autosomal dominant trait with right bundle branch block and ST elevation. Barth syndrome is an X-linked disorder with dilated cardiomyopathy, cyclic neutropenia and skeletal myopathy. Hypertrophic cardiomyopathy in infancy may be related to metabolic diseases, particularly glycogen storage diseases; the familial form predisposes to sudden death. Arrhythmias following cardiac surgery may occur after closure of a ventricular septal defect (VSD) or damage to the conduction system.

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.

A novel locus for autosomal-dominant dilated cardiomyopathy maps to chromosome 7q22.3-31.1

Inherited dilated cardiomyopathy (DCM) is a genetically and phenotypically very heterogeneous disease. DCM is caused by mutations in multiple genes encoding proteins that are involved in force generation, force transmission, energy production and several signalling pathways. Thus, the pathophysiology of heart failure is complex and not yet fully understood. Familial forms of DCM let the way to identify new key proteins by positional cloning and to study respective pathomechanisms that are critical for normal cardiac function, but may not have been correlated with heart disease before. Here we report a three-generation pedigree including 16 individuals affected by dilated cardiomyopathy without additional phenotypes. The pedigree is consistent with autosomal-dominant inheritance and age-related penetrance. A genome-wide linkage analysis excluded linkage to all known DCM genes and loci, whereas several close markers on chromosome 7q22.3-31.1 segregated with the disease (maximum logarithm of odds score, 4.20 at D7S471 and D7S501). The disease causing mutation lies in a 9.73 Mb interval between markers D7S2545 and D7S2554 that contains no known cytoskeletal genes. Coding exons of the candidate genes LAMB1, LAMB4 and PIK3CG were screened but no mutations were identified.

Mutational analysis of the beta- and delta-sarcoglycan genes in a large number of patients with familial and sporadic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is defined by ventricular dilatation associated with impaired contractile function. Approximately one-third of idiopathic dilated cardiomyopathy cases are due to inherited gene mutations. Mutations in the beta- and delta-sarcoglycan genes have been described in limb girdle muscular dystrophy and/or isolated DCM. In this study, the aim was to investigate the prevalence of these genes in isolated DCM. We screened these two genes for mutations in 99 unrelated patients with sporadic or familial DCM. The coding exon and intron-exon boundaries of each gene were amplified by polymerase chain reaction. Mutation analyses were performed by single-strand conformation polymorphism for the beta-sarcoglycan gene and by direct sequencing for the delta-sarcoglycan gene. New polymorphisms, as well as already described ones, were found in these two genes, but none appeared to be responsible for dilated cardiomyopathy. We, therefore, conclude that these genes are not responsible for idiopathic isolated dilated cardiomyopathy in our population. Furthermore, based on previously published and present data, we could estimate the prevalence of delta-sarcoglycan gene mutations to be less than 1% in idiopathic dilated cardiomyopathy, demonstrating that this gene is only marginally implicated in the disease.

Locus for atrial fibrillation maps to chromosome 6q14-16

BACKGROUND

Atrial fibrillation (AF), the most common clinical arrhythmia, is a major cause of morbidity and mortality. Although AF is often associated with other cardiovascular conditions, many patients present without an obvious etiology. Inherited forms of AF exist, but the causative gene has been defined only in a single family. We have identified a large family (family FAF-1) in which AF segregates as a Mendelian trait.

METHODS AND RESULTS

Thirty-four family members were evaluated by 12-lead ECG, echocardiogram, 24-hour Holter monitoring, and laboratory studies. Individuals with electrocardiographically documented AF were defined as affected. Subjects were considered unaffected if they were >60 years of age, had no personal history of AF, and had no offspring with a history of AF. DNA was extracted and genotypic analyses were performed using polymorphic microsatellite markers. Evidence of linkage was obtained on chromosome 6, with a peak 2-point logarithm of the odds (LOD) score of 3.63 (theta=0) at the marker D6S1021. A maximal multipoint LOD score of 4.9 was obtained between D6S286 and D6S1021, indicating odds of approximately 100 000:1 in favor of this interval as the location of the gene defect responsible for AF in this family. The LOD scores were robust to changes in penetrance and allele frequency. Haplotype analyses further supported this minimal genetic interval.

CONCLUSIONS

We have mapped a novel locus for AF to chromosome 6q14-16. The identification of the causative gene in this interval will be an important step in understanding the fundamental mechanisms of AF.

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

BACKGROUND

Dilated and hypertrophic cardiomyopathies are primary myocardial diseases that cause considerable morbidity and mortality. Although these cardiomyopathies are clinically heterogeneous, genetic factors play an important role in their etiology and pathogenesis. The defects in the cardiac actin (ACTC) gene can cause both cardiomyopathies. The aim of our study was to screen for variants in the ACTC gene in patients with dilated or hypertrophic cardiomyopathy from Eastern Finland.

MATERIALS AND METHODS

Altogether, 32 patients with dilated and 40 patients with hypertrophic cardiomyopathy were included in the study. Commonly approved diagnostic criteria were applied, and secondary cardiomyopathies were carefully excluded. All 6 exons of the ACTC gene were amplified with polymerase chain reaction and screened for variants with single-strand conformation polymorphism analysis.

RESULTS AND CONCLUSION

We did not find any new or previously reported variants. Our results indicate that defects in the ACTC gene do not explain dilated cardiomyopathy or hypertrophic cardiomyopathy in subjects from Eastern Finland and confirm earlier results that the ACTC gene does not play an important role in the genetics of dilated or hypertrophic cardiomyopathies.

Genes and their polymorphisms in mono- and multifactorial cardiomyopathies: towards pharmacogenomics in heart failure

Cardiomyopathies are diseases of the myocardium associated with cardiac dysfunction, and are classified as dilated cardiomyopathy (DCM), hypertropic cardiomyopathy (HCM) and restrictive cardiomyopathy. Heart failure and sudden death are the two major complications. Also, since DCM is the primary indication for heart transplantation and HCM the primary cause of sudden death in young athletes, the socioeconomic impact of these diseases is important. Recently, the role of the genetic background in both monogenic and multifactorial cardiomyopathies has been studied, which has led to a better understanding of the underlying mechanisms that promote the development and progression of these diseases. Preliminary data suggest interactions between pharmacological treatment and genetic polymorphisms, which appear to be the first steps towards the application of pharmacogenetics in heart failure.

Periodic rescreening is indicated for family members at risk of developing familial dilated cardiomyopathy

OBJECTIVES

This study evaluated the role of clinical rescreening of family members at risk for familial dilated cardiomyopathy (FDC).

BACKGROUND

Familial dilated cardiomyopathy is a genetic cardiomyopathy that usually is transmitted in an autosomal dominant pattern and may underlie from one-quarter to one-half of idiopathic dilated cardiomyopathy (IDC) diagnoses. Thus, FDC may present with advanced heart failure (HF) or sudden cardiac death (SCD). Because FDC may respond to medical intervention, we have previously recommended that screening of first-degree relatives (parents, siblings, children) of patients diagnosed with IDC be undertaken to rule out FDC, and that with a diagnosis of FDC in the kindred, unaffected but at-risk family members be rescreened every three to five years. METHODS; Follow-up screening (history, examination, electrocardiogram, echocardiography) of a large family with FDC was performed six years after initial screening. Of 68 family members who underwent rescreening, two (one with left ventricular enlargement only, one with a left bundle branch block) presented with advanced HF and SCD, respectively. Two additional subjects, asymptomatic at initial screening, were also affected with FDC at follow-up.

CONCLUSIONS

Considerable vigilance for disease presentation and progression is indicated in at-risk members of a kindred with FDC, especially those with incipient FDC.

Molecular Mechanisms of Inherited Cardiomyopathies

Cardiomyopathies are diseases of heart muscle that may result from a diverse array of conditions that damage the heart and other organs and impair myocardial function, including infection, ischemia, and toxins. However, they may also occur as primary diseases restricted to striated muscle. Over the past decade, the importance of inherited gene defects in the pathogenesis of primary cardiomyopathies has been recognized, with mutations in some 18 genes having been identified as causing hypertrophic cardiomyopathy (HCM) and/or dilated cardiomyopathy (DCM). Defining the role of these genes in cardiac function and the mechanisms by which mutations in these genes lead to hypertrophy, dilation, and contractile failure are major goals of ongoing research. Pathophysiological mechanisms that have been implicated in HCM and DCM include the following: defective force generation, due to mutations in sarcomeric protein genes; defective force transmission, due to mutations in cytoskeletal protein genes; myocardial energy deficits, due to mutations in ATP regulatory protein genes; and abnormal Ca2+ homeostasis, due to altered availability of Ca2+ and altered myofibrillar Ca2+ sensitivity. Improved understanding that will result from these studies should ultimately lead to new approaches for the diagnosis, prognostic stratification, and treatment of patients with heart failure.

Are we ready for pharmacogenomics in heart failure?

Heart failure is a major health problem and is associated with a high mortality and morbidity. Recently, the role of the genetic background in the onset and development of the disease has been evidenced in both heart failure with and without systolic dysfunction, and in familial and non-familial forms of this condition. Familial forms of dilated cardiomyopathy are more frequent than previously thought. Various modes of inheritance and phenotypes have been reported and this condition appears genetically highly heterogenous. Five genes (dystrophin, cardiac actin, desmin, lamin A/C and delta-sarcoglycan), and additional loci, have been identified in families in which dilated cardiomyopathy is isolated or associated with other cardiac or non-cardiac symptoms. It has been postulated that the molecular defect involved could lead to abnormal interactions between cytoskeletal proteins, responsible either for defect in force transmission or for membrane disruption. More recently, the identification of mutations in genes encoding sarcomeric proteins has led to a second hypothesis in which the disease might also result from a force generation defect. In non-monogenic dilated cardiomyopathy, susceptibility genes (role in the development of the disease) and modifier genes (role in the evolution/prognosis of the disease) have so far been identified. Some data suggest that the efficacy of angiotensin converting enzyme inhibitors, and side-effects, might be related to some genetic polymorphisms, such as the I/D polymorphism of the angiotensin converting enzyme gene. Although preliminary, these data are promising and might be the first step towards application of phamacogenetics in heart failure. This is of paramount importance as the medical treatment of heart failure is characterized by the need for polypharmacy. One of the major challenges of the next millenium, therefore, will be to identify genetic factors which might help define responders to major treatment classes, including angiotensin converting enzyme inhibitors, beta-adrenoreceptor antagonists, angiotensin AT1 receptor antagonists, spironolactone, vasopeptidase inhibitors and endothelin receptor antagonists.

[Genetic myocardiopathies: present and future]

Heart failure is a major health problem and is associated with a high mortality and morbidity. Recently, the role of the genetic background in the onset and the development of the disease has been evidenced in both heart failure with and without systolic dysfunction, and in familial and non familial forms of this condition. Several genes and loci are know identified as responsible for dilated cardiomyopathies and for hypertrophic cardiomyopathies in familial and monogenic forms. Susceptibility genes and modifier genes are also studied in nonfamilial forms of dilated cardiomyopathies. The analysis of genetic factors that predispose to heart failure looks promising. It should allow to better understand the underlying mechanisms that promote the development and the progression of the disease, to identify subjects at risk for the disease who would benefit of an early medical management and promote the development of pharmacogenetics.