Familial dilated cardiomyopathy: clinical features in French families

Genetics and Genomics of Single-Gene Cardiovascular Diseases: Common Hereditary Cardiomyopathies as Prototypes of Single-Gene Disorders

This is the first of 2 review papers on genetics and genomics appearing as part of the series on "omics." Genomics pertains to all components of an organism's genes, whereas genetics involves analysis of a specific gene or genes in the context of heredity. The paper provides introductory comments, describes the basis of human genetic diversity, and addresses the phenotypic consequences of genetic variants. Rare variants with large effect sizes are responsible for single-gene disorders, whereas complex polygenic diseases are typically due to multiple genetic variants, each exerting a modest effect size. To illustrate the clinical implications of genetic variants with large effect sizes, 3 common forms of hereditary cardiomyopathies are discussed as prototypic examples of single-gene disorders, including their genetics, clinical manifestations, pathogenesis, and treatment. The genetic basis of complex traits is discussed in a separate paper.

High yield of LMNA mutations in patients with dilated cardiomyopathy and/or conduction disease referred to cardiogenetics outpatient clinics

BACKGROUND

Among the most frequently encountered mutations in dilated cardiomyopathy (DCM) are those in the lamin A/C (LMNA) gene. Our goal was to analyze the LMNA gene in patients with DCM and/or conduction disease referred to the cardiogenetics outpatient clinic and to evaluate the prevalence of LMNA mutations and their clinical expression.

METHODS AND RESULTS

The LMNA gene was screened in 61 index patients. Eleven mutations (including 6 novel) were identified, mainly in the subgroup of familial DCM with cardiac conduction disease (3/10 index patients) and in patients with DCM and Emery-Dreifuss, Limb-Girdle, or unclassified forms of muscular dystrophy (7/8 index patients). In addition, a mutation was identified in 1 of 4 families with only cardiac conduction disease. We did not identify any large deletions or duplications. Genotype-phenotype relationships revealed a high rate of sudden death and cardiac transplants in carriers of the p.N195K mutation. Our study confirmed that the p.R225X mutation leads to cardiac conduction disease with late or no development of DCM, underscoring the importance of this mutation in putative familial "lone conduction disease." Nearly one third of LMNA mutation carriers had experienced a thromboembolic event.

CONCLUSIONS

This study highlights the role of LMNA mutations in DCM and related disorders. A severe phenotype in p.N195K mutation carriers and preferential cardiac conduction disease in p.R225X carriers was encountered. Because of the clinical variability, including the development of associated symptoms in time, LMNA screening should be considered in patients with DCM or familial lone conduction disease.

Severe Myocardial Fibrosis Caused by a Deletion of the 5’ End of the Lamin A/C Gene

OBJECTIVES

The goal of this study was to identify the underlying gene defect in a family with inherited myocardial fibrosis.

BACKGROUND

A large family with an autosomal dominantly inherited form of myocardial fibrosis with a highly malignant clinical outcome has been investigated. Because myocardial fibrosis preceded the clinical and echocardiographic signs, we consider the disease to be a hereditary form of cardiac fibrosis.

METHODS

Twenty-five family members were clinically evaluated, and 5 unaffected and 8 affected family members were included in a genome-wide linkage study.

RESULTS

The highest logarithm of the odds (LOD) score (LOD = 2.6) was found in the region of the lamin AC (LMNA) gene. The LMNA mutation analysis, both by denaturing gradient gel electrophoresis and sequencing, failed to show a mutation. Subsequent Southern blotting, complementary deoxyribonucleic acid sequencing, and multiplex ligation-dependent probe amplification analysis, however, revealed a deletion of the start codon-containing exon and an adjacent noncoding exon. In vitro studies demonstrated that the deletion results in the formation of nuclear aggregates of lamin, suggesting that the mutant allele is being transcribed.

CONCLUSIONS

This novel LMNA deletion causes a distinct, highly malignant cardiomyopathy with early-onset primary cardiac fibrosis likely due to an effect of the shortened mutant protein, which secondarily leads to arrhythmias and end-stage cardiac failure.

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.

Expanding the phenotype of LMNA mutations in dilated cardiomyopathy and functional consequences of these mutations

AIMS

Mutations in the lamin A/C gene (LMNA) have been reported to be involved in dilated cardiomyopathy (DCM) associated with conduction system disease and/or skeletal myopathy. The aim of this study was to perform a mutational analysis of LMNA in a large white population of patients affected by dilated cardiomyopathy with or without associated symptoms.

METHODS

We performed screening of the coding sequence of LMNA on DNA samples from 66 index cases, and carried out cell transfection experiments to examine the functional consequences of the mutations identified.

RESULTS

A new missense (E161K) mutation was identified in a family with early atrial fibrillation and a previously described (R377H) mutation in another family with a quadriceps myopathy associated with DCM. A new mutation (28insA) leading to a premature stop codon was identified in a family affected by DCM with conduction defects. No mutation in LMNA was found in cases with isolated dilated cardiomyopathy. Functional analyses have identified potential physiopathological mechanisms involving identified mutations, such as haploinsufficiency (28insA) or intermediate filament disorganisation (E161K, R377H).

CONCLUSION

For the first time, a specific phenotype characterised by early atrial fibrillation is associated with LMNA mutation. Conversely, mutations in LMNA appear as a rare cause of isolated dilated cardiomyopathy. The variable phenotypes observed in LMNA-DCM might be explained by the variability of functional consequences of LMNA mutations.

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.

Functional consequences of an LMNA mutation associated with a new cardiac and non-cardiac phenotype

Heritable dilated cardiomyopathy is a genetically highly heterogeneous disease. To date 17 different chromosomal loci have been described for autosomal dominant forms of dilated cardiomyopathy with or without additional clinical manifestations. Among the 10 mutated genes associated with dilated cardiomyopathy, the lamin A/C (LMNA) gene has been reported in forms associated with conduction-system disease with or without skeletal muscle myopathy. For the first time, we report here a French family affected with a new phenotype composed of an autosomal dominant severe dilated cardiomyopathy with conduction defects or atrial/ventricular arrhythmias, and a specific quadriceps muscle myopathy. In all previously reported cases with both cardiac and neuromuscular involvement, neuromuscular disorders preceded cardiac abnormalities. The screening of the coding sequence of the LMNA gene on all family members was performed and we identified a missense mutation (R377H) in the lamin A/C gene that cosegregated with the disease in the family. Cell transfection experiments showed that the R377H mutation leads to mislocalization of both lamin and emerin. These results were obtained in both muscular (C2C12) and non-muscular cells (COS-7). This new phenotype points out the wide spectrum of neuromuscular and cardiac manifestations associated with lamin A/C mutations, with the functional consequence of this mutation seemingly associated with a disorganization of the lamina.

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.

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.

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

Dilated cardiomyopathy (DCM) is a heart-muscle disease characterized by ventricular dilatation and impaired heart contraction and is heterogeneous both clinically and genetically. To date, 12 candidate disease loci have been described for autosomal dominant DCM. We report the identification of a new locus on chromosome 6q12-16 in a French family with 9 individuals affected by the pure form of autosomal dominant DCM. This locus was found by using a genomewide search after exclusion of all reported disease loci and genes for DCM. The maximum pairwise LOD score was 3.52 at recombination fraction 0.0 for markers D6S1644 and D6S1694. Haplotype construction delineated a region of 16.4 cM between markers D6S1627 and D6S1716. This locus does not overlap with two other disease loci that have been described in nonpure forms of DCM and have been mapped on 6q23-24 and 6q23. The phospholamban, malic enzyme 1-soluble, and laminin-alpha4 genes were excluded as candidate genes, using single-strand conformation polymorphism or linkage analysis.