The Genetic Bases of Cardiomyopathies

Noninvasive detection of fibrosis applying contrast-enhanced cardiac magnetic resonance in different forms of left ventricular hypertrophy relation to remodeling

OBJECTIVES

We aimed to evaluate the incidence and patterns of late gadolinium enhancement (LGE) in different forms of left ventricular hypertrophy (LVH) and to determine their relation to severity of left ventricular (LV) remodeling.

BACKGROUND

Left ventricular hypertrophy is an independent predictor of cardiac mortality. The relationship between LVH and myocardial fibrosis as defined by LGE cardiovascular magnetic resonance (CMR) is not well understood.

METHODS

A total of 440 patients with aortic stenosis (AS), arterial hypertension (AH), or hypertrophic cardiomyopathy (HCM) fulfilling echo criteria of LVH underwent CMR with assessment of LV size, weight, function, and LGE. Patients with increased left ventricular mass index (LVMI) resulting in global LVH in CMR were included in the study.

RESULTS

Criteria were fulfilled by 83 patients (56 men, age 57 +/- 14 years; AS, n = 21; AH, n = 26; HCM, n = 36). Late gadolinium enhancement was present in all forms of LVH (AS: 62%, AH: 50%; HCM: 72%, p = NS) and was correlated with LVMI (r = 0.237, p = 0.045). There was no significant relationship between morphological obstruction and LGE. The AS subjects with LGE showed higher LV end-diastolic volumes than those without (1.0 +/- 0.2 ml/cm vs. 0.8 +/- 0.2 ml/cm, p < 0.015). Typical patterns of LGE were observed in HCM but not in AS and AH.

CONCLUSIONS

Fibrosis as detected by CMR is a frequent feature of LVH, regardless of its cause, and depends on the severity of LV remodeling. As LGE emerges as a useful tool for risk stratification also in nonischemic heart diseases, our findings have the potential to individualize treatment strategies.

Genetic deletion of arginine 14 in phospholamban causes dilated cardiomyopathy with attenuated electrocardiographic R amplitudes

BACKGROUND

Familial dilated cardiomyopathy is a highly heterogeneous genetic disease. Thus, identification of disease-causing mutations is a challenging and time-consuming task. Genotype-phenotype associations may alleviate identification of the underlying mutation.

OBJECTIVE

The purpose of this study was to investigate cardiac phenotypes within a family harboring a familial dilated cardiomyopathy-related mutation in the gene encoding phospholamban.

METHODS

Complete genetic and clinical analyses were performed in a family with familial dilated cardiomyopathy due to the PLN-R14Del mutation. Family relatives were studied by ECG, Holter ECG, echocardiography, ECG body surface potential mapping, and cardiac magnetic resonance imaging.

RESULTS

A candidate gene approach resulted in identification of a heterozygous deletion of arginine 14 in the gene encoding phospholamban (PLN-R14Del) segregating with dilated cardiomyopathy in the family pedigree. Mutation carriers suffered from familial dilated cardiomyopathy associated with cardiac death between the ages of 26 and 50 years. Interestingly, all adult mutation carriers revealed strikingly attenuated R amplitudes on standard ECG, regardless of the absence or presence of echocardiographic abnormalities. Gadolinium-enhanced cardiac magnetic resonance imaging showed late enhancement in PLN-R14Del carriers with preserved ejection fraction. Late enhancement was regionally related to areas of most pronounced R-amplitude attenuation as assessed by body surface potential mapping.

CONCLUSION

Attenuated R amplitudes were identified as an early ECG phenotype in a family with familial dilated cardiomyopathy due to the PLN-R14Del mutation. All adults harboring PLN-R14Del had attenuated R waves irrespective of echocardiographic abnormalities. The study findings suggest a mutation-related remodeling process preceding ventricular dysfunction.

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.

Ubiquitin-proteasome system impairment caused by a missense cardiac myosin-binding protein C mutation and associated with cardiac dysfunction in hypertrophic cardiomyopathy

The ubiquitin-proteasome system is responsible for the disappearance of truncated cardiac myosin-binding protein C, and the suppression of its activity contributes to cardiac dysfunction. This study investigated whether missense cardiac myosin-binding protein C gene (MYBPC3) mutation in hypertrophic cardiomyopathy (HCM) leads to destabilization of its protein, causes UPS impairment, and is associated with cardiac dysfunction. Mutations were identified in Japanese HCM patients using denaturing HPLC and sequencing. Heterologous expression was investigated in COS-7 cells as well as neonatal rat cardiac myocytes to examine protein stability and proteasome activity. The cardiac function was measured using echocardiography. Five novel MYBPC3 mutations -- E344K, DeltaK814, Delta2864-2865GC, Q998E, and T1046M -- were identified in this study. Compared with the wild type and other mutations, the E334K protein level was significantly lower, it was degraded faster, it had a higher level of polyubiquination, and increased in cells pretreated with the proteasome inhibitor MG132 (50 microM, 6 h). The electrical charge of its amino acid at position 334 influenced its stability, but E334K did not affect its phosphorylation. The E334K protein reduced cellular 20 S proteasome activity, increased the proapoptotic/antiapoptotic protein ratio, and enhanced apoptosis in transfected Cos-7 cells and neonatal rat cardiac myocytes. Patients carrying the E334K mutation presented significant left ventricular dysfunction and dilation. The conclusion is the missense MYBPC3 mutation E334K destabilizes its protein through UPS and may contribute to cardiac dysfunction in HCM through impairment of the ubiquitin-proteasome system.

Identification of mutational hot spots in LMNA encoding lamin A/C in patients with familial dilated cardiomyopathy

The familial form of dilated cardiomyopathy (DCM) occurs in about 20%-50% of DCM cases. It is a heterogeneous genetic disease: mutations in more than 20 different genes have been shown to cause familial DCM. LMNA, encoding the nuclear membrane protein lamin A/C, is one of the most important disease gene for that disease. Therefore, we analyzed the LMNA gene in a large cohort of 73 patients with familial DCM. Clinical examination (ECG, echocardiography, and catheterization) was followed by genetic characterization of LMNA by direct sequencing. We detected five heterozygous missense mutations (prevalence 7%) in five different families characterized by severe DCM and heart failure with conduction system disease necessitating pacemaker implantation and heart transplantation. Four of these variants clustered in the protein domain coil 1B, which is important for lamin B interaction and lamin A/C dimerization. Although we identified two novel mutations (E203V, K219T) besides three known ones (E161K, R190Q, R644C), it was remarkable that four mutations represent LMNA hot spots. DCM patients with LMNA mutations show a notable homogenous severe phenotype as we could confirm in our study. Testing LMNA in such families seems to be recommended because genotype information in an individual could definitely be useful for the clinician.

Impact of multiple gene mutations in determining the severity of cardiomyopathy and heart failure

1. Familial hypertrophic cardiomyopathy (FHC) is a primary cardiac disorder characterized by myocardial hypertrophy that demonstrates substantial diversity in both genetic causes and clinical manifestations. 2. Clinical heterogeneity can be explained by the causative gene (at least 13 have been identified to date), the position of the amino acid residue affected by a mutation within the protein (over 450 mutations have been reported to date) and modifying genetic and environmental factors. 3. Multiple mutations are found in up to 5% of human FHC cases, who typically present with a more severe phenotype compared with single-mutation carriers (i.e. earlier onset of disease, greater left ventricular hypertrophy and a higher incidence of sudden cardiac death events). 4. Multiple mutations usually involve MYH7, MYBPC3 and, to a lesser extent, TNNI2, reflecting the higher contribution of mutations in these genes to FHC. 5. Multiple-mutation mouse models appear to mimic the human multiple-mutation phenotype and, thus, will help improve our understanding of disease pathogenesis. The models provide a tool for future studies of disease mechanisms and signalling pathways in FHC and its sequelae (i.e. heart failure and sudden death), thereby allowing identification of novel targets for potential therapies and disease prevention strategies.

HLA-DPbeta chain may confer the susceptibility to hepatitis C virus-associated hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a heart muscle disease characterized by hypertrophy and diastolic dysfunction of cardiac ventricles. It is suggested that one possible aetiology of HCM is the hepatitis C virus (HCV) infection, but molecular mechanisms underlying development of HCV-associated HCM (HCV-HCM) remains unknown. Because the human leucocyte antigen (HLA) molecule is involved in the control of progression/suppression of viral infection, extensive HLA allelic diversity may modulate the post-infectious course of HCV and pathogenesis of HCV-HCM. Here we undertook a case-control study with 38 patients with HCV-HCM and 132 unrelated healthy controls to reveal the potential impact of polymorphisms in seven classical and two non-classical HLA genes on the pathogenesis of HCV-HCM. It was found that DPB1*0401 and DPB1*0901 were significantly associated with increased risk to HCV-HCM in dominant model (P < 0.028, OR = 3.94, 95% confidence interval (CI) = 1.19, 13.02) and in recessive model (P < 0.007, OR = 9.85, 95% CI = 1.83, 53.04), respectively. The disparity in the gene-dose effect by two susceptible DPB1 alleles may be attributable to the difference between the susceptible (36 A and 55 A) and resistant (8L, 9F, 11G, 57E and 76M) residue-combination consisting of DPbeta anchor pocket for antigenic peptide-binding. These results implied that the HLA-DP molecules with specificity pocket appropriate for HCV antigen(s) might confer the progressive process of HCM among the HCV-infected individuals.

Familial hypertrophic cardiomyopathy-related cardiac troponin C mutation L29Q affects Ca2+ binding and myofilament contractility

The cardiac troponin C (cTnC) mutation, L29Q, has been found in a patient with familial hypertrophic cardiomyopathy. We previously showed that L29, together with neighboring residues, Asp2, Val28, and Gly30, plays an important role in determining the Ca(2+) affinity of site II, the regulatory site of mammalian cardiac troponin C (McTnC). Here we report on the Ca(2+) binding characteristics of L29Q McTnC and D2N/V28I/L29Q/G30D McTnC (NIQD) utilizing the Phe(27) --> Trp (F27W) substitution, allowing one to monitor Ca(2+) binding and release. We also studied the effect of these mutants on Ca(2+) activation of force generation in single mouse cardiac myocytes using cTnC replacement, together with sarcomere length (SL) dependence. The Ca(2+)-binding affinity of site II of L29Q McTnC(F27W) and NIQD McTnC(F27W) was approximately 1.3- and approximately 1.9-fold higher, respectively, than that of McTnC(F27W). The Ca(2+) disassociation rate from site II of L29Q McTnC(F27W) and NIQD McTnC(F27W) was not significantly different than that of control (McTnC(F27W)). However, the rate of Ca(2+) binding to site II was higher in L29Q McTnC(F27W) and NIQD McTnC(F27W) relative to control (approximately 1.5-fold and approximately 2.0-fold respectively). The Ca(2+) sensitivity of force generation was significantly higher in myocytes reconstituted with L29Q McTnC (approximately 1.4-fold) and NIQD McTnC (approximately 2-fold) compared with those reconstituted with McTnC. Interestingly, the change in Ca(2+) sensitivity of force generation in response to an SL change (1.9, 2.1, and 2.3 mum) was significantly reduced in myocytes containing L29Q McTnC or NIQD McTnC. These results demonstrate that the L29Q mutation enhances the Ca(2+)-binding characteristics of cTnC and that when incorporated into cardiac myocytes, this mutant alters myocyte contractility.

Molecular defects associated with antithrombin deficiency and dilated cardiomyopathy in a Japanese patient

OBJECTIVE

The molecular basis for the antithrombin (AT) deficiency and dilated cardiomyopathy (DCM) combined in a Japanese patient was investigated.

METHODS

We analyzed candidate genes -SERPINC1 for AT deficiency, and TNNT2 and LMNA for DCM. In addition, we examined the characteristics of recombinant mutant AT and evaluated the LMNA mutation associated with DCM by molecular modeling.

RESULTS

Genome sequencing of SERPINC1 revealed a C-to-A transversion in exon 6 that resulted in a p.Pro439Thr mutation of AT, which was previously reported as a pleiotropic effect type II AT deficiency (AT Budapest5). However, expression experiments with recombinant 439Thr-AT showed normal heparin affinity, slightly reduced secretion, and low specific activity, which suggested that this mutation exhibits an intermediate feature of type I and type II AT deficiencies. In a survey of gene abnormalities causing DCM, we found no causative gene defect in TNNT2; however, we identified a G-to-C transversion in LMNA that resulted in a novel p.Asp357His mutation in lamin A/C. This acidic-to-basic residue substitution might have impaired the head-to-tail association of two lamin dimers leading to DCM. Further, we identified both SERPINC1 and LMNA mutations in the patient's daughter and son, both of whom had AT deficiency. These data suggested that a p.Pro439Thr mutation in SERPINC1 and a p.Asp357His mutation in LMNA might have cosegregated in this family, associated with AT deficiency and DCM, respectively.

CONCLUSIONS

We identified missense mutations in SERPINC1 and LMNA genes to be associated with AT deficiency and DCM, respectively, which might have cosegregated in the family of the patient.

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.

Mutations in the Z-band protein myopalladin gene and idiopathic dilated cardiomyopathy

AIMS

Idiopathic dilated cardiomyopathy (DCM) is a cardiac disorder characterized by left ventricular dilatation and impaired systolic contraction. It is a major cause of heart failure and heart transplantation. DCM is of genetic origin in approximately 30% of cases and genetically heterogeneous with the identification of numerous disease genes. However, many new disease genes remain to be discovered. Focusing on gene products located in the sarcomere of cardiomyocytes as disease-causing candidates, we screened the gene encoding the sarcomeric Z-band protein myopalladin (MYPN, OMIM 608517) for mutation.

METHODS AND RESULTS

We sequenced the coding region in 114 (65 familial and 49 sporadic cases) independent DCM patients' DNA and functionally analysed the identified mutations. We identified four independent heterozygous mutations in two families (R1088H and I83fsX105) and two sporadic cases (V1195M, P1112L). For the three missense mutations, the substituted amino acids were conserved among species. All mutations were absent from 400 control subjects. Specific immunolabelling of heart tissue from a proband carrying the R1088H mutation showed a decreased localization of myopalladin at the Z-band area of left ventricular cardiac myofibrils. Analysis of the effects of the mutations after transfection in rat neonate cardiomyocytes indicated sarcomere disorganization and premature cell death associated with the V1195M and P1112L myopalladin expression. Allele-specific expression analysis of mRNA from a patient harbouring the I83fsX105 mutation indicated the absence of the mutated transcript, suggesting a haploinsufficiency mechanism.

CONCLUSION

Based on genetic, histological, and functional evidence, we identified a new gene associated with DCM and observed mutations in 3-4% of cases in a population of European descent.

The contribution of familial and heritable risks in heart failure

PURPOSE OF REVIEW

The purpose of this review is to summarize the recent literature regarding the familial heritability of heart failure and to discuss the possible mechanisms through which this risk is mediated.

RECENT FINDINGS

Data from the Framingham Heart Study recently showed that the parental occurrence of heart failure increases the risk of heart failure in offspring. Although the mechanisms mediating this increased risk are not elucidated, heritable risks of heart failure may result from genes affecting the cardiac or vascular systems. Alternatively, familial risk may be mediated partly through the inheritance of recognized or as yet unidentified risk factors for heart failure. Heritable components or genetic loci for quantitative traits contribute to the development of hypertension, coronary artery disease, cardiomyopathies, valvular heart disease, and metabolic conditions, which collectively increase the risk of heart failure.

SUMMARY

A careful assessment of the family history of heart failure and associated risk factors may identify treatable targets that can potentially reduce the likelihood of developing heart failure, and can assist in the implementation of preventive strategies for risk populations with stages A and B heart failure.

Predict, prevent and personalize: Genomic and proteomic approaches to cardiovascular medicine

Genomic and proteomic approaches to cardiovascular medicine promise to revolutionize our understanding of disease initiation and progression. This improved appreciation of pathophysiology may be translated into avenues of clinical utility. Gene-based presymptomatic prediction of illness, finer diagnostic subclassifications and improved risk assessment tools will permit earlier and more targeted intervention. Pharmacogenetics will guide our therapeutic decisions and monitor response to therapy. Personalized medicine will require the integration of clinical information, stable and dynamic genomics, and molecular phenotyping. Bioinformatics will be crucial in translating these data into useful applications, leading to improved diagnosis, prediction, prognostication and treatment. The present paper reviews the potential contributions of genomic and proteomic approaches in developing a more personalized approach to cardiovascular medicine.