Mutations in the human delta-sarcoglycan gene in familial and sporadic dilated cardiomyopathy

Steroid treatment causes deterioration of myocardial function in the {delta}-sarcoglycan-deficient mouse model for dilated cardiomyopathy

AIMS

As oral corticosteroids have a beneficial effect on muscle strength in Duchenne muscular dystrophy, it has been suggested that they may also be a useful treatment in the pathologically related sarcoglycanopathies. The delta-sarcoglycan-deficient mouse (Sgcd-null) is a model for both limb girdle muscular dystrophy 2F (LGMD2F) and dilated cardiomyopathy.

METHODS AND RESULTS

To study the effect of oral corticosteroids on cardiac function, we treated 8-week-old Sgcd-null mice with prednisolone (1.5 mg/kg body weight/day orally) for 8 weeks. In vivo cardiac function was assessed by pressure-volume loops using a conductance catheter. We found a well-compensated cardiomyopathy at baseline in Sgcd-null mice with decreased myocardial contractility, increased preload, and decreased afterload, maintaining a high cardiac output. Cardiac haemodynamics, surprisingly, did not improve in prednisolone-treated mice, but instead deteriorated with evidence of ventricular stiffening. On histology, after steroid treatment there was increased myocardial cell damage and increased myocardial fibrosis.

CONCLUSION

Prednisolone led to a decompensation of cardiac haemodynamics in Sgcd-null mice and induced additional cardiac damage. On the basis of these findings, although mouse models may not completely replicate the human situation for LGMD2F, we conclude that careful cardiac monitoring is clearly indicated in patients on long-term corticosteroids.

Xanthine oxidase inhibition improves left ventricular dysfunction in dilated cardiomyopathic hamsters

BACKGROUND

Oxidative stress is implicated in cardiac remodeling and failure. We tested whether xanthine oxidase (XO) inhibition could decrease myocardial oxidative stress and attenuate left ventricular (LV) remodeling and dysfunction in the TO-2 hamster model of dilated cardiomyopathy.

METHODS AND RESULTS

TO-2 hamsters were randomized to treatment with the XO inhibitor, allopurinol, or vehicle from 6 to 12 weeks of age. F1B hamsters served as controls. TO-2 hamsters treated with vehicle progressively developed severe LV systolic dysfunction and dilation between 6 and 12 weeks. Marked cardiac fibrosis was apparent in these hamsters at 12 weeks in comparison with F1B controls. The ratio of reduced to oxidized glutathione (GSH/GSSG) was decreased and malondialdehyde levels were increased in the hearts of vehicle-treated TO-2 hamsters. Treatment with allopurinol from 6 to 12 weeks attenuated LV dysfunction and dilation as well as myocardial fibrosis and the upregulation of a fetal-type cardiac gene. Allopurinol also inhibited both the decrease in GSH/GSSG ratio and the increase in malondialdehyde levels in the heart.

CONCLUSIONS

These results indicate that chronic XO inhibition with allopurinol attenuates LV remodeling and dysfunction as well as myocardial oxidative stress in this model of heart failure. Allopurinol may prove beneficial for the treatment of heart failure.

Caveolin-3 T78M and T78K missense mutations lead to different phenotypes in vivo and in vitro

Caveolins are the principal protein components of caveolae, invaginations of the plasma membrane involved in cell signaling and trafficking. Caveolin-3 (Cav-3) is the muscle-specific isoform of the caveolin family and mutations in the CAV3 gene lead to a large group of neuromuscular disorders. In unrelated patients, we identified two distinct CAV3 mutations involving the same codon 78. Patient 1, affected by dilated cardiomyopathy and limb girdle muscular dystrophy (LGMD)-1C, shows an autosomal recessive mutation converting threonine to methionine (T78M). Patient 2, affected by isolated familiar hyperCKemia, shows an autosomal dominant mutation converting threonine to lysine (T78K). Cav-3 wild type (WT) and Cav-3 mutations were transiently transfected into Cos-7 cells. Cav-3 WT and Cav-3 T78M mutant localized at the plasma membrane, whereas Cav-3 T78K was retained in a perinuclear compartment. Cav-3 T78K expression was decreased by 87% when compared with Cav-3 WT, whereas Cav-3 T78M protein levels were unchanged. To evaluate whether Cav-3 T78K and Cav-3 T78M mutants behaved with a dominant negative pattern, Cos-7 cells were cotransfected with green fluorescent protein (GFP)-Cav-3 WT in combination with either mutant or WT Cav-3. When cotransfected with Cav-3 WT or Cav-3 T78M, GFP-Cav-3 WT was localized at the plasma membrane, as expected. However, when cotransfected with Cav-3 T78K, GFP-Cav-3 WT was retained in a perinuclear compartment, and its protein levels were reduced by 60%, suggesting a dominant negative action. Accordingly, Cav-3 protein levels in muscles from a biopsy of patient 2 (T78K mutation) were reduced by 80%. In conclusion, CAV3 T78M and T78K mutations lead to distinct disorders showing different clinical features and inheritance, and displaying distinct phenotypes in vitro.

Revised spectrum of mutations in sarcoglycanopathies

To define the spectrum of mutations in alpha-, beta-, gamma-, and delta-sarcoglycan (SG) genes, we analyzed these genes in 69 probands with clinical and biological criteria compatible with the diagnosis of autosomal recessive limb-girdle muscular dystrophy. For 48 patients, muscle biopsies were available and multiplex western blot analysis of muscle proteins showed significant abnormalities of alpha- and gamma-SG. Our diagnostic strategy includes multiplex western blot, sequencing of SG genes, multiplex quantitative-fluorescent PCR and RT-PCR analyses. Mutations were detected in 57 patients and homozygous or compound heterozygous mutations were identified in 75% (36/48) of the patients with abnormal western blot, and in 52% (11/21) of the patients without muscle biopsy. Involvement of alpha-SG was demonstrated in 55.3% of cases (26/47), whereas gamma- and beta-SG were implicated in 25.5% (12/47) and in 17% (8/47) of cases, respectively. Interestingly, we identified 25 novel mutations, and a significant proportion of these mutations correspond to deletions (identified in 14 patients) of complete exon(s) of alpha- or gamma-SG genes, and partial duplications (identified in 5 patients) of exon 1 of beta-SG gene. This study highlights the high frequency of exonic deletions of alpha- and gamma-SG genes, as well as the presence of a hotspot of duplications affecting exon 1 of the beta-SG gene. In addition, protein analysis by multiplex western blot in combination with mutation screening and genotyping results allowed to propose a comprehensive and efficient diagnostic strategy and strongly suggested the implication of additional genes, yet to be identified, in sarcoglycanopathy-like disorders.

Phosphorylation status of regulatory proteins and functional characteristics in myocardium of dilated cardiomyopathy of Syrian hamsters

To understand the pathophysiology of hereditary cardiomyopathy, we measured the phosphorylation status of regulatory proteins, troponin I (TnI), troponin T (TnT), myosin light chain 2 (MLC2), and myosin-binding protein C (MyBP-C), and the Ca2+-dependence of tension development and ATPase activity in skinned right ventricular trabeculae obtained from cardiomyopathic (TO-2 strain, n = 8) and control (F1B strain, n = 8) hamsters. The Ca2+ sensitivities of tension development and ATPase activity (mean +/- SD) were significantly (P < 0.0001) higher in the TO-2 strain (pCa50 5.64 +/- 0.04 in tension and 5.65 +/- 0.04 in ATPase activity) than in the F1B strain (pCa50 5.48 +/- 0.03 in tension and 5.51 +/- 0.03 in ATPase activity). No significant differences in their maximum values were observed between TO-2 (40.8 +/- 7.4 mN/mm2 in tension and 0.52 +/- 0.15 micromol/l/s in ATP consumption) and F1B (42.3 +/- 8.5 mN/mm2 in tension and 0.58 +/- 0.41 micromol/l/s in ATP consumption) preparations, indicating that the tension cost (ATPase activity/tension development) in TO-2 was quite similar to that in F1B. The phosphorylation levels of MLC2 and TnI were significantly (P < 0.01) lower in TO-2 than in F1B. These results suggest that the increase in the Ca2+ sensitivities of tension development and the ATPase activity in TO-2 hearts result from the decreased basal level of TnI phosphorylation, and these features can be considered to produce the incomplete diastolic relaxation and partly improve the systolic function in TO-2 hearts.

Inherited arrhythmias: a National Heart, Lung, and Blood Institute and Office of Rare Diseases workshop consensus report about the diagnosis, phenotyping, molecular mechanisms, and therapeutic approaches for primary cardiomyopathies of gene mutations affecting ion channel function

The National Heart, Lung, and Blood Institute and Office of Rare Diseases at the National Institutes of Health organized a workshop (September 14 to 15, 2006, in Bethesda, Md) to advise on new research directions needed for improved identification and treatment of rare inherited arrhythmias. These included the following: (1) Na+ channelopathies; (2) arrhythmias due to K+ channel mutations; and (3) arrhythmias due to other inherited arrhythmogenic mechanisms. Another major goal was to provide recommendations to support, enable, or facilitate research to improve future diagnosis and management of inherited arrhythmias. Classifications of electric heart diseases have proved to be exceedingly complex and in many respects contradictory. A new contemporary and rigorous classification of arrhythmogenic cardiomyopathies is proposed. This consensus report provides an important framework and overview to this increasingly heterogeneous group of primary cardiac membrane channel diseases. Of particular note, the present classification scheme recognizes the rapid evolution of molecular biology and novel therapeutic approaches in cardiology, as well as the introduction of many recently described diseases, and is unique in that it incorporates ion channelopathies as a primary cardiomyopathy in consensus with a recent American Heart Association Scientific Statement.

Which skeletal myoblasts and how to be transplanted for cardiac repair?

Clinical efficacy of skeletal myoblast (skMb) transplantation is controversial whether this treatment produces beneficial outcome in patients with dilated cardiomyopathy (DCM). Based on immunological tolerance between wild-type and DCM hamsters with the deletion of delta-sarcoglycan (SG) gene, skMb engraftment in TO-2 myocardium (3x10(5) cells in approximately 100mg heart) was verified by the donor-specific expression of delta-SG transgene constitutively produced throughout myogenesis. At 5 weeks after the transplantation, the cell rates expressing fast-myosin heavy chain (MHC) exceeded slow-MHC in delta-SG(+) cells. Fifteen weeks after (corresponding to approximately 12 years in humans), fast MHC(+) cells nullified, but the delta-SG(+) and slow MHC(+) cell number remained unaltered. These skMbs fused with host cardiomyocytes via connexin-43 and intercalated disc, modestly improving the hemodynamics without arrhythmia, when engrafted skMbs were sparsely disseminated in autopsied myocardium. These results provide us evidence that disseminating delivery of slow-MHC(+) myoblasts is promising for repairing DCM heart using histocompatible skeletal myoblasts in future.

Impact of delta-sarcoglycan gene polymorphism on the occurrence of coronary spastic angina in Japanese patients with hypertrophic cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) frequently complain of angina-like symptoms in the absence of organic coronary stenoses. Coronary spasm might cause myocardial ischemia in HCM patients. Delta-sarcoglycan plays a crucial role in the pathogenesis of HCM and coronary spasm in a mouse model.

METHODS AND RESULTS

This is a retrospective, single-center study with a small sample size. Seventy patients with HCM underwent coronary angiography and received acetylcholine provocation test. Coronary risk factors and 5'-untranslated region (UTR) G to C polymorphism on delta-sarcoglycan gene (n=64) were evaluated in the HCM patients. In 31 (44.3%) of 70 HCM patients, coronary spasm was induced by the provocation. None of the coronary risk factors was significantly different between the coronary spasm group and the non-coronary spasm group. The 5'-UTR gene polymorphism was associated with the occurrence of coronary spasm with an additive effect on the coexistence (p=0.025). Multiple logistic regression analysis showed that the C allele of 5'-UTR polymorphism was a significant risk factor for coronary spasm in patients with HCM (odds ratio, 3.1; 95% confidence interval, 1.0 to 9.5; p=0.045) that was independent of traditional coronary risk factors.

CONCLUSIONS

The 5'-UTR polymorphism on delta-sarcoglycan gene was associated with coronary spasm in Japanese patients with HCM.

Dysferlin-mediated membrane repair protects the heart from stress-induced left ventricular injury

Dilated cardiomyopathy is a life-threatening syndrome that can arise from a myriad of causes, but predisposition toward this malady is inherited in many cases. A number of inherited forms of dilated cardiomyopathy arise from mutations in genes that encode proteins involved in linking the cytoskeleton to the extracellular matrix, and disruption of this link renders the cell membrane more susceptible to injury. Membrane repair is an important cellular mechanism that animal cells have developed to survive membrane disruption. We have previously shown that dysferlin deficiency leads to defective membrane resealing in skeletal muscle and muscle necrosis; however, the function of dysferlin in the heart remains to be determined. Here, we demonstrate that dysferlin is also involved in cardiomyocyte membrane repair and that dysferlin deficiency leads to cardiomyopathy. In particular, stress exercise disturbs left ventricular function in dysferlin-null mice and increases Evans blue dye uptake in dysferlin-deficient cardiomyocytes. Furthermore, a combined deficiency of dystrophin and dysferlin leads to early onset cardiomyopathy. Our results suggest that dysferlin-mediated membrane repair is important for maintaining membrane integrity of cardiomyocytes, particularly under conditions of mechanical stress. Thus, our study establishes what we believe is a novel mechanism underlying the cardiomyopathy that results from a defective membrane repair in the absence of dysferlin.

Reduced life span with heart and muscle dysfunction in Drosophila sarcoglycan mutants

In humans, genetically diverse forms of muscular dystrophy are associated with a disrupted sarcoglycan complex. The sarcoglycan complex resides at the muscle plasma membrane where it associates with dystrophin. There are six known sarcoglycan proteins in mammals whereas there are only three in Drosophila melanogaster. Using imprecise P element excision, we generated three different alleles at the Drosophila delta-sarcoglycan locus. Each of these deletions encompassed progressively larger regions of the delta-sarcoglycan gene. Line 840 contained a large deletion of the delta-sarcoglycan gene, and this line displayed progressive impairment in locomotive ability, reduced heart tube function and a shortened life span. In line 840, deletion of the Drosophila delta-sarcoglycan gene produced disrupted flight muscles with shortened sarcomeres and disorganized M lines. Unlike mammalian muscle where degeneration is coupled with ongoing regeneration, no evidence for regeneration was seen in this Drosophila sarcoglycan mutant. In contrast, line 28 was characterized with a much smaller deletion that affected only a portion of the cytoplasmic region of the delta-sarcoglycan protein and left intact the transmembrane and extracellular domains. Line 28 had a very mild phenotype with near normal life span, intact cardiac function and normal locomotive activity. Together, these data demonstrate the essential nature of the transmembrane and extracellular domains of Drosophila delta-sarcoglycan for normal muscle structure and function.

Mutation of delta-sarcoglycan is associated with Ca(2+) -dependent vascular remodeling in the Syrian hamster

We examined whether mutation of the delta-sarcoglycan gene, which causes dilated cardiomyopathy, also alters the vascular smooth muscle cell (VSMC) phenotype and arterial function in the Syrian hamster CHF 147. Thoracic aorta media thickness showed marked variability in diseased hamsters with zones of atrophy and hypertrophied segments. CHF-147 VSMCs displayed a proliferating/"synthetic" phenotype characterized by the absence of the smooth muscle myosin heavy chain SM2, dystrophin, and Ca(2+)-handling proteins, and the presence of cyclin D1. In freshly isolated VSMCs from CHF 147 hamsters, voltage-independent basal Ca(2+) channels showed enhanced activity similar to that in proliferating wild-type (WT) cells. The transcription factor NFAT (nuclear factor of activated T cells) was spontaneously active in freshly isolated CHF 147 VSMCs, as in proliferating VSMCs from WT hamsters. Mibefradil inhibited B-type channels, NFAT activity, and VSMC proliferation. CHF 147 hamsters had abundant apoptotic cells distributed in patches along the aorta, and clusters of inactive mitochondria were observed in 25% of isolated CHF 147 cells, whereas no such clusters were seen in WT cells. In conclusion, mutation of the delta-sarcoglycan gene increases plasma membrane permeability to Ca(2+), activates the Ca(2+)-regulated transcription factor NFAT, and leads to spontaneous mitochondrial aggregation, causing abnormal VSMC proliferation and apoptosis.

Progression of heart failure was suppressed by inhibition of apoptosis signal-regulating kinase 1 via transcoronary gene transfer

OBJECTIVES

We examined whether the inhibition of apoptosis signal-regulating kinase 1 (ASK1) would attenuate the progression of heart failure in TO-2 hamsters with hereditary dilated cardiomyopathy.

BACKGROUND

Heart failure remains the leading cause of mortality and requires novel therapies targeting the biologically relevant processes within cardiomyocytes that lead to cell death. Apoptosis signal-regulating kinase 1 is a key signaling molecule for cardiomyocyte death.

METHODS

We generated recombinant adeno-associated virus (rAAV) expressing an N-terminal truncated form of the dominant-negative mutant of ASK1 (ASKdeltaN(KR)). TO-2 hamsters were subjected to an in vivo rAAV transcoronary transfer.

RESULTS

ASKdeltaN(KR) retained its dominant-negative activity in vitro. The rAAV expressing ASKdeltaN(KR) treatment inhibited ASK1 activation in the hamster hearts and suppressed progression of ventricular remodeling such as chamber dilation, impairment of contractile and relaxation functions, and fibrosis. Inhibition of ASK1 reduced the number of apoptotic cells and selectively attenuated c-Jun NH2-terminal kinase activation. Although the deficiency of delta-sarcoglycan, a genetic defect in the hamster, leads to the degradation of dystrophin, the treatment significantly protected hearts from this degradation, probably by inhibiting calpain activation.

CONCLUSIONS

Apoptosis signal-regulating kinase 1 is involved in the pathogenesis of heart failure progression, mediated through c-Jun NH2-terminal kinase-mediated apoptosis and calpain-dependent dystrophin cleavage, and may be a therapeutic target to treat patients with heart failure.

Current treatment of adult Duchenne muscular dystrophy

Patients with Duchenne muscular dystrophy (DMD) are living longer into adulthood due to a variety of improvements in health care practices. This growing patient population presents new therapeutic challenges. In this article, we review the literature on current treatment of adult DMD as well as our own experience as a multidisciplinary team actively caring for 23 men ages 19-38 years of age. Approximately one quarter of our adult DMD patients have remained on moderate dose corticosteroids. Daily stretching exercises are recommended, particularly of the distal upper extremities. Cardiomyopathy is anticipated, detected, and treated early with afterload reduction. Oxygen saturation monitoring, noninvasive positive pressure ventilation and cough assist devices are routinely used. Other medical issues such as osteoporosis, gastrointestinal and urinary symptoms are addressed. Current and future therapies directed at prolonging the lifespan of those with DMD will result in further increases in this adult population with special needs and concerns. These needs are best addressed in a multidisciplinary clinic.

SGCE missense mutations that cause myoclonus-dystonia syndrome impair ε-sarcoglycan trafficking to the plasma membrane: modulation by ubiquitination and torsinA

Myoclonus-dystonia syndrome (MDS) is a genetically heterogeneous disorder characterized by myoclonic jerks often seen in combination with dystonia and psychiatric co-morbidities and epilepsy. Mutations in the gene encoding epsilon-sarcoglycan (SGCE) have been found in some patients with MDS. SGCE is a maternally imprinted gene with the disease being inherited in an autosomal dominant pattern with reduced penetrance upon maternal transmission. In the central nervous system, epsilon-sarcoglycan is widely expressed in neurons of the cerebral cortex, basal ganglia, hippocampus, cerebellum and the olfactory bulb. epsilon-Sarcoglycan is located at the plasma membrane in neurons, muscle and transfected cells. To determine the effect of MDS-associated mutations on the function of epsilon-sarcoglycan we examined the biosynthesis and trafficking of wild-type and mutant proteins in cultured cells. In contrast to the wild-type protein, disease-associated epsilon-sarcoglycan missense mutations (H36P, H36R and L172R) produce proteins that are undetectable at the cell surface and are retained intracellularly. These mutant proteins become polyubiquitinated and are rapidly degraded by the proteasome. Furthermore, torsinA, that is mutated in DYT1 dystonia, a rare type of primary dystonia, binds to and promotes the degradation of epsilon-sarcoglycan mutants when both proteins are co-expressed. These data demonstrate that some MDS-associated mutations in SGCE impair trafficking of the mutant protein to the plasma membrane and suggest a role for torsinA and the ubiquitin proteasome system in the recognition and processing of misfolded epsilon-sarcoglycan.

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.

Nuclear sequestration of δ-sarcoglycan disrupts the nuclear localization of lamin A/C and emerin in cardiomyocytes

Sarcoglycan is a membrane-associated protein complex found at the plasma membrane of cardiomyocytes and skeletal myofibers. Recessive mutations of delta-sarcoglycan that eliminate expression, and therefore function, lead to cardiomyopathy and muscular dystrophy by producing instability of the plasma membrane. A dominant missense mutation in the gene encoding delta-sarcoglycan was previously shown to associate with dilated cardiomyopathy in humans. To investigate the mechanism of dominantly inherited cardiomyopathy, we generated transgenic mice that express the S151A delta-sarcoglycan mutation in the heart using the alpha-myosin heavy-chain gene promoter. Similar to the human delta-sarcoglycan gene mutation, S151A delta-sarcoglycan transgenic mice developed dilated cardiomyopathy at a young age with enhanced lethality. Instead of placement at the plasma membrane, delta-sarcoglycan was found in the nucleus of S151A delta-sarcoglycan cardiomyocytes. Retention of delta-sarcoglycan in the nucleus was accompanied by partial nuclear sequestration of beta- and gamma-sarcoglycan. Additionally, the nuclear-membrane-associated proteins, lamin A/C and emerin, were mislocalized throughout the nucleoplasm. Therefore, the S151A delta-sarcoglycan gene mutation acts in a dominant negative manner to produce trafficking defects that disrupt nuclear localization of lamin A/C and emerin, thus linking together two common mechanisms of inherited cardiomyopathy.

Molecular cardiology and genetics in the 21st century--a primer

The terminology and technology of molecular genetics and recombinant DNA have become an essential part of academic cardiology and will soon be applied at the bedside. The treatise includes a brief summary of the essentials of the DNA molecule, the more common techniques, and their application to genetics and molecular cardiology. It is written to be understood by physicians, scientists, and paramedical personnel who would not necessarily have a background in molecular biology. Inherent in the DNA molecule are three properties fundamental to all of the diagnostic and therapeutic applications, namely, the ability of DNA to separate into single strands, recombine (annealment or hybridization), and the presence of the negative charge enables DNA fragments to be separated easily by electrophoresis. Genetic linkage analysis of a family with an inherited disease enables one to identify the gene without knowing its protein product. Over 50 diseases in cardiology due to single-gene disorders have been identified and multiple mutations have been detected. The new therapeutic frontier will be stem cells and nuclear transfer. Identification of genes responsible for coronary artery disease made possible by genome-wide single nucleotide polymorphism (SNP) mapping techniques paves the way for personalized medicine.

Differential myolysis of myocardium and skeletal muscle in hamsters with dilated cardiomyopathy: beneficial protective effect of diltiazem

BACKGROUND

Although dilated cardiomyopathic hamsters (TO-2) with mutation of the delta-sarcoglycan gene exhibit histological features of muscular dystrophy, it remains to be elucidated whether both myocardium and skeletal muscle are injured in a similar manner.

METHODS AND RESULTS

The progression of myolysis in both myocardium and skeletal muscle were assessed biochemically and pathologically in TO-2 and F1B control hamsters. Left ventricular (LV) function was assessed by echocardiography and cardiac catheterization. Both the plasma concentration of cardiac troponin T and the plasma activity of alpha-hydroxybutyrate dehydrogenase (HBD) peaked at 8 weeks of age, and thereafter reduced greatly in TO-2 hamsters. Activity of creatine kinase (CK) in TO-2 hamsters was significantly greater than in controls throughout the observation period. Pathological findings of both nuclear chain and central nuclei in skeletal muscles were observed in TO-2 hamsters throughout the observation period, suggesting regeneration. LV dysfunction was first evident at 8 weeks of age and deteriorated thereafter in TO-2 hamsters. Treatment of TO-2 hamsters with diltiazem from 5 to 8 weeks of age could avert the LV functional deterioration and the increment in alpha-HBD activity, but CK activity was unchanged.

CONCLUSIONS

Despite myolysis in skeletal muscle occurring consistently throughout the observation period, cardiac myolysis occurred predominantly in the early phase. These initial cardiac events might involve coronary spasm and/or calcium overload in the myocardium.

Familial inflammatory dilated cardiomyopathy

BACKGROUND

Systematic family screening has recently identified dilated cardiomyopathy as an inherited disorder in up to 30% of cases. Mutations in genes encoding proteins responsible for myocardial architecture have been identified, but additional pathophysiological mechanisms including inflammatory reactions have been proposed.

AIMS

Identification and characterization of familial DCM, where at least one affected family member fulfils the criteria for inflammatory DCM may lead to a better understanding of the aetiology and pathogenesis of (inflammatory) DCM.

METHODS AND RESULTS

Ten families were examined. In six families, clinical characteristics and mode of inheritance were compatible with pure fDCM, fDCM with conduction defect and autosomal recessive fDCM. In four families, (auto-)immune features were diagnosed in affected and non-affected family members.

CONCLUSIONS

Familial DCM with an inflammatory component was identified as a specific subgroup of familial DCM. In most cases, the inflammatory process seems to modify, i.e. aggravate, the "classic, cytoskeletopathic" familial DCM, but in some, especially when taking clinical and genetic aspects into account, inflammatory (auto-)immune features can be addressed as the leading pathogenetic principle. Further elucidation of these families may provide a better insight into pathophysiologic processes and may aid in the development of specific therapeutic strategies.

The limb-girdle muscular dystrophies--diagnostic strategies

The limb-girdle muscular dystrophies are a group of disorders where our understanding of their underlying molecular basis has made huge strides over the past years, revealing great heterogeneity at the clinical and molecular level. The availability of direct protein and/ or gene based approaches to diagnosis means that these disorders can now be precisely defined, and such definition of a precise diagnosis is increasingly allowing directed management for these diseases by the ability to predict specific complications such as those of the cardiac or respiratory systems. An algorithm combining clinical, biochemical and molecular testing is described which will aid precision of diagnosis and direct specific testing towards the cases most likely to benefit. This brings advantages for the patients of today in recognising the specific risks of their disorders, and in the future will be the starting point for specific gene and protein based therapies.

Redefining Heart Failure

In this era of genomics, new technologies and the information that they generate have a wide range of potential applications to heart failure. Though there has not been widespread practical use of genomic information in everyday practice, there are many examples of how this information is beginning to transform the way we look at disease states in terms of diagnosis, prognosis, and treatment. The experience of oncology and other fields helps inform the heart failure field of not only the use of this information in investigating diagnosis, prognosis, and treatment response, but the reciprocal nature of this information. This information can be clinically useful (for instance, predicting treatment response) as well as further drive laboratory investigation (teasing out the biological pathways in non-responders to treatment can be a focus of new drug discovery); this is the essence of translational medicine. We believe that this is a good time to review where new technologies and information they generate can be placed into our classic understanding of heart failure: that is how we might redefine cardiomyopathy given our new information. Here we will review genomic evidence to date and how it can and may be considered in the evaluation and management of cardiomyopathies.

Myocardial Cx43 expression in the cases of sudden death due to dilated cardiomyopathy

PURPOSE

Probing into myocardial connexin (Cx) 43 expression in the cases of sudden death due to dilated cardiomyopathy (DCM) and relationship between Cx43 expression and sudden death.

METHOD

Myocardial Cx43 was detected with immunohistochemical staining in the cases of 11 sudden death caused by DCM and 14 cases of control group who died of violent reasons and other diseases, which were autopsied in our department from 1997 to 2003.

RESULT

Of 11 cases of DCM, there were 10 men and 1 woman with ranging in age from 7 to 49 years old (x (37.8) years old for 9 adult cases). Of 14 cases in the control group, there were 10 men and 4 women with ranging in age from 11 to 53 years old (x (29.9) years old for 11 adult cases). Myocardial Cx43 expression was obviously decreased in DCM group. Positive dyeing spots were different in size, distribution, color and disparity, some of them were distributed in the form of particle. Obvious change had not been observed in the cases of control group or with only slight changes in coloring degree and expressive area. The quantitative data showed that there was significant difference between two groups (p=0.0075) about Cx43 expressive area, but there was no difference between the left and right ventricles (p>0.05) in each group itself. And there was not difference between the two groups about average optical density of expression.

CONCLUSION

Myocardial Cx43 expression is obviously reduced in the patients with DCM who die suddenly. The alteration of quantity and distribution of myocardial Cx43 expression is probably related to sudden death of the patients with DCM.

Molecular genetics of sudden cardiac death in small animals - a review

Sudden cardiac death in small animals is uncommon but often occurs due to cardiac conduction defects or myocardial diseases. Primary cardiac conduction defects are mainly caused by mutations in genes involved in impulse conduction processes (e.g., gap-junction genes and transcription factors) or repolarisation processes (e.g., ion-channel genes), whereas primary cardiomyopathies are mainly caused by defective force generation or force transmission due to gene mutations in either sarcomeric or cytoskeleton proteins. Although over 50 genes have been identified in humans directly or indirectly related to sudden cardiac death, no genetic aetiologies have been identified in small animals. Sudden cardiac deaths have been also reported in German Shepherds and Boxers. A better understanding of molecular genetic aetiologies for sudden cardiac death will be required for future study toward unveiling aetiology in sudden cardiac death in small animals.

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.

Inhibition of protein phosphatase 1 by inhibitor-2 gene delivery ameliorates heart failure progression in genetic cardiomyopathy

The type 1 protein phosphatase (PP1) has been reported to be overactivated in the failing heart, leading to a depression in cardiac function. We investigated whether in vivo PP1 inhibition by myocardial gene transfer of inhibitor-2 (INH-2), an endogenous PP1 inhibitor, alleviates heart failure (HF) progression in the cardiomyopathic (CM) hamster, a well-established HF model. Adenoviral INH-2 gene delivery improved % fractional shortening of the left ventricle (LV) accompanied by reduced chamber size at 1 wk. In vivo myocardial INH-2 gene delivery induced an increase in cytosolic PP1 catalytic subunit alpha (PP1Calpha) without inducing the corresponding increase in cytosolic PP1 activity. On the other hand, INH-2 delivery induced a decrease in microsomal PP1Calpha, resulting in a preferential decrease in microsomal PP1 activity, thereby increasing in phospholamban phosphorylation at Ser16. INH-2 gene transfer alleviated brain natriuretic peptide expression, presumably reflecting improved cardiac function. Moreover, adeno-associated virus-mediated INH-2 gene delivery significantly extended the survival time for 3 mo. These results indicate that increased PP1 activity is an exacerbating factor during progression of genetic cardiomyopathy and modulation of PP1 activity by INH-2 provides a potential new treatment for HF without activating protein kinase A signaling in cardiomyocytes.

Delta-sarcoglycan is necessary for early heart and muscle development in zebrafish

Delta-sarcoglycan, one member of the sarcoglycan complex, is a very conservative muscle-specific protein exclusively expressed in the skeletal and cardiac muscles of vertebrates. Mutations in sarcoglycans are known to be involved in limb-girdle muscular dystrophy (LGMD) and dilated cardiomyopathy (DCM) in humans. To address the role of delta-sarcoglycan gene in zebrafish development, we have studied expression pattern of delta-sarcoglycan in zebrafish embryos and examined the role of delta-sarcoglycan in zebrafish embryonic development by morpholino. Strong expression of delta-sarcoglycan was observed in various muscles including those of the segment, heart, eye, jaw, pectoral fin, branchial arches, and swim bladder in zebrafish embryo. Delta-sarcoglycan was also expressed in midbrain and retina. Knockdown of delta-sarcoglycan resulted in severe abnormality in both the cardiac and skeletal muscles. Some severe ones displayed serious morphological abnormality such as hypoplastic head, linear heart, very weak heartbeats, and runtish trunk, all dead within 5 dpf. Whole-mount in situ hybridization analysis showed that adaxial cells and muscle pioneers were affected in delta-sarcoglycan knockdown embryos. In addition, absence of delta-sarcoglycan protein severely delayed the cardiac development and influenced the differentiation of cardiac muscle, and the cardiac left-right asymmetry was dramatically changed in morpholino-treated embryos. These data together suggest that delta-sarcoglycan plays an important role in early heart and muscle development.

Autophagic cardiomyocyte death in cardiomyopathic hamsters and its prevention by granulocyte colony-stimulating factor

In UM-X7.1 hamster model of human dilated cardiomyopathy, heart failure progressively develops and causes 50% mortality by 30 weeks of age. Through ultrastructural analysis, we found that many cardiomyocytes of this model contain typical autophagic vacuoles including degraded mitochondria, glycogen granules, and myelin-like figures. In addition, ubiquitin, cathepsin D, and Rab7 were overexpressed as determined by immunoassays. Importantly, most cardiomyocytes with leaky plasma membranes were positive for cathepsin D, suggesting a direct link between autophagic degeneration and cell death. Meanwhile, cardiomyocyte apoptosis appeared insignificant. Granulocyte colony-stimulating factor (10 microg/kg/day), injected 5 days/week from 15 to 30 weeks of age, improved survival among 30-week-old hamsters (100% versus 53% in the untreated hamsters, P < 0.0001); ventricular function and remodeling, increased cardiomyocyte size, and reduced myocardial fibrosis followed by a dramatic reduction in the autophagic findings were also seen. Granulocyte colony-stimulating factor also down-regulated tumor necrosis factor-alpha and increased activities of Akt signal transducer and activator of transcription-3, and matrix metalloproteinases. However, there was no clear evidence of transdifferentiation from bone marrow cells into cardiomyocytes. In conclusion, autophagic death is important for cardiomyocyte loss in the cardiomyopathic hamster, and the beneficial effect of granulocyte colony-stimulating factor acts mainly via an anti-autophagic mechanism rather than anti-apo-ptosis or regeneration.

Alpha B-crystallin mutation in dilated cardiomyopathy

Mutations in genes for sarcomeric proteins such as titin/connectin are known to cause dilated cardiomyopathy (DCM). However, disease-causing mutations can be identified only in a small proportion of the patients even in the familial cases, suggesting that there remains yet unidentified disease-causing gene(s) for DCM. To explore the novel disease gene for DCM, we examined CRYAB encoding alphaB-crystallin for mutation in the patients with DCM, since alphaB-crystallin was recently reported to associate with the heart-specific N2B domain and adjacent I26/I27 domain of titin/connectin, and we previously reported a N2B mutation, Gln4053ter, in DCM. A missense mutation of CRYAB, Arg157His, was found in a familial DCM patient and the mutation affected the evolutionary conserved amino acid residue among alpha-crystallins. Functional analysis revealed that the mutation decreased the binding to titin/connectin heart-specific N2B domain without affecting distribution of the mutant crystallin protein in cardiomyocytes. In contrast, another CRYAB mutation, Arg120Gly, reported in desmin-related myopathy decreased the binding to both N2B and striated muscle-specific I26/27 domains and showed intracellular aggregates of the mutant protein. These observations suggest that the Arg157His mutation may be involved in the pathogenesis of DCM via impaired accommodation to the heart-specific N2B domain of titin/connectin and its disease-causing mechanism is different from the mutation found in desmin-related myopathy.

Functional analysis of titin/connectin N2-B mutations found in cardiomyopathy

Hypertrophic cardiomyopathy and dilated cardiomyopathy are two major clinical phenotypes of "idiopathic" cardiomyopathy. Recent molecular genetic analyses have now revealed that "idiopathic" cardiomyopathy is caused by mutations in genes for sarcomere components. We have recently reported several mutations in titin/connectin gene found in patients with hypertrophic cardiomyopathy or dilated cardiomyopathy. A hypertrophic cardiomyopathy-associated titin/connectin mutation (Arg740Leu) was found to increase the binding to actinin, while other dilated cardiomyopathy-associated titin/connectin mutations (Ala743Val and Val54Met) decreased the binding to actinin and Tcap/telethonin, respectively. We also reported several other mutations in the N2-B region of titin/connectin found in hypertrophic cardiomyopathy and dilated cardiomyopathy. Since the N2-B region expresses only in the heart, it was speculated that functional alterations due to the mutations cause cardiomyopathies. In this study, we investigated the functional changes caused by the N2-B region mutations by using yeast-two-hybrid assays. It was revealed that a hypertrophic cardiomyopathy-associated mutation (Ser3799Tyr) increased the binding to FHL2 protein, whereas a dilated cardiomyopathy-associated mutation (Gln4053ter) decreased the binding. In addition, another TTN mutation (Arg25618Gln) at the is2 region was found in familial DCM. Because FHL2 protein is known to tether metabolic enzymes to N2-B and is2 regions of titin/connectin, these observations suggest that altered recruitment of metabolic enzymes to the sarcomere may play a role in the pathogenesis of cardiomyopathies.

The canine sarcoglycan delta gene: BAC clone contig assembly, chromosome assignment and interrogation as a candidate gene for dilated cardiomyopathy in Dobermann dogs

Dilated cardiomyopathy (DCM) is a common disease of the myocardium recognized in human, dog and experimental animals. Genetic factors are responsible for a large proportion of cases in humans, and 17 genes with DCM causing mutations have been identified. The genetic origin of DCM in the Dobermann dogs has been suggested, but no disease genes have been identified to date. In this paper, we describe the characterization and evaluation of the canine sarcoglycan delta (SGCD), a gene implicated in DCM in human and hamster. Bacterial artificial chromosomes (BACs) containing the canine SGCD gene were isolated with probes for exon 3 and exons 4-8 and were characterized by Southern blot analysis. BAC end sequences were obtained for four BACs. Three of the BACs overlapped and could be ordered relative to each other and the end sequences of all four BACs could be anchored on the preliminary assembly of the dog genome sequence (www. ensembl.org). One of the BACs of the partial contig was localized by fluorescent in situ hybridization to canine chromosome 4q22, in agreement with the dog genome sequence. Two highly informative polymorphic microsatellite markers in intron 7 of the SGCD gene were identified. In 25 DCM-affected and 13 non DCM-affected dogs seven different haplotypes could be distinguished. However, no association between any of the SGCD variants and the disease locus was apparent.

Drosophila as a model for the identification of genes causing adult human heart disease

Drosophila melanogaster genetics provides the advantage of molecularly defined P-element insertions and deletions that span the entire genome. Although Drosophila has been extensively used as a model system to study heart development, it has not been used to dissect the genetics of adult human heart disease because of an inability to phenotype the adult fly heart in vivo. Here we report the development of a strategy to measure cardiac function in awake adult Drosophila that opens the field of Drosophila genetics to the study of human dilated cardiomyopathies. Through the application of optical coherence tomography, we accurately distinguish between normal and abnormal cardiac function based on measurements of internal cardiac chamber dimensions in vivo. Normal Drosophila have a fractional shortening of 87 +/- 4%, whereas cardiomyopathic flies that contain a mutation in troponin I or tropomyosin show severe impairment of systolic function. To determine whether the fly can be used as a model system to recapitulate human dilated cardiomyopathy, we generated transgenic Drosophila with inducible cardiac expression of a mutant of human delta-sarcoglycan (deltasg(S151A)), which has previously been associated with familial dilated cardiomyopathy. Compared to transgenic flies overexpressing wild-type deltasg, or the standard laboratory strain w(1118), Drosophila expressing deltasg(S151A) developed marked impairment of systolic function and significantly enlarged cardiac chambers. These data illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and the applicability of the vast genetic resources available in Drosophila to systematically study the genetic mechanisms responsible for human cardiac disease.

Gene therapy prevents disruption of dystrophin-related proteins in a model of hereditary dilated cardiomyopathy in hamsters

BACKGROUND

The TO-2 hamster is an animal model of dilated cardiomyopathy (DCM). It has genetic and clinical features in common with humans who carry the gene deletion or mutation of the delta-sarcoglycan (SG) gene, a component in dystrophin-related proteins (DRP). DRP stabilise the sarcolemma during cardiac contraction. We performed in vivo gene therapy of the TO-2 hamster, whose heart is defective in all four SG proteins, to determine its potential as a model for therapy for DCM. In addition to the hereditary origin, heart failure is aggravated by treatment with catecholamines and ameliorated by the administration of some kinds of beta-antagonist both in humans and in TO-2 hamsters.

METHODS

Gene therapy for DCM was achieved by supplementing the delta-SG gene with rAAV vector and intramurally delivering rAAV-delta-SG into the cardiac apex and left ventricle.

RESULTS

This treatment resulted in: (i) a sustained and non-pathogenic expression of both the transcript and transgene of delta-SG and all other SG proteins; (ii) improvement to both morphological and physiological deterioration; and (iii) rescued prognosis compared with untreated TO-2 hamsters, and TO-2 hamsters transfected with reporter gene alone. Another acute heart-failure model was prepared by high-dose isoproterenol treatment in Wistar rats, which resulted in: (i) translocation of dystrophin, but not delta-SG, from the cardiac sarcolemma to the myoplasm; and (ii) fragmentation of dystrophin, probably due to the activation of endogenous protease(s) or proteasome(s) that contributed to muscular dystrophy-like degeneration occurring specifically in cardiomyocytes.

CONCLUSIONS

Both the TO-2 hamster and the isoproterenol-treated Wistar rat models commonly experience disruption of dystrophin or DRP. Targeting the responsible gene with the use of a potent vector may provide a novel strategy for the treatment of advanced heart failure.

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.

Primary Prophylaxis of Sudden Death in Hypertrophic Cardiomyopathy, Arrhythmogenic Right Ventricular Cardiomyopathy, and Dilated Cardiomyopathy

We present an evidence-based overview of primary prevention of sudden cardiac death. Several recent studies have provided important data regarding pharmacologic and device-based therapy for patients with conditions that confer high risk for sudden death. A rational approach to these therapies, with emphasis on implanted cardiovertor defibrillators, is discussed.

Gene mutations in adult Japanese patients with dilated cardiomyopathy

BACKGROUND

Some patients with dilated cardiomyopathy (DCM) have mutations of the genes that encode sarcomeric or cytoskeletal proteins of cardiomyocytes, but the prevalence of these mutations in Japan remains unclear.

METHODS AND RESULTS

A group of 99 unrelated adult patients with DCM (familial n=27, sporadic n=72) were screened for the following genes: cardiac beta-myosin heavy chain, cardiac myosin-binding protein C (MYBPC3), regulatory and essential myosin light chains, alpha cardiac actin, alpha tropomyosin, cardiac troponin T, cardiac troponin I, cardiac troponin C, dystrophin, and lamin A/C. A mutation (R820Q) in MYBPC3 was found in an aged patient. In addition, dystrophin mutations were identified in 3 male patients (2 with exon 45-48 deletion and 1 with exon 48-52 deletion). The prevalence of dystrophin mutations in male patients with DCM was 4.4% (3 of 68). No mutations involving amino acid changes were identified in the other genes.

CONCLUSIONS

Although cases of adult patients with DCM caused by mutations of the genes encoding sarcomeric or cytoskeletal proteins of cardiomyocytes are infrequent in Japan, it may be advisable to screen older DCM patients for MYBPC3 mutations, and male patients with familial DCM for dystrophin mutations.

[Review: genetics of familial dilated cardiomyopathy]

Dilated cardiomyopathy is the most frequent cardiomyopathy. Twenty to 35% of dilated cardiomyopathies are familial. The transmission of the disease is most frequently dominant autosomic. Dilated cardiomyopathy is genetically heterogeneous. Hence, mutations have been identified on 14 genes, and 9 loci have been associated to familial dilated cardiomyopathy. The incriminated mechanisms in the pathogeny of dilated cardiomyopathy include mutations on proteins of the sarcomere, the cytosqueletton, the nuclear membrane or involved in calcium signaling. This review indicates the genes and proteins implicated in the pathogeny of familial dilated cardiomyopathy, and their potential clinical effects.