Brief report: deficiency of a dystrophin-associated glycoprotein (adhalin) in a patient with muscular dystrophy and cardiomyopathy

Analysis of Cardiac Metabolic Remodeling in Heart Failure Using Nuclear Medicine and Its Application: Japanese Society of Nuclear Cardiology Award

Heart failure is associated with a significant change in the energy metabolism of the heart. We aimed to elucidate the altered energetics during the progression of heart failure. We used radioactive metabolic tracers to assess the substrate uptake. In a rat model of heart failure, the glucose uptake increased significantly at the stage of left ventricular hypertrophy, whereas the uptake of fatty acids decreased at the stage of heart failure, with decreased energy reserve during the transition of cardiac hypertrophy to failure. Metabolic modulator which enhances glucose oxidation ameliorated the decrease in cardiac function. We also validated the close correlation with mitochondrial membrane potentials and ^99mtechnetium sestamibi (^99mTc-MIBI) in vivo and at the organ level. The retention of ^99mTc-MIBI signals was correlated with the severity of heart failure. Nuclear medicine is a powerful tool to understand the mechanism of cardiac remodeling in heart failure.

Cardiac involvement in Dutch patients with sarcoglycanopathy: a cross-sectional cohort and follow-up study

INTRODUCTION

The aim of this study is to describe the frequency, nature, severity, and progression of cardiac abnormalities in a cohort of Dutch sarcoglycanopathy patients.

METHODS

In this cross-sectional cohort study, patients were interviewed using a standardized questionnaire and assigned a functional score. Electrocardiography (ECG), echocardiography, and 24-h ECG were performed.

RESULTS

Twenty-four patients with sarcoglycanopathy had a median age of 25 years (range, 8-59 years). Beta blockers were used by 13%, and 17% used angiotensin-converting enzyme inhibitors. ECG abnormalities were present in 5 (21%), and 4 (17%) fulfilled the criteria for dilated cardiomyopathy (DCM). There were no significant differences in median age or severity of disease between patients with or without DCM. Eleven patients were examined earlier. Median follow-up time was 10 years. Two of the 11 patients (18%) developed DCM during follow-up.

CONCLUSIONS

Seventeen percent of the patients with sarcoglycanopathy were found to have dilated cardiomyopathy. We recommend biannual cardiac monitoring, including ECG and echocardiography.

Occult left ventricular dysfunction diagnosed by myocardial performance index in patients with limb girdle muscle dystrophy: A case control study

The myocardial performance index (MPI) was assessed in 30 patients with limb girdle muscle dystrophy (LGMD) with a normal left ventricular ejection fraction (greater than 50%), as well as in 30 age- and sex-matched healthy adults with a left ventricular ejection fraction greater than 50%. MPIs derived by pulsed-wave Doppler and tissue Doppler were also compared. The MPI was 0.37±0.09 in the LGMD patients and 0.29±0.09 in the control group (P=0.003). These data show that patients with LGMD have occult cardiac dysfunction as evidenced by a higher MPI than the controls. There was good agreement between the MPIs measured by pulsed-wave Doppler and tissue Doppler methods in these patients.

A novel paradigm for therapeutic basis of advanced heart failure--assessment by gene therapy

The precise mechanism(s) of the progression of advanced heart failure (HF) should be determined to establish strategies for its treatment or prevention. Based on pathological, molecular, and physiological findings in 3 animal models and human cases, we propose a novel scheme that a vicious cycle formed by increased sarcolemma (SL) permeability, preferential activation of calpain over calpastatin, and translocation and cleavage of dystrophin (Dys) commonly lead to advanced HF. The aim of this article was to assess our recent paradigm that disruption of myocardial Dys is a final common pathway to advanced HF, irrespective of its hereditary or acquired origin, but not intended to provide a comprehensive overview of the various factors that may be involved in the course of HF in different clinical settings. In addition, each component of Dys-associated proteins (DAP) was heterogeneously degraded in vivo and in vitro, i.e. Dys and alpha-sarcoglycan (SG) were markedly destroyed using isolated calpain 2, while delta-SG was not degraded at all. The up-regulation of calpain 2 was confirmed through previously published data that remain insufficient for precise evaluation, supporting our new scheme that the activation of calpain(s) is involved in the steady process of Dys cleavage. In addition, somatic gene therapy is discussed as a potential option to ameliorate the physiological/metabolic indices and to improve the prognosis.

A novel scheme of dystrophin disruption for the progression of advanced heart failure

The precise mechanism of the progression of advanced heart failure is unknown. We assessed a new scheme in two heart failure models: (I) congenital dilated cardiomyopathy (DCM) in TO-2 strain hamsters lacking delta-sarcoglycan (SG) gene and (II) administration of a high-dose of isoproterenol, as an acute heart failure in normal rats. In TO-2 hamsters, we followed the time course of the histological, physiological and metabolic the progressions of heart failure to the end stage. Dystrophin localization detected by immunostaining age-dependently to the myoplasm and the in situ sarcolemma fragility evaluated by Evans blue entry was increased in the same cardiomyocytes. Western blotting revealed a limited cleavage of the dystrophin protein at the rod domain, strongly suggesting a contribution of endogenous protease(s). We found a remarkable up-regulation of the amount of calpain-1 and -2, and no change of their counterpart, calpastatin. After supplementing TO-2 hearts with the normal delta-SG gene in vivo, these pathological alterations and the animals' survival improved. Furthermore, dystrophin but not delta-SG was disrupted by a high dose of isoproterenol, translocated from the sarcolemma to the myoplasm and fragmented. These results of heart failure, irrespective of the hereditary or acquired origin, indicate a vicious cycle formed by the increased sarcolemma permeability, preferential activation of calpain over calpastatin, and translocation and cleavage of dystrophin would commonly lead to advanced heart failure.

A new form of autosomal dominant limb-girdle muscular dystrophy (LGMD1G) with progressive fingers and toes flexion limitation maps to chromosome 4p21

Limb-girdle muscular dystrophy (LGMD) is a genetic disorder characterized by progressive weakness of pelvic and scapular girdles and great clinical variability. It is a highly heterogeneous disease with 16 identified loci: six of them autosomal dominant (AD) (LGMD1) and 10 autosomal recessive (AR) (LGMD2). The responsible genes are known for three of the AD-LGMD and for all 10 AR-LGMD. Linkage analysis excluded these 16 loci in a Brazilian-Caucasian family with 12 patients affected by AD late-onset LGMD associated with progressive fingers and toes flexion limitation. Biceps muscle biopsy from one of the patients showed a predominantly myopathic histopathological pattern, associated with rimmed vacuoles. A genomewide scan was performed which mapped a new locus for this disorder at 4p21 with a maximum two-point lod score of 6.62 for marker D4S2964. Flanking markers place this locus between D4S2947 and D4S2409, within an interval of 9 cM. We propose to classify this AD form of LGMD as LGMD1G.

Dystrophin disruption in enterovirus-induced myocarditis and dilated cardiomyopathy: from bench to bedside

Genetic defects of the dystrophin-glycoprotein complex (DGC) cause hereditary dilated cardiomyopathy. Enteroviruses can also cause cardiomyopathy and we have previously described a mechanism involved in enterovirus-induced dilated cardiomyopathy: The enteroviral protease 2A directly cleaves dystrophin in the hinge 3 region, leading to functional dystrophin impairment. During infection of mice with coxsackievirus B3, the DGC in the heart is disrupted and the sarcolemmal integrity is lost in virus-infected cardiomyocytes. Additionally, dystrophin deficiency markedly increases enterovirus-induced cardiomyopathy in vivo, suggesting a pathogenetic role of the dystrophin cleavage in enterovirus-induced cardiomyopathy. Here, we extend these experimental findings to a patient with dilated cardiomyopathy due to a coxsackievirus B2 myocarditis. Endomyocardial biopsy specimens showed an inflammatory infiltrate and myocytolysis. Immunostaining for the enteroviral capsid antigen VP1 revealed virus-infected cardiomyocytes. Focal areas of cardiomyocytes displayed a loss of the sarcolemmal staining pattern for dystrophin and beta-sarcoglycan identical to previous findings in virus-infected mouse hearts. In vitro, coxsackievirus B2 protease 2A cleaved human dystrophin. These findings demonstrate that in human coxsackievirus B myocarditis a focal disruption of the DGC can principally occur and may contribute to the pathogenesis of human enterovirus-induced dilated cardiomyopathy.

[A new paradigm for the progression of advanced heart failure]

To clarify the precise mechanism for the progression of advanced heart failure (AdHF), we assessed the scheme in two HF models, using (I) TO-2 strain hamsters sharing common genetic and clinical features to human families with the delta-sarcoglycan (SG) gene mutation and (II) administration of a high-dose (HD) of isoproterenol (Isp) to normal rats. Delta-SG is a component in dystrophin (Dys)-related proteins that stabilize the sarcolemma (SL) during repeated heart beats. In TO-2, we followed time course of hemodynamics, immunostaining and Western blotting of Dys and in situ SL permeability by Evans blue uptake with or without the gene therapy. Dys was age-dependently translocated from the SL to myoplasm (MP) where the SL instability accompanied the fragmentation of Dys. By gene therapy to supplement the normal delta-SG gene in hearts in vivo, we found that Dys translocation was selectively improved in cardiomyocytes expressing the delta-SG transgene, where the SL fragility was ameliorated. Most importantly, the survival period of the animals was prolonged. Furthermore, Dys but not delta-SG was also time-dependently shifted with a HD of Isp from the SL to MP and fragmented, while delta-SG was preserved intact. We present a novel paradigm that disruption of Dys, but not delta-SG per se, leads to AdHF irrespective of hereditary or acquired origin.

Specific assembly pathway of sarcoglycans is dependent on beta- and delta-sarcoglycan

Mutations in sarcoglycans (SG) have been reported to cause autosomal-recessive limb-girdle muscular dystrophy (LGMD) and dilated cardiomyopathy. In skeletal and cardiac muscle, sarcoglycans exist as a complex of four transmembrane proteins (alpha-, beta-, gamma-, and delta-SG). In this study, the assembly of the sarcoglycan complex was examined in a heterologous expression system. Our results demonstrated that the assembly process occurs as a discrete stepwise process. We found that beta-SG appears to play an initiating role and its association with delta-SG is essential for the proper localization of the sarcoglycan complex to the cell membrane. The incorporation of alpha-SG into the sarcoglycan complex occurs at the final stage by interaction with gamma-SG. These findings were supported by chemical cross-linking of endogenous sarcoglycans in cultured myotubes. We have also provided evidence that glycosylation-defective mutations in beta-SG and a common mutation in gamma-SG (C283Y) disrupt sarcoglycan-complex formation. Our proposed model for the assembly and structure of sarcoglycans should generate important insight into their function in muscle as well as their role in muscular dystrophies and cardiomyopathies.

Combined study with FDG PET and Tl SPECT in patients with idiopathic dilated cardiomyopathy

This study aimed to determine whether combined examinations of myocardial 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) and stress-redistribution 201Tl single-photon emission computed tomography (Tl SPECT) were useful in clarifying myocardial ischaemia and evaluating the prognosis in patients with idiopathic dilated cardiomyopathy (IDCM). Twenty-two patients with IDCM underwent echocardiography, cardiac catheterization, FDG PET, and Tl SPECT. In scintigraphic analysis, the total defect score (TDS) was semiquantitatively determined as the sum of scores of the 17 left ventricular (LV) segments with a 5-point scale (0 as normal to 4 as absent). Patients were classified according to the scintigraphic findings as follows: eight patients with small defects on Tl and FDG (TDS < or = 20) (group I), eight patients with small defects on FDG (TDS < or = 20) with FDG uptake increased relative to Tl or 'mismatch' (group II), and six patients with large defects on FDG and Tl (TDS >20) (group III). Eleven patients (50%) showed reversible defects on Tl and all showed preserved FDG uptake. The patients in group III had significantly lower LV ejection fraction (LVEF) (P<0.05, respectively) and a poorer prognosis as shown by the Kaplan-Meier event-free curve compared with those in groups I and II (P<0.01, respectively). Although patients in group II had significantly greater TDS on Tl compared with those in group I (P<0.01), no significant differences in LVEF and prognosis were found between patients in groups I and II. In multivariate analysis, a TDS on FDG revealed an independent predictor of subsequent cardiac events. In conclusion, such mismatched areas can be assumed to consist of impaired but viable myocardium, and may be associated with ischaemia of the microvasculature. Impaired myocardial glucose metabolism is a more powerful predictor of future cardiac events than perfusion abnormality in patients with IDCM.

LGMD2E patients risk developing dilated cardiomyopathy

Sarcoglycan gene mutations cause various limb-girdle muscular dystrophies. The sarcoglycans are expressed both in skeletal and cardiac muscle but, surprisingly, so far only a few sarcoglycanopathy patients have had documented cardiomyopathy. We studied six patients with beta-sarcoglycanopathy. Immunohistochemical and immunoblot analysis performed on skeletal muscle biopsies from five patients, showed the loss of all sarcoglycans in three cases and marked reduction in two patients. Non-invasive cardiac examinations revealed that three patients had cardiac involvement: one had a severe Duchenne-like dystrophy, lethal dilated cardiomyopathy, and shared the same mutation reported in another cardiomyopathic patient; the other two patients had limb-girdle dystrophy and moderate cardiac involvement (one of them has a novel gene mutation). Given the age profile of the patients studied, the 50% cardiac involvement found in our LGMD2E patients is likely to be a conservative estimate. Careful cardiac monitoring should be carried out in beta-sarcoglycanopathy patients who are at high risk of developing cardiomyopathy.

Molecular diagnosis of myocardial disease

Myocardial disorders are major causes of morbidity and mortality, including heart failure, sudden death and the need for heart transplantation. The two most common forms of myocardial disorders, dilated cardiomyopathy and hypertrophic cardiomyopathy are paradigms of left ventricular systolic dysfunction and diastolic dysfunction. The genetics of these disorders are increasingly understood with the sarcomere playing a central role in the development of HCM and the link between sarcomere and sarcolemma being key to the development of DCM. In this review, the genetics of the myocardial diseases will be described.

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Cardiomyopathy is independent of skeletal muscle disease in muscular dystrophy

Dystrophin and its associated proteins, the sarcoglycans, are normally expressed in heart and skeletal muscle. Mutations that alter the expression of these membrane-associated proteins lead to muscular dystrophy (MD) and cardiomyopathy in humans. Because of the timing and nature of the accompanying cardiomyopathy, it has been suggested that cardiomyopathy develops as a secondary consequence of skeletal muscle dysfunction in the muscular dystrophies. To determine whether skeletal muscle dystrophy contributes to the development of sarcoglycan-mediated cardiomyopathy, we used mice lacking gamma-sarcoglycan and inserted a transgene that "rescued" gamma-sarcoglycan expression only in skeletal muscle. Gamma-sarcoglycan was expressed in skeletal muscle under the control of the skeletal muscle-specific myosin light chain 1/3 promoter. Gamma-sarcoglycan-null mice expressing this transgene fully restore gamma-sarcoglycan expression. Furthermore, the transgene-rescued mice lack the focal necrosis and membrane permeability defects that are a hallmark of MD. Despite correction of the skeletal muscle disease, focal degeneration and membrane permeability abnormalities persisted in cardiac muscle, and notably persisted in the right ventricle. Therefore, heart and skeletal muscle defects are independent processes in sarcoglycan-mediated muscular dystrophies and, as such, therapy should target both skeletal and cardiac muscle correction to prevent sudden death due to cardiomyopathy in the muscular dystrophies.

Sarcolemmal proteins and the spectrum of limb-girdle muscular dystrophies

Proteins of the sarcolemma are of crucial importance for the pathogenesis of muscular dystrophies. This update focuses on the dystrophin-associated proteins including the dystroglycan and sarcoglycan complexes, caveolin-3, dysferlin, and the extracellular matrix component collagen type VI. The molecular findings are correlated with some of the clinical phenotypes that are part of the limb-girdle muscular dystrophy spectrum, including fukutin-related proteinopathy (LGMD 21), the sarcoglycanopathies (LGMD 2C-F), caveolinopathy (LGMD 1C), dysferlinopathy (LGMD 2B), and finally Bethlem myopathy. Although recent progress has been tremendous, much remains to be learned about the pathophysiological consequences caused by a deficiency of any one of these components.

Immunohistologic evidence of myocardial disease in apparently healthy relatives of patients with dilated cardiomyopathy

OBJECTIVES

This study investigated whether apparently healthy relatives of patients with idiopathic dilated cardiomyopathy (DCM) who have left ventricular enlargement (LVE) have biopsy evidence of underlying myocardial disease.

BACKGROUND

Left ventricular enlargement with normal systolic function is common among asymptomatic relatives of patients with DCM. Although there is circumstantial evidence to suggest that LVE may be a marker of early DCM, its pathophysiologic significance remains uncertain.

METHODS

Over six years, 767 asymptomatic relatives of 183 consecutive patients with DCM were evaluated: 37 (5%) had DCM and 104 (14%) had LVE (left ventricular end-diastolic dimension >112% predicted) with normal systolic function. Right ventricular biopsy was performed in 32 relatives with LVE, 14 patients with symptomatic DCM and 6 control subjects with normal ventricular function undergoing elective coronary artery bypass graft surgery. Histologic and immunohistochemical analyses, including quantitative double immunofluorescence, were performed for leukocyte markers (CD3 and CD68), intercellular adhesion molecule-1 (ICAM-1) and human leukocyte antigen class II antigens (DR and DQ).

RESULTS

Histologic findings consistent with DCM were present in 50% of the patients with DCM, 25% of the relatives with LVE and 0% of the control subjects. The median CD3 count was 2.4/mm(2) in patients with DCM, 4/mm(2) in relatives with LVE and 0 in control subjects (p = 0.04). Using a threshold of >7 cells/mm(2), 21% of patients with DCM and 25% of relatives with LVE were CD3-positive (p = 0.01). Quantitative analysis demonstrated DR expression on 55.8+/-22.8%, 63.5+/-18.8% and 30.9+/-15.7% of the endothelial surface in patients with DCM, relatives and control subjects, respectively (p = 0.003). Corresponding values for ICAM expression were 35.6+/-15.1%, 36.7+/-14.5% and 17.3+/-7.9% (p = 0.013). When combining inflammatory and histologic changes, 28 (86%) of LVE, 14 (100%) of DCM and no control biopsies were abnormal (p < 0.001).

CONCLUSIONS

Most asymptomatic relatives of patients with DCM with LVE have histopathologic and immunopathologic findings similar to those of patients with established disease. Clinical identification and follow-up of such individuals are warranted to prevent presentation with advanced DCM and to enable assessment of interventions aimed at attenuating disease progression.

Evaluation of cardiac and respiratory involvement in sarcoglycanopathies

Sarcoglycanopathies constitute a subgroup of limb-girdle recessive muscular dystrophies due to defects in sarcoglycan complex that comprises five distinct transmembrane proteins called alpha-, beta-, gamma-, delta-and epsilon-sarcoglycans. As it is well known that sarcoglycans are expressed both in heart and in skeletal muscles and a complete deficiency in delta-sarcoglycan is the cause of the Syrian hamster BIO.14 cardiomyopathy, we studied cardiac and respiratory involvement in 20 patients with sarcoglycanopathies by clinical, electrocardiographic, echocardiographic, scintigraphic and spirometric assessments. A normal heart function was found in 31.3% of all patients; a preclinical cardiomyopathy in 43.7%; an arrhythmogenic cardiomyopathy in 6.3% and initial signs of dilated cardiomyopathy in 18.7%. In one patient the data were examined retrospectively. No correlation was found between cardiac and skeletal muscle involvement. With reference to the type of sarcoglycanopathy, signs of hypoxic myocardial damage occurred in beta-, gamma- and delta-sarcoglycanopathies, while initial signs of a dilated cardiomyopathy in gamma- and delta-sarcoglycanopathies were found. A normal respiratory function was observed in 23.5% of all patients, a mild impairment in 35.4%, a moderate impairment in 29.4%, and a severe impairment in 11.7%.

Evaluation of the cardiac actin gene in Doberman Pinschers with dilated cardiomyopathy

OBJECTIVE

To evaluate the coding region of the cardiac actin gene in Doberman Pinschers with dilated cardiomyopathy (DCM) for mutations that could be responsible for the development of the condition

ANIMALS

28 dogs (16 Doberman Pinschers with DCM and 12 mixed-breed control dogs).

PROCEDURE

Ten milliliters of blood was collected from each dog for DNA extraction. Polymerase chain reaction (PCR) primers were designed to amplify canine exonic regions, using the sequences of exons 2 to 6 of the cardiac actin gene. Single-stranded conformational polymorphism analysis was performed for each exon with all samples. Autoradiographs were analyzed for banding patterns specific to affected dogs. The DNA sequencing was performed on a selected group of affected and control dogs.

RESULTS

Molecular analysis of exons 2 to 6 of the cardiac actin gene did not reveal any differences in base pairs between affected dogs and control dogs selected for DNA evaluation.

CONCLUSIONS

Mutations in exons 5 and 6 of the cardiac actin gene that have been reported in humans with familial DCM do not appear to be the cause of familial DCM in Doberman Pinschers. Additionally, evaluation of exons 2 to 6 for causative mutations did not reveal a cause for inherited DCM in these Doberman Pinschers. Although there is evidence that DCM in Doberman Pinschers is an inherited problem, a molecular basis for this condition remains unresolved. Evaluation of other genes coding for cytoskeletal proteins is warranted.

Use of western immunoblot for evaluation of myocardial dystrophin, alpha-sarcoglycan, and beta-dystroglycan in dogs with idiopathic dilated cardiomyopathy

OBJECTIVE

To evaluate the potential importance of dystrophin, alpha-sarcoglycan (adhalin), and beta-dystroglycan, by use of western blot analysis, in several breeds of dogs with dilated cardiomyopathy.

SAMPLE POPULATION

Myocardial samples obtained from 12 dogs were evaluated, including tissues from 7 dogs affected with dilated cardiomyopathy, 4 control dogs with no identifiable heart disease (positive control), and 1 dog affected with Duchenne muscular dystrophy (negative control for dystrophin). Of the affected dogs, 4 breeds were represented (Doberman Pinscher, Dalmatian, Bullmastiff, and Irish Wolfhound).

PROCEDURE

Western blot analysis was used for evaluation of myocardial samples obtained from dogs with and without dilated cardiomyopathy for the presence of dystrophin and 2 of its associated glycoproteins, alpha-sarcoglycan and beta-dystroglycan.

RESULTS

Detectable differences were not identified between dogs with and without myocardial disease in any of the proteins evaluated.

CONCLUSIONS AND CLINICAL RELEVANCE

Abnormalities in dystrophin, alpha-sarcoglycan, and beta-dystroglycan proteins were not associated with the development of dilated cardiomyopathy in the dogs evaluated in this study. In humans, the development of molecular biological techniques has allowed for the identification of specific causes of dilated cardiomyopathy that were once considered to be idiopathic. The use of similar techniques in veterinary medicine may aid in the identification of the cause of idiopathic dilated cardiomyopathy in dogs, and may offer new avenues for therapeutic intervention.

Dissociation of sarcoglycans and the dystrophin carboxyl terminus from the sarcolemma in enteroviral cardiomyopathy

Enteroviral infection can cause an acquired form of dilated cardiomyopathy. We recently reported that dystrophin is cleaved, functionally impaired, and morphologically disrupted in vitro as well as in vivo during infection with coxsackievirus B3. Genetic dystrophin truncations lead to a marked decrease in dystrophin-associated glycoproteins, whereas expression of only the naturally occurring dystrophin carboxyl terminus, Dp-71, restores the sarcolemmal association of the dystrophin-associated glycoproteins. We sought to determine whether acute cleavage of dystrophin leads to a dissociation of the carboxyl-terminal dystrophin fragment and of the sarcoglycans from the sarcolemma during coxsackievirus B3 infection. We found that in cultured cardiac myocytes and murine hearts infected with coxsackievirus B3, the sarcolemmal localization of the dystrophin carboxyl terminus is lost. The dystrophin-associated glycoproteins alpha-, beta-, gamma-, and delta-sarcoglycan and beta-dystroglycan were markedly decreased in the membrane fraction of infected cells in culture, and the typical sarcolemmal localization for each of these proteins was lost in coxsackievirus-B3-infected cardiomyocytes in vivo. Furthermore, sucrose gradient ultracentrifugation demonstrated that delta-sarcoglycan was physically dissociated from dystrophin within the membrane fraction. In vivo, the sarcolemmal integrity was functionally impaired with Evans blue dye uptake even though there was no generalized disruption of the sarcolemma of infected myocytes evidenced by intact wheat germ agglutinin staining. In analogy to hereditary sarcoglycanopathies, this disintegration of the sarcoglycan complex may, in addition to the dystrophin cleavage, play an important role in the pathogenesis of enterovirus-induced cardiomyopathy. These results imply a potential role for disruption of the sarcoglycans in an acquired form of heart failure.

Cardiomyopathy and heart transplantation in children

Cardiomyopathy is one of the most common causes of death in children with heart disease. Increasingly, dilated cardiomyopathy is recognized to be familial, and specific gene products related to the myocyte cytoskeleton and contractile proteins have been identified. Other associations with metabolic disease, dysmorphic syndromes, and neuromuscular disease are important to establish, particularly in pediatric patients, to guide therapy and patient selection for transplantation. Survival in children with dilated cardiomyopathy depends on accurate diagnosis and aggressive therapy. Patients may respond to conventional treatment for heart failure or may deteriorate, requiring mechanical support. Extracorporeal membrane oxygenation has been used effectively for mechanical support in children until improvement occurs or as a bridge to transplantation. For those who are listed, the mortality rate while waiting for a donor organ averages approximately 20%. Survival after transplantation is good, with an intermediate survival rate of approximately 70%. Late survival remains to be determined in the current cyclosporin era but may in fact be improving. However, increased organ donation or strategies to increase the size of the organ donor pool, such as xenotransplantation, are needed to significantly reduce the rate of mortality while waiting.

Association of nonsense mutation of dystrophin gene with disruption of sarcoglycan complex in X-linked dilated cardiomyopathy

BACKGROUND

In a systematic analysis of inherited forms of cardiomyopathy, we previously identified a family with X-linked dilated cardiomyopathy characterised by a mutation in the rod region of dystrophin. We have now attempted to eludicate the genetic mechanism involved in this disease, as well as the role of dystrophin-associated glycoproteins.

METHODS

The affected dystrophin epitope, which lacks binding to the dys-1 antibody, was analysed by single-strand conformation polymorphism analysis, reverse-transcription PCR, and DNA sequencing. Effects on dystrophin-associated glycoproteins were studied by immunohistochemistry and western blotting.

FINDINGS

A translation-termination mutation (C4148T) in exon 29 of the dystrophin gene was found in all affected family members. Alternative splicing rescued the reading frame and led to the expression of a dystrophin molecule lacking 50 aminoacids both in cardiac and skeletal muscle. Immunohistochemical analysis of the dystrophin-associated proteins revealed a reduction of beta-sarcoglycan and delta-sarcoglycan in the sarcolemma of cardiac muscle but not skeletal muscle tissue. However, western blotting revealed similar amounts of sarcoglycan subunits in both tissues.

INTERPRETATION

The molecular mechanism of this subtype of X-linked cardiomyopathy may be explained by a conformational change in exon-29-deleted dystrophin, resulting in disruption of the sarcoglycan assembly in heart muscle but not skeletal muscle.

Disruption of heart sarcoglycan complex and severe cardiomyopathy caused by beta sarcoglycan mutations

Two young males with limb-girdle muscular dystrophy (LGMD) resulting from sarcoglycan deficiency died at 27 (patient 1) and 18 years (patient 2) of severe cardiomyopathy. Genetic analysis showed that they were compound heterozygotes for mutations in the beta sarcoglycan gene. One of these mutations, an 8 bp duplication in exon 3, was common to both patients. The second mutation in patient 2 was a 4 bp deletion at the splice donor site of intron 2, not reported previously. Patient 2 had more severe heart and skeletal muscle defects with faster deterioration; no sarcoglycans were detected in his skeletal muscle. The second mutation in patient 1, inferred because the unaffected father carries the 8 bp duplication, was not found. In patient 1, both heart and skeletal muscle were analysed and showed reduction of all sarcoglycans in both tissues and incorrect localisation of alpha and gamma sarcoglycans in heart. Therefore mutations in one sarcoglycan gene can disrupt the entire sarcoglycan complex in both skeletal and cardiac muscle. Differing expression patterns of sarcoglycan components in heart and skeletal muscle could be the result of alternatively spliced transcripts in these tissues. By sequencing an alternative transcript, highly expressed in the heart and skeletal muscle of patient 1, we found an 87 bp cryptic exon not previously reported. Although cardiomyopathy can result from mutations in alpha and gamma sarcoglycans, we show for the first time that the condition can also be caused by mutations in the beta sarcoglycan gene. This report therefore expands the phenotype of sarcoglycanopathies and suggests that cardiac function in LGMD patients with defective sarcoglycan expression should be monitored.

Sarcoglycans in muscular dystrophy

Muscular dystrophy is a heterogeneous genetic disease that affects skeletal and cardiac muscle. The genetic defects associated with muscular dystrophy include mutations in dystrophin and its associated glycoproteins, the sarcoglycans. Furthermore, defects in dystrophin have been shown to cause a disruption of the normal expression and localization of the sarcoglycan complex. Thus, abnormalities of sarcoglycan are a common molecular feature in a number of dystrophies. By combining biochemistry, molecular cell biology, and human and mouse genetics, a growing understanding of the sarcoglycan complex is emerging. Sarcoglycan appears to be an important, independent mediator of dystrophic pathology in both skeletal muscle and heart. The absence of sarcoglycan leads to alterations of membrane permeability and apoptosis, two shared features of a number of dystrophies. beta-sarcoglycan and delta-sarcoglycan may form the core of the sarcoglycan subcomplex with alpha- and gamma-sarcoglycan less tightly associated to this core. The relationship of epsilon-sarcoglycan to the dystrophin-glycoprotein complex remains unclear. Animals lacking alpha-, gamma- and delta-sarcoglycan have been described and provide excellent opportunities for further investigation of the function of sarcoglycan. Dystrophin with dystroglycan and laminin may be a mechanical link between the actin cytoskeleton and the extracellular matrix. By positioning itself in close proximity to dystrophin and dystroglycan, sarcoglycan may function to couple mechanical and chemical signals in striated muscle. Sarcoglycan may be an independent signaling or regulatory module whose position in the membrane is determined by dystrophin but whose function is carried out independent of the dystrophin-dystroglycan-laminin axis.

Cardiomyopathy in duchenne, becker, and sarcoglycanopathies: a role for coronary dysfunction?

Dilated cardiomyopathy is a feature of Duchenne and Becker muscular dystrophies and occasionally of sarcoglycanopathies. Its pathogenesis is unknown. Patients with myotonic dystrophy have an impairment of coronary smooth muscle and this could contribute to their cardiomyopathy. We used positron emission tomography (PET) to study myocardial blood flow and coronary vasodilator reserve at baseline and during hyperemia in 7 Duchenne, 8 Becker, and 5 sarcoglycanopathy patients. The study was normal in all Becker patients. In contrast, baseline myocardial blood flow was increased and coronary vasodilator reserve blunted in Duchenne and sarcoglycanopathy patients despite normal hyperemic myocardial blood flow. The reduction of coronary vasodilator reserve was due to an increased baseline myocardial blood flow. In Duchenne dystrophy, but not in sarcoglycanopathies, correction for cardiac workload normalized the coronary vasodilator reserve. In the latter patients, abnormal baseline myocardial blood flow could be due to vascular smooth muscle dysfunction.

Making sense of the limb-girdle muscular dystrophies

The clinical heterogeneity which has long been recognized in the limb-girdle muscular dystrophies (LGMD) has been shown to relate to the involvement of a large number of different genes. At least eight forms of autosomal recessive LGMD and three forms of autosomal dominant disease are now recognized and can be defined by the primary gene or protein involved, or by a genetic localization. These advances have combined the approaches of positional cloning and candidate gene analysis to great effect, with the pivotal role of the dystrophin-associated complex confirmed through the involvement of at least four dystrophin-associated proteins in different subtypes of autosomal recessive LGMD (the sarcoglycanopathies). Two novel mechanisms may have to be postulated to explain the involvement of the calpain 3 and dysferlin genes in other forms of LGMD. Using the diagnostic tools which have become available as a result of this increased understanding, the clinical features of the various subtypes are also becoming clearer, with useful diagnostic and prognostic information at last available to the practising clinician.

Familial dilated cardiomyopathy: evidence for genetic and phenotypic heterogeneity. Heart Muscle Disease Study Group

OBJECTIVES

This study was performed to evaluate the characteristics, mode of inheritance and etiology of familial dilated cardiomyopathy (FDC).

BACKGROUND

A genetic form of disease transmission has been identified in a relevant proportion of patients with dilated cardiomyopathy (DCM). Variable clinical characteristics and patterns of inheritance, and an increased frequency of cardiac antibodies have been reported. An analysis of FDC may improve the understanding of the disease and the management of patients.

METHODS

Of 350 consecutive patients with idiopathic DCM, 281 relatives from 60 families were examined. Family studies included clinical examination, electrocardiography, echocardiography and blood sampling. Of the 60 DCM index patients examined, 39 were attributable to FDC and 21 were due to sporadic DCM. Clinical features, histology, mode of inheritance and autoimmune serology were examined, molecular genetic studies were undertaken and the difference between familial and sporadic forms was analyzed.

RESULTS

Only a younger age (p = 0.0005) and a higher ejection fraction (p = 0.03) could clinically distinguish FDC patients from those with sporadic DCM. However, a number of distinct subtypes of FDC were identified: 1) autosomal dominant, the most frequent form (56%); 2) autosomal recessive (16%), characterized by worse prognosis; 3) X-linked FDC (10%), with different mutations of the dystrophin gene; 4) a novel form of autosomal dominant DCM with subclinical skeletal muscle disease (7.7%); 5) FDC with conduction defects (2.6%), and 6) rare unclassifiable forms (7.7%). The forms with skeletal muscle involvement were characterized by a restrictive filling pattern; the forms with isolated cardiomyopathy had an increased frequency of organ-specific cardiac autoantibodies. Histologic signs of myocarditis were frequent and nonspecific.

CONCLUSIONS

Familial dilated cardiomyopathy is frequent, cannot be predicted on a clinical or morphologic basis and requires family screening for identification. The phenotypic heterogeneity, different patterns of transmission, different frequencies of cardiac autoantibodies and the initial molecular genetic data indicate that multiple genes and pathogenetic mechanisms can lead to FDC.

Heart involvement in muscular dystrophies due to sarcoglycan gene mutations

Mutations in the sarcoglycan genes cause autosomal-recessive muscular dystrophies. Because sarcoglycan genes and their protein products are highly expressed both in skeletal and cardiac muscle, patients with these mutations might be expected to be at risk to develop dilated cardiomyopathy. We therefore studied 13 patients with alpha-, beta-, gamma-sarcoglycan gene mutations by thorough cardiological assessment. Electrocardiographic or echocardiographic abnormalities were observed in about 30% of cases showing a severe course of muscular dystrophy. No correlation was found between the presence of cardiac abnormalities and the type of mutation or sarcoglycan gene involved. The cardiac involvement was never severe, but it may be detected in early stages of the muscle disease. The absence of overt cardiac dysfunction may be due to lower sarcoglycan protein expression in cardiac than skeletal muscle or to less sarcolemmal instability at the myocardial level, possibly related to the different distribution of forces generated by contraction of the myocardium with respect to proximal limb-girdle muscles.

Delineation of genomic deletion in cardiomyopathic hamster

Cardiomyopathic hamster is a representative animal model for autosomal recessive cardiomyopathy. We have previously shown that the transcript of delta-sarcoglycan is missing in the heart of cardiomyopathic hamster due to genomic deletion. Here we define the normal genomic region deleted in cardiomyopathic hamster, which spans about 30 kb interval and includes the two first exons of the delta-sarcoglycan gene. RNA blot analysis using genomic DNA fragments covering the entire deletion as probes failed to detect any transcript other than delta-sarcoglycan in normal hamster heart, suggesting that delta-sarcoglycan is the only transcript defective in the heart of cardiomyopathic hamster.

Enteroviral protease 2A cleaves dystrophin: evidence of cytoskeletal disruption in an acquired cardiomyopathy

Enteroviruses such as Coxsackievirus B3 can cause dilated cardiomyopathy, but the mechanism of this pathology is unknown. Mutations in cytoskeletal proteins such as dystrophin cause hereditary dilated cardiomyopathy, but it is unclear if similar mechanisms underlie acquired forms of heart failure. We demonstrate here that purified Coxsackievirus protease 2A cleaves dystrophin in vitro as predicted by computer analysis. Dystrophin is also cleaved during Coxsackievirus infection of cultured myocytes and in infected mouse hearts, leading to impaired dystrophin function. In vivo, dystrophin and the dystrophin-associated glycoproteins alpha-sarcoglycan and beta-dystroglycan are morphologically disrupted in infected myocytes. We suggest a molecular mechanism through which enteroviral infection contributes to the pathogenesis of acquired forms of dilated cardiomyopathy.

Advances in molecular genetics of dilated cardiomyopathy. The Heart Muscle Disease Study Group

In clinical surveys, familial dilated cardiomyopathy (FDC) has been demonstrated in 20% to 30% of patients. In these patients, the cause of the disease lies at the DNA level. Molecular genetic studies represent the tools for the understanding of the etiology of FDC and are currently producing relevant advances: 6 different loci have been mapped so far. The only known disease gene is the dystrophin gene causing X-linked dilated cardiomyopathy, but other cytoskeletal proteins, such as adhalin, could be involved. In familial right ventricular cardiomyopathy (or arrhythmogenic right ventricular dysplasia) characterized by isolated or prevalent right ventricular involvement, three further disease loci have been identified.

The sarcoglycan complex in limb-girdle muscular dystrophy

The involvement of the sarcoglycan complex in the pathogenesis of muscular dystrophy is becoming increasingly clear. Sarcoglycan gene mutations lead to four forms of autosomal recessive limb-girdle muscular dystrophy. Recent progress has been made with the identification of novel mutations and their correlations with disease. Through this research, a better understanding the molecular pathogenesis of limb-girdle muscular dystrophy has been gained. Finally, animal models are now being used to study viral-mediated gene transfer for the future treatment of this disease.

Evidence of left ventricular dysfunction in children with merosin-deficient congenital muscular dystrophy

BACKGROUND

Deficiency of the sarcolemmal protein dystrophin has been linked to dilated cardiomyopathy. Some children with congenital muscular dystrophy have a deficiency of the laminin alpha2 chain of merosin, an extracellular matrix protein linked to dystrophin through a group of glycoproteins. It has been shown that deficiency in one of these glycoproteins is responsible for muscular dystrophy and dilated cardiomyopathy. Children with laminin alpha2 deficiency may be at risk for development of cardiomyopathy.

METHODS AND RESULTS

We studied the cardiac function of a cohort of 16 children with congenital muscular dystrophy by using 2-dimensional echocardiography. The expression of the laminin alpha2 of merosin in the patients was determined on a skin or muscle biopsy. Two of 6 merosin-deficient children had an ejection fraction <40%. The average ejection fraction of the merosin-deficient children was 43%+/-11%, which was significantly lower than the merosin-positive children (53%+/-5%, P=.03).

CONCLUSIONS

This study suggests that a deficiency of laminin alpha2 can give rise to dilated cardiomyopathy, supporting the idea that defects of dystrophin, or of associated proteins, can cause dilated cardiomyopathy in addition to muscular dystrophy.

From dystrophinopathy to sarcoglycanopathy: evolution of a concept of muscular dystrophy

Duchenne and Becker muscular dystrophies are collectively termed dystrophinopathy. Dystrophinopathy and severe childhood autosomal recessive muscular dystrophy (SCARMD) are clinically very similar and had not been distinguished in the early 20th century. SCARMD was first classified separately from dystrophinopathy due to differences in the mode of inheritance. Studies performed several years ago clarified some immunohistochemical and genetic characteristics of SCARMD, but many remained to be clarified. In 1994, the sarcoglycan complex was discovered among dystrophin-associated proteins. Subsequently, on the basis of our immunohistochemical findings which indicated that all components of the sarcoglycan complex are absent in SCARMD muscles, and the previous genetic findings, we proposed that a mutation of any one of the sarcoglycan genes leads to SCARMD. This hypothesis explained and predicted various characteristics of SCARMD at the molecular level, most of which have been verified by subsequent discoveries in our own as well as various other laboratories. SCARMD is now called sarcoglycanopathy, which is caused by a defect of any one of four different sarcoglycan genes, and thus far mutations in sarcoglycan genes have been documented in the SCARMD patients. In this review, the evolution of the concept of sarcoglycanopathy separate from that of dystrophinopathy is explained by comparing studies on these diseases.

The role of cytoskeletal proteins in cardiomyopathies

Cardiomyopathies are serious heart muscle disorders in children and adults, which result in morbidity and premature death. These disorders include hypertrophic cardiomyopathy, dilated cardiomyopathy and restrictive cardiomyopathy. Recently, mutations in seven genes, all encoding sarcomeric proteins, have been identified as causes of familial hypertrophic cardiomyopathy. The genes include those encoding the beta-myosin heavy chain, alpha-tropomyosin, cardiac troponin T, myosin binding protein-C, myosin essential light chain, myosin regulatory light chain, and troponin I. Advances in the understanding of dilated cardiomyopathy have been made recently as well and it appears as if cytoskeletal proteins play a central role. Dystrophin has been identified as the gene responsible for X-linked dilated cardiomyopathy and this protein, which is also responsible for Duchenne and Becker muscular dystrophy, plays an important role in myocyte and cardiomyocyte function. Mutations in other cytoskeletal proteins such as metavinculin, alpha-dystroglycan, alpha- and gamma-sarcoglycan, and muscle LIM protein have also been found to result in dilated cardiomyopathy, suggesting that cytoskeletal proteins play a central role in cardiac function.

The heart in limb girdle muscular dystrophy

OBJECTIVE

To assess the frequency, nature, and severity of cardiac abnormalities in limb girdle muscular dystrophy, and its relation to age and weakness in various genotypes.

DESIGN

In 26 autosomal dominant, 38 autosomal recessive, and 33 sporadic strictly defined patients with limb girdle muscular dystrophy, cardiac evaluation included history, physical examination, chest x ray, electrocardiography, 24 hour ECG Holter monitoring, and echocardiography. In 35 of the 71 autosomal recessive and sporadic cases muscle biopsies were available for sarcoglycan analysis.

MAIN RESULTS

Dilated cardiomyopathy was present in one autosomal dominant case and in three advanced autosomal recessive or sporadic patients, of whom two were found to have alpha sarcoglycan deficiency. Two of these three patients and three other cases showed ECG abnormalities known to be characteristic of the dystrophinopathies. A strong association between the absence of alpha sarcoglycan and the presence of dilated cardiomyopathy was found (p = 0.04). In six autosomal dominant cases there were atrioventricular (AV) conduction disturbances, increasing in severity with age and in concomitant presence of muscle weakness. Pacemaker implantation was necessary in four.

CONCLUSIONS

10% of these patients had clinically relevant cardiac abnormalities. In autosomal dominant limb girdle muscular dystrophy one subtype characterised by muscle weakness and AV conduction disturbances is recognised. In the course of autosomal recessive/sporadic limb girdle muscular dystrophy, dilated cardiomyopathy may develop, probably related to deficiency of dystrophin associated proteins.

Both hypertrophic and dilated cardiomyopathies are caused by mutation of the same gene, delta-sarcoglycan, in hamster: an animal model of disrupted dystrophin-associated glycoprotein complex

Cardiomyopathy (CM) is a primary degenerative disease of myocardium and is traditionally categorized into hypertrophic and dilated CMs (HCM and DCM) according to its gross appearance. Cardiomyopathic hamster (CM hamster), a representative model of human hereditary CM, has HCM and DCM inbred sublines, both of which descend from the same ancestor. Herein we show that both HCM and DCM hamsters share a common defect in a gene for delta-sarcoglycan (delta-SG), the functional role of which is yet to be characterized. A breakpoint causing genomic deletion was found to be located at 6.1 kb 5' upstream of the second exon of delta-SG gene, and its 5' upstream region of more than 27.4 kb, including the authentic first exon of delta-SG gene, was deleted. This deletion included the major transcription initiation site, resulting in a deficiency of delta-SG transcripts with the consequent loss of delta-SG protein in all the CM hamsters, despite the fact that the protein coding region of delta-SG starting from the second exon was conserved in all the CM hamsters. We elucidated the molecular interaction of dystrophin-associated glycoproteins including delta-SG, by using an in vitro pull-down study and ligand overlay assay, which indicates the functional role of delta-SG in stabilizing sarcolemma. The present study not only identifies CM hamster as a valuable animal model for studying the function of delta-SG in vivo but also provides a genetic target for diagnosis and treatment of human CM.

Multicore myopathy with restrictive cardiomyopathy

A 10-y-old girl is presented who suffered mild muscular weakness and exercise intolerance from the age of 1 y onwards, with progression appearing from the age of about 8 y. Multicore myopathy and restrictive cardiomyopathy were diagnosed. Literature concerning the coexistence of multicore myopathy and cardiomyopathy is reviewed.

Dilated cardiomyopathy: a genetic approach

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Muscle pathology and clinical features of the sarcolemmopathies

We report the clinical features and the muscle pathology in 2 patients with congenital muscular dystrophy (CMD) secondary to merosin deficiency and in 2 patients with sarcoglycan (adhalin) deficiency. Electron microscopic examination revealed sarcolemmal defects in non-necrotic muscle fibers in all cases. These pathological findings are indistinguishable from those of Duchenne/Becker muscular dystrophy. We suggest that the similarities in histological findings reflect a common pathogenetic mechanism, i.e., a structural weakening of the sarcolemma with an increased susceptibility to rupture under mechanical stress. We propose the term sarcolemmopathy as an all-encompassing rubric for these disorders.

Clinical approach to genetic cardiomyopathy in children

BACKGROUND

Cardiomyopathy (CM) remains one of the leading cardiac causes of death in children, although in the majority of cases, the cause is unknown. To have an impact on morbidity and mortality, attention must shift to etiology-specific treatments. The diagnostic evaluation of children with CM of genetic origin is complicated by the large number of rare genetic causes, the broad range of clinical presentations, and the array of specialized diagnostic tests and biochemical assays.

METHODS AND RESULTS

We present a multidisciplinary diagnostic approach to pediatric CM of genetic etiology. We specify criteria for abnormal left ventricular systolic performance and structure that suggest CM based on established normal echocardiographic measurements and list other indications to consider an evaluation for CM. We provide a differential diagnosis of genetic conditions associated with CM, classified as inborn errors of metabolism, malformation syndromes, neuromuscular diseases, and familial isolated CM disorders. A diagnostic strategy is offered that is based on the clinical presentation: biochemical abnormalities, encephalopathy, dysmorphic features or multiple malformations, neuromuscular disease, apparently isolated CM, and pathological specimen findings. Adjunctive treatment measures are recommended for severely ill patients in whom a metabolic cause of CM is suspected. A protocol is provided for the evaluation of moribund patients.

CONCLUSIONS

In summary, we hope to assist pediatric cardiologists and other subspecialists in the evaluation of children with CM for a possible genetic cause using a presentation-based approach. This should increase the percentage of children with CM for whom a diagnosis can be established, with important implications for treatment, prognosis, and genetic counseling.