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

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

Dystrophin: from non-ischemic cardiomyopathy to ischemic cardiomyopathy

Dystrophin and its associated proteins form a scaffold underneath the cardiomyocyte membrane and connect the intracellular cytoskeleton to the extracellular matrix. Dystrophin localizes at the X chromosome, whose mutations might result in Duchenne muscular dystrophy, Becker muscular dystrophy and X-linked dilated cardiomyopathy. In addition to these genetic dilated cardiomyopathies, some acquired dilated cardiomyopathy like viral dilated cardiomyopathy is also related to dystrophin disruption or aberrant cleavage. In this review, we summarize the structure and distribution of dystrophin and researches of dystrophin in genetic and viral dilated cardiomyopathy. Moreover, we hypothesize that dystrophin play a critical role in ventricular remodeling in ischemic myocardium and treatment targeting restoration of dystrophin onto membrane could benefit for ischemic cardiomyopathy.     

Mutations in the dystrophin gene are associated with sporadic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is the major indication for heart transplantation. Approximately 30% of all DCM is thought to be inherited, while 70% is sporadic. Mutations in the dystrophin gene have been associated with the uncommon X-linked form of DCM. We hypothesized that missense mutations and other less severe mutations of the dystrophin gene might predispose to the common form of sporadic DCM. To test this hypothesis, 22kb of genomic dystrophin DNA was scanned with DOVAM-S in each of the 22 patients with sporadic DCM, including all 79 coding sequences and splice junctions, as well as six alternative exon 1 dystrophin isoforms (484kb, total). Three putative new mutations (IVS5+1 G>T, K18N, and F3228L) and seven polymorphisms were identified. The splice site mutation IVS5+1 is predicted to cause skipping of exon 5, which is within a region containing an actin binding site. The missense mutations occur at amino acids that display substantial evolutionary conservation. Screening of 236 control individuals failed to identify these three mutations. The three patients with putative mutations had CK-MM (creatine kinase, skeletal muscle) levels greater than 250 units while the 14 patients without mutations for which CK-MM were available had values ranging from 20 to 200. The first comprehensive mutation scanning of the exons and splice junctions of the dystrophin gene in patients with sporadic DCM presents the evidence that point mutations are associated with sporadic DCM without clinical evidence of skeletal myopathy. It may be prudent to measure CK-MM in all patients with dilated cardiomyopathy to identify candidates at high risk for dystrophin mutations.     

Dilated cardiomyopathy and new 16 bp deletion in exon 44 of the Dystrophin gene: the possible role of repeated motifs in mutation generation

Here we report a boy with dilated cardiomyopathy and severe Duchenne muscular dystrophy (DMD). The disease-causing mutation was a new 16 bp deletion in exon 44 of the dystrophin gene, which led to frameshifting and premature translation termination. This deletion in exon 44 was associated with dilated cardiomyopathy. The dystrophin region in exon 44 might be considered as one of the high-risk regions in which mutations could lead to myocardial damage, dilated cardiomyopathy, and early death. The abundance of repeated motifs was detected within the deleted segment and in the region. These sequence motifs might be involved in secondary structure formation and thus they could participate in the mutation generation.     

Clinical features of patients with Becker muscular dystrophy and deletions of the rod domain of dystrophin geneCSCD

Objective: To explore the clinical features of patients carrying deletions of the rod domain of the dystrophin gene. Methods: Clinical data of 12 Chinese patients with Becker muscular dystrophy (BMD) and such deletions was reviewed. Results: Most patients complained of muscle weakness of lower limbs. Two patients had muscle cramps, one had increased creatine kinase (CK) level, and one had dilated cardiomyopathy. Conclusion: Compared with DMD, the clinical features of BMD are much more variable, particularly for those carrying deletions of the rod domain of the dystrophin gene. Muscular weakness may not be the sole complaint of BMD. The diagnosis of BMD cannot be excluded by moderately elevated CK. For male patients with dilated cardiomyopathy, the possibility of BMD should be considered. © 2018 West China University of Medical Sciences. All rights reserved.     

Missense mutations in the rod domain of the lamin A/C gene as causes of dilated cardiomyopathy and conduction-system disease

BACKGROUND: Inherited mutations cause approximately 35 percent of cases of dilated cardiomyopathy; however, few genes associated with this disease have been identified. Previously, we located a gene defect that was responsible for autosomal dominant dilated cardiomyopathy and conduction-system disease on chromosome 1p1-q21, where nuclear-envelope proteins lamin A and lamin C are encoded by the LMNA (lamin A/C) gene. Mutations in the head or tail domain of this gene cause Emery-Dreifuss muscular dystrophy, a childhood-onset disease characterized by joint contractures and in some cases by abnormalities of cardiac conduction during adulthood. METHODS: We evaluated 11 families with autosomal dominant dilated cardiomyopathy and conduction-system disease. Sequences of the lamin A/C exons were determined in probands from each family, and variants were confirmed by restriction-enzyme digestion. The genotypes of the family members were ascertained. RESULTS: Five novel missense mutations were identified: four in the alpha-helical-rod domain of the lamin A/C gene, and one in the lamin C tail domain. Each mutation caused heritable, progressive conduction-system disease (sinus bradycardia, atrioventricular conduction block, or atrial arrhythmias) and dilated cardiomyopathy. Heart failure and sudden death occurred frequently within these families. No family members with mutations had either joint contractures or skeletal myopathy. Serum creatine kinase levels were normal in family members with mutations of the lamin rod but mildly elevated in some family members with a defect in the tail domain of lamin C. CONCLUSIONS: Genetic defects in distinct domains of the nuclear-envelope proteins lamin A and lamin C selectively cause dilated cardiomyopathy with conduction-system disease or autosomal dominant Emery-Dreifuss muscular dystrophy. Missense mutations in the rod domain of the lamin A/C gene provide a genetic cause for dilated cardiomyopathy and indicate that this intermediate filament protein has an important role in cardiac conduction and contractility.     

A novel mutation, Arg71Thr, in the δ-sarcoglycan gene is associated with dilated cardiomyopathy

Approximately 20–35% of cases of idiopathic dilated cardiomyopathy are familial. DCM-associated mutations have been reported in 13 genes including the desmin, -sarcoglycan, and metavinculin genes. This study screened for variants in these genes in Finnish patients with DCM. All coding regions of the desmin and -sarcoglycan genes and the metavinculin-specific exon of the vinculin gene were screened in 52 DCM patients from eastern Finland by PCR-SSCP. We detected a novel mutation, Arg71Thr, in the -sarcoglycan gene in two members of a small DCM family. One of the mutation carriers fulfills diagnostic criteria for DCM and is also symptomatic. The other mutation carrier has slightly dilated left ventricle and well preserved systolic function. Therefore carriers of the Arg71Thr mutation had a relatively mild phenotype and a late onset of the disease. Disease-associated mutations were not found in the desmin gene or the metavinculin-specific exon of the vinculin gene. We conclude that the desmin and -sarcoglycan genes are not predominant disease-causing genes in patients with DCM in eastern Finland.Abbreviations DCM Dilated cardiomyopathy - ECG Electrocardiography - LGMD2F Limb-girdle muscular dystrophy 2F - PCR Polymerase chain reaction - SSCP Single-strand conformation polymorphism     

Nuclear sequestration of delta-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.     

Decreased Myocardial Expression of Dystrophin and Titin mRNA and Protein in Dilated Cardiomyopathy: Possibly an Adverse Effect of TNF-α

Background and aims  

While the molecular basis of dilated cardiomyopathy (DCM) remains uncertain, concrete evidence is emerging that sarcomeric and cytoskeleton gene expression of myocardium isolated from failing versus non-failing patients differ dramatically. The central aim to this work was to find out the possible role of dystrophin and titin along with the TNF-α in the pathogenesis of cardiomyopathy.     

Meta-analysis of clinical characteristics of 299 carriers of LMNA gene mutations: do lamin A/C mutations portend a high risk of sudden death?

This study evaluated common clinical characteristics of patients with lamin A/C gene mutations that cause either isolated dilated cardiomyopathy or dilated cardiomyopathy in association with skeletal muscular dystrophy. We pooled clinical data of all published carriers of lamin A/C gene mutations as cause of skeletal and/or cardiac muscle disease and reviewed ECG findings. Cardiac dysrhythmias were reported in 92% of patients after the age of 30 years; heart failure was reported in 64% after the age of 50. Sudden death was the most frequently reported mode of death (46%) in both the cardiac and the neuromuscular phenotype. Carriers of lamin A/C gene mutations often received a pacemaker (28%). However, this intervention did not alter the rate of sudden death. Review of the ECG findings typically showed a low amplitude P wave and prolongation of the PR interval with a narrow QRS complex. This meta-analysis suggests that cardiomyopathy due to lamin A/C gene mutations portends a high risk of sudden death, and that this risk does not differ between subjects with predominantly cardiac or neuromuscular disease. This implies then that all carriers of a lamin A/C gene mutation need to be carefully screened with particular emphasis also on tachyarrhythmias. Prospective studies are needed to evaluate risk stratification and proper treatment strategies.     

Cardiac involvement in Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a common form of muscular dystrophy frequently involving cardiac muscle, thus leading to dilated cardiomyopathy. Clinical outcome and prognosis is frequently determined by the involvement of the cardiac conduction system causing symptomatic bradyarrhythmias, as well as tachyarrhythmias and, if untreated, frequent sudden cardiac death. Typical features of the cardiac involvement of EDMD are presented, caused by a novel missense mutation in the splice receptor sequence of intron 6 of the LMNA gene on chromosome 1, encoding for the lamin A/C gene, consistent with the autosomal dominant form of EDMD.     

Utility of dystrophin and utrophin staining in childhood muscular dystrophy

To determine the utility of dystrophin and utrophin staining in the differential diagnosis of childhood muscular dystrophy. Fifty muscle biopsies of histologically confirmed cases of childhood muscular dystrophy, below 16 years of age, were stained immunohistochemically for dystrophin and utrophin. All the 30 muscle biopsies of patients with Duchenne muscular dystrophy (DMD) showed all or majority of muscle fibers deficient for dystrophin and positive for utrophin. In the 4 female DMD carriers there was mosaic pattern of staining for dystrophin and reciprocal positivity for utrophin. All the muscle biopsies of patients with other childhood onset muscular dystrophies were positive for dystrophin and negative for utrophin. This study shows that dystrophin staining differentiates DMD and DMD carriers from other childhood muscular dystrophies and utrophin staining is of no added value. Utrophin up-regulation may compensate for structural deficiency in dystrophic muscle.     

Redefinition of Dystrophin Isoform Distribution in Mouse Tissue by RT-PCR Implies Role in Nonmuscle Manifestations of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by a defect in a 427-kDa membrane-associated protein: dystrophin. The DMD gene also encodes several shorter isoforms which are believed to participate in nonmuscle manifestations of DMD, including abnormal retinal electrophysiology, dilated cardiomyopathy, mental retardation, and hearing defects. The purpose of this work was to determine the normal tissue expression of full-length dystrophin (Dp427) and the dystrophin isoforms Dp260, Dp140, Dp116, and Dp71, to aid in understanding what roles these isoforms might play in DMD nonmuscle manifestations. RT-PCR was performed on mRNA isolated from wild-type C57BL/6J mouse tissues, including brain, cardiac muscle, eye, intestine, kidney, liver, lung, skeletal muscle, spleen, stomach, testis, thymus, and uterus. RT-PCR amplification demonstrated that the isoforms were in a number of tissues which had not been revealed by previous Western and Northern blot analyses. Dp427 was expressed at equal levels in all tissues. Dp260 and Dp140 were present in all tissues tested, but the levels of expression varied. Dp116 was expressed in a subset of tissues and levels of expression varied. Dp71 was constitutively expressed in all tissues, suggesting that this isoform plays a basic role in normal tissue function. The expanded tissue distribution supports the hypothesis that dystrophin isoforms serve essential and unique functions, necessitating further investigation into their potential roles in DMD nonmuscle manifestations.     

Dystrobrevin deficiency at the sarcolemma of patients with muscular dystrophy

Mutations in the genes encoding dystrophin or dystrophin-associated proteins are responsible for Duchenne muscular dystrophy or various forms of limb-girdle muscular dystrophies respectively. We have recently cloned the gene for the murine 87 kDa postsynaptic protein dystrobrevin, a dystrophin-associated protein. Anti-dystrobrevin antibodies stain the sarcolemma in normal skeletal muscle indicating that dystrobrevin co-localises with dystrophin and the dystrophin- associated protein complex. By contrast, dystrobrevin membrane staining is severely reduced in muscles of Duchenne muscular dystrophy patients, consistent with dystrobrevin being a dystrophin-associated protein. Interestingly, dystrobrevin staining at the sarcolemma is dramatically reduced in patients with limb-girdle muscular dystrophy arising from the loss of one or all of the sarcoglycan components. Normal dystrobrevin staining is observed in patients with other forms of limb- girdle muscular dystrophy where dystrophin and the rest of the dystrophin-associated protein complex are normally expressed and in other neuromuscular disorders. Our results show that dystrobrevin- deficiency is a generic feature of dystrophies linked to dystrophin and the dystrophin-associated proteins. This is the first indication that a cytoplasmic component of the dystrophin-associated protein complex may be involved in the pathogenesis of limb-girdle muscular dystrophy.      

Does δ-sarcoglycan-associated autosomal-dominant cardiomyopathy exist?

In this study we clinically and genetically characterize a consanguineous family with a homozygous novel missense mutation in the δ-sarcoglycan gene and a second δ-sarcoglycan mutation that has previously been reported to cause severe autosomal-dominant dilated cardiomyopathy. We identified a novel missense mutation in exon 6 (p.A131P) of the δ-sarcoglycan gene, which in a homozygous state leads to the clinical picture of a limb girdle muscular dystrophy. In four heterozygous carriers for the mutation, aged 3–64 years, a second sequence variant in exon 6 (p.S151A) of the δ-sarcoglycan gene was detected on the other allele. This second missense change had previously been reported to be responsible for fatal autosomal-dominant dilated cardiomyopathy at young age. Comprehensive clinical and cardiac investigation in all of the compound heterozygous family members revealed no signs of cardiomyopathy or limb girdle muscular dystrophy. Our findings demonstrate that, even in the presence of a second disease-causing mutation, the p.S151A mutation in the δ-sarcoglycan gene does not result in cardiomyopathy. This finding questions the pathological relevance of this sequence variant for causing familial autosomal-dominant dilated cardiomyopathy and thereby the role of the δ-sarcoglycan gene in general as a disease-causing gene for autosomal-dominant dilated cardiomyopathy.     

Function Induced Modifications of Gene Expression: an Alternative Approach to Gene Therapy of Duchenne Muscular Dystrophy

In Duchenne muscular dystrophy a large gene that codes for dystrophin is altered. The possibility that the defective gene/protein could be at least in part substituted by other molecules that the diseased muscle is able to produce and that have a function similar to that of dystrophin is being discussed. Muscle fibres have a tremendous adaptive potential, and the expression of several protein isoforms can be induced by either stretch or long-term change of activity. The exploitation of this ability of muscle cells to express new genes, which would code for proteins that will not be alien to the individual, for treatment of Duchenne muscular dystrophy is being considered. The argument for this approach is strengthened by results that in patients with Duchenne muscular dystrophy the progress of the disease can be slowed with changes of muscle activity.     

Additional dystrophin fragment in Becker muscular dystrophy may result from proteolytic cleavage at deletion junctions.

Becker muscular dystrophy is usually caused by intragenic dystrophin gene deletions that result in production of an internally deleted protein. Previous studies have detected what appears to be a unique dystrophin degradation product that appears only in muscle biopsies from patients with Becker muscular dystrophy. This dystrophin fragment is always seen in addition to the "full-size" dystrophin of the expected size for a given gene deletion. It is only found in biopsies from patients with mutations in the deletion-prone region encompassing exons 45-53, but it does not appear to correlate with any observable phenotype at the clinical level. By correlating the size and locations of dystrophin gene deletions with the size of this degradation product, together with use of region-specific dystrophin antisera, we find that proteolytic cleavage may occur at the deletion breakpoints, perhaps due to alterations of the secondary and/or tertiary structures of the protein. This cleavage results in loss of the carboxy-terminal domains that are thought to be important for interactions between dystrophin and other membrane-bound proteins.