Genomic screening for beta-sarcoglycan gene mutations: missense mutations may cause severe limb-girdle muscular dystrophy type 2E (LGMD 2E)

Autosomal recessive limb-girdle muscular dystrophies (LGMDs) are genetically heterogeneous. A subgroup of these disorders is caused by mutations in the dystrophin-associated sarcoglycan complex. Truncating mutations in the 43 kDa beta-sarcoglycan gene (LGMD 2E) were originally identified in a sporadic case of Duchenne-like muscular dystrophy, and a common missense mutation (T151R) was identified independently in Indiana Amish pedigrees with a milder form of LGMD. To facilitate mutational analysis of larger numbers of patients directly from genomic DNA, as opposed to reverse transcribed RNA from muscle biopsies, we have determined the genomic structure of the beta-sarcoglycan gene. The open reading frame of the beta-sarcoglycan coding region extends over six exons. Primers were designed for PCR amplification of single exons from genomic DNA and subsequent single strand conformation polymorphism (SSCP) analysis. We screened 15 patients from the Brazilian LGMD patient population, 13 of whom followed a severe course. Most of the patients had been assessed previously for deficiency of alpha- sarcoglycan immunofluorescence on muscle biopsy sections as a marker for disease of the sarcoglycan complex. Novel mutations in two familial and two sporadic cases of severe childhood-onset LGMD were identified. Only one of these patients carried a truncating mutation (homozygous 2 bp deletion, FS164TER), while the other three carried missense mutations (homozygous R91P, homozygous M100K, heterozygous recessive L108R; only one allele could be identified in this family). All three missense mutations occurred in exon 3, coding for the immediate extracellular domain. Complete absence for all three of the known sarcoglycans was noted by immunohistochemistry on muscle biopsy sections of the patients.      

Evaluation of sarcoglycans, vinculin-talin-integrin system and filamin2 in alpha- and gamma-sarcoglycanopathy: an immunohistochemical study

The sarcoglycan subcomplex (SGC) is a well-known system of interaction between extracellular matrix and sarcolemma-associated cytoskeleton in skeletal and cardiac muscle. The SGC is included in the DGC made up of sarcoplasmic subcomplex and a dystroglycan subcomplex. Recent developments in molecular genetics have demonstrated that the mutation of each single sarcoglycan gene, causes a series of recessive autosomal muscular dystrophies, dystrophin-positive, called sarcoglycanopathies or limb girdle muscular dystrophies. Our recent studies have demonstrated that costameres are a proteic machinery made up of DGC and vinculin-talin-integrin system, also revealing the colocalization of sarcoglycans and integrins in adult human skeletal muscle. These results may support the hypothesis of the existence of a bidirectional signalling between sarcoglycans and integrins in cultured L6 myocytes. The hypothesis of bidirectional signalling between sarcoglycans and integrins could be supported by the identification of a skeletal and cardiac muscle filamin2 as a gamma-sarcoglycan, delta-sarcoglycan and, hypothetically, beta1 integrin interacting protein. Our results, acquired with an immunofluorescence study on adult human skeletal muscle affected by LGMD type 2D and 2C, showed that in LGMD2D: a) alpha-sarcoglycan staining is severely reduced; b) the beta-gamma-delta-sarcoglycan subunit and all tested integrins staining are clearly detectable; c) filamin2 is normal and shows a costameric distribution. In LGMD2C: a) alpha-sarcoglycan staining is preserved; b) the beta-gamma-delta-sarcoglycan subunit staining is severely reduced; c) the alpha7B-integrin is slightly reduced and beta1D-integrin is severely reduced; d) filamin2 is severely reduced. Other tested proteins of the two systems show a normal staining pattern in both sarcoglycanopathies. Our study seems to confirm, for the first time on adult human skeletal muscle of subjects affected by LGMDs, the hypo-theses of: a) the existence, in mouse myotubes in culture, of two distinct subunits in sarcoglycans subcomplex; b) the presence of a bidirectional signalling between sarcoglycans and integrins, previously demonstrated on rat cultured L6 myocytes; c) the interaction of FLN2 with both sarcoglycans and integrins. These results may stimulate the search of yet unidentified common interactors of both fiber-extracellular matrix interaction systems.     

A first missense mutation in the delta sarcoglycan gene associated with a severe phenotype and frequency of limb-girdle muscular dystrophy type 2F (LGMD2F) in Brazilian sarcoglycanopathies.

Among the heterogeneous group of autosomal recessive limb-girdle muscular dystrophies (AR LGMDs), the sarcoglycanopathies (LGMD2C-2F) represent a subgroup characterised by defects in the gamma, alpha, beta, and delta sarcoglycan genes, respectively. Genotype-phenotype correlations in these forms of AR LGMD are important to enhance our understanding of protein function. Regarding LGMD2F, only two homozygous frameshift mutations have been reported to date in patients with a severe phenotype. In the present report, through screening 23 unrelated AR LGMD patients, we identified three subjects with LGMD2F, two with a previously reported frameshift mutation and the other homozygous for a new missense mutation in the delta sarcoglycan gene. Interestingly, this new mutation is also associated with a severe clinical course. In addition, our results suggest that this form of severe AR LGMD is not very rare in our population.     

A cross section of autosomal recessive limb-girdle muscular dystrophies in 38 families

Limb-girdle muscular dystrophies constitute a broad range of clinical and genetic entities. We have evaluated 38 autosomal recessive limb-girdle muscular dystrophy (LGMD2) families by linkage analysis for the known loci of LGMD2A-F and protein studies using immunofluorescence and western blotting of the sarcoglycan complex. One index case in each family was investigated thoroughly. The age of onset and the current ages were between 11/2 and 15 years and 6 and 36 years, respectively. The classification of families was as follows: calpainopathy 7, dysferlinopathy 3, alpha sarcoglycan deficiency 2, beta sarcoglycan deficiency 7, gamma sarcoglycan deficiency 5, delta sarcoglycan deficiency 1, and merosinopathy 2. There were two families showing an Emery-Dreifuss phenotype and nine showing no linkage to the LGMD2A-F loci, and they had preserved sarcoglycans. gamma sarcoglycan deficiency seems to be the most severe group as a whole, whereas dysferlinopathy is the mildest. Interfamilial variation was not uncommon. Cardiomyopathy was not present in any of the families. In sarcoglycan deficiencies, sarcoglycans other than the primary ones may also be considerably reduced; however, this may not be reflected in the phenotype. Many cases of primary gamma sarcoglycan deficiency showed normal or only mildly abnormal delta sarcoglycan staining.     

Genetic epidemiology of muscular dystrophies resulting from sarcoglycan gene mutations.

BACKGROUND: The autosomal recessive limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous muscle diseases characterised by progressive proximal limb muscle weakness. Six different loci have been mapped and pathogenetic mutations in the genes encoding the sarcoglycan complex components (alpha-, beta-, gamma-, and delta-sarcoglycan) have been documented. LGMD patients affected with primary "sarcoglycanopathies" are classified as LGMD2D, 2E, 2C, and 2F, respectively. METHODS: A geographical area in north east Italy (2,319,147 inhabitants) was selected for a genetic epidemiological study on primary sarcoglycanopathies. Within the period 1982 to 1996, all patients living in this region and diagnosed with muscular dystrophy were seen at our centre. Immunohistochemical and immunoblot screening for alpha-sarcoglycan protein deficiency was performed on all muscle biopsies from patients with a progressive muscular dystrophy of unknown aetiology and normal dystrophin. Sarcoglycan mutation analyses were conducted on all patient muscle biopsies shown to have complete or partial absence of alpha-sarcoglycan immunostaining or a decreased quantity of alpha-sarcoglycan protein on immunoblotting. RESULTS: Two hundred and four patient muscle biopsies were screened for alpha-sarcoglycan protein deficiency and 18 biopsies showed a deficiency. Pathogenetic mutations involving one gene for sarcoglycan complex components were identified in 13 patients: alpha-sarcoglycan in seven, beta-sarcoglycan in two, gamma-sarcoglycan in four, and none in the delta-sarcoglycan gene. The overall prevalence of primary sarcoglycanopathies, as of 31 December 1996, was estimated to be 5.6 x 10(-6) inhabitants. CONCLUSION: The prevalence rate estimated in this study is the first to be obtained after biochemical and molecular genetic screening for sarcoglycan defects.     

Further evidence for the organisation of the four sarcoglycans proteins within the dystrophin-glycoprotein complex

Based on the pattern of distribution of the SG proteins in patients with LGMD2C and 2D, and on the observed decreased abundance of dystrophin through WB in some sarcoglycans (SG) patients, we have recently suggested that alpha, beta and delta subunits of sarcoglycan complex might be more closely associated and that gamma-SG might interact more directly with dystrophin. Two additional SG patients here reported give further support to these suggestions: an LGMD2F patient showed patchy labelling for gamma-SG, despite the lack of staining of the other three SG proteins; an LGMD2C boy showed deficiency in dystrophin by means of WB and IF, comparable with an DMD manifesting carrier. These two patients represent further evidence of a closer relation of alpha, beta and delta-SG than of gamma-SG and of the possible association of gamma-SG with dystrophin. In addition the LGMD2C patient illustrates the potential risk of misdiagnosis using only dystrophin analysis, in cases with no positive family history, or when DNA analysis is not informative.     

Abnormalities of dystrophin, the sarcoglycans, and laminin alpha2 in the muscular dystrophies.

Abnormalities of dystrophin, the sarcoglycans, and laminin alpha2 are responsible for a subset of the muscular dystrophies. In this study we aim to characterise the nature and frequency of abnormalities of these proteins in an Australian population and to formulate an investigative algorithm to aid in approaching the diagnosis of the muscular dystrophies. To reduce ascertainment bias, biopsies with dystrophic (n=131) and non-dystrophic myopathic (n=71) changes were studied with antibodies to dystrophin, alpha, beta, and gamma sarcoglycan, beta dystroglycan, and laminin alpha2, and results were correlated with clinical phenotype. Abnormalities of dystrophin, the sarcoglycans, or laminin alpha2 were present in 61/131 (47%) dystrophic biopsies and in 0/71 myopathic biopsies, suggesting that immunocytochemical study of dystrophin, the sarcoglycans, and laminin alpha2 may, in general, be restricted to patients with dystrophic biopsies. Two patients with mutations identified in gamma sarcoglycan had abnormal dystrophin (by immunocytochemistry and immunoblot), showing that abnormalities of dystrophin may be a secondary phenomenon. Therefore, biopsies should not be excluded from sarcoglycan analysis on the basis of abnormal dystrophin alone. The diagnostic yield was highest in those with severe, rapidly progressive limb-girdle weakness (92%). Laminin alpha2 deficiency was identified in 5/131 (4%) patients; 215 patients presented after infancy, indicating that abnormalities of laminin alpha2 are not limited to the congenital muscular dystrophy phenotype. Overall patterns of immunocytochemistry and immunoblotting provided a guide to mutation analysis and, on the basis of this study, we have formulated a diagnostic algorithm to guide the investigation of patients with muscular dystrophy.     

Zeta-sarcoglycan,a novel component of the sarcoglycan complex,is reduced in muscular dystrophy

The dystrophin glycoprotein complex (DGC) is found at the plasma membrane of muscle cells, where it provides a link between the cytoskeleton and the extracellular matrix. A subcomplex within the DGC, the sarcoglycan complex, associates with dystrophin and mediates muscle membrane stability. Mutations in sarcoglycan genes lead to muscular dystrophy and cardiomyopathy in both humans and mice. In invertebrates, there are three sarcoglycan genes, while in mammals there are additional sarcoglycan genes that probably arose from gene duplication events. We identified a novel mammalian sarcoglycan, zeta-sarcoglycan, that is highly related to gamma-sarcoglycan and delta-sarcoglycan. We generated a zeta-sarcoglycan-specific antibody and found that zeta-sarcoglycan associated with other members of the sarcoglycan complex at the plasma membrane. Additionally, zeta-sarcoglycan was reduced at the membrane in muscular dystrophy, consistent with a role in mediating membrane stability. zeta-Sarcoglycan was also found as a component of the vascular smooth muscle sarcoglycan complex. Together, these data demonstrate that zeta-sarcoglycan is an integral component of the sarcoglycan complex and, as such, is important in the pathogenesis of muscular dystrophy.     

The sarcoglycan complex in the six autosomal recessive limb-girdle muscular dystrophies

To enhance our understanding of the autosomal recessive limb-girdle muscular dystrophy (LGMD), patients from six genetically distinct forms (LGMD2A to LGMD2F) were studied with antibodies directed against four sarcoglycan subunits (alpha-, beta-, gamma-, delta-SG), dystrophin, beta-dystroglycan (beta-DG) and merosin. All patients with LGMD2A and 2B had a mild clinical course while those with a primary sarcoglycan mutation (LGMD2C to 2F) had a range of clinical severity. Dystrophin and merosin immunofluorescence pattern was positive in patients with all six AR LGMDs. The majority of patients with a severe Duchenne-like phenotype presented total absence of the SG complex. However, some exceptions were found in 13q linked patients, indicating that the presence of a certain labelling for components of the SG may not be prognostic for a milder phenotype. The observation that the primary absence of alpha-SG results in the total absence of beta- and delta-SG but not of gamma-SG suggests that the alpha-, beta- and delta-subunits of sarcoglycan may be more closely associated. A secondary reduction in dystrophin amount was seen in patients with primary sarcoglycan mutations, which was most marked in patients with primary beta-, gamma- and delta-SG deficiencies. In contrast, beta-DG staining was retained in all patients, suggesting that the association between SG and DG subcomplexes is not so strong. Based on the above findings, we have refined the model for the interaction among the known glycoproteins of the sarcoglycan complex, within the DGC.      

Molecular and genetic characterization of sarcospan: insights into sarcoglycan-sarcospan interactions

Autosomal recessive limb girdle muscular dystrophies 2C-2F represent a family of diseases caused by primary mutations in the sarcoglycan genes. We show that sarcospan, a novel tetraspan-like protein, is also lost in patients with either a complete or partial loss of the sarcoglycans. In particular, sarcospan was absent in a gamma-sarcoglycanopathy patient with normal levels of alpha-, beta- and delta-sarcoglycan. Thus, it is likely that assembly of the complete, tetrameric sarcoglycan complex is a prerequisite for membrane targeting and localization of sarcospan. Based on our findings that sarcospan is integrally associated with the sarcoglycans, we screened >50 autosomal recessive muscular dystrophy cases for mutations in sarcospan. Although we identified three intragenic polymorphisms, we did not find any cases of muscular dystrophy associated with primary mutations in the sarcospan gene. Finally, we have identified an important case of limb girdle muscular dystrophy and cardiomyopathy with normal expression of sarcospan. This patient has a primary mutation in the gamma-sarcoglycan gene, which causes premature truncation of gamma-sarcoglycan without affecting assembly of the mutant gamma-sarcoglycan into a complex with alpha-, beta- and delta-sarcoglycan and sarcospan. This is the first demonstration that membrane expression of a mutant sarcoglycan-sarcospan complex is insufficient in preventing muscular dystrophy and cardiomyopathy and that the C-terminus of gamma-sarcoglycan is critical for the functioning of the entire sarcoglycan-sarcospan complex. These findings are important as they contribute to a greater understanding of the structural determinants required for proper sarcoglycan-sarcospan expression and function.     

HnRNP G and Tra2beta: opposite effects on splicing matched by antagonism in RNA binding

The hnRNP G family comprises three closely related proteins, hnRNP G, RBMY and hnRNP G-T. We showed previously that they interact with splicing activator proteins, particularly hTra2beta, and suggested that they were involved in regulating Tra2-dependent splicing. We show here that hnRNP G and hTra2beta have opposite effects upon the incorporation of several exons, both being able to act as either an activator or a repressor. HnRNP G acts via a specific sequence to repress the skeletal muscle-specific exon (SK) of human slow skeletal alpha-tropomyosin, TPM3, and stimulates inclusion of the alternative non-muscle exon. The binding of hnRNP G to the exon is antagonized by hTra2beta. The two proteins also have opposite effects upon a dystrophin pseudo-exon. This exon is incorporated in a patient to a higher level in heart muscle than skeletal muscle, causing X-linked dilated cardiomyopathy. It is included to a higher level after transfection of a mini-gene into rodent cardiac myoblasts than into skeletal muscle myoblasts. Co-transfection with hnRNP G represses incorporation in cardiac myoblasts, whereas hTra2beta increases it in skeletal myoblasts. Both the cell specificity and the protein responses depend upon exon sequences. Since the ratio of hnRNP G to Tra2beta mRNA in humans is higher in skeletal muscle than in heart muscle, we propose that the hnRNP G/Tra2beta ratio contributes to the cellular splicing preferences and that the higher proportion of hnRNP G in skeletal muscle plays a role in preventing the incorporation of the pseudo-exon and thus in preventing skeletal muscle dystrophy.     

Rescue of sarcoglycan mutations by inhibition of endoplasmic reticulum quality control is associated with minimal structural modifications

Sarcoglycanopathies (SGP) are a group of autosomal recessive muscle disorders caused by primary mutations in one of the four sarcoglycan genes. The sarcoglycans (α-, β-, γ-, and δ-sarcoglycan) form a tetrameric complex at the muscle membrane that is part of the dystrophin-glycoprotein complex and plays an essential role for membrane integrity during muscle contractions. We previously showed that the most frequent missense mutation in α-sarcoglycan (p.R77C) leads to the absence of the protein at the cell membrane due to its blockade by the endoplasmic reticulum (ER) quality control. Moreover, we demonstrated that inhibition of the ER α-mannosidase I activity using kifunensine could rescue the mutant protein localization at the cell membrane. Here, we investigate 25 additional disease-causing missense mutations in the sarcoglycan genes with respect to intracellular fate and localization rescue of the mutated proteins by kifunensine. Our studies demonstrate that, similarly to p.R77C, 22 of 25 of the selected mutations lead to defective intracellular trafficking of the SGs proteins. Six of these were saved from ER retention upon kifunensine treatment. The trafficking of SGs mutants rescued by kifunensine was associated with mutations that have moderate structural impact on the protein.     

Combined deficiency of alpha and epsilon sarcoglycan disrupts the cardiac dystrophin complex

Cardiomyopathy is a puzzling complication in addition to skeletal muscle pathology for patients with mutations in β-, γ- or δ-sarcoglycan (SG) genes. Patients with mutations in α-SG rarely have associated cardiomyopathy, or their cardiac pathology is very mild. We hypothesize that a fifth SG, ε-SG, may compensate for α-SG deficiency in the heart. To investigate the function of ε-SG in striated muscle, we generated an Sgce-null mouse and a Sgca-;Sgce-null mouse, which lacks both α- and ε-SGs. While Sgce-null mice showed a wild-type phenotype, with no signs of muscular dystrophy or heart disease, the Sgca-;Sgce-null mouse developed a progressive muscular dystrophy and a more anticipated and severe cardiomyopathy. It shows a complete loss of residual SGs and a strong reduction in both dystrophin and dystroglycan. Our data indicate that ε-SG is important in preventing cardiomyopathy in α-SG deficiency.     

A rare form of limb girdle muscular dystrophy (type 2E) seen in an Iranian family detected by autozygosity mapping

Sarcoglycanopathies (SGPs) constitute a subgroup of autosomal recessive limb girdle muscular dystrophies (LGMDs) which are caused by mutations in sarcoglycan (SGs) genes. SG proteins form a core complex consisting of α, β, γ and δ sarcoglycans which are encoded by SGCA, SGCB, SGCG and SGCD genes, respectively. Genetic defect, in any of these SG proteins, results in instability of the whole complex. This effect can be helpful in interpreting muscle biopsy results. Autozygosity mapping is a gene mapping approach which can be applied in large consanguineous families for tracking the defective gene in most autosomal recessive disorders. In the present study, we used autozygosity mapping, to find the gene responsible for muscular dystrophy. Proband was a 10-year-old boy referred to our center for ruling out DMD (Duchenne muscular dystrophy). According to the pedigree and clinical reports, we assessed him for SGPs. Haplotyping, using the four short tandem repeat (STR) markers for each of the SG genes, showed that the phenotype may segregate with SGCB gene; and observing two crossing overs which occurred within the gene suggested that the mutation might be in the first two exons of SGCB gene. Mutation analysis showed a 26?bp duplication (10?bp before the initiation codon till 13?bp after the ATG start codon). This will cause a frameshift in protein synthesis.     

Sarcoglycanopathies and the risk of undetected deletion alleles in diagnosis

We have designed Multiplex Amplifiable Probe Hybridization (MAPH) probes for 28 exons of the sarcoglycan genes SGCA, SGCB, SGCG, and SGCD. The set was used to screen DNA from limb-girdle muscular dystrophy (LGMD) patients for the presence of pathogenic deletion or duplication mutations. An unexpected heterozygous deletion of SGCG exon 7 was detected in a patient from a consanguineous family in which a known c.525delT mutation segregates. The exon 7 deletion was inherited from the father, who was part of the consanguineous c.525delT branch of the family but who did not carry the c.525delT mutation. A similar, homozygous deletion had been identified in two unrelated LGMD patients from southern Italy. The deletion breakpoints were mapped, isolated, and sequenced, and were identical in all cases. Haplotype analysis showed the same alleles segregating with the mutation in all three patients, suggesting a common ancestor. Exonic deletions in sarcoglycanopathies appear to be rare events. However, we recommend screening for exonic deletions/duplications in patients where a mutation has not been identified in both alleles, as well as in seemingly homozygous cases where segregation of the mutations can not be confirmed in the parents.     

Loss of the sarcoglycan complex and sarcospan leads to muscular dystrophy in beta-sarcoglycan-deficient mice.

beta-Sarcoglycan, one of the subunits of the sarcoglycan complex, is a transmembranous glycoprotein which associates with dystrophin and is the molecule responsible for beta-sarcoglycanopathy, a Duchenne-like autosomal recessive muscular dystrophy. To develop an animal model of beta-sarcoglycanopathy and to clarify the role of beta-sarcoglycan in the pathogenesis of the muscle degeneration in vivo, we developed beta-sarcoglycan-deficient mice using a gene targeting technique. beta-Sarcoglycan-deficient mice (BSG(-)(/-)mice) exhibited progressive muscular dystrophy with extensive degeneration and regeneration. The BSG(-)(/-)mice also exhibited muscular hypertrophy characteristic of beta-sarcoglycanopathy. Immunohistochemical and immunoblot analyses of BSG(-)(/-)mice demonstrated that deficiency of beta-sarcoglycan also caused loss of all of the other sarcoglycans as well as of sarcospan in the sarcolemma. On the other hand, laminin-alpha2, alpha- and beta-dystroglycan and dystrophin were still present in the sarcolemma. However, the dystrophin-dystroglycan complex in BSG(-)(/-)mice was unstable compared with that in the wild-type mice. Our data suggest that loss of the sarcoglycan complex and sarcospan alone is sufficient to cause muscular dystrophy, that beta-sarcoglycan is an important protein for formation of the sarcoglycan complex associated with sarcospan and that the role of the sarcoglycan complex and sarcospan may be to strengthen the dystrophin axis connecting the basement membrane with the cytoskeleton.     

Myoferlin, a candidate gene and potential modifier of muscular dystrophy

Dysferlin, the gene product of the limb girdle muscular dystrophy (LGMD) 2B locus, encodes a membrane-associated protein with homology to Caenorhabditis elegans fer-1. Humans with mutations in dysferlin ( DYSF ) develop muscle weakness that affects both proximal and distal muscles. Strikingly, the phenotype in LGMD 2B patients is highly variable, but the type of mutation in DYSF cannot explain this phenotypic variability. Through electronic database searching, we identified a protein highly homologous to dysferlin that we have named myoferlin. Myoferlin mRNA was highly expressed in cardiac muscle and to a lesser degree in skeletal muscle. However, antibodies raised to myoferlin showed abundant expression of myoferlin in both cardiac and skeletal muscle. Within the cell, myoferlin was associated with the plasma membrane but, unlike dysferlin, myoferlin was also associated with the nuclear membrane. Ferlin family members contain C2 domains, and these domains play a role in calcium-mediated membrane fusion events. To investigate this, we studied the expression of myoferlin in the mdx mouse, which lacks dystrophin and whose muscles undergo repeated rounds of degeneration and regeneration. We found upregulation of myoferlin at the membrane in mdx skeletal muscle. Thus, myoferlin ( MYOF ) is a candidate gene for muscular dystrophy and cardiomyopathy, or possibly a modifier of the muscular dystrophy phenotype.     

SMAD signaling drives heart and muscle dysfunction in a Drosophila model of muscular dystrophy

Loss-of-function mutations in the genes encoding dystrophin and the associated membrane proteins, the sarcoglycans, produce muscular dystrophy and cardiomyopathy. The dystrophin complex provides stability to the plasma membrane of striated muscle during muscle contraction. Increased SMAD signaling due to activation of the transforming growth factor-β (TGFβ) pathway has been described in muscular dystrophy; however, it is not known whether this canonical TGFβ signaling is pathogenic in the muscle itself. Drosophila deleted for the γ/δ-sarcoglycan gene (Sgcd) develop progressive muscle and heart dysfunction and serve as a model for the human disorder. We used dad-lacZ flies to demonstrate the signature of TGFβ activation in response to exercise-induced injury in Sgcd null flies, finding that those muscle nuclei immediately adjacent to muscle injury demonstrate high-level TGFβ signaling. To determine the pathogenic nature of this signaling, we found that partial reduction of the co-SMAD Medea, homologous to SMAD4, or the r-SMAD, Smox, corrected both heart and muscle dysfunction in Sgcd mutants. Reduction in the r-SMAD, MAD, restored muscle function but interestingly not heart function in Sgcd mutants, consistent with a role for activin but not bone morphogenic protein signaling in cardiac dysfunction. Mammalian sarcoglycan null muscle was also found to exhibit exercise-induced SMAD signaling. These data demonstrate that hyperactivation of SMAD signaling occurs in response to repetitive injury in muscle and heart. Reduction of this pathway is sufficient to restore cardiac and muscle function and is therefore a target for therapeutic reduction.