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Limb-girdle muscular dystrophy type 2E (LGMD2E), resulting from mutations in β-sarcoglycan (SGCB), is a progressive dystrophy with deteriorating muscle function, respiratory failure, and cardiomyopathy in 50% or more of LGMD2E patients. SGCB knockout mice share many of the phenotypic deficiencies of LGMD2E patients. To investigate systemic SGCB gene transfer to treat skeletal and cardiac muscle deficits, we designed a self-complementary AAVrh74 vector containing a codon-optimized human SGCB transgene driven by a muscle-specific promoter. We delivered scAAV.MHCK7.hSGCB through the tail vein of SGCB−/− mice to provide a rationale for a clinical trial that would lead to clinically meaningful results. This led to 98.1% transgene expression across all muscles that was accompanied by improvements in histopathology. Serum creatine kinase (CK) levels were reduced following treatment by 85.5%. Diaphragm force production increased by 94.4%, kyphoscoliosis of the spine was significantly reduced by 48.1%, overall ambulation increased by 57%, and vertical rearing increased dramatically by 132% following treatment. Importantly, no adverse effects were seen in muscle of wild-type mice injected systemically with scAAV.hSGCB. In this well-defined model of LGMD2E, we have demonstrated the efficacy and safety of systemic scAAV.hSGCB delivery, and these findings have established a path for clinically beneficial AAV-mediated gene therapy for LGMD2E.

Limb–girdle muscular dystrophy type 2E/R4 (LGMD2E/R4) is a rare disease that currently has no cure. It is caused by defects in the SGCB gene, mainly missense mutations, which cause the impairment of the sarcoglycan complex, membrane fragility, and progressive muscle degeneration. Here, we studied the fate of some β-sarcoglycan (β-SG) missense mutants, confirming that, like α-SG missense mutants, they are targeted for degradation through the ubiquitin–proteasome system. These data, collected using HEK-293 cells expressing either the I119F- or Y184C mutants of β-SG, were subsequently confirmed in primary myotubes derived from an LGMD2E/R4 patient carrying a homozygous I92T mutation. The knowledge that β-SG with an amino acid substitution shares a pathway of degradation with α-SG mutants, allowed us to explore the pharmacological approach successfully tested in LGMD2D/R3. Several CFTR correctors, particularly corrector C17, preserved β-SG mutants from degradation and promoted localization at the sarcolemma of the entire SG complex. The presence of the complex, despite containing a mutated subunit, improved sarcolemma integrity, as evidenced by the reduced creatine kinase release from myotubes under hypoosmotic stress. These results suggest that β-SG missense mutants undergo proteasomal degradation as α-SG mutants, and that CFTR correctors, particularly C17, may be used as a potential therapeutic option for recovering and stabilizing the SG complex in patients with sarcoglycanopathies.

Microdeletion syndromes are commonly transmitted as dominant traits and are frequently associated with variably expressed pleiotropic phenotypes. Nonlethal homozygous microdeletions, on the other hand, are very rare. Here, we delineate the fifth and so far largest homozygous microdeletion in nonmalignancies of approximately 400 kb on chromosome 4q11‐q12 in a large consanguineous East‐Anatolian family with six affected patients. The deleted region contains the beta‐sarcoglycan gene (SGCB), the predicted gene SPATA18 (spermatogenesis associated 18 homolog) and several expressed sequence tags. Patients presented with a severe and progressive Duchenne‐like muscular dystrophy phenotype, a combination of hyperlaxity and joint contractures, chest pain, palpitations, and dyspnea. © 2005 Wiley‐Liss, Inc.

Autosomal recessive muscular dystrophies called “sarcoglycanopathies” result from mutations in the genes encoding α‐, β‐, γ‐, or δ‐sarcoglycan complex components. The present study involved six unrelated families from Northern Italy showing mutations in the β‐ or γ‐sarcoglycan genes. An 8 bp duplication in the β‐sarcoglycan gene and 1 bp insertion in the γ‐sarcoglycan gene occur with high frequency in our population. These mutations have never been reported thus far in other countries. Many patients are homozygotes for a single mutation, although they derived from non‐consanguineous marriages. We suggest that these alleles are “private” mutations of this geographical region. A panel of highly informative microsatellite markers that map in the β‐ and γ‐sarcoglycan gene locus was used to assess the haplotypes among affected patients and control population, in order to test the presence of linkage disequilibrium. We found that the 8 bp duplication in the β‐sarcoglycan gene and the 1 bp insertion in the γ‐sarcoglycan gene are in linkage disequilibrium with neighbouring polymorphisms. The recurrence of specific sarcoglycan mutations in Northern Italy is probably due to a founder effect, combined with a relative genetic isolation. Hum Mutat 16:13–17, 2000. © 2000 Wiley‐Liss, Inc.