Gamma-sarcoglycan is a protein that in humans is encoded by the SGCG gene.[5][6] The α to δ-sarcoglycans are expressed predominantly (β) or exclusively (α, γ and δ) in striated muscle.[7] A mutation in any of the sarcoglycan genes may lead to a secondary deficiency of the other sarcoglycan proteins, presumably due to destabilisation of the sarcoglycan complex.[8] The disease-causing mutations in the α to δ genes cause disruptions within the dystrophin-associated protein (DAP) complex in the muscle cell membrane.[9] The transmembrane components of the DAP complex link the cytoskeleton to the extracellular matrix in adult muscle fibres,[10] and are essential for the preservation of the integrity of the muscle cell membrane.[11]
SGCG | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | SGCG, A4, DAGA4, DMDA, DMDA1, LGMD2C, MAM, SCARMD2, SCG3, TYPE, 35DAG, gamma-SG, sarcoglycan gamma, LGMDR5 | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 608896 MGI: 1346524 HomoloGene: 194 GeneCards: SGCG | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Gamma-sarcoglycan is one of several sarcolemmal transmembrane glycoproteins that interact with dystrophin, probably to provide a link between the membrane associated cytoskeleton and the extracellular matrix. Defects in the protein can lead to early onset autosomal recessive muscular dystrophy, in particular limb-girdle muscular dystrophy, type 2C (LGMD2C).[6]
Human SGCG gene maps to chromosome 13 at q12, spans over 100 kb of DNA and includes 8 exons.[12]
Gamma-sarcoglycan is a type II transmembrane protein and consists of 291 amino acids. It has a 35 amino acid intracellular N-terminal region, a 25 amino acid single transmembrane domain, and a 231 amino acid extra-cellular C-terminus.[8]
Sarcoglycanopathies are autosomal recessive limb girdle muscular dystrophies (LGMDs) caused by mutations in any of the four sarcoglycan genes: α (LGMD2D), β (LGMD2E), γ (LGMD2C) and δ (LGMD2F).[7] Severe childhood autosomal recessive muscular dystrophy (SCARMD) is a progressive muscle-wasting disorder that segregates with microsatellite markers at γ-sarcoglycan gene. Mutations in the γ-sarcoglycan gene were first described in the Maghreb countries of North Africa,[13] where γ-sarcoglycanopathy has a higher than usual incidence. One common mutation, Δ-521T, which causes a severe phenotype, occurs both in the Maghreb population and in other countries.[12] A Cys283Tyr mutation has been identified in the Gypsy population causing a severe phenotype and a Leu193Ser mutation which causes a mild phenotype.[5][14]