The sarcoglycan complex is known to be involved in limb-girdle muscular dystrophy (LGMD) and is composed of at least three proteins: ␣-, -, and ␥-sarcoglycan. ␦-Sarcoglycan has now been identified as a second 35-kDa sarcolemmal transmembrane glycoprotein that shares high homology with ␥-sarcoglycan and is expressed mainly in skeletal and cardiac muscle. Biochemical analysis has demonstrated that ␥-and ␦-sarcoglycan are separate entities within the sarcoglycan complex and that all four sarcoglycans exist in the complex on a stoichiometrically equal basis. Immunohistochemical analysis of skeletal muscle biopsies from patients with LGMD2C, LGMD2D, and LGMD2E demonstrated a reduction of the entire sarcoglycan complex in these muscular dystrophies. Furthermore, we have mapped the human ␦-sarcoglycan gene to chromosome 5q33-q34 in a region overlapping the recently linked autosomal recessive LGMD2F locus.The dystrophin-glycoprotein complex (DGC) 1 (1-4) in skeletal muscle is a complex of sarcolemmal proteins and glycoproteins. It is composed of dystrophin, a cytoskeletal actin-binding protein (5-7); the syntrophins, a 59-kDa triplet of intracellular proteins that bind the C-terminal domain of dystrophin (8 -12); ␣-dystroglycan, a 156-kDa extracellular proteoglycan that binds the G domain of laminin (13-15); -dystroglycan, a 43-kDa transmembrane glycoprotein (2, 3, 13) that binds the cysteine-rich region of dystrophin (16, 17); ␣-, -, and ␥-sarcoglycan, transmembrane glycoproteins of 50, 43, and 35 kDa, respectively (18 -24); and a 25-kDa transmembrane protein (1-4). Recent experiments have demonstrated the existence of two complexes within the DGC (24, 25): the dystroglycan complex, composed of ␣-and -dystroglycan, and the sarcoglycan complex, consisting of ␣-, -, and ␥-sarcoglycan.Defects in DGC components lead to muscle fiber necrosis, the major pathological event in muscular dystrophies (26). In Duchenne muscular dystrophy (DMD), mutations in the dystrophin gene cause the loss of dystrophin and a reduction of the dystrophin-associated proteins (2, 5). One form of congenital muscular dystrophy has recently been characterized as being caused by mutations in the laminin ␣2-chain gene (27, 28). Limb-girdle muscular dystrophy (LGMD) represents a clinically and genetically heterogeneous class of disorders (29, 30). They are inherited as either autosomal dominant or recessive traits. An autosomal dominant form, LGMD1A, was mapped to 5q31-q33 (31, 32), while six genes involved in the autosomal recessive forms were mapped to 15q15.1 (LGMD2A) (33), 2p16-p13 (LGMD2B) (34), 13q12 (LGMD2C) (23,35,36),20), 4q12 (LGMD2E) (21,22), and most recently 5q33-q34 (LGMD2F) (37). Patients with LGMD2C, -2D, and -2E have a deficiency of components of the sarcoglycan complex resulting from mutations in the genes encoding ␥-, ␣-, and -sarcoglycan, respectively (19, 21-23, 38 -40). The gene responsible for LGMD2A has been identified as the musclespecific calpain (41), whereas the genes responsible for LGMD1A, -2B, and -2F are still unknow...