Qualitative or quantitative defects of delta-sarcoglycan

Qualitative or quantitative defects of delta-sarcoglycan (encoded by the SGCD gene) are associated with limb-girdle muscular dystrophy type R6 (LGMDR6), formerly known as limb-girdle muscular dystrophy type 2F (LGMD2F). Delta-sarcoglycan is a component of the sarcoglycan complex, which is part of the dystrophin-associated glycoprotein complex (DGC) that provides structural stability to the muscle cell membrane (sarcolemma) during contraction. When delta-sarcoglycan is absent, reduced, or dysfunctional, the entire sarcoglycan subcomplex can be destabilized, leading to progressive muscle fiber damage and degeneration. The disease primarily affects the skeletal muscular system, with progressive proximal muscle weakness involving the pelvic and shoulder girdle muscles. Onset is typically in childhood, often before the age of 10 years, and the condition can progress to severe disability with loss of ambulation. Cardiomyopathy, particularly dilated cardiomyopathy, is a recognized and clinically significant feature that can occur independently of or alongside skeletal muscle involvement. Elevated serum creatine kinase (CK) levels are a hallmark laboratory finding. Respiratory insufficiency may develop as the disease progresses due to weakness of respiratory muscles. There is currently no cure for LGMDR6. Management is supportive and multidisciplinary, including physical therapy to maintain mobility, cardiac monitoring and treatment of cardiomyopathy, respiratory support when needed, and orthopedic interventions for contractures or scoliosis. Gene therapy approaches targeting the SGCD gene are under investigation in preclinical and early clinical research settings. Genetic counseling is recommended for affected families.

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