Alpha-dystroglycan is a component of the Dystrophin Associated Protein complex (DAP) which binds to various ligands in the extracellular matrix of muscle and other tissues, including laminin-alpha2, perlecan, neurexin and agrin. Disruption of the interaction between alpha-dystroglycan and its ligands has severe consequences for muscle and brain function and structure. The pathological hallmark is reduced immunolabeling of skeletal muscle with antibodies recognizing glycosylated epitopes on alpha-dystroglycan.