DAG1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: The presence of O-mannosylated glycans on α-dystroglycan is known to be essential for mediating its binding to extracellular ligands in the basal lamina, and their loss is thought to be central to the pathogenesis of the dystroglycanopathies [2, 3, 16].