ART4 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: Common mechanism underling dystroglycanopathies is the reduced or absent glycosylation of DAG1, a transmembrane glycoprotein that acts in the dystrophin–glycoprotein complex at the neuromuscular junction and in CNS, connecting the actin associated cytoskeleton to the extracellular matrix in skeletal muscle cells, neurons, and glia.