It is now well known that genes responsible for the biosynthesis of the O-mannosyl-linked glycans on alpha dystroglycan (αDG) are required for proper binding of laminin and other extracellular matrix proteins to αDG and that defective glycosylation resulting from their mutation leads to various forms of dystroglycanopathy, which have skeletal muscle pathology and sometimes also pathology of the eye and brain13, 31. This evidence concerns the gene DAG1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan.