DAG1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: Muscular dystrophies with evidence of reduced glycosylation of the transmembrane glycoprotein α-dystroglycan on skeletal muscle biopsy [1] are collectively termed α-dystroglycanopathy (α-DG) [2–4], and they constitute a clinically and genetically heterogeneous group of autosomal recessive muscular dystrophies with variable neurological and ophthalmic involvement.