DAG1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: Primary dystroglycanopathies resulting from mutations in the DAG1 gene that encodes dystroglycan are quite rare, however secondary dystroglycanopathies, of which there are multiple types, occur due to mutations in multiple genes involved in the glycosylation of α-dystroglycan (selected examples discussed ahead).