DAG1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: Using a model of severe dystroglycanopathy (IspdL79*) and Dystroglycan conditional mutants, we now show that Dystroglycan is required for proper development of several major axon tracts, including commissural axons in the spinal cord and several major axon tracts in the forebrain.