DAG1 and muscular dystrophy: Extensive O-glycosylation of α-dystroglycan (α-DG) is required for normal muscle function, and defects in this process result in various forms of muscular dystrophy (Michele et al., 2002; Ohtsubo and Marth, 2006; Yoshida-Moriguchi and Campbell, 2015; Praissman et al., 2016; Sheikh et al., 2017).