RXYLT1 and neuromuscular disease caused by qualitative or quantitative defects of alpha-dystroglycan: However, the functionally relevant glycan structure of α-DG has not been well delineated, notwithstanding that several mutants associated with dystroglycanopathy have been identified in fukutin14, fukutin-related protein (FKRP)15, UDP-GlcNAc:βGal β-1,3-N-acetylglucosaminyltransferase 1 (B3GNT1)16, isoprenoid synthase domain containing (ISPD)17, 18, 19, and transmembrane protein 5 (TMEM5)19, which are associated with impaired formation of α-DG laminin-binding glycans.