LARGE1 serves as a glycosyltransferase which participates in glycosylation of the muscle membrane protein alpha-dystroglycan. Mutations of LARGE1 lead to hypoglycosylation of alpha-dystroglycan and cause congenital muscular dystrophy (MDC1D) associated with severe mental retardation. Altered alpha-dystroglycan glycosylation may also play a role in cancer, as hypoglycosylation of the protein and loss of laminin binding have been demonstrated in invasive carcinoma cells.