The function of RXYLT1 (ribitol xylosyltransferase 1, ENSG00000118600) is as follows. Acts as a UDP-D-xylose:ribitol-5-phosphate beta1,4- xylosyltransferase, which catalyzes the transfer of UDP-D-xylose to ribitol 5-phosphate (Rbo5P) to form the Xylbeta1-4Rbo5P linkage on O- mannosyl glycan (Probable) (PubMed:27733679, PubMed:29477842). Participates in the biosynthesis of the phosphorylated O-mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N-acetylglucosamine-beta-4- (phosphate-6-)mannose), a carbohydrate structure present in alpha- dystroglycan (DAG1), which is required for binding laminin G-like domain-containing extracellular proteins with high affinity (Probable) (PubMed:25279699, PubMed:27601598, PubMed:27733679). {ECO:0000269|PubMed:25279699, ECO:0000269|PubMed:27601598, ECO:0000269|PubMed:27733679, ECO:0000269|PubMed:29477842, ECO:0000305|PubMed:27130732}.