XYLT1 (Xylosyltransferase 1): XYLT1 is an enzyme involved in the biosynthesis of proteoglycans, essential components of the extracellular matrix. It catalyses the addition of xylose to specific serine residues, a crucial step in forming connective tissues. Mutations in XYLT1 can cause skeletal and connective tissue disorders, highlighting its significance in tissue development and maintenance.