The function of UXS1 (UDP-glucuronate decarboxylase 1, ENSG00000115652) is as follows. Catalyzes the NAD-dependent decarboxylation of UDP-glucuronic acid to UDP-xylose (PubMed:22810237, PubMed:23656592, PubMed:25521717, PubMed:40836090). Necessary for the biosynthesis of the core tetrasaccharide in glycosaminoglycan biosynthesis (PubMed:22810237, PubMed:23656592, PubMed:25521717, PubMed:40836090). Catalyzes the synthesis of UDP-xylose in two steps: the hydroxyl group of UDP- glucuronic acid is first oxidized using an enzyme-bound NAD(+) as electron acceptor, favoring the decarboxylation yielding a UDP-4- ketoxylose reaction intermediate and a reduced cofactor NADH bound to the catalytic pocket (PubMed:22810237, PubMed:40836090). In the second step, the 4-keto group is reduced resulting in UDP-xylose and the restoration of the enzyme to its NAD(+)-bound form (PubMed:22810237, PubMed:40836090). {ECO:0000269|PubMed:22810237, ECO:0000269|PubMed:23656592, ECO:0000269|PubMed:25521717, ECO:0000269|PubMed:40836090}.