However, this hypothesis is in discrepancy with the evidence that ARF does not usually occur in patients with low hypouricemia due to classical xanthinuria, either type I, deficient in xanthine dehydrogenase (XDH) activity (MIM#278300); or type II, deficient in both XDH and aldehyde oxidase (MIM#603592) [19]. Here, AOX1 is linked to xanthinuria.