A rare metabolic disorder characterized by excessive levels of xanthine in the urine. It is caused by a deficiency of the enzymes xanthine dehydrogenase (as in xanthinuria type I) and enzyme aldehyde oxidase (as in xanthinuria type II) as well as sulfite oxidase which are needed to metabolize xanthine. The metabolic abnormality causes severe xanthinuria with neurological symptoms. The condition may be an inherited or acquired (due to certain drug therapies) deficiency. See also Molybdenum, cofactor deficiency, inherited