part of part of has part has part characteristic of has modifier xanthine Xanthinuria Xanthinuria is generally caused by a defect in the xanthine oxidase, an enzyme that catalyzes the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. The formation of xanthine stones in the urinary tract is the main evidence of this abnormality. Abnormal urinary nucleobase concentration abnormal increased amount urine