A case of classical xanthinuria (type 1) with diabetes mellitus and Hashimoto's thyroiditis

In a 62-year-old woman with non-insulin-dependent diabetes mellitus and Has himoto's thyroiditis, hypouricemia was detected by a routine examination. H er plasma uric acid level was markedly low and urinary excretion of uric ac id was undetectable. The high plasma and urine levels of xanthine were obse rved, although those of hypoxanthine were within normal ranges at rest afte r an overnight fast. After taking diet, plasma concentration and urinary ex cretion of hypoxanthine were markedly increased together with those of xant hine. The xanthine oxidase activity of duodenal mucosa was below the limits of detection. Allopurinol was metabolized to oxypurinol and pyrazinamide t o 5-hydroxypyrazinamide in spite of no activity of xanthine oxidase, sugges ting that aldehyde oxidase converted allopurinol to oxypurinol and pyrazina mide to 5-hydroxypyrazinamide. Based on these findings, she was diagnosed a s having a subtype of classical xanthinuria type 1 with the normal plasma c oncentration of hypoxanthine in fast. (C) 1999 Elsevier Science B.V. All ri ghts reserved.