Asymptomatic hereditary xanthinuria: a case report.

A 22-year-old man with hereditary xanthinuria is reported. A biochemical study of the patient showed elevated serum levels of xanthine and hypoxanthine with concomitant increases in urinary excretion of xanthine and hypoxanthine. The xanthine oxidase activity in the duodenal mucosa of the patient was about 1.5% of normal value. Urinary excretion of xanthine and hypoxanthine of his parents and his eldest brother were significantly higher than the corresponding normal values, but the values were much less than those of the patient. The results suggested that the patient was homozygote, and his parents and his eldest brother were heterozygotes.