Types of Stones
Xanthine

These stones may result from a genetic disorder in patients who have an enzyme deficiency. They have a deficiency of the enzyme xanthine oxidase, which results in the production of xanthine and hypoxanthine rather than uric acid as an end product of purine metabolism. Urinary calculi occur in about a third of patients with this enzyme deficiency. These calculi may also develop in patients taking allopurinol, an xanthine-oxidase inhibitor. Pure xanthine stones are radiolucent, but approximately a third of patients with xanthinuria there may be a calcium salt mixture to render these stones slightly radio-opaque. These stones tend to be small, round or oval.

Suggested readings
Ogawa A, Watanabe K, Minejima N: Renal xanthine stone in Lesch-Nyhan syndrome treated with allopurinol. Urology 26:56, 1985.

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