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