Xanthinuria, also known as xanthine oxidase deficiency.
X is a rare genetic disorder causing the accumulation of xanthine, due to a deficiency of the enzyme xanthine oxidase.
High concentrations of xanthine in blood and urine, can lead to renal failure and xanthine kidney stones.
X is one of the rarest types of kidney stones.
Xanthine oxidase is an enzyme necessary for converting xanthine to uric acid.
There is no specific treatment: maintaining a high fluid intake and avoiding foods that are high in purine.