Wiktionary
xanthinuria
n. 1 An abnormally high level of xanthine in one's urine. 2 The genetic disorder that causes this.
Wikipedia
Xanthinuria
Xanthinuria, also known as xanthine oxidase deficiency, is a rare genetic disorder causing the accumulation of xanthine. It is caused by a deficiency of the enzyme xanthine oxidase.
It was first formally characterized in 1954.