the genetic disorder that causes this.
xanthinuria: a rare metabolic disorder that is caused by lack of an enzyme needed to process xanthine, an alkaloid found in caffeine; theobromine; theophylline; and related substances. unchecked, xanthinuria can lead to kidney stone formation. treatment involves avoiding foods and drinks that contain xanthine derivatives, such as coffee, tea, and cola. classic xanthinuria is inherited in an autosomal recessive manner and involves a defect in the enzyme xanthine dehydrogenase. medicinenet.com
the combined incidence of hereditary xanthinuria types i and ii is estimated to be about 1 in 69,000 people worldwide. however, researchers suspect that the true incidence may be higher because some affected individuals have no symptoms and are never diagnosed with the condition. hereditary xanthinuria appears to be more common in people of mediterranean or middle eastern ancestry. about 150 cases of this condition have been reported in the medical literature. medlineplus.gov