Xanthinuria, Xanthine Stone Disease

Xanthinuria is a descriptive term for excess urinary excretion of the purine base xanthine. Xanthine is a nitrogenous by-product of the metabolism of certain proteins. It is normally found in the muscles, liver, spleen, pancreas, and urine and is broken down and degraded to uric acid by the enzyme xanthine dehydrogenase. When there is a deficiency of this enzyme, xanthine accumulates in the plasma and urine and causes disorders of blood vessels, muscles, kidneys, bladder stones and eventually kidney failure.

Classic xanthinuria is one form of xanthinuria that is divided into two types based on the enzyme deficiency. Both types are inherited in an autosomal recessive manner.

Forms of Xanthinuria

Classic xanthinuria type I is the result of a deficiency of xanthine dehydrogenase enzyme. Type II xanthinuria is characterized by a deficiency of xanthine dehydrogenase and a related enzyme, aldehyde oxidase.

Organs Affected by Xanthinuria

The primary organs affected in xanthinuria are the kidney and, to a lesser extent, skeletal muscles and joints. Kidney complications are initiated by the formation of xanthine crystals in the tubules, leading to stone formation. Irritation of the tubular epithelium by xanthine crystals results in bloody urine (hematuria), whereas renal tissue deposits induce an inflammation of the kidneys. Urolithiasis (stones in the urinary tract) is the most common clinical manifestation of the xanthinuria. Further kidney complications include acute and chronic kidney failure and even end-stage kidney disease.

Dog and Cat Breeds At Risk

In dogs and cats, xanthinuria is an uncommon metabolic disorder clinically manifested as urolithiasis. Affected animals may have few or no clinical signs except for the formation of xanthine stones. The disease has been reported in Cavalier King Charles spaniels, Dachshunds, Himalayan cats.

Management of Xanthinuria

The stones can be removed surgically, but the disease tends to recur. Since alkalinization (making less acidic) has little affect upon the solubility of xanthine it adds little to the therapeutic regimen. Allopurinol, an inhibitor of xanthine oxidase (the enzyme responsible for catalyzing the conversion of xanthine and hypoxanthine to uric acid) is recommended to decrease urinary uric acid excretion in dogs. Allopurinol treatment must be accompanied y a low purine diet.³ High fluid intake is the key to therapy. Dehydration is to be avoided whenever possible. Foods with high purine content such as liver, kidney, bacon, veal, venison, turkey should be avoided. There currently is no drug available that will reduce the risk of xanthine stone formation in these rare patients.

References

1. Xanthine urolithiasis in a cat: a case report and evaluation of a candidate gene for xanthine dehydrogenase. Journal of Feline Medicine & Surgery , Volume 9 , Issue 6, Pages 503 - 508S . Tsuchida, A . Kagi, H . Koyama, M . Tagawa
2. Michael E. Moran. Uric Acid Stone Disease
3. P. Nagaraja Rao, Nagaraja P. Rao, John P. Kavanagh, Glenn M. Preminger. Urinary Tract Stone Disease