A rare occurrence of xanthine urolithiasis in siblings with Lesch–Nyhan syndrome treated with Allopurinol—a case report
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Introduction
Lesch–Nyhan syndrome (LNS) is an X-linked disorder affecting the metabolism of the purine salvage pathway leading to excessive serum uric acid production. Treatment of hyperuricemia with Allopurinol is usually effective to lower serum uric acid concentration to acceptable levels. Allopurinol blocks the conversion of hypoxanthine and xanthine to serum uric acid in the purine degradation pathway. The effect of Allopurinol may result in excessive buildup of xanthine, potentially resulting in urolithiasis composed of xanthine. This rare occurrence poses a unique challenge maintaining a balance between lowering hyperuricemia and preventing the development of xanthine urolithiasis. This case report includes two siblings with LNS treated with Allopurinol who developed xanthine urolithiasis.
Case description
Patients are siblings, a 22-year-old male and a 21-year-old female, with LNS diagnosed in early childhood. They both share similar manifestations of the disease and were treated with Allopurinol with an intended therapeutic window of serum uric acid levels since diagnosis. Both were prone to developing urolithiasis and nephrolithiasis, the male more than the female, regardless of the medical regimen. Uric acid and calcium levels were normal in the serum and urine. Chemical analysis of calculi eliminated by both siblings revealed xanthine stones.
Conclusions
Patients with LNS tend to develop stones composed of urate. Rarely, they can also precipitate stones composed of xanthine resulting from its buildup in serum and urine by Allopurinol. This complication should be considered in all patients undergoing treatment with Allopurinol. Careful clinical monitoring and dose adjustments of Allopurinol must balance the need to control hyperuricemia with avoiding excessive blockade of hypoxanthine.
