Acquired xanthinuria is generally iatrogenic. Allopurinol treatment, administered to block XOR and prevent uric acid overproduction, leads to the accumulation of xanthine. Rarely, in the setting of aggressive chemotherapy with rapid tumor lysis or in patients with HPRT deficiency on allopurinol therapy, complications of renal failure can develop from xanthine crystal nephropathy. The disease is acquired xanthinuria (Monarch Disease Ontology term MONDO_0021180).