A case of renal hypouricemia associated with increased plasma oxypurine concentration due to its decreased excretion

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We report a case of decreased urate and increased oxypurine concentrations in plasma due to impaired renal handling of these purines. The patient was a 50-year-old man suffering from Parkinsonism. His serum urate concentration was low (0.98±0.02mg/dl [58.3±1.2μmol/l ]; Mean ± S. E. ), but renal urate clearance and percentage of urate clearance to creatinine clearance were high (30.3 ±1.6ml/min and 31.4±1.2%, respectively), and were not affected by pyrazinamide or probenecid loading. These findings indicated that hypouricemia in this case was caused by impaired tubular reabsorption of urate. On the other hand, his plasma oxypurine concentrations were elevated (hypoxanthine 5.90±1.55μmol/l vs. normal controls 1.72±0.08; xanthine 1.32±0.05 vs.0.49±0.02), and plasma inosine level was also high (2.52±0.29 vs.0.41±0.05). The xanthine oxidase activity and oxypurine concentration in the liver were normal. We studied the renal clearance of oxypurine and inosine in this patient. His renal clearance of oxypurine was about 50% of normal controls (CHX/Ccr 11.8±1.1% vs.25.0±1.6; CX/Ccr 25.5±2.6 vs.46.5±2.4). Clearance of inosine (CIno/Ccr) was also reduced to 25% of normal controls (7.2±0.5 vs.29.4±5.9). These results suggested that increased plasma concentration of oxypurine in this patient was due to the decreased renal excre tion of oxypurine.
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