Two cases of renal hypouricemia with nephrolithiasis

We treated two cases of renal hypouricemia with nephrolithiasis. The serum uric acid level of the first patient was 1.5 mg/dl, and the ratio of uric acid clearance to creatinine clearance (CUA/Ccr) was 75.7%. In the benzbromarone (BZB) suppression test, CUA/Ccr was increased from 60.4% to 130.0%, but was not decreased in response to the pyrazinamide (PZA) suppression test. This patient was considered to have a presecretory reabsorptive urate transportation defect. His condition was also associated with IgA nephropathy. The serum uric acid level in the second patient was 1.0 mg/dl and CUA/Ccr was 56.0%. Neither PZA nor BZB had a significant effect on CUA/Ccr. He was considered to have a subtotal uric acid transportation defect. Both patients were incidentally found to have nephrolithiasis. The second patient had abnormal maximum tubular secretory capacity for para-aminohippurate (PAH) (TmPAH), and was found to have two kinds of proximal tubular abnormalities related to uric acid and PAH.