Underexcretory-type hyperuricemia, disproportionate to the reduced glomerular filtration rate, in two boys with mild proteinuria.

Two unrelated boys with mild persistent proteinuria and underexcretory-type hyperuricemia of more than 9.0 mg/dl (535 mumols/l) are described. The proteinuria was detected at age 10 and 6 years, respectively. The fractional excretion of uric acid in both was low at 2-3%, when the creatinine clearance was decreased by about 50%. Tissue examination revealed focal interstitial fibrosis in both patients and medullary urate crystals in one patient in whom medullary tissue was obtained on biopsy. An immunofluorescence study was negative for immunoglobulins, complements and fibrin. Treatment of hyperuricemia did not prevent further deterioration of their renal function. One of them underwent a renal transplantation and then his serum uric acid level returned to the normal range. Neither patient had a family history of hyperuricemia, gout or inherited progressive renal disease. Both patients are likely to be sporadic cases of familial nephropathy with gout, an autosomal dominant disease, due to a new mutation. Hyperuricemia due to diminished uric acid clearance may be a risk factor or predictor for the development of progressive renal disease in some subjects.