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Hereditary nephropathy associated with hyperuricemia and gout.

BACKGROUND
The clinical characteristics of hereditary nephropathy associated with hyperuricemia or gout have not been fully described, and the pathogenetic role of increased serum urate concentration is controversial.


METHODS
We examined the clinical characteristics of 14 patients and purine metabolism of seven patients, while they were on a purine-restricted diet, in two families with hereditary nephropathy associated with asymptomatic hyperuricemia or gout. Results of plasma and urinary purine measurements were compared with those obtained in 25 patients with gout and renal insufficiency and in 25 normal subjects. Eight subjects in both families were followed up for a mean of 44 months. Allopurinol was given to all patients and enalapril maleate to hypertensive subjects.


RESULTS
All patients had some combination of hyperuricemia, gout, renal insufficiency, arterial hypertension, and reduced kidney size. Decreased glomerular filtration rate was proportional to the decreased renal plasma flow. Renal vascular resistance was markedly increased in the patients with diminished renal plasma flow. All patients with familial nephropathy showed diminished urinary uric acid, hypoxanthine, and xanthine excretion rates. Purine under-excretion was more severe in affected patients with familial nephropathy than in patients with gout and renal insufficiency. Kidney biopsy specimens from three patients with familial nephropathy showed tubulointerstitial lesions and ischemic changes in glomeruli but no uric acid crystals. The kidney uric acid content was normal. Allopurinol treatment normalized serum urate levels, but serum creatinine concentrations increased and creatinine clearance decreased in all patients with familial nephropathy. One patient with gout only at initial evaluation developed renal failure during the follow-up period.


CONCLUSIONS
Increased serum urate concentrations in hereditary nephropathy associated with hyperuricemia and gout are due to severe impairment of uric acid excretion. Hyperuricemia does not appear, however, to be of pathogenetic relevance and may be a consequence of a primary disruption of renal hemodynamics.