Urinary glycosaminoglycans as risk factors for uric acid nephrolithiasis: case control study in a Sardinian genetic isolate.

OBJECTIVES: To assess the clinical association between glycosaminoglycan (GAG) excretion and uric acid (UA) nephrolithiasis by measuring urinary GAG levels in a case-control study conducted in a Sardinian genetic isolate. Inhibitors of crystallization such as GAGs seem to be involved in kidney stone formation. METHODS: Overnight (12-hour) urinary excretion of GAGs, calcium, oxalate, and UA were measured in urine samples from 60 patients who had formed at least one urinary stone (UA or mixed) and 52 healthy controls. The total GAG concentration was measured by a dye-binding assay, and the values were normalized against creatinine to obtain values in micrograms of GAG per milligram creatinine. Statistical analysis was performed using t tests and logistic regression analysis. RESULTS: No significant difference was found between the two groups with respect to calcium and oxalate concentrations. Nonetheless, stone formers had significantly lower levels of GAGs (29.5 +/- 2.2 versus 36.4 +/- 3.9 microg/mg creatinine, P = 0.003) and greater levels of UA (385.11 +/- 38.2 versus 298.43 +/- 31.4 mg/12 hr, P = 0.0010) than did the normal controls. CONCLUSIONS: We report that the lower excretion of GAGs in stone formers could impair their inhibitory activity on UA stone formation, and, as a consequence, it may represent a risk factor for this form of urolithiasis.