Treatment of cystinuria

Cystine urolithiasis is the only clinical expression of cystinuria, an auto somal recessive genetic defect of the transepithelial transport of cystine and other dibasic amino acids in the kidney. Stones form due to the increas ed excretion of cystine, which is poorly soluble at normal urine pH. Cystin e stones are often resistent to extracorporeal shock wave lithotripsy, so t hat percutaneous surgery or ureteroscopy are the preferred techniques of st one extraction. Medical preventative treatment is based on high diuresis (g reater than or equal to 1.5 l/m(2) per day) well distributed throughout the day and night, and urine alkalinization up to pH 7.5 by means of sodium bi carbonate and/or potassium citrate. When these basal measures are ineffecti ve at preventing stone recurrence or dissolving pre-existing stones, sulfhy dryl agents such as D-penicillamine or tiopronin, which form highly soluble mixed disulfides with cystine moieties, are to be added to urine dilution and alkalinization, especially when cystine excretion is in excess of 750 m g/day (3 mmol/day). Frequent clinical and ultrasound follow-up is needed to encourage patient compliance and assess efficacy and tolerance of treatmen t.