Cystinuria: pathogenesis and treatment.

Cystinuria is an inherited disorder of cystine and dibasic amino acids involving renal and intestinal transport mechanisms. Cystine stones are caused by the excessive renal excretion of cystine due to its low solubility in urine. The prevalence of homozygous cystinuria appears to vary in different parts of the world. Cystine stones frequently occur in the second or third decade of life, with an occasional occurrence in infancy and in old age. Urinary cystine excretion exceeding 250 mg/g creatinine is usually diagnostic of homozygous cystinuria. The goal of treatment is to reduce the urinary cystine concentration below its solubility limit (250 mg/l).