18 Cystinuria

Abstract

Cystinuria is a disorder of the amino acid transport of cystine and the dibasic amino acids lysine, ornithine, and arginine, which normally occurs in the gut and in the renal tubules after glomerular filtration. Although this defect is evident in epithelial cells of both the kidney and the gut, the clinical manifestations result from a failure of the kidney to reabsorb cystine, leading to excess cystine in the urine. Cystine, but not the dibasic amino acids, has low solubility in acidic urine. Only small rises above the normal concentration exceed the saturation point in acidic urine (Treacher 1966), predisposing the individual to the formation of cystine crystals, uroliths, and urinary obstruction. Cystine calculi can be found from the kidney to the bladder and urethra. The impaired intestinal absorption and renal resorption of cystine and dibasic amino acids do not appear to lead to any clinical deficiency states in dogs and humans, as these are not essential amino acids (Palacin et al. 2001).

Cystinuria was first described in humans nearly 200 years ago when Wollaston reported a new type of renal stone, which he referred to as cystic oxide (Wollaston 1810; Segal and Thier 1995; Palacin et al. 2001). Cystinuria received special recognition as one of the four diseases that Sir Archibald Garrod proposed, in 1908, as “inborn errors of metabolism,” caused by lack of specific metabolic enzymes (Garrod 1908). Although it is now known that an enzyme deficiency is not the defect in cystinuria, the disease has served as the...