pediatrics
Cystinuria
Pathophysiology of Cystinuria
The primary defect results in diminished renal proximal tubular reabsorption of cystine and increased urinary cystine concentration. Cystine is poorly soluble in acidic urine, so when its urinary concentration exceeds its solubility, crystals precipitate and cystine Urinary Calculi form. Males are generally affected more than females. Resorption of other dibasic amino acids (lysine, ornithine,arginine) is also impaired but causes no problems because these amino acids have an alternative transport system separate from that shared with cystine. Furthermore, they are more soluble than cystine in urine, and their increased excretion does not result in crystal or stone formation. Their absorption (and that of cystine) is also decreased in the small bowel. 