Editing Stones: Epidemiology and Pathogenesis (section)

=== Causes ===
*'''Cystinuria'''
** '''An inherited autosomal recessive disorder caused by mutations of SLC7A9 or SLC3A1'''
** '''Results in inadequate renal tubular reabsorption of the amino acids Cystine, Ornithine, Lysine, and Arginine (COLA), and also inadequate intestinal absorption of these amino acids'''
*** Several factors determine the solubility of cystine, including cystine concentration, pH, ionic strength, and urinary macromolecules
** May be accompanied by other metabolic abnormalities
**'''Sodium nitroprusside spot test will turn urine purple in the presence of cystine.'''
*** '''Used for screening purposes to identify patients with cystine stone disease''' who are undergoing a 24 hour urine collection for evaluation.