Cystinuria

  • Hereditary defect of renal PCT and intestinal amino acid transporter that prevents reabsorption of Cystine, Ornithine, Lysine, and Arginine (COLA).
  • Patients do not develop amino acid deficiencies, as these amino acids are absorbed in sufficient quantities as oligopeptides.
  • Excess cystine in the urine can lead to recurrent precipitation of hexagonal cystine stones (A)
    • Risk factors of cysteine precipitation include low urine pH < 7, pre-existing crystal nidus & supersaturation.
  • Treatment: urinary alkalinization (eg, potassium citrate, acetazolamide) and chelating agents (eg, penicillamine) ↑ solubility of cystine stones; good hydration.
  • Autosomal recessive. Common (1:7000).
  • Urinary cyanide-nitroprusside test is diagnostic.
  • Cystine is made of 2 cysteines connected by a disulfide bond.

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