• Definition: an inherited genetic disorder characterized by the accumulation of cystine in the kidneys and bladder due to a disruption of amino acid transporter function in the proximal convoluted tubule and intestine.
• Pathophysiology: impaired renal reabsorption of dibasic amino acids (cystine, ornithine, arginine, lysine) → accumulation of cystine in the urine → frequent formation of hexagonal cystine stones

Mnemonic

Cystine, Ornithine, Lysine, and Arginine (COLA) share a common transporter in kidney and intestine.

• Clinical features: recurrent nephrolithiasis > Cystine stones, starting as early as childhood
• Diagnostics
  • Urine microscopy: hexagonal cystine stones
  • Urinary cyanide nitroprusside test: positive
• Treatment: increase cystine solubility to counter the formation of renal stones
  • Adequate hydration
  • Urinary alkalinization: acetazolamide, potassium citrate
  • Chelating agents: penicillamine