Cystinuria

• Facts:
  Group of disorders characterized by impaired amino acid transport
  
  Defective transport of dibasic amino acids (cystine, lysine, arginine, orthinine) by the brush borders of renal tubular and intestinal epithelial cells
  
• History / PE:
  Family history of renal stones
  Recurrent stones "since childhood"
• Diagnosis:
  Hexagonal crystals (urinalysis)
  Positive urinary cyanide nitroprusside test (detects elevated cystine)
• Notes:
  Cystine is poorly soluble in water, leading to formation of hard, radiopaque renal stones
• See Also:
  Nephrolithiasis