Question
Cystinuria is associated with excretion of which Amino Acids in urine:
A. Cysteine, lysine, Tyrosine, and alanine
B. Cysteine, lysine, ornithine, and alanine
C. Cysteine, ornithine, lysine and arginine
D. Cysteine, Ornithine, Lysine, Arginine
Show Answer
|
Correct Answer » D
Explanation
|
|
Cystinuria
- Biochemical Defect: An autosomal recessive disorder that results in the formation of a defective amino acid transporter in the renal tubule and intestinal epithelial cells.
- Pathophysiology: The amino acid transporter is responsible for transporting cystine, ornithine, lysine, and arginine. Defective tubular reabsorption of these amino acids in the kidneys results in increased cystine in the urine, which can precipitate and cause kidney stones.
- Clinical Manifestations: Cystine kidney stones presenting with severe, intermittent flank pain and hematuria.
- Lab findings: Increased urinary excretion of cystine, ornithine, arginine, and lysine on urine amino acid chromatography; hematuria and cystine crystals (hexagonal) on the cooling of acidified urine sediment.
- Imaging: Radiopaque kidney stones on CT scan. The most specific test is the cyanide–nitroprusside test
Treatment: Low-methionine diet; increased fluid intake; acetazolamide to alkalinize the urine. If this fails then patients are usually started on chelating therapy with penicillamine.
