Question:
In cystinuria, a reabsorption defect is present for all of the following amino acids, EXCEPT:
In cystinuria, a reabsorption defect is present for all of the following amino acids, EXCEPT:
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Use COLA - which listed amino acid is not in that group?
Updated On: Jun 23, 2026
- Lysine
- Citrulline
- Arginine
- Ornithine
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Cystinuria is an autosomal recessive disorder caused by a defective dibasic amino acid transporter in the renal tubule and intestinal epithelium.
Step 2: The affected transporter handles the dibasic amino acids cystine, ornithine, lysine and arginine. A useful mnemonic is COLA (Cystine, Ornithine, Lysine, Arginine). Defective reabsorption of these leads to increased urinary excretion, with cystine precipitating to form hexagonal crystals and radiopaque stones.
Step 3: Citrulline is not a substrate of this transporter, so its reabsorption is unaffected. Therefore the EXCEPT answer is Citrulline.
Step 4: Lysine, arginine and ornithine are all part of the COLA group whose transport is defective, which is why each of them is excreted in excess in cystinuria and cannot be the exception.
Step 2: The affected transporter handles the dibasic amino acids cystine, ornithine, lysine and arginine. A useful mnemonic is COLA (Cystine, Ornithine, Lysine, Arginine). Defective reabsorption of these leads to increased urinary excretion, with cystine precipitating to form hexagonal crystals and radiopaque stones.
Step 3: Citrulline is not a substrate of this transporter, so its reabsorption is unaffected. Therefore the EXCEPT answer is Citrulline.
Step 4: Lysine, arginine and ornithine are all part of the COLA group whose transport is defective, which is why each of them is excreted in excess in cystinuria and cannot be the exception.
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