Question:medium
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:
Show Hint
Use COLA - which listed amino acid is not in that group?
Updated On: Jun 23, 2026
- Lysine
- Citrulline
- Arginine
- Ornithine
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Recall the single transporter that fails in cystinuria. It carries only the dibasic (and cystine) amino acids, summarised by the memory aid COLA.
Step 2: Expand COLA: $Cystine$, $Ornithine$, $Lysine$, $Arginine$. These four spill into the urine because their shared renal carrier is broken, and cystine's poor solubility produces the characteristic stones.
Step 3: Now scan the options against COLA. Lysine, arginine and ornithine all belong to the group, so all three show defective reabsorption.
Step 4: Citrulline is absent from COLA - it uses different handling and is not lost in cystinuria. The question asks for the odd one out, so citrulline is the answer.
\[\boxed{\text{Citrulline}}\]
Step 2: Expand COLA: $Cystine$, $Ornithine$, $Lysine$, $Arginine$. These four spill into the urine because their shared renal carrier is broken, and cystine's poor solubility produces the characteristic stones.
Step 3: Now scan the options against COLA. Lysine, arginine and ornithine all belong to the group, so all three show defective reabsorption.
Step 4: Citrulline is absent from COLA - it uses different handling and is not lost in cystinuria. The question asks for the odd one out, so citrulline is the answer.
\[\boxed{\text{Citrulline}}\]
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