All of the following amino acids are excreted in cystinuria, EXCEPT:
**Core Concept**
Cystinuria is a genetic disorder characterized by the defective reabsorption of certain amino acids in the kidneys, leading to their excessive excretion in the urine. This condition is caused by mutations in the SLC3A1 or SLC7A9 genes, which encode proteins involved in the transport of cystine and other dibasic amino acids.
**Why the Correct Answer is Right**
The correct answer is related to the specific amino acids that are affected by cystinuria. In this condition, cystine, lysine, arginine, and ornithine are abnormally reabsorbed in the kidneys due to the defective transport proteins. This results in their excessive excretion in the urine, which can lead to the formation of cystine stones. The correct answer should be an amino acid that is not typically associated with cystinuria.
**Why Each Wrong Option is Incorrect**
* **Option A:** Cystine is a key amino acid involved in cystinuria, as it is one of the amino acids that is abnormally reabsorbed in the kidneys.
* **Option B:** Lysine is another amino acid that is affected by cystinuria, as it is also abnormally reabsorbed in the kidneys.
* **Option D:** Ornithine is a dibasic amino acid that is typically associated with cystinuria, as it is abnormally reabsorbed in the kidneys.
**Clinical Pearl / High-Yield Fact**
In patients with cystinuria, the excessive excretion of cystine and other dibasic amino acids can lead to the formation of cystine stones, which are a common complication of this condition.
**Correct Answer:** C. Histidine is not typically associated with cystinuria, making it the correct answer.