Amino acids excreted in the urine in cystinosis
**Core Concept**
Cystinosis is a rare genetic disorder characterized by the accumulation of cystine within lysosomes due to a defect in the cystinosin transporter. This leads to the breakdown of lysosomes and subsequent organ damage. The condition is caused by mutations in the CTNS gene.
**Why the Correct Answer is Right**
Cystinosis is associated with the accumulation of cystine in the lysosomes of renal tubular cells, leading to Fanconi syndrome and renal failure. The cystine is excreted in the urine in its dimeric form, cystine. This is due to the impaired transport of cystine out of the lysosomes by the cystinosin transporter. The accumulation of cystine leads to the breakdown of lysosomes, resulting in cellular damage and organ dysfunction.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct amino acid involved in cystinosis. While cystinuria involves the excretion of cystine in the urine, it is a different condition from cystinosis.
**Option B:** This option is incorrect because it is not a known amino acid associated with cystinosis. The condition is specifically characterized by the accumulation of cystine.
**Option C:** This option is incorrect because it does not accurately describe the amino acid involved in cystinosis. The condition is not characterized by the excretion of lysine in the urine.
**Clinical Pearl / High-Yield Fact**
Cystinosis is a rare genetic disorder that can lead to renal failure and other systemic complications if left untreated. Early diagnosis and treatment with cysteamine can help slow the progression of the disease.
**Correct Answer:** C. Cystine