The transpoer gene defective in Hanup’s disease:
**Core Concept**
Hanup's disease, also known as Hartnup disease, is a rare genetic disorder that affects the body's ability to absorb certain amino acids from the diet. This condition is characterized by impaired transport of neutral amino acids across the intestinal epithelium and kidney proximal tubules, leading to their excessive excretion in the urine.
**Why the Correct Answer is Right**
The defective gene responsible for Hanup's disease is the SLC6A19 gene, which encodes for a neutral amino acid transporter called B0AT1. This transporter plays a crucial role in the reabsorption of neutral amino acids in the kidneys and intestines. The mutation in the SLC6A19 gene leads to a deficiency of this transporter, resulting in the impaired absorption of neutral amino acids and the characteristic symptoms of Hanup's disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the correct gene responsible for Hanup's disease. While the SLC6A19 gene is indeed involved, other genes may be associated with similar disorders.
* **Option B:** This option is incorrect because it refers to a different genetic disorder, cystinuria, which is caused by mutations in the SLC3A1 and SLC7A9 genes.
* **Option C:** This option is incorrect because it refers to a different gene, SLC6A8, which is associated with X-linked Kanner syndrome, a disorder characterized by intellectual disability and muscle weakness.
* **Option D:** This option is incorrect because it is a placeholder and does not provide a valid answer.
**Clinical Pearl / High-Yield Fact**
Hanup's disease is a rare genetic disorder that highlights the importance of amino acid transport in maintaining proper bodily functions. The impaired absorption of neutral amino acids can lead to a range of symptoms, including pellagra, a condition caused by niacin deficiency.
**Correct Answer:** C.