Hartnup disease is due to defective transport of –
**Core Concept**
Hartnup disease is a rare genetic disorder caused by a defect in the transport of neutral amino acids in the small intestine and kidneys. This condition is characterized by impaired absorption of amino acids, leading to a variety of clinical manifestations.
**Why the Correct Answer is Right**
The correct answer is related to the defective transport of neutral amino acids. In Hartnup disease, there is a mutation in the SLC6A19 gene, which encodes a neutral amino acid transporter called B0,AT1. This transporter is responsible for the reabsorption of neutral amino acids in the kidneys and their absorption in the small intestine. The defective transport of neutral amino acids leads to their excessive excretion in the urine and impaired absorption from the gut, resulting in a range of clinical symptoms.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Hartnup disease is not primarily related to the transport of basic amino acids. Basic amino acids are transported by a different set of transporters, and their defective transport is associated with a different condition.
* **Option B:** This option is incorrect because Hartnup disease is not related to the transport of acidic amino acids. Acidic amino acids are also transported by a different set of transporters, and their defective transport is associated with a different condition.
* **Option C:** This option is incorrect because Hartnup disease is not related to the transport of glucose or galactose. The transport of glucose and galactose is mediated by a different set of transporters and is associated with a different condition.
**Clinical Pearl / High-Yield Fact**
Hartnup disease is a rare genetic disorder that can be associated with a range of clinical manifestations, including pellagra-like symptoms, ataxia, and skin rashes. It is essential to consider this condition in the differential diagnosis of patients presenting with these symptoms, particularly if they have a history of gastrointestinal symptoms or a family history of the disorder.
**Correct Answer: D. Neutral amino acids.**