Harup disease causes deficiency of ?
**Core Concept**
Harup disease, also known as Hartnup disease, is a rare autosomal recessive disorder affecting the metabolism of amino acids. It is characterized by impaired absorption of neutral amino acids from the gastrointestinal tract.
**Why the Correct Answer is Right**
Hartnup disease is caused by mutations in the SLC6A19 gene, which encodes the neutral amino acid transporter 1 (NAAT1). This transporter is responsible for the reabsorption of neutral amino acids in the kidneys and intestines. In Hartnup disease, the defective NAAT1 leads to impaired reabsorption of tryptophan, an essential amino acid, resulting in its excessive excretion in the urine. The deficiency of tryptophan in Hartnup disease leads to various clinical manifestations, including pellagra-like symptoms, ataxia, and psychiatric disturbances.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not relate to the underlying pathophysiology of Hartnup disease.
* **Option B:** This option is incorrect because it is not directly associated with the genetic or molecular mechanisms of Hartnup disease.
* **Option C:** This option is incorrect because it is not a known consequence of Hartnup disease.
**Clinical Pearl / High-Yield Fact**
Hartnup disease is a rare genetic disorder that highlights the importance of amino acid metabolism in maintaining normal physiological function. It is essential for medical students to recognize the clinical manifestations of Hartnup disease, including pellagra-like symptoms, to diagnose and manage this condition effectively.
**Correct Answer:** D. Tryptophan