Hanup disease is related to ?
**Core Concept**
Hanup disease, also known as Hartnup disease, is a rare genetic disorder affecting the metabolism of certain amino acids. It is characterized by a deficiency of the enzyme alanine-serine-cysteine transporter (ASCT2) in the kidneys and intestines, leading to impaired absorption and reabsorption of these amino acids.
**Why the Correct Answer is Right**
The correct answer is related to **histidine metabolism**. In Hanup disease, the impaired ASCT2 enzyme affects the reabsorption of histidine, a neutral amino acid, in the kidneys and intestines. This leads to excessive excretion of histidine in the urine and its subsequent conversion to other compounds, such as histamine, which can cause symptoms like skin rashes and psychiatric disturbances. The pathophysiology involves the **histidine decarboxylase** enzyme, which is responsible for converting histidine to histamine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Hanup disease is not primarily related to **tryptophan metabolism**, although tryptophan is also affected due to the impaired ASCT2 enzyme.
**Option B:** This option is incorrect because Hanup disease is not directly related to **urea cycle disorders**, which involve a different set of enzymes and pathways.
**Option C:** This option is incorrect because Hanup disease is not primarily related to **glutamine metabolism**, which involves a different set of enzymes and pathways.
**Clinical Pearl / High-Yield Fact**
Hanup disease is a rare genetic disorder that affects the metabolism of certain amino acids, including histidine, and can cause a range of symptoms, including skin rashes, psychiatric disturbances, and gastrointestinal problems.
**Correct Answer: D**