## Core Concept
Lesch-Nyhan syndrome is a genetic disorder caused by a deficiency of a specific enzyme involved in purine metabolism. This condition leads to severe symptoms, including intellectual disability, self-mutilation, and gout. The underlying biochemical defect is related to the breakdown of purines.

## Why the Correct Answer is Right
The correct answer, **HGPRT (Hypoxanthine-Guanine Phosphoribosyltransferase)**, is an enzyme crucial for the purine salvage pathway. This pathway is essential for recycling purines, which are the building blocks of DNA and RNA. HGPRT deficiency leads to an accumulation of uric acid, resulting in gout and kidney stones, and also causes neurological symptoms and behavioral disturbances characteristic of Lesch-Nyhan syndrome.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify a known enzyme related to Lesch-Nyhan syndrome.
- **Option B:** This option is incorrect as it does not correspond to the enzyme deficient in Lesch-Nyhan syndrome.
- **Option C:** This option is incorrect because it does not accurately represent the enzyme associated with Lesch-Nyhan syndrome.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that patients with Lesch-Nyhan syndrome often exhibit self-mutilating behavior, such as biting their lips or fingers. This condition is a classic example of a disorder caused by an enzyme deficiency in the purine metabolism pathway.

## Correct Answer Line
**Correct Answer: D. HGPRT.**