Lesch-Nyhan syndrome is caused by deficiency of which enzyme?
**Core Concept**
Lesch-Nyhan syndrome is a genetic disorder characterized by excessive uric acid production, leading to severe neurological symptoms and self-mutilating behavior. This condition is caused by a deficiency of an enzyme crucial for purine metabolism.
**Why the Correct Answer is Right**
Lesch-Nyhan syndrome is caused by a deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT), an enzyme that plays a key role in the salvage pathway of purine metabolism. In the absence of HPRT, purines are degraded to uric acid, resulting in hyperuricemia. This enzyme deficiency leads to the accumulation of uric acid in the body, causing the characteristic symptoms of Lesch-Nyhan syndrome, including neurological dysfunction, kidney stones, and severe joint pain.
**Why Each Wrong Option is Incorrect**
**Option A:** Xanthine oxidase is an enzyme involved in purine catabolism, but its deficiency does not lead to Lesch-Nyhan syndrome. Instead, it would result in xanthinuria, a different genetic disorder.
**Option B:** Adenine phosphoribosyltransferase (APRT) is another enzyme involved in purine salvage, but its deficiency leads to a different condition, APRT deficiency, characterized by kidney stones and renal failure.
**Option C:** Uricase is an enzyme involved in uric acid degradation, but its deficiency is not associated with Lesch-Nyhan syndrome.
**Clinical Pearl / High-Yield Fact**
Lesch-Nyhan syndrome is an X-linked recessive disorder, meaning it primarily affects males, as they have only one X chromosome. Females can be carriers of the mutation, but they are usually asymptomatic due to X-chromosome inactivation.
**Correct Answer:** C.