The enzyme deficient in Lesch Nyhan syndrome is:
**Core Concept**
Lesch Nyhan syndrome is a genetic disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme plays a crucial role in purine metabolism, specifically in the recycling of hypoxanthine and guanine to form IMP (inosine monophosphate). Its deficiency leads to an accumulation of uric acid and other purine metabolites.
**Why the Correct Answer is Right**
The deficiency of HGPRT in Lesch Nyhan syndrome results in a buildup of uric acid and other toxic purine metabolites. This is because HGPRT is responsible for converting hypoxanthine and guanine into IMP, which can then be converted into GTP. Without functional HGPRT, these purines are instead converted into uric acid, leading to hyperuricemia and the subsequent symptoms of Lesch Nyhan syndrome. The mutation in the HPRT1 gene leads to a complete loss of HGPRT activity, resulting in the severe clinical manifestations of the disorder.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct enzyme. While xanthine oxidase is involved in purine metabolism, it is not the enzyme deficient in Lesch Nyhan syndrome.
**Option B:** This option is incorrect because it is not a known enzyme associated with Lesch Nyhan syndrome. The disorder is specifically related to the deficiency of HGPRT, not another enzyme.
**Clinical Pearl / High-Yield Fact**
Lesch Nyhan syndrome is a classic example of a genetic disorder caused by a deficiency of a single enzyme. It highlights the importance of maintaining proper purine metabolism and the consequences of its disruption.
**Correct Answer:** C. HGPRT (Hypoxanthine-Guanine Phosphoribosyltransferase)