A 1-year-old child presented with involuntary movements which were choreoathetoid in nature, spasticity, dystonias and intellectual disability. The speech of the child was dysahric and mother also gave history of compulsive biting. Some inherited disorder was suspected. The child was normal at bih. Lab findings revealed increased uric acid levels. The enzyme deficient in the above condition catalyses which of the following reactions.

**Core Concept**
The child's symptoms, including choreoathetoid movements, spasticity, dystonias, intellectual disability, dysarthric speech, and compulsive biting, suggest a neurodegenerative disorder. The presence of increased uric acid levels and normal birth history hint towards a genetic disorder. The enzyme deficiency in this condition is related to the metabolism of a specific neurotransmitter.

**Why the Correct Answer is Right**
The child's symptoms are characteristic of Lesch-Nyhan syndrome, a genetic disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme is crucial for the purine metabolism pathway, where it catalyzes the conversion of hypoxanthine to inosine monophosphate (IMP) and guanine to guanosine monophosphate (GMP). The deficiency of HGPRT leads to the accumulation of uric acid and the depletion of guanine nucleotides, resulting in the characteristic symptoms of Lesch-Nyhan syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the purine metabolism pathway or the enzyme deficiency associated with Lesch-Nyhan syndrome.
**Option B:** This option is incorrect because it does not describe the correct reaction catalyzed by the enzyme deficient in Lesch-Nyhan syndrome.
**Option C:** This option is incorrect because it does not accurately describe the reaction catalyzed by HGPRT.

**Clinical Pearl / High-Yield Fact**
Lesch-Nyhan syndrome is a classic example of a genetic disorder caused by a deficiency of a single enzyme, highlighting the importance of understanding the biochemical pathways involved in human disease.

**Correct Answer:** C. HGPRT catalyzes the conversion of hypoxanthine to inosine monophosphate (IMP) and guanine to guanosine monophosphate (GMP).

✓ Correct Answer: A. Guanine to GMP