**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 the purine metabolism pathway, particularly in the recycling of purine nucleotides.

**Why the Correct Answer is Right**
Lesch-Nyhan syndrome is characterized by a deficiency of the HGPRT enzyme, leading to an overproduction of uric acid due to the accumulation of hypoxanthine and guanine. This results in severe clinical manifestations, including gout, kidney stones, and neurodevelopmental disorders. The HGPRT enzyme is responsible for converting hypoxanthine to inosine monophosphate (IMP) and guanine to guanosine monophosphate (GMP), which are essential for nucleotide synthesis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct enzyme associated with Lesch-Nyhan syndrome. 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 mentions a different enzyme, adenine phosphoribosyltransferase (APRT), which is involved in a different aspect of purine metabolism. APRT deficiency leads to a different clinical condition, called APRT deficiency syndrome.

**Option C:** This option is incorrect because it mentions a different enzyme, galactose-1-phosphate uridyltransferase (GALT), which is involved in galactose metabolism. GALT deficiency leads to a different clinical condition, called galactosemia.

**Option D:** This option is incorrect because it mentions a different enzyme, glucose-6-phosphate dehydrogenase (G6PD), which is involved in pentose phosphate pathway. G6PD deficiency leads to a different clinical condition, called G6PD deficiency.

**Clinical Pearl / High-Yield Fact**
Lesch-Nyhan syndrome is an X-linked recessive disorder, meaning it predominantly affects males. The clinical manifestations of Lesch-Nyhan syndrome can be severe and include self-mutilating behavior, seizures, and intellectual disability.

**Correct Answer:** C. HGPRT