**Question:** Lesch-Nyhan syndrome is a sex-linked recessive disorder. Which enzyme deficiency causes this disorder?

**Core Concept:** Lesch-Nyhan syndrome is a rare genetic disorder characterized by excessive uric acid production due to the deficiency of an enzyme. This enzyme deficiency leads to the accumulation of uric acid in the body, causing severe neurological symptoms.

**Why the Correct Answer is Right:** Lesch-Nyhan syndrome is caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyl-transerase (HPRT). HPRT is involved in the purine nucleotide salvage pathway, which is responsible for recycling of purine nucleotides. In a healthy individual, this pathway efficiently removes excess uric acid from the body. In Lesch-Nyhan syndrome, due to the deficiency of HPRT, the purine nucleotide salvage pathway is impaired, leading to the accumulation of uric acid and subsequent neurological symptoms.

**Why Each Wrong Option is Incorrect:**

A. HPRT deficiency: This is incorrect because it is the correct answer to the question.
B. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) is not the correct answer as it is the correct enzyme responsible for the deficiency in Lesch-Nyhan syndrome.
C. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: Similar to option B, this is also incorrect as it refers to the correct enzyme.
D. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: This option is incorrect as it repeats the correct enzyme name.

**Clinical Pearl:** The clinical features of Lesch-Nyhan syndrome include hyperuricemia, dystonia, choreoathetosis, self-injurious behavior, and cognitive impairment. Ensuring proper diagnosis and management of this condition is crucial due to the severity of symptoms and potential for improvement with appropriate treatment.

**Correct Answer:** Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency.

**Why Each Wrong Option is Incorrect:**

A. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: This option is incorrect as it is the correct enzyme deficiency.
B. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: Similar to option A, this is also incorrect, as it refers to the correct enzyme deficiency.
C. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: This option is incorrect because it is another reference to the correct enzyme deficiency.
D. Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency: This option is incorrect as it is the correct enzyme deficiency.

**Core Concept:** Hypoxanthine-guanine phosphoribosyl-transerase (HPRT) deficiency is a genetic