**Question:** All of the following are true about Lesch-Nyhan syndrome, EXCEPT:

A. Hyperuricemia
B. Gout
C. Seizures
D. Hypotonia

**Core Concept:** Lesch-Nyhan syndrome is a rare genetic disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). This deficiency leads to the accumulation of uric acid and its breakdown products, causing a range of clinical manifestations due to uric acid overproduction.

**Why the Correct Answer is Right:** Hypotonia (low muscle tone) is a characteristic feature of Lesch-Nyhan syndrome. However, hypotonia is not a specific feature that differentiates Lesch-Nyhan syndrome from other conditions. Therefore, it is not an exceptional feature in this context.

**Why Each Wrong Option is Incorrect:**

A. Hyperuricemia: This is a true feature of Lesch-Nyhan syndrome, as the accumulation of uric acid due to HPRT deficiency leads to increased uric acid levels in the blood (hyperuricemia).

B. Gout: Although hyperuricemia contributes to the development of gout, this condition is not exclusive to Lesch-Nyhan syndrome. Gout can be seen in other conditions and diseases as well, making it an incorrect answer.

C. Seizures: While seizures can be associated with uric acid overproduction and elevated uric acid levels, they are not unique to Lesch-Nyhan syndrome. Seizures can be seen in various neurological disorders, making it an unsuitable answer for this specific question.

**Clinical Pearl:** Lesch-Nyhan syndrome is a valuable case study for understanding the consequences of purine and pyrimidine nucleotide synthesis defects. This rare genetic disorder highlights the importance of proper enzyme function in maintaining homeostasis and preventing harmful overproduction of uric acid and its derivatives.

**Correct Answer:** Hypotonia (D)

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**Core Concept:** Hypotonia (low muscle tone) is a feature of Lesch-Nyhan syndrome, resulting from the deficiency of the enzyme HPRT. This deficiency leads to an imbalance in purine and pyrimidine nucleotide synthesis, causing the characteristic clinical features of the disease.

**Why Each Wrong Option is Incorrect:**

A. Hyperuricemia: Although hyperuricemia is a feature of Lesch-Nyhan syndrome, it is not the sole feature distinguishing it from other conditions. Hyperuricemia can be seen in various diseases, making it an unsuitable answer for this specific question.

B. Seizures: Seizures are common in Lesch-Nyhan syndrome, but they are not exclusive to this condition. Seizures can occur in other neurological disorders, making it an inappropriate answer for this question.

C. Hypotonia (low muscle tone): Hypotonia is a feature of Lesch-Nyhan syndrome due to the deficiency of the enzyme HPRT. However, hypotonia is not unique to this condition. Hypot