**Core Concept:** Lesch-Nyhan syndrome is a genetic disorder caused by deficiency of an enzyme called hypoxanthine-guanine phosphoribosyltransferase (HPRT). This enzyme plays a crucial role in purine nucleotides recycling, and its deficiency leads to the accumulation of uric acid and other toxic compounds in the body.

**Why the Correct Answer is Right:** HPRT deficiency in Lesch-Nyhan syndrome results in a buildup of toxic compounds like hypoxanthine, guanine, and xanthine in the body. These substances can damage various tissues and organs, leading to the clinical manifestations seen in the syndrome.

**Why Each Wrong Option is Incorrect:**

A. Hypoxanthine phosphoribosyl-pyrophosphate synthetase (HPRTS) deficiency: This is a different enzyme than HPRT and is not associated with Lesch-Nyhan syndrome.

B. Deficiency of adenylosuccinate lyase (ADSL): This enzyme is involved in another pathway, and its deficiency does not result in the clinical features seen in Lesch-Nyhan syndrome.

C. Deficiency of xanthine dehydrogenase: This enzyme is involved in the synthesis of xanthine nucleotides and is not relevant to the pathogenesis of Lesch-Nyhan syndrome.

D. Deficiency of 5'-nucleotidase: This enzyme is involved in the degradation of nucleotides and is not related to the clinical features of Lesch-Nyhan syndrome.

**Clinical Pearl:** Lesch-Nyhan syndrome is a rare genetic disorder caused by HPRT deficiency, which results in the accumulation of toxic purine nucleotides and their toxic products, leading to the characteristic clinical features.