A 65-year-old man with chronic tophaceous gout has a white chalky deposit removed from the olecranon bursa. Microscopy with polarized light shows negatively birefringent needle-shaped crystals. The enzyme whose deficiency leads to secondary gout in Lesch-Nyhan syndrome is:

• A Adenosine deaminase
• B Purine nucleoside phosphorylase
• C Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) ✓
• D Xanthine oxidase

Explanation

Lesch-Nyhan syndrome is an X-linked disorder caused by complete deficiency of HGPRT, the enzyme responsible for salvage of hypoxanthine and guanine back to IMP and GMP. Without salvage, purines are catabolized to uric acid in excess, causing severe hyperuricemia and gout. The syndrome also features neurologic manifestations including self-mutilation and choreoathetosis. Xanthine oxidase inhibitors (allopurinol) reduce uric acid synthesis and are used therapeutically.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.