A 68-year-old man who lives alone and eats mostly canned food presents with painful, swollen gums that bleed easily, perifollicular hemorrhages on his legs, and poor wound healing. He has no history of liver disease. The underlying biochemical defect in this condition is impaired hydroxylation of which amino acid residue in collagen?

• A Lysine
• B Hydroxyproline
• C Glycine
• D Proline ✓

Explanation

The patient has scurvy due to vitamin C deficiency. Vitamin C is a cofactor for prolyl hydroxylase, which hydroxylates proline residues to hydroxyproline, essential for collagen triple helix stability. Without this modification, collagen is weak, causing bleeding gums and perifollicular hemorrhages. Lysine is also hydroxylated, but proline hydroxylation is the critical defect. Hydroxyproline is the product, not the substrate.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.