A 4-year-old child presents with swollen, bleeding gums, perifollicular haemorrhages over the lower limbs, and poor wound healing. The underlying biochemical defect responsible for these manifestations is impaired:

• A Gamma-carboxylation of glutamic acid residues in clotting factors
• B Methylation of homocysteine to methionine
• C Decarboxylation of pyruvate to acetyl-CoA
• D Hydroxylation of proline and lysine residues in procollagen ✓

Explanation

The child has scurvy (vitamin C deficiency). Vitamin C is a cofactor for prolyl and lysyl hydroxylases, which hydroxylate proline and lysine in procollagen. Without hydroxylation, collagen triple helix formation is defective, causing fragile capillaries and poor wound healing. Option A describes vitamin K's role in clotting factor activation, a tempting distractor because the child has bleeding.

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.