Vitamin K deficiency leads to decreased gamma-carboxylation of which factors?

• A. II, VII, IX, X
• B. II, VII, IX
• C. VIII, IX
• D. V, VIII

Answer: (A)

Vitamin K acts as a cofactor for gamma-glutamyl carboxylase to add gamma-carboxyl groups to specific glutamate residues on certain clotting factors. This modification creates gamma-carboxyglutamate (Gla) motifs that bind calcium, enabling the factors to assemble on phospholipid surfaces and function in the coagulation cascade. The factors that require this gamma-carboxylation are II (prothrombin), VII, IX, and X. When vitamin K is deficient, these factors are produced but cannot be properly activated, leading to impaired coagulation. Thus, vitamin K deficiency decreases gamma-carboxylation of II, VII, IX, and X. Factors V and VIII do not depend on this vitamin K–mediated modification, which is why they are not affected in this context.