APC resistance is most commonly due to a mutation in which factor?

APC resistance is most commonly due to a mutation in which factor?

• A. Factor II
• B. Factor V
• C. Protein C
• D. Protein S

Answer: (B)

APC resistance happens when activated protein C can’t effectively inactivate a coagulation factor, so thrombin generation stays high and clotting is promoted. The most common cause is a mutation in Factor V, known as Factor V Leiden. This mutation changes a site on Factor V that APC normally cleaves, making Factor Va resistant to inactivation. As a result, Factor Va continues to catalyze the conversion of prothrombin to thrombin, increasing the tendency to form clots. Factor II mutations raise prothrombin levels and boost thrombin production, but not by making Factor V resistant to APC. Protein C or Protein S deficiencies disrupt regulation of the system, but the classic APC resistance mechanism is tied to Factor V Leiden.

APC resistance happens when activated protein C can’t effectively inactivate a coagulation factor, so thrombin generation stays high and clotting is promoted. The most common cause is a mutation in Factor V, known as Factor V Leiden. This mutation changes a site on Factor V that APC normally cleaves, making Factor Va resistant to inactivation. As a result, Factor Va continues to catalyze the conversion of prothrombin to thrombin, increasing the tendency to form clots.

Factor II mutations raise prothrombin levels and boost thrombin production, but not by making Factor V resistant to APC. Protein C or Protein S deficiencies disrupt regulation of the system, but the classic APC resistance mechanism is tied to Factor V Leiden.