Leiden mutation involves:
**Core Concept**
The Leiden mutation is a genetic variation in the factor V gene that affects the coagulation pathway. Specifically, it involves a point mutation in the factor V gene that leads to resistance to activated protein C (APC), resulting in an increased risk of thrombosis.
**Why the Correct Answer is Right**
The Leiden mutation is a single-point mutation at position 1691 in the factor V gene, where a glutamine (Gln) is replaced by an arginine (Arg) at position 506 (R506Q). This mutation leads to a loss of the APC cleavage site in factor V, rendering it resistant to inactivation by APC. As a result, the factor V molecule remains active for a longer period, contributing to the formation of blood clots.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the Leiden mutation does not involve a change in the prothrombin gene, which is associated with a different type of thrombophilia.
* **Option B:** This option is incorrect because the Leiden mutation does not involve a change in the antithrombin gene, which is a different protein involved in regulating coagulation.
* **Option C:** This option is incorrect because the Leiden mutation does not involve a change in the protein C gene, which is the protein that is affected by the mutation.
**Clinical Pearl / High-Yield Fact**
The Leiden mutation is a common inherited risk factor for venous thromboembolism, particularly in young women. It is essential to identify this mutation in patients with a history of recurrent thrombosis to guide anticoagulation therapy.
**Correct Answer: D. The Leiden mutation involves a point mutation in the factor V gene that leads to resistance to activated protein C (APC).**