What is Factor V Leiden

Factor V Leiden is a genetic blood disorder that increases the risk of developing abnormal blood clots, a condition known as thrombophilia, due to a specific mutation in a protein required for blood clotting.

Understanding the Condition

In individuals with Factor V Leiden, the body’s blood clotting mechanism is slightly overactive. Normally, a protein called Factor V helps form clots to stop bleeding, and a regulatory protein called Protein C eventually turns it off. In people with this condition, the Factor V protein is mutated, making it resistant to being turned off by Protein C. This means the blood remains in a "pro-thrombotic" state longer than necessary, increasing the likelihood of deep vein thrombosis (DVT) in the legs or pulmonary embolisms in the lungs.

Systems Affected and Prevalence

Factor V Leiden primarily affects the circulatory system. However, it also has significant implications for the reproductive system, as it can increase the risk of pregnancy complications, such as recurrent miscarriage or preeclampsia. It is one of the most common inherited thrombophilias, affecting approximately 3% to 7% of the general Caucasian population, though prevalence varies significantly by geographic ancestry. It is less common in individuals of African or Asian descent.

Classification and Inheritance

This condition is classified by how the mutation is inherited. You can be heterozygous (inheriting one copy of the mutation from one parent) or homozygous (inheriting a copy from both parents). While those with the heterozygous form have a moderately increased risk of clotting, those with the homozygous form face a significantly higher risk. Unlike many other blood disorders that present with outward physical symptoms, Factor V Leiden is typically asymptomatic until a clot develops.

Key Differentiators

What sets Factor V Leiden apart from other clotting disorders is its specific molecular mechanism of Protein C resistance. While other conditions like Protein C or Protein S deficiency involve a lack of anticoagulant proteins, this condition involves a "gain-of-function" mutation where the clotting factor itself simply refuses to be deactivated. Most people with this condition will never experience a clot, as environmental triggers—such as surgery, long-distance travel, or hormonal birth control—are often required to provoke an event.

Medical Disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Always seek the advice of your hematologist or other qualified health provider with any questions regarding your health or medical condition.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Factor V Leiden thrombophilia


• Orphanet: Factor V Leiden mutation


• National Heart, Lung, and Blood Institute (NHLBI): Factor V Leiden