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Factor 5 Leiden: Causes, Symptoms & Treatment

Factor 5 Leiden is a genetic blood clotting disorder that increases the risk of thrombosis. It is the most common inherited cause of excessive blood clotting.

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Things worth knowing about "Factor 5 Leiden"

Factor 5 Leiden is a genetic blood clotting disorder that increases the risk of thrombosis. It is the most common inherited cause of excessive blood clotting.

What is Factor 5 Leiden?

Factor 5 Leiden (also written as Factor V Leiden) is a genetic mutation affecting clotting factor V that leads to an increased tendency to form blood clots, a condition known as thrombophilia. It is the most common inherited thrombophilia in the Western population, occurring in approximately 3–8% of people of European descent. The name comes from the Dutch city of Leiden, where the mutation was first described in 1994.

Causes and Inheritance

The condition is caused by a point mutation in the F5 gene on chromosome 1, in which the amino acid arginine is replaced by glutamine at a specific position. This change makes Factor V resistant to inactivation by the natural anticoagulant activated Protein C (APC).

Heterozygous mutation: Only one copy of the gene is affected. The risk of thrombosis is approximately 3–8 times higher than average.
Homozygous mutation: Both copies of the gene are affected. The risk of thrombosis is approximately 50–80 times higher than average.

The mutation is inherited in an autosomal dominant pattern, meaning that inheriting just one affected copy is sufficient to increase clotting risk.

Mechanism of Action

Under normal circumstances, activated Protein C inactivates Factor Va to prevent excessive blood clotting. In individuals with Factor 5 Leiden, the mutated Factor Va is resistant to this deactivation. As a result, it remains active for longer and promotes the formation of thrombi (blood clots), particularly in the veins.

Symptoms

Many carriers of the mutation experience no symptoms and never develop a thrombosis. Symptoms typically only appear when a blood clot forms:

Swelling, pain, and redness in a leg (deep vein thrombosis, DVT)
Sudden shortness of breath, chest pain, or rapid heartbeat (pulmonary embolism)
In pregnant women: increased risk of miscarriage and pregnancy-related complications

Risk Factors for Thrombosis

The risk of developing a blood clot increases further in the presence of:

Use of oral contraceptives (the pill)
Pregnancy and the postpartum period
Prolonged immobility (e.g., long-haul flights, bed rest)
Surgery or injury
Additional clotting disorders
Older age

Diagnosis

Diagnosis is established through:

Molecular genetic testing: Detection of the specific gene mutation by PCR analysis from a blood sample (gold standard).
APC resistance test: A coagulation test that detects reduced sensitivity to activated Protein C. An abnormal result is confirmed by genetic testing.

Testing is recommended for individuals with a personal or family history of thrombosis, pregnant women with thrombotic events, and before initiating hormone therapy in those with a relevant risk profile.

Treatment and Prevention

Not every carrier of the mutation requires drug treatment. The treatment decision depends on an individual risk assessment:

No treatment: Carriers without a prior thrombosis and without additional risk factors are often managed with close monitoring only.
Anticoagulation (blood thinners): Following a thrombosis, treatment with anticoagulants (e.g., heparin, warfarin, direct oral anticoagulants such as rivaroxaban or apixaban) is usually initiated.
Preventive measures: In high-risk situations (e.g., pregnancy, surgery), preventive heparin therapy may be used.
Lifestyle measures: Regular physical activity, avoiding prolonged immobility, and wearing compression stockings can help reduce the risk.

References

Dahlbäck B. - Advances in understanding pathogenic mechanisms of thrombophilic disorders. Blood. 2008;112(1):19-27. PubMed.
Rosendaal FR, Reitsma PH. - Genetics of venous thrombosis. Journal of Thrombosis and Haemostasis. 2009;7(Suppl 1):301-304.
National Heart, Lung, and Blood Institute (NHLBI) - Factor V Leiden Thrombophilia. www.nhlbi.nih.gov.

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