Factor V Leiden

Factor V Leiden (FVL, R506Q, p.Arg506Gln, 1691G>A) is an inherited form of thrombophilia or blood clotting disorder. Around 3-8 percent of those with European ancestry have this condition.1

What Is Factor V Leiden?

Factor v leiden

Factor V is a protein involved in clotting. When Factor V is activated, blood begins to clot. The clotting process is switched off by Activated Protein C. The Leiden kind of Factor V does not switch off. The result is that people with Factor V Leiden are more prone to developing blood clots.

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What are the symptoms of Factor V Leiden?

The only real symptom of Factor V Leiden is the presence of a blood clot. If the blood clot occurred in someone unlikely to experience clots, Factor V Leiden might be suspected. These scenarios include:

  • The occurrence of a blood clot in someone younger than 50
  • Recurring DVTs or PEs
  • History of miscarriages
  • A blood clot in unusual sites such as the brain or liver
  • Family history of Factor V Leiden2

How do you diagnose Factor V Leiden?

Factor V Leiden is usually diagnosed by a blood test called a coagulation screening test. However, people may also be diagnosed with a Factor V DNA Screen.

What is the difference between heterozygous and homozygous?

People inherit two copies of every gene; one from the mother, one from the father. Those who have one copy of a gene are called heterozygous. Those who have two of the same gene are called homozygous.

Heterozygous Factor V Leiden

Heterozygous people will have one gene for normal Factor V and one for Factor V Leiden. This is the most common form of Factor V Leiden, and is found in about 5% of the white population.3 People who are heterozygous have 3-5 times an increased risk of getting blood clots than a normal person.

Homozygous Factor V Leiden

Homozygous people have two copies of the Leiden gene and thus are more prone to complications. This form of Factor V is rare, impacting only 1 percent of those with Factor V Leiden. Homozygotes have close to a 100% lifetime risk of a thrombotic event.4

How does Factor V Leiden impact women?

Women who have Factor V Leiden have special medical considerations. They should not take birth control pills or other forms of estrogen. Estrogen increases the rate of blood clots that lead to deadly complications deep vein thrombosis (DVT) or pulmonary embolism. These women also have an even greater risk of developing clotting complications in pregnancy.

Factor V Leiden also increases the risk of pregnancy loss.5

What is the treatment for Factor V Leiden?

If there are no symptoms and no other risk factors, doctors will monitor people with Factor V Leiden. However, if blood clots have occurred or may occur, doctors will prescribe an anticoagulant such as Warfarin.

What are things you can do to prevent blood clots?

While there is no way to completely prevent blood clots, you can lower your risk by eliminating risk factors. These include:

  • Quitting smoking
  • Avoiding obesity
  • Staying hydrated
  • Exercising often
  • Avoiding estrogen-containing drugs, e.g. birth control
  • Avoiding long periods of inactivity
  • Using compression stockings

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