A Genetic Clotting Condition or Thrombophilia

Factor V Leiden (FVL) is a genetic clotting disorder. In the US, 1 in 20 Caucasians and about 1 in 100 African-Americans in the United States have this. FVL. FVL increases a person’s risk for dangerous blood clots. The chance increases if a woman has FVL and is uses hormonal birth control pills, rings, or patches.

You make a protein called factor V that helps your blood clot. However, if you have a DNA mutation in the gene used to make the factor V protein, you have the “factor V Leiden” mutation.  The mutation was named after a city called Leiden, where they did research on the first family found to have the mutation.  If you have the factor V Leiden mutation, you have an inherited thrombophilia or clotting disorder.

Carriers of the factor V Leiden mutation have a clearly increased risk of deep vein thrombosis (i.e. blood clots in the leg veins), but factor V Leiden is only a weak risk factor for blood clots in the lungs (pulmonary embolism or PE). This differential effect of Factor V Leiden on the risk for these 2 types of vein clots is known as the “Factor V Leiden paradox”.

Factor V Leiden and the tendency to develop blood clots

Normally you produce factor V protein to help your blood clot, and you produce greater amounts after you have a damaged blood vessel.

Other proteins, including protein C and protein S control the amount of factor V protein you produce.  Protein C and protein S combine to help you break up your factor V, and prevent you from reusing it to make blood clots.

Testing for factor V Leiden

  • Factor V Leiden testing is done with a blood sample. There are two types of tests that can determine whether you have factor V Leiden.
  • In some cases, a sample may be tested to see if your blood is resistant to activated protein C (one of the proteins that helps control factor V).
  • If your blood is resistant to activated protein C, there is a 90-95% likelihood that you have a mutation in the factor V gene.
  • A genetic test is usually done to confirm your results on the activated protein C blood test.
  • Sometimes, the genetic test is ordered for you first, without ever doing the activate protein C testing.  In this case, the DNA is isolated or separated from blood cells and your factor V gene is examined to see if there is a mutation in your DNA code. If a mutation is found, then you have factor V Leiden.

Prevalence of factor V Leiden

It is estimated that about 5% (1 out of 20) of Caucasians (white people) have factor V Leiden. It is more common in individuals of European ancestry. In the United States, approximately 1-2% (1 in 100 to 1 in 50) of African Americans, Hispanic Americans and Native Americans also have the mutation. Factor V Leiden is rare in Asians.

Signs and Symptoms of Blood Clots – What You Need to Know

If you have FVL, you need to be aware of the symptoms of DVTs so you can seek medical attention.

If you have a Deep Vein Thrombosis or DVT (leg or arm clot), you will notice:

Pain or tenderness in your arm or leg – often described as a cramp or Charley horse -with one or more of the following:

  1. Swelling
  2. Red or purple skin color
  3. Warm to the touch

If a piece of a DVT breaks off and travels to the lung, it can cause a lung clot. We call this a pulmonary embolism or PE. A PE can be a life threatening medical emergency. You need to seek immediate medical attention if you have symptoms of a PE.

If you have a Pulmonary Embolism or PE (lung clot), you may experience:

  • Hard to breath or shortness of breath
  • Chest pain – especially when trying to breathe
  • Rapid or racing heart beat
  • Fainting or passing out
  • Coughing up blood

Resources for More Information

You can read more about FVL at these links below:

  1. Factor V Leiden Information for Patients and Families:  (2007) Explains what factor V Leiden is and how it affects clotting, how it is diagnosed, and how you get factor V Leiden. It also gives tips to avoid blood clots, risks you can’t avoid, how you know when you get a blood clot, and how you can pass factor V Leiden on to your children. From Hamilton Health Sciences/McMaster Children’s Hospital.
  2. Factor V Leiden: (2003) This patient oriented journal article explains the clotting process, and defines factor V Leiden, how you get it, how it is diagnosed and treated, implications for women, testing of family members and minimizing risks. From the American Heart Association’s Circulation Journal.
  3. Factor V Leiden Thrombophilia: (August 2010) Explains what factor V Leiden is, how common it is, the genetic changes it causes, how it is inherited, resources for managing FVL, and information about genetic testing for it. From the National Institutes of Health, National Library of Medicine, Genetic Home Reference.
  4. Learning About Factor V Leiden Thrombophilia: (2011) Explains what FVL is, including its symptoms, how it is diagnosed and treated, and what is known about the heredity of FVL. From the The National Human Genome Research Institute of the National Institutes of Health.
  5. Factor V Leiden Thrombophilia: (2010) Discusses the characteristics of FVL, how it is diagnosed, treated, and managed, risks (including during pregnancy, prevention of complications, and extensive genetic information with genotype/phenotype correlations. GeneReviews™ [Internet] from the National Center for Biological Information of the National Library of Medicine of the National Institutes of Health.
  6. Factor V Leiden Storybook for Children by John Puetz, MD. A children’s book about Factor V Leiden. This is a downloadable pdf file of a storybook on Factor V Leiden for children.
  7. What is Factor V Leiden? from “100 questions and answers about DVT and PE”

You can read about people who have had FVL and Blood Clots in their own voices.

Patient Stories of FVL

January 2014