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Genetic and Rare Diseases Information Center (GARD)

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Factor V Leiden thrombophilia


* Not a rare disease
Other Names for this Disease
  • APC resistance, Leiden type
  • Hereditary resistance to activated protein C
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Your Question

My grandmother on my dad's side has two copies of the factor V Leiden gene mutation. I have one copy. Do I need to go and see a hematologist to get on blood thinners, or is there really nothing that they would do since I only have the one copy? Also, if I have one copy does that mean that my father has two copies of it or could he possibly have only the one copy as well?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What does it mean to have a factor V Leiden gene mutation?

Factor V is a gene that plays a critical role in the formation of blood clots in response to injury.[1][2] Factor V Leiden is the name of a mutation in the factor V gene that can cause thrombophilia (an increased tendency to form abnormal blood clots in blood vessels).

People can inherit one or two copies of the factor V Leiden gene mutation from their parents.  Individuals who inherit one copy of the factor V Leiden mutation from a parent are called heterozygotes. People who inherit two copies of the mutation, one from each parent, are called homozygotes.

People who have the factor V Leiden mutation are at somewhat higher than average risk for a type of clot that forms in large veins in the legs (deep venous thrombosis, or DVT) or a clot that travels through the bloodstream and lodges in the lungs (pulmonary embolism, or PE).[1][2]
Last updated: 6/29/2012

What is the risk for developing a clot if you have one factor V Leiden gene mutation?

A person with one copy of the factor V Leiden mutation has about 4 to 8 times greater risk of developing a clot compared to someone who does not have a mutation. For the average person, the risk of developing an abnormal blood clot is about 1 in 1,000 per year. If you have one copy of the factor V Leiden mutation, your risk increases to approximately 4 to 8 in 1,000.[1][3]

There are other factors that may contribute to the risk of having a clot. These include the following:[1][2]

  • Having other genetic mutations that increase your risk for a clot
  • Getting older
  • Having surgery
  • Sitting for long periods (e.g. on a long airplane ride)
  • Taking birth control pills and other female hormones
  • Giving birth to a child within the last 6 months
  • Experiencing traumas or fractures
Last updated: 6/29/2012

Do people with a single factor V Leiden gene mutation require treatment?

The management of individuals with factor V Leiden depends on their medical history.

People with factor V Leiden who have had a deep venous thrombosis (DVT) or pulmonary embolism (PE) are usually treated with blood thinners, or anticoagulants. Anticoagulants such as heparin and warfarin are given for varying amounts of time depending on the person's situation.

Lifelong treatment with anticoagulants is usually not given to an individual who has never had a DVT or PE, or has only had one, unless there are additional risk factors present. Having had a DVT or PE in the past increases a person's risk for developing another one in the future, but having factor V Leiden does not seem to add to the risk of having a second clot.

Individuals are also counseled about reducing or eliminating other factors that may add to one's risk of developing a clot in the future. These individuals may require temporary treatment with an anticoagulant during periods of particularly high risk, such as major surgery.[4]

Factor V Leiden increases the risk of developing a DVT during pregnancy by about seven times. This risk should be discussed with a woman’s obstetrician and hematologist. Most women with factor V Leiden have normal pregnancies and only require close follow-up during pregnancy. For those with a history of DVT or PE, treatment with an anticoagulant during a subsequent pregnancy can prevent recurrent problems.[4]

To learn more about your specific treatment options, we recommend that you speak with your healthcare provider.
Last updated: 6/29/2012

My paternal grandmother has two factor V Leiden gene mutations, and I have one. Does this mean my father has one or two mutations?

We cannot discuss your family member’s specific risks for having a factor V Leiden gene mutation(s). However, below we have provided general information about how factor V Leiden can be passed through families which you may find helpful.

Each person inherits two copies of every gene, one from their mother and the other copy from their father. In order to inherit two copies of a gene mutation, each parent needs to carry at least one copy of the gene mutation. An individual with two copies of the gene mutation will pass one of the copies to their child. An individual with one copy of the gene mutation has a 50% chance of passing the gene mutation to their child. It is hard to determine if an individual will inherit one copy or two copies of a gene mutation if you do not know the genetic status of both parents for that particular gene.

Your family members can learn more about their specific risks for factor V Leiden thrombophilia by speaking with a genetic professional. Information on how you can find local genetics services is provided below.
Last updated: 6/29/2012

How common is factor V Leiden thrombophilia?

The factor V Leiden mutation is the most common inherited predisposition to abnormal blood clotting in the United States. It has a prevalence of about 5% in the Caucasian population. A person with a factor V Leiden mutation may be heterozygous or, more rarely, homozygous. Those who are heterozygous have a 3 to 8 fold greater risk of developing a venous thromboembolism than those who don't carry the mutation; while those who are homozygous have a 50 to 80 fold increased risk of thrombosis.[5]
Last updated: 8/8/2011

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 10/18/2013