What is Factor V Leiden?

Clotting can mean the difference between life and death. In normal, healthy people, clotting prevents blood loss; in others, the clotting mechanism doesn’t work properly and clots will overstay their welcome.

Thrombophilia is a general term for any disorder that puts someone at a higher risk of developing blood clots. Factor V Leiden is one of the newly recognized thrombophilias.

Factor V Leiden is a genetic mutation that was discovered just 16 years ago by a group of scientists in the Netherlands. Although this was quite recent, scientists now estimate that the mutation occurred in a single individual in northern Europe about 30,000 years ago.

Scientists have known about Factor V deficiency – formerly, and sometimes still, referred to as Activated Protein C Resistance – since 1943, but did not pinpoint the exact genetic location of the mutation until 1994. A group of researchers in Leiden, Netherlands, discovered that people with the Factor V Leiden mutation have a simple transposition of the amino acids glutamine and arginine at a specific genetic location.

Who has Factor V Leiden?

Because this is a genetic mutation, parents are able to pass this on to their children. It is an autosomal dominant trait, which means that each parent who carries the mutation has a fifty percent chance of passing it on. It is estimated that three to eight percent of white people in North America and Europe carry at least one copy of this gene. Factor V Leiden, in fact, is the most common hereditary thrombophilia among Europeans, and the concentration is even higher among people of northern European or Mediterranean descent. Sweden has the highest rate, with up to 15% of Swedish people having at least one copy of the Factor V Leiden mutation.

Where did the mutation originate?

According to researcher Ariella Zivelin as published in a 1998 edition of Blood Journal, Factor V Leiden “originated from a single mutational event that took place about 21,000 to 34,000 years ago after the evolutionary divergence of non-Africans from Africans and of Caucasians from Mongoloids.” Proof of this theory is found in the fact that the Factor V Leiden mutation is extremely rare in Asians and Native Americans, and is also relatively rare in Hispanics and Africans.

What are the risks?

Compared to normal, healthy individuals, people with one copy of the Factor V Leiden mutation are up to eight times more likely to develop a life-threatening clot at some point in life. People with two copies are 80 times as likely.

The biggest risks for individuals with Factor V Leiden are pulmonary embolism and deep vein thrombosis. In fact, according the Genetics Home Reference, up to 30% of patients with a deep vein thrombosis or a pulmonary embolism are found to have the Factor V Leiden mutation. Women with Factor V Leiden are at a higher risk of pregnancy complications such as pre-eclampsia, premature labor, placental abruption, miscarriage, and even stillbirth.

It is important to note that Factor V Leiden does not appear to put an individual at any higher risk of heart attack or stroke — even though these dangerous events are also caused by clots. They are caused by a different type of clot.

How is it diagnosed?

Factor V Leiden can be diagnosed with a simple genetic test, which can also determine whether a person is heterozygous (carrying one copy of the mutation — just one copy from one parent) or homozygous (carrying two copies of the mutation — one copy from each parent).

Because Factor V Leiden cannot be diagnosed without a definitive genetic test (there are no symptoms, other than a clot substantial enough to cause injury or death), many people do not realize they have the condition until they suffer a clotting incident and are subsequently tested. Once a patient has been diagnosed, it is imperative that they follow their doctor’s orders, and make lifestyle changes to reduce their risks of suffering another clot, or death.

If you are diagnosed with Factor V Leiden

Certain risk factors will increase the odds of clotting in those with Factor V Leiden:

-Smoking.
-The use of estrogen birth control in women, known to increase the risk of clotting six-fold, according to the University of Illinois.
-Sitting still for a long period of time (on a long flight, or when recovering from surgery, for example).
-Pregnancy.

The only way to prevent future clotting is to avoid the known risk factors, and if necessary, to use medicines that thin the blood or slow coagulation. Treatments like a daily low-dose aspirin regimen and/or low molecular-weight heparin have been proven effective.

In patients with a prior clotting incident, doctors will sometimes prescribe a drug called Warfarin (also known by its generic counterpart’s name, coumadin), but never in pregnant women – this drug is recognized by the Food and Drug Administration as dangerous during pregnancy because it crosses the placenta.

30,000 years ago, a random genetic mutation occurred in a single individual. This mutation was passed from this one person to thousands, and then to millions. For centuries, when these affected humans would suffer a sudden pulmonary embolism or lose a fetus after forming a clot, they probably assumed the answer was somewhere inside of them; they could never have imagined that it was contained on tiny blueprints within their cells – that nature’s simple mistake on one chromosome could be the cause.