What is Factor v Leiden

There are a number of genetically inherited blood coagulation disorders. Factor V Leiden is the most common of these seen in the United States. According to Factor V Leiden.org, it occurs in about 5% of the Caucasian population and 1.2% of the African American population.

As a genetic disorder, Factor V Leiden is not a disease and as such cannot be cured, only managed. The defective gene affects the blood clotting Factor 5 (V) causing an affected person to be more prone to developing clots (thromboses) within their blood vessels. This tendency to form thromboses is known as thrombophilia.

The tendency to develop thromboses depends on whether the person has inherited the gene from one parent (heterozygous) or both (homozygous). In a person with heterozygous V Leiden, the risk of developing a venous thrombosis is greater than in someone without the defective gene. If the person is homozygous for the V Leiden gene then the risk of thrombosis is even greater.

According to Genetics Home Reference, not everyone with the genetic mutation will develop symptoms of thrombophilia. approximately one in 1,000 people per year will develop an abnormal blood clot, the presence of one copy of the factor V Leiden mutation increases that risk to three to eight in 1,000, and having two copies of the mutation may raise the risk to as high as eighty in 1,000.

A gene known as the F5 gene codes for a protein called coagulation factor V. It is a mutation in this gene that causes Factor V Leiden thrombophilia. The blood coagulation system relies on a series of protein interactions to ensure proper clot formation. The protein known as activated protein C (APC) acts on factor V and inactivates it. By inactivating factor V, APC prevents blot clots from becoming too large.  In people with factor V Leiden, APC is unable to inactivate the mutated protein. This allows the clotting process to continue for an excessive time, leading to the formation of abnormal blood clots.

The interaction of APC with the mutated protein formed in Factor V Leiden thrombophilia has led to the condition having other names. These names are APC resistance, Leiden type and hereditary resistance to activated protein C.

The most common symptom of Factor V Leiden thrombophilia is the pain associated with developing a thrombosis in one of the veins in the leg. This results in the affected leg becoming swollen, painful and red. More rarely the clot forms in the pulmonary veins leading to some form of respiratory distress. The degree of this distress may be minor to severe. Clots in other veins such as those of the arms are rare but do occur occasionally.

Normally treatment is only required when abnormal clots are detected. Treatment of clots requires some form of anticoagulant therapy such as Warfarin or Heparin. Depending on the number and severity of the clots, this treatment may take several months.

The condition may also lead to an increased risk of miscarriage in pregnant women. Most women with factor V Leiden thrombophilia have normal pregnancies. However, pregnant women who have two copies of the defective gene (homozygous) may require heparin anticoagulant, as may heterozygous women who have previously developed abnormal clots. Pregnant women carrying the gene may also benefit from wearing support stockings in the latter part of their pregnancy to help prevent thromboses from forming.