Factor V Leiden: Are there different types?

Factor V Leiden is a common inherited clotting disorder. There are two forms of this disorder — heterozygous and homozygous. Heterozygous is the more common of the two forms.

Factor V Leiden is caused by a gene mutation in clotting factor V. This mutation causes factor V to respond more slowly to protein C, an anti-clotting factor that normally controls the activity of factor V. As a result, people with factor V Leiden have an increased risk of blood clots (thrombophilia).

The gene responsible for the normal production of factor V has two copies. If you inherit only one copy of the defective gene, you are heterozygous. If you inherit two copies — one from each parent — you are homozygous. Those who are homozygous have a much greater risk of blood clots in veins deep within muscle (deep vein thrombosis) that may travel to the lungs (pulmonary embolism) than do those who are heterozygous.

Factor V Leiden may be detected by special blood tests. If blood clots develop, treatment may include anti-clotting (anticoagulant) medications, such as warfarin (Coumadin).