Factor V Leiden is a genetic trait known to predispose people to the formation of blood clots. People with this trait have a variant of Factor V, a protein found in blood and involved in clotting mechanisms, that resists activated protein C, causing clots to develop even after the body releases enzymes to halt the clotting mechanism. This trait can be identified in people during routine screening conducted as part of a diagnostic process, or when they specifically request testing due to concerns about a family history of this genetic variation.
People of European ancestry are more likely to have the Leiden variation of Factor V, first identified in the Netherlands in the 1990s. It is estimated that around three to eight percent of people with European ancestry have at least one copy of the defective gene. Symptoms can vary, depending on the exact variation and how many copies of the gene someone has; for people with Factor V Leiden, the development of blood clots and complications like pulmonary emboli, where a clot enters the respiratory tract, is a potential risk.
Known as a hypercoagulability disorder because it increases the coagulation of the blood, Factor V Leiden is identified by performing a screening test on a patient's blood to see how resistant it is to protein C. In most cases, when this screening shows that the blood is resistant to activated protein C, it means the patient has Factor V Leiden. Combined with a family history of the gene, as well as blood clots in the patient's personal medical history, this can be a strong diagnostic indicator.
Some patients live with this genetic variation their whole lives without being aware of it, either because they are carrying a relatively mild mutation of the gene, or as a result of simply being lucky when it comes to the formation of blood clots. Other individuals may develop symptoms like thrombosis at various points in their lives, usually in response to known risks like flying and certain medications.
People concerned about hereditary blood disorders can opt to undergo genetic testing to screen for common genetic variations. The testing should be supervised by a genetic counselor who can also provide advice and assistance when the test results come back. People with Factor V Leiden can generally live healthy lives, have children, and engage in normal activities, but they do need to be more alert to clotting issues and the early warning signs of thrombosis, and they may be advised to avoid certain risks or to take extra precautions.