Dear Doctor Column, October 21, 2002

Question:

Can you give me some information on the blood disorder Factor V?

Answer:

You are probably asking about a condition called Factor V Leiden, since Factor V deficiency is a very rare bleeding disorder. Factor V Leiden is the most common hereditary blood coagulation disorder in the U.S., found in 5% of the Caucasian population and 1.2% of the African-American population. This condition increases a person's risk of developing blood clots.

Factor V is a protein in the blood that plays a role in the coagulation cascade, the chain reaction that is set in motion when a blood vessel is injured. Factor V accelerates the activity of thrombin, an enzyme that helps to form a clot to seal the vessel and stop bleeding. When Factor V has a particular mutation, called Factor V Leiden, blood clotting is enhanced and can occur in the absence of obvious injury to the blood vessel. This is the basis of thrombosis —— a stationary blood clot that forms along the wall of a blood vessel, frequently obstructing blood flow. Occasionally, portions of the blood clot break away and travel to distant sites, such as the lung.

Factor V Leiden is a hereditary disease, which means that it is passed on from the parents to the child at the time of conception. When a person has only one gene for Factor V Leiden, he or she is called heterozygous and has a risk of developing thrombosis that is two to eight times the risk of those without Factor V Leiden. If both genes for Factor V have the mutation, he or she is called homozygous, and the risk of developing thrombosis increases to approximately 80 times that of people without the Factor V Leiden. This factor affects males and females in equal numbers. A simple blood test, available since 1993, can test for this disorder.

Factor V Leiden is associated with the following complications:

• Venous thrombosis (blood clots in the veins, especially in women who take oral contraceptives)
• Unexplained miscarriages
• Blood clots in the lungs (or anywhere else)
• Gallbladder dysfunction
• Pre-eclampsia and/or eclampsia (toxic substances in the blood, while pregnant) or other complications of pregnancy, such as very small babies
• Stroke and/or heart attack

Your physician will determine if you or a member of your family needs to be tested for Factor V Leiden. Most people with this condition do not need treatment, but if they are under conditions such as prolonged immobilization or pregnancy they may receive an anticoagulant to prevent thrombosis.

For more information, visit this Thrombophilia support page.