Thrombophilia is a blood clotting disorder in which the blood has a tendency to clot more than normal. The word "thrombophilia" comes from the Greek words thrombo which means "clot" and philia which means "love of."

Thrombophilia leads to an increased risk of developing potentially dangerous blood clots in the veins (venous thrombosis).

What Causes Thrombophilia?
Thrombophilia and Blood Clots

What Causes Thrombophilia?

Both factor V and prothrombin (also known as factor II) are proteins in the blood needed for normal blood clotting. The two most common forms of inherited thrombophilia are factor V Leiden and the prothrombin mutation.

A genetic alteration in the factor V gene is called factor V Leiden (pronounced lie-den). An alteration in the prothrombin gene is called the prothrombin mutation. People with one or more of these genetic alterations have thrombophilia.

Factor V Leiden is the most common form of inherited thrombophilia. When factor V Leiden is present, the shape of the factor V protein changes. This changed protein is not as well recognized by anoher blood protein that dissolves blood clots quickly (activated protein C, also known as APC). So, blood clots dissolve 10 times more slowly than normal, leading to clots that stay in the veins for a longer period of time.

Prothrombin is a blood clotting factor produced in the liver. When the prothrombin mutation is present, levels of prothrombin are 30 percent higher than normal. This makes blood clot more readily than normal.

Thrombophilia and Blood Clots

How much can an inherited thrombophilia increase your risk of having a blood clot? For a person with one factor V Leiden gene, the genetic risk of having a blood clot is 5 to 7 times higher than the average person's risk. For a person with two factor V Leiden genes, the risk can be up to 80 times higher.

For one prothrombin mutation, the genetic risk is 2 to 3 times the average person's risk. For people with more than one type of inherited thrombophilia, the risk is even greater.

Most people with an inherited thrombophilia will never have a dangerous blood clot, but some will, especially if they have a combination of other lifestyle risk factors or triggering events that add additional risks.