Factor V Leiden Factor V Leiden is a blood clotting disorder. It is not a disease. Factor V is a protein that is needed for blood to clot properly. Some people do not have the normal Factor V protein. Instead, they have an different form called Factor V Leiden. This is caused by a change (mutation) in the gene for this protein. The different gene that makes the Factor V Leiden protein is inherited from one or both parents. The Factor V Leiden protein is harder to ?turn off? than the normal Factor V protein. This makes blood clots more likely to form, a condition called thrombophilia. If you have Factor V Leiden, you have a greater chance of developing blood clots. Blood clots in the deep veins in your legs (called deep vein thrombosis or DVT) or in your lungs (called pulmonary embolus or PE) can be dangerous. Treatment: There is no treatment that can prevent this disorder or make it go away. However, there are things that you can do to reduce your chances of developing a dangerous blood clot. You do need treatment with ?blood thinners? if you have had a blood clot or develop one in the future. These medications (called anti-coagulants) help to prevent clotting. If you have never had a blood clot, you do not need treatment with blood thinners. In situations where there is a greater chance of clotting (such as surgery, a leg cast, a serious illness or pregnancy) you may be treated with blood thinners until the risk has passed.