There are a number of inherited (genetic) blood conditions that may lead to blood clots in veins. One of the more common conditions is called the Prothrombin Gene Mutation (also known as the prothrombin G20210A mutation).  If you have the prothrombin gene mutation, you may be at an increased risk of having a clot in your vein. The prothrombin gene mutation occurs in about 0.7-4.0 percent of the Caucasian (white) population, and is rarely found in persons of Asian or African origin. 

Causes of blood clotting
Your body normally forms blood clots when a blood vessel is injured. Our bodies naturally keep the clotting process in check. However, if one of the mechanisms that help to stop clotting is not functioning correctly, it may result in abnormal clotting. Inherited disorders contribute to about one-half of all clotting episodes that occur in a vein. The prothrombin gene mutation is fairly common, but is not the only inherited abnormality contributing to blood clotting.

Inherited abnormalities are especially suspected if clotting occurs in someone who is relatively young, if the clotting has occurred in an unusual site or in multiple sites or if other members of the family have had clotting.
 
Non-inherited risk factors for clotting in veins include

• Pregnancy
• Oral contraceptive use
• Extreme obesity
• Cancer
• Trauma
• Major surgery
• Prolonged bed rest or inactivity
• Presence of a lupus anticoagulant
• Possibly hormone-replacement therapy
• Incidence of clotting increases with age

Clotting in a vein
Most clots in a vein are deep vein thrombosis (DVT) and usually occur in a leg. In the United States, about a half million people are treated each year for DVT. When blood clots form in veins, they get in the way of blood flow and cause swelling, pain and warmth (called phlebitis). Occasionally, a part of the clot may break off and travel in the blood stream to the lungs. This is called a pulmonary embolus (PE) and can be life threatening. Symptoms of PE can include shortness of breath with or without activity, increased and/or irregular heart rate, chest pain, sudden loss of consciousness or coughing up blood.

Prothrombin gene mutation test
Your physician may request that you have a prothrombin gene mutation test if you:

• have a clot in a vein
• have a family or personal history of clotting in the veins
• have another inherited clotting disorder
• have a documented family history of prothrombin gene mutation

You will need to have about two teaspoons of blood drawn from a vein in your arm. Check with your insurance company about coverage for this test. Most insurance companies will provide coverage.

Identifying a genetic cause of clotting:

• Establishes reason for clotting
• Identifies persons and families at increased risk for future clotting
• Reduces incidence of future clotting through preventive measures

Inheriting the prothrombin gene mutation
Genes are in the center of each of our cells and come in pairs. If the prothrombin gene mutation is identified in an individual, it usually means that one gene out of the pair is altered (this is called a mutation) and the other gene is working correctly.   Both males and females with one altered prothrombin gene have an increased chanced of clotting and a 50 percent chance of passing that gene on to each of his/her children. Less commonly, an altered gene may be passed on from both parents, resulting in individuals with an even greater risk of clotting.  If a person inherits two working (normal) genes, he/she goes not have an increased chance of clotting and cannot pass on an altered prothrombin gene to any of his/her children.
 
 
Risk for clotting with prothrombin gene mutation
In the general population, one person in 1,000 has a DVT each year. The risk for clotting is increased threefold in thsoe who inherit one altered prothrombin gene, and is further increased in those who receive two altered prothrombin genes (one from each parent), although the rates have not been clearly identified. These rates are in comparison to people without an inherited gene.

Prothrombin Gene Mutation in women
Women who are pregnant or are using oral contraceptives that contain estrogen are at an increased risk for clotting. A woman with the prothrombin gene mutation who uses oral contraceptives has a risk for deep vein clotting sixteenfold over the rate for a woman who is not using oral contraceptives and does not have the prothrombin gene mutation. Women who have the prothrombin gene mutation (either one or two copies) and are considering either taking oral contraceptives, getting pregnant or are pregnant should consult their hematologist to determine the need for a blood thinner to prevent clotting.

Management of individuals with Prothrombin Gene Mutation
People who have inherited the prothrombin gene mutation may need to receive medication to help prevent clotting at high-risk times. These include pregnancy, major surgery, prolonged bed rest or inactivity or trauma. These same people would require more prolonged courses of treatment after a clotting episode. The decision is best made with your doctor and is determined by the risk involved, your personal clotting and general health history. Genetic counseling and testing is available to you and your family.

Avoiding risk factors
If you or a family member has the prothrombin gene mutation, it is important to avoid other risk factors that may be under your control, including:

• Periods of prolonged inactivity. Examples may include long car rides/plane trips, illnesses that confine you to bed, major surgery and having a cast or an injury to your leg. It is important for you to try to move your legs frequently and avoid sitting for longer than one-and-a-half to two hours at a time.
• Oral contraceptive use and hormone replacement therapy. These therapies carry an increased risk for clotting. Talk to your primary care provider or specialist about possible risks and benefits of therapy before taking the medication.
• Pregnancy. If you are planning to become pregnant and you or a family member has a history of clotting, tell your primary care provider or specialist of the prothrombin gene mutation so you receive appropriate care.