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Age, major surgery, immobility, pregnancy, and various chronic illnesses are known risk factors for venous thromboembolism.

An inherited risk factor can be identified in over half of patients with DVT without identifiable cause or thrombosis at a young age.

The Factor V Leiden mutation is associated with increased tendency to form abnormal blood clots.

Deep vein thromboses most often occur in leg veins

When a blood clot (thrombus) forms inside a person´s vein, he or she is said to suffer from venous thrombosis. If the vein affected by a blood clot is deep inside the body, rather than close to the surface of the body, the condition is referred to as deep vein thrombosis (DVT) and most often occurs in the veins of the legs or pelvis.

Venous blood clots can break off and lodge in the lungs

Patients with deep vein thrombosis are in danger of suffering a pulmonary embolism, which occurs when a venous blood clot breaks off (completely or partially), travels with the bloodstream and lodges in one of lung’s narrow arteries. The resulting blockage of blood flow can cause permanent damage to the affected lung, heart failure and death.

DVT can go undetected until it causes pulmonary embolism

Individuals who suffer from either deep vein thrombosis or pulmonary embolism are collectively diagnosed as having venous thromboembolism. Each year, one out of 1000 individuals of European ancestry in the United States is diagnosed for the first time with venous thromboembolism. About one-third of people with this condition experience a pulmonary embolism and one-third develops venous thromboembolism again within ten years of the initial diagnosis. The proportion of people with venous thromboembolism is likely to be underestimated as it is well recognized that a number of cases remain undiagnosed.

A number of genetic factors contribute to the risk of VTE

It is believed that a number of genetic factors contribute to the development of venous thromboembolism. One of these is Factor V Leiden, a mutation in the Factor V gene on chromosome 1 that results in thrombophilia, or an increased tendency to form abnormal blood clots in blood vessels. Individuals with this mutation have a three to four-fold increased risk of developing venous thromboembolism in their lifetime. The Factor V Leiden variant is quite common in populations of European ancestry, but less common in other ethnicity groups. Scientists have confirmed the association of two more variants on chromosomes 4 and 9 with increased risk of developing venous thromboembolism.

deCODEme can calculate your genetic risk

The deCODEme Complete Scan and the deCODEme Cardio Scan identify these variants and use them to provide customers of European descent with a personalized interpretation of their genetic risk for developing venous thromboembolism.

At present, the necessary scientific information to interpret the genetic risk for customers of other ethnicities is not available. This information will be added as soon as it becomes available and we are assured of its quality.

Risk factors

• Age and gender. Age is a strong risk factor for development of venous thromboembolism with a dramatic increase after age 60. Recurrent venous thromboembolism is more common in men than women.
• Surgeries. Major surgery, as well as trauma and fractures, are known to increase the risk of venous thromboembolism.
• Chronic illnesses. Increased risk of venous thromboembolism accompanies various chronic illnesses such as cancer, stroke and congestive heart failure. A previous diagnosis of VTE is a risk factor for further episodes.
• Immobility Immobility due to surgery, trauma, and chronic illness is associated with venous thromboembolism as described above. Prolonged bed rest and long journeys by airplane or car, even in otherwise assumed healthy individuals, also increase the risk of venous thromboembolism.
• Other conditions that have been associated with greater risk of VTE include pregnancy, the postpartum period, varicose veins, obesity, estrogen treatment and the antiphospholipid antibody syndrome.
• Ethnicity. In the United States the incidence of venous thromboembolism has been found to be highest in African-Americans followed by individuals of European descent. The risk for Hispanics is about half that of populations of European origin while Asians are at a markedly lower risk.
• Genetics. An inherited risk factor can be identified in over half of patients with deep venous thrombosis without identifiable cause or thrombosis at a young age. Factor V Leiden, is detected in about 5% of individuals of European origin, but is rare in other ethnic groups. The reported frequency in Hispanics is around 2%, 1% in African-Americans and 0.5% or less in Asians.

Prevention and treatment

Avoiding long periods of immobility helps prevent the formation of deep vein thrombosis. Once a blood clot has developed in a deep vein, the treatment goals include preventing enlargement of the blood clot, preventing a pulmonary embolism and preventing recurrences of venous thrombosis.

The mainstay of therapy is anticoagulation (thinning of the blood) with duration of treatment depending on number of episodes and the presence or absence of blood clots in the lungs. Occasionally a permanent metal filter is placed in the largest vein below the heart (the inferior vena cava) to prevent large blood clots from reaching the arteries of the lung.

More information

You can find out more information about venous thromboembolism by talking with your doctor and visiting these Web sites:

• American Heart Association
• Medline Plus – Trusted Health Information for You
• National Heart Lung and Blood Institute
• Society of Interventional Radiology
• Thrombophilia Awareness Project

Scientific references

1. Anderson FA Jr, Spencer FA. Risk factors for venous thromboembolism. Circulation. 2003 Jun 17;107(23 Suppl 1):I9-16.
2. Lee R. Factor V Leiden: a clinical review. Am J Med Sci. 2001 Aug;322(2):88-102.
3. Ridker PM, Miletich JP, Hennekens CH, Buring JE. Ethnic distribution of factor V Leiden in 4047 men and women. Implications for venous thromboembolism screening. JAMA. 1997 Apr 23-30;277(16):1305-7.
4. Trégouët DA, Heath S, Saut N, et al. Common susceptibility alleles are unlikely to contribute as strongly as the FV and ABO loci to VTE risk: results from a GWAS approach. Blood. 2009 May 21;113(21):5298-303. Epub 2009 Mar 10.
5. White RH. The epidemiology of venous thromboembolism. Circulation. 2003 Jun 17;107(23 Suppl 1):I4-8.

This content was last reviewed on February 11, 2010.

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