Prothrombin thrombophilia is an inherited clotting disorder that causes an increased risk of abnormal blood clots known as venous thromboembolisms (VTE). One common type of VTE is deep vein thrombosis, clots which most often occur in the legs. Clots in other locations of the body are possible, but less common. These clots are caused by an overproduction of a clot-promoting protein called prothrombin. Clotting episodes can be life-threatening, but if detected, they are treatable.
While prothrombin thrombophilia increases clotting risks, the effects of the disease vary greatly from person to person. Many people with the disease never develop abnormal clotting while some experience repeated clots before the age of 30.
People with prothrombin thrombophilia will be more likely to develop a clot if they also have another clotting disorder such as factor V Leiden thrombophilia, protein S deficiency, or hyperhomocysteinemia. In women, oral contraceptives, hormone replacement therapy, and pregnancy can all compound the risk for developing a VTE.
The risk of developing a VTE is also influenced by whether a person is heterozygous for the condition — that is, has one normal copy of a mutation known as G20210A and one copy with a mutation — or is homozygous, meaning he or she has two mutated copies.
One copy of the mutation (heterozygous)
Overall, adults with one copy of the G20210A mutation are 2 to 4 times more likely to develop a clot then the general population. As children, their risks are 3 to 4 times greater, although most people with prothrombin thrombophilia will not develop abnormal clots as children.
Pregnant women with one copy of the G20210A mutation have a 3 to 15 times greater risk of developing a VTE than the general population. Some studies have indicated that pregnant women with the disease are at greater risk for pregnancy loss and other complications. However, studies on this topic have shown conflicting results. In general this risk is very small unless the woman has other risk factors. Overall, the chance of a successful pregnancy is high.
Women heterozygous for prothrombin thrombophilia who take oral contraceptives have a 16 to 59 times greater risk of developing VTE than the general population. In these women, 60% of VTEs are associated with oral contraceptive use.
Air travel may increase the risk for a VTE.
Two copies of the mutation (homozygous)
In general, the VTE risks for homozygotes are presumed higher than the risks for heterozygotes (listed above), however the exact numbers are not known.
Limited studies have indicated that women homozygous for prothrombin thrombophilia who also take oral contraceptives have a 17 to 86 times greater risk of developing a VTE.
In the United States, 2 to 5% of the Caucasian population and 0.3% of the Black population has one copy of the G20210A mutation. In Southern Europe, 3% of the population has one copy of the mutation while in Northern Europe, that figure falls to 1.7%. The mutation is extremely rare in Asian, African, and Native American populations.
Roughly 1 in 10,000 people have two copies of the G20210A mutation in populations where the mutation is prevalent.
Until an abnormal clotting incident occurs, no specific treatment is needed for people with prothrombin thrombophilia. Women with the disease-causing mutations should avoid oral contraceptives and hormone replacement therapy. There is not yet any consensus on how pregnant women with the disease should be treated.
Physicians will treat any clotting abnormality according to standard protocols, typically with anti-coagulant medication such as heparin or warfarin. People with more than one abnormal clot may be advised by their doctor to take these drugs preventatively, however the risk of clotting must be weighed against the risk of excessive bleeding caused by the drugs. Graduated compression stockings may also be recommended following a VTE.
A physician may recommend that someone with prothrombin thrombophilia be tested for additional clotting disorders, as these can greatly elevate the risk for abnormal clotting.
The prognosis for a person with prothrombin thrombophilia is generally good. Most will not ever experience a clotting episode while those that do typically experience these episodes in adulthood. Clotting episodes can be life-threatening, but if detected, they are treatable.
Explanations of an extensive number of genetic diseases written by the U.S. government's National Institutes of Health.
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