Inherited Thrombophilia: Genetics, Prevalence, Testing Guidelines
What is Thrombophilia?
This inherited condition increases your risk for deep vein thrombosis, DVT. Learn how thrombophilia is diagnosed and treated.
By Elizabeth Shimer Bowers
Medically Reviewed by Farrokh Sohrabi, MD
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Most often, blood clotting is a good thing — a necessary response, in fact, to keep your body from bleeding excessively when you're injured. But clotting, or coagulation as it's also called, can be dangerous when clots form when they aren't supposed to. That's the case with deep vein thrombosis (DVT), blood clots that form in a vein deep inside the body, usually the legs.
Particularly at risk for this are people with a blood clot disorder called thrombophilia, also known as hypercoagulability. This condition makes someone more likely to develop abnormal blood clots which can be life-threatening. Thrombophilia increases DVT risk. And, left untreated, blood clots can break off, start moving through the blood, and block blood flow to a major organ, possibly causing severe damage or death. That's why proper thrombophilia diagnosis is so important.
Increased DVT Risk in Thrombophilia
“Most thrombophilias are genetic,” meaning they're inherited from one or both parents, said Keith McCrae, MD, a physician in the department of hematologic oncology and blood disorders at the Cleveland Clinic in Ohio. “There are also risk factors for blood clots that are not genetic, such as taking oral contraceptives, being immobilized due to recent surgery, or cancer. But most are inherited," said Dr. McCrae.
Thrombophilias that are present from birth are called congenital thrombophilias. One of the most common of these is factor V Leiden. “Factor V Leiden is more common in people of Northern European descent," Dr. McCrae said. "Not all people with factor V Leiden will develop blood clots, however."
There are also other types of inherited thrombophilias, including prothrombin G2021A mutation, antithrombin III deficiency, protein C deficiency, and protein S deficiency.
Thrombophilia is not caused by genetics alone. “Thrombophilia results from interactions between genetics and a person’s environment — something we call multifactorial inheritance,” said Michelle Kluge, a genetic counselor at the Mayo Clinic in Rochester, Minn.
Thrombophilia: a Genetic Condition
“In general, thrombophilia is inherited in an autosomal dominant manner,” said Michelle Alabek, a genetic counselor at the Hemophilia Center of Western Pennsylvania in Pittsburgh. She explained, “Everyone has two copies of certain genes that should work to stop clot formation appropriately. If one or both copies of a gene aren't working in a person, he or she will be at increased risk for thrombosis" (formation of a clot).
Whether someone has thrombophilia also depends on how many copies of the nonworking gene that person inherited. “If an individual has one copy of a gene that does not work and one copy that does work, they are heterozygous for thrombophilia," Alabek said. "Heterozygous individuals have a 50 percent risk of passing the nonworking gene on to their children. If both copies of a person’s genes are not working, that person is homozygous, and these people always pass on one nonworking copy of the gene to their children.”
Alabek added that a person can inherit faulty genes from both sides of the family, which would increase risk for congenital thrombophilia. “It is also possible to have more than one thrombophilia, which would further increase risk of thrombosis,” she said.
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Receiving a Thrombophilia Diagnosis
Several scenarios might prompt someone to seek evaluation for a possible thrombophilia diagnosis.
“People with a strong family history of thrombosis may want to be evaluated by a genetics professional, such as a genetic counselor, as well as a hematologist, especially if they have other thrombophilia risk factors, such as undergoing surgery or taking oral contraceptives,” Kluge said. “These professionals can discuss individual thrombophilia risk factors, both genetic and environmental, as well as your personal risk for developing a blood clot. They can also help you determine the appropriate next steps."
Another reason to seek evaluation for thrombophilia diagnosis, according to McCrae, would be development of a blood clot at an early age. “The incidence of a thrombotic event in someone who is 21 years old is about one in 750,000," he said. "In someone who is 55 or 60, it is about one in 150. So age is a major risk factor."
Seeking a thrombophilia diagnosis also may be called for if a clot forms in an unusual place. “The majority of clots form in the legs, but someone with a congenital thrombophilia may develop a clot around the intestines or liver — very unusual places for thrombosis unless someone has a thrombophilia,” McCrae said.
Many people with thrombophilias never go on to develop blood clots, but for those who do, there are effective ways of managing thrombophilia.
Treatment for Thrombophilia
“The majority of people with one of the more common thrombophilias will not develop a blood clot, and until someone develops a clot, they usually aren’t treated,” McCrae said. “Once a person develops a clot, there is some controversy in the medical community about managing thrombophilia.
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