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Antithrombin III deficiency is a rare disease that predisposes individuals to developing potentially serious blood clots. A genetic mutation impairs the body's ability to make functional antithrombin III enzymes, which play a vital role in preventing coagulation. Without treatment, a severe deficiency may lead to life-threatening clots in the lungs, heart, or elsewhere in the body. Most cases of antithrombin III deficiency can be effectively managed with daily doses of blood-thinning medications.
There is normally a careful balance of enzymes in the bloodstream; enzymes such as thrombin and factor X prevent the blood from becoming too thin, and chemicals such as antithrombin III and heparin prevent the blood from thickening. In the case of an antithrombin III deficiency, coagulating enzymes prosper and the risk of clotting is high.
There are two main types of antithrombin III deficiency, both of which are inherited in an autosomal dominant pattern. In type one, a genetic mutation impairs the body's ability to produce new antithrombin. In type two, there are approximately normal levels of the enzyme, but they fail to function properly.
Many people who inherit antithrombin III deficiency never experience clotting disorders or other health problems. Symptoms are most likely to arise around the age of 30, though it is possible to experience clots much earlier or later in life. The risk of developing clots is increased in people who smoke or suffer from high blood pressure, high cholesterol, and obesity.
A blood clot can cause a variety of symptoms depending on its site and size. Deep vein thrombosis in one of the legs is the most common place for a clot in people with the disorder, and may cause leg swelling and throbbing pain. Additional symptoms may include shortness of breath, dizziness, a bloody cough, and full-body weakness.
Most cases of antithrombin III deficiency are diagnosed before patients experience dangerous clots. Routine blood tests for other conditions might reveal unusually low levels of antithrombin and increased activity of coagulating enzymes. Genetic testing can confirm that a patient does indeed carry a specific genetic mutation. Imaging tests such as ultrasounds and echocardiographs are usually performed to screen for existing clots and check for possible damage in the heart, liver, kidneys, and other organs.
People who have antithrombin III deficiencies but do not develop symptoms may not need treatment. Instead, doctors generally recommend that they attend regular health checkups to ensure that problems do not arise. If clotting does occur, patients are started on a daily regimen of anticoagulant drugs, such as warfarin, heparin, or synthetic antithrombin. Surgery may be needed to break up a large blood clot in an emergency situation.
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