What is antithrombin III deficiency?

Antithrombin III deficiency is a rare disease that predisposes people to developing potentially serious blood clots. A genetic mutation impairs the body's ability to produce functional antithrombin III enzymes, which play a vital role in preventing clotting. Without treatment, a severe deficiency can lead to life-threatening blood clots forming in the lungs, heart, or elsewhere in the body. Most cases of antithrombin III deficiency can be managed effectively with daily doses of anticoagulant medications.

There is normally a careful balance of enzymes in the bloodstream; enzymes like thrombin and factor X keep the blood from getting too thin, and chemicals like antithrombin III and heparin keep the blood from getting too thick. In the case of an antithrombin III deficiency, the clotting enzymes thrive and the risk of coagulation 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 make new antithrombin. In type two, there are approximately normal levels of the enzyme, but they are not working properly.

Many people who inherit antithrombin III deficiency never experience bleeding disorders or other health problems. Symptoms are most likely to arise around the age of 30, although it is possible to experience clots much earlier or later in life. The risk of developing blood clots is increased in people who smoke or have high blood pressure, high cholesterol, and obesity.

A blood clot can cause a variety of symptoms depending on its location and size. Deep vein thrombosis in one of the legs is the most common place for a clot in people with the disorder and can cause leg swelling and throbbing pain. Additional symptoms may include shortness of breath, dizziness, bloody cough, and weakness of the whole body.

Most cases of antithrombin III deficiency are diagnosed before patients experience dangerous clots. Routine blood tests for other conditions may reveal unusually low levels of antithrombin and increased activity of clotting enzymes. Genetic testing can confirm that a patient carries a specific genetic mutation. Imaging tests, such as ultrasounds and echocardiograms, are usually done to check for existing clots and to check for possible damage to 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 make sure no problems arise. If clotting occurs, patients are started on a daily regimen of anticoagulant medications, 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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