A parent who carries the mutated gene has a 50 percent chance of passing it on to each child. Someone who inherits one mutated gene faces a five- to seven-fold increased risk of developing a serious and potentially life-threatening clot. Someone with two of the damaged genes has a 25- to 50-fold increased risk. Approximately one person in 5,000 among whites in the US and Europe has two of the mutated genes.
Because the risk of suffering a clot is about one in 1,000 people a year in the general population, the increased risk associated with factor V Leiden is not to be taken lightly: 5 to 7 in 1,000 people each year for those with one mutant gene and 25 to 50 per 1,000 in those with two mutant genes. The risk is greatest in individuals who have more than one clotting defect, as well as in people who smoke or are overweight.
A Danish study of 9,253 adults found that in people who did not smoke, were not overweight and were younger than 40, the 10-year risk of clots and emboli was 1 percent in those with one mutated gene and 3 percent in those with two damaged genes. But the risk increased to 10 percent in people with one mutated gene and 51 percent in those with two abnormal genes if they smoked, were overweight and were older than 60.
ACCURATE TESTING
Two blood tests can detect factor V Leiden. One, the APC resistance assay, is 95 percent accurate and could be used for screening. It measures the anticoagulant response to activated protein C. A definitive but more costly diagnosis, also performed on blood, can be made by genetic analysis of the factor V gene.
One or both tests are recommended for people with DVT, pulmonary embolism, premature stroke, repeated miscarriage, a family history of clots or a known factor V mutation in a blood relative. Thus, Bloom’s three daughters should be tested, because each has a 50 percent chance of carrying the defective gene.
For people with a personal or family history of clots, testing can help avert clotting complications when they undergo major surgery, are treated for cancer, anticipate pregnancy or plan to take oral contraceptives, estrogen therapy or a drug like tamoxifen.
In women with factor V Leiden, for example, treatment with an anticoagulant during pregnancy can reduce the risk of pregnancy loss. Women needing contraception might be wise to avoid birth control pills and instead choose a method that would not increase their risk of clots. And a person who is hospitalized or needs surgery can be treated with blood thinners and mechanical compression boots.
Though factor V Leiden alone does not seem to raise the risk of arterial clots, something as simple as daily therapy with low-dose aspirin may help prevent a heart attack or stroke in people with factor V Leiden if they have additional risk factors.
Preventive action is also important during long periods of immobilization, including long car and plane rides. Drinking plenty of water to prevent dehydration, avoiding alcohol, taking frequent walks and wearing elastic stockings can lower the risk of clots on such excursions.
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