At risk for thrombosis: FXII autoantibodies and the antiphospholipid syndrome
- Factor XII autoantibodies as a novel marker for thrombosis and adverse obstetric history in patients with systemic lupus erythematosus
- Annals of the Rheumatic Diseases, Volume 66, Number 4, April 2007, pp. 533-536
What is the topic?
People with lupus who have antiphospholipid antibodies (aPL) are at risk for blood clots, including heart attacks, strokes, clots in the legs, lungs, or other organs, and pregnancy complications.
Several blood tests are commonly used to detect the antiphospholipid syndrome, such as anticardiolipin antibodies (aCL), lupus anticoagulant (LA), and anti-beta 2 glycoprotein I (aB2). However, there are a large number of other tests that might be as good or better than these, since people with the antiphospholipid syndrome have antibodies to many different blood clotting proteins.
What did the researchers hope to learn?
Factor XII (FXII) is a protein that plays a role in preventing blood clots. The researchers wanted to find out if the presence of antibodies to FXII (anti-FXII) could be used to identify lupus patients at risk for thrombosis and pregnancy complications.
Who was studied?
127 lupus patients were included in this study (123 women, 4 men); 46 of these patients had a history of thrombosis and 22 fulfilled the criteria for a diagnosis of antiphospholipid syndrome. Of the women whose pregnancy histories were available, 20% had one or more miscarriages and only 57% had completely uncomplicated pregnancies. In addition to these lupus patients, the researchers also obtained blood samples from 123 healthy people, who had no history of lupus, thrombosis, or pregnancy complications in order to compare the blood test results.
How was the study conducted?
The researchers analyzed blood samples using a test called ELISA to compare the levels of anti-FXII antibodies with other antiphospholipid antibodies in the lupus patients who had thrombosis and obstetric complications. They also distinguished between patients who had thrombosis in their arteries and those who had thrombosis in their veins.
What did the researchers find?
Anti-FX II antibodies were present in 40% of the lupus patients, as opposed to only 7% of the healthy people. Having anti-FXII was associated with a blood clotting history, and this was more pronounced in the case of clots in the arteries than clots in the veins. There was also a higher level of one particular subset of anti-FXII in patients with pregnancy difficulties than was seen in the healthy group.
What were the limitations of the study?
Anti-FXII antibodies may occur more frequently in lupus patients in general and in those with a history of blood clots, but were not seen in the majority of the lupus patients studied. Other aPL antibodies were detected in many of these patients, and how these antibodies affect disease, alone or together, is still not well understood.
In current practice, most clinical tests for aPL autoantibodies in lupus patients do not look for the presence of anti-FXII antibodies. However, if further research verifies these preliminary findings, this may prove to be a useful diagnostic test.
What do the results mean for you?
Doctors can prescribe a number of preventive measures (e.g., low-dose aspirin, antimalarial medications and sometimes other anticoagulants) if they are concerned that a lupus patient might be at risk for developing blood clots or pregnancy complications. This study suggests the possibility that screening for anti-FXII antibodies could provide further information that would help doctors evaluate a patient’s overall risk for such complications.