APS is an autoimmune disease which can cause frequent clotting in arteries and veins and/or miscarriages. The clotting results from the presence of proteins in the blood called anti-phospholipid autoantibodies (commonly called APL) formed against the personís own tissues. These autoantibodies interfere with coagulation, leading to increased clot formation or thrombosis (in which blood flow stops due to a clot).
The damage caused by this clotting can vary depending on the site of the clot. For instance, repeated small clots in the heart can cause heart valve thickening or damage, with the risk of releasing clots into blood (called an arterial embolism). APL also may be associated with heart attacks in young people without any known cardiac risk factors. Blood clots in the arteries in the heart can lead to heart attacks, while blood clots in the arteries in the brain can result in strokes. Blood clots from APL can occur anywhere in the circulation and can affect any organ in the body.
Clots forming in the veins most frequently occur in the lower legs. Blood clots in the leg veins can break off and travel to the lung, causing a very serious condition called pulmonary embolism. Pulmonary embolism blocks blood flow to the lung and decreases the amount of oxygen in the blood.
In a few cases, repeated thrombotic events may take place in a short time, leading to the progressive damage of several organs. This acute and life-threatening condition is called catastrophic APS.
Patients with APS may suffer from other problems including low number of platelets, mottled purplish discoloration of the skin (livedo reticularis), and skin ulcerations.
For pregnant women, APL can lead to early and late miscarriage, and pre-eclampsia (high blood pressure and protein in the urine during pregnancy). Originally it was suggested that APL were responsible for clots in the placentaís blood vessels, causing fetal growth retardation. APL also may directly attack the placental tissues, blocking their growth and development.