APS is an autoimmune disorder in which the body appears to recognize certain phospholipids (fatty molecules that are important components of a cell's membrane) as foreign substances and produces antibodies against them. It is associated with the production of one or more autoantibodies that interfere with the blood clotting process in a way that is not fully understood. People with APS may experience blood clots leading to heart attack, stroke or in the case of women, loss of the fetus during pregnancy. APS may occur in patients with lupus and related autoimmune diseases or as a primary syndrome in otherwise healthy individuals.
In APS, blood clots may affect any part of the body. In addition to stroke and heart attack, abnormalities of the heart valves, kidney disease, thrombocytopenia (a low level of platelets in the blood) and leg ulcers have been associated with the disorder. APS takes a particular toll during pregnancy, when the syndrome may cause miscarriage, stillbirth, retarded growth of the fetus or toxemia and high blood pressure. In the general population, APS may account for 20 percent of deep vein thrombosis cases, one-third of strokes in people under age 50, and 5 to 15 percent of recurrent miscarriages.
Antiphospholipid syndrome may affect anyone, but is most frequently seen in women of child-bearing age and in those with another autoimmune disorder. According to the March of Dimes, APS is the most common acquired thrombophilia, affecting up to 5% of pregnant women.