What Is Antiphospholipid Antibody Syndrome?

Antiphospholipid (AN-te-fos-fo-LIP-id) antibody syndrome (APS) is an autoimmune disorder. Autoimmune disorders occur if the body's immune system makes antibodies that attack and damage tissues or cells. 

Antibodies are a type of protein. They usually help defend the body against infections. In APS, however, the body makes antibodies that mistakenly attack phospholipids—a type of fat. 

Phospholipids are found in all living cells and cell membranes, including blood cells and the lining of blood vessels.

When antibodies attack phospholipids, cells are damaged. This damage causes blood clots to form in the body's arteries and veins. (These are the vessels that carry blood to your heart and body.)

Usually, blood clotting is a normal bodily process. Blood clots help seal small cuts or breaks on blood vessel walls. This prevents you from losing too much blood. In APS, however, too much blood clotting can block blood flow and damage the body's organs.