Antiphospholipid syndrome (APS) is an autoimmune disorder in which the body makes antibodies to its own phospholipids or plasma proteins. Antiphospholipid syndrome (APS) can occur in individuals without any associated disease. This is called primary APS. The disorder may also occur with systemic lupus erythematosus (SLE) or another rheumatic or autoimmune disorder. This is called secondary APS. Antiphospholipid antibodies can be found in as many as 50% of people with lupus and in 1-5% of the rest of the population. About Guide to Rare Diseases Mary Kugler explains with more details about antiphospholipid syndrome causes, diagnosis, symptoms, and treatment, including the fact women with APS may have frequent miscarriages or premature births.