Antiphospholipid syndrome (APS) is a condition in which a heterogeneous group of antibodies, IgG, IgM, or both, are produced that are directed against phospholipid-protein complexes. Antiphospholipid antibodies found in Antiphospholipid Syndrome include lupus anticoagulant (LA), anti-cardiolipin antibodies (ACA), and anticardiolipin beta-2 glycoprotein (anti-ß2 GPI) complexes. Identified in the mid-1980s by Hughes as a condition associated with Systemic Lupus Erythematosus, it has more recently been recognized to occur in three forms:
- Primary Antiphospholipid Syndrome (Primary APS) occurs in patients with no other systemic autoimmune disorder
- Associated APS occurs in patients with other systemic autoimmune disorders such as SLE and Rheumatoid Arthritis (RA)
- Catastrophic APS is when there are multiple organ thromboses and failure with a mortality rate of more than 50%
Within the larger classification of APS, two additional syndromes have been identified: the Anticardiolipin Antibody (aCL) syndrome and the Lupus Anticoagulant Syndrome (LAC). Both syndromes can be associated with thrombosis, thrombocytopenia, or fetal loss.
The prevalence of APS is approximately 5% in the general population and increases with age. Antibodies linked to thromboembolic events are those that are directed toward anionic phospholipids. One proposed mechanism suggests that Annexin A2, an endothelial cell surface receptor, mediates endothelial cell activation by antiphospholipid and anti-beta-2 glycoprotein-I antibodies. Normally Annexin V prevents the formation of coagulation complexes on the phospholipid surface. Disruption of Annexin V by the antiphospholipid could lead to endothelial cell activation with increased coagulation complex formation and thrombosis.
