Antiphospholipid antibody syndrome

Antiphospholipid syndrome (APS) is a complex autoimmune disease often connected to systemic lupus erythematosus. Main features are specific antiphospholipid antibodies (aPL), thrombosis (arterial, venous or microvascular) and/or pregnancy complications and failure. The involved antibodies are directed against plasma proteins such as beta-2-glycoprotein1 (beta 2GPI) or prothrombin which depends on negatively charged phospholipids. Antibody-beta 2GPI complexes bind to a variety of receptors on different cell types, including endothelial cells, platelets, monocytes and trophoblasts and may trigger intracellular signalling and inflammatory responses. There is increased expression of tissue factor on monocytes and endothelial cells, interference in protein C anticoagulant pathways, inhibition of fibrinolysis and inhibition of annexin V binding to phospholipids. Pregnancy failure may be due to thrombosis in placental bed, although alternative mechanism may explain the tendency to very early losses prior to placentation. Clotting tests such as activated partial thromboplastin time (aPTT) and diluted Russell`s viper venom test (dRVVT) show a prolonged time for coagulation despite prothrombotic state. Clotting test could be misleading so clinical judgement is mandatory.