[Antiphospholipid syndrome. Pathogenesis, molecular basis and clinical aspects]

In 1983 the antiphospholipid syndrome was first described as an independent clinical entity by Graham Hughes and characterized by thrombosis, thrombocytopenia and recurrent fetal losses. In the following years evidence accumulated from various studies that the thrombotic events in the antiphospholipid syndrome correlate with elevated serum titers of antiphospholipid antibodies. These autoantibodies represent a very heterogeneous group as multiple specificities against various negatively charged phospholipids are found. Most commonly described are antibodies against cardiolipin, but also cross-reactivities between the different phospholipids are observed. Moreover, efficient binding of antiphospholipid antibodies against a phospholipid requires the presence of certain protein-cofactors which on the other hand can be antigens themselves.

Although numerous animal models strongly indicate that antiphospholipid antibodies play a causal role in the pathogenesis of the disease, the exact pathogenetic mechanisms are still to be elucidated. There is accumulating evidence from in vitro studies with poly- and monoclonal antiphospholipid antibodies that these autoantibodies are able to interfere with all aspects of the hemostatic balance. Influences of antiphospholipid antibodies on plasmatic processes of the coagulation cascade as well as antithrombotic and fibrinolytic mechanisms are described. Furthermore, antiphospholipid antibodies are able to exert prothrombotic effects on cells participating in hemostasis, mainly platelets and endothelial cells.

Therapeutic approaches to the antiphospholipid syndrome today are mainly restricted to the prevention of further thrombosis by permanent anticoagulation. Although 30-50% of all patients, according to the literature, with moderately to highly elevated antiphospholipid antibody titers develop the clinical symptoms of the syndrome, there are only few studies investigating the benefits of a prophylactic anticoagulation of the affected patients. There is an urgent need for prospective clinical studies to clarify this question. Therapy of nonthrombotic manifestations of the antiphospholipid syndrome are scarcely standardized. In obstetrics, treatment with aspirin, heparin and steroids is the main approach. Here also controlled studies are restricted to small numbers of patients and are therefore of limited validity.