Thrombosis in the Antiphospholipid Syndrome

Thrombosis in the antiphospholipid syndrome Reyhan D‹Z KÜÇÜKKAYA Division of Hematology, Department of Internal Medicine, Istanbul University, Istanbul School of Medicine, Istanbul, TURKEY Turk J Hematol 2006;23(1): 5-14 INTRODUCTION her autoimmune disorders, especially with systemic lupus erythematosus (SLE)[8]. Besi- Antiphospholipid antibodies (aPLA) are des these autoimmune conditions, aPLA may heterogenous antibodies directed against be present in healthy individuals, in patients phospholipid–protein complexes. Antiphosp- with hematologic and solid malignancies, in holipid syndrome (APS) is diagnosed when ar- patients with certain infections [syphilis, lep- terial and/or venous thrombosis or recurrent rosy, human immunodeficiency virus (HIV), fetal loss occurs in a patient in whom scre- cytomegalovirus (CMV), Epstein-Barr virus ening for aPLA are positive. Because both (EBV), etc.], and in patients being treated thrombosis and fetal loss are common in the with some drugs (phenothiazines, procaina- population, persistent positivity of aPLA is mide, phenytoin etc.). Those antibodies are important. This syndrome is predominant in defined as “alloimmune aPLA”, and they are females (female to male ratio is 5 to 1), espe- generally transient and not associated with cially during the childbearing years[1-7]. the clinical findings of APS[9]. A minority of As in the other autoimmune disorders, APS patients may acutely present with mul- aPLA and APS may accompany other autoim- tiple simultaneous vascular occlusions affec- mune diseases and certain situations. APS is ting small vessels predominantly, and this is referred to as “primary” when it occurs alone termed as “catastrophic APS (CAPS)”[1-7]. or “secondary” when it is associated with ot- Milestones in the Antiphospholipid Syndrome History Antifosfolipid sendromu The first antiphospholipid antibodies we- Anahtar Kelimeler: Antifosfolipid sendromu, Antifosfolipid re discovered by Wasserman et al.[10] in antikorlar, Tromboz. 1906. Wasserman developed a complement- Key Words: Antiphospholipid syndrome, Antiphospholipid fixation test by incubating the serum of pati- antibadies, Thrombosis. ents with a saline extract of liver obtained from fetuses with congenital syphilis. This 5 Diz Küçükkaya R. Thrombosis in the antiphospholipid syndrome test became the basis of the VDRL (Venereal of the “autoimmune” aPLA, other phospholi- Disease Research Laboratory) test which is pid-binding proteins including prothrombin, now also used for non-specific aPLA scre- protein C, protein S, and annexin V have be- ening. Mass screening of Wasserman test en described as playing a similar role. showed that many patients with autoimmu- In 1998, preliminary classification crite- ne diseases had “false-positive” results. Mary ria for the classification of “definite” APS we- Pangborn[11] in 1946 isolated “cardiolipin” re described at an international meeting in from the bovine heart as an antigenic target Sapporo, Japan[1]. Clinical criteria included the for Wasserman test. In 1972, Feinstein vascular thrombosis and pregnancy morbi- and Rapaport[12] showed an association bet- dity. Laboratory criteria were established as ween false-positive syphilis screening tests the detection of LAs, and presence of anticar- and the presence of a circulating anticoagu- diolipin IgG and IgM antibodies (Table 1). Ac- lant, termed as “lupus anticoagulant (LA)”. cording to these criteria, “definite” APS is Actually it is a misnomer, as more than 50% considered if a patient has at least one clini- of the patients with LA do not have SLE, and cal and one laboratory criteria[1]. Validation although LA acts as an anticoagulant in vit- studies showed that Sapporo criteria have ro, in vivo it is paradoxically associated with 71% sensitivity and 98% specificity in the di- thrombotic events. In 1980, Perumal Thiaga- agnosis of “definite” APS patients[21]. rajan[13] demonstrated that an Immunoglo- buline M (IgM) antibody with LA activity Antiphospolipid Antibodies (aPLA) cross-reacted with negatively charged phosp- Antiphospholipid antibodies are a hetero- holipids. In 1983 Harris and colleagues[14] geneous family of immunoglobulins. Despite described a radioimmunoassay for anticardi- their name, aPLA do not bind to phospholi- olipin antibodies (ACLA) that was conside- pids alone, but are directed to plasma prote- rably more sensitive than previous tests. ins which are complexed with negatively Subsequently an enzyme-linked immunosor- charged phospholipids. Although several an- bent assay (ELISA) test for ACLA was develo- ti-phospholipid antibodies are defined, in ped[15]. The clinical associations of thrombo- two of those (ACLA and LA) clinical studies sis and fetal loss were found to be similar in confirmed an association with the clinical patients with ACLA and LA. In 1985 Graham complications of APS. Hughes et al.[16] introduced the term “anticardiolipin syndrome”, which was soon Anticardiolipin antibodies are measured changed to “antiphospholipid syndrome” in by ELISA, and reported by GPL ad MPL units [22] 1987[17]. In the first APS classification arteri- for IgG and IgM ACLA, respectively . In pa- al thrombosis, venous thrombosis, recurrent tients with APS, ACLA are not simply direc- fetal loss and thrombocytopenia were regar- ted to the cardiolipin antigen, it recognizes ded as clinical criteria; LA positivity and mo- β2-GPI –cardiolipin complexes in the ELISA derate or high ACLA IgG/IgM positivity were microplates. Since low titer ACLA may be regarded as laboratory criteria. present in the normal population, moderate (20-80 GPL, 20-50 MPL) to high positive (mo- In 1990, two groups independently de- re than 80 GPL or 50 MPL) results are ne- monstrated that ACLA required protein co- eded for the diagnosis of APS[23]. factors for binding to the phospholipids[18,19]. The most common of these prote- Lupus anticoagulants are screened by ins was β2-glycoprotein (GP)-I which binds to phospholipid-dependent coagulation tests the anionic phospholipids and also posses- (e.g. activated partial thromboplastin time, ses an anticoagulant activity[20]. Although kaolin clotting time, Russell’s viper venom β2-glycoprotein-I is the predominant target clotting time, dilute prothrombin time, or textarin time). Prolonged screening test sho- 6 Turk J Hematol 2006;23(1):5-14 Thrombosis in the antiphospholipid syndrome Diz Küçükkaya R. Table 1. Sapporo criteria for the classification of the APS[1]* A. Clinical criteria: 1. Vascular thrombosis: One or more clinical episodes of arterial, venous, or small vessel thrombosis, in any tissue or organ. Thrombosis must be confirmed by imaging studies or histopathology. 2. Pregnancy morbidity: a. One or more unexplained deaths of a morphologically normal fetus at or beyond 10th week of gestation, or b. One or more premature births of a morphologically normal neonate at or before 34th week of gestation because of severe pre-eclampsia, or severe placental insufficiency, or c. Three or more unexplained consecutive abortions before the 10th week of gestation. B. Laboratory criteria: 1. Anticardiolipin IgG or IgM antibodies present at moderate or high levels in the blood on two or more occasions at least six weeks apart, 2. Lupus anticoagulants present in plasma on two or more occasions at least six weeks apart, detected ac- cording to the guidelines of the International Society on Thrombosis and Hemostasis. * Definite antiphospholipid syndrome (APS) is considered to be present if at least one of the clinical and one of the laboratory criteria are met. uld not be corrected by mixing of normal Although it has been shown that both an- plasma (mixing studies), but rather by addi- ti-β2-GPI and anti-prothrombin antibodies tion of phospholipid (phospholipid neutrali- might be associated with clinical features of zation procedure). For the diagnosis of LA, APS, most of these studies are retrospective, other coagulopathies including specific fac- and these antibodies are not included in the tor inhibitors should be excluded[24]. Sapporo criteria[1]. β2-GPI is a plasma protein with high affi- Other aPLA (antibodies directed to zwitte- nity for negatively charged phospholipids. It rionic phospholipids, anti-phosphatidylseri- has been shown that most of the ACLA are ne, anti-phosphatidylinositol, anti-phospha- β2-GPI-dependent[18,19]. Since β2-GPI neut- tidylglycerol, etc) may be detected in patients ralizes negatively charged phospholipids and with APS. The clinical importance of other inhibits coagulation cascade, the presence of aPLA are unclear in the absence of a positive anti-β2-GPI antibodies may predispose to LA and/or ACLA test[1]. thrombosis. There are also some aPLA that can bind Anti-prothrombin antibodies may be pre- directly to negatively charged phospholipids [4-6] sent in 50-90% of APS patients . Anti- themselves. These aPLA do not require a prothrombin antibodies may cause hypoth- phospholipid binding protein (i.e. β2-GPI). rombinemia and may be associated with ble- They may be seen in patients with infectious eding symptoms in patients with APS. Bajaj diseases such as syphilis, HIV and EBV in- [25] et al. showed that anti-prothrombin anti- fections, and usually do not cause a throm- bodies are non-neutralizing antibodies, which botic complication. Routine screening tests bound prothrombin without inhibiting its may not distinguish infection-induced (so- conversion to thrombin. They suggested that called “non-pathogenic”) anti-cardiolipin an- hypoprothrombinemia resulted from the ra- tibodies[3].

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