Sticky Platelet Syndrome and the Role of Glycoprotein Receptors: A Review of Literature

Abstract

Thrombotic events are mainly caused by defects in circulating plasma proteins and platelets. Normally, the formers include hereditary clotting defects [e.g. deficiencies in protein-S (PS), in protein-C (PC), in antithrombin (AT) genes, or factor V Leiden, and Prothrombin (PT) G20210A substitution] and autoimmune diseases [(anti-phospholipid-antibodies syndrome (APA)]. Although these conditions are well-described in literature, prothrombotic platelet disorders are less well understood. The sticky platelet syndrome (SPS) is a congenital, autosomal dominant disorder, associated with both arterial and venous thromboembolic events. In pregnant women, complications such as fetal growth retardation and fetal loss have been reported. It is characterized by in vitro platelets hyperaggregability (platelet-rich plasma; PRP) triggered by different agonists responsible for its subclassifcation: adenosine diphosphate (ADP) plus epinephrine (type I), epinephrine alone (type II, the most frequent), or ADP alone (type III). Clinically, patients may present with acute myocardial infarction (AMI), transient cerebral ischemic attacks (TIA), angina pectoris, stroke, peripheral arterial thrombosis, retinal thrombosis, and venous thrombosis (VT) even during oral anticoagulant therapy. Conversely, low-dose aspirin treatment ameliorates the clinical symptoms and normalizes hyperaggregability. Clinical symptoms, especially arterial, often present following emotional stress. Combinations of SPS with other congenital prothrombotic defects have been described. Currently, a precise and definite etiology of this defect is not recognized, but receptors on the platelet surface are considered strongly involved candidates. Normal levels of platelet factor 4 (PF4) and betathromboglobulin (βTG) in plasma suggest that the platelets are not activated at all times; accordingly they appear to become hyperactive upon ADP or adrenaline release. In vivo clumping could temporarily or permanently occlude a vessel, leading to the described clinical manifestations. The syndrome appears to be prominent particularly in patients with unexplained arterial vascular occlusions. Despite studies investigating the role of platelet glycoprotein in SPS have been conducted, the precise defect(s) responsible for the syndrome remains unknown. This review discusses on the SPS and about the main receptors on the platelet surface, including some polymorphisms that appear to be involved in the pathology.