GP6 A gene on chromosome 19q13.4 that encodes a 58-kD platelet membrane glycoprotein, which plays a central role in the collagen-induced platelet activation and aggregation. Injury to the vessel wall and damage to the endothelial lining exposes the subendothelial matrix to blood flow, resulting in deposition of platelets. Collagen, especially types I, III and VI, are the most thrombogenic macromolecules of the extracellular matrix. The adhesion of platelets to collagen results in activation, leading to platelet secretion, recruitment of additional platelets and aggregation resulting in a platelet plug, which limits blood loss. However, collagen exposure after rupture of atherosclerotic plaques results in thrombus formation and may lead to myocardial infarction or stroke.