Bernard-Soulier syndrome is a rare genetic disorder that affects the blood platelets, causing a bleeding disorder that can be severe. There are several synonyms for this condition, including giant platelet syndrome, giant thrombasthenia, and hereditary macrothrombocytopenia. These terms refer to the unique feature of the disease, which is the oversized platelets that do not function properly. The condition is caused by mutations in one of three genes that affect the platelet glycoprotein complex, which is essential for platelet adhesion to damaged blood vessels. Although rare, Bernard-Soulier syndrome can cause bleeding and bruising, and it may require treatment with platelet transfusions or other therapies to manage symptoms.