Giant platelet disorders, also known as macrothrombocytopenia, are rare disorders featuring abnormally large platelets, thrombocytopenia and a tendency to bleeding. Giant platelets cannot stick adequately to injured blood vessel walls, resulting in abnormal bleeding when injured. Giant platelet disorder occurs for inherited diseases like Bernard¨CSoulier syndrome, gray platelet syndrome and May¨CHegglin anomaly.

Reference
Wiki: Macrothrombocytopenia