The document discusses thalassemia, an inherited blood disorder characterized by smaller red blood cells with less hemoglobin. It is most common in people from the Mediterranean, Africa, and Southeast Asia. Thalassemia occurs when the body makes an abnormal form of hemoglobin or not enough hemoglobin, impairing the red blood cells' ability to carry oxygen. Diagnosing thalassemia involves assessing symptoms of anemia and testing hemoglobin levels.