Which genetic disorder causes abnormal hemoglobin, leading to red blood cells with a sickle shape?

• A. Sickle cell anemia
• B. Iron-deficiency anemia
• C. Thalassemia
• D. Aplastic anemia

Answer: (A)

A genetic change in the beta-globin gene produces abnormal hemoglobin S. When oxygen is released, HbS polymerizes and the red blood cells become deformed into a sickle shape. These rigid, crescent-shaped cells can block small vessels and are more easily destroyed, leading to hemolytic anemia. This specific mechanism—a mutation causing abnormal hemoglobin that sickles under low oxygen—defines sickle cell anemia. The other conditions involve different causes of anemia (iron deficiency, defective globin production with different cell shapes, or bone marrow failure) and do not produce sickling of red blood cells.