_IMG_01_13-sickle_cell_anemia.jpg AligN=RighT The sickle cell mutation causes the hemoglobin molecule to form long chains when oxygen levels are low, producing sickled red blood cells (RBC). The sickled RBC block capillaries and small blood vessels, causing damage to organs. The sickled RBC also break easily, leading to reduced oxygen carrying capacity, or anemia.