Sickle cell anemia is an inherited disorder in which there is a mutation in one of the 287 amino acids that make up the beta chain of hemoglobin. This slight change causes abnormal folding of the hemoglobin chains so that the hemoglobin forms stiff rods. The resultant red blood cells are crescent shaped (hence the term “sickle cells”) when they unload oxygen or when the oxygen content of blood is reduced. These crescent shaped red blood cells are fragile and can rupture easily and form clots in small vessels.