Deletions of alpha globin are common and found in approximately 5% of the world s population.They are especially common among Africans and people of African ancestry, as well as in India, China, and the Pacific Islands, where prevalence can range from 5 - 80%. A single deletion has little effect on the red blood cell, but two deletions can give rise to alpha thalassemia, a mild microcytic anemia. Patients with sickle cell disease who have two alpha globin deletions tend to have a higher hemoglobin level, smaller red blood cells, and a lower fraction of circulating reticulocytes consistent with decreased hemolysis and red cell turnover. They also have a lower number of dense or irreversibly sickled cells. These changes might explain why alpha globin deletions reduce the severity of sickle cell disease.