Sickle cell anemia: A genetic blood disease due to the presence of an abnormal form of hemoglobin, namely hemoglobin S. Hemoglobin is the molecule in red blood cells that transports oxygen from the lungs to the farthest areas of the body.

Sickle cell anemia affects millions of people throughout the world. It is particularly common among people whose ancestors came from sub-Saharan Africa; Spanish-speaking regions (South America, Cuba, Central America); Saudi Arabia; India; and Mediterranean countries, such as Turkey, Greece, and Italy. In the USA, sickle cell disease occurs in about 1 in every 500 African-American births and 1 in every 1,000-1,400 Hispanic-American births.

Sickle cell anemia is caused by an error in a gene that makes the beta globin chain of hemoglobin. The resultant abnormal hemoglobin (sickle hemoglobin) deforms the red blood cells when they are under low oxygen conditions. Children who inherit 2 copies of the sickle gene, one from each parent, have sickle cell anemia. Children who inherit the sickle gene from only one parent do not have the disease, but will carry the sickle cell trait. Individuals with sickle cell trait generally have no symptoms. About 2 million Americans (or 1 in 12 African-Americans) carry the sickle gene.