This is a condition of the blood cells that affects mainly persons of African or mediterranean descent (Italian, Spanish, etc.). It is caused by an inherited abnormality of the oxygen carrying protein of the blood (hemoglobin). The abnormality is such that the red blood cells behave normally under normal conditions, but certain factors can cause an abnormal clumping together of the hemoglobin. When this happens the red cells assume a characteristic sickle-like shape - hence the name.