Sickle cell anemia is a genetic blood disorder that affects the shape of red blood cells. Normally, these cells are round and flexible, allowing them to move easily through blood vessels. In sickle cell anemia, the cells become rigid and shaped like a crescent or sickle, which can block blood flow and cause pain. This condition is caused by a mutation in the hemoglobin gene, which is responsible for carrying oxygen in the blood. Sickle cell anemia is inherited, meaning it can be passed from parents to children. It is more common in individuals of African, Mediterranean, and Middle Eastern descent.