Sickle cell anemia, or sickle cell disease (SCD), is a genetic disease of the red blood cells (RBCs). Normally, RBCs are shaped like discs, which gives them the flexibility to travel through even the smallest blood vessels. However, with this disease, the RBCs have an abnormal crescent shape resembling a sickle. This makes them sticky and rigid and prone to getting trapped in small vessels, which blocks blood from reaching different parts of the body. This can cause pain and tissue damage. SCD is an autosomal recessive condition. You need two copies of the gene to have the disease. If you have only one copy of the gene, you are said to have sickle cell trait.