An inherited disorder of red blood cells characterized by lifelong anemia and recurrent painful episodes. The sickle cell mutation is caused by a single nucleotide effecting a change in the β-globin gene, resulting in the substitution of valine for glutamic acid as the sixth amino acid of β-globin. The short circulatory survival of red blood cells that contain sickle cell hemoglobin S results in anemia, and their abnormal rigidity contributes to painful obstruction of small blood vessels.