sickle cell thalassemia, a double heterozygous anemia in which the genes for sickle cell and for thalassemia are both inherited. A mild form and a severe form may be identified, depending on the degree of suppression of beta-chain synthesis by the thalassemia gene. In the mild form, synthesis is only partially suppressed, and the red blood cells may contain from 25% to 35% normal hemoglobin A, along with a greater concentration of hemoglobin S. The clinical course is relatively mild. In the severe form, beta-chain synthesis is completely suppressed and only hemoglobin S appears in the red blood cells. The clinical course is generally as severe as in homozygous sickle cell anemia. See also hemoglobinopathy, hemoglobin S, hemoglobin SC (Hb SC) disease.
