A genetically inherited recessive condition in which red blood cells are distorted resulting in severe anemia and related symptoms that are often fatal in childhood. Sickle-cell trait is the result of a pleiotropic gene. People who are heterozygous for this trait rarely have these debilitating and ultimately fatal problems but do have a high degree of immunity to malaria. Sickle cell trait is at its highest frequency among Central African populations and among people whose ancestors came from that region. Sickle-cell trait is also known as sickle-cell anemia.