In humans, a condition in which a person is heterozygous for codominant alleles of the hemoglobin subunit beta (HBB) gene and produces both normal hemoglobin proteins (hgb) and abnormal hemoglobin proteins (hemoglobin S, which causes red blood cells (RBCs) to assume a sickle, or crescent, shape). In environments where malaria is endemic, humans with Sickle Cell Trait have a selective advantage as it confers some resistance to malaria. Sickle cells prevent the malaria parasite from stealing actin (a protein that maintains the pliable internal skeleton of RBCs). Actin is used by the parasite to transport another protein, adhesin (produced by the parasite), to the cell surface. Adhesin causes the infected red blood cells to adhere to each other and to vessel walls, resulting in microvascular inflammation. A person with Sickle Cell Trait does not display the severe symptoms of Sickle Cell Disease.
Sickle Cell Trait