Contributors: Michael J. Paxhia and Sharon Fekrat
Sickle cell disease (sickle cell hemoglobinopathy)  is a hemoglobinopathy. A heterozgous state of hemoglobin S results in sickle cell trait, whereas persons with homozygous hemoglobin S have sickle cell anemia [anemia - sickle cell]. It is one of the most widespread and well known genetic diseases and results from a mutation in the HBB gene that encodes for the beta polypeptide part of globin. A simple base chain in the nucleic acid alters the mRNA triplet coding for glutamic acid (GAG) in the sixth position from the N-terminal of the beta polypeptide chain to a triplet coding for valine (GUG). This single amino acid change causes deoxygenated hemoglobin S to associate into long fibers which distort the erythrocytes into a characteristic sickle shape. Hypoxic states, such as respiratory infections or high altitude flying, reduce hemoglobin S to relatively insoluble long rods. Aside from secondary effects of anemia the eye is commonly affected in sickle cell anemia because of occlusovascular disease.