Star-shaped clusters of hemoglobin S polmers develop commonly. Despite their imposing appearance, the sickle hemoglobin polymers are held together by very weak forces. The abnormal valine amino acid at position 6 in the beta globin chain interacts weakly with the beta globin chain in an adjacent sickle hemoglobin molecule. The weak nature of the interaction opens one strategy to treat sickle cell disease. All people have fetal hemoglobin in their circulation before birth.
Fetal hemoglobin protects the unborn child and newborns from the effects of sickle cell hemoglobin.
Unfortunately, this hemoglobin disappears within the first year after birth. One approach to treating sickle cell disease is to rekindle production of fetal hemoglobin. The drug, hydroxyurea induces fetal hemoglobin production in some patients with sickle cell disease and improves the clinical condition of some people. The schematic diagram shows the changes that occur as sickle or normal red cells release oxygen in the microcirculation. In contrast, the hemoglobin polymerizes in sickle red cells when they release oxygen, as shown in the lower panel.