It has been known for over half a century that humans produce different forms of hemoglobin, a tetramer of α- and β-like hemoglobin chains, throughout ontogeny. The switch from fetal to adult hemoglobin occurs around the time of birth when erythropoiesis shifts from the fetal liver to the bone marrow. Naturally, diseases caused by defective adult β-globin genes, such as sickle cell disease and β-thalassemia manifest themselves as production of fetal hemoglobin fades. Reversal of …