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. Author manuscript; available in PMC: 2021 Feb 24.
Published in final edited form as: Clin Pharmacol Ther. 2020 Oct 8;109(1):73–81. doi: 10.1002/cpt.2028

Figure 1.

Figure 1

Developmental hemoglobin switching. This illustrates the developmental hemoglobin switching that occurs during and after gestation. Embryonic hemoglobins are rapidly silenced in the first weeks of gestation and fetal hemoglobin predominates until late in the third trimester, when adult forms of hemoglobin begin to be produced. For infants without sickle cell anemia (SCA), this fetal hemoglobin (HbF) silencing is rapid with very little residual HbF by 6–12 months of age. For infants with SCA, HbF silencing is more gradual and children have a variable degree of residual HbF with further reductions in HbF levels through approximately the first 5 years of life. Figure adapted from multiple sources.69