Contains two alpha chains and two gamma chains with a higher O2 affinity than adult hemoglobin A composed of two alpha and two beta chains.
Fetal hemoglobin has strong anti-polymerization properties because its Gamma-globulin subunits form mixed hybrid tetramers of two alpha globin chains with one gamma globin and one sickle beta-globin chain that are largely excluded from the polymer.
Known also as hemoglobin F.
Most adults have hemoglobin F levels that average about 1%.
In patients with sickle cell disease higher concentrations and had fibin F (HbF) associated with milder clinical disease, with fewer painful crises and adverse events.
Elevated levels of fetal hemoglobin are associated with improved morbidity and mortality in patients with transfusion dependent thalassemia and sickle cell disease.
Fetal hemoglobin production is regulated so the level of gamma globin that is produced in utero decreases postnatally as the production of beta globin adult hemoglobin consisting of two alpha and two beta chains increases.
The transcription factor BCL11a is required for globin switching.
Abrogating BCL11a expression erythroid lineage cells may provide curative treatments for hemoglobinopathies.
Neonates and infants with transfusion dependent thalassemia or sickle cell disease are typically asymptomatic while their fetal hemoglobin levels remain high and become symptomatic during the first year of life when the synthesis of fetal hemoglobin declines.
In patients with transfusion dependent thalassemia or sickle cell disease who inherit persistence of fetal hemoglobin, in which fetal expression continues into adulthood, have a little or no disease.
Hemoglobin F inhibits polymerization of sickle hemoglobin.
It is suggested that if the hemoglobin of each erythrocyte consisted of approximately 30% fetal hemoglobin, the complications of sickle cell disease would be prevented or reversed: cell based gene therapy can achieve this goal.
Hydroxyurea lowers the frequency of painful crises, acute chest syndrome, and transfusions in adults with sickle cell disease by increasing hemoglobin F levels.
Starting hydroxyurea at a young age in sickle cell patients can sustain HbF levels at 20%.