Some adults with sickle cell anemia have high levels of fetal hemoglobin. any reason for this?

Epigenetics and drug: We know that sickle cell patients that have increased Hemoglobin F typically have less sickle cell complications. This is the basis for using Hydroxyurea in sickle cell patients. Some individuals have elevated Hemoglobin F levels due to differences in the genetic region of the beta and gamma globin genes that prevent the normal shutting-off of the gamma globin gene. This leads to increased HGB f.