DNA methylation matters: methylation of the γ-globin ( <i>HBG</i> ) gene promoters is required for postnatal silencing of HbF

Sufficient levels of fetal hemoglobin (HbF) can ameliorate the pathophysiologic basis of sickle cell disease and β-thalassemia postnatally. DNA methylation has long been posited to mediate silencing of HbF expression, but this has been controversial. Recent publications provide definitive evidence for the critical role of HBG gene promoter methylation in silencing and insight into the mechanisms involved. The data support a model in which methylation of CpG sites in the HBG promoters and repressive transcription factors recruit the MBD2-NuRD chromatin remodeling complex, which enforces silencing. These findings have implications for the treatment of β-globin disorders.