A natural regulatory mutation in the proximal promoter elevates fetal expression by creating a de novo GATA1 site.

β-hemoglobinopathies, such as sickle cell disease and β-thalassemia, result from mutations in the adult gene. Reactivating the developmentally silenced fetal gene elevates fetal hemoglobin levels and ameliorates symptoms of β-hemoglobinopathies. The continued expression of fetal into adulthood occurs naturally in a genetic condition termed hereditary persistence of fetal hemoglobin (HPFH). Point mutations in the fetal proximal promoter can cause HPFH. The -113A>G HPFH mutation falls within the -115 cluster of HPFH mutations, a binding site for the fetal repressor BCL11A. We demonstrate that the -113A>G HPFH mutation, unlike other mutations in the cluster, does not disrupt BCL11A binding but rather creates a de novo binding site for the transcriptional activator GATA1. Introduction of the -113A>G HPFH mutation into erythroid cells using the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) system increases GATA1 binding and elevates fetal levels. These results reveal the mechanism by which the -113A>G HPFH mutation elevates fetal and demonstrate the sensitivity of the fetal promoter to point mutations that often disrupt repressor binding sites but here create a de novo site for an erythroid activator.