Integration of mutational and epigenetic analyses of the β-globin locus. Genomic deletions mapped in thalassemic patients and HPFH individuals are indicated with black bars (top). We report the 10 HPFH mutations removing the 3.5-kb region and the 13 β-thalassemia-associated deletions, which do not include this region. The 13.6-kb, the 7.2-kb Corfu and the 3.5-kb target regions are depicted as red bars. The 3.5-kb region contains a putative BCL11A binding site and several GATA1 binding sites (retrieved from Xu et al,^27,31 and Jawaid et al⁴⁵), single-nucleotide polymorphisms associated with high HbF levels, and a 250-bp polypyrimidine-rich sequence targeted by the PYR complex. We analyzed the histone modification pattern of the β-globin locus in human adult and fetal erythroblasts²⁷  (in blue and lavender, respectively; bottom). Epigenetic modifications typical of active chromatin regions, such as H3K27 acetylation (H3K27ac), H3K4 trimethylation (H3K4me3), H3K36 trimethylation (H3K36me3), and RNA polymerase II binding (PolII), mark the β- and δ-globin and the γ-globin genes in adult and fetal erythroblasts, respectively. Typical repressive chromatin markers (H3K9 trimethylation, H3K9me3 and H3K27 trimethylation, H3K27me3) were absent in the β-globin locus of both adult and fetal erythroblasts. The 3.5-kb target region, as well as inactive γ-globin genes, were preferentially enriched in H3K36 dimethylation (H3K36me2) in adult cells. HBB, β-globin gene; HBD, δ-globin gene; HBBP1, β-globin pseudogene 1; BGLT3, β-globin locus transcript 3 gene; HBG1, Aγ-globin gene; HBG2, Gγ-globin gene. The enhancer located 3′ to the poly(A) site of the β-globin gene is indicated as HBB enhancer.