Human β-globin locus. Positions of the embryonic ϵ gene, fetal γ genes, Ψβ pseudogene, and adult δ and β genes are indicated. The Corfu deletion is represented as a black bar below the map. The minimal region of difference resulting in either HPFH or thalassemia phenotype is marked with vertical dashed lines. The arrow in this region represents the fetal-to-adult chromatin boundary/intergenic transcription start site.