KLF1 target genes and associated clinical phenotypes. KLF1 is a master regulator of ∼700 genes in human erythroid cells involved in a wide variety of molecular processes (blue circles). Deregulated expression of a subset or all of these genes, depending on the KLF1 variant, leads to a diverse array of erythroid phenotypes (gray circles). HbA, adult hemoglobin (α₂β₂); HbA2, adult hemoglobin 2 (α₂δ₂); PK, pyruvate kinase; ZnPP, zinc protoporphyrin.