HBG2 and Schnyder corneal dystrophy: Together, the three major HbF loci, the β-globin gene cluster on chromosome 11 (Xmn1-HBG2—a gamma-globin promoter polymorphism), BCL11A on chromosome 2, and HBS1L-MYB on chromosome 6, account for about 50% of HbF variability in healthy persons and 20%–30% in individuals with SCD in many populations [7, 9–13].