MYB and Schnyder corneal dystrophy: The expression of adult HbF is a quantitative trait that is subject to several predisposing loci affecting the persistence of HbF in adulthood, particularly three principal loci; BCL11A, HBS1L-MYB intergenic variants and the five sequence polymorphisms along the β-globin gene cluster that confer the SCD haplotype [1–3].