G6PD and Schnyder corneal dystrophy: Other genetic polymorphisms with an established influence on the SCD phenotype have been identified, including, HbF modifiers (XmnI, BCL11A, and HBS1L-MYB polymorphisms), uridine-diphosphoglucuronate glucuronosyltransferase (UGT1A1) promoter polymorphisms, and Glucose-6-phosphate dehydrogenase (G6PD) deficiency [12–14].