In SCD, at least one of the beta-globin subunits in hemoglobin is replaced with hemoglobin S. In sickle cell anemia, which is a common form of SCD, hemoglobin S replaces both beta-globin subunits in the hemoglobin.1 SCD is one of the most common single-gene disorders worldwide. This evidence concerns the gene HBB and Schnyder corneal dystrophy.