Homozygosity for the abnormal hemoglobin variant S (HbS) is the most common type of SCD and causes the most severe clinical phenotype, termed sickle cell anemia (Figure 1); however, patients with SCD may display other genotypes due to combination of the HbS gene with other non-HbS variants such as HbC, HbE, and HbD or to the many types of HbS-β-thalassemia (14). Here, HBD is linked to Schnyder corneal dystrophy.