While recent genome-wide association studies aimed at mapping modifier genes which influence clinical severity of sickle cell anemia and Hb E/β0-thalassemia revealed linkages to the OR region upstream of the β-globin gene [32], [33], our present studies are consistent with the hypothesis that the OR52A1 [4], [5] locus in the downstream OR region plays an important role in influencing clinical severity in this type of β-thalassemia. The gene discussed is OR52A1; the disease is sickle cell disease.