Hb S beta-plus thalassemia, type 2 requires very little medical attention
| Hb S / thalassemia combination | Affected populations | Severity | Comments |
| Hb S beta thalassemia | North Africa, India, and the Mediterranean region, especially Greece and Turkey. | Varies | Hb S beta-plus thalassemia, type 1 and Hb S beta-minus thalassemia need supportive therapy and may have severe anemia |
| Hb SA alpha-plus thalassemia | Common in persons of African ancestry | Usually asymptomatic | Less hemoglobin S produced than in persons with Hb S trait |
| Hb SS-alpha thalassemia (either plus or zero) | African and Mediterranean ancestry | Mild anemia midway in severity between sickle cell disease and trait | Produce increased levels of Hb F in proportion to the number of alpha gene deletions present. This acts to retard the sickling process. |
