The exact clinical syndrome produced by alpha thalassemia depends on how many of the four alpha chain genes are deleted. The more genes deleted, the more severe the anemia.
Alpha Thalassemia Trait | Hemoglobin H Disease | Alpha Thalassemia Major |
Two alpha genes are deleted | Three alpha genes are deleted causing the production of the abnormal hemoglobin H | All four alpha genes are deleted causing the excess gamma chains to form the abnormal hemoglobin Barts. |
Mild microcytic hypochromic anemia without clinical symptoms or the need for treatment | Abnormal hemoglobin H has a high affinity for oxygen and does not release it to oxygen-craving tissues as easily. As a result, mild to moderate microcytic hypochromic anemia results. | Hydrops fetalis develops and intrauterine exchange transfusions are needed for any possibility of live birth |
| Target cells, jaundice, splenomegaly, and Hb H aggregates are present | Patient is reliant on blood transfusions to live and the only cure is a bone marrow transplant |