Hi Slade,
Bone marrow is overactive in thals, because they produce many defective red blood cells, RBCs, and those are filtered out, mostly by the spleen (this is the cause of enlarged spleens in thals). In response to producing defective RBCs, the body works harder to produce more RBCs, trying to provide enough good RBCs to carry hemoglobin and its oxygen throughout the body. Many patients will still have anemia, as the body cannot produce enough hemoglobin to fill the body's needs, regardless of how many RBCs it tries to pump out. One other observation I have made is that minors who have normal Hb levels almost always have RBC levels that are quite high, indicating that the added bone marrow activity is sufficient to raise the Hb to normal. However, these patients still report health issues and this is the result of all the defective red blood cells breaking down, along with the imbalance of alpha to beta globin, which basically wreaks havoc on the body. The creation of free radicals and oxidation caused by this process should be addressed with a diet and supplements high in antioxidants.
The problems of thalassemia are a combination of not enough hemoglobin and the problems that the unmatched globin chains cause. This second part is understood by very few doctors.