HBB and alpha thalassemia spectrum: When asked to identify the main mechanism of ineffective erythropoiesis, many CoE and non-CoE physicians incorrectly selected “formation of unstable beta globin homotetramers,” characteristic of alpha thalassemia (47% and 39%, respectively), while about one-third correctly selected “precipitation of excess free alpha chains in red blood cell precursors” characteristic of beta thalassemia (37% and 39%).