Recent evidence indicates that EPO and iron are required for ROS generation in erythroblasts, and that ROS are necessary for terminal erythropoiesis [44] while unchecked ROS accumulation results in anemia (Friedman et al., 2001; Hebbel, 1990; Kong et al., 2004; Lee et al., 2004; Neumann et al., 2003). Here, EPO is linked to anemia (phenotype).