EPO and anemia (phenotype): Thus, it is also used clinically to stimulate erythropoiesis in anemia resulting from chronic kidney disease, myelodysplastic syndromes, or cancer.1–4 Epo signals via its receptor EpoR.5,6 Deletion of Epo or EpoR in mice leads to embryonic lethality due to severe anemia, underscoring the relevance of Epo-EpoR signaling in red blood cell production.