Ineffective erythropoiesis may cause anemia and is particularly relevant in myelodysplastic syndromes (MDS) and in homozygous β-thalassemia, where small mother against decapentaplegic (SMAD) signaling is altered and activin receptor ligand traps have been shown to correct the hyperactivation of SMAD2/3. Here, SMAD2 is linked to anemia (phenotype).