HAMP and anemia: Two proposed erythroid hepcidin regulators are the TGF-β /BMP superfamily modulators growth and differentiation factor 15 (GDF15) and twisted gastrulation 1 (TWSG1), at least in the context of ineffective erythropoiesis in iron loading anemias (Tanno et al., 2007, 2009) (Figure 1).