Sensing of acute changes in serum iron concentration and transferrin saturation also converges on the BMP–SMAD pathway, involving transferrin receptor 1 (TfR1/CD71), transferrin receptor 2 (TfR2), the haemochromatosis protein HFE and BMP receptors (although not requiring BMP6 induction) (reviewed in [47]). This evidence concerns the gene TFR2 and hereditary hemochromatosis.