There are hypoxia responsive elements (HREs) in the promoters of FPN1, DMT1, and DCYTB (also known as CYBRD1) and the physiological importance of these HRE–HIF interactions has been demonstrated in the duodenum of Hif2α conditional knockout mice, where expression of FPN1, DMT1, and DCYTB does not increase in response to iron deficiency, suggesting that HIF2α has an important physiological role in transcriptional regulation of iron homeostasis (Mastrogiannaki et al., 2009; Shah et al., 2009). This evidence concerns the gene SLC40A1 and Iron deficiency anemia.