The transient nature of anemia likely relies on the differential contribution during development of two regulatory regions controlling the expression of the Epo gene: the enhancer containing an RXR/RAR binding site (the DR2 site) adjacent to a hypoxia response element bound by the hypoxia-inducible factor (HIF1) and the promoter, containing a GATA binding site. The gene discussed is EPO; the disease is anemia.