Deficiency of Irp2 increases the expression of the iron storage protein ferritin and decreases expression of the iron importer TfR1, leading to functional iron deficiency (lack of biologically available iron) in conjunction with apparent ferric iron overload caused by sequestration of iron in ferritin; and the notion that there is functional iron deficiency is also supported by deficiency of mitochondrial complex I/II activity (Figure 1; Jeong et al., 2011). This evidence concerns the gene IREB2 and nutritional disorder.