Effect of Hfe deficiency or secondary iron overload on hepatic iron concentrations and Bmp6, Id1, and Hamp gene expression in 7-week-old B6 and D2 mice. Fold change in nonheme tissue iron content and expression ratio (and SE) of Bmp6, Id1, and Hamp transcripts normalized to the reference gene mRNA (Hprt) in Hfe-deficient mice relative to wild-type controls and in wild-type mice fed an iron-rich diet for 3 weeks relative to wild-type mice fed a standard rodent diet (5-10 mice per group). Statistical significance was determined using randomization tests. *P < .05; **P < .01; ***P < .001. Data are provided for 2 genetic backgrounds, C57BL/6 (B6) and DBA/2 (D2). At 7 weeks of age, wild-type mice of the 2 backgrounds have similar levels of Bmp6, Id1, and Hamp transcripts (supplemental Figure 1, available on the Blood website; see the Supplemental Materials link at the top of the online article). However, Hfe-deficient mice of the D2 background have significantly more Bmp6 mRNA than Hfe-deficient mice of the B6 background (P = .001). Wild-type B6 mice fed the iron-rich diet for 3 weeks also have significantly more Bmp6 mRNA than wild-type D2 mice fed the same diet (P = .001). Absolute values (instead of fold changes) corresponding to the same data are provided in supplemental Figure 2.