Because hepatic Hamp expression in both the complete and liver-specific Tfr2-null mice was decreased at a similar age as the Hnf4aΔH mice used in this study (32, 33) and because HAMP is the downstream regulator of TFR2, up-regulation of Hamp might be the main reason why Hnf4aΔH mice do not show hemochromatosis despite the down-regulation of Tfr2 expression. The gene discussed is HAMP; the disease is hemochromatosis type 1.