Serum ferritin levels in

Fth^+/+ andFth^+/− mice between 5 and 25 weeks of age. Serum ferritin levels were measured by the same ELISA that was used to measure tissue L ferritin content, with slight modifications (see “Materials and methods”). Results are expressed as micrograms of recombinant L ferritin per milliliter. The nonlinear regression curve is shown for both genotypes. The mean value was 43.6 ± 8.5 μg/L for the controls and 255 ± 25 μg/L for age-matched heterozygous animals. The P value calculated by the unpaired t test with Welch correction wasP = .0001. ▪, Fth^+/+; ■,Fth^+/−.