Homozygotes are recognizable by their pallor at birth. The red cells are smaller than normal and hypochromic from 15 days of gestation onward, but they are present in normal or greater than normal numbers (J:5167). Viability and fertility may be reduced and, on some genetic backgrounds, skin lesions occur early in life (J:5236). The anemia appears to be due to a generalized impairment of cellular iron uptake involving transfer of iron from the intestinal lumen to the mucosa as well as from plasma to erythroblasts (J:5293, J:5555, J:5306). Increased levels of free erythrocyte protoporphyrin have been reported in mice with microcytic anemia (J:31039). This mutation has been identified as missense mutation of Slc11a2, thus identifying Slc11a2 as an iron transport gene (J:42052). Microcytic anemia had been reported as a mutation in the Nfe2 nuclear DNA-binding protein gene, on the basis of an amino acid substitution in Nfe2 in microcytic anemia mice. However, non-anemic mice of a different inbred strain were also shown to have the same substitution (J:11821), and it was also shown that the anemia was not corrected by insertion of a wild-type Nfe2 transgene (J:22119).