Despite similar body weight, spleen weight was higher in Fpn‐cKO mice, with the presence of extramedullary haematopoiesis (Figure 2A–C) which might account for the observed increase in RBC, as an attempt to counteract peripheral anaemia; in line with this finding, the BM was hypocellular (Figure 2D). The gene discussed is SLC40A1; the disease is anemia (phenotype).