SLC40A1 and hemochromatosis: Consistent with the smooth muscle-specific nature of the myh11-driven cre recombinase, and with the notion that FPN in smooth muscle cells is not involved in systemic iron homeostasis, fpnC326Yfl/fl SMMHC-CreERT2+ mice did not differ from age-matched fpnC326Yfl/fl controls in terms of serum and tissue iron indices, unlike ubiquitous fpnC326Y-KI mice which show the classical hemochromatosis phenotype (SI Appendix, Fig. S1 B–D).