Several polymorphisms of the iron homeostasis genes have been associated with risk factors for AMD: Tfr1, Tfr2 (obesity, tobacco) [142], Dmt1 [143], Irp1 and Irp2 [143], and heme oxygenases 1 and 2 (HO1/2) [144]. The gene discussed is HMOX1; the disease is obesity due to melanocortin 4 receptor deficiency.