ZSF1 rats, which are the F1 progeny of a cross between two rat strains that are heterozygous for mutant alleles of the leptin receptor gene (lean female Zucker diabetic [ZDF,+/fa] x male spontaneously hypertensive heart failure rats [SHHF,+/facp]), have been studied as a model of obesity and metabolic syndrome as well as diabetes and its complications (Tofovic et al., 2000; Bilan et al., 2011). The gene discussed is LEPR; the disease is obesity due to melanocortin 4 receptor deficiency.