Part of the discrepancies between our results and those from other laboratories may be due to at least two important differences when rodent obesity models are considered [31,32]: 1) the genetic background—our WT and KO animals are Nnt+/+ backgrounds while some of the other groups used the spontaneously mutated Nnt-/- mice from Jackson Laboratories [9,29]. The gene discussed is NNT; the disease is obesity due to melanocortin 4 receptor deficiency.