The mouse harboring the amorphic R165W mutant allele represents a good model for the MC4R-linked familial early-onset obesity as it mimics many of the characteristics observed in humans with MC4R loss-of-function mutations, such as hyperphagia, increase in linear growth, early-onset obesity, as well as symptoms of type 2 diabetes such as elevated glycemia (3). Here, MC4R is linked to obesity due to melanocortin 4 receptor deficiency.