Melanocortin-4 receptor mutations paradoxically reduce preference for palatable foods.

Haploinsufficiency of the melanocortin-4 receptor (MC4R) results in melanocortin obesity syndrome, the most common monogenic cause of severe early onset obesity in humans. The syndrome, which produces measurable hyperphagia, has focused attention on the role of MC4R in feeding behavior and macronutrient intake. Studies show that inhibition of MC4R signaling can acutely increase the consumption of high-fat foods. The current study examines the chronic feeding preferences of mice with deletion of one or both alleles of the MC4R to model the human syndrome. Using two-choice diet paradigms with high-fat or high-carbohydrate foods alongside normal chow, we show, paradoxically, that deletion of one allele has no effect, whereas deletion of both alleles of the MC4R actually decreases preference for palatable high-fat and high-sucrose foods, compared with wild-type mice. Nonetheless, we observed hyperphagic behavior from increased consumption of the low-fat standard chow when either heterozygous or homozygous mutant animals were presented with dietary variety. Thus, decreased MC4R signaling in melanocortin obesity syndrome consistently yields hyperphagia irrespective of the foods provided, but the hyperphagia appears driven by variety and/or novelty, rather than by a preference for high-fat or high-carbohydrate foodstuffs.