Interestingly, high-fat diet feeding increased the body weight and weight gain of wild-type, orexin-deficient, and Ox2r-deficient mice at 9 weeks old compared with animals fed regular chow; the body weight and weight gain of Ox1r-deficient mice were similar, regardless of diet, suggesting that Ox1r-deficient mice were resistant to diet-induced obesity (Figures 1B and 1C). Here, HCRTR1 is linked to obesity due to melanocortin 4 receptor deficiency.