MCHR1 and obesity due to melanocortin 4 receptor deficiency: In support of the role of MCH/MCHR1 signaling in the regulation of food intake and energy balance, MCHR1 knockout mice (MCHR1−/−) are lean, have an increased metabolic rate and are resistant to diet-induced obesity (Marsh et al. 2002; Kokkotou et al. 2005).