Consistent with this interpretation, rodents and humans with mutations in MC4R are hyperphagic and obese (Fan et al., 1997; Farooqi et al., 2003, 2000; Huszar et al., 1997), while MC3R knockout (KO) mice exhibit minor late onset obesity (Butler et al., 2000; Chen et al., 2000), without noticeable hyperphagia when provided ad libitum access to regular chow diet. The gene discussed is MC3R; the disease is obesity disorder.