LEP and obesity due to melanocortin 4 receptor deficiency: Genetic disruption of the gene encoding leptin (ob) or its receptor (Lepr) leads to marked obesity, hyperphagia and reduced BAT thermogenesis in mice (Thenen and Mayer, 1976; Leiter et al., 1983; Garris, 1987, 1989; Malik and Young, 1996; Mizuno et al., 1998; Garris and Garris, 2004; Goncalves et al., 2009).