UCP1 and obesity due to melanocortin 4 receptor deficiency: A considerable number of experiments has failed to detect an increased level of Ucp1 mRNA expression in iBAT despite attenuated obesity and reduced energy efficiency (Madsen et al., 2008; Ma et al., 2011; Freudenberg et al., 2012; Hao et al., 2012; Liisberg et al., 2016b).