The ATF3−/− mice fed a HFD in our study showed obesity with increased WAT weight in both subcutaneous (iWAT) and visceral depots (mWAT and rWAT) (Fig. 5a) and increased expression of many adipogenic/lipogenic genes in iWAT (Fig. 5b) In addition, the expression of browning and mitochondrial genes was reduced in the iWAT and BAT of obese ATF3−/− mice (Fig. 5c, d), likely because of the reduced transdifferentiation of WAT to BAT; therefore, ATF3−/− mice showed a loss of normal thermoregulation with low body temperature under acute cold stress (Fig. 6a). The gene discussed is ATF3; the disease is obesity due to melanocortin 4 receptor deficiency.