UCP1 and obesity due to melanocortin 4 receptor deficiency: On the other hand, other models of BAT dysfunction have a paradoxical resistance to obesity such as mice with targeted deletion of the UCP-1 gene, or deletion of all isoforms of TRα (Thra-0/0), or a knock in of a different dominant negative mutation in TRα (R384C) [18]–[20].