UCP1 and obesity due to melanocortin 4 receptor deficiency: UCP1 is located in the inner mitochondrial membrane of brown adipocytes and is activated with cold exposure via adrenergic stimulation, where it uncouples dissipation of the mitochondrial proton gradient from ATP production, creating an energy-generating futile cycle.2 There is significant interest in BAT as a potential pharmacological target in obesity and associated metabolic disease.4