A decade later, the preciseroles of UCP2 and UCP3 remain a matter of debate [2–4].Like UCP1, UCP2 and UCP3 lower the mitochondrial membraneprotomotive potential, but it is unclear whether dissipation ofmetabolic energy as heat is their primary biological function.However, their capacity to protect against obesity has beendemonstrated, at least for UCP3, in experimental settings based ontransgenic mice overexpressing the protein in muscle [5]. The gene discussed is UCP1; the disease is obesity due to melanocortin 4 receptor deficiency.