To determine how TRPV1 deficiency affects obesity induced by UCP1 knockout, we generated TRPV1/UCP1 double knockout mice (TRPV1−/−/UCP1−/−) by crossbreeding TRPV1−/− mice with UCP1−/− mice. The gene discussed is UCP1; the disease is obesity due to melanocortin 4 receptor deficiency.