The biological role(s) proposed for UCP3 in energy homeostasis have been ba
sed primarily upon amino acid sequence homology to UCP1. Spontaneous mutati
ons of UCP3> have been described in humans, but not in rodents. The functio
nal consequences-or lack thereof-of these mutations in humans will be of gr
eat importance in elucidating the biology of this protein. The results of t
wo such studies are summarized here.