GPR27 is a member of the G protein-coupled receptors (GPCRs), a large family of receptors that have a similar structure characterized by 7 transmembrane domains. Activation of GPCRs by extracellular stimuli such as neurotransmitters, hormones, or light induces an intracellular signaling cascade mediated by heterotrimeric GTP-binding proteins, or G proteins.[supplied by OMIM, May 2010].