GPR19 is a 415 amino acid protein with two potential glycosylation sites and one disulfide bond that belongs to Orphan G-protein-coupled receptors (GPCRs) with unknown ligand. In mice, GPR19 is highly expressed in the nervous system during embryonic development as well as in specific regions of the mouse adult brain, including the olfactory bulb, the hippocampus, the hypothalamic nuclei, and the cerebellum. It shows low levels of expression in the heart, liver, and kidney. In humans, GPR19 has been reported in regions overlapping with the dopamine D2 receptor in the brain and peripheral nervous system. It was also found in human embryonic stem cells. GPR19 gene was reported to be overexpressed with small cell lung cancer and metastatic melanomas.