Among orphan GPCRs, GPR158 is of particular interest as a novel GPCR, as it has been shown to play a critical role in the etiology of cancers and mental illnesses, e.g., prostate cancer [16], glioma [17] and depression [18,19], though the properties of GPR158 are yet to be fully elucidated. The gene discussed is GPR158; the disease is prostate cancer.