The protein encoded by OPRL1 is a member of the 7 transmembrane G protein-coupled receptor family, which acts as a receptor for endogenous nociceptin/orphanin FQ and is involved in a variety of biological functions and the regulation of neurobehavioral behaviours, including depression, anxiety, learning, memory, motor activity and drug dependence and addiction40–43. This evidence concerns the gene OPRL1 and major depressive disorder.