HCRT and Alzheimer disease: The high sequence identity between GPR103 and the orexin receptors (OX1R, OX2R), along with their overlapping expression in the PVN and VMH, combined with their overlapping functional domains, assumed that there may be some association of the OX/OXR and QRFP/GRP103 systems and in AD (Jiang et al., 2003).