QRFPR and Alzheimer disease: HCRTR2 has been implicated in substance use disorders (K. T. Schmeichel et al., 2015; Aldridge et al., 2022; Chen et al., 2024), and QRFP has been shown to exert neuroprotective effects in AD via heterodimerization of QRFPR with orexin receptors (J. Davies et al., 2015).