OPRM1 and Alzheimer disease: We did not find a significantly different association between the PIT effect andthe OPRM1 polymorphism between patients with AD and HCs, whichpartly reflects the ongoing debate and contradictory results published so far onthe association between the OPRM1 genotype and AD (Hendershot et al.,2016; Kong et al.,2017; Ray andHutchison, 2004; Sloan et al., 2018).