We have shown blunted endogenous opioid release capacity in both AD and GD (Mick et al., 2016; Turton et al., 2020) using [11C]carfentanil, a MOR selective positron emission tomography (PET) ligand (Vardanyan and Hruby, 2014). The gene discussed is OPRM1; the disease is Alzheimer disease.