However, [11C]carfentanil PET is an indirect measure of MOR density and higher BPND could instead result from lower endogenous opioid binding to MORs, possibly due to blunted endogenous opioid release capacity as we have previously shown in AD and GD (Mick et al., 2016; Turton et al., 2020). Here, OPRM1 is linked to Alzheimer disease.