MAPT and Alzheimer disease: PET biomarker cutoffs for staging were established using a Gaussian mixture model implemented via the mclust package (Fraley et al., 2012) in R (R Core Team, 2023) within the RStudio environment (Posit Team, 2023), consistent with prior applications of GMM for deriving amyloid and tau-PET thresholds in AD research (Quattrini et al., 2023; Therriault et al., 2021).