We have identified 7 31P-MRS studies investigating HEP variability with normal aging (Longo et al., 1993; Constans et al., 1995; Rae et al., 2003; Forester et al., 2010; Schmitz et al., 2018; Cuenoud et al., 2020; Rietzler et al., 2022), in addition to 4 studies focusing on individuals at risk for AD (e.g., family history and/or APOE4 genotype) (Mosconi et al., 2021; Jett et al., 2022a, 2023; Parasoglou et al., 2022). This evidence concerns the gene APOE and Alzheimer disease.