Given prior work suggesting CSF Aβ42 levels (Bilgel et al., 2018) and APOE-ε4 status (Vemuri et al., 2010) may exert adverse effects prior to neurodegeneration, we also hypothesized early and middle MCI would relate to CSF Aβ42 concentrations and APOE-ε4 status, while late MCI participants closer to the clinical threshold for dementia would have more phosphorylated tau-related injury, including neurodegeneration. This evidence concerns the gene APOE and dementia.