These studies included: (i) samples of cognitively normal older adults with neuroimaging biomarker information (and CSF markers in some of them); or (ii) older adults considered to be at higher risk for AD (that may thus in part represent the preclinical AD stage), such as older adults showing pathological levels of Aβ deposition or carrying the ε4 allele of the Apolipoprotein (APOE) gene (the highest known genetic risk factor for sporadic AD). The gene discussed is APOE; the disease is Alzheimer disease.