APOE and Alzheimer disease: (4) Biological mechanisms underlying different forms of dementia resembling AD may differ,45 and only ≈19% of the AD cases used for the GWAS used were autopsy confirmed (moreover, AD subtypes were not taken into account).18 (5) APOE SNPs may have both direct and indirect (e.g., through their influence on risks of other diseases) effects on risk of AD.