APOE and Alzheimer disease: Notably, a 2024 study22 found that almost all APOE4 homozygotes exhibited AD pathology and had significantly higher levels of AD biomarkers, including cerebrospinal fluid Aβ1-42 and p-tau, amyloid-β as measured by positron emission tomography, plasma p-tau, and plasma NfL, suggesting that the APOE4 may serve as a proxy for AD pathology.