APOE and Alzheimer disease: In comparison to APOE 3/3, the most common APOE genotype, APOE4 is found in about 25% of the population and in about 60% of persons with the clinical and neuropathological diagnosis of AD, with each additional allele copy associated with a higher risk and earlier age at onset of AD biomarker changes, cognitive decline, and dementia.1, 2, 3, 4, 5, 6, 7, 8, 9, 10