APOE and Alzheimer disease: When broken down by the specific genotype frequencies, APOE3/4 individuals represent about 21% of the cognitively normal Caucasian population, vs. about 41% of Caucasian AD patients (odds ratio [OR] 3.2), whereas APOE4/4 individuals have a genotype frequency of about 2% in the cognitively normal Caucasian population, vs. about 15% in the AD-affected Caucasian population (OR 14.9) [7].