APOE and Alzheimer disease: We examined the expression of the 12 genes from Table 1 across AD, MCI, and HC for individuals that lacked an allele ε4 of apolipoprotein E (APOE2/3 or APOE3/3) and compared this to individuals with one or two ε4 alleles (APOE3/4 or APOE4/4) (Table 2).