In heterozygotes AD, APOE ε4 mRNA expression is increased in patients with AD compared with healthy controls: genetic variability in the neural expression at the APOE locus contributes to AD risk. APOE ε3ε4 heterozygote subjects (high ε4 expressors and/or low ε3 expressors) were more likely to develop AD than subjects with high ε3 expressors and/or low ε4 expressors. This evidence concerns the gene APOE and Alzheimer disease.