For example, more than one-third of non-carriers of the ε4 allele of Apolipoprotein E (ApoE) gene (ApoE4) with a clinical diagnosis of mild or moderate AD have low Aβ levels, and the diagnostic accuracy of the clinical criteria may be limited, not even reaching 77%, with 20–30% of patients having a clinical diagnosis AD that does not match the neuropathological diagnosis [3,4,5]. This evidence concerns the gene APOE and Alzheimer disease.