APOE and Alzheimer disease: Recent studies have shown that the APOE protein and additional proteins associated with APOE genotypes can be detected in serum (Emilsson et al., 2018) and plasma (Muenchhoff et al., 2017; Rezeli et al., 2015; Simon et al., 2012; Sun et al., 2018), thus opening the way to new research avenues to both decipher the mechanisms linking genotypes to phenotypes, and to provide sensitive, noninvasive biomarkers of AD or progression of cognitive decline or protection from these phenotypes.