APOE and early-onset autosomal dominant Alzheimer disease: Apolipoprotein E is the primary lipid transporter in brain tissue with carriers of the APOE4 allelic variant at several fold increased risk of Alzheimer’s disease (~three- and ~15-fold increase in risk in APOE3/E4 and APOE4/E4, respectively, relative to the wild-type genotype) [44,45].