This concept becomes clear in the context of Alzheimer’s disease (AD), where much progress in understanding the molecular pathology underlying the neurodegeneration observed in human patients has led to the emergence of different mouse models that exhibit one or more AD hallmarks (b-amyloid, presenilins, apolipoprotein E, and Tau) (Knowles et al., 2009; Sterniczuk et al., 2010; Filali et al., 2012; Youmans et al., 2012). Here, APOE is linked to Alzheimer disease.