Aside from small sample sizes and different analytic methods, differences in findings of age-related CBF change might also be attributable to vascular risk factors (Birdsill et al., 2013; Bangen et al., 2014), sub-clinical cerebrovascular disease (Crane et al., 2015; Gregg et al., 2015), sedentary behavior (Zlatar et al., 2014), APOE genotype (Rane et al., 2013; Wierenga et al., 2013), and AD family history (Fleisher et al., 2009; Okonkwo et al., 2014). Here, APOE is linked to Alzheimer disease.