APOE and Cognitive impairment: Second, a small number in our 65+ group indeed may have a degree of undiagnosed mild cognitive impairment, and up to 40% “cognitively normal” elderly adults may have amyloid burden detectable by PET (Mielke et al., 2012), while the amyloid status of our subjects cannot be ascertained, especially since APOE genotyping and cerebrospinal fluid sampling was not performed.