APP and Alzheimer disease: While the prion levels in brain samples with AD were heterogeneous across the age range examined, the overall mean values for Aβ prion infectivity in the sAD (P < 0.0001), fAD APP (P < 0.0001), and fAD PSEN1 (P < 0.0001) cohorts were at least 15 times greater than the cognitively neurotypical age-matched controls (Fig. 2B).