We previously reported that PrPC declines with age in the human brain [17] but there was no significant difference in age between the sporadic AD and control cases (mean age ± SEM; 82.5±1.4 years and 76.5±2.7 years, respectively, p = 0.204) (Table 1 and Table S1), indicating that the reduction of PrPC in individuals with sporadic AD cannot simply be attributed to the effects of age. Here, PRNP is linked to Alzheimer disease.