The reasons may be the cognitively normal group (n = 37) in that study was biased towards patients who showed decline (6 participants progressed to MCI and 4 participants to dementia) over 4 years, and the rate of APOE ε4 carriership (42%) in cognitively normal group was higher than reported in the previous studies (17–29%) [7, 9]. This evidence concerns the gene APOE and dementia.