To assess how plasma Aβ1-42 may serve as a biomarker for AD risk, a subgroup analysis of the Rotterdam study of over 450 older individuals (mean age of 68 years) found that lower plasma Aβ1-42 levels were associated with increased dementia incidence (HR = 1.27 [1.02–1.58]), especially among those individuals that were non-APOE ε4 carriers (HR = 1.47 [1.09–1.99]) [93]. This evidence concerns the gene APOE and dementia.