We hypothesized that PCSK9 impacts on Alzheimer's disease (AD) risk in an <i>APOE</i> genotype dependent manner.<h4>Methods</h4>We used the Framingham Heart Study (FHS) Offspring cohort (Gen 2), with data on plasma PCSK9 protein concentration, as the baseline exposure for 1,704 study subjects. Here, APOE is linked to Alzheimer disease.