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. The gene discussed is PCSK9; the disease is Alzheimer disease.