Propensity-matched cases and controls were similar except for three characteristics: i) As expected, APOE-ε4 homozygotes and heterozygotes were more frequent in both AD and MCI cases than in controls; ii) although over 60% of controls and cases in both cohorts had at least 16 years of education, the AD cohort had more cases with 12 years of education than controls; iii) the AD cohort had more cases with history of cerebrovascular disease than controls, and the MCI cohort had fewer cases with a history of atherosclerosis than controls. The gene discussed is APOE; the disease is Alzheimer disease.