In 1993, Roses and colleagues first reported that an individual’s risk of developing Alzheimer’s disease (AD) is increased if they carry the ε4 allele of apolipoprotein E (APOE) [1–3], an important apolipoprotein that had primarily been studied for its role in transporting cholesterol and other lipids through the periphery and within the brain [4–6]. The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.