<h4>Introduction</h4>Carriers of the ε4 allele of the apolipoprotein E (<i>APOE</i>) gene have an increased risk for Alzheimer's disease (AD) and amyloid-related imaging abnormalities (ARIAs) upon anti-amyloid beta (Αβ) immunotherapy. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.