A retired electrician aged 78 years with a family history (mother and 2 maternal aunts) of Alzheimer’s disease (AD) was diagnosed with mild cognitive impairment (preclinical AD) 5 years ago, followed by progression during the past 2½ years to mild AD, manifested primarily by declining ability to manage day-to-day responsibilities. Except for systolic hypertension that is well controlled with amlodipine 5 mg/day, he was in relatively good health. At a follow-up appointment, his neurologist suggested initiating treatment with an anti-amyloid beta monoclonal antibody (Aβ mAb). The patient’s spouse noticed documentation in his records of apolipoprotein E (ApoE) ε4 carrier status, and she asked about the significance of this finding.