Apolipoprotein ε4 (APOE ε4) is the strongest allelic risk factor for late-onset Alzheimer’s disease (AD).1 US-based studies suggest that the prevalence and effects of APOE ε4 vary by race/ethnicity.2 These ethnoracial differences matter because APOE ε4 is often related to adverse events and outcomes,3,4 and self-identified ethnoracial data provide an inexpensive approach to make recruitment decisions, estimating risk profiles, and tailoring interventions. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.