Carriers of the apolipoprotein E gene (APOE) ε4 allele (~ 25% of white Europeans) have a higher risk of Alzheimer’s disease (AD) (odds ratio of ~3 for heterozygotes and ~15 for homozygotes) while carriers of the rarer ε2 allele have a lower AD risk (odds ratio of 0.6) compared with carriers of the most common APOE ε3ε3 genotype [1, 2]. The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.