Presence of the APOE-ε4 allele is responsible for around a quarter of heritability for the most common form of dementia, Alzheimer disease.24 APOE-ε4 has been reported as associated with an increased risk of various vascular diseases,25,26 with inconsistent associations observed for nonvascular diseases, such as depression27 and cancer.28 This evidence concerns the gene APOE and early-onset autosomal dominant Alzheimer disease.