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 The gene discussed is APOE; the disease is dementia.