To test whether genetic variants in PICALM, BIN1, CD2AP, and RIN3—suggested to be involved in blood–brain barrier amyloid-β transcytosis pathways—associate with Alzheimer’s disease, all dementia, suggested vascular dementia, and stroke, and whether such associations are independent of the strong ε4 APOE risk allele. The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.