ApoE4 is the high risk variant of the APOE gene, the gene most associated with increased risk for late-onset Alzheimer's disease. Wikipedia shows that it is not a direct determinant of the disease - at least a third of patients with Alzheimer's disease are ApoE4 negative and some ApoE4 homozygotes never develop the disease. Yet those with ApoE4/ApoE4 have ~20x risk of developing Alzheimer's. Alternative Names: ApoE 4, ApoE-4, Apolipoprotein E4 protein, ApoE-4 protein, ApoE 4 protein, ApoE4, Apo-A4 protein, Apo E4 protein