Investigators have shown that even low levels of the Alzheimer's-associated APOE4 protein can increase the number and density of amyloid brain plaques, related neuronal damage, and the amount of soluble amyloid within the brain in mouse models of the disease. APOE2, a rare variant that has been associated with protection from Alzheimer's of actually reduced A-beta deposition, retention and neurotoxicity, suggesting the potential for gene-therapy-based treatment.