APOE and Cognitive impairment: Later, Strandberg et al. (2005) found maximally increased risk of cognitive impairment, in elderly home-dwellers, in association with a combination of three factors: seropositivity for herpesviridae, presence of APOE-ε4, and low education, the data indicating that not only APOE-ε4, but also the epsilon3 haplotype, is a risk factor for dementia.