APOE and Cognitive impairment: While the APOE-ε4 genotype is a major risk factor for AD with an allelic frequency of 15% in whites, in patients with TIA or stroke-only APOE-ε4, homozygosity was associated with increased risk of dementia post-stroke yet was present in less than 2% of patients.50 Cerebral amyloid angiopathy (CAA), a vascular disease which causes stroke and dementia, apparently is also not associated with the APOE-ε4 genotype, even in patients with severe CAA.51 R4VaD should progress understanding of different contributors to cognitive impairment in the presence of cerebrovascular disease.