APOE and brain ischemia: In clinical studies, the lack of an association between the APOE epsilon4 allele and signs of visible angiography vasospasm but the presence of an association between the allele and an increased risk of delayed cerebral ischemia after SAH have linked ApoE to the cerebral microcirculation, probably through coagulation and fibrinolytic cascade impairment and microthrombosis (13).