A prospective cohort study found a higher incidence of delirium in patients undergoing craniotomy and that collapse of the blood‐brain barrier (BBB) is an early biomarker of cognitive impairment and is strongly associated with the classical susceptibility gene (the epsilon4 allele of the apolipoprotein E (APOE4)) in AD.30, 31, 32. Here, APOE is linked to Alzheimer disease.