Notably, the groups differed in terms of the expression of the ε4 allele of apolipoprotein E (APOE ε4), the largest genetic risk factor for Alzheimer’s disease13, and cognitive testing scores, with the AD group being significantly more likely to carry APOE ε4 and to have lower cognitive testing scores than CU and LMCI subjects. Here, APOE is linked to Alzheimer disease.