A logistic regression testing the effect of the APOE locus in all individuals (before restricting to APOE-ε4 homozygotes) and adjusting for age, sex and principal components, found the allelic effect of ɛ4 to be OR = 3.91 (3.65–4.18), p = 0 in a logistic regression on AD status. Here, APOE is linked to Alzheimer disease.