A possible explanation for this is that in the higher age group the APOE‐e4 risk allele is already depleted due to AD and other conditions affecting mortality associated with the allele; indeed, the allele frequency of APOE‐e4 has been reported to decrease from 0.18 at age 60 to 0.09 at age 90 in individuals of European ancestry (McKay et al., 2011). This evidence concerns the gene APOE and Alzheimer disease.