The ε4 allele of the apolipoprotein E (APOE4) is a strong genetic risk factor for late onset of AD22 and is a common isoform of APOE; 25% of the global population carries at least 1 allele of that isoform.23 Patients with AD who carry APOE4 show worse cognitive outcomes compared with individuals with AD who are noncarriers. This evidence concerns the gene APOE and Alzheimer disease.