The presence of the ε4 isoform of Apolipoprotein E (APOE) remains the most significant risk factor for developing sAD with those heterozygous for the ε4 allele having an approximately fourfold increased risk of developing AD, while those homozygous for ε4 have an approximately 12-fold increased risk [4]. The gene discussed is APOE; the disease is Alzheimer disease.