The most common and strongest genetic risk factor for AD is the apolipoprotein E (APOE) epsilon 4 allele, which increases the risk of developing AD approximately threefold in heterozygotes and even more among homozygotes (Corder et al., 1995; Farrer et al., 1997; van Duijn et al., 1994). The gene discussed is APOE; the disease is Alzheimer disease.