Early-onset AD is strongly linked to autosomal dominant mutations in amyloid precursor protein (APP) and presenilin genes [PSEN1, PSEN2; (Blennow et al., 2006)] while the most common genetic variant for late-onset AD is apolipoprotein E (APOE), a three-allele polymorphism (ε2, ε3, and ε4) where ε4 is the high-risk allele (Corder et al., 1993). The gene discussed is APOE; the disease is Alzheimer disease.