APOE and Alzheimer disease: A common polymorphism in the apolipoprotein E (APOE) genotype located on chromosome 19q13 has been established as the most prevalent genetic risk factor for late-onset AD in Caucasian ethnic groups, which include the Russian ethnic population used in this study (Saunders et al., 1993; Schmechel et al., 1993; Farrer et al., 1997; Rogaev, 1999).