Genomic DNA was extracted from peripheral blood by using a Blood Genomic DNA Extraction Kit (Qiagen NV, Venlo, the Netherlands). Multiplex amplification refractory mutation system polymerase chain reaction was used to determine the APOE genotype. According to the method previously described,23 (link) these subjects were divided into three groups, E2 (e2/e2 and e2/e3), E3 (e3/e3), and E4 (e2/e4, e3/e4, and e4/e4).24 (link)