Detailed procedures for genotyping, including for BDNF Val66Met SNP (rs6265), can be found in previous reports (Saykin et al., 2010 (link); Shen et al., 2010 (link)). Briefly, 7mL of blood was taken in EDTA tubes, and genomic DNA was extracted using the QIAamp DNA Blood Maxi Kit (Qiagen, Inc., Valencia, CA). Next, to exclude for any degraded DNA samples, 50ng of genomic DNA was qualitatively analyzed with a 1% Tris-acetate-EDTA agarose gel. Samples were then analyzed using the Illumina Human-610-Quad BeadChip (Illumina, Inc., San Diego, CA). The APOE SNPs (rs429358 and rs7412) were not available on the Illumina Human610-Quad BeadChip. Thus, these SNPs were genotyped separately by polymerase chain reaction amplification and HhaI restriction enzyme digestion. The digested products were ran on a 4% Metaphor Gel and visualized by ethidium bromide staining to analyze the APOE genotype (Potkin et al., 2009 (link); Saykin et al., 2010 (link)).