Blood kits

The biomarker included in this study was APOE genotype. Genotyping of the PATH sample has been previously described^{16 (link)}. Briefly, genomic DNA was extracted from buccal swabs using Qiagen Blood kits. Two TaqMan assays were performed to ascertain the genotypes of the two SNPs defining the APOE alleles, rs429358 and rs7412. Overall, 95.3% of the 20 s cohort, 90.6% of the 40 s cohort, and 90.1% of the 60 s cohort provided buccal swabs. Genotype frequencies did not deviate from the Hardy–Weinberg equilibrium. After removing participants carrying the APOE e2/e4 genotype, APOE genotype status was coded into three categories (E4+/E4−, E4+/E4+, or E4−/E4−).

Genotyping of the PATH sample has been described previously^{34 (link)}. In summary, Qiagen Blood kits were used to extract genomic DNA from buccal swabs at baseline (wave 1). Overall, 90.1% of the 60s cohort provided buccal swabs. Genotypes of the two SNPs that define the APOE alleles (rs429358 and rs7412) were detected using TaqMan assays. The allele frequency distribution for each of the two SNPs was in accordance with the Hardy–Weinberg equilibrium denoting validity of the genotyping. APOE allele status was included in the analysis to examine the impact of the protective effect of APOE ɛ2 (for participants who had APOE ɛ2/ɛ4 combinations)^{1 (link)} and increased Alzheimer’s Disease risk associated with homozygous APOE ɛ4 presentation (i.e. participants who have APOE ɛ4/ɛ4).