Blood samples taken at baseline and stored at −80 °C were used for genetic analyses. DNA from whole blood samples was extracted using a salting out procedure. APOE data was directly genotyped and determined based on allelic combinations of the SNPs rs7412 and rs429358 using predesigned TaqMan SNP genotyping assays (Applied Biosystems, Foster City, CA). Genotypes were analyzed in an endpoint allelic discrimination read using the Bio‐RAD CFX Connect System (Bio‐Rad Laboratories, Hercules, CA).
Later, genome-wide SNP analyses were performed from extracted whole blood DNA using the Illumina Infinium OncoArray and Global Screening Array BeadChips (Illumina, San Diego, CA, USA)26 (link). General genotyping quality control assessment was done following the Nature Protocols article from Anderson et al.27 (link). Imputation of the quality controlled data was conducted using the Michigan Imputation Server, where SHAPEIT2 was used to phase the data and Minimac 4 was used to impute to the HRC Version r1.1 24 reference panel28 (link),29 (link).
Later, genome-wide SNP analyses were performed from extracted whole blood DNA using the Illumina Infinium OncoArray and Global Screening Array BeadChips (Illumina, San Diego, CA, USA)26 (link). General genotyping quality control assessment was done following the Nature Protocols article from Anderson et al.27 (link). Imputation of the quality controlled data was conducted using the Michigan Imputation Server, where SHAPEIT2 was used to phase the data and Minimac 4 was used to impute to the HRC Version r1.1 24 reference panel28 (link),29 (link).