DNA was isolated from whole blood (n=688) or, when unavailable, from saliva (n=125). DNA samples were sent to the Applied Genomics Technology Facility (Wayne State University, Detroit, MI, USA) for genotyping using the HumanOmniExpress BeadChips (Illumina, San Diego, CA, USA). Further details regarding genotyping procedures have been published previously.44 We genotyped 730 525 SNPs. Samples were removed because of low call rate (<95%) and duplicate issues, with a remaining sample of 413 women and 365 men. A total of 688 890 SNPs passed quality control filters (call rate >95%, minor allele frequency >0.01, Hardy–Weinberg disequilibrium P>1 × 10−6). Genotype reports generated using Illumina GenomeStudioGT v. 1.8.4 software were used to generate PLINK input files (that is, lgen, map and fam files). We used the MDS analysis of genome-wide identity-by-state data implemented in PLINK to determine ancestry in the whole sample. The analysis was conducted using the 688 890 SNPs that passed quality control filters previously described. The first two components from the MDS analysis identified clearly separated clusters that correlate with self-reported ethnicity identification. The first two MDS components distinguished
