Genotyping was performed at the Genome Technology Access Center at Washington University School of Medicine in St. Louis (http://gtac.wustl.edu/) using the Illumina Human OmniExpress array 12.VI (Illumina, San Diego, CA, USA). A total of 707,557 autosomal SNPs passed quality control (Wang et al. 2012a). SNPs with a minor allele frequency (MAF) below 5% (n=115,872) were excluded from further analysis. One hundred eighteen families, who self-reported European descent were included in the dataset. We utilized EIGENSTRAT (Price et al. 2006) along with HapMap European reference samples to confirm European ancestry.
