location and Illumina genotyping. We then performed quality control (QC) steps (below, and with additional details in the Supplementary Text), using visual inspection of principal components plots (comparing cases to controls) as well as QQ and Manhattan plots (for evidence of systematic bias) to identify suitably matched controls. All samples in this report are of European ancestry. As shown in Supplementary Figure S1, all of the datasets (except for Finland) form a gradient of clusters when visualized in a scatter plot of the first two principal components, as expected based on known population genetic features (16).
