In the African American samples, we performed a preliminary PCA of cases and controls. We excluded 68 controls from further study as the analysis showed that these individuals had ancestry that was neither European nor African. The two dimensional PCA of the remaining samples is visualized in Figure 2. Dimensions above the first one did not show significant population structure. The first dimension, displayed horizontally, represents amount of European ancestry. We computed the amount of European ancestry in our cases to verify that this was not statistically different among cases and controls.
