To detect potential stratification of our GWAS sample, we analyzed our sample using software Structure 2.2 (24). When 2,000 randomly selected un-linked markers were used to cluster our subjects, all subjects of the sample were tightly clustered together under all assigned values (i.e., 2, 3, or 4) for the assumed number of population strata, k; these results suggest no population stratification. The results are shown in Appendix III.
