We performed a GWA study of BD separately in individuals of European ancestry (EA) and of African ancestry (AA) using a variety of methods to control for population substructure and admixture among the individuals of AA. Our study is the first GWA study of BD involving individuals of AA. In addition to standard single locus analyses within the EA and AA groups, we also assess the extent to which single nucleotide polymorphisms (SNPs) exhibite evidence of genetic background-dependent effects or allelic heterogeneity across the EA and AA individuals. Although more than 190 GWA studies have been performed to date (12) these studies have virtually all been with EA subjects (NHGRI catalog of published GWA studies: http://www.genome.gov/gwastudies/), raising important questions as to the generalizability of the results to other populations. We assessed the consistency of the SNPs exhibiting the strongest associations with BD in our study with previously published results of BD GWA studies. We tested variation at ANK3, which is a candidate gene that was implicated in an earlier GWA study (15) and identified as genome-wide significant in a recent
