Additive Genetic Variation in Schizophrenia Risk Is Shared by Populations of African and European Descent

To investigate the extent to which the proportion of schizophrenia's additive genetic variation tagged by SNPs is shared by populations of European and African descent, we analyzed the largest combined African descent (AD [n = 2,142]) and European descent (ED [n = 4,990]) schizophrenia case-control genome-wide association study (GWAS) data set available, the Molecular Genetics of Schizophrenia (MGS) data set. We show how a method that uses genomic similarities at measured SNPs to estimate the additive genetic correlation (SNP correlation [SNP-r(g)]) between traits can be extended to estimate SNP-r(g) for the same trait between ethnicities. We estimated SNP-r(g) for schizophrenia between the MGS ED and MGS AD samples to be 0.66 (SE = 0.23), which is significantly different from 0 (P(SNP-rg (= 0)) = 0.0003), but not 1 (p((SNP-rg = 1)) = 0.26). We re-estimated SNP-r(g) between an independent ED data set (n = 6,665) and the MGS AD sample to be 0.61 (SE = 0.21, P(SNP-rg = 0) = 0.0003, p((SNP-rg = 1)) = 0.16). These results suggest that many schizophrenia risk alleles are shared across ethnic groups and predate African-European divergence.