SNP data can also be used to estimate the genetic correlation (tagged by common variation) between disorders (42) (Fig. 2). Some disorders clearly share genetic risk: Between BPD and SCZ the correlation is 0.68; between BPD and major depressive disorder, the correlation is 0.47. Six genome-wide significant loci are associated with a combined BP+SCZ phenotype (42). However, SNPs for both BP and SCZ were genome-wide significant in CACNA1C, ANK3 and ITIH3-ITIH4, but not in MHC, ODZ4, TCF4 and other loci that were genome-wide significant for either disorder separately. Thus, both polygenic risk scores (42) and GWAS hits (42) discriminate between disorders, and both overlapping and disease specific genetic risk factors can be identified (43).
