Of the six genome-wide significant loci in our BP+SCZ vs controls analysis only two (CACNA1C, MHC) are present at that level in the individual disease analyses (Supplementary Figure 2a-b), highlighting the benefits of combining genetically related disease samples. In all but one region, these loci have near equivalent effect sizes and frequencies between BP and SCZ. The exception is the most significantly associated region found in SCZ (MHC) that has a considerably weaker association in BP. This distinction could point to a biologically relevant difference in disease etiology possibly related to immune function. The most significant result in this study implicates calcium channels as particularly important to risk of both of these disorders. In fact, CACNA1C appears to be more strongly associated to BP and SCZ than other psychiatric disorders including autism spectrum disorder, attention deficit-hyperactivity disorder and major depressive disorder (14). In a joint analysis of these disorders, it was the only genome-wide significant finding where the inclusion of all five disorders was not the most significant model.
