To gain maximal power for interaction analysis, we combined genotypes at both SNPs into binary variables. Odds ratios (OR) were calculated for interaction at minor allele carriers of the two SNPs verse all other genotypes, and a likelihood ratio test was performed for assessing the significance of the interaction. We also interrogated genotype associations with brain transcript expression in a public database about genetic regulation of transcript expression in the human brain for rs1000731 in DISC1 and rs10089 in SLC12A2 (Heinzen et al., 2008).
