the GWAS (thus, genetic outliers and related individuals were removed) and corrected using genotyping wave and psychiatric disorders as covariates as well as the same principal components from PCA which were used in the GWAS . Since gene expression among the different brain tissues is highly correlated, we corrected the P-value for each gene by the total number genes tested in all tissues with a valid model available for the gene, with respect to CHRNA2 we corrected for 13,166 genes tested in three tissues, thus P-values < 3.8x10−6 (0.05/13,166) were considered statistical significant for this gene. This is in line with recent approaches used to correct for multiple testing in transcriptome wide association studies using imputed gene expression81.
