Classifying subjects by their history of substance abuse revealed a significant reduction in ACTB expression (P = 0.028), but including substance abuse in the main ANOVA showed no significant effect due to substance abuse (P>0.1) while the reduced ACTB mRNA in schizophrenia remained significant (planned contrast schizophrenia<controls, P = 0.031) with a trend for a reduction in bipolar subjects (P = 0.095) suggesting that the effect of substance abuse on ACTB mRNA is driven primarily by confounding with psychiatric diagnosis. Here, ACTB is linked to schizophrenia.