Catechol O-methyltransferase (COMT) mRNA expression in the dorsolateral prefrontal cortex of patients with schizophrenia

Human prefrontal cortical neurons express catechol O-methyltransferase (COMT), an enzyme that inactivates the neurotransmitter dopamine. A functional polymorphism of COMT, Val^108/158 Met, affects prefrontal function, and the high-activity Val allele has been reported to be a genetic risk factor for schizophrenia. We used in situ hybridization histochemistry to measure mRNA levels of COMT in the dorsolateral prefrontal cortex (DLPFC) of patients with schizophrenia (N = 14) and of normal controls (N = 15). While the groups did not differ in terms of mean level of COMT mRNA, there was a significantly different laminar pattern of COMT mRNA expression in pyramidal neurons (F = 2.68, df = 4,108, P < 0.04); patients with schizophrenia had relatively lower levels in the superficial (II/III) layers and higher levels in the intermediate/deep (IV/V) layers (P<0.01), while in controls, the expression was homogeneous across layers. Neither the mean level nor the laminar distribution of COMT mRNA was related to the Val^108/158 Met genotype, suggesting that the feedback regulation of mRNA level is not a compensation for the functional effect of the COMT polymorphism. The disease-related laminar difference of COMT expression may be involved in dysregulation of dopamine signaling circuits in the DLPFC of patients with schizophrenia.