Aggressive behavior in schizophrenia is associated with the low enzyme activity COMT polymorphism: a replication study.

We have previously reported that increased aggressive behavior in schizophrenic patients may be associated with a polymorphism at codon 158 of the catechol O-methyltransferase (COMT) gene that encodes a low enzyme activity variant. The finding has been replicated by one group, but not others. The discordant findings could be due to statistical errors or methodological issues in the assessment of aggressive/violent behavior. Consequently, additional studies are needed. Patients with schizophrenia (SZ) were assessed for violent behavior using the Lifetime History of Aggression (LHA) scale, an 11-item questionnaire that includes Aggression, Self-Directed Aggression, and Consequences/Antisocial Behavior subscales. DNA was genotyped for the COMT 158 polymorphism, as well as a functional polymorphism in the monoamine oxidase A (MAOA) gene promoter. Similar to our previously reported findings, a statistically significant association was found between aggressive behavior in SZ and the COMT 158 polymorphism; mean LHA scores were higher in subjects homozygous for 158Met, the low enzyme activity COMT variant (F(2,105) = 5.616, P = 0.005). Analysis of the major LHA subscales revealed that the association with 158Met was due to high scores on the Aggression, and Self-Directed Aggression subscales, but not the Consequences/Antisocial Behavior subscale. No significant association was detected for the MAOA gene alone. Our findings provide further support that COMT is a modifying gene that plays a role in determining interindividual variability in the proclivity for outward and self-directed aggressive behavior found in some schizophrenic patients.