Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Olanzapine-induced DNA methylation in the hippocampus and cerebellum in genes mapped to human 22q11 and implicated in schizophrenia Melkaye G. Melka a , Nagalingam Rajakumar b , Richard O’Reilly b and Shiva M. Singh a Background Although there is indirect evidence that the effects of antipsychotic drugs may involve modulation of dopamine transmission, their mechanism of action is poorly understood. We hypothesized that antipsychotic drugs mediate their effects by epigenetic modulation. Here, we tested the effect of an antipsychotic, olanzapine, on the DNA methylation status of genes following chronic treatment using rat-specific methylation arrays. Methods Forty-eight hours after the last dose of olanzapine/vehicle, rats were habituated to an open-field activity-monitoring chamber for 30 min to verify whether stress-induced locomotor activity was reduced in olanzapine-treated rats. To test this hypothesis, we examined the effect of olanzapine, a commonly used atypical antipsychotic drug, on the DNA methylation status of 49 genes mapped to human 22q11 and implicated in schizophrenia. Genomic DNA isolated from the cerebellum, hippocampus, and liver of olanzapine-treated (n = 2) and control (n = 2) rats were analyzed using rat-specific methylation arrays. Results Significantly reduced locomotor activity of olanzapine-treated rats confirmed the therapeutic efficacy of the drug administered. The effects of olanzapine have been shown through significantly increased (P < 0.01) DNA methylation of genes affecting several networks mainly (i) neurological disease, inflammatory disease, and inflammatory response and (ii) cancer, cell death and survival, tumor morphology. Also, proline degradation and L-DOPA degradation were affected by olanzapine-induced DNA methylation. Further, from a set of genes in the 22q11.2 microdeletions that has been implicated previously in psychosis, 29 genes showed increased methylation following olanzapine treatment. Conclusion The results showed that considerable number of genes (34/49) mapped to human 22q11 and implicated in schizophrenia were affected by olanzapine-induced DNA methylation. The results suggest that DNA methylation may play a role in the therapeutic efficacy of olanzapine. Psychiatr Genet 00:000–000 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. Psychiatric Genetics 2014, 00:000–000 Keywords: antipsychotics, DNA methylation, olanzapine, psychosis a Molecular Genetics Unit, Department of Biology and b Department of Psychiatry, The University of Western Ontario, London, Ontario, Canada Correspondence to Shiva M. Singh, PhD, Molecular Genetics Unit, Department of Biology, Western Science Centre, The University of Western Ontario, London, ON, Canada N6A 5B7 Tel: + 1 519 661 3135; fax: + 1 519 661 3935; e-mail: ssingh@uwo.ca Received 2 June 2014 Revised 6 October 2014 Accepted 24 October 2014 Introduction Schizophrenia is a debilitating psychiatric disorder with complex inheritance patterns (McGuffin et al., 1994). Not surprisingly, the search for the genetic factors responsible for this disease has been the major focus of modern research on schizophrenia (Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014). This research, however, has been difficult. What is now obvious is that a number of genes and genetic mechanisms including de-novo mutations may contribute toward this disease (Escudero and Johnstone, 2014). Yet, no gene or genetic mechanism is viewed as necessary for the devel- opment of this disease. The most recognized and recurring mutation associated with this disease is a deletion asso- ciated with 22q11. The del22q11 occurs at a rate of one in 4000 births, but ∼ 1% of schizophrenic patients have del22q11 (Goodship et al., 1998). The best estimates show that the risk for schizophrenia in patients with del22q11 is 20–25 times higher than that in the general population (Bassett and Chow, 2008). The clinical features of patients with schizophrenia are for all practical purposes indis- tinguishable whether they do or do not carry del22q11. This observation has led to a special focus on genes localized to the common deletion representing the 3.0 Mb region covering del22q11 (Uddin et al., 2006). This region contains more than 45 genes and a hemizygous loss of ∼ 30 genes has been observed in most individuals with del22q11, both with and without schizophrenia (Meechan et al., 2007). The causes of schizophrenia associated with del22q11 remain to be identified as no critical 22q11 region is both necessary and sufficient for the manifesta- tion of schizophrenia. This leads to a dilemma. If no gene (s) deletion or mutation is involved in del22q11 patients with schizophrenia, why is the risk for schizophrenia 20–25 times higher in del22q11 individuals compared with the general population? Original article 1 0955-8829 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/YPG.0000000000000069