ORIGINAL RESEARCH ARTICLE Separate and interacting effects within the catechol-O-methyltransferase (COMT) are associated with schizophrenia HY Handoko 1,2,4 , DR Nyholt 2,4 , NK Hayward 2 , DA Nertney 1 , DE Hannah 1 , LC Windus 1 , CM McCormack 1 , HJ Smith 1,2 , C Filippich 1,2 , MR James 2 and BJ Mowry 1,3 1 Queensland Centre for Mental Health Research, The Park, Centre for Mental Health, Wacol, QLD, Australia; 2 Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, QLD, Australia; 3 Department of Psychiatry, University of Queensland, Brisbane, QLD, Australia Several lines of evidence have implicated the catechol-O-methyltransferase (COMT) gene as a candidate for schizophrenia (SZ) susceptibility, not only because it encodes a key dopamine catabolic enzyme but also because it maps to the velocardiofacial syndrome region of chromosome 22q11 which has long been associated with SZ predisposition. The interest in COMT as a candidate SZ risk factor has led to numerous case–control and family-based studies, with the majority placing emphasis on examining a functional Val/Met polymorphism within this enzyme. Unfortunately, these studies have continually produced conflicting results. To assess the genetic contribution of other COMT variants to SZ susceptibility, we investigated three single-nucleotide polymorphisms (SNPs) (rs737865, rs4633, rs165599) in addition to the Val/Met variant (rs4680) in a highly selected sample of Australian Caucasian families containing 107 patients with SZ. The Val/Met and rs4633 variants showed nominally significant associations with SZ (Po0.05), although neither of the individual SNPs remained significant after adjusting for multiple testing (most significant P ¼ 0.1174). However, haplotype analyses showed strong evidence of an association; the most significant being the three-marker haplotype rs737865-rs4680-rs165599 (global P ¼ 0.0022), which spans more than 26 kb. Importantly, conditional analyses indicated the presence of two separate and interacting effects within this haplotype, irrespective of gender. In addition, our results indicate the Val/Met polymorphism is not disease-causing and is simply in strong linkage disequilibrium with a causative effect, which interacts with another as yet unidentified variant B20 kb away. These results may help explain the inconsistent results reported on the Val/Met polymorphism and have important implications for future investigations into the role of COMT in SZ susceptibility. Molecular Psychiatry (2005) 10, 589–597. doi:10.1038/sj.mp.4001606 Published online 26 October 2004 Keywords: COMT; schizophrenia; chromosome 22; single-nucleotide polymorphism; dopamine; complex disorder Schizophrenia (SCZD (MIM 181500)) is a severe, debilitating disorder characterised by delusional beliefs, hallucinations, disordered speech, and defi- cits in emotional and social behaviour with an average lifetime morbid risk of 1%. Several lines of evidence have implicated the catechol-O-methyl- transferase gene (COMT (MIM 116790)) as a candidate for schizophrenia (SZ), not only due to it encoding a key dopamine catabolic enzyme but also because it maps to the velocardiofacial syndrome (VCFS (MIM 192430)) region of chromosome 22 which has been long-associated with SZ. Over 20% of patients with VCFS also have SZ or schizoaffective (SA) disorder; 1,2 moreover, the 1.5–3 Mb microdeletions associated with VCFS have been found in 0.6–2% of adult SZ 3 patients and in 6% of cases with onset below the age of 16 years. 4 The COMT region on chromosome band 22q11.2 was in the eighth ranked bin of the genome scan meta-analysis of SZ 5 and gave a Po0.00009 in another meta-analysis. 6 COMT has a common functional substitution of Valine for Methionine at position 158/108 (codon 158 of the membrane-bound form, MB-COMT; codon 108 of the soluble form, S-COMT) with the Met allele being more thermolabile even at physiological tem- perature. 7 The Val variant has a higher enzymatic activity leading to more efficient degradation of dopamine, and lower than normal prefrontal Received 22 June 2004; revised 03 September 2004; accepted 15 September 2004 Correspondence: Associate Professor B Mowry, Queensland Centre for Mental Health Research, The Park, Centre for Mental Health, Wacol, QLD 4076, Australia. E-mail: bryan_mowry@qcmhr.uq.edu.au 4 These authors contributed equally Molecular Psychiatry (2005) 10, 589–597 & 2005 Nature Publishing Group All rights reserved 1359-4184/045 $30.00 www.nature.com/mp