American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 141B:935 –938 (2006) Brief Research Communication Catechol-O-methyltransferase and the Clinical Features of Psychosis J.L. McClay,1* A. Fanous,1 E.J.C.G. van den Oord,1 B.T. Webb,1 D. Walsh,2 F.A. O’Neill,3 K.S. Kendler,1 and X. Chen1 1 Department of Psychiatry, Medical College of Virginia of Virginia Commonwealth University, Richmond, Virginia The Health Research Board, Dublin, Ireland 3 The Department of Psychiatry, The Queens University, Belfast, Northern Ireland 2 A functional polymorphism (Val-158-Met) at the Catechol-O-methyltransferase (COMT) locus has been identified as a potential etiological factor in schizophrenia. Yet the association has not been convincingly replicated across independent samples. We hypothesized that phenotypic heterogeneity might be diluting the COMT effect. To clarify the putative association, we performed an exploratory analysis to test for association between COMT and five psychosis symptom scales. These were derived through factor analysis of the Operational Criteria Checklist for Psychiatric Illness. Our sample was the Irish Study of High Density Schizophrenia Families, a large collection consisting of 268 multiplex families. This sample has previously shown a small but significant effect of the COMT Val allele in conferring risk for schizophrenia. We tested for preferential transmission of COMT alleles from parent to affected offspring (n ¼ 749) for each of the five factor-derived scales (negative symptoms, delusions, hallucinations, mania, and depression). Significant overtransmission of the Val allele was found for mania (P < 0.05) and depression (P ¼ 0.01) scales. Examination of odds ratios (ORs) revealed a heterogeneous effect of COMT, whereby it had no effect on Negative Symptoms, but largest impact on Depression (OR ¼ 1.4). These results suggest a modest affective vulnerability conferred by this allele in psychosis, but will require replication. ß 2006 Wiley-Liss, Inc. KEY WORDS: COMT; functional polymorphism; OPCRIT; psychiatric symptoms Please cite this article as follows: McClay JL, Fanous A, van den Oord EJCG, Webb BT, Walsh D, O’Neill FA, Kendler KS, Chen X. 2006. Catechol-O-Methyltransferase and the Clinical Features of Psychosis. Am J Med Genet Part B 141B:935–938. The Catechol-O-methyltransferase (COMT) gene has long been considered a candidate for psychosis. It not only encodes a key dopamine catabolic enzyme, but also maps to the Velo- *Correspondence to: J.L. McClay, Department of Psychiatry, 800 East Leigh St, Richmond, VA, 23298-0126. E-mail: email@example.com Received 27 July 2005; Accepted 21 June 2006 DOI 10.1002/ajmg.b.30401 ß 2006 Wiley-Liss, Inc. Cardio-Facial Syndrome (VCFS) region on chromosome 22 [O’Donovan et al., 2003]. VCFS, caused by a deletion at 22q11, carries a greatly increased risk for psychosis, with up to 30% of affected individuals displaying psychotic symptoms [Murphy et al., 1999]. A nonsynonymous polymorphism (Val-158-Met) at the COMT locus has been shown to affect the function of the encoded enzyme, whereby the Val allele confers increased activity and thermostability [Lotta et al., 1995; Lachman et al., 1996]. This polymorphism has been associated with schizophrenia in several studies [e.g., Li et al., 1996; Shifman et al., 2002; Chen et al., 2004], but the evidence is not universally in favor of an association. Many studies, mostly employing the case-control design, have produced negative results [e.g., Daniels et al., 1996; Karayiorgou et al., 1998; Norton et al., 2002]. One meta-analysis has concluded in favor of the Val allele, at least in populations of European ancestry, but the associated effect size is estimated to be small [Glatt et al., 2003]. A more recent large-scale linkage disequilibrium study and meta-analysis found only minimal nonsignificant evidence for an overrepresentation of the Val allele in schizophrenics [Fan et al., 2005]. Schizophrenia can present different clinical manifestations in different individuals, and two general approaches have been used to describe them. The classical subtypes typify the categorical approach, and these are well established in the DSM and ICD classification systems. The dimensional approach, on the other hand, describes the disorder quantitatively, usually as factors of symptoms extracted through factor analysis. Three, four and five factor models have been proposed, as reviewed by Peralta and Cuesta . Whilst the dimensional and categorical models are not inconsistent, the dimensional approach has proven to most accurately describe the clinical characteristics of the illness [Van Os et al., 1999]. The putative association between COMT and schizophrenia has been described as promising but not yet persuasive [O’Donovan et al., 2003]. We considered possible reasons for this uncertainty, and hypothesized that the effect of this gene may be specific to particular clinical features of psychosis. This being the case, such specific effects could be diluted when testing directly for association with schizophrenia, and perhaps account for the sporadic replication thus far experienced. Therefore, in this study, we examine the association of COMT alleles with psychosis symptom dimensions derived from the Operational Criteria Checklist for Psychiatric Illness (OPCRIT) [McGuffin et al., 1991]. Subjects came form the Irish Study of High Density Schizophrenia Families (ISHDSF), a large collection consisting of 268 multiplex families. Details of the ISHDSF can be found elsewhere [Kendler et al., 1996]. This sample has already demonstrated a small, but significant, overtransmission of the COMT Val allele to affected individuals, at the P < 0.05 level [see Chen et al., 2004]. The odds ratio (OR) statistic gives a 936 McClay et al. suitable measure of the magnitude of disease-marker association, and can be calculated for vertical transmissions analyzed in a transmission disequilibrium test (TDT) framework [Kazeem and Farrall, 2005]. In the ISHDSF, the COMT Val allele is significantly overtransmitted to schizophrenics, with an OR of 1.15. Our previous work also examined two further single nucleotide polymorphisms (SNPs), in addition to that conferring the Val-158-Met amino acid substitution (rs4680). From 50 to 30 , with respect to the gene, the three SNPs examined were: rs737865-rs4680-rs165599. These had been previously shown to constitute a highly significant risk haplotype for schizophrenia in a sample of Ashkenazi Jews, with alleles G-G-G at the three markers being overtransmitted to affected individuals [Shifman et al., 2002]. In the ISHDSF, the haplotype comprising of alleles A-G-A was significantly overtransmitted to cases (OR ¼ 1.3), whereas the high-risk haplotype described by Shifman et al. was undertransmitted. Whilst there is a lack of consensus on the particular risk haplotype across samples, the two studies agree on the G allele at rs4680 (conferring Val) as a risk factor for schizophrenia. These considerations, in addition to the well-characterized functional effect of rs4680, led to its selection for further analysis with specific clinical features of psychosis in this study. The OPCRIT checklist is a phenotypic instrument, designed for use in a best-estimate procedure, in which psychosis symptom and course features are coded by an experienced clinician. This allows integration of the relative prominence of clinical features over the course of illness. For each subject with psychosis (defined as lifetime occurrence of any psychotic episode, n ¼ 749) the OPCRIT was completed by KSK based on a review of typically detailed hospital records and in-depth personal interviews. These ratings reflected both the severity of the symptoms as well as their chronicity. OPCRIT items for ISHDSF subjects were entered into factor analysis, carried out as described by Fanous et al. . Five factors were extracted, and 56 of the OPCRIT items were used to generate corresponding factor derived scales, viz: negative symptoms, delusions, hallucinations, mania, and depression. The symptoms included in each factor were consistent with theory and expectation and a complete breakdown of items in each scale is shown in Fanous et al. . The number of items per scale ranged from 7 (hallucinations) to 16 (depression). These ordinal data were not normally distributed, with each scale being to a greater or lesser extent positively skewed. We therefore chose an analysis strategy suitable to this data and our sample type [van den Oord, 1999], whereby individuals were classified into high and low scoring categories for each symptom dimension. Our intention was to pick out groups of highly affected individuals in each category without compromising power to detect association. Since the threshold for high versus low in each category is somewhat arbitrary, multiple thresholds were imposed on the OPCRIT symptom factors (top 20, 30, and 40% of cases, respectively). Genotyping was carried out as described previously [Chen et al., 2004]. We initially carried out an exploratory analysis for all individuals in the sample with psychotic symptoms. On the basis of this exploratory analysis, we then analyzed a selected subgroup refined by psychiatric diagnosis. In each case, we tested for preferential vertical transmission of COMT alleles to individuals with high symptom counts, that is, scoring above the relevant threshold, for each of the OPCRIT factors. For these tests of association, we used the TDT as implemented in TRANSMIT [Clayton, 1999], a program that improves power to detect association by reconstructing genotype data where information on one parent is missing. The bootstrap option in TRANSMIT was used to generate empirical P values to overcome bias where multiple triads were assessed within the same family. The results of the initial exploratory analysis are shown in Table I. Significant associations were found with mania (P < 0.05) and depression (P ¼ 0.012) symptoms at the 30% TABLE I. Within-Family Transmission Tests of Association for COMT Alleles and the Five Dimensions of the OPCRIT Scale Transmissions (Val) Top 20% threshold Negative symptoms Delusions Hallucinations Mania Depression Top 30% threshold Negative symptoms Delusions Hallucinations Mania Depression Top 40% threshold Negative symptoms Delusions Hallucinations Mania Depression Families Observed Expected w2 (1 df) P-value Odds ratio 124 110 173 103 96 149 130 239 120 127 146.7 124.9 230.7 119.3 122.7 0.21 1.15 1.97 0.02 0.83 0.662 0.304 0.138* 0.89 0.251 0.97 1.1 1.14 1.02 1.19 162 158 173 160 131 211 217 239 207 196 208.2 208.1 230.7 194.6 183.3 0.23 2.28 1.97 4.27 4.39 0.645 0.116 0.138* 0.042 0.012 1.01 1.13 1.14 1.16 1.38 202 184 239 209 176 284 264 356 287 272 277.3 255.7 344.7 274.6 257.4 1.09 1.62 2.45 3.4 4.81 0.329 0.206 0.106 0.072 0.022 1.08 1.12 1.13 1.16 1.32 Tests of association between COMT and the five OPCRIT symptom dimensions, examined at three thresholds of decreasing stringency (20, 30, and 40%, respectively). All individuals with any lifetime occurrence of psychosis (n ¼ 749) were included in this analysis. Sample size for each test of association is given as the number of families with transmissions to ‘‘affected’’ offspring, that is, those individuals scoring above the relevant threshold for each symptom dimension (second column). Tests of association using TRANSMIT are based on 50,000 bootstrap samples, with those scoring P < 0.05 highlighted in bold. *The Hallucinations scale yielded the same integer cut-off value for both the 20 and 30% thresholds, so that an identical single test accounts for both levels. COMT and Psychosis Dimensions 937 TABLE II. Tests of Association for the Five OPCRIT Symptom Dimensions, at the 30% Threshold Only, After Exclusion of Patients With Affective Disorders Transmissions (Val) Top 30% threshold Negative symptoms Delusions Hallucinations Mania Depression Families Observed Expected w2 (1 df) P-value Odds ratio 148 136 150 107 80 192 180 206 128 110 188.3 173 197.8 118.9 101.3 0.44 1.69 2.13 3.62 4.14 0.534 0.2 0.122 0.06 0.04 1.01 1.11 1.17 1.14 1.45 Individuals with a primary diagnosis of schizoaffective or affective disorder were omitted from this analysis, to examine if the COMT association remained consistent. This reduced sample comprised of 606 psychotic cases. Sample size for each test of association is given as the number of families with transmissions to ‘‘affected’’ offspring, that is, those individuals scoring above the 30% threshold for each symptom dimension (second column). Tests of association using TRANSMIT are based on 50,000 bootstrap samples, with those scoring P < 0.05 are highlighted in bold. threshold. Depression remained significant at the 40% threshold (P ¼ 0.022), whereas mania displayed merely a trend approaching significance. At the most stringent 20% threshold, no symptom scales were significantly associated, but this is most likely a result of small numbers and resulting low power offsetting any gains afforded by increased selection. A broad pattern of overtransmission of the Val allele was observed. When complete triads only were examined, the results were consistent in terms of direction and ORs with the results shown in Table I, but did not achieve statistical significance due to reduced power, relative to the complete analysis. To correct for multiple testing we first used the ‘‘lowest slope’’ method, known to be conservatively biased towards one [Hsueh et al., 2003]. This estimated the number of true null hypotheses to be as low as p0 ¼ 0.64. Another way to look at the significant results is to compute the positive false discovery rate pFDR [Storey, 2002, 2003], which was 0.33. This means that the estimated proportion of false discoveries among the three significant tests was 33%. Both of these correction methods are valid for correlated tests [Van den Oord, 2005]. The ORs for the tests of association shown in Table I highlight a consistent heterogeneity in the COMT effect, apparent at all three thresholds, with the largest effects seen with depression symptoms. Delusions, hallucinations, and mania symptoms all exhibit ORs broadly in line with that observed in the sample for diagnosis of schizophrenia (1.15). Negative symptoms show no effect at all with a consistent OR of 1.0 for all thresholds. This initial exploratory analysis included all individuals displaying psychotic symptoms, but the total phenotyped group of 749 individuals included 109 with schizoaffective disorder and 29 with a primary diagnosis of an affective disorder, mostly bipolar. To prevent the possibility that the observed association with affective symptoms was coming solely from these individuals, we re-examined the threshold yielding the clearest results (30%) for all symptom factors, with these individuals excluded. The results are presented in Table II. The association with depression symptoms remained intact, whilst mania symptoms exhibited a borderline trend towards significance. However, the estimated ORs were highly consistent with those observed for all cases with psychosis (Table I). It therefore appears that the putative association is not solely attributable to those in the sample with diagnosis of schizoaffective or affective disorder. This study yields initial tentative evidence that the COMT Val allele acts as a modest risk factor for affective symptoms, particularly depression, in patients with psychosis. Previous work on the ISHDSF sample [Kendler et al., 1997] has shown affective symptoms to be significantly correlated in sib pairs concordant for schizophrenia. This observation could, in part, be explained by allele sharing at the COMT locus in siblings. Considering molecular evidence, the COMT Val allele may increase liability for affective disorders, such as early-onset major depressive disorder [Massat et al., 2005], irrespective of psychosis. Further recent evidence has led to the suggestion that COMT is a common risk factor for both schizophrenia and bipolar disorder [Shifman et al., 2004]. However, taken as a whole, evidence relating COMT and affective disorders can appear confusing and contradictory. Many studies have found no association between COMT and bipolar or major depression [e.g., Kunugi et al., 1997], whilst others have reported associations, but with the low activity Met allele, both for bipolar [Li et al., 1997; Kirov et al., 1998] and unipolar depression [Ohara et al., 1998]. However, many of these early studies suffered from very small sample sizes, and may have capitalized on chance or other factors. The relationship between the COMT gene and psychiatric disorders is considered to be complex, with possible pleiotropic effects [Kunugi et al., 1997; Shifman et al., 2004; Massat et al., 2005]. As evidence, several different etiological pathways are influenced by this important gene, such as prefrontal cognition in schizophrenia [Goldberg et al., 2003] or emotional processing in the amygdala and prefrontal cortex [Smolka et al., 2005]. 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