d-Amino acid oxidase (DAO) genotype and mood symptomatology in schizophrenia

Neuroscience Letters 426 (2007) 97–100 d-Amino acid oxidase (DAO) genotype and mood symptomatology in schizophrenia Aiden Corvin ∗ , Gary Donohoe, Kevin McGhee, Kevin Murphy, Niamh Kenny, Siobhan Schwaiger, Jeanne Marie Nangle, Derek Morris, Michael Gill Neuropsychiatric Genetics Group, Institute of Molecular Medicine, Trinity College Dublin, St. James Hospital, James’s Street, Dublin 8, Ireland Received 27 April 2007; received in revised form 1 August 2007; accepted 5 September 2007 Abstract A series of genetic studies have identified the d-amino acid oxidase (DAO) gene as potentially contributing to schizophrenia susceptibility. An interacting gene, d-amino acid oxidase activator (DAOA) has also been implicated and it has been suggested that variation at these genes may influence the efficiency of glutamate gating at N-methyl-d-aspartate-type (NMDA) receptors. However, recent data suggests that DAOA may influence susceptibility to mood episodes across the spectrum of psychotic disorders rather than contributing to a specific psychosis phenotype. The aim of this study was to determine whether risk variation at DAO is similarly associated with affective or other clinical symptoms in psychosis. We have previously reported association between risk variation at DAO and schizophrenia in an Irish case–control sample. In this study we investigated the relationship between a defined genetic risk variant at DAO and PANSS-derived clinical symptom factors in a sample of 249 patients using principal component and Kruskal–Wallis analyses. Carriers of the DAO risk variant scored significantly higher on the ‘depression/anxiety’ factor than non-carriers (H = 9.02, d.f. = 2, p = 0.01). These data suggest a potential role for DAO in susceptibility to depressive symptoms in schizophrenia, but a more general role for DAO in affective disorders cannot be excluded. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Psychosis; Depression/anxiety; Susceptibility genes; DAO d-Amino acid oxidase (DAO) is a peroxisomal enzyme expressed in the human brain, which is known to oxidize dserine and may have a regulatory role in NMDA receptor function. At least five independent genetic association studies support the involvement of DAO in schizophrenia susceptibility (reviewed in [4,15]). The original study by Chumakov et al. identified association with a novel gene (G72/G30); protein interaction between this gene and DAO; and epistasis between the genes in contributing to schizophrenia risk [1]. The authors proposed that the DAO and G72/G30 (subsequently renamed d-amino acid oxidase activator (DAOA)) genes contribute to schizophrenia susceptibility by altering the efficiency of glutamate gating at the N-methyl-d-aspartate-type (NMDA) receptor ion channel. This hypothesis is supported by evidence that individuals with schizophrenia have reduced serum levels of d-serine, a decreased ratio of d-serine/DAO expression and increased DAOA expression [5–7,12]. Thera- ∗ Corresponding author. Tel.: +353 1 608 3272; fax: +353 1 679 8558. E-mail address: acorvin@tcd.ie (A. Corvin). 0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.09.002 peutic benefits have also been reported in schizophrenia patients treated with d-serine and other NMDA glycine-binding site agonists [13]. As molecular genetic data has accrued, there has been speculation that variation at certain genes may contribute to a mood-psychosis spectrum rather than to discrete categorical diagnoses such as schizophrenia or bipolar disorder [3]. The aim of this study was to characterize the clinical effects of variation at the DAO gene. There is strong a priori evidence to suggest that DAO risk alleles may contribute to the expression of affective symptoms in schizophrenia and possibly in other disorders. First, DAO have been implicated in genetic susceptibility to another mood-psychosis spectrum disorder namely bipolar disorder [3]. Second, DAO is located in a chromosomal region that has been linked to recurrent depressive disorder in a large study of almost 500 sibling pairs [8]. Third, studies have reported association between DAOA/G30 and mood congruent persecutory symptoms in bipolar disorder [9]. Finally, in a recent study of bipolar disorder and schizophrenia, variation at DAOA/G30 influenced susceptibility to major mood episodes rather than categorical diagnoses [14]. If DAO and DAOA are mood-psychosis 98 A. Corvin et al. / Neuroscience Letters 426 (2007) 97–100 spectrum genes contributing to the same molecular pathway one would expect that DAO also influences susceptibility to mood symptoms in psychosis populations. We have recently identified evidence for association with DAO in a European case–control sample, most significantly at marker re3918346 (χ2 = 6.69, p value = 0.01, OR = 1.32 (1.06–1.65)), where the C allele was over-represented in a sample of 373 schizophrenia cases compared to 812 controls [2]. Association has also been reported at this marker in three other published studies of Caucasian schizophrenia populations, although two of the studies report a different direction of effect [15]. The purpose of the current study was to investigate the relationship between the DAO risk allele in our sample and clinical symptoms in schizophrenia. We hypothesized that carriers of the DAO risk variant in this population are likely to have more prominent depressive symptoms than noncarriers. The study received the approval of the relevant local ethics committees governing the recruitment centres and was carried out in accordance with the Declaration of Helsinki. The investigation included 249 ethnically Irish individuals meeting DSM-IV criteria for schizophrenia (n = 196) or schizoaffective disorder (n = 59). Cases were recruited, with written informed consent, primarily through local mental health services in the Republic of Ireland. Participants were interviewed by a psychiatrist or psychiatric nurse trained to use the Structured Clinical Interview for DSM (SCID-P) and Positive and Negative Symptom Scale (PANSS) rated on the basis of worst documented episode of illness. Diagnoses were made by the consensus lifetime best estimate method using DSM-IV criteria and all available information (SCID interview, family or staff report and medical records). In a previous investigation of DAO we had genotyped four SNPs across the gene and identified significant evidence of association at the SNP rs3918346. Given this finding and positive reports from other samples at the SNP, to reduce the number of tests performed, only this SNP was investigated in the current study. The SNP rs3918346 was genotyped using the Taqman® assay (Applied Biosystems, Warrington, UK) on an ABI PRISM 7900HT Sequence Detection System. The genotype frequencies were in Hardy–Weinberg equilibrium for case and control samples. The 30 items of the PANSS were submitted to a principal components analysis (PCA) with varimax rotation implemented in the program SPSS version 12. Determination of the number of factors that best accounted for covariance among these items was based on scree plot analysis and an eigenvalue greater than 1 (this information is available as a Supplementary table). Carriers and non-carriers of the risk allele were than compared on the mean score on each factor. Given the unequal n-sizes between groups, this was carried out using a series of non-parametric Kruskal–Wallis tests. Analyses were carried out as a comparison between patients carrying two copies (n = 159), one copy (n = 79) and 0 copies (n = 13) of the risk variant (allele C at rs3918346). No differences were observed between carriers and non-carriers on age, gender, duration of illness, or medication prescribed (typical, atypical or clozapine) (see Table 1). Following principal components analysis of the PANSS items, five factors emerged with eigenvalues greater than 1 and accounting for greater than 5% of symptom variance. The factors identified were consistent with results of previous analyses in chronic schizophrenia or functional psychosis and with clinical expectation. These factors collectively accounted for 58% of total symptom variance and were characterized as ‘negative’, ‘delusional/thought disorder’, ‘perceptual/cognitive’, ‘depression/anxiety’ and ‘hostility/impulsivity’ symptom factors. In a series of Kruskal–Wallis tests for each factor, risk allele carriers had significantly higher scores for the ‘depression/anxiety’ factor (H = 9.02, d.f. = 2, p = 0.01). In a post hoc comparison between carriers and non-carriers of individual PANSS items for this factor, this effect was explained by carriers Table 1 (A) Comparisons between cases with 0, 1 and 2 risk alleles for demographic variables (χ2 -tests, d.f. = 2) and (B) Kruskal–Wallis analyses of the five factors (H-tests, d.f. = 2); (**p = 0.01) Part (A) Age Gender (% male) Duration of illness Diagnosis (% SZ) Prescribed atypicals (%) Prescribed Clozapine (%) Part (B) PANSS factors Delusional/thought disorder Negative Perceptual/cognitive Depression/anxiety Hostility/impulsivity 2 risk alleles (n = 159) 1 risk allele (n = 79) 0 risk alleles (n = 13) χ2 44.43 (13.78) 69.2 20.54 (7.8) 74.8 59.7 17.6 43.29 (15.37) 62 19.43 (81.2) 75.9 48.1 22.8 45.62 (13.57) 61.5 21.62 (11.1) 92.3 38.5 15.4 0.31 1.36 0.49 2.52 1.04 4.40 2 risk alleles (n = 159) 1 risk allele (n = 79) 0 risk alleles (n = 13) H 0.0146 (0.998) 0.0837 (0.964) 0.0858 (0.920) 0.1234 (1.00) −0.0081(0.997) 0.0739 (−0.180) −0.1467 (0.170) −0.0407 (−0.119) −0.1536 (−0.493) 0.0494 (−0.235) 1.03904 (0.898) 1.04791 (0.847) 1.09568 (0.940) 0.9203 (1.01) 0.9601(1.22) 0.27 2.94 0.22 9.02** 1.25 A. Corvin et al. / Neuroscience Letters 426 (2007) 97–100 of two or one copy of the risk allele having significantly higher scores on ‘guilt’ (H = 19.2, d.f. = 2, p = 6 × 10−5 ) and ‘anxiety’ (H = 5.9, d.f. = 2, p = 0.05) items (see Table 1). To our knowledge this is the first study to investigate clinical correlates of DAO risk variation in schizophrenia. We selected a single DAO variant (rs3918346) for examination as this had the largest effect size in our sample and has been reported as associated with schizophrenia in four independent studies. We were interested in whether DAO variation contributes to mood symptoms in schizophrenia. Based on our factor analysis of PANSS symptoms we observed that the risk variant was associated with higher scores on the depressive factor, in particular with symptoms of guilt and anxiety. This suggests that DAO may contribute to depressive symptoms in psychosis. An alternative explanation is that DAO modifies severity of depressive symptoms, as the measure used in this study reflected an estimate of ‘worst-ever’ PANSS symptoms. These hypotheses can be plausibly tested using longitudinal measures of clinical symptoms, for example, available through prospective first episode studies. In interpreting this data it is important to be clear that the association with DAO is statistical and that functional risk variants at the gene have yet to be identified. The risk allele identified is unlikely to represent the causative variant at DAO and may be in linkage disequilibrium with one or more functional variants at the locus. The marker investigated here has been associated with schizophrenia susceptibility in four studies of Caucasian schizophrenia cohorts (but not in Asian samples), but these studies are evenly divided as to which is the ‘risk’ allele. Potential reasons for this are manifold and may represent the effect of allelic heterogeneity, a ‘signal’ from different combinations of risk variants or false positive reports. Additional association and sequencing studies are required to explore and characterize risk variation at the gene as a prelude to identifying how this may contribute to cellular pathogenesis. We do not report a statistical correction for the number of clinical factors tested because the factors are not completely independent and there is prior data for involvement of this locus in mood symptoms. However, the reported finding would meets traditional significance criteria after conservative Bonferroni correction for the five tests performed. There is growing evidence that putative schizophrenia or psychosis genes may contribute to different aspects of clinical symptomatology (for review, see [10]). This study contributes to converging evidence for involvement of DAO (and the interacting gene DAOA) with a cluster of symptoms involving guilt, anxiety and depression. As previously mentioned DAO maps to an identified susceptibility locus for recurrent depressive disorder [8]. The DAOA gene has been associated with mood congruent persecutory delusions in bipolar disorder and mood episodes across psychotic disorders [9,14]. Beyond the psychosis phenotype there are DAOA associations reported with susceptibility to panic disorder and major depressive disorder [10,11]. The current finding, if independently confirmed, suggests that DAO, DAOA and potentially other genes involved in NMDA function should also be more widely investigated for association with affective and anxiety disorder phenotypes. 99 Acknowledgements The authors are grateful to all the participants in this study and to the support of our funding agencies, namely, The Health Research Board of Ireland (HRB) and Science Foundation Ireland (SFI). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.neulet.2007.09.002. References [1] I. Chumakov, M. Blumenfeld, O. Guerassimenko, L. Cavarec, M. Palicio, H. Abderrahim, L. Bougueleret, C. Barry, H. Tanaka, P. La Rosa, A. Puech, N. Tahri, A. Cohen-Akenine, S. Delabrosse, S. Lissarrague, F.P. Picard, K. Maurice, L. Essioux, P. Millasseau, P. Grel, V. Debailleul, A.M. Simon, D. Caterina, I. Dufaure, K. Malekzadeh, M. Belova, J.J. Luan, M. Bouillot, J.L. Sambucy, G. 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