- Email: [email protected]
Gene–gene interaction between MAOA and COMT in suicidal behavior
Neuroscience Letters 383 (2005) 151–154
Gene–gene interaction between MAOA and COMT in suicidal behavior Vincenzo De Luca a,b,∗ , Subi Tharmalingam a , Tricia Sicard a , James L. Kennedy a a
Neurogenetics Section, Clarke Site, Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, 250 College Street R-30, Toronto, Ont., Canada M5T 1R8 b Department of Neuroscience and Behavioral Sciences, Section of Psychiatry, University of Naples “Federico II”, Italy Received 23 December 2004; received in revised form 23 December 2004; accepted 1 April 2005
Abstract Several lines of evidence suggest that suicidal behavior is associated with altered noradrenergic neurotransmission. Noradrenaline (NA) is catabolized by monoamine oxidase A (MAOA) and cathecol-O-methyl transferase (COMT). We hypothesized that the genes encoding MAOA and COMT might contain genetic variation conferring increased risk for attempted suicide. In order to test this hypothesis, we genotyped the 941T>G and the promoter VNTR polymorphisms in the MAOA gene and the Val 108/158 Met COMT polymorphism in 305 families with at least one member having bipolar disorder (BD). No association with history of suicide attempt was found either in the MAOA polymorphisms (VNTR:LRS = 1.90, d.f. = 1, p = 0.16; 941T>G:LRS = 1.39, d.f. = 1, p = 0.23), or with the Val 158 Met polymorphism (LRS = 1.61, d.f. = 1, p = 0.20). When we performed the haplotype analysis for MAOA gene, we found no association between suicide attempt and haplotype distribution (LRS = 3.07, d.f. = 2, p = 0.21). As both genes are involved in degrading noradreanline, we also tested the hypothesis of epistasis between MAOA polymorphisms and Val158Met, however, no additive effect was found in conferring risk for suicide attempt. These findings suggest that MAOA and COMT genes may not influence suicidal behavior in patients with bipolar disorder. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Parasuicide; Genetics; Bipolar disorder; Noradrenaline; COMT; MAOA
Suicide is a major contributor to the morbidity and mortality in individual with bipolar disorder (BD). The lifetime suicide risk is 19% in bipolar disorder patients [11]. Of patients with bipolar disorder, 25–60% generate at least one suicide attempt during the course of their illness [4]. Genetic factors have been generally implicated in the etiology of suicide, although the precise mechanism and amount of the genetic contribution are not yet well established [21,23]. The noradrenergic system is thought to be involved in aggressive behavior [2]. Furthermore, catecolaminergic dysfunction has been suggested in suicide based on several observations. For example, high concentration of noradrenaline (NA) with decreased alpha2-adrenergic bindings ∗ Corresponding author. Tel.: +1 416 535 8501x4421; fax: +1 416 979 4666. E-mail address: Vincenzo [email protected] (V. De Luca).
0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.04.001
were also observed in the prefrontal cortex of suicide victims [1], and low levels of 3-methoxy-4-hydorxyphenylglycol, a metabolite of NA were also observed in subjects who attempted suicide [12,18,22]. Monoamine oxidase A (MAOA) is a mitochondrial enzyme, which degrades noradrenaline and is the primary target for monoamine oxidase inhibitors (MAOIs); the polymorphisms in MAO-A gene have been associated with suicide [5] and impulsive behavior [10]. Furthermore, a significant elevation of MAOA activity has been reported in the hypothalamic region of post-mortem brain from suicide victims [24]. The MAOA gene is located on chromosome Xp11.23–11.4. The MAOA upstream regulatory region has a 30 bp variable number tandem repeat (MAOA–uVNTR) with two common alleles of three and four repeat elements, which are found to be associated with low and high transcription levels, respectively. A 941T>G polymorphism in exon 8 was reported by Hotamisligil and
152
V. De Luca et al. / Neuroscience Letters 383 (2005) 151–154
Breakfield [8] with 941T allele associated with low MAOA activity. Cathecol-O-methyl transferase (COMT) enzyme, encoded by a gene located on chromosome 22q11, metabolizes the noradrenaline that diffuses in synaptic cleft. A Val158Met polymorphism has been identified in the COMT gene, in which the allele encoding valine has relatively high COMT activity over the one encoding methionine [14]. The methionine allele was associated with violent parasuicide specifically in male schizophrenics [20]. The existence of alternative noradrenaline catabolism means that one pathway can compensate for blockade in the other; there is a negative correlation between MAO deaminated metabolites and catechol-O-metylated metabolites [7]. Thus, we speculated that the combination of functional alleles in MAOA and COMT genes would predispose to suicidal behavior. The aim of this study was to investigate whether there is association between Val158Met or MAOA functional polymorphisms and suicidality, as well as to examine whether the combination of functional alleles in MAOA and COMT genes would predict a predisposition to suicidal behavior. Thus, MAOA and COMT data were analyzed together to look for interaction on susceptibility to suicidality. The study population consisted of 336 bipolar patients from 305 nuclear families who were recruited in the Toronto area. The mean age at the time of the interview was 35.36 ± 10.37 S.D. Subjects ranged in age from 16 to 67. The mean age at onset for bipolar disorder was 20 ± 7.58 S.D., with female subjects comprising 62% of the sample. Eighty-six patients attempted suicide. The SCID-I was administered to all subjects by trained clinical interviewers. Suicidality was assessed on a quantitative scale, with the following order: 1 = Thoughts of death, 2 = Suicide Ideation, 3 = Suicide Plan, 4 = Suicide Attempt. Among the bipolar patients, 267 patients had history of suicide ideas or attempts and the mean score for all 336 suicide ideation/behaviour scores was 2.1 ± 1.4. For the attempters, the age of onset of BP was 19.16 ± 8.36 and the mean age at interview was 34.84 ± 11.02. Genomic DNA was obtained from peripheral leukocytes, using high salt extraction methods [15]. Genotypes of the MAOA–uVNTR polymorphism was determined by PCR and electrophoresis on 3.0% high resolution agarose gel. The MAOA 941T>G polymorphism was detected by Fnu4HI restriction enzyme digestion and COMT Val148Met by NlaIII according to Kunugi et al. [13]. Allelic and haplotype transmission tests in suicide attempters were performed using TDTphase [6], which estimates haplotype transmission based on an expectation maximization (EM) algorithm and gives a haplotype relative risk statistic. Separate TDT analysis was done for male attempters based on the previous findings. The continuous trait of suicidality was analyzed using QPDTPHASE [6] with X-linked option when we analyze MAOA and FBAT version 1.5.1 [9]. The MAOA–COMT interaction was tested using PedSplit [17].
Table 1 MAOA Haplotype TDT in attempters Haplotype
Ta
NTb
χ2
p
3-T 3-G 4-T
5 11 42
8 17 33
0.7827 1.687 2.895
0.37 0.19 0.08
LRS = 3.076, d.f. = 2, p = 0.2. a Transmitted haplotype count. b Untransmitted haplotype count.
The main results for single marker TDT in the attempter group was not found to be significant for both MAOA (uVNTR Global χ2 allele-wise = 1.9, d.f. = 1, p = 0.16; 941T>G LRS = 1.39, d.f. = 1, p = 0.23; 941T 16 versus 10 transmissions) and COMT (LRS = 1.61, d.f. = 1, p = 0.20, Met158 36 versus 26 transmissions). However, our analysis of the Met allele in only male attempters yielded a slight trend for Met overtransmission (18 versus 9; LRS = 3.05, d.f. = 1, p = 0.08). The quantitative analysis of suicide specifiers with QPDTPHASE showed no significant association with alleles in both MAOA and COMT, however, in regard to quantitative trait there was a trend, a trend was observed with the Met allele and a higher severity score in male (χ2 = 2.35, d.f. = 1, p = 0.12). The global D for MAOA uVNTR–T941G was 0.79. The linkage between four repeat and T941 is strong in our study population (D = 0.80; r2 = 0.44; 4-T haplotype 61.5%). For the MAOA haplotypes of these two polymorphisms in the attempter population, the TDTphase analysis showed a non-significant global χ2 (LRS = 3.07, d.f. = 2, p = 0.21). All three frequent haplotypes showed equal rates of transmission (Table 1). When we analyzed the haplotypes in the bipolar sample according to the suicide specifiers quantitative trait, we found no association with any haplotypes using QPDTPHASE (Table 2). When we analyzed the MAOA–COMT interaction with suicide attempt, the conditional TDT was performed for COMT polymorphism stratifying for high and low expression repeats and 941T>G genotypes in MAOA. We ran the conditional TDT with COMT as this yield more informative families than MAOA TDT which only takes into account maternal transmissions. The conditional TDT has shown a trend for overtransmission of Met allele when we stratify the sample for high expression genotypes in uVNTR (20 versus 10 LRS = 3.39, d.f. = 1, p = 0.06) and TT genotypes in 941T>G
Table 2 QPDTPHASE suicide specifiers (quantitative trait analysis) Haplotype
Z
pa
Count
Frequency
Meanb
3-T 3-G 4-T 4-G
1.001 0.203 0.406 1.126
0.3166 0.8386 0.6842 0.2602
70.3 120.8 378.3 19.5
0.11 0.20 0.63 0.03
1.94 2.14 2.10 1.16
a b
Global test: χ2 = 1.858, d.f. = 3, p = 0.60. Trait mean is 2.09.
V. De Luca et al. / Neuroscience Letters 383 (2005) 151–154
(24 versus 13 LRS = 3.32, d.f. = 1, p = 0.06). However, the global χ2 of CTDT was not significant for COMT–MAOA uVNTR (χ2 = 7.86, d.f. = 6, p = 0.24) and COMT–MAOA 941T/G (χ2 = 7.44, d.f. = 6, p = 0.28). When we examined the suicide specifiers as a quantitative trait using FBAT, COMT alleles showed no biased transmissions when we stratified for uVNTR genotypes and 941T/G; the global χ2 was not significant in both interaction (COMT–uVNTR: χ2 = 2.92, d.f. = 6, p = 0.81; COMT–941T/G: χ2 = 5.98, d.f. = 6, p = 0.42). To our knowledge, this work represents the first study to investigate the interaction of MAOA and COMT genes in suicidal behavior. Our results indicate that it is unlikely that the two genes alone are conferring risk for suicidal behavior in our bipolar sample, however, combined analysis seem to produce interesting trends. The three polymorphisms chosen have adequate heterozigosity and our sample of 305 families considering the Met158 as the risk allele, with an additive model, for a significance level = 0.05 has power >80% in regards to qualitative analysis as calculated by the program PBAT [16]. We found a trend for the Met allele conferring susceptibility to suicide in male attempters according to Nolan et al. [20], thus given the relatively small sample size of the suicide attempter group and the interesting trend, larger samples are needed in future investigations of the MAOA–COMT interaction. The main strengths of this study are the gene–gene interaction and the family based approach strategy that is not sensitive to population stratification. The main limitation is that we assessed the suicide attempters but clearly did not study suicide completers. Another limitation is that we did not explore the adversity/life events that were found to modulate the effect of the low activity MAOA genotypes [3]. The SCID interview that we used for this sample does not include a specific score for adversity/life events, thus the trend that we found could become significant in relation to the presence/absence of stressful life events. In conclusion this study has found that the Met allele for COMT could be associated with suicide attempt but needs to interact with high expression allele in MAOA gene or the male gender to increase its penetrance.
Acknowledgement Dr V. De Luca is supported by a Postdoctoral Research Fellowship and a Pilot Grant from the American Foundation for Suicide Prevention.
References [1] V. Arango, P. Ernsberger, A.F. Sved, J.J. Mann, Quantitative autoradiography of alpha 1- and alpha 2-adrenergic receptors in the cerebral cortex of controls and suicide victims, Brain Res. 630 (1993) 271–282.
153
[2] O. Cases, I. Seif, J. Grimsby, P. Gaspar, K. Chen, S. Pournin, U. Muller, M. Aguet, C. Babinet, J.C. Shih, Aggressive behavior and altered amounts of brain serotonin and norepinephrine in mice lacking MAOA, Science 268 (1995) 1763–1766. [3] A. Caspi, J. McClay, T.E. Moffitt, J. Mill, J. Martin, I.W. Craig, A. Taylor, R. Poulton, Role of genotype in the cycle of violence in maltreated children, Science 297 (2002) 851–854. [4] Y.W. Chen, S.C. Dilsaver, Lifetime rates of suicide attempts among subjects with bipolar and unipolar disorders relative to subjects with other Axis I disorders, Biol. Psychiatry 39 (1996) 896– 899. [5] L. Du, G. Faludi, M. Palkovits, P. Sotonyi, D. Bakish, P.D. Hrdina, High activity-related allele of MAO-A gene associated with depressed suicide in males, Neuroreport 13 (2002) 1195–1198. [6] F. Dudbridge, Pedigree disequilibrium tests for multilocus haplotypes, Genet. Epidemiol. 25 (2003) 115–121. [7] G. Eisenhofer, J.P. Finberg, Different metabolism of norepinephrine and epinephrine by catechol-O-methyltransferase and monoamine oxidase in rats, J. Pharmacol. Exp. Ther. 268 (1994) 1242–1251. [8] G.S. Hotamisligil, X.O. Breakefield, Human monoamine oxidase A gene determines levels of enzyme activity, Am. J. Hum. Genet. 49 (1991) 383–392. [9] S. Hovarth, X. Xu, N.M. Laird, The family based association test method: strategies for studying general genotype–phenotype associations, Eur. J. Hum. Genet. 9 (2001) 301–306. [10] Y.Y. Huang, S.P. Cate, C. Battistuzzi, M.A. Oquendo, D. Brent, J.J. Mann, An association between a functional polymorphism in the monoamine oxidase a gene promoter, impulsive traits and early abuse experiences, Neuropsychopharmacology 29 (2004) 1498–1505. [11] K.R. Jaminson, Suicide and bipolar disorder, J. Clin. Psychiatry 61 (Suppl. 9) (2000) 47–51. [12] J.S. Jones, B. Stanley, J.J. Mann, A.J. Frances, J.R. Guido, L. Traskman-Bendz, R. Winchel, R.P. Brown, M. Stanley, CSF 5-HIAA and HVA concentrations in elderly depressed patients who attempted suicide, Am. J. Psychiatry 147 (1990) 1225–1227. [13] H. Kunugi, H.P. Vallada, P.C. Sham, F. Hoda, M.J. Arranz, T. Li, S. Nanko, R.M. Murray, P. McGuffin, M. Owen, M. Gill, D.A. Collier, Catechol-O-methyltransferase polymorphisms and schizophrenia: a transmission disequilibrium study in multiply affected families, Psychiatr. Genet. 7 (1997) 97–101. [14] H.M. Lachman, D.F. Papolos, T. Saito, Y.M. Yu, C.L. Szumlanski, R.M. Weinshilboum, Human catechol-O-methyltransferase pharmacogenetics: description of a functional polymorphism and its potential application to neuropsychiatric disorders, Pharmacogenetics 6 (1996) 243–250. [15] D.K. Lahiri, J.I. Nurnberger Jr., A rapid non-enzymatic method for the preparation of HMW DNA from blood for RFLP studies, Nucleic Acids Res. 19 (1991) 5444. [16] C. Lange, PBAT: Analytical Power Calculations for Family-Based Association Test (v 0.1), Department of Biostatistics, Harvard School of Public Health, 2001. [17] M.B. Lanktree, L. VanderBeek, F.M. Macciardi, J.L. Kennedy, PedSplit: pedigree management for stratified analysis, Bioinformatics 20 (2004) 2315–2316. [18] D. Lester, The concentration of neurotransmitter metabolites in the cerebrospinal fluid of suicidal individuals: a meta-analysis, Pharmacopsychiatry 28 (1995) 45–50. [20] K.A. Nolan, J. Volavka, P. Czobor, A. Cseh, H. Lachman, T. Saito, J. Tiihonen, A. Putkonen, T. Hallikainen, I. Kotilainen, P. Rasanen, M. Isohanni, M.R. Jarvelin, M.K. Karvonen, Suicidal behavior in patients with schizophrenia is related to COMT polymorphism, Psychiatr. Genet. 10 (2000) 117–124. [21] A. Roy, Genetic and biologic risk factors for suicide in depressive disorders, Psychiatr. Q. 64 (1993) 345–358. [22] A. Roy, H. Agren, D. Pickar, M. Linnoila, A.R. Doran, N.R. Cutler, S.M. Paul, Reduced CSF concentrations of homovanillic acid and homovanillic acid to 5-hydroxyindoleacetic acid ratios in depressed
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patients: relationship to suicidal behavior and dexamethasone nonsuppression, Am. J. Psychiatry 143 (1986) 1539–1545. [23] A. Roy, D. Nielsen, G. Rylander, M. Sarchiapone, N. Segal, Genetics of suicide in depression, J. Clin. Psychiatry 60 (Suppl. 2) (1999) 12–17 (discussion 18–20, 113–116).
[24] F. Sherif, J. Marcusson, L. Oreland, Brain gamma-aminobutyrate transaminase and monoamine oxidase activities in suicide victims, Eur. Arch. Psychiatry Clin. Neurosci. 241 (1991) 139– 144.
Gene–gene interaction between MAOA and COMT in suicidal behavior Vincenzo De Luca a,b,∗ , Subi Tharmalingam a , Tricia Sicard a , James L. Kennedy a a
Neurogenetics Section, Clarke Site, Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, 250 College Street R-30, Toronto, Ont., Canada M5T 1R8 b Department of Neuroscience and Behavioral Sciences, Section of Psychiatry, University of Naples “Federico II”, Italy Received 23 December 2004; received in revised form 23 December 2004; accepted 1 April 2005
Abstract Several lines of evidence suggest that suicidal behavior is associated with altered noradrenergic neurotransmission. Noradrenaline (NA) is catabolized by monoamine oxidase A (MAOA) and cathecol-O-methyl transferase (COMT). We hypothesized that the genes encoding MAOA and COMT might contain genetic variation conferring increased risk for attempted suicide. In order to test this hypothesis, we genotyped the 941T>G and the promoter VNTR polymorphisms in the MAOA gene and the Val 108/158 Met COMT polymorphism in 305 families with at least one member having bipolar disorder (BD). No association with history of suicide attempt was found either in the MAOA polymorphisms (VNTR:LRS = 1.90, d.f. = 1, p = 0.16; 941T>G:LRS = 1.39, d.f. = 1, p = 0.23), or with the Val 158 Met polymorphism (LRS = 1.61, d.f. = 1, p = 0.20). When we performed the haplotype analysis for MAOA gene, we found no association between suicide attempt and haplotype distribution (LRS = 3.07, d.f. = 2, p = 0.21). As both genes are involved in degrading noradreanline, we also tested the hypothesis of epistasis between MAOA polymorphisms and Val158Met, however, no additive effect was found in conferring risk for suicide attempt. These findings suggest that MAOA and COMT genes may not influence suicidal behavior in patients with bipolar disorder. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Parasuicide; Genetics; Bipolar disorder; Noradrenaline; COMT; MAOA
Suicide is a major contributor to the morbidity and mortality in individual with bipolar disorder (BD). The lifetime suicide risk is 19% in bipolar disorder patients [11]. Of patients with bipolar disorder, 25–60% generate at least one suicide attempt during the course of their illness [4]. Genetic factors have been generally implicated in the etiology of suicide, although the precise mechanism and amount of the genetic contribution are not yet well established [21,23]. The noradrenergic system is thought to be involved in aggressive behavior [2]. Furthermore, catecolaminergic dysfunction has been suggested in suicide based on several observations. For example, high concentration of noradrenaline (NA) with decreased alpha2-adrenergic bindings ∗ Corresponding author. Tel.: +1 416 535 8501x4421; fax: +1 416 979 4666. E-mail address: Vincenzo [email protected] (V. De Luca).
0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.04.001
were also observed in the prefrontal cortex of suicide victims [1], and low levels of 3-methoxy-4-hydorxyphenylglycol, a metabolite of NA were also observed in subjects who attempted suicide [12,18,22]. Monoamine oxidase A (MAOA) is a mitochondrial enzyme, which degrades noradrenaline and is the primary target for monoamine oxidase inhibitors (MAOIs); the polymorphisms in MAO-A gene have been associated with suicide [5] and impulsive behavior [10]. Furthermore, a significant elevation of MAOA activity has been reported in the hypothalamic region of post-mortem brain from suicide victims [24]. The MAOA gene is located on chromosome Xp11.23–11.4. The MAOA upstream regulatory region has a 30 bp variable number tandem repeat (MAOA–uVNTR) with two common alleles of three and four repeat elements, which are found to be associated with low and high transcription levels, respectively. A 941T>G polymorphism in exon 8 was reported by Hotamisligil and
152
V. De Luca et al. / Neuroscience Letters 383 (2005) 151–154
Breakfield [8] with 941T allele associated with low MAOA activity. Cathecol-O-methyl transferase (COMT) enzyme, encoded by a gene located on chromosome 22q11, metabolizes the noradrenaline that diffuses in synaptic cleft. A Val158Met polymorphism has been identified in the COMT gene, in which the allele encoding valine has relatively high COMT activity over the one encoding methionine [14]. The methionine allele was associated with violent parasuicide specifically in male schizophrenics [20]. The existence of alternative noradrenaline catabolism means that one pathway can compensate for blockade in the other; there is a negative correlation between MAO deaminated metabolites and catechol-O-metylated metabolites [7]. Thus, we speculated that the combination of functional alleles in MAOA and COMT genes would predispose to suicidal behavior. The aim of this study was to investigate whether there is association between Val158Met or MAOA functional polymorphisms and suicidality, as well as to examine whether the combination of functional alleles in MAOA and COMT genes would predict a predisposition to suicidal behavior. Thus, MAOA and COMT data were analyzed together to look for interaction on susceptibility to suicidality. The study population consisted of 336 bipolar patients from 305 nuclear families who were recruited in the Toronto area. The mean age at the time of the interview was 35.36 ± 10.37 S.D. Subjects ranged in age from 16 to 67. The mean age at onset for bipolar disorder was 20 ± 7.58 S.D., with female subjects comprising 62% of the sample. Eighty-six patients attempted suicide. The SCID-I was administered to all subjects by trained clinical interviewers. Suicidality was assessed on a quantitative scale, with the following order: 1 = Thoughts of death, 2 = Suicide Ideation, 3 = Suicide Plan, 4 = Suicide Attempt. Among the bipolar patients, 267 patients had history of suicide ideas or attempts and the mean score for all 336 suicide ideation/behaviour scores was 2.1 ± 1.4. For the attempters, the age of onset of BP was 19.16 ± 8.36 and the mean age at interview was 34.84 ± 11.02. Genomic DNA was obtained from peripheral leukocytes, using high salt extraction methods [15]. Genotypes of the MAOA–uVNTR polymorphism was determined by PCR and electrophoresis on 3.0% high resolution agarose gel. The MAOA 941T>G polymorphism was detected by Fnu4HI restriction enzyme digestion and COMT Val148Met by NlaIII according to Kunugi et al. [13]. Allelic and haplotype transmission tests in suicide attempters were performed using TDTphase [6], which estimates haplotype transmission based on an expectation maximization (EM) algorithm and gives a haplotype relative risk statistic. Separate TDT analysis was done for male attempters based on the previous findings. The continuous trait of suicidality was analyzed using QPDTPHASE [6] with X-linked option when we analyze MAOA and FBAT version 1.5.1 [9]. The MAOA–COMT interaction was tested using PedSplit [17].
Table 1 MAOA Haplotype TDT in attempters Haplotype
Ta
NTb
χ2
p
3-T 3-G 4-T
5 11 42
8 17 33
0.7827 1.687 2.895
0.37 0.19 0.08
LRS = 3.076, d.f. = 2, p = 0.2. a Transmitted haplotype count. b Untransmitted haplotype count.
The main results for single marker TDT in the attempter group was not found to be significant for both MAOA (uVNTR Global χ2 allele-wise = 1.9, d.f. = 1, p = 0.16; 941T>G LRS = 1.39, d.f. = 1, p = 0.23; 941T 16 versus 10 transmissions) and COMT (LRS = 1.61, d.f. = 1, p = 0.20, Met158 36 versus 26 transmissions). However, our analysis of the Met allele in only male attempters yielded a slight trend for Met overtransmission (18 versus 9; LRS = 3.05, d.f. = 1, p = 0.08). The quantitative analysis of suicide specifiers with QPDTPHASE showed no significant association with alleles in both MAOA and COMT, however, in regard to quantitative trait there was a trend, a trend was observed with the Met allele and a higher severity score in male (χ2 = 2.35, d.f. = 1, p = 0.12). The global D for MAOA uVNTR–T941G was 0.79. The linkage between four repeat and T941 is strong in our study population (D = 0.80; r2 = 0.44; 4-T haplotype 61.5%). For the MAOA haplotypes of these two polymorphisms in the attempter population, the TDTphase analysis showed a non-significant global χ2 (LRS = 3.07, d.f. = 2, p = 0.21). All three frequent haplotypes showed equal rates of transmission (Table 1). When we analyzed the haplotypes in the bipolar sample according to the suicide specifiers quantitative trait, we found no association with any haplotypes using QPDTPHASE (Table 2). When we analyzed the MAOA–COMT interaction with suicide attempt, the conditional TDT was performed for COMT polymorphism stratifying for high and low expression repeats and 941T>G genotypes in MAOA. We ran the conditional TDT with COMT as this yield more informative families than MAOA TDT which only takes into account maternal transmissions. The conditional TDT has shown a trend for overtransmission of Met allele when we stratify the sample for high expression genotypes in uVNTR (20 versus 10 LRS = 3.39, d.f. = 1, p = 0.06) and TT genotypes in 941T>G
Table 2 QPDTPHASE suicide specifiers (quantitative trait analysis) Haplotype
Z
pa
Count
Frequency
Meanb
3-T 3-G 4-T 4-G
1.001 0.203 0.406 1.126
0.3166 0.8386 0.6842 0.2602
70.3 120.8 378.3 19.5
0.11 0.20 0.63 0.03
1.94 2.14 2.10 1.16
a b
Global test: χ2 = 1.858, d.f. = 3, p = 0.60. Trait mean is 2.09.
V. De Luca et al. / Neuroscience Letters 383 (2005) 151–154
(24 versus 13 LRS = 3.32, d.f. = 1, p = 0.06). However, the global χ2 of CTDT was not significant for COMT–MAOA uVNTR (χ2 = 7.86, d.f. = 6, p = 0.24) and COMT–MAOA 941T/G (χ2 = 7.44, d.f. = 6, p = 0.28). When we examined the suicide specifiers as a quantitative trait using FBAT, COMT alleles showed no biased transmissions when we stratified for uVNTR genotypes and 941T/G; the global χ2 was not significant in both interaction (COMT–uVNTR: χ2 = 2.92, d.f. = 6, p = 0.81; COMT–941T/G: χ2 = 5.98, d.f. = 6, p = 0.42). To our knowledge, this work represents the first study to investigate the interaction of MAOA and COMT genes in suicidal behavior. Our results indicate that it is unlikely that the two genes alone are conferring risk for suicidal behavior in our bipolar sample, however, combined analysis seem to produce interesting trends. The three polymorphisms chosen have adequate heterozigosity and our sample of 305 families considering the Met158 as the risk allele, with an additive model, for a significance level = 0.05 has power >80% in regards to qualitative analysis as calculated by the program PBAT [16]. We found a trend for the Met allele conferring susceptibility to suicide in male attempters according to Nolan et al. [20], thus given the relatively small sample size of the suicide attempter group and the interesting trend, larger samples are needed in future investigations of the MAOA–COMT interaction. The main strengths of this study are the gene–gene interaction and the family based approach strategy that is not sensitive to population stratification. The main limitation is that we assessed the suicide attempters but clearly did not study suicide completers. Another limitation is that we did not explore the adversity/life events that were found to modulate the effect of the low activity MAOA genotypes [3]. The SCID interview that we used for this sample does not include a specific score for adversity/life events, thus the trend that we found could become significant in relation to the presence/absence of stressful life events. In conclusion this study has found that the Met allele for COMT could be associated with suicide attempt but needs to interact with high expression allele in MAOA gene or the male gender to increase its penetrance.
Acknowledgement Dr V. De Luca is supported by a Postdoctoral Research Fellowship and a Pilot Grant from the American Foundation for Suicide Prevention.
References [1] V. Arango, P. Ernsberger, A.F. Sved, J.J. Mann, Quantitative autoradiography of alpha 1- and alpha 2-adrenergic receptors in the cerebral cortex of controls and suicide victims, Brain Res. 630 (1993) 271–282.
153
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