Original Paper Neuropsychobiology 2014;69:154–158 DOI: 10.1159/000358839
Received: April 29, 2013 Accepted after revision: January 20, 2014 Published online: April 26, 2014
Association Study of GABRG2 Polymorphisms with Suicidal Behaviour in Schizophrenia Patients with Alcohol Use Disorder Clement C. Zai a, b Gwyneth C. Zai a–c Arun K. Tiwari a Mirko Manchia d, e, f Vincenzo de Luca a, b Sajid A. Shaikh a John Strauss a James L. Kennedy a–c a
Neurogenetics Section, Neuroscience Research Department, Centre for Addiction and Mental Health, and Department of Psychiatry, and c Institute of Medical Science, University of Toronto, Toronto, Ont., and d Departments of Psychiatry and e Pharmacology, Dalhousie University, Halifax, N.S., Canada; f Department of Public Health, Clinical and Molecular Medicine, University of Cagliari, Cagliari, Italy b
Key Words Schizophrenia · Suicide specifier · Alcohol dependence · GABAA γ2 GABRG2 · Genetics
Abstract Background: Schizophrenia is a severe neuropsychiatric disorder where the role of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, has been implicated in its aetiopathophysiology. Several genes coding for GABAA subunits, including the GABRG2 gene that encodes the γ2 subunit, are clustered at 5q31–q35, a chromosomal region that is associated with schizophrenia in genome scan studies. We recently reported GABRG2 to be associated with schizophrenia in our case-control and family samples. Methods: We tested eight single-nucleotide polymorphisms spanning the GABRG2 gene for an association with suicidal behaviour in our schizophrenia sample of European ancestry (n = 197), taking into account history of alcohol abuse or dependence. Results: We found the haplotypes of the rs183294 and rs209356 markers to be significantly associated with history of suicide attempt (p < 0.01) as well as suicide specifier scores (p < 0.05). The association appeared to be originating in patients with a history of alcohol dependence or abuse. Conclusions: Taken together, the results of the present study
© 2014 S. Karger AG, Basel 0302–282X/14/0693–0154$39.50/0 E-Mail [email protected] www.karger.com/nps
suggest that GABRG2 may be involved in suicidal behaviour in schizophrenia patients with alcohol dependence or abuse, but replications are required. These results may help in the discovery of novel treatments for alcoholism and/or prevention of suicide. © 2014 S. Karger AG, Basel
Introduction
Schizophrenia is a severe neuropsychiatric disorder that affects approximately 1% of the general population [1]. Among schizophrenia patients, up to half have attempted suicide [2], and 5% will commit suicide [3], making the prediction and management of suicidal behaviour an imperative endeavour in the treatment of schizophrenia patients [4]. A number of risk factors have been found to increase the risk for suicidality, including comorbid alcohol use disorders and family history [5]. A review of cohort studies of completed suicides reported a 9.79 time higher risk for suicide among individuals with alcohol use disorders than in the general population [6]. Family, adoption, and twin studies support a substantial genetic component of suicidality [reviewed in 7].
Dr. James L. Kennedy Centre for Addiction and Mental Health R31 250 College Street Toronto, ON M5T1R8 (Canada) E-Mail jim.kennedy @ camh.ca
The GABAA receptor γ2 subunit is essential for the benzodiazepine binding at the GABAA receptor and modulates the sensitivity of GABAA receptors to alcohol [8, 9]. The short isoform (γ2S) confers greater sensitivity to benzodiazepine than the long isoform (γ2L) [10], possibly due to the sensitivity of γ2L subunit-containing GABAA to zinc inhibition [11]. Using open-field activity monitoring and elevated plus maze, genetically modified mice with decreased GABRG2 expression exhibited enhanced anxiety-related phenotypes [12, 13]; interestingly, anxiety disorders in humans have been shown to increase the odds of first-onset suicide ideation and attempt [14]. In terms of alcohol dependence, GABRG2 expression is reduced in postmortem hippocampi of alcoholics [15]. Moreover, in depressed suicide victims, the dorsolateral prefrontal cortical mRNA expression of GABRG2 was down-regulated when compared to nonsuicide controls independent of alcohol dependence [16]. These evidences suggest that alcohol may decrease GABRG2 expression, which in turn may increase suicide-related anxiety, making GABRG2 an intriguing target for studying the genetics of alcohol-related suicidal behaviour. We previously reported a possible association between the GABRG2 gene and schizophrenia [17]. Here, we hypothesize that there is an association between GABRG2 and suicidal behaviour in these schizophrenia patients. We also hypothesize an association between GABRG2 and suicidal behaviour in schizophrenia patients with history of alcohol use disorder.
0.20; alpha = 0.05; additive model). In accordance with the Declaration of Helsinki, we obtained voluntary written informed consent from each study participant after the nature of the study was explained to them, and the study was approved by the Institutional Research Ethics Board. DNA extraction and genotyping was carried out as described previously [17]. Briefly, genomic DNA was purified from blood lymphocytes [21]. Nineteen single-nucleotide polymorphisms (SNPs) were genotyped using either TaqMan genotyping assays (ABI Prism® 7000/7500, Life Technologies Inc., Foster City, Calif., USA) or an Illumina custom genotyping platform [22]. Eight SNPs, of which two were genotyped with TaqMan assays, were selected based on r2 < 0.8 and minor allele frequency of ≥0.2 as previously described [17]. Hardy-Weinberg equilibrium and linkage disequilibrium were assessed using Haploview version 4 [23]. We conducted logistic regression with suicide history (yes/ no) as the dependent variable and the genotypes as predictive factor. We also conducted a linear regression analysis with suicide specifier scores as the dependent variable and genotypes as predictive factor (Statistical Package for the Social Sciences version 15). Allele and haplotype analyses were carried out in a sliding two-window approach (UNPHASED version 3.1.5) [24]. We included the following covariates in the model: age when recruited, sex, and history of alcohol abuse or dependence. We also analyzed individuals with history of alcohol abuse or dependence separately from those without history of alcohol use disorder.
Results
Our sample (n = 197, of which 58 have had a prior history of at least one suicide attempt) was recruited at the Centre for Addiction and Mental Health. It consisted of unrelated chronic psychiatric patients (70% males) who satisfied the diagnostic criteria for schizophrenia (n = 193) or schizoaffective (n = 4) disorder based on the Structured Clinical Interview for DSM-IV (SCID-I) [18–20] with an average age of 37.3 ± 10.4 years. We excluded patients with history of major neurological disorders, serious substance use disorder, and head injury with significant loss of consciousness. All the patients had to have European ancestry (determined by selfreported ethnicity of grandparents) to minimize potential heterogeneity. Suicidal behaviour (n = 193) was assessed during the interview, where suicide specifier was scored as follows: 0 as being nonsuicidal, 1 as having previous thoughts of one’s own death, 2 as having prior history of suicidal ideation, 3 as having planned suicide(s), 4 as having attempted suicide(s), and 5 as having attempted violent suicide(s). Information on history of alcohol abuse or dependence was available for 159 patients of which 41 had a history of alcohol dependence or abuse. Our sample has over 80% power to detect an odds ratio of 2.05 (minor allele frequency =
The genotypes of the eight tested SNPs did not deviate significantly from Hardy-Weinberg equilibrium (p > 0.05). Our analysis of the eight SNPs with history of suicide attempt using logistic regression and suicide specifier using linear regression did not yield significant findings (table 1; p > 0.05). However, the haplotype window consisting of rs183294 and rs209356 was significantly associated with both variables (history of suicide attempt: p = 0.0075; suicide specifier: p = 0.014; online suppl. table S1, www.karger.com/doi/10.1159000358839). Specifically, compared to other haplotypes, the C-A haplotype was overrepresented in the group of suicide attempters (p = 0.0014, odds ratio = 2.487, 95% confidence interval: 1.41– 4.39) and was associated with higher suicide specifier scores (p = 0.0034, additive value = 0.23, 95% confidence interval: 0.074–0.39). In schizophrenia patients with history of alcohol abuse or dependence, we found the rs209356 GG genotype to be overrepresented in the group of suicide attempters (p = 0.009, odds ratio = 5.20, 95% confidence interval: 0.98–27.56). We also detected the rs183294-rs209356 haplotype window to be associated with history of suicide attempt (p = 0.0019) and suicide specifier (p = 0.0013),
GABRG2 and Suicidal Behaviour in Schizophrenia
Neuropsychobiology 2014;69:154–158 DOI: 10.1159/000358839
Methods
155
Table 1. Results from association analysis of GABRG2 SNPs with suicidal behaviour in our schizophrenia sample of European ancestry
SNP
Genotype
Cases Controls
Suicide specifier
Allele
Cases
Controls
GABRG2_rs183294
TT TC CC p
5 18 24
14 55 41 0.16
2.13 ± 1.77 1.44 ± 1.73 2.21 ± 1.71 0.16
T
28
83
C
66
137 0.161
GG GA AA p
6 24 17
18 67 27 0.153
1.96 ± 1.73 1.64 ± 1.77 2.04 ± 1.74 0.233
G
36
103
A
58
121 0.191
CC CG GG p
10 22 13
18 60 30 0.778
1.89 ± 1.77 1.68 ± 1.79 2.00 ± 1.70 0.843
C
42
96
G
48
120 0.786
TT TC CC p
4 19 22
9 41 58 0.741
1.86 ± 1.92 1.93 ± 1.82 1.71 ± 1.71 0.864
T
27
59
C
63
157 0.753
AA AG GG p
7 25 13
16 49 43 0.314
2.00 ± 1.73 1.86 ± 1.85 1.66 ± 1.67 0.562
A
39
81
G
51
135 0.321
TT TG GG p
25 16 4
57 41 10 0.68
1.71 ± 1.79 1.88 ± 1.70 2.00 ± 1.94 0.933
T
66
155
G
24
61 0.664
AA AG GG p
15 22 10
37 50 24 0.97
1.62 ± 1.79 1.90 ± 1.67 1.98 ± 1.90 0.589
A
52
124
G
42
98 0.97
AA AG GG p
2 14 29
7 34 67 0.566
1.82 ± 1.99 1.88 ± 1.76 1.76 ± 1.75 0.584
A
18
48
G
72
168 0.536
GABRG2_rs209356
GABRG2_rs209357
GABRG2_rs211037
GABRG2_rs365054
GABRG2_rs2422106
GABRG2_rs211013
GABRG2_rs647625
Suicide specifier
0.096 (–0.039, 0.230) 0.162
0.071 (–0.057, 0.200) 0.276
0.012 (–0.117, 0.142) 0.850
0.0136 (–0.130, 0.157) 0.852
–0.039 (–0.171, 0.092) 0.559
0.006 (–0.137, 0.149) 0.937
0.037 (–0.090, 0.164) 0.567
0.048 (–0.110, 0.206) 0.551
Values are shown as numbers, mean ± SD or estimated additive values (95% confidence interval). p values for genotype test for suicide attempter/nonattempter status from logistic regression, p values for genotype test for suicide specifier from linear regression, p values for allele test for suicide attempter/nonattempter status from UNPHASED, and p values for allele test for suicide specifier from UNPHASED.
with the C-A haplotype being overrepresented in suicide attempters (haplotype-specific p = 0.00039, odds ratio = 7.98, 95% confidence interval: 2.30–27.69) and associated with higher suicide specifier scores (haplotype-specific p = 0.00032, additive value = 0.62, 95% confidence interval: 0.25–0.99). We did not find significant associations in schizophrenia patients without history of alcohol abuse or dependence. 156
Neuropsychobiology 2014;69:154–158 DOI: 10.1159/000358839
Discussion
This is, to our knowledge, the first study to examine SNPs across the GABRG2 gene for possible association with suicidal behaviour. We report here an association between the haplotype window consisting of rs183294 and rs209356 in the 5′ region of GABRG2 and history of suicide attempt as well as suicide specifier scores. When Zai /Zai /Tiwari /Manchia /de Luca / Shaikh /Strauss /Kennedy
we analyzed available expression and genotype data for rs183294 and rs209354 (an SNP highly correlated to rs209356) on BrainCloud [25], we did not find the risk C-A haplotype to be associated with significant changes to prefrontal cortical GABRG2 mRNA expression. However, it is not known whether the presence of this haplotype may change the ratio of γ2L to γ2S [26], whether this haplotype may change the expression of GABRG2 in other brain regions [27], or whether this haplotype may be associated with changes to GABRG2 levels induced by alcohol. GABRG2 may be modulating suicidal behaviour through its regulation of the GABAA receptor, which in turn interacts with other neurotransmitter systems implicated in suicidality. In fact, the GABA system interacts with the serotonin system, and deficiency in gabrg2, in particular, gives rise to anxious and depressive-like behaviour in rodents that can be normalized by serotoninand/or norepinephrine-reuptake inhibitors [28]. This interaction may also involve the hypothalamic-pituitaryadrenal axis, as demonstrated by the observations that vasopressin and corticotrophin release hormone levels increase with a GABAA antagonist [29, reviewed in 30]. Further studies of this neurotransmitter network in suicidal behaviour are needed to clarify these interrelationships. Our findings need to be replicated in larger samples, especially if we are conducting analyses within subgroups. In addition, as GABRG2 resides in a cluster that includes other GABAA receptor genes such as GABRA2,
future work will include exploring other GABAA receptor subunit genes in alcohol use disorder and suicidal behaviour. The role of depressive symptoms may be an important covariate to consider, however, we did not have this phenotype for our sample. In conclusion, our findings suggest a possible role of the GABAA γ2 subunit in suicidal behaviour. These findings encourage further studies and the development of GABA-modulating agents as potential medications for the prevention of suicidal behaviour [31].
Acknowledgments We acknowledge the following funding sources: Canadian Institutes for Health Research (J.L.K., V.d.L., J.B.V.), American Foundation for Suicide Prevention (C.C.Z., V.d.L., J.S.), Eli Lilly Canada (C.C.Z.), Brain and Behavior Research Foundation/ NARSAD (C.C.Z., A.K.T.). The funding sources have no further role in the study design, data collection/analysis/interpretation, or manuscript writing/submission. G.C.Z. is currently in the Clinician-Scientist Program of her psychiatry residency training program at the University of Toronto. We thank the participants of this study.
Disclosure Statement J.L.K. has been a consultant to GSK, Sanofi-Aventis, and Dainippon-Sumitomo, and received honoraria from Eli Lilly, Novartis, and Roche. All other authors report no conflicts of interest.
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GABRG2 and Suicidal Behaviour in Schizophrenia
7 Zai CC, de Luca V, Strauss J, Tong RP, Sakinofsky I, Kennedy JL: Genetic factors and suicidal behavior; in Dwivedi Y (ed): The Neurobiological Basis of Suicide. Boca Raton, Taylor & Francis/CRC Press, 2012. 8 Qi ZH, Song M, Wallace MJ, Wang D, Newton PM, McMahon T, Messing RO: Protein kinase C epsilon regulates gamma-aminobutyrate type A receptor sensitivity to ethanol and benzodiazepines through phosphorylation of gamma2 subunits. J Biol Chem 2007; 282:33052–33063. 9 Wafford KA, Burnett DM, Leidenheimer NJ, Burt DR, Wang JB, Kofuji P, Sikela JM: Ethanol sensitivity of the GABAA receptor expressed in Xenopus oocytes requires 8 amino acids contained in the gamma 2L subunit. Neuron 1991;7:27–33. 10 Quinlan JJ, Firestone LL, Homanics GE: Mice lacking the long splice variant of the gamma 2 subunit of the GABA(A) receptor are more sensitive to benzodiazepines. Pharmacol Biochem Behav 2000;66:371–374.
11 Boileau AJ, Pearce RA, Czajkowski C: The short splice variant of the gamma 2 subunit acts as an external modulator of GABA(A) receptor function. J Neurosci 2010; 30: 4895– 4903. 12 Chandra D, Korpi ER, Miralles CP, De Blas AL, Homanics GE: GABAA receptor gamma 2 subunit knockdown mice have enhanced anxiety-like behavior but unaltered hypnotic response to benzodiazepines. BMC Neurosci 2005;6:30. 13 Crestani F, Lorez M, Baer K, Essrich C, Benke D, Laurent JP, Mohler H: Decreased GABAAreceptor clustering results in enhanced anxiety and a bias for threat cues. Nat Neurosci 1999;2:833–839. 14 ten Have M, de Graaf R, van Dorsselaer S, Verdurmen J, van ‘t Land H, Vollebergh W, Beekman A: Incidence and course of suicidal ideation and suicide attempts in the general population. Can J Psychiatry 2009;54:824– 833.
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27 Valerio A, Tinti C, Spano P, Memo M: Rat pituitary cells selectively express mRNA encoding the short isoform of the y2 GABAA receptor subunit. Brain Res Mol Brain Res 1992;13:145–150. 28 Shen Q, Fuchs T, Sahir N, Luscher B: GABAergic control of critical developmental periods for anxiety- and depression-related behavior in mice. PLoS One 2012;7:e47441. 29 Cole RL, Sawchenko PE: Neurotransmitter regulation of cellular activation and neuropeptide gene expression in the paraventricular nucleus of the hypothalamus. J Neurosci 2002;22:959–69. 30 Anisman H, Merali Z, Poulter MO: GammaAminobutyric Acid Involvement in Depressive Illness Interactions with CorticotropinReleasing Hormone and Serotonin; in Dwivedi Y (ed): Frontiers in Neuroscience: The Neurobiological Basis of Suicide, chapter 4. Boca Raton, CRC Press, 2012. 31 Mann JJ, Currier D: Medication in Suicide Prevention Insights from Neurobiology of Suicidal Behavior; in Dwivedi Y (ed): Frontiers in Neuroscience: The Neurobiological Basis of Suicide, chapter 21. Boca Raton, CRC Press, 2012.
Zai /Zai /Tiwari /Manchia /de Luca / Shaikh /Strauss /Kennedy
Copyright: S. Karger AG, Basel 2014. Reproduced with the permission of S. Karger AG, Basel. Further reproduction or distribution (electronic or otherwise) is prohibited without permission from the copyright holder.
Received: April 29, 2013 Accepted after revision: January 20, 2014 Published online: April 26, 2014
Association Study of GABRG2 Polymorphisms with Suicidal Behaviour in Schizophrenia Patients with Alcohol Use Disorder Clement C. Zai a, b Gwyneth C. Zai a–c Arun K. Tiwari a Mirko Manchia d, e, f Vincenzo de Luca a, b Sajid A. Shaikh a John Strauss a James L. Kennedy a–c a
Neurogenetics Section, Neuroscience Research Department, Centre for Addiction and Mental Health, and Department of Psychiatry, and c Institute of Medical Science, University of Toronto, Toronto, Ont., and d Departments of Psychiatry and e Pharmacology, Dalhousie University, Halifax, N.S., Canada; f Department of Public Health, Clinical and Molecular Medicine, University of Cagliari, Cagliari, Italy b
Key Words Schizophrenia · Suicide specifier · Alcohol dependence · GABAA γ2 GABRG2 · Genetics
Abstract Background: Schizophrenia is a severe neuropsychiatric disorder where the role of γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, has been implicated in its aetiopathophysiology. Several genes coding for GABAA subunits, including the GABRG2 gene that encodes the γ2 subunit, are clustered at 5q31–q35, a chromosomal region that is associated with schizophrenia in genome scan studies. We recently reported GABRG2 to be associated with schizophrenia in our case-control and family samples. Methods: We tested eight single-nucleotide polymorphisms spanning the GABRG2 gene for an association with suicidal behaviour in our schizophrenia sample of European ancestry (n = 197), taking into account history of alcohol abuse or dependence. Results: We found the haplotypes of the rs183294 and rs209356 markers to be significantly associated with history of suicide attempt (p < 0.01) as well as suicide specifier scores (p < 0.05). The association appeared to be originating in patients with a history of alcohol dependence or abuse. Conclusions: Taken together, the results of the present study
© 2014 S. Karger AG, Basel 0302–282X/14/0693–0154$39.50/0 E-Mail [email protected] www.karger.com/nps
suggest that GABRG2 may be involved in suicidal behaviour in schizophrenia patients with alcohol dependence or abuse, but replications are required. These results may help in the discovery of novel treatments for alcoholism and/or prevention of suicide. © 2014 S. Karger AG, Basel
Introduction
Schizophrenia is a severe neuropsychiatric disorder that affects approximately 1% of the general population [1]. Among schizophrenia patients, up to half have attempted suicide [2], and 5% will commit suicide [3], making the prediction and management of suicidal behaviour an imperative endeavour in the treatment of schizophrenia patients [4]. A number of risk factors have been found to increase the risk for suicidality, including comorbid alcohol use disorders and family history [5]. A review of cohort studies of completed suicides reported a 9.79 time higher risk for suicide among individuals with alcohol use disorders than in the general population [6]. Family, adoption, and twin studies support a substantial genetic component of suicidality [reviewed in 7].
Dr. James L. Kennedy Centre for Addiction and Mental Health R31 250 College Street Toronto, ON M5T1R8 (Canada) E-Mail jim.kennedy @ camh.ca
The GABAA receptor γ2 subunit is essential for the benzodiazepine binding at the GABAA receptor and modulates the sensitivity of GABAA receptors to alcohol [8, 9]. The short isoform (γ2S) confers greater sensitivity to benzodiazepine than the long isoform (γ2L) [10], possibly due to the sensitivity of γ2L subunit-containing GABAA to zinc inhibition [11]. Using open-field activity monitoring and elevated plus maze, genetically modified mice with decreased GABRG2 expression exhibited enhanced anxiety-related phenotypes [12, 13]; interestingly, anxiety disorders in humans have been shown to increase the odds of first-onset suicide ideation and attempt [14]. In terms of alcohol dependence, GABRG2 expression is reduced in postmortem hippocampi of alcoholics [15]. Moreover, in depressed suicide victims, the dorsolateral prefrontal cortical mRNA expression of GABRG2 was down-regulated when compared to nonsuicide controls independent of alcohol dependence [16]. These evidences suggest that alcohol may decrease GABRG2 expression, which in turn may increase suicide-related anxiety, making GABRG2 an intriguing target for studying the genetics of alcohol-related suicidal behaviour. We previously reported a possible association between the GABRG2 gene and schizophrenia [17]. Here, we hypothesize that there is an association between GABRG2 and suicidal behaviour in these schizophrenia patients. We also hypothesize an association between GABRG2 and suicidal behaviour in schizophrenia patients with history of alcohol use disorder.
0.20; alpha = 0.05; additive model). In accordance with the Declaration of Helsinki, we obtained voluntary written informed consent from each study participant after the nature of the study was explained to them, and the study was approved by the Institutional Research Ethics Board. DNA extraction and genotyping was carried out as described previously [17]. Briefly, genomic DNA was purified from blood lymphocytes [21]. Nineteen single-nucleotide polymorphisms (SNPs) were genotyped using either TaqMan genotyping assays (ABI Prism® 7000/7500, Life Technologies Inc., Foster City, Calif., USA) or an Illumina custom genotyping platform [22]. Eight SNPs, of which two were genotyped with TaqMan assays, were selected based on r2 < 0.8 and minor allele frequency of ≥0.2 as previously described [17]. Hardy-Weinberg equilibrium and linkage disequilibrium were assessed using Haploview version 4 [23]. We conducted logistic regression with suicide history (yes/ no) as the dependent variable and the genotypes as predictive factor. We also conducted a linear regression analysis with suicide specifier scores as the dependent variable and genotypes as predictive factor (Statistical Package for the Social Sciences version 15). Allele and haplotype analyses were carried out in a sliding two-window approach (UNPHASED version 3.1.5) [24]. We included the following covariates in the model: age when recruited, sex, and history of alcohol abuse or dependence. We also analyzed individuals with history of alcohol abuse or dependence separately from those without history of alcohol use disorder.
Results
Our sample (n = 197, of which 58 have had a prior history of at least one suicide attempt) was recruited at the Centre for Addiction and Mental Health. It consisted of unrelated chronic psychiatric patients (70% males) who satisfied the diagnostic criteria for schizophrenia (n = 193) or schizoaffective (n = 4) disorder based on the Structured Clinical Interview for DSM-IV (SCID-I) [18–20] with an average age of 37.3 ± 10.4 years. We excluded patients with history of major neurological disorders, serious substance use disorder, and head injury with significant loss of consciousness. All the patients had to have European ancestry (determined by selfreported ethnicity of grandparents) to minimize potential heterogeneity. Suicidal behaviour (n = 193) was assessed during the interview, where suicide specifier was scored as follows: 0 as being nonsuicidal, 1 as having previous thoughts of one’s own death, 2 as having prior history of suicidal ideation, 3 as having planned suicide(s), 4 as having attempted suicide(s), and 5 as having attempted violent suicide(s). Information on history of alcohol abuse or dependence was available for 159 patients of which 41 had a history of alcohol dependence or abuse. Our sample has over 80% power to detect an odds ratio of 2.05 (minor allele frequency =
The genotypes of the eight tested SNPs did not deviate significantly from Hardy-Weinberg equilibrium (p > 0.05). Our analysis of the eight SNPs with history of suicide attempt using logistic regression and suicide specifier using linear regression did not yield significant findings (table 1; p > 0.05). However, the haplotype window consisting of rs183294 and rs209356 was significantly associated with both variables (history of suicide attempt: p = 0.0075; suicide specifier: p = 0.014; online suppl. table S1, www.karger.com/doi/10.1159000358839). Specifically, compared to other haplotypes, the C-A haplotype was overrepresented in the group of suicide attempters (p = 0.0014, odds ratio = 2.487, 95% confidence interval: 1.41– 4.39) and was associated with higher suicide specifier scores (p = 0.0034, additive value = 0.23, 95% confidence interval: 0.074–0.39). In schizophrenia patients with history of alcohol abuse or dependence, we found the rs209356 GG genotype to be overrepresented in the group of suicide attempters (p = 0.009, odds ratio = 5.20, 95% confidence interval: 0.98–27.56). We also detected the rs183294-rs209356 haplotype window to be associated with history of suicide attempt (p = 0.0019) and suicide specifier (p = 0.0013),
GABRG2 and Suicidal Behaviour in Schizophrenia
Neuropsychobiology 2014;69:154–158 DOI: 10.1159/000358839
Methods
155
Table 1. Results from association analysis of GABRG2 SNPs with suicidal behaviour in our schizophrenia sample of European ancestry
SNP
Genotype
Cases Controls
Suicide specifier
Allele
Cases
Controls
GABRG2_rs183294
TT TC CC p
5 18 24
14 55 41 0.16
2.13 ± 1.77 1.44 ± 1.73 2.21 ± 1.71 0.16
T
28
83
C
66
137 0.161
GG GA AA p
6 24 17
18 67 27 0.153
1.96 ± 1.73 1.64 ± 1.77 2.04 ± 1.74 0.233
G
36
103
A
58
121 0.191
CC CG GG p
10 22 13
18 60 30 0.778
1.89 ± 1.77 1.68 ± 1.79 2.00 ± 1.70 0.843
C
42
96
G
48
120 0.786
TT TC CC p
4 19 22
9 41 58 0.741
1.86 ± 1.92 1.93 ± 1.82 1.71 ± 1.71 0.864
T
27
59
C
63
157 0.753
AA AG GG p
7 25 13
16 49 43 0.314
2.00 ± 1.73 1.86 ± 1.85 1.66 ± 1.67 0.562
A
39
81
G
51
135 0.321
TT TG GG p
25 16 4
57 41 10 0.68
1.71 ± 1.79 1.88 ± 1.70 2.00 ± 1.94 0.933
T
66
155
G
24
61 0.664
AA AG GG p
15 22 10
37 50 24 0.97
1.62 ± 1.79 1.90 ± 1.67 1.98 ± 1.90 0.589
A
52
124
G
42
98 0.97
AA AG GG p
2 14 29
7 34 67 0.566
1.82 ± 1.99 1.88 ± 1.76 1.76 ± 1.75 0.584
A
18
48
G
72
168 0.536
GABRG2_rs209356
GABRG2_rs209357
GABRG2_rs211037
GABRG2_rs365054
GABRG2_rs2422106
GABRG2_rs211013
GABRG2_rs647625
Suicide specifier
0.096 (–0.039, 0.230) 0.162
0.071 (–0.057, 0.200) 0.276
0.012 (–0.117, 0.142) 0.850
0.0136 (–0.130, 0.157) 0.852
–0.039 (–0.171, 0.092) 0.559
0.006 (–0.137, 0.149) 0.937
0.037 (–0.090, 0.164) 0.567
0.048 (–0.110, 0.206) 0.551
Values are shown as numbers, mean ± SD or estimated additive values (95% confidence interval). p values for genotype test for suicide attempter/nonattempter status from logistic regression, p values for genotype test for suicide specifier from linear regression, p values for allele test for suicide attempter/nonattempter status from UNPHASED, and p values for allele test for suicide specifier from UNPHASED.
with the C-A haplotype being overrepresented in suicide attempters (haplotype-specific p = 0.00039, odds ratio = 7.98, 95% confidence interval: 2.30–27.69) and associated with higher suicide specifier scores (haplotype-specific p = 0.00032, additive value = 0.62, 95% confidence interval: 0.25–0.99). We did not find significant associations in schizophrenia patients without history of alcohol abuse or dependence. 156
Neuropsychobiology 2014;69:154–158 DOI: 10.1159/000358839
Discussion
This is, to our knowledge, the first study to examine SNPs across the GABRG2 gene for possible association with suicidal behaviour. We report here an association between the haplotype window consisting of rs183294 and rs209356 in the 5′ region of GABRG2 and history of suicide attempt as well as suicide specifier scores. When Zai /Zai /Tiwari /Manchia /de Luca / Shaikh /Strauss /Kennedy
we analyzed available expression and genotype data for rs183294 and rs209354 (an SNP highly correlated to rs209356) on BrainCloud [25], we did not find the risk C-A haplotype to be associated with significant changes to prefrontal cortical GABRG2 mRNA expression. However, it is not known whether the presence of this haplotype may change the ratio of γ2L to γ2S [26], whether this haplotype may change the expression of GABRG2 in other brain regions [27], or whether this haplotype may be associated with changes to GABRG2 levels induced by alcohol. GABRG2 may be modulating suicidal behaviour through its regulation of the GABAA receptor, which in turn interacts with other neurotransmitter systems implicated in suicidality. In fact, the GABA system interacts with the serotonin system, and deficiency in gabrg2, in particular, gives rise to anxious and depressive-like behaviour in rodents that can be normalized by serotoninand/or norepinephrine-reuptake inhibitors [28]. This interaction may also involve the hypothalamic-pituitaryadrenal axis, as demonstrated by the observations that vasopressin and corticotrophin release hormone levels increase with a GABAA antagonist [29, reviewed in 30]. Further studies of this neurotransmitter network in suicidal behaviour are needed to clarify these interrelationships. Our findings need to be replicated in larger samples, especially if we are conducting analyses within subgroups. In addition, as GABRG2 resides in a cluster that includes other GABAA receptor genes such as GABRA2,
future work will include exploring other GABAA receptor subunit genes in alcohol use disorder and suicidal behaviour. The role of depressive symptoms may be an important covariate to consider, however, we did not have this phenotype for our sample. In conclusion, our findings suggest a possible role of the GABAA γ2 subunit in suicidal behaviour. These findings encourage further studies and the development of GABA-modulating agents as potential medications for the prevention of suicidal behaviour [31].
Acknowledgments We acknowledge the following funding sources: Canadian Institutes for Health Research (J.L.K., V.d.L., J.B.V.), American Foundation for Suicide Prevention (C.C.Z., V.d.L., J.S.), Eli Lilly Canada (C.C.Z.), Brain and Behavior Research Foundation/ NARSAD (C.C.Z., A.K.T.). The funding sources have no further role in the study design, data collection/analysis/interpretation, or manuscript writing/submission. G.C.Z. is currently in the Clinician-Scientist Program of her psychiatry residency training program at the University of Toronto. We thank the participants of this study.
Disclosure Statement J.L.K. has been a consultant to GSK, Sanofi-Aventis, and Dainippon-Sumitomo, and received honoraria from Eli Lilly, Novartis, and Roche. All other authors report no conflicts of interest.
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