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The role of BDNF genetic polymorphisms in bipolar disorder with psychiatric comorbidities
Journal of Affective Disorders 131 (2011) 307–311
Contents lists available at ScienceDirect
Journal of Affective Disorders j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j a d
Research report
The role of BDNF genetic polymorphisms in bipolar disorder with psychiatric comorbidities Fernando Silva Neves a,d, Leandro Malloy-Diniz a, Marco Aurélio Romano-Silva a,c,d, Simone Becho Campos a, Débora Marques Miranda a, Luiz De Marco a, Patrícia Gomes Figueira a, Marie-Odile Krebs b, Humberto Correa a,b,c,d,⁎ a b c d
Neuroscience Program-UFMG, Brazil Paris Descartes University, INSERM, U894 Centre of Psychiatry and Neuroscience, Sainte-Anne Hospital, Paris, France Pharmacology and Molecular Biochemistry Program-UFMG, Brazil Department of Mental Health, Faculty of Medicine, Federal University of Minas Gerais-UFMG, Brazil
a r t i c l e
i n f o
Article history: Received 22 May 2010 Received in revised form 2 November 2010 Accepted 24 November 2010 Available online 16 December 2010 Keywords: Bipolar disorder Psychiatric comorbidity BDNF Polymorphism Association study
a b s t r a c t Background: Bipolar disorder (BD) is a complex disorder where genetic factors play a major role in its etiology. Probably, no other axis I diagnosis has a co-morbidity prevalence as high as BD. Since BDNF is involved in different ways in various psychiatric disorders we hypothesized that its genetic polymorphisms could be associated with the co-morbidity phenomenon in BD. Methods: We studied 320 subjects (160 BD patients and 160 healthy controls). Genotyping was performed using made-to-order TaqMan genotyping assays (rs4923463, rs6265, rs2049045, and rs7103411). Statistical analyses were performed using UNPHASED version 3.0.12 and Haploview 4.1. Results: No genotypic, allelic or haplotype differences were found between bipolar patients and healthy controls. Concerning exclusively the rs4923463 (G/G) there was a significant association with alcoholism (p= 0.009), smoking (p= 0.006) and violent suicide attempt (p= 0.03). We further found that the G-G haplotype (rs4923463–rs2049045) (adjusted p = 0.029) and the G-T haplotype (rs4923463–rs7103411) (adjusted p = 0.029) were significantly more frequent in the group with alcoholism co-morbidity when compared with the group without this co-morbidity. Limitations: Sample size and retrospective assessment of suicide behavior and psychiatric comorbidities. Conclusions: The results obtained in our study indicate that BDNF variants may confer susceptibility to additional psychiatric diagnosis in BD. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Bipolar disorder (BD) has a high prevalence of psychiatric comorbidity (Kessler et al., 1997) which contributes with a poor outcome including lack of treatment response, rapid
⁎ Corresponding author. Department of Mental Health, Faculty of Medicine, Federal University of Minas Gerais, Alfredo Balena Avenue, 190, CEP 30130-100, Belo Horizonte-MG, Brazil. Tel.: + 55 31 3248 9785. E-mail address: [email protected] (H. Correa). 0165-0327/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jad.2010.11.022
cycling periods and premature death by suicide (McElroy et al., 2001; Schiavone et al., 2004; Simon et al., 2004; Kessler et al., 2005; Ostacher et al., 2006; Neves et al., 2009). Moreover, genetic epidemiological studies in families of BD probands have demonstrated a higher prevalence of psychiatric co-morbidities in their relatives, such as panic disorder, schizophrenia related disorders, alcoholism and suicidal behavior (Schulze et al., 2006; Goldstein and Levitt, 2007; Palomo et al., 2007; Merikangas et al., 2008), suggesting that the same genetic factors could confer predisposition for BD and other psychiatric disorders (Kendler, 2005).
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F.S. Neves et al. / Journal of Affective Disorders 131 (2011) 307–311
The Brain Derived Neurotrophic Factor (BDNF) gene which has a particular polymorphism, the Val66Met (rs6265), that impairs BDNF trafficking and secretion, has been extensively studied (Martinowich et al., 2007). A meta-analysis did not find association with BD (Kanazawa et al., 2007) but another one found a modest association (Fan and Skalar, 2008). However, some studies have examined the association between the Val66Met polymorphism in BD patients with rapid cycling (Müller et al., 2006; Green et al., 2006) or early onset mania (Tang et al., 2008) suggesting that this polymorphism is associated with some BD characteristics but not with BD diagnosis. This data could, at least partially, explain the previous opposite results. This polymorphism has also been studied in many other diverse psychiatric diagnosis such as adult attention/hyperactivity disorder, schizophrenia, anxiety disorders, major depression, post-partum depression, substance related disorders, and eating disorder, with many positive and also negative findings (Figueira et al., 2010; Bulgin et al., 2008; Lanktree et al., 2008; Rybakowski, 2008; Gratacòs et al., 2007). This myriad of associations may be in part explained by the fact that BDNF has a diffuse brain distribution being highly expressed in key cerebral structures related to psychiatric disorders such as the hippocampus, amygdala, pre-frontal cortex and hypothalamus (Pruunsild et al., 2007) and most likely plays a role in many different conditions and symptoms. In this study we aimed to assess the association between four BDNF SNPs located at the 3′ end of the BDNF gene, including the Val66Met, and BD diagnosis and co-morbidities. We hypothesize that since BDNF is implicated in many psychiatric disorders and symptoms it could help to explain co-morbidities in BD. 2. Methods We studied 160 unrelated bipolar I patients diagnosed according to the DSM-IV criteria based on a structured
interview (MINI-PLUS) (Amorim, 2000). Diagnosis of borderline personality disorder was performed using the SCID for Axis II personality disorders (First et al., 1995). Patients were euthymic as determined by the Brazilian adaptation of the Beck Depression Inventory (BDI) (Gorenstein and Andrade, 1996) and the Young Mania Rating Scale (YMRS) (Vilela et al., 2005). Healthy controls were 152 subjects all free of an axis I DSM-IV diagnosis who were also assessed by MINI-PLUS. All subjects were self-assigned Caucasian. The study was approved by the local ethics committee and all participants signed an informed consent after a full explanation of the study. Suicide attempt history was assessed using a semistructured interview in addition to a review of medical records as previously described (Campi-Azevedo et al., 2003). Blood sample was collected and DNA was obtained using standard protocol. Genotyping was performed using madeto-order TaqMan genotyping assays (rs4923463, rs6265, rs2049045, and rs7103411) listed in order of chromosomal position (Applied Biosystems, Foster City, CA). Comparisons between categorical variables were compared using chi-square or fisher's test. Continuous variables were compared using Student's t-test. Genotype and haplotype associations and 1000 permutation tests were performed using the UNPHASED software package version 3.0.12 (www. mrcbsu.cam.ac.uk/personal/frank/software/unphased/). The Hardy–Weinberg equilibrium was calculated using Haploview 4.1 (www.broad.mit.edu/mpg/haploview/). Results were considered significant when p ≤ 0.05. 3. Results Patient and control groups did not differ in terms of age or gender. All SNPs were in the Hardy–Weinberg equilibrium in both groups. No significant differences in genotypic, allelic or haplotype were found between BD patients and healthy controls (Table 1).
Table 1 Allele and genotype frequencies of the BDNF gene polymorphisms. SNP
rs4923463
rs6265
rs2049045
rs7103411
Allele and genotype G A GG GA AA T C TT TC CC G C GG GC CC T C TT TC CC
Frequency BD patients
Healthy controls
0.1531 0.8469 0.0312 0.2437 0.7250 0.1156 0.8844 0.0125 0.2062 0.7813 0.8781 0.1219 0.7688 0.2187 0.0125 0.8375 0.1625 0.7063 0.2625 0.0312
0.1719 0.8281 0.0500 0.2437 0.7063 0.0981 0.9019 0.0316 0.1329 0.8354 0.8662 0.1338 0.7643 0.2038 0.0318 0.8386 0.1614 0.7089 0.2595 0.0316
X2 (df)
p
OR (95% CI)
0.413
0.520
0.737
0.691
0.512
0.474
4.195
0.123
0.2008
0.654
1.471
0.479
0.0014
0.969
0.004
0.998
1.00 1.14 1.00 1.60 1.64 1.00 0.83 1.00 3.93 2.58 1.00 0.89 1.00 1.06 0.35 1.00 1.08 1.00 1.01 0.99
(ref.) (0.75–1.74) (ref.) (0.48–5.30) (0.52–5.17) (ref.) (0.50–1.37) (ref.) (0.69–22.1) (0.45–12.4) (ref.) (0.56–1.43) (ref.) (0.62–1.83) (0.07–2.05) (ref.) (0.66–1.53) (ref.) (0.61–1.68) (0.27–3.51)
F.S. Neves et al. / Journal of Affective Disorders 131 (2011) 307–311
Analysis of the rs4923463 showed an association between the frequency of the genotype allele GG and the presence of smoking (p = 0.006) and alcoholism (p = 0.009) in patients with bipolar disorder. We also found an association between genotype allele GA in rs4923463 and violent suicide attempt (p = 0.03) in patients with bipolar disorder (Table 2). The other studied polymorphisms were not associated with any co-morbidity including the rs6265 (Val66Met). The G-G haplotype (rs4923463–rs2049045) (adjusted p = 0.029) and the G-T haplotype (rs4923463–rs7103411) (adjusted p = 0.029) were significantly more frequent in the group that had alcoholism co-morbidity when compared with the group without alcoholism co-morbidity. 4. Discussion In this study no associations were found between BD patients and healthy controls. Our results show that one polymorphism, the rs4923463, was associated with smoking, alcoholism and violent suicide attempt in bipolar patients, even after adjusted for multiple comparisons. No associations were observed with the other polymorphisms including the extensively studied Val66Met. The G-G haplotype (rs4923463– rs2049045) and the G-T haplotype (rs4923463–rs7103411) were significantly more frequent in the group that had alcoholism co-morbidity when compared with the group without alcoholism co-morbidity. These results remained after permutation tests.
309
To date few studies examined the rs4923463 polymorphism (Squassina et al., 2010; Lencz et al., 2009; Lanktree et al., 2008; Bulgin et al., 2008; Zai et al., 2007) and to our knowledge our study is the first one assessing bipolar disorder diagnosis and its co-morbidities. The four studied polymorphisms were chosen within and surrounding the 3′ end of BDNF, including the functional Val66Met (rs6265) polymorphism. The rs4923463 is in linkage disequilibrium and is adjacent to the functional polymorphism Val66Met (Lanktree et al., 2008). The results obtained in our study indicate that some BDNF variants may confer susceptibility to an additional psychiatric diagnosis in BD. Suicidal behavior is not considered a psychiatric diagnosis, but it has been suggested that it runs in families independent of psychiatric diagnoses (Brent et al., 1996). However, a recent study showed that the lifetime prevalence of BD was significantly greater among first-degree relatives of suicide than non-suicide probands and the prevalence of BD in families was associated with an increased risk of developing mood disorder and subsequently committing or attempting suicide (Cavazzoni et al., 2007). Smoking is also not considered a co-morbidity. Nevertheless in view of the higher smoking prevalence in BD as compared with the general population (Diaz et al., 2009), the association between smoking and suicidal behavior (Ostacher et al., 2009; Neves and Correa, 2007) as well with a worse outcome in BD (Ostacher et al., 2006) we thought it would be important to include this variable in our study.
Table 2 Association of BDNF polymorphism rs4923463 with lifetime history of suicide behavior and psychiatric co-morbidities. Co-morbidities N = 160
Genotype
Smoking (n = 83)
GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA
Alcoholism (n = 52)
Other drug addiction (n = 26)
Panic disorder (n = 32)
Generalized anxiety disorder (n = 74)
Borderline (n = 34)
Psychotic episodes (n = 31)
Suicide attempt (n = 74)
Violent suicide attempt (n = 31)
a b
X2 (df)
rs4923463
GG, genotype polymorphic. Adjusted p-value from the 1000 permutation test.
a
Patients with co-morbidity
Patients without co-morbidity
5 20 58 5 11 36 3 5 18 3 5 24 4 14 56 3 8 23 1 7 23 4 21 49 3 4 24
0 19 58 0 28 80 2 34 98 2 34 92 1 25 60 2 31 93 4 32 93 1 18 67 1 17 25
p (adjusted p) b
6.73 (2)
0.0034 (0.0060)
11.69 (2)
0.0028 (0.0099)
5.28 (2)
0.0711 (0.0869)
5.25 (2)
0.0724 (0.0809)
4.31 (2)
0.1159 (0.1339)
3.67 (2)
0.1593 (0.2228)
0.006 (2)
0.9665 (0.9201)
4.06 (2)
0.1312 (0.1389)
7.77 (2)
0.0205 (0.0389)
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Our data shows that only five patients carried the rs4923463 polymorphism in GG homozygosis, a result that could infer a low statistical power. Yet significant differences were obtained in sub-comparisons with smaller numbers but not in the largest two groups (bipolar versus health controls). This contrast suggests that Type I error is not a likely explanation for our results. Population stratification is a potential causation for type II error in any case–control study. Here, we studied a sample of only self-assigned Caucasian Brazilians but as previously described, physical assessment is not a good predictor of genomic ancestry in Brazil (Parra et al., 2003) and ethnical bias stratification cannot be reliably excluded. In conclusion, we were able to show an association between a BDNF polymorphism and some co-morbidities (smoking, alcoholism, and violent suicide attempt) in BD but not with a BD diagnosis itself. This data shows that taking into account co-morbidities is of pivotal importance when performing association studies between BD and BDNF polymorphisms. Further studies with a larger sample are required to corroborate our results. Role of funding source This work received funding support from FAPEMIG and CNPq, which had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication. Conflict of interest All authors declare that there are no conflicts of interest in connection with this submitted manuscript.
Acknowledgements This study was supported by the Instituto Nacional de Ciência e Tecnologia de Medicina Molecular (INCT/CNPq/ MCT, FAPEMIG) and CNPq grant #473674/2009-2. Professor Humberto Correa is supported by CNPq's postdoctoral fellowship program. References Amorim, P., 2000. Mini International Neuropsychiatric Interview (MINI): validation of a short structured diagnostic psychiatric interview. Rev. Bras. Psiquiatria 22, 106–115. Brent, D.A., Bridge, J., Johnson, B.A., Connolly, J., 1996. Suicidal behavior runs in families. A controlled family study of adolescent suicide victims. Arch. Gen. Psychiatry 53 (12), 1145–1152. Bulgin, N.L., Strauss, J.S., King, N.A., Shaikh, S.A., George, C.J., Fox, N.A., Barr, C.L., Kovacs, M., Kennedy, J.L., 2008. Association study of theta EEG asymmetry and brain-derived neurotrophic factor gene variants in childhood-onset mood disorder. Neuromolecular Med. 10 (4), 343–355. Campi-Azevedo, A.C., Boson, W., De Marco, L., Romano-Silva, M.A., Correa, H., 2003. Association of the serotonin transporter promoter polymorphism with suicidal behavior. Mol. Psychiatry 8 (11), 899–900. Cavazzoni, P., Grof, P., Duffy, A., Grof, E., Müller-Oerlinghausen, B., Berghöfer, A., Ahrens, B., Zvolsky, P., Robertson, C., Davis, A., Hajek, T., Alda, M., 2007. Heterogeneity of the risk of suicidal behavior in bipolar-spectrum disorders. Bipolar Disord. 9 (4), 377–385. Diaz, F.J., James, D., Botts, S., Maw, L., Susce, M.T., de Leon, J., 2009. Tobacco smoking in bipolar patients: a comparison of the general population, schizophrenia, and major depression. Bipolar Disord. 11 (2), 145–165. Fan, J., Skalar, P., 2008. Genetics of bipolar disorder: focus on BDNF Val66Met polymorphism. Novartis Found. Symp. 289, 60–72 (discussion, 72-3, 87-93). Figueira, P., Malloy-Diniz, L., Campos, S.B., Miranda, D.M., Romano-Silva, M.A., De Marco, L., Neves, F.S., Correa, H., 2010. An association study between the Val66Met polymorphism of the BDNF gene and postpartum depression. Arch. Womens Ment. Health 13 (3), 285–289.
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Contents lists available at ScienceDirect
Journal of Affective Disorders j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j a d
Research report
The role of BDNF genetic polymorphisms in bipolar disorder with psychiatric comorbidities Fernando Silva Neves a,d, Leandro Malloy-Diniz a, Marco Aurélio Romano-Silva a,c,d, Simone Becho Campos a, Débora Marques Miranda a, Luiz De Marco a, Patrícia Gomes Figueira a, Marie-Odile Krebs b, Humberto Correa a,b,c,d,⁎ a b c d
Neuroscience Program-UFMG, Brazil Paris Descartes University, INSERM, U894 Centre of Psychiatry and Neuroscience, Sainte-Anne Hospital, Paris, France Pharmacology and Molecular Biochemistry Program-UFMG, Brazil Department of Mental Health, Faculty of Medicine, Federal University of Minas Gerais-UFMG, Brazil
a r t i c l e
i n f o
Article history: Received 22 May 2010 Received in revised form 2 November 2010 Accepted 24 November 2010 Available online 16 December 2010 Keywords: Bipolar disorder Psychiatric comorbidity BDNF Polymorphism Association study
a b s t r a c t Background: Bipolar disorder (BD) is a complex disorder where genetic factors play a major role in its etiology. Probably, no other axis I diagnosis has a co-morbidity prevalence as high as BD. Since BDNF is involved in different ways in various psychiatric disorders we hypothesized that its genetic polymorphisms could be associated with the co-morbidity phenomenon in BD. Methods: We studied 320 subjects (160 BD patients and 160 healthy controls). Genotyping was performed using made-to-order TaqMan genotyping assays (rs4923463, rs6265, rs2049045, and rs7103411). Statistical analyses were performed using UNPHASED version 3.0.12 and Haploview 4.1. Results: No genotypic, allelic or haplotype differences were found between bipolar patients and healthy controls. Concerning exclusively the rs4923463 (G/G) there was a significant association with alcoholism (p= 0.009), smoking (p= 0.006) and violent suicide attempt (p= 0.03). We further found that the G-G haplotype (rs4923463–rs2049045) (adjusted p = 0.029) and the G-T haplotype (rs4923463–rs7103411) (adjusted p = 0.029) were significantly more frequent in the group with alcoholism co-morbidity when compared with the group without this co-morbidity. Limitations: Sample size and retrospective assessment of suicide behavior and psychiatric comorbidities. Conclusions: The results obtained in our study indicate that BDNF variants may confer susceptibility to additional psychiatric diagnosis in BD. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Bipolar disorder (BD) has a high prevalence of psychiatric comorbidity (Kessler et al., 1997) which contributes with a poor outcome including lack of treatment response, rapid
⁎ Corresponding author. Department of Mental Health, Faculty of Medicine, Federal University of Minas Gerais, Alfredo Balena Avenue, 190, CEP 30130-100, Belo Horizonte-MG, Brazil. Tel.: + 55 31 3248 9785. E-mail address: [email protected] (H. Correa). 0165-0327/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jad.2010.11.022
cycling periods and premature death by suicide (McElroy et al., 2001; Schiavone et al., 2004; Simon et al., 2004; Kessler et al., 2005; Ostacher et al., 2006; Neves et al., 2009). Moreover, genetic epidemiological studies in families of BD probands have demonstrated a higher prevalence of psychiatric co-morbidities in their relatives, such as panic disorder, schizophrenia related disorders, alcoholism and suicidal behavior (Schulze et al., 2006; Goldstein and Levitt, 2007; Palomo et al., 2007; Merikangas et al., 2008), suggesting that the same genetic factors could confer predisposition for BD and other psychiatric disorders (Kendler, 2005).
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F.S. Neves et al. / Journal of Affective Disorders 131 (2011) 307–311
The Brain Derived Neurotrophic Factor (BDNF) gene which has a particular polymorphism, the Val66Met (rs6265), that impairs BDNF trafficking and secretion, has been extensively studied (Martinowich et al., 2007). A meta-analysis did not find association with BD (Kanazawa et al., 2007) but another one found a modest association (Fan and Skalar, 2008). However, some studies have examined the association between the Val66Met polymorphism in BD patients with rapid cycling (Müller et al., 2006; Green et al., 2006) or early onset mania (Tang et al., 2008) suggesting that this polymorphism is associated with some BD characteristics but not with BD diagnosis. This data could, at least partially, explain the previous opposite results. This polymorphism has also been studied in many other diverse psychiatric diagnosis such as adult attention/hyperactivity disorder, schizophrenia, anxiety disorders, major depression, post-partum depression, substance related disorders, and eating disorder, with many positive and also negative findings (Figueira et al., 2010; Bulgin et al., 2008; Lanktree et al., 2008; Rybakowski, 2008; Gratacòs et al., 2007). This myriad of associations may be in part explained by the fact that BDNF has a diffuse brain distribution being highly expressed in key cerebral structures related to psychiatric disorders such as the hippocampus, amygdala, pre-frontal cortex and hypothalamus (Pruunsild et al., 2007) and most likely plays a role in many different conditions and symptoms. In this study we aimed to assess the association between four BDNF SNPs located at the 3′ end of the BDNF gene, including the Val66Met, and BD diagnosis and co-morbidities. We hypothesize that since BDNF is implicated in many psychiatric disorders and symptoms it could help to explain co-morbidities in BD. 2. Methods We studied 160 unrelated bipolar I patients diagnosed according to the DSM-IV criteria based on a structured
interview (MINI-PLUS) (Amorim, 2000). Diagnosis of borderline personality disorder was performed using the SCID for Axis II personality disorders (First et al., 1995). Patients were euthymic as determined by the Brazilian adaptation of the Beck Depression Inventory (BDI) (Gorenstein and Andrade, 1996) and the Young Mania Rating Scale (YMRS) (Vilela et al., 2005). Healthy controls were 152 subjects all free of an axis I DSM-IV diagnosis who were also assessed by MINI-PLUS. All subjects were self-assigned Caucasian. The study was approved by the local ethics committee and all participants signed an informed consent after a full explanation of the study. Suicide attempt history was assessed using a semistructured interview in addition to a review of medical records as previously described (Campi-Azevedo et al., 2003). Blood sample was collected and DNA was obtained using standard protocol. Genotyping was performed using madeto-order TaqMan genotyping assays (rs4923463, rs6265, rs2049045, and rs7103411) listed in order of chromosomal position (Applied Biosystems, Foster City, CA). Comparisons between categorical variables were compared using chi-square or fisher's test. Continuous variables were compared using Student's t-test. Genotype and haplotype associations and 1000 permutation tests were performed using the UNPHASED software package version 3.0.12 (www. mrcbsu.cam.ac.uk/personal/frank/software/unphased/). The Hardy–Weinberg equilibrium was calculated using Haploview 4.1 (www.broad.mit.edu/mpg/haploview/). Results were considered significant when p ≤ 0.05. 3. Results Patient and control groups did not differ in terms of age or gender. All SNPs were in the Hardy–Weinberg equilibrium in both groups. No significant differences in genotypic, allelic or haplotype were found between BD patients and healthy controls (Table 1).
Table 1 Allele and genotype frequencies of the BDNF gene polymorphisms. SNP
rs4923463
rs6265
rs2049045
rs7103411
Allele and genotype G A GG GA AA T C TT TC CC G C GG GC CC T C TT TC CC
Frequency BD patients
Healthy controls
0.1531 0.8469 0.0312 0.2437 0.7250 0.1156 0.8844 0.0125 0.2062 0.7813 0.8781 0.1219 0.7688 0.2187 0.0125 0.8375 0.1625 0.7063 0.2625 0.0312
0.1719 0.8281 0.0500 0.2437 0.7063 0.0981 0.9019 0.0316 0.1329 0.8354 0.8662 0.1338 0.7643 0.2038 0.0318 0.8386 0.1614 0.7089 0.2595 0.0316
X2 (df)
p
OR (95% CI)
0.413
0.520
0.737
0.691
0.512
0.474
4.195
0.123
0.2008
0.654
1.471
0.479
0.0014
0.969
0.004
0.998
1.00 1.14 1.00 1.60 1.64 1.00 0.83 1.00 3.93 2.58 1.00 0.89 1.00 1.06 0.35 1.00 1.08 1.00 1.01 0.99
(ref.) (0.75–1.74) (ref.) (0.48–5.30) (0.52–5.17) (ref.) (0.50–1.37) (ref.) (0.69–22.1) (0.45–12.4) (ref.) (0.56–1.43) (ref.) (0.62–1.83) (0.07–2.05) (ref.) (0.66–1.53) (ref.) (0.61–1.68) (0.27–3.51)
F.S. Neves et al. / Journal of Affective Disorders 131 (2011) 307–311
Analysis of the rs4923463 showed an association between the frequency of the genotype allele GG and the presence of smoking (p = 0.006) and alcoholism (p = 0.009) in patients with bipolar disorder. We also found an association between genotype allele GA in rs4923463 and violent suicide attempt (p = 0.03) in patients with bipolar disorder (Table 2). The other studied polymorphisms were not associated with any co-morbidity including the rs6265 (Val66Met). The G-G haplotype (rs4923463–rs2049045) (adjusted p = 0.029) and the G-T haplotype (rs4923463–rs7103411) (adjusted p = 0.029) were significantly more frequent in the group that had alcoholism co-morbidity when compared with the group without alcoholism co-morbidity. 4. Discussion In this study no associations were found between BD patients and healthy controls. Our results show that one polymorphism, the rs4923463, was associated with smoking, alcoholism and violent suicide attempt in bipolar patients, even after adjusted for multiple comparisons. No associations were observed with the other polymorphisms including the extensively studied Val66Met. The G-G haplotype (rs4923463– rs2049045) and the G-T haplotype (rs4923463–rs7103411) were significantly more frequent in the group that had alcoholism co-morbidity when compared with the group without alcoholism co-morbidity. These results remained after permutation tests.
309
To date few studies examined the rs4923463 polymorphism (Squassina et al., 2010; Lencz et al., 2009; Lanktree et al., 2008; Bulgin et al., 2008; Zai et al., 2007) and to our knowledge our study is the first one assessing bipolar disorder diagnosis and its co-morbidities. The four studied polymorphisms were chosen within and surrounding the 3′ end of BDNF, including the functional Val66Met (rs6265) polymorphism. The rs4923463 is in linkage disequilibrium and is adjacent to the functional polymorphism Val66Met (Lanktree et al., 2008). The results obtained in our study indicate that some BDNF variants may confer susceptibility to an additional psychiatric diagnosis in BD. Suicidal behavior is not considered a psychiatric diagnosis, but it has been suggested that it runs in families independent of psychiatric diagnoses (Brent et al., 1996). However, a recent study showed that the lifetime prevalence of BD was significantly greater among first-degree relatives of suicide than non-suicide probands and the prevalence of BD in families was associated with an increased risk of developing mood disorder and subsequently committing or attempting suicide (Cavazzoni et al., 2007). Smoking is also not considered a co-morbidity. Nevertheless in view of the higher smoking prevalence in BD as compared with the general population (Diaz et al., 2009), the association between smoking and suicidal behavior (Ostacher et al., 2009; Neves and Correa, 2007) as well with a worse outcome in BD (Ostacher et al., 2006) we thought it would be important to include this variable in our study.
Table 2 Association of BDNF polymorphism rs4923463 with lifetime history of suicide behavior and psychiatric co-morbidities. Co-morbidities N = 160
Genotype
Smoking (n = 83)
GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA GG GA AA
Alcoholism (n = 52)
Other drug addiction (n = 26)
Panic disorder (n = 32)
Generalized anxiety disorder (n = 74)
Borderline (n = 34)
Psychotic episodes (n = 31)
Suicide attempt (n = 74)
Violent suicide attempt (n = 31)
a b
X2 (df)
rs4923463
GG, genotype polymorphic. Adjusted p-value from the 1000 permutation test.
a
Patients with co-morbidity
Patients without co-morbidity
5 20 58 5 11 36 3 5 18 3 5 24 4 14 56 3 8 23 1 7 23 4 21 49 3 4 24
0 19 58 0 28 80 2 34 98 2 34 92 1 25 60 2 31 93 4 32 93 1 18 67 1 17 25
p (adjusted p) b
6.73 (2)
0.0034 (0.0060)
11.69 (2)
0.0028 (0.0099)
5.28 (2)
0.0711 (0.0869)
5.25 (2)
0.0724 (0.0809)
4.31 (2)
0.1159 (0.1339)
3.67 (2)
0.1593 (0.2228)
0.006 (2)
0.9665 (0.9201)
4.06 (2)
0.1312 (0.1389)
7.77 (2)
0.0205 (0.0389)
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Our data shows that only five patients carried the rs4923463 polymorphism in GG homozygosis, a result that could infer a low statistical power. Yet significant differences were obtained in sub-comparisons with smaller numbers but not in the largest two groups (bipolar versus health controls). This contrast suggests that Type I error is not a likely explanation for our results. Population stratification is a potential causation for type II error in any case–control study. Here, we studied a sample of only self-assigned Caucasian Brazilians but as previously described, physical assessment is not a good predictor of genomic ancestry in Brazil (Parra et al., 2003) and ethnical bias stratification cannot be reliably excluded. In conclusion, we were able to show an association between a BDNF polymorphism and some co-morbidities (smoking, alcoholism, and violent suicide attempt) in BD but not with a BD diagnosis itself. This data shows that taking into account co-morbidities is of pivotal importance when performing association studies between BD and BDNF polymorphisms. Further studies with a larger sample are required to corroborate our results. Role of funding source This work received funding support from FAPEMIG and CNPq, which had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication. Conflict of interest All authors declare that there are no conflicts of interest in connection with this submitted manuscript.
Acknowledgements This study was supported by the Instituto Nacional de Ciência e Tecnologia de Medicina Molecular (INCT/CNPq/ MCT, FAPEMIG) and CNPq grant #473674/2009-2. Professor Humberto Correa is supported by CNPq's postdoctoral fellowship program. References Amorim, P., 2000. Mini International Neuropsychiatric Interview (MINI): validation of a short structured diagnostic psychiatric interview. Rev. Bras. Psiquiatria 22, 106–115. Brent, D.A., Bridge, J., Johnson, B.A., Connolly, J., 1996. Suicidal behavior runs in families. A controlled family study of adolescent suicide victims. Arch. Gen. Psychiatry 53 (12), 1145–1152. Bulgin, N.L., Strauss, J.S., King, N.A., Shaikh, S.A., George, C.J., Fox, N.A., Barr, C.L., Kovacs, M., Kennedy, J.L., 2008. Association study of theta EEG asymmetry and brain-derived neurotrophic factor gene variants in childhood-onset mood disorder. Neuromolecular Med. 10 (4), 343–355. Campi-Azevedo, A.C., Boson, W., De Marco, L., Romano-Silva, M.A., Correa, H., 2003. Association of the serotonin transporter promoter polymorphism with suicidal behavior. Mol. Psychiatry 8 (11), 899–900. Cavazzoni, P., Grof, P., Duffy, A., Grof, E., Müller-Oerlinghausen, B., Berghöfer, A., Ahrens, B., Zvolsky, P., Robertson, C., Davis, A., Hajek, T., Alda, M., 2007. Heterogeneity of the risk of suicidal behavior in bipolar-spectrum disorders. Bipolar Disord. 9 (4), 377–385. Diaz, F.J., James, D., Botts, S., Maw, L., Susce, M.T., de Leon, J., 2009. Tobacco smoking in bipolar patients: a comparison of the general population, schizophrenia, and major depression. Bipolar Disord. 11 (2), 145–165. Fan, J., Skalar, P., 2008. Genetics of bipolar disorder: focus on BDNF Val66Met polymorphism. Novartis Found. Symp. 289, 60–72 (discussion, 72-3, 87-93). Figueira, P., Malloy-Diniz, L., Campos, S.B., Miranda, D.M., Romano-Silva, M.A., De Marco, L., Neves, F.S., Correa, H., 2010. An association study between the Val66Met polymorphism of the BDNF gene and postpartum depression. Arch. Womens Ment. Health 13 (3), 285–289.
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