Abstract
Background
Human anxiety disorders are complex diseases with relatively unknown etiology. Dysfunction of the GABA system has been implicated in many neuropsychiatric conditions, including anxiety and depressive disorders. In this investigation, we explored four GABA receptor genes for their possible associations with genetic risk for anxiety disorders and depression.
Methods
Our study sample consisted of 589 cases and 539 controls selected from a large population-based twin registry based upon a latent genetic risk factor shared by several anxiety disorders, major depression, and neuroticism. We subjected these to a two-stage protocol, in which all candidate genetic markers were screened for association in stage 1 (N=376), the positive results of which were tested for replication in stage 2 (N=752). We analyzed data from 26 single nucleotide polymorphisms (SNPs) from four GABA receptor genes: GABRA2, GABRA3, GABRA6, and GABRG2.
Results
Of the 26 SNPs genotyped in stage 1, we identified two markers in GABRA3 that met the threshold (p ≤ .1) to be tested in stage 2. Phenotypic associations of these two markers failed to replicate in stage 2.
Conclusions
These findings suggest that common variation in the GABRA2, GABRA3, GABRA6, and GABRG2 genes does not play a major role in liability to anxiety spectrum disorders.
Keywords: anxiety disorder, depressive disorder, neuroticism, genetic association study, GABA-A receptors
Introduction
Anxiety is an adaptive response to an impending danger that is integral to an organism's ability to cope with or avoid a threat. Anxiety disorders (ANX) categorize a grouping of syndromes, including generalized anxiety disorder (GAD), panic disorder, and phobias, where the primary features are abnormal manifestations of anxiety (excessive worry and nervousness, panic attacks, or phobic fears, respectively). These conditions carry a substantial burden of distress and impairment, with lifetime prevalence rates around the world ranging from 5 to 31%, higher than those found for mood or substance use disorders (1). In addition, ANX have high comorbidity rates with each other and with other psychiatric and medical disorders, further compromising the quality of life for sufferers (2).
Much research has been done to understand the genetics of ANX, which carry a heritability of 30% or more (3). Some studies suggest that they share genetic risk factors with depressive disorders and anxious personality traits (4-7). Identifying the specific genes that contribute to the development or maintenance of ANX may offer new insights into the pathophysiology of these disorders and the potential for more effective treatments.
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammalian central nervous system and regulates many physiological and psychological processes. Both animal and human studies associate variations in GABA in the mammalian forebrain with anxiety and depression (8). For example, the GABAA receptor is the site of action for anxiolytic drugs of the benzodiazepine and barbiturate classes. Also, GABA concentrations are increased with selective serotonin reuptake inhibitors (SSRIs), the other major drug class currently used to treat ANX as well as depressive disorders. Thus, GABA is strongly implicated in multiple anxiety-related processes.
Although GABA acts through both GABAA and GABAB receptors to decrease neurotransmission, we will focus on the GABAA subtype due to its robustly demonstrated relationship with anxiety (9). In particular, several studies have documented altered benzodiazepine binding at cerebral GABAA receptors in panic disorder (10;11). Functional GABAA receptors are typically constructed of five subunits drawn from eight different classes (α, β, etc.) (see (12)for a comprehensive overview). Each subunit is encoded by a distinct gene and differentially expressed in the brain, suggesting that mutation in any one gene could, in principle, contribute to the symptoms of anxiety-related disorders. For the current study, we identified a group of GABA receptor genes with prior suggestive association in anxiety-related phenotypes.
The GABAA α2 subunit, primarily expressed in the limbic system, likely mediates the anxiolytic effects of benzodiazepines (13). The gene that encodes this protein, GABRA2, has been associated with alcohol dependence in several studies (14;15). ANX is known to have high comorbidity rates with alcoholism, and one study suggests that part of the association of this gene with alcohol dependence may be accounted for by anxious temperament (16).
Pharmacological studies have specifically implicated the GABAA α3 subunit in anxiety (17). Genetic studies of GABRA3 gene also support its potential role in mood disorder phenotypes. Fiorelli and colleagues (18) provided evidence that mice with global deletion of the GABRA3 gene had more depression-related behaviors. The human GABRA3 gene is located in Xq28 region, an area that has been linked to the genetic transmission of bipolar affective disorder (reviewed in (19)). Genetic association has been reported between the GABRA3 and both bipolar (20) and unipolar (21) mood disorders, although earlier studies failed to detect these associations (22;23).
GABRA6 is involved in several factors contributing to ANX pathology. Sen and colleagues reported an association between a GABRA6 receptor coding polymorphism and neuroticism (24), a personality trait related to both anxiety and depression. Variation in GABRA6 has also been associated with increased production of cortisol and increased blood pressure in response to psychological stress (25).
A broad role of GABRG2 in anxiety-related behavior was demonstrated by Crestani and colleagues, whereby γ2 heterozygous mice with resulting reduced GABAA receptor clustering showed increased fear of a novel environment (26). These mice also exhibited increased reactivity toward naturally aversive stimuli and enhanced responses to trace fear conditioning. We are aware of no prior association analyses of this gene with human internalizing phenotypes.
Due to the tentative evidence available thus far, we sought to further assess the potential genetic association between these four GABA receptor genes and ANX.
Methods and Materials
Subjects
The subjects in this study are participants in the longitudinal population-based Virginia Adult Twin Study of Psychiatric and Substance Use Disorders (VATSPSUD) (27;28). All subjects were Caucasians born in Virginia. Their age (mean ± SD, range) at time of last interview was (37 ± 9 years, 20-58) for men and (36 ± 8 years, 21-62) for women. Approval of the local institutional review board was obtained from all subjects before data collection.
Diagnostic Measures
We obtained lifetime psychiatric diagnoses via face-to-face or telephone structured psychiatric interview based on the Structured Clinical Interview for DSM-III-R (SCID) (29). We used DSM-III-R (30) diagnostic criteria to assess lifetime major depression, modified DSM-III-R criteria for lifetime generalized anxiety disorder and panic disorder (31;32), and an adaptation of DSM-III criteria for phobias (33). Neuroticism was assessed using the 12 items from the short form of the Eysenck Personality Questionnaire (EPQ) (34) via self-report questionnaire.
Sample Selection
As described previously (35), we used a two-stage association design in which candidate loci were screened in stage 1, the positive results of which were tested for replication in stage 2. The parameters for this design were calculated using the LGA program (36) to achieve 80% power to detect markers that explained 1-2% of the variance of the liability distribution while controlling the false discovery rate at 0.1 (37). Using the extreme selection strategy outlined below, LGA indicated that we needed about 350 subjects in the stage 1 and 1,000 in the stage 2 sample to achieve this. If any of the markers genotyped in stage 1 met the estimated threshold p-value of 0.1 or less, they are then followed up in the stage 2 sample.
Starting with a sample of 9270 twin subjects, we used multivariate structural equation modeling to estimate a latent genetic risk factor for neuroticism that is highly correlated (range 0.6-0.8) with genetic susceptibility to major depression, generalized anxiety disorder, panic disorder, agoraphobia, and social phobia (7). One member from each twin pair for whom DNA was available (N=3176 pairs) was selected as a case or control based upon the pair scoring above the 80th or below the 20th percentile, respectively, of the genetic factor extracted from the above analysis. Thus, subjects selected for genotyping (and their co-twins) were determined to be high (cases) or low (controls) on genetic susceptibility for several highly related internalizing phenotypes. This produced a total sample of 1,128 independent subjects for genotyping, consisting of 589 cases (350 males, 239 females) and 539 controls (343 males, 196 females). Using the parameters prescribed by the LGA program, 376 and 752 subjects were used in stages 1 and 2, respectively.
Statistical Analysis
We used Pearson's χ2 tests to assess allelic or genotypic differences by marker between cases and control subjects, separately by stage to check for consistency of results across the two stages. For analysis of GABRA3 located on the X chromosome, we performed the analyses for men and women separately. We used the program HAPLOVIEW 4.1 (38) to test for Hardy-Weinberg equilibrium (HWE) violations (threshold of p=0.01) and to characterize linkage disequilibrium (LD) between the markers in our sample.
Genotyping
DNA was extracted from buccal epithelial cells obtained via cytology brushes (39). Reactions were performed in 96-well plates SNPs were genotyped by the 5′ nuclease cleavage assay (also called TaqMan method) (40). Reactions were performed in 98-well plates with 5 μl reaction volume containing 0.25 μl of 20× Assays_on-Demand™ SNP assay mix, 2.5 μl of TaqMan universal PCR master mix, and 5 ng of genomic DNA. Each 96-well plate contains samples for either cases or control, and these are intercalated onto a single 384-well plate within a genotyping run to reduce the risk of batch effects differentially affecting cases versus controls. The conditions for PCR were initial denaturizing at 95 °C for 10 minutes, followed by 40 cycles of 92 °C for 15 seconds and 60 °C for 1 minute. After the reaction, fluorescence intensities for reporter 1 (VIC, excitation = 520 ±10 nm, emission = 550 ± 10 nm) and reporter 2 (FAM, excitation = 490 ±10 nm, emission = 510 ± 10 nm) were read by the Analyst fluorescence plate reader (LJL Biosytems, Sunnyvale, CA). Genotypes were scored by a Euclidian clustering algorithm and and checked for deviations from Hardy-Weinberg equilibrium. We performed duplicate genotyping on a subset of plates as a quality control check and for any assays that did not perform optimally.
We selected SNP markers with MAF > 0.05 in each of the four GABA genes with the aim to tag the major haplotypes in the Caucasian panel of the HapMap project (41). Specifically, we used pair-wise tagging in the Tagger module of HAPLOVIEW 4.1 (38) with HapMap Phase II (release 22) data to select SNPs that captured > 80% of the HapMap markers with r2 > 0.8. We note that the decision to capture only 80% of the markers was a tradeoff between competing ideals of minimizing genotyping cost and maximizing coverage of the genes. This provided 3 tagging SNPs for GABRA2, 7 SNPs for GABRA3, 3 SNPs for GABRA6, and 12 SNPs for GABRG2.
Results
The genotype and allele frequencies and χ2 association results for all the markers in the four GABA genes genotyped in stage 1 are listed in tables 1-4. For GABRA2, GABRG2 and GABRA6, none of the markers passed the stage 1 p-value threshold of p < 0.1. All markers in these three genes were within HWE. In the GABRA3 gene located on the X chromosome, markers 3 and 4 met the threshold p-value of p < .1. (Note: because males are hemizygous for X chromosome markers, HWE and genotypic association testing were performed only for the female subjects.) In GABRA3, all markers were in HWE except rs4828694, which was then excluded from further analyses. We genotyped markers 3 and 4 from GABRA3 gene in the stage 2 sample, but their association failed to replicate (allelic p-values 0.63 and 0.32, respectively).
Table 1.
Stage 1 Association Results (N=188 cases, 188 controls) for GABRA2 (chromosomal band 4p12, length 140.5 Kb)
| Marker | Marker ID | Alleles (major) | Group | Genotypes (%) | Genotypic p-Value | Alleles (%) | Allelic p-Value | |||
|---|---|---|---|---|---|---|---|---|---|---|
| A1/A1 | A1/A2 | A2/A2 | A1 | A2 | ||||||
| 1 | rs279867 | G/T (G) |
Cases | 27.7 | 48.6 | 23.7 | 0.87 | 52.0 | 58.0 | 0.60 |
| Controls | 25.3 | 49.4 | 25.3 | 50.0 | 50.0 | |||||
| 2 | rs279828 | A/C (C) |
Cases | 26.1 | 52.2 | 21.6 | 0.41 | 52.2 | 47.8 | 0.29 |
| Controls | 24.4 | 47.8 | 27.2 | 48.4 | 51.6 | |||||
| 3 | rs1442062 | A/G (A) |
Cases | 51.1 | 42.7 | 6.2 | 0.53 | 72.5 | 27.5 | 0.77 |
| Controls | 52.0 | 39.0 | 9.0 | 71.5 | 28.5 | |||||
Table 4.
Stage 1 Association Results (N=188 cases, 188 controls) for GABRG2 (chromosomal band 5q34, length 87.9 Kb)
| Marker | Marker ID | Alleles (major) | Group | Genotypes (%) | Genotypic p-Value | Alleles (%) | Allelic p-Value | |||
|---|---|---|---|---|---|---|---|---|---|---|
| A1/A1 | A1/A2 | A2/A2 | A1 | A2 | ||||||
| 1 | rs17060039 | C/T (T) |
Cases | 81.6 | 18.4 | 0 | 0.29 | 90.8 | 9.2 | 0.32 |
| Controls | 85.9 | 14.1 | 0 | 92.9 | 7.1 | |||||
| 2 | rs183294 | C/T (C) |
Cases | 40.7 | 43.4 | 15.9 | 0.47 | 65.9 | 34.1 | 0.31 |
| Controls | 43.4 | 45.1 | 11.5 | 62.4 | 37.6 | |||||
| 3 | rs209353 | C/T (T) |
Cases | 31.2 | 50.9 | 17.9 | 0.85 | 56.6 | 43.4 | 0.87 |
| Controls | 32.0 | 48.0 | 20.0 | 56.0 | 44.0 | |||||
| 4 | rs209358 | C/T (T) |
Cases | 34.1 | 44.7 | 21.1 | 0.76 | 56.4 | 43.6 | 0.79 |
| Controls | 33.3 | 48.1 | 18.6 | 57.4 | 42.6 | |||||
| 5 | rs211037 | C/T (C) |
Cases | 57.2 | 38.9 | 3.9 | 0.28 | 76.7 | 24.4 | 0.73 |
| Controls | 58.5 | 34.1 | 7.4 | 75.6 | 24.4 | |||||
| 6 | rs211032 | C/T (C) |
Cases | 47.2 | 42.2 | 10.6 | 0.46 | 68.3 | 31.7 | 0.28 |
| Controls | 51.1 | 41.8 | 7.1 | 72.0 | 28.0 | |||||
| 7 | rs210984 | G/T (T) |
Cases | 69.5 | 28.8 | 1.7 | 0.86 | 83.9 | 16.1 | 0.94 |
| Controls | 68.6 | 30.3 | 1.1 | 83.7 | 16.3 | |||||
| 8 | rs169793 | A/T (A) |
Cases | 32.9 | 47.2 | 19.9 | 0.29 | 56.5 | 43.5 | 0.11 |
| Controls | 39.9 | 45.2 | 14.9 | 62.5 | 37.5 | |||||
| 9 | rs17060106 | A/C (A) |
Cases | 71.7 | 26.7 | 1.6 | 0.95 | 85.0 | 15.0 | 0.77 |
| Controls | 70.1 | 28.3 | 1.6 | 84.2 | 15.8 | |||||
| 10 | rs12520992 | A/C (A) |
Cases | 73.1 | 23.6 | 3.3 | 0.86 | 84.9 | 15.1 | 0.57 |
| Controls | 75.6 | 21.6 | 2.8 | 86.4 | 13.6 | |||||
| 11 | rs211014 | A/C (C) |
Cases | 59.4 | 35.0 | 5.6 | 0.75 | 76.9 | 23.1 | 0.73 |
| Controls | 59.9 | 36.3 | 3.8 | 78.0 | 22.0 | |||||
| 12 | rs424740 | A/T (T) |
Cases | 36.7 | 52.8 | 10.5 | 0.16 | 63.1 | 36.9 | 0.67 |
| Controls | 39.3 | 44.4 | 16.3 | 61.5 | 38.5 | |||||
Discussion
Previous research has implicated the potential involvement of the GABA system in anxiety disorder phenotypes (ANX). In this study, we investigated the possible associations between ANX and four GABA receptor genes, GABRA2, GABRA3, GABRA6, and GABRG2. We analyzed SNPs tagging the major allelic variation in these genes in a sample selected for extremes of common genetic risk across ANX, major depression, and neuroticism. The resulting sample of 589 cases (high genetic risk) and 539 controls (low genetic risk) were entered into a 2-stage association study in which all markers were screened in stage 1, with those showing suggestive association analyzed in stage 2.
In the stage 1 analyses, all markers, with the exception of two in the GABRA3 gene, failed to meet our criterion of p < .1 for further genotyping in stage 2. These two markers, however, did not exhibit association in the larger stage 2 sample. Our 2-stage association design with relatively high detection power revealed no significant association between these four GABA genes and ANX.
The involvement of the GABA system as a whole has been strongly linked to several neuropsychiatric phenotypes, especially ANX. Prior research found preliminary, mostly tentative evidence for association of various GABA receptor genes and a range of anxiety-related phenotypes. If these genes do contain susceptibility loci for ANX, there are a number of possible reasons why we may not have detected a significant association signal. First, our 2-stage study design, while providing a balance between Type 1 and Type 2 errors, may have reduced the overall power to detect variants of small effect size, since we genotype all of the markers in only the smaller stage 1 screening sample. Second, we selected only four of many GABA subunit receptor genes for study, leaving open the possibility that other genes from this group may play a role in ANX. Interestingly, a recent follow-up of a genome-wide association study for bipolar disorder found significant association with five GABA receptor genes, all different than those tested herein (42). Third, we took advantage of the HapMap database to select tagging SNPs across the candidate genes rather than select specific, possibly functional markers as was done in some earlier studies. For example, it is likely that our SNP selection was not able to tag the low frequency exonic SNP in the GABRA6 gene reported to be associated with neuroticism in one prior study (24) (We could not confirm this in silico, since this SNP is not currently in the HapMap database.) As noted earlier, we chose tag SNPs with the aim to capture 80% of the markers available in HapMap, thus excluding a smaller proportion of polymorphisms that might be associated with our phenotypes. Finally, we did not test a range of specific phenotypes as had been examined in prior studies; instead, our strategy was to detect association with a common genetic liability to ANX, major depression, and neuroticism. Thus, we cannot rule out involvement of these genes in specific (rather than common) liability to individual disorders. In the context of these potential limitations, the results obtained from this genetic association study suggest that common polymorphisms in the GABRA2, GABRA3, GABRA6, and GABRG2 genes are unlikely to play a major role in ANX liability.
Table 2.
Stage 1 Association Results (N=188 cases, 188 controls) for GABRA3 (chromosomal band Xq28, length 284.2 Kb): males [M] (N=196), females [F] (N=180), and together [All]
| Marker | Marker ID | Alleles (major) | Group | Genotypes (%) | Genotypic p-Value | Alleles (%) | Allelic p-Value | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| A1/A1 | A1/A2 | A2/A2 | F a | A1 | A2 | All | M | F | ||||
| 1 | rs11094547 | C/T (C) |
Cases | 63.9 | 15.8 | 20.2 | 0.18 | 78.0 | 22.0 | 0.18 | 0.15 | 0.57 |
| Controls | 68.5 | 19.1 | 12.4 | 73.0 | 27.0 | |||||||
| 2 | rs12833553 | A/G (G) |
Cases | 79.8 | 11.8 | 8.4 | 0.21 | 85.2 | 14.8 | 0.23 | 0.61 | 0.27 |
| Controls | 85.1 | 7.2 | 7.7 | 88.7 | 11.3 | |||||||
| 3 | rs6627221 | C/T (T) |
Cases | 72.2 | 15.0 | 12.8 | 0.47 | 80.4 | 19.6 | 0.089* | 0.13 | 0.31 |
| Controls | 80.4 | 10.9 | 8.7 | 85.9 | 14.1 | |||||||
| 4 | rs2201169 | C/T (T) |
Cases | 76.9 | 13.4 | 9.7 | 0.38 | 83.0 | 17.0 | 0.088* | 0.27 | 0.19 |
| Controls | 83.8 | 9.5 | 6.7 | 88.1 | 11.9 | |||||||
| 5 | rs11797836 | A/G (A) |
Cases | 83.9 | 11.5 | 4.6 | 0.46 | 88.5 | 11.5 | 0.37 | 0.66 | 0.20 |
| Controls | 86.8 | 8.0 | 5.2 | 90.9 | 9.1 | |||||||
| 6 | rs5969896 | A/G (G) |
Cases | 82.4 | 11.9 | 5.7 | 0.90 | 88.2 | 11.8 | 0.71 | 0.27 | 0.70 |
| Controls | 81.2 | 9.9 | 8.9 | 87.2 | 12.8 | |||||||
Because GABRA3 is located on the X chromosome, genotypic values are available only for females
p values that met the stage 1 screening threshold p < .1.
Table 3.
Stage 1 Association Results (N=188 cases, 188 controls) for GABRA6 (chromosomal band 5q34, length 16.9 Kb)
| Marker | Marker ID | Alleles (major) | Group | Genotypes (%) | Genotypic p-Value | Alleles (%) | Allelic p-Value | |||
|---|---|---|---|---|---|---|---|---|---|---|
| A1/A1 | A1/A2 | A2/A2 | A1 | A2 | ||||||
| 1 | rs1992647 | C/T (T) |
Cases | 40.1 | 45.0 | 14.9 | 0.99 | 62.6 | 37.4 | 0.95 |
| Controls | 40.1 | 44.6 | 15.4 | 62.4 | 37.6 | |||||
| 2 | rs13172914 | C/T (C) |
Cases | 33.9 | 46.1 | 20.0 | 0.99 | 56.9 | 43.1 | 0.92 |
| Controls | 33.3 | 46.5 | 20.2 | 56.6 | 43.4 | |||||
| 3 | rs6883758 | C/G (C) |
Cases | 71.2 | 25.9 | 2.9 | 0.90 | 84.2 | 15.8 | 0.65 |
| Controls | 69.0 | 27.8 | 3.2 | 82.9 | 17.1 | |||||
Acknowledgments
This work was supported by NIH grant K08 MH-66277 and a Pfizer/SWHR Scholars Award (JMH). We acknowledge the contribution of the Virginia Twin Registry, now part of the Mid-Atlantic Twin Registry (MATR), to ascertainment of subjects for this study. The MATR, directed by Dr. J. Silberg, has received support from the National Institutes of Health, the Carman Trust and the WM Keck, John Templeton and Robert Wood Johnson Foundations.
Footnotes
Financial Disclosures: None
Reference List
- 1.Kessler RC, Angermeyer M, Anthony JC, DE Graaf R, Demyttenaere K, Gasquet I, DE Girolamo G, Gluzman S, Gureje O, Haro JM, Kawakami N, Karam A, Levinson D, Medina Mora ME, Oakley Browne MA, Posada-Villa J, Stein DJ, Adley Tsang CH, Aguilar-Gaxiola S, Alonso J, Lee S, Heeringa S, Pennell BE, Berglund P, Gruber MJ, Petukhova M, Chatterji S, Ustun TB. Lifetime Prevalence and Age-of-Onset Distributions of Mental Disorders in the World Health Organization's World Mental Health Survey Initiative. World Psychiatry. 2007;6(3):168–76. [PMC free article] [PubMed] [Google Scholar]
- 2.Kessler RC, Chiu WT, Demler O, Merikangas KR, Walters EE. Prevalence, Severity, and Comorbidity of 12-Month DSM-IV Disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry. 2005;62(6):617–27. doi: 10.1001/archpsyc.62.6.617. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Hettema JM, Neale MC, Kendler KS. A Review and Meta-Analysis of the Genetic Epidemiology of Anxiety Disorders. Am J Psychiatry. 2001;158(10):1568–78. doi: 10.1176/appi.ajp.158.10.1568. [DOI] [PubMed] [Google Scholar]
- 4.Middeldorp CM, Cath DC, Van Dyck R, Boomsma DI. The Co-Morbidity of Anxiety and Depression in the Perspective of Genetic Epidemiology. A Review of Twin and Family Studies. Psychol Med. 2005;35(5):611–24. doi: 10.1017/s003329170400412x. [DOI] [PubMed] [Google Scholar]
- 5.Jardine R, Martin NG, Henderson AS. Genetic Covariation Between Neuroticism and the Symptoms of Anxiety and Depression. Genet Epidemiol. 1984;1(2):89–107. doi: 10.1002/gepi.1370010202. [DOI] [PubMed] [Google Scholar]
- 6.Scherrer JF, True WR, Xian H, Lyons MJ, Eisen SA, Goldberg J, Lin N, Tsuang MT. Evidence for Genetic Influences Common and Specific to Symptoms of Generalized Anxiety and Panic. J Affect Disord. 2000;57(1-3):25–35. doi: 10.1016/s0165-0327(99)00031-2. [DOI] [PubMed] [Google Scholar]
- 7.Hettema JM, Neale MC, Myers JM, Prescott CA, Kendler KS. A Population-Based Twin Study of the Relationship Between Neuroticism and Internalizing Disorders. Am J Psychiatry. 2006;163(5):857–64. doi: 10.1176/ajp.2006.163.5.857. [DOI] [PubMed] [Google Scholar]
- 8.Kalueff AV, Nutt DJ. Role of GABA in Anxiety and Depression. Depress Anxiety. 2007;24(7):495–517. doi: 10.1002/da.20262. [DOI] [PubMed] [Google Scholar]
- 9.Roy-Byrne PP. The GABA-Benzodiazepine Receptor Complex: Structure, Function, and Role in Anxiety. J Clin Psychiatry. 2005;66 2:14–20. [PubMed] [Google Scholar]
- 10.Malizia AL, Cunningham VJ, Bell CJ, Liddle PF, Jones T, Nutt DJ. Decreased Brain GABA(A)-Benzodiazepine Receptor Binding in Panic Disorder: Preliminary Results From a Quantitative PET Study. Arch Gen Psychiatry. 1998;55(8):715–20. doi: 10.1001/archpsyc.55.8.715. [DOI] [PubMed] [Google Scholar]
- 11.Hasler G, Nugent AC, Carlson PJ, Carson RE, Geraci M, Drevets WC. Altered Cerebral Gamma-Aminobutyric Acid Type A-Benzodiazepine Receptor Binding in Panic Disorder Determined by [11C]Flumazenil Positron Emission Tomography. Arch Gen Psychiatry. 2008;65(10):1166–75. doi: 10.1001/archpsyc.65.10.1166. [DOI] [PubMed] [Google Scholar]
- 12.Sieghart W, Sperk G. Subunit Composition, Distribution and Function of GABA(A) Receptor Subtypes. Curr Top Med Chem. 2002;2(8):795–816. doi: 10.2174/1568026023393507. [DOI] [PubMed] [Google Scholar]
- 13.Low K, Crestani F, Keist R, Benke D, Brunig I, Benson JA, Fritschy JM, Rulicke T, Bluethmann H, Mohler H, Rudolph U. Molecular and Neuronal Substrate for the Selective Attenuation of Anxiety. Science. 2000 Oct 6;290(5489):131–4. doi: 10.1126/science.290.5489.131. [DOI] [PubMed] [Google Scholar]
- 14.Edenberg HJ, Dick DM, Xuei X, Tian H, Almasy L, Bauer LO, Crowe RR, Goate A, Hesselbrock V, Jones K, Kwon J, Li TK, Nurnberger JI, Jr, O'Connor SJ, Reich T, Rice J, Schuckit MA, Porjesz B, Foroud T, Begleiter H. Variations in GABRA2, Encoding the Alpha 2 Subunit of the GABA(A) Receptor, Are Associated With Alcohol Dependence and With Brain Oscillations. Am J Hum Genet. 2004;74(4):705–14. doi: 10.1086/383283. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Covault J, Gelernter J, Hesselbrock V, Nellissery M, Kranzler HR. Allelic and Haplotypic Association of GABRA2 With Alcohol Dependence. Am J Med Genet B Neuropsychiatr Genet. 2004 Aug 15;129B(1):104–9. doi: 10.1002/ajmg.b.30091. [DOI] [PubMed] [Google Scholar]
- 16.Enoch MA, Schwartz L, Albaugh B, Virkkunen M, Goldman D. Dimensional Anxiety Mediates Linkage of GABRA2 Haplotypes With Alcoholism. Am J Med Genet B Neuropsychiatr Genet. 2006 Sep 5;141(6):599–607. doi: 10.1002/ajmg.b.30336. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Atack JR, Hutson PH, Collinson N, Marshall G, Bentley G, Moyes C, Cook SM, Collins I, Wafford K, McKernan RM, Dawson GR. Anxiogenic Properties of an Inverse Agonist Selective for Alpha3 Subunit-Containing GABA A Receptors. Br J Pharmacol. 2005;144(3):357–66. doi: 10.1038/sj.bjp.0706056. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Fiorelli R, Rudolph U, Straub CJ, Feldon J, Yee BK. Affective and Cognitive Effects of Global Deletion of Alpha3-Containing Gamma-Aminobutyric Acid-A Receptors. Behav Pharmacol. 2008;19(5-6):582–96. doi: 10.1097/FBP.0b013e32830dc0c7. [DOI] [PubMed] [Google Scholar]
- 19.Hayden EP, Nurnberger JI., Jr Molecular Genetics of Bipolar Disorder. Genes Brain Behav. 2006;5(1):85–95. doi: 10.1111/j.1601-183X.2005.00138.x. [DOI] [PubMed] [Google Scholar]
- 20.Massat I, Souery D, Del Favero J, Oruc L, Noethen MM, Blackwood D, Thomson M, Muir W, Papadimitriou GN, Dikeos DG, Kaneva R, Serretti A, Lilli R, Smeraldi E, Jakovljevic M, Folnegovic V, Rietschel M, Milanova V, Valente F, Van Broeckhoven C, Mendlewicz J. Excess of Allele1 for Alpha3 Subunit GABA Receptor Gene (GABRA3) in Bipolar Patients: a Multicentric Association Study. Mol Psychiatry. 2002;7(2):201–7. doi: 10.1038/sj.mp.4000953. [DOI] [PubMed] [Google Scholar]
- 21.Henkel V, Baghai TC, Eser D, Zill P, Mergl R, Zwanzger P, Schule C, Bottlender R, Jager M, Rupprecht R, Hegerl U, Moller HJ, Bondy B. The Gamma Amino Butyric Acid (GABA) Receptor Alpha-3 Subunit Gene Polymorphism in Unipolar Depressive Disorder: a Genetic Association Study. Am J Med Genet B Neuropsychiatr Genet. 2004 Apr 1;126B(1):82–7. doi: 10.1002/ajmg.b.20137. [DOI] [PubMed] [Google Scholar]
- 22.Puertollano R, Visedo G, Saiz-Ruiz J, Llinares C, Fernandez-Piqueras J. Lack of Association Between Manic-Depressive Illness and a Highly Polymorphic Marker From GABRA3 Gene. Am J Med Genet. 1995 Oct 9;60(5):434–5. doi: 10.1002/ajmg.1320600514. [DOI] [PubMed] [Google Scholar]
- 23.Massat I, Souery D, Del Favero J, Oruc L, Jakovljevic M, Folnegovic V, Adolfsson R, Kaneva R, Papadimitriou G, Dikeos D, Jazin E, Milanova V, Van Broeckhoven C, Mendlewicz J. Lack of Association Between GABRA3 and Unipolar Affective Disorder: a Multicentre Study. Int J Neuropsychopharmacol. 2001;4(3):273–8. doi: 10.1017/S1461145701002449. [DOI] [PubMed] [Google Scholar]
- 24.Sen S, Villafuerte S, Nesse R, Stoltenberg SF, Hopcian J, Gleiberman L, Weder A, Burmeister M. Serotonin Transporter and GABAA Alpha 6 Receptor Variants Are Associated With Neuroticism. Biol Psychiatry. 2004 Feb 1;55(3):244–9. doi: 10.1016/j.biopsych.2003.08.006. [DOI] [PubMed] [Google Scholar]
- 25.Uhart M, McCaul ME, Oswald LM, Choi L, Wand GS. GABRA6 Gene Polymorphism and an Attenuated Stress Response. Mol Psychiatry. 2004;9(11):998–1006. doi: 10.1038/sj.mp.4001535. [DOI] [PubMed] [Google Scholar]
- 26.Crestani F, Lorez M, Baer K, Essrich C, Benke D, Laurent JP, Belzung C, Fritschy JM, Luscher B, Mohler H. Decreased GABAA-Receptor Clustering Results in Enhanced Anxiety and a Bias for Threat Cues. Nat Neurosci. 1999;2(9):833–9. doi: 10.1038/12207. [DOI] [PubMed] [Google Scholar]
- 27.Kendler KS, Prescott CA. A Population-Based Twin Study of Lifetime Major Depression in Men and Women. Arch Gen Psychiatry. 1999;56(1):39–44. doi: 10.1001/archpsyc.56.1.39. [DOI] [PubMed] [Google Scholar]
- 28.Kendler KS, Prescott CA. Genes, Environment, and Psychopathology: Understanding the Causes of Psychiatric and Substance Use Disorders. New York: Guilford Press; 2006. [Google Scholar]
- 29.Spitzer RL, Williams JBW. Structured Clinical Interview for DSM-III-R (SCID) New York: Biometrics Research Department, New York State Psychiatric Institute; 1985. [Google Scholar]
- 30.American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. Revised Third. Washington, DC: American Psychiatric Association; 1987. [Google Scholar]
- 31.Hettema JM, Prescott CA, Kendler KS. A Population-Based Twin Study of Generalized Anxiety Disorder in Men and Women. J Nerv Ment Dis. 2001;189(7):413–20. doi: 10.1097/00005053-200107000-00001. [DOI] [PubMed] [Google Scholar]
- 32.Kendler KS, Gardner CO, Prescott CA. Panic Syndromes in a Population-Based Sample of Male and Female Twins. Psychol Med. 2001;31(6):989–1000. doi: 10.1017/s0033291701004226. [DOI] [PubMed] [Google Scholar]
- 33.American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. Third. Washington, DC: American Psychiatric Association; 1980. [Google Scholar]
- 34.Eysenck HJ, Eysenck SBG. Manual of the Eysenck Personality Questionnaire. London: Hodder and Stoughton; 1975. [Google Scholar]
- 35.Hettema JM, An SS, Neale MC, Bukszar J, van den Oord EJ, Kendler KS, Chen X. Association Between Glutamic Acid Decarboxylase Genes and Anxiety Disorders, Major Depression, and Neuroticism. Mol Psychiatry. 2006;11(8):752–62. doi: 10.1038/sj.mp.4001845. [DOI] [PubMed] [Google Scholar]
- 36.Robles JR, van den Oord EJ. Lga972: a Cross-Platform Application for Optimizing LD Studies Using a Genetic Algorithm. Bioinformatics. 2004 Nov 22;20(17):3244–5. doi: 10.1093/bioinformatics/bth348. [DOI] [PubMed] [Google Scholar]
- 37.van den Oord EJ, Sullivan PF. False Discoveries and Models for Gene Discovery. Trends Genet. 2003;19(10):537–42. doi: 10.1016/j.tig.2003.08.003. [DOI] [PubMed] [Google Scholar]
- 38.Barrett JC, Fry B, Maller J, Daly MJ. Haploview: Analysis and Visualization of LD and Haplotype Maps. Bioinformatics. 2005 Jan 15;21(2):263–5. doi: 10.1093/bioinformatics/bth457. [DOI] [PubMed] [Google Scholar]
- 39.Straub RE, Sullivan PF, Ma Y, Myakishev MV, Harris-Kerr C, Wormley B, Kadambi B, Sadek H, Silverman MA, Webb BT, Neale MC, Bulik CM, Joyce PR, Kendler KS. Susceptibility Genes for Nicotine Dependence: a Genome Scan and Followup in an Independent Sample Suggest That Regions on Chromosomes 2, 4, 10, 16, 17 and 18 Merit Further Study. Mol Psychiatry. 1999;4(2):129–44. doi: 10.1038/sj.mp.4000518. [DOI] [PubMed] [Google Scholar]
- 40.Livak KJ. Allelic Discrimination Using Fluorogenic Probes and the 5′ Nuclease Assay. Genet Anal. 1999;14(5-6):143–9. doi: 10.1016/s1050-3862(98)00019-9. [DOI] [PubMed] [Google Scholar]
- 41.The International HapMap Project. Nature. 2003 Dec 18;426(6968):789–96. doi: 10.1038/nature02168. [DOI] [PubMed] [Google Scholar]
- 42.Craddock N, Jones L, Jones IR, Kirov G, Green EK, Grozeva D, Moskvina V, Nikolov I, Hamshere ML, Vukcevic D, Caesar S, Gordon-Smith K, Fraser C, Russell E, Norton N, Breen G, St Clair D, Collier DA, Young AH, Ferrier IN, Farmer A, McGuffin P, Holmans PA, Donnelly P, Owen MJ, O'donovan MC. Strong Genetic Evidence for a Selective Influence of GABA(A) Receptors on a Component of the Bipolar Disorder Phenotype. Mol Psychiatry. 2008 Jul 1; doi: 10.1038/mp.2008.66. [DOI] [PMC free article] [PubMed] [Google Scholar]