Association study of GABRG2 polymorphisms with suicidal behaviour in schizophrenia patients with alcohol use disorder.

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 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.

The brain-derived neurotrophic factor gene in suicidal behaviour: a meta-analysis.

Suicide is a prominent public health problem. Its aetiology is complex, and the brain-derived neurotrophic factor (BDNF) has been implicated. We performed the first meta-analysis of the functional BDNF marker Val66Met (rs6265, 196G>A) in suicidal behaviour using data from 11 previously published samples plus our present sample (total n=3352 subjects, 1202 with history of suicidal behaviour. The meta-analysis including all 12 studies showed a trend for the Met-carrying genotypes and Met allele conferring risk for suicide (random-effects model p=0.096; ORMet-carrier=1.13, 95% CI 0.98-1.30, and random-effects model p=0.032; ORMet=1.16, 95% CI 1.01-1.32, respectively). Furthermore, we found the Met allele and the Met allele-carrying genotypes to be associated with history of suicide attempt (eight studies; allelic meta-analysis--random-effects model: p=0.013; fixed-effects model: p=0.006; genotypic meta-analysis--random-effects model: p=0.017; fixed-effects model: p=0.008). Taken together, the results from our study suggest that BDNF Val66Met is involved in suicidality. Further studies are required to elucidate its role in suicidal behaviour.

Post-traumatic stress disorder in the Canadian Longitudinal Study on Aging: A genome-wide association study.

OBJECTIVE: Canada exhibits one of highest lifetime prevalence for post-traumatic stress disorder (PTSD), but the etiology of this debilitating mental health condition still remains largely unknown. This study aims to examine the genetics of PTSD in the Canadian Longitudinal Study on Aging (CLSA) to identify potential genetic factors involved in the development of PTSD. METHOD: The CLSA sample was screened for primary (PTSD status) and secondary outcomes (avoidance, detachment, guardedness, and nightmares) based on the Primary Care PTSD Screen Scale (PC-PTSD). After GWAS quality control and whole-genome imputation, single-marker, gene-based, and polygenic risk score (PRS) analyses were performed. RESULTS: Based on available genotype and phenotype data, N = 16,535 individuals were selected for the analyses. While genome-wide analyses did not show significant findings for our primary and secondary outcomes, PRS analyses showed variable levels of association between PC-PTSD items with trauma, major depressive disorder, schizophrenia, bipolar disorder, educational attainment, and insomnia (p < 5e-4). CONCLUSION: This is the first GWAS of PTSD status and individual PC-PTSD items in a population sample of older adults from Canada. This study was also able to replicate findings from previous studies. Genetic investigations into individual symptom components of PTSD may help untangle the complex genetic architecture of PTSD.

Liver enzyme CYP2D6 gene and tardive dyskinesia.

Background: Tardive dyskinesia (TD) is an iatrogenic involuntary movement disorder occurring after extended antipsychotic use with unclear pathogenesis. CYP2D6 is a liver enzyme involved in antipsychotic metabolism and a well-studied gene candidate for TD. Materials & methods: We tested predicted CYP2D6 metabolizer phenotype with TD occurrence and severity in our two samples of European chronic schizophrenia patients (total n = 198, of which 82 had TD). Results: TD occurrence were associated with extreme metabolizer phenotype, controlling for age and sex (p = 0.012). In other words, individuals with either increased and no CYP2D6 activity were at higher risk of having TD. Conclusion: Unlike most previous findings, TD occurrence may be associated with both extremes of CYP2D6 metabolic activity rather than solely for poor metabolizers.

Towards precision medicine in generalized anxiety disorder: Review of genetics and pharmaco(epi)genetics.

Generalized anxiety disorder (GAD) is a prevalent and chronic mental disorder that elicits widespread functional impairment. Given the high degree of non-response/partial response among patients with GAD to available pharmacological treatments, there is a strong need for novel approaches that can optimize outcomes, and lead to medications that are safer and more effective. Although investigations have identified interesting targets predicting treatment response through pharmacogenetics (PGx), pharmaco-epigenetics, and neuroimaging methods, these studies are often solitary, not replicated, and carry several limitations. This review provides an overview of the current status of GAD genetics and PGx and presents potential strategies to improve treatment response by combining better phenotyping with PGx and improved analytical methods. These strategies carry the dual benefit of delivering data on biomarkers of treatment response as well as pointing to disease mechanisms through the biology of the markers associated with response. Overall, these efforts can serve to identify clinical, genetic, and epigenetic factors that can be incorporated into a pharmaco(epi)genetic test that may ultimately improve treatment response and reduce the socioeconomic burden of GAD.

An examination of genes, stress and suicidal behavior in two First Nations communities: The role of the brain-derived neurotropic factor gene.

Suicide claims over 800,000 lives each year worldwide. Suicide rates in indigenous populations in Canada are about double that of the national average, making it a serious public health issue. Numerous factors are involved in suicide risk, including genetic factors, as well as various psychosocial stressors, such as historical experience with the Indian Residential School system for Indigenous populations, as well as protective variables such as social support. Here, we report the first genetic study of suicidal behaviors that includes multiple measures of stress and social supports. We investigated the role of the functional Val66Met marker (rs6265) in the Brain-Derived Neurotropic Factor (BDNF) gene in suicidal ideation and suicide attempt in a First Nations community sample (N = 278). We did not find a significant association between the BDNF rs6265 marker and suicidal behaviors. We found childhood adversities, recent life stress, chronic stress, perceived stress, difficulties, and hazardous alcohol use to be associated with both suicidal ideation and suicide attempt. Thus, while additional studies with larger samples are required to elucidate the genetic component of suicide, addressing environmental stressors may be important for suicide prevention.

Association Study of the Complement Component C4 Gene in Tardive Dyskinesia.

Tardive dyskinesia (TD) is a movement disorder that may develop in schizophrenia patients being treated long-term with antipsychotic medication. TD interferes with voluntary movements and leads to stigma, and can be associated with treatment non-adherence. The etiology of TD is unclear, but it appears to have a genetic component. There is emerging evidence of immune dysregulation in TD. In the current study, we set out to investigate the complex schizophrenia-associated complement component 4 (C4) gene for possible association with TD occurrence and TD severity as assessed by the Abnormal Involuntary Movement Scale (AIMS) in a sample of 129 schizophrenia patients of European ancestry. We have genotyped the copy numbers of long and short forms of C4A and C4B gene variants in 129 European ancestry patients with schizophrenia or schizoaffective disorder. We did not find predicted C4A or C4B expression to be nominally associated with TD risk or severity. However, we found the number of copies of C4BL to be nominally associated with TD severity (p = 0.020).

Genetic study of eight AKT1 gene polymorphisms and their interaction with DRD2 gene polymorphisms in tardive dyskinesia.

Tardive dyskinesia (TD) is a motor adverse effect of chronic antipsychotic medication. It has been suggested to involve dopamine neurotransmission system changes. AKT1 acts downstream of the D(2) receptor that is blocked by all antipsychotics to some degree. The AKT1 gene has not been investigated in TD. We examined eight polymorphisms spanning the AKT1 gene and their association with TD in our schizophrenia sample of 193 Caucasians, 76 of which with TD. AKT1 polymorphisms and haplotypes were not significantly associated with TD. However, we detected a significant interaction between rs6275 of DRD2 and rs3730358 of AKT1 (p<1 x 10(-5)).

Genetics of tardive dyskinesia: Promising leads and ways forward.

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

New findings in pharmacogenetics of schizophrenia.

PURPOSE OF REVIEW: This review highlights recent advances in the investigation of genetic factors for antipsychotic response and side effects. RECENT FINDINGS: Antipsychotics prescribed to treat psychotic symptoms are variable in efficacy and propensity for causing side effects. The major side effects include tardive dyskinesia, antipsychotic-induced weight gain (AIWG), and clozapine-induced agranulocytosis (CIA). Several promising associations of polymorphisms in genes including HSPG2, CNR1, and DPP6 with tardive dyskinesia have been reported. In particular, a functional genetic polymorphism in SLC18A2, which is a target of recently approved tardive dyskinesia medication valbenazine, was associated with tardive dyskinesia. Similarly, several consistent findings primarily from genes modulating energy homeostasis have also been reported (e.g. MC4R, HTR2C). CIA has been consistently associated with polymorphisms in the HLA genes (HLA-DQB1 and HLA-B). The association findings between glutamate system genes and antipsychotic response require additional replications. SUMMARY: The findings to date are promising and provide us a better understanding of the development of side effects and response to antipsychotics. However, more comprehensive investigations in large, well characterized samples will bring us closer to clinically actionable findings.

Association study of BDNF and DRD3 genes with alcohol use disorder in Schizophrenia.

Alcohol use disorder (AUD) is a leading risk factor of disease burden in the world. It is also commonly comorbid with over 20% of schizophrenia patients. The brain-derived neurotrophic factor (BDNF) and dopamine D3 receptor (DRD3) have been implicated in alcohol drinking behaviour. Previous genetic studies of the BDNF and DRD3 genes produced mixed findings; however, only one study investigated two BDNF genetic markers with alcohol dependence in schizophrenia patients. We investigated 15 single-nucleotide polymorphisms (SNPs) in DRD3 and four SNPs in BDNF for possible association with alcohol abuse or dependence in schizophrenia patients of European ancestry (N = 195). The patients were assessed for the occurrence of alcohol abuse or alcohol dependence using the Structured Clinical Interview for DSM-IV Axis I Disorders, Patient Edition (SCID-I/P). We found the BDNF Val66Met to be associated with alcohol dependence (p = 0.004). We also found haplotypes across BDNF to be nominally associated with alcohol dependence. Analyses of DRD3 markers and haplotypes yielded mostly negative findings. Our findings support a role of the BDNF gene in alcohol dependence in schizophrenia patients. Larger samples are required to confirm our findings, particularly those of BDNF haplotypes.

Sequence Analysis of Drug Target Genes with Suicidal Behavior in Bipolar Disorder Patients.

BACKGROUND: A number of genes have been implicated in recent genome-wide association studies of suicide attempt in bipolar disorder. More focused investigation of genes coding for protein targets of existing drugs may lead to drug repurposing for the treatment and/or prevention of suicide. METHODS: We analyzed 2,457 DNA variants across 197 genes of interest to GlaxoSmithKline across the pipeline in our sample of European patients suffering from bipolar disorder (N = 219). We analyzed these variants for a possible association with the suicide severity score (ranging from suicidal ideation/plan to serious suicide attempt) from the Schedule for Clinical Assessment in Neuropsychiatry. We conducted tests of individual variants and gene-based tests. RESULTS: We found a number of DNA variants in the transforming growth factor beta receptor 1 gene (TGFBR1) to be suggestively associated with suicide severity scores (p < 0.005). The gene-based tests also pointed to TGFBR1 to be associated with suicide severity (p = 0.0001). However, these findings were not replicated in an independent bipolar disorder sample. CONCLUSIONS: We report no significant association between DNA sequences of drug target genes and suicidal behavior. Additional larger sequencing studies could further interrogate associations between variants in drug target genes and suicidal behavior.

Association study of Disrupted-In-Schizophrenia-1 gene variants and tardive dyskinesia.

Tardive dyskinesia (TD) is an involuntary movement disorder that occurs in ∼20% of patients after extended antipsychotic use. Its pathophysiology is unclear; however, familial patterns and gene association studies indicate an inherited component to risk. The disrupted in schizophrenia 1 (DISC1) gene was selected for analysis because it interacts with and regulates two important proteins involved in antipsychotic medication action: the dopamine D2 receptor and the cAMP phosphodiesterase type IVB (PDE4B). The D2 receptor is the obligate target of all existing antipsychotic medications, and PDE4B hydrolyzes cAMP, a core signaling molecule activated by agonist binding to the D2 receptor. Notably, PDE4B inhibitors such as rolipram have been shown to reduce TD-like behaviours in animal models. Nine single-nucleotide polymorphisms (SNPs) in the DISC1 gene were investigated in a sample of 193 chronic schizophrenia patients for association with the presence and severity of TD, with age and sex as additional variables. TD severity was measured using the Abnormal Involuntary Movement Scale (AIMS). Two DISC1 SNPs were associated with TD severity (uncorrected p < 0.05), but these findings did not survive correction for multiple testing. This preliminary investigation suggests that DISC1 gene variants do not affect risk for TD or severity.

Investigation of the HSPG2 Gene in Tardive Dyskinesia - New Data and Meta-Analysis.

Tardive dyskinesia (TD) is a movement disorder that may occur after extended use of antipsychotic medications. The etiopathophysiology is unclear; however, genetic factors play an important role. The Perlecan (HSPG2) gene was found to be significantly associated with TD in Japanese schizophrenia patients, and this association was subsequently replicated by an independent research group. To add to the evidence for this gene in TD, we conducted a meta-analysis specific to the relationship of HSPG2 rs2445142 with TD occurrence, while also adding our unpublished genotype data. Overall, we found a significant association of the G allele with TD occurrence (p = 0.0001); however, much of the effect appeared to originate from the discovery dataset. Nonetheless, most study samples exhibit the same trend of association with TD for the G allele. Our findings encourage further genetic and molecular studies of HSPG2 in TD.

Investigation of the genetic interaction between BDNF and DRD3 genes in suicidical behaviour in psychiatric disorders.

OBJECTIVES: Suicide is a serious public health concern, and it is partly genetic. The brain-derived neurotrophic factor (BDNF) gene has been a strong candidate in genetic studies of suicide (Dwivedi et al., Arch Gen Psychiatry 2010;60:804-815; Zai et al., Prog Neuropsychopharmacol Biol Psychiatry 2012;34:1412-1418) and BDNF regulates the expression of the dopamine D3 receptor. OBJECTIVE: We examined the role of the BDNF and DRD3 genes in suicide. METHODS: We analysed four tag single-nucleotide polymorphisms (SNPs) in BDNF and 15 SNPs in the D3 receptor gene DRD3 for possible association with suicide attempt history in our Canadian sample of Schizophrenia (SCZ) patients of European ancestry (N = 188). RESULTS: In this sample, we found a possible interaction between the BDNF Val66Met and DRD3 Ser9Gly SNPs in increasing the risk of suicide attempt(s) in our SCZ sample. Specifically, a larger proportion of SCZ patients who were carrying at least one copy of the minor allele at each of the Val66Met and Ser9Gly functional markers have attempted suicides compared to patients with other genotypes (Bonferroni P < 0.05). However, we could not replicate this finding in samples from other psychiatric populations. CONCLUSIONS: Taken together, the results from the present study suggest that an interaction between BDNF and DRD3 may not play a major role in the risk for suicide attempt, though further studies, especially in SCZ, are required.

The role of brain-derived neurotrophic factor (BDNF) gene variants in antipsychotic response and antipsychotic-induced weight gain.

BACKGROUND: Brain-derived neurotrophic factor (BDNF) has extensive effects on the nervous system including cell survival, differentiation, neuronal growth and maintenance, as well as cell death. Moreover, it promotes synaptic plasticity and interacts with dopaminergic and serotonergic neurons, suggesting an important role on the alteration of brain function with antipsychotic medications and induced weight gain in schizophrenia patients. The differential effects of BDNF gene variants could lead to changes in brain circuitry that would in turn cause variable response to antipsychotic medication. Therefore, we hypothesized that genetic variation in this candidate gene helps in explaining the inter-individual variation observed in antipsychotic drug treatment with respect to response and induced weight gain. METHOD: We examined four single-nucleotide polymorphisms across the BDNF gene, including Val66Met (rs6265). Prospective BPRS change scores and weight change after six weeks were obtained from a total of 257 schizophrenia patients of European ancestry. RESULTS: The markers rs11030104 and Val66Met were associated with antipsychotic response (P=0.04; 0.007, respectively). On the other hand, marker rs1519480 was associated with weight gain (P=0.04). Moreover, a two-marker haplotype across rs6265 and rs1519480 was associated with weight change (P=0.001). Results with Val66Met in response, and results with rs6265-rs1519480 haplotypes remained significant at the modified Bonferroni corrected alpha of 0.017. CONCLUSION: BDNF genetic variants might play an important role in predicting antipsychotic response and antipsychotic-induced weight gain. However, replication in larger and independent samples is required.

Association study of BDNF and DRD3 genes in schizophrenia diagnosis using matched case-control and family based study designs.

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with prominent genetic etiologic factors. The dopamine receptor DRD3 gene is a strong candidate in genetic studies of SCZ because of the dopamine hypothesis of SCZ and the selective expression of D(3) in areas of the limbic system implicated in the disease. We examined 15 single-nucleotide polymorphisms (SNPs) in DRD3 in our sample of European origin consisting of 95 small nuclear SCZ families and 167 case-control pairs. We also examined four BDNF SNPs in our samples because of evidence for BDNF regulation of DRD3 expression (Guillin et al., 2001). We found a nominally significant genotypic association with rs7633291 and allelic association with rs1025398 alleles. However, these observations did not survive correction for multiple testing. We did not find a statistically significant association with the other DRD3 and BDNF polymorphisms. Taken together, the results from the present study suggest that BDNF and DRD3 may not be involved in SCZ susceptibility.

Genetic study of BDNF, DRD3, and their interaction in tardive dyskinesia.

Tardive dyskinesia (TD) is a neuroleptic-induced movement disorder. Its pathophysiology is unclear. The most consistent genetic findings have shown an association with the Ser9Gly polymorphism of the DRD3 gene. However, only few polymorphisms within DRD3 has been tested, and a comprehensive examination of DRD3 in TD is still lacking. Further, brain-derived neurotrophic factor (BDNF), a neuronal growth and survival peptide, regulates DRD3 expression and may be involved in the neuronal degeneration observed in TD. In the present study, we investigated 15 tag DRD3 polymorphisms and four tag BDNF polymorphisms for association with TD in our sample of Caucasian schizophrenia patients (N=171). While BDNF markers showed no association, a haplotype containing rs3732782, rs905568, and rs7620754 in the 5' region of DRD3 was associated with TD diagnosis (p[10,000 permutations]=0.007). We also found evidence of interaction between BDNF and DRD3 polymorphisms. Further studies are needed to confirm these findings.

Association study of tardive dyskinesia and twelve DRD2 polymorphisms in schizophrenia patients.

Tardive dyskinesia (TD) is a side-effect of chronic antipsychotic medication. Abnormalities in dopaminergic activity in the nigrostriatal system have been most often suggested to be involved because the agents which cause TD share in common potent antagonism of dopamine D2 receptors (DRD2), that notably is not balanced by effects such as more potent serotonin (5-HT)2A antagonism. Thus, a number of studies have focused on the association of dopamine system gene polymorphisms and TD. The most consistent findings have been found with the Ser9Gly polymorphism of the DRD3 gene. Although DRD2 has long been hypothesized to be the main target for antipsychotics, only a few polymorphisms in DRD2 have been investigated for their potential involvement in the aetiology of TD. In the present study, we investigated 12 polymorphisms spanning the DRD2 gene and their association with TD in our European Caucasian (n=202) and African-American (n=30) samples. Genotype frequencies for a functional polymorphism, C957T (Duan et al., 2003; Hirvonen et al., 2004), and the adjacent C939T polymorphism were found to be significantly associated with TD (p=0.013 and p=0.022 respectively). DRD2 genotypes were not significantly associated with TD severity as measured by AIMS (Abnormal Involuntary Movement Scale) with the exception of a trend for C939T (p=0.071). Both TD and total AIMS scores were found to be significantly associated with two-marker haplotypes containing C939T and C957T (p=0.021 and p=0.0087 respectively). Preliminary results indicated that C957T was also associated with TD in our African-American sample (p=0.047). Taken together, the present study suggests that DRD2 may be involved in TD in the Caucasian population, although further studies are warranted.