Polymorphisms in the glutamate decarboxylase 1 gene associated with heroin dependence

Impaired striatal glutamate/GABA regulation in violent offenders with antisocial personality disorder and psychopathy

Men with antisocial personality disorder (ASPD) with or without psychopathy (+/-P) are responsible for most violent crime in society. Development of effective treatments is hindered by poor understanding of the neurochemical underpinnings of the condition. Men with ASPD with and without psychopathy demonstrate impulsive decision-making, associated with striatal abnormalities in functional neuroimaging studies. However, to date, no study has directly examined the potential neurochemical underpinnings of such abnormalities. We therefore investigated striatal glutamate: GABA ratio using Magnetic Resonance Spectroscopy in 30 violent offenders (16 ASPD-P, 14 ASPD + P) and 21 healthy non-offenders. Men with ASPD +/- P had a significant reduction in striatal glutamate : GABA ratio compared to non-offenders. We report, for the first time, striatal Glutamate/GABA dysregulation in ASPD +/- P, and discuss how this may be related to core behavioral abnormalities in the disorders.

Glutamate decarboxylase 1 gene polymorphisms are associated with respiratory symptoms in panic disorder

BACKGROUND

Genetic factors play an important role in the pathogenesis of panic disorder (PD). However, the effect of genetic variants on PD remains controversial.

AIM

To evaluate the associations between glutamate decarboxylase 1 (GAD1) gene polymorphisms and PD risk and assess the effect of GAD1 gene polymorphisms on the severity of clinical symptoms in PD.

METHODS

We recruited 230 PD patients and 224 healthy controls in this study. All participants were assessed for anxiety and panic symptom severity using the Hamilton Anxiety Rating Scale (HAM-A) and Panic Disorder Severity Scale (PDSS). GAD1 gene polymorphisms (rs1978340 and rs3749034) were genotyped and assessed for allele frequencies.

RESULTS

There were no significant differences between cases and controls in the genotype distributions or allele frequencies of GAD1 (rs1978340 and rs3749034). In addition, the effect of GAD1 (rs1978340 and rs3749034) on PD severity was not significant. However, regarding respiratory symptoms, patients with the GAD1 rs1978340 A/A genotype had significantly higher scores than those with the A/G or G/G genotype.

CONCLUSION

Here, we showed that the A/A genotype of GAD1 rs1978340 was associated with increased severity of respiratory symptoms in patients with PD.

Association between methylation in the promoter region of the GAD2 gene and opioid use disorder

DNA methylation is one of the epigenetic mechanisms involved in opioid use disorder. GAD2 is a key catalyticase in gamma amino butyric acid (GABA) synthesis from glutamate, that is implicated in opioid-induced rewarding effect. To reveal the relationship and the underlying mechanism between GAD2 gene methylation and opioid use disorder, we first examined and compared the methylation levels in the promoter region of the GAD2 gene in peripheral blood between 120 patients with opioid use disorder and 110 healthy controls by using a targeted approach. A diagnostic model with methylation biomarkers was established to distinguish opioid use disorder and healthy control groups. Correlations between methylation levels in the promoter region of the GAD2 gene and the duration and dosage of opioid use were then determined. Finally, the transcription factors that potentially bind to the target sequences including the detected CpG sites were predicted with the JASPAR database. Our results demonstrated that hypermethylation in the promoter region of the GAD2 gene was associated with opioid use disorder. A diagnostic model based on 10 methylation biomarkers could distinguish the opioid use disorder and healthy control groups. Several correlations between methylation levels in the GAD2 gene promoter and the duration and dosage of opioid use were observed. Transcription factors TFAP2A, Arnt and Runx1 were predicted to bind to the target sequences including several CpG sites detected in the present study in the GAD2 gene promoter. Our findings highlight and extend the role of DNA methylation in the GAD2 gene in opioid use disorder.

GABRB2, a key player in neuropsychiatric disorders and beyond

The GABA receptors represent the main inhibitory system in the central nervous system that ensure synaptogenesis, neurogenesis, and the regulation of neuronal plasticity and learning. GABAA receptors are pentameric in structure and belong to the Cys-loop superfamily. The GABRB2 gene, located on chromosome 5q34, encodes the β2 subunit that combines with the α and γ subunits to form the major subtype of GABAA receptors, which account for 43% of all GABAA receptors in the mammalian brain. Each subunit probably consists of an extracellular N-terminal domain, four membrane-spanning segments, a large intracellular loop between TM3 and TM4, and an extracellular C-terminal domain. Alternative splicing of the RNA transcript of the GABRB2 gene gives rise at least to four long and short isoforms with dissimilar electrophysiological properties. Furthermore, GABRB2 is imprinted and subjected to epigenetic regulation and positive selection. It has been associated with schizophrenia first in Han Chinese, and subsequently validated in other populations. Gabrb2 knockout mice also exhibited schizophrenia-like behavior and neuroinflammation that were ameliorated by the antipsychotic drug risperidone. GABRB2 was also associated with other neuropsychiatric disorders including bipolar disorder, epilepsy, autism spectrum disorder, Alzheimer's disease, frontotemporal dementia, substance dependence, depression, internet gaming disorder, and premenstrual dysphoric disorder. Recently, it has been postulated that GABRB2 might be a potential marker for different cancer types. As GABRB2 has a pivotal role in the central nervous system and is increasingly recognized to contribute to human diseases, further understanding of its structure and function may expedite the generation of new therapeutic approaches.

Association study of Catechol-o-methyltransferase and Alpha-1-adrenergic receptor gene polymorphisms with multiple phenotypes of heroin use disorder

Heroin use disorder is a chronic relapsing brain disease containing multiple phenotypes. These phenotypes vary among heroin users and might be influenced by genetic factors. Single-nucleotide polymorphisms (SNPs) of catechol-O-methyltransferase (COMT) and alpha-1-adrenergic receptor (ADRA1A) genes are associated with heroin use disorder. However, it has not been clarified which phenotypes of heroin use disorder are related to these genes. To address this question, we recruited 801 unrelated heroin users and divided them into different subgroups according to four important phenotypes of heroin use disorder. Then 7 SNPs in the functional region of these genes were systematically screened and genotyped using a SNaPshot assay. We found that the A allele of ADRA1A rs1048101 was associated with a shorter duration of transition from first use to addiction. Subjects with the C allele of ADRA1A rs3808585 were more susceptible to memory impairment after heroin use disorder. Subjects with the G allele of COMT rs769224 were more likely to take a higher dose of heroin every day. Our study confirmed the association between polymorphisms of COMT and ADRA1A with those specific phenotypes of heroin use disorder, which will be instructive for the precise treatment of the disease.

Pharmacogenetics of drug dependence: Polymorphisms of genes involved in GABA neurotransmission

GABA plays a critical role in brain reward pathways via projecting signals from the ventral tegmental area to the nucleus accumbens. Activation of the reward circuitry by abused drugs induces abnormalities of GABA neurotransmission. Recent studies have indicated the involvement of GABAergic genes in the mechanism of drug dependence and its consequences. The aim of this paper is to provide a brief review of association studies of GABA-related genes with drug dependence. Single nucleotide polymorphisms (SNPs) in genes involved in GABA neurotransmission such as GABA receptor genes (GABR, GABBR), and glutamic acid decarboxylase genes (GAD) are the focus of this review as potential risk factors for drug dependence and its consequence psychosis.

GAD1 but not GAD2 polymorphisms are associated with heroin addiction phenotypes

INTRODUCTION

Heroin addiction is a chronic complex brain disease that contains multiple phenotypes, which vary widely among addicts and may be affected by genetic factors. A total of 801 unrelated heroin addicts were recruited and divided into different subgroups according to eight phenotypes of heroin addiction. Polymorphisms in GAD1 (rs3762555, rs3762556, rs3791878, rs3749034, rs11532313 and rs769395) and GAD2 (rs2839669, rs2839670 and rs2236418) were genotyped using the SNaPshot assay. Associations between genetic variants and the eight phenotypes were mainly assessed by binary logistic regression.

RESULTS

We found that the frequencies of G allele of GAD1 rs3749034 and rs3762555 were associated with daily dose of methadone use and memory change after heroin addiction. The C allele frequency of GAD1 rs3762556 was associated with lower daily dose of methadone use. In GAD1, SNPs rs3762556, rs3762555, rs3791878 and rs3749034 had strong linkage, and the frequency of the C-G-C-A haplotype was higher in the lower dose of methadone group. Patients with the TT genotype of rs11542313 were maintained on lower dose of methadone than patients with the CC genotype. The G alleles of rs3762555 and rs3749034 were lower, while the T allele of rs11542313 was higher, in the memory decreased group. The results of association analyses of GAD2 with phenotypes of heroin addiction showed no significant differences.

CONCLUSION

GAD1 polymorphisms were associated with phenotypes of heroin addiction, especially the daily dose of methadone use and memory change in the Han Chinese population. These results may provide individualized guidance for the treatment of heroin addiction.

Biochemical Diagnosis in Substance and Non-substance Addiction

An optimal biochemical marker for addiction would be some easily traced molecules in body specimens, which indicates indulgent addictive behaviors, or susceptibility to certain addictive stimuli. In this chapter, we discussed existing literature about possible biomarkers, and classified them into three categories: origin forms and metabolites of substances, markers from biochemical responses to certain addiction, and genetic and epigenetic biomarkers suggesting susceptibility to addiction. In every category, we examined studies concerning certain type of addiction one by one, with focuses mainly on opiates, psychostimulants, and pathological gambling. Several promising molecules were highlighted, including those of neurotrophic factors, inflammatory factors, and indicators of vascular injury, and genetic and epigenetic biomarkers such as serum miRNAs. DNA methylation signatures and signal nucleotide polymorphism of candidate gene underlying the addiction.

Association of polymorphisms in GAD1 and GAD2 genes with methamphetamine dependence

AIM

Association between polymorphisms in GAD genes and methamphetamine (METH) dependence was investigated in the Thai population.

MATERIALS & METHODS

Genotypes of rs769404 and rs701492 in GAD1 and rs2236418 in GAD2 polymorphisms were determined in 100 METH-dependent male subjects and 102 matched controls.

RESULTS

The genotype and allele frequencies of rs2236418 (GAD2) were associated with METH dependence and METH with psychosis, in which the G allele was related to increased risk. The presence of the rs769404-rs701492 (GAD1) C-C haplotype was associated with METH psychosis.

CONCLUSION

This study indicates that genetic variability in GAD1 and GAD2 contributes to risk of METH dependence and METH psychosis in the Thai population and indicates the role of the GABAergic system in these disorders.

Glutamatergic and GABAergic susceptibility loci for heroin and cocaine addiction in subjects of African and European ancestry

BACKGROUND

Drug addiction, a leading health problem, is a chronic brain disease with a significant genetic component. Animal models and clinical studies established the involvement of glutamate and GABA neurotransmission in drug addiction. This study was designed to assess if 258 variants in 27 genes of these systems contribute to the vulnerability to develop drug addiction.

METHODS

Four independent analyses were conducted in a sample of 1860 subjects divided according to drug of abuse (heroin or cocaine) and ancestry (African and European).

RESULTS

A total of 11 SNPs in eight genes showed nominally significant associations (P<0.01) with heroin and/or cocaine addiction in one or both ancestral groups but the associations did not survive correction for multiple testing. Of these SNPs, the GAD1 upstream SNP rs1978340 is potentially functional as it was shown to affect GABA concentrations in the cingulate cortex. In addition, SNPs GABRB3 rs7165224; DBI rs12613135; GAD1 SNPs rs2058725, rs1978340, rs2241164; and GRIN2A rs1650420 were previously reported in associations with drug addiction or related phenotypes.

CONCLUSIONS

The study supports the involvement of genetic variation in the glutamatergic and GABAergic systems in drug addiction with partial overlap in susceptibility loci between cocaine and heroin addiction.

Genetics of opiate addiction

Addiction to MOP-r agonists such as heroin (and also addiction to prescription opioids) has reemerged as an epidemic in the twenty first century, causing massive morbidity. Understanding the genetics contributing to susceptibility to this disease is crucial for the identification of novel therapeutic targets, and also for discovery of genetic markers which would indicate relative protection or vulnerability from addiction, and relative responsiveness to pharmacotherapy. This information could thus eventually inform clinical practice. In this review, we focus primarily on association studies of heroin and opiate addiction, and further describe the studies which have been replicated in this field, and are thus more likely to be useful for translational efforts.

Association analysis of GABRB3 promoter variants with heroin dependence

GABRB3 encoding the β3 subunit of GABAA receptor has been implicated in multiple neuropsychiatric disorders, including substance abuse. Previous studies reported that SNPs at the 5' regulatory region of GABRB3 could regulate GABRB3 gene expression and associated with childhood absence epilepsy (CAE). The study aimed to investigate whether SNPs at the 5' regulatory region of GABRB3 were associated with heroin dependence in our population. We first re-sequenced 1.5 kb of the 5'regulatory region of GABRB3 gene to examine the SNP profile in the genomic DNA of 365 control subjects. Then, we conducted a case-control association analysis between 576 subjects with heroin dependence (549 males, 27 females) and 886 controls (472 males, 414 females) by genotyping the rs4906902 as a tag SNP. We also conducted a reporter gene assay to assess the promoter activity of two major haplotypes derived from SNPs at this region. We detected 3 common SNPs (rs4906902, rs8179184 and rs20317) at this region that had strong pair-wise linkage disequilibrium. The C allele of rs4906902 was found to be associated with increased risk of heroin dependence (odds ratio:1.27, p = 0.002). Two major haplotypes (C-A-G and T-G-C) derived from these 3 SNPs accounted for 99% of this sample, and reporter gene activity assay showed that haplotype C-A-G that contained the C allele of the tag SNP rs4906902 had higher activity than haplotype T-G-C. Our data suggest that GABRB3 might be associated with heroin dependence, and increased expression of GABRB3 might contribute to the pathogenesis of heroin dependence.

Advances in genetic studies of substance abuse in China

Summary

The importance of genetic factors in substance addiction has long been established. The rationale for this work is that understanding of the function of addiction genes and delineation of the key molecular pathways of these genes would enhance the development of novel therapeutic targets and biomarkers that could be used in the prevention and management of substance abuse. Over the past few years, there has been a substantial increase in the number of genetic studies conducted on addiction in China; these studies have primarily focused on heroin, alcohol, and nicotine dependence. Most studies of candidate genes have concentrated on the dopamine, opioid, and serotonin systems. A number of genes associated with substance abuse in Caucasians are also risk factors in Chinese, but several novel genes and genetic risk factors associated with substance abuse in Chinese subjects have also been identified. This paper reviews the genetic studies of substance abuse performed by Chinese researchers. Genotypes and alleles related to addictive behavior in Chinese individuals are discussed and the contributions of Chinese researchers to the international corpus of knowledge about the genetic understanding of substance abuse are described.

Increased densities of nitric oxide synthase expressing neurons in the temporal cortex and the hypothalamic paraventricular nucleus of polytoxicomanic heroin overdose victims: possible implications for heroin neurotoxicity

Heroin is one of the most dangerous drugs of abuse, which may exert various neurotoxic actions on the brain (such as gray matter loss, neuronal apoptosis, mitochondrial dysfunction, synaptic defects, depression of adult neurogenensis, as well as development of spongiform leucoencephalopathy). Some of these toxic effects are probably mediated by the gas nitric oxide (NO). We studied by morphometric analysis the numerical density of neurons expressing neuronal nitric oxide synthase (nNOS) in cortical and hypothalamic areas of eight heroin overdose victims and nine matched controls. Heroin addicts showed significantly increased numerical densities of nNOS immunoreactive cells in the right temporal cortex and the left paraventricular nucleus. Remarkably, in heroin abusers, but not in controls, we observed not only immunostained interneurons, but also cortical pyramidal cells. Given that increased cellular expression of nNOS was accompanied by elevated NO generation in brains of heroin addicts, these elevated levels of NO might have contributed to some of the known toxic effects of heroin (for example, reduced adult neurogenesis, mitochondrial pathology or disturbances in synaptic functioning).

A population-based association study of casein kinase 1 epsilon loci with heroin dependence in Han Chinese

Pharmacogenetic studies have confirmed that the genetic variant of the casein kinase 1 epsilon (Csnk1ε) gene contributes to response variability to amphetamine and methamphetamine in both mice and humans. A polymorphism in the Csnk1ε gene has been reported to be associated with heroin dependence. In this study, to identify markers contributing to the genetic susceptibility of the Csnk1ε gene to heroin dependence, we examined the potential association between heroin dependence and 14 single nucleotide polymorphisms (SNPs; rs1997644, rs135764, rs867198, rs135763, rs135757, rs6001090, rs5750581, rs1534891, rs1005473, rs3890379, rs2075984, rs2075983, rs135749, and rs135745) of the Csnk1ε gene using the MassARRAY system. Participants included 398 heroin-dependent patients and 436 healthy controls from a Han Chinese population. The result revealed a strong association between the rs135745 (3'-untranslated region) genotype distribution and heroin dependence (P = 0.0006). The frequency of the C allele was significantly higher in the heroin-dependent patients than in the healthy controls (χ(2) = 7.172, P = 0.007, OR = 1.426, 95 % CI = 1.099-1.849). Further genotype and clinical phenotype correlation study of the rs135745 carriers showed that the amount of heroin self-injection was higher in patients with the GC + CC genotype compared to the patients with the GG genotypes (P < 0.01). Strong linkage disequilibrium (LD) was observed in block 1, block 2, and block 3 (D' > 0.9), whereas significant evidence of LD was not observed between these SNPs in our sample population. These findings point to a role for Csnk1ε polymorphisms in heroin dependence among the Han Chinese population and may be informative for future genetic or neurobiological studies on heroin dependence.