Genome-wide linkage analysis of heroin dependence in Han Chinese: results from Wave Two of a multi-stage study

Risk Assessment for Heroin Use and Craving Score Using Polygenic Risk Score

Addiction is characterized by drug-craving, compulsive drug-taking, and relapse, and results from the interaction between multiple genetic and environmental factors. Reward pathways play an important role in mediating drug-seeking and drug-taking behaviors, and relapse. The objective of this study was to identify heroin addicts who carry specific genetic variants in their dopaminergic reward systems. A total of 326 heroin-dependent patients undergoing methadone maintenance therapy (MMT) were recruited from the Addiction Center of the China Medical University Hospital. A heroin-use and craving questionnaire was used to evaluate the urge for heroin, the daily or weekly frequency of heroin usage, daily life disturbance, anxiety, and the ability to overcome heroin use. A general linear regression model was used to assess the associations of genetic polymorphisms in one's dopaminergic reward system with heroin-use and craving scores. Results: The most significant results were obtained for rs2240158 in GRIN3B (p = 0.021), rs3983721 in GRIN3A (p = 0.00326), rs2129575 in TPH2 (p = 0.033), rs6583954 in CYP2C19 (p = 0.033), and rs174699 in COMT (p = 0.036). These were all associated with heroin-using and craving scores with and without adjustments for age, sex, and body mass index. We combined five variants, and the ensuing dose-response effect indicated that heroin-craving scores increased with the numbers of risk alleles (p for trend = 0.0008). These findings will likely help us to understand the genetic mechanism of craving, which will help in predicting the risk of relapse in clinical practice and the potential for therapies to target craving in heroin addiction.

Genome-Wide Association Study of Opioid Cessation

The United States is experiencing an epidemic of opioid use disorder (OUD) and overdose-related deaths. However, the genetic basis for the ability to discontinue opioid use has not been investigated. We performed a genome-wide association study (GWAS) of opioid cessation (defined as abstinence from illicit opioids for >1 year or <6 months before the interview date) in 1130 African American (AA) and 2919 European ancestry (EA) participants recruited for genetic studies of substance use disorders and who met lifetime Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for OUD. Association tests performed separately within each ethnic group were combined by meta-analysis with results obtained from the Comorbidity and Trauma Study. Although there were no genome-wide significant associations, we found suggestive associations with nine independent loci, including three which are biologically relevant: rs4740988 in PTPRD (p_{AA + EA} = 2.24 × 10⁻⁶), rs36098404 in MYOM2 (p_EA = 2.24 × 10⁻⁶), and rs592026 in SNAP25-AS1 (p_EA = 6.53 × 10⁻⁶). Significant pathways identified in persons of European ancestry (EA) are related to vitamin D metabolism (p = 3.79 × 10⁻²) and fibroblast growth factor (FGF) signaling (p = 2.39 × 10⁻²). UK Biobank traits including smoking and drinking cessation and chronic back pain were significantly associated with opioid cessation using GWAS-derived polygenic risk scores. These results provide evidence for genetic influences on opioid cessation, suggest genetic overlap with other relevant traits, and may indicate potential novel therapeutic targets for OUD.

Construction and Analysis of Protein-Protein Interaction Network of Heroin Use Disorder

Heroin use disorder (HUD) is a complex disease resulting from interactions among genetic and other factors (e.g., environmental factors). The mechanism of HUD development remains unknown. Newly developed network medicine tools provide a platform for exploring complex diseases at the system level. This study proposes that protein–protein interactions (PPIs), particularly those among proteins encoded by casual or susceptibility genes, are extremely crucial for HUD development. The giant component of our constructed PPI network comprised 111 nodes with 553 edges, including 16 proteins with large degree (k) or high betweenness centrality (BC), which were further identified as the backbone of the network. JUN with the largest degree was suggested to be central to the PPI network associated with HUD. Moreover, PCK1 with the highest BC and MAPK14 with the secondary largest degree and 9^th highest BC might be involved in the development HUD and other substance diseases.

Sex-specific linkage scans in opioid dependence

Sex influences risk for opioid dependence (OD). We hypothesized that sex might interact with genetic loci that influence the risk for OD. Therefore we performed an analysis to identify sex-specific genomic susceptibility regions for OD using linkage. Over 6,000 single nucleotide polymorphism (SNP) markers were genotyped for 1,758 African- and European-American (AA and EA) individuals from 739 families, ascertained via affected sib-pairs with OD and/or cocaine dependence. Autosomewide non-parametric linkage scans, stratified by sex and population, were performed. We identified one significant linkage region, segregating with OD in EA men, at 71.1 cM on chromosome 4 (LOD = 3.29; point-wise P = 0.00005; empirical autosome-wide P = 0.042), which significantly differed from the linkage signal at the same location in EA women (empirical P = 0.002). Three suggestive linkage signals were identified at 181.3 cM on chromosome 7 (LOD = 2.18), 104 cM on chromosome 11 (LOD = 1.85), and 60.9 cM on chromosome 16 (LOD = 1.93) in EA women. In AA men, four suggestive linkage signals were detected at 201.1 cM on chromosome 3 (LOD = 2.32), 152.9 cM on chromosome 6 (LOD = 1.86), 16.8 cM on chromosome 7 (LOD = 1.95), and 36.1 cM on chromosome 17 (LOD = 1.99). The significant region, mapping to 4q12-4q13.1, harbors several OD candidate genes with interconnected functionality, including VEGFR, CLOCK, PDCL2, NMU, NRSF, and IGFBP7. In conclusion, these results provide an evidence for the existence of sex-specific and population-specific differences in OD. Furthermore, these results provide positional information that will facilitate the use of targeted next-generation sequencing to search for genes that contribute to sex-specific differences in OD. © 2016 Wiley Periodicals, Inc.

Psychiatric genetics in China: achievements and challenges

To coordinate research efforts in psychiatric genetics in China, a group of Chinese and foreign investigators have established an annual “Summit on Chinese Psychiatric Genetics” to present their latest research and discuss the current state and future directions of this field. To date, two Summits have been held, the first in Changsha in April, 2014, and the second in Kunming in April, 2015. The consensus of roundtable discussions held at these meetings is that psychiatric genetics in China is in need of new policies to promote collaborations aimed at creating a framework for genetic research appropriate for the Chinese population: relying solely on Caucasian population-based studies may result in missed opportunities to diagnose and treat psychiatric disorders. In addition, participants agree on the importance of promoting collaborations and data sharing in areas where China has especially strong resources, such as advanced facilities for non-human primate studies and traditional Chinese medicine: areas that may also provide overseas investigators with unique research opportunities. In this paper, we present an overview of the current state of psychiatric genetics research in China, with emphasis on genome-level studies, and describe challenges and opportunities for future advances, particularly at the dawn of “precision medicine.” Together, we call on administrative bodies, funding agencies, the research community, and the public at large for increased support for research on the genetic basis of psychiatric disorders in the Chinese population. In our opinion, increased public awareness and effective collaborative research hold the keys to the future of psychiatric genetics in China.

Association of dopamine receptor gene polymorphism and psychological personality traits in liability for opioid addiction

There is a clear evidence that same psychoactive substance may cause various individual physiological reactions in same environmental conditions. Although there is a general attitude on equal liability to opioid addiction, latest genetic analysis findings imply there are certain quantifiable factors that could lead to elevated individual liability towards development of opioid addiction. The goal of this study was to investigate association of certain personality traits and genetic factors (separately and in combination) with heroin addiction. Total of 200 individuals participated in the study: 100 patients on Metadone Maintenance Treatment (MMT) and 100 age and sex matched healthy volunteers. All were medically examined, interviewed and psychologically evaluated using Eysenck personality questionnaire (EPQ) and genotyped for DRD2 (rs1800497) using PCR-RFLP method. Overrepresentation of certain personality traits (neuroticism, psychoticism and extraversion/ intraversion), together with environemental risk factors such as: upbringing within incomplete families and familial history of psychotropic substances abuse, are associated with high-risk development of opioid addiction.

ALDH2 is associated to alcohol dependence and is the major genetic determinant of "daily maximum drinks" in a GWAS study of an isolated rural Chinese sample

Alcohol dependence (AD) is a moderately heritable phenotype with a small number of known risk genes mapped via linkage or candidate gene studies. We considered 313 males from among 595 members of documented, extended pedigrees in which AD segregates collected in Northern Hunan Province, China. A joint analysis of both males and females could not be performed as the difference in alcohol consumption variance was too large. Genome-wide association analyses were performed for approximately 300,000 single nucleotide polymorphisms (SNPs). Significant associations found in the ALDH2 region for AD (minimum P = 4.73 × 10(-8)) and two AD-related phenotypes: flushing response (minimum P = 4.75 × 10(-26)) and maximum drinks in a 24-hr period (minimum P = 1.54 × 10(-16)). Association of previous candidate SNP, rs10774610 in CCDC63, was confirmed but resulted from linkage disequilibrium with ALDH2. ALDH2 is strongly associated with flushing response, AD, and maximum drinks in males, with nonsynonymous SNP rs671 explaining 29.2%, 7.9%, and 22.9% of phenotypic variation, respectively, in this sample. When rs671 was considered as a candidate SNP in females, it explained 23.6% of the variation in flushing response, but alcohol consumption rates were too low among females-despite familial enrichment for AD-for an adequate test of association for either AD or maximum drinks. These results support a mediating effect of aldehyde dehydrogenase deficiency on alcohol consumption in males and a secondary, culturally mediated limitation on alcohol consumption by females that should be appropriately modeled in future studies of alcohol consumption in populations where this may be a factor.

The genetics of substance dependence

A large segment of the population suffers from addiction to alcohol, smoking, or illicit drugs. Not only do substance abuse and addiction pose a threat to health, but the consequences of addiction also impose a social and economic burden on families, communities, and nations. Genome-wide linkage and association studies have been used for addiction research with varying degrees of success. The most well-established genetic factors associated with alcohol dependence are in the genes encoding alcohol dehydrogenase (ADH), which oxidizes alcohol to acetaldehyde, and aldehyde dehydrogenase (ALDH2), which oxidizes acetaldehyde to acetate. Recently emerging genetic studies have linked variants in the genes encoding the α3, α5, and β4 nicotinic acetylcholine receptor subunits to smoking risk. However, the influence of these well-established genetic variants accounts for only a small portion of the heritability of alcohol and nicotine addiction, and it is likely that there are both common and rare risk variants yet to be identified. Newly developed DNA sequencing technologies could potentially advance the detection of rare variants with a larger impact on addiction risk.

Genome-wide association study identifies genes that may contribute to risk for developing heroin addiction

OBJECTIVES

We have used genome-wide association studies to identify variants that are associated with vulnerability to develop heroin addiction.

METHODS

DNA from 325 methadone stabilized, former severe heroin addicts and 250 control individuals were pooled by ethnicity (Caucasian and African-American) and analyzed using the Affymetrix GeneChip Mapping 100 K Set. Genome-wide association tests were conducted.

RESULTS

The strongest association with vulnerability to develop heroin addiction, with experiment-wise significance (P=0.035), was found in Caucasians with the variant rs10494334, a variant in an unannotated region of the genome (1q23.3). In African Americans, the variant most significantly associated with the heroin addiction vulnerability was rs950302, found in the cytosolic dual specificity phosphatase 27 gene DUSP27 (point-wise P=0.0079). Furthermore, analysis of the top 500 variants with the most significant associations (point-wise P< or =0.0036) in Caucasians showed that three of these variants are clustered in the regulating synaptic membrane exocytosis protein 2 gene RIMS2. Of the top 500 variants in African-Americans (point-wise P< or =0.0238), three variants are in the cardiomyopathy associated 3 gene CMYA3.

CONCLUSION

This study identifies new genes and variants that may increase an individual's vulnerability to develop heroin addiction.

ChIP-chip analysis of neurexins and other candidate genes for addiction and neuropsychiatric disorders

Several addiction susceptibility genes have been mapped by linkage and genomewide association. However, functional alleles associated with disease risk have not been identified, with a few possible exceptions. In addition, little is known about the cis- and trans-acting factors involved in regulating their expression. To address these issues, we used a ChIP-chip approach to identify regulatory elements in fetal-brain- targeting genes implicated in addiction and other neuropsychiatric conditions. Our data point to a number of putative regulatory elements, several of which, we show, are functionally significant. Many established or putative regulatory elements map near-disease-associated SNPs. These regions would be of interest to survey for patient-specific functional variants involved in disease susceptibility.

Search for genetic markers and functional variants involved in the development of opiate and cocaine addiction and treatment

Addiction to opiates and illicit use of psychostimulants is a chronic, relapsing brain disease that, if left untreated, can cause major medical, social, and economic problems. This article reviews recent progress in studies of association of gene variants with vulnerability to develop opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems. In addition, we provide the first evidence of a cis-acting polymorphism and a functional haplotype in the PDYN gene, of significantly higher DNA methylation rate of the OPRM1 gene in the lymphocytes of heroin addicts, and significant differences in genotype frequencies of three single-nucleotide polymorphisms of the P-glycoprotein gene (ABCB1) between "higher" and "lower" methadone doses in methadone-maintained patients. In genomewide and multigene association studies, we found association of several new genes and new variants of known genes with heroin addiction. Finally, we describe the development and application of a novel technique: molecular haplotyping for studies in genetics of drug addiction.

Genetics of drug dependence

Drug-dependence disorders (we focus here on cocaine, opioid, and nicotine dependence) are genetically influenced. Risk genes have been located based primarily on genetic linkage studies, and identified primarily based on genetic association studies. In this article we review salient results from linkage, association, and genome-wide association study methodologies, and discuss future prospects for risk allele identification based on these, and on newer, methodologies. Although considerable progress has been made, it is likely that the application of more extensive sequencing than has previously been practical will be required to identify a fuller range of risk variants.