Chronic alcohol consumption may induce gene expression alterations in brain reward regions such as the prefrontal cortex (PFC), modulating the risk of alcohol use disorders (AUDs). Transcriptome profiles of 23 AUD cases and 23 matched controls (16 pairs of males and 7 pairs of females) in postmortem PFC were generated using Illumina’s HumanHT-12 v4 Expression BeadChip. Probe-level differentially expressed genes and gene modules in AUD subjects were identified using multiple linear regression and weighted gene co-expression network analyses. The enrichment of differentially co-expressed genes in alcohol dependence-associated genes identified by genome-wide association studies (GWAS) was examined using gene set enrichment analysis. Biological pathways overrepresented by differentially co-expressed genes were uncovered using DAVID bioinformatics resources. Three AUD-associated gene modules in males [Module 1 (561 probes mapping to 505 genes): r=0.42, Pcorrelation=0.020; Module 2 (815 probes mapping to 713 genes): r=0.41, Pcorrelation=0.020; Module 3 (1,446 probes mapping to 1,305 genes): r=−0.38, Pcorrelation=0.030] and one AUD-associated gene module in females [Module 4 (683 probes mapping to 652 genes): r=0.64, Pcorrelation=0.010] were identified. Differentially expressed genes mapped by significant expression probes (Pnominal≤0.05) clustered in Modules 1 and 2 were enriched in GWAS-identified alcohol dependence-associated genes [Module 1 (134 genes): P=0.028; Module 2 (243 genes): P=0.004]. These differentially expressed genes, including ALDH2, ALDH7A1, and ALDH9A1, are involved in cellular functions such as aldehyde detoxification, mitochondrial function, and fatty acid metabolism. Our study revealed differentially co-expressed genes in postmortem PFC of AUD subjects and demonstrated that some of these differentially co-expressed genes participate in alcohol metabolism.
Alcohol use disorders; postmortem prefrontal cortex; genome-wide gene expression; co-expression; gene set enrichment analysis; biological pathways
We report a GWAS for cocaine dependence (CD) in three sets of African- and European-American subjects (AAs and EAs, respectively), to identify pathways, genes, and alleles important in CD risk.
The discovery GWAS dataset (n=5,697 subjects) was genotyped using the Illumina OmniQuad microarray (890,000 analyzed SNPs). Additional genotypes were imputed based on the 1000 Genomes reference panel. Top-ranked findings were evaluated by incorporating information from publicly available GWAS data from 4,063 subjects. Then, the most significant GWAS SNPs were genotyped in 2,549 independent subjects.
We observed one genomewide-significant (GWS) result: rs7086629 at the FAM53B (“family with sequence similarity 53, member B”) locus. This was supported in both AAs and EAs; p-value (meta-analysis of all samples) =4.28×10−8. The gene maps to the same chromosomal region as the maximum peak we observed in a previous linkage study. NCOR2 (nuclear receptor corepressor 1) SNP rs150954431 was associated with p=1.19×10−9 in the EA discovery sample. SNP rs2456778, which maps to CDK1 (“cyclin-dependent kinase 1”), was associated with cocaine-induced paranoia in AAs in the discovery sample only (p=4.68×10−8).
This is the first study to identify risk variants for CD using GWAS. Our results implicate novel risk loci and provide insights into potential therapeutic and prevention strategies.
Cocaine dependence; cocaine-induced paranoia; GWAS; population genetics; European-American and African-American populations
Results from Genome-Wide Association Studies (GWAS) have shown that complex diseases are often affected by many genetic variants with small or moderate effects. Identifications of these risk variants remain a very challenging problem. There is a need to develop more powerful statistical methods to leverage available information to improve upon traditional approaches that focus on a single GWAS dataset without incorporating additional data. In this paper, we propose a novel statistical approach, GPA (Genetic analysis incorporating Pleiotropy and Annotation), to increase statistical power to identify risk variants through joint analysis of multiple GWAS data sets and annotation information because: (1) accumulating evidence suggests that different complex diseases share common risk bases, i.e., pleiotropy; and (2) functionally annotated variants have been consistently demonstrated to be enriched among GWAS hits. GPA can integrate multiple GWAS datasets and functional annotations to seek association signals, and it can also perform hypothesis testing to test the presence of pleiotropy and enrichment of functional annotation. Statistical inference of the model parameters and SNP ranking is achieved through an EM algorithm that can handle genome-wide markers efficiently. When we applied GPA to jointly analyze five psychiatric disorders with annotation information, not only did GPA identify many weak signals missed by the traditional single phenotype analysis, but it also revealed relationships in the genetic architecture of these disorders. Using our hypothesis testing framework, statistically significant pleiotropic effects were detected among these psychiatric disorders, and the markers annotated in the central nervous system genes and eQTLs from the Genotype-Tissue Expression (GTEx) database were significantly enriched. We also applied GPA to a bladder cancer GWAS data set with the ENCODE DNase-seq data from 125 cell lines. GPA was able to detect cell lines that are biologically more relevant to bladder cancer. The R implementation of GPA is currently available at http://dongjunchung.github.io/GPA/.
In the past 10 years, many genome wide association studies (GWAS) have been conducted to identify the genetic bases of complex human traits. As of January, 2014, more than 12,000 single-nucleotide polymorphisms (SNPs) have been reported to be significantly associated with at least one complex trait/disease. On one hand, about 85% of identified risk variants are located in non-coding regions, which motivates a systematic understanding of the function of non-coding variants in regulatory elements in the human genome. On the other hand, complex diseases are often affected by many genetic variants with small or moderate effects. To address these issues, we propose a statistical approach, GPA, to integrating information from multiple GWAS datasets and functional annotation. Notably, our approach only requires marker-wise p-values as input, making it especially useful when only summary statistics, instead of the full genotype and phenotype data, are available. We applied GPA to analyze GWAS datasets of five psychiatric disorders and bladder cancer, where the central nervous system genes, eQTLs from the Genotype-Tissue Expression (GTEx), and the ENCODE DNase-seq data from 125 cell lines were used as functional annotation. The analysis results suggest that GPA is an effective method for integrative data analysis in the post-GWAS era.
Emerging evidence suggests that neuroadaptations to alcohol may result from chronic alcohol consumption-induced expression changes of microRNAs (miRNAs) and their target genes. Studies with animal or cell culture models have demonstrated that ethanol exposure leads to miRNA expression alterations. However, there is limited information on miRNA expression in the brains of subjects with alcohol use disorders (AUDs). The present study aimed to analyze expression changes of miRNAs and their target genes in postmortem prefrontal cortex (PFC) of AUD subjects.
Genome-wide miRNA and mRNA expression was examined in postmortem PFC of 23 European Australia AUD cases and 23 matched controls using the Illumina HumanHT-12 v4 Expression BeadChip array, which targets 43,270 coding transcripts and 3,961 non-coding transcripts (including 574 miRNA transcripts). Multiple linear regression analysis and permutation test were performed to identify differentially expressed miRNAs and their target mRNAs. Target gene prediction, Gene Set Enrichment Analysis (GESA), and DAVID functional annotation clustering analysis were applied to identify AUD-associated gene sets and biological modules.
Two miRNAs and 787 coding genes were differentially expressed in the PFC of AUD cases [miR-130a (downregulated): Ppermutation=0.023, miR-604 (upregulated): Ppermutation=0.019, coding genes: 1.6×10−5≤Ppermutation≤0.05; but all P values did not survive multiple-testing correction]. GESA showed that the 202 predicted target genes of miR-130a were highly enriched in differentially expressed genes (Pnominal<0.001), but not the 116 predicted target genes of miR-604 (Pnominal=0.404). DAVID functional clustering further revealed that the hub target genes (e.g., ITPR2 and ATP1A2) of miRNA130a were mainly responsible for regulating ion channel function.
This study provides evidence that downregulation of miR-130a may lead to altered expression of a number of genes in the PFC of AUD subjects. Further studies are warranted to confirm these findings in replication samples and other reward-related brain regions.
microRNA; alcohol use disorders; postmortem prefrontal cortex; expression microarray
ADH1B and ADH1C variants have been robustly associated with alcohol phenotypes in East Asian populations but less so in non-Asian populations where prevalence of the most protective ADH1B allele is low (generally <5%). Further, the joint effects of ADH1B and ADH1C on alcohol phenotypes have been unclear. Therefore, we tested the independent and joint effects of ADH1B and ADH1C on alcohol phenotypes in an Israeli sample, with higher prevalence of the most protective ADH1B allele than other non-Asian populations.
A structured interview assessed lifetime drinking and alcohol use disorders (AUDs) in adult Israeli household residents. Four single nucleotide polymorphisms (SNPs) were genotyped: ADH1B (rs1229984, rs1229982, rs1159918) and ADH1C (rs698). Regression analysis examined the association between alcohol phenotypes and each SNP (absence vs. presence of the protective allele) as well as rs698/rs1229984 diplotypes (also indicating absence or presence of protective alleles) in lifetime drinkers (N=1,129).
Lack of the ADH1B rs1229984 protective allele was significantly associated with consumption- and AUD-related phenotypes (OR=1.77 for AUD; OR=1.83 for risk drinking), while lack of the ADH1C rs698 protective allele was significantly associated with AUD-related phenotypes (OR=2.32 for AUD). Diplotype analysis indicated that jointly, ADH1B and ADH1C significantly influenced AUD-related phenotypes. For example, among those without protective alleles for ADH1B or ADH1C, OR for AUD was 1.87 as compared to those without the protective allele for ADH1B only and 3.16 as compared to those with protective alleles at both ADH1B and ADH1C.
This study adds support for the relationship of ADH1B and ADH1C to alcohol phenotypes in non-Asians. Further, these findings help clarify the mixed results from previous studies by showing that ADH1B and ADH1C jointly effect AUDs, but not consumption. Studies of the association of alcohol phenotypes and either ADH1B or ADH1C alone may employ an oversimplified model, masking relevant information.
ADH1B; ADH1C; Alcohol use disorders; Alcohol consumption; Israel
Posttraumatic stress disorder (PTSD) is a moderately heritable anxiety disorder that may develop after exposure to trauma. However, only few genetic variants that relate to PTSD have been studied. This study examined the relationship between 12 single nucleotide polymorphisms (SNPs) in the corticotropin-releasing hormone receptor 1 gene (CRHR1) and post-disaster PTSD symptoms and diagnosis in adults exposed to 2004 Florida hurricanes. CRHR1 regulates the hypothalamic-pituitary-adrenal (HPA) axis; dysregulation of the HPA axis is characteristic of stress phenotypes. Final analyses were conducted in the European-American (EA) subsample (n=564) due to population stratification. After correction for multiple testing, rs12938031 and rs4792887 remained associated with post-hurricane PTSD symptoms. Additionally, rs4792887 was associated with post-hurricane diagnosis of PTSD. This study is the first to examine CRHR1 in relation to PTSD in adults, and provides evidence for the importance of CRHR1 variation in the etiology of PTSD. Although results are preliminary and require replication, they justify follow-up efforts to characterize how this gene relates to PTSD.
Posttraumatic stress disorder; CRHR1; HPA axis; disasters; trauma
Functional variants that contribute to genomewide association study (GWAS) signals are difficult to identify. MicroRNAs could contribute to some of these gene-trait relationships. We compiled a set of GWAS trait gene SNPs that were predicted to affect microRNA regulation of mRNA. Trait associations were tested in a sample of 6725 European-American (EA) and African-American (AA) subjects that were interviewed using the polydiagnostic SSADDA to diagnose major psychiatric disorders. A predicted miR-330-3p target site SNP (rs41305272) in mitogen-activated protein kinase kinase 5 (MAP2K5) mRNA was in LD (d’=1.0, r2=0.02) with a reported GWAS-identified variant for restless legs syndrome (RLS), a disorder frequently comorbid with anxiety and depression, possibly because of a shared pathophysiology. We examined the SNP’s association with mood and anxiety-related disorders. Rs41305272 was associated with agoraphobia (Ag) in EAs (odds ratio[OR]=1.95, p=0.007; 195 cases) and AAs (OR=3.2, p=0.03; 148 cases) and major depressive disorder (MDD) in AAs (OR=2.64, p=0.01; 427 cases), but not EAs (465 cases). Rs41305272*T carrier frequency was correlated with the number of anxiety and depressive disorders diagnosed per subject. RLS was not evaluated in our subjects. Predicted miR-330-3p target genes were enriched in pathways relevant to psychiatric disorders. These findings suggest that microRNA target site information may be useful in the analysis of GWAS signals for complex traits. MiR-330-3p and MAP2K5 are potentially important contributors to mood and anxiety-related traits. With support from additional studies, these findings could add to the large number of risk genes identified through association to medical disorders that have primary psychiatric effects.
restless legs syndrome; depression; miR-330; MEK5; GWAS
Male bonnet monkeys (Macaca radiata) were subjected to the Variable Foraging Demand (VFD) early stress paradigm as infants, MRI scans were completed an average of four years later, and behavioral assessments of anxiety and ex-vivo corpus callosum (CC) measurements were made when animals were fully matured. VFD rearing was associated with smaller CC size, CC measurements were found to correlate with fearful behavior in adulthood, and ex-vivo CC assessments showed high consistency with earlier MRI measures. Region of Interest (ROI) hippocampus and whole brain voxel- based morphometry assessments were also completed and VFD rearing was associated with reduced hippocampus and inferior and middle temporal gyri volumes. Animals were also characterized according to serotonin transporter genotype (5-HTTLPR), and the effect of genotype on imaging parameters was explored. The current findings highlight the importance of future research to better understand the effects of stress on brain development in multiple regions, including the corpus callosum, hippocampus, and other regions involved in emotion processing. Nonhuman primates provide a powerful model to unravel the mechanisms by which early stress and genetic makeup interact to produce long-term changes in brain development, stress reactivity, and risk for psychiatric disorders.
stress; monkeys; corpus callosum; hippocampus; brain abnormalities; 5-HTTLPR
Brain-derived neurotrophic factor (BDNF) is a neurotrophin that promotes neuronal survival, growth, and differentiation. The role of BDNF in learning and memory suggests that it may also modulate the clinical course of Alzheimer’s disease (AD). This study aimed to determine whether BDNF genetic variants are related to premorbid educational attainment, progression of cognitive and functional decline, and associated neuropsychiatric symptoms in AD patients. A sample of AD subjects (N = 341) was genotyped for the BDNF polymorphisms: Val66Met, C270T, and G-712A. Subjects received tests of cognition and daily function at baseline and at multiple subsequent time points. They were also characterized for the frequency and severity of neuropsychiatric symptoms. There was a significant effect of Val66Met genotype on educational attainment (F = 7.49, df = 2,329, P = 0.00066), with Met/Met homozygotes having significantly lower education than both the Val/Met and Val/Val groups. No association was observed between any BDNF polymorphism and measures of cognitive or functional decline. The T-allele of the C270T polymorphism was associated with a higher prevalence of neuropsychiatric symptoms and specifically with the presence of hallucinations. The effect of the Val66Met polymorphism on premorbid educational attainment is intriguing and should be verified in a larger sample.
Activities of daily living; Alzheimer’s disease; brain-derived neurotrophic factor; cognition; education; single nucleotide polymorphism
Childhood emotional abuse (CEA) is a pervasive problem associated with negative sequelae such as elevated depressive symptoms. Key stress-related genes, such as the 5-HTTLPR polymorphism, interact with childhood abuse to produce elevated depressive symptoms in older adolescent girls, but not in older adolescent boys. To date, studies have not examined this relationship as a function of CEA specifically or among younger adolescents. To extend prior work, we examined the effects of the 5-HTTLPR and CEA on depressive symptoms among 10–12-year-old youth. Based on previous findings, we expected a main effect of CEA on depressive symptoms among all youth, but only expected an interactive effect between the 5-HTTLPR and CEA on depressive symptoms in girls. In the current study, 222 youth (mean age 11.02 years, 44.1% girls, 51.6% Caucasian, 33.0% African American, 2.7% Latino, and 12.7% other) and their parent(s)/guardian(s) completed the Revised Child Anxiety and Depression Scale and the Emotional Abuse subscale of the Childhood Trauma Questionnaire and provided saliva samples for genotyping the 5-HTTLPR. Results indicate that CEA, but not the 5-HTTLPR, was related to elevated depressive symptoms among boys. Among girls, each copy of the s allele of the 5-HTTLPR was related to increased depressive symptoms, but only for those who had experienced CEA. Our results extend prior findings by specifically examining CEA and by focusing on 10–12-year-old youth. These results, although preliminary, suggest that focusing on the interplay between putative genetic markers and a broader range of environmental events, such as CEA, might allow researchers to determine factors differentially influencing the later emergence of sex differences in depressive symptoms.
emotional abuse; depressive symptoms; 5-HTTLPR; sex differences; early adolescence
The COMT Val158Met polymorphism may be a risk factor for nicotine addiction. This study examined the influence of the COMT Val158Met polymorphism on subjective, physiological, and cognitive effects of intravenous (IV) nicotine use in African American (AAs) (n=56) and European American (EAs) (n=68) smokers. Overnight abstinent smokers received saline followed by 0.5 and 1.0 mg/70 kg doses of nicotine, administered 30 minutes apart. Smokers with Val/Val genotype, compared to Met carriers, had greater negative subjective effects from IV nicotine and had more severe withdrawal severity following overnight abstinence from smoking. Women with Val/Val genotype reported greater difficulty concentrating and irritability than men with Val/Val or Met carrier genotypes. The Val/Val genotype was associated with better performance on the math task and in AA smokers it was associated with greater systolic blood pressure. These results support the rationale of pharmacologically inhibiting COMT to aid with smoking cessation among Val/Val genotype smokers.
Nicotine; Genetics; Pharmacogenetic; Smoking; Cigarette; COMT
Although the prevalence of depression among medical interns substantially exceeds that of the general population, the specific factors responsible are not well understood. Recent reports of a moderating effect of a genetic polymorphism (5-HTTLPR) in the serotonin transporter protein gene on the likelihood that life stress will precipitate depression may help to understand the development of mood symptoms in medical interns.
To identify psychological, demographic and residency program factors that associate with depression among interns and use medical internship as a model to study the moderating effects of this polymorphism using a prospective, within-subject design that addresses the design limitations of earlier studies.
Prospective cohort study
13 United States hospitals
740 interns entering participating residency programs
Main outcome measures
Subjects were assessed for depressive symptoms using the Patient Health Questionnaire (PHQ-9), a series of psychological traits and 5-HTTLPR genotype prior to internship and then assessed for depressive symptoms and potential stressors at 3-month intervals during internship.
The PHQ-9 depression score increased from 2.4 prior to internship to a mean of 6.4 during internship (p<0.001). The proportion of participants who met PHQ-9 criteria for depression increased from 3.9% prior to internship to a mean of 25.7% during internship (p<0.001). A series of factors measured prior to internship (female sex, U.S. medical education, difficult early family environment, history of major depression, lower baseline depressive symptom score and higher neuroticism) and during internship (increased work hours, perceived medical errors and stressful life events) were associated with a greater increase in depressive symptoms during internship. In addition, subjects with at least one copy of a less transcribed 5-HTTLPR allele reported a greater increase in depressive symptoms under the stress of internship (p=0.002).
There is a marked increase in depressive symptoms during medical internship. Specific individual, internship and genetic factors are associated with the increase in depressive symptoms.
Graduate; Medical; Education; Residency; Serotonin; Transporter
Little is known about the specificity of the interaction of serotonin transporter 5-HTTLPR genotype x trauma exposure in relation to contemporary structural models of PTSD symptomatology, which suggest that 4- or 5-factor models provide a better representation of this phenotypic expression of this disorder.
One hundred forty-nine respondents of a representative sample of adults affected by Hurricane Ike were interviewed 2 to 5 months after this 2008 disaster.
After adjustment for age, sex, and ancestral proportion scores, the interaction of 5-HTTPLR genotype x trauma exposure was significantly associated with both severity (β=.40, p<.001) and probable diagnosis (Wald=4.55, p=.033; odds ratio=3.81, 95%CI=1.11–13.03) of Ike-related PTSD. Respondents with the low-expression variant of the 5-HTTPLR polymorphism (S allele) who were highly exposed to Hurricane Ike reported significantly greater severity of PTSD symptoms and were more likely to screen positive for PTSD than respondents homozygous for the L allele who were highly exposed to Hurricane Ike. Confirmatory factor analyses revealed that a 5-factor model of intercorrelated re-experiencing, avoidance, numbing, dysphoric arousal, and anxious arousal symptoms provided the best structural representation of PTSD symptomatology. The 5-HTTPLR genotype x exposure interaction was significant only for anxious arousal (β=.44, p<.001) and re-experiencing (β=.35, p<.001) symptoms, but not avoidance, numbing, or dysphoric arousal symptoms (all β’s≤.20, all p’s>.13).
The small sample size and employment of self-report measures may limit generalizability of these findings.
Results of this pilot study suggest that the low-expression variant of the 5-HTTLPR polymorphism modifies risk for PTSD, but that this effect may be specific to anxious arousal and re-experiencing symptoms.
Serotonin transporter gene; Posttraumatic stress disorder; Trauma; Disaster
Genetic heterogeneity could reduce the power of linkage analysis to detect risk loci for complex traits such as alcohol dependence (AD). Previously, we performed a genomewide linkage analysis for AD in African-Americans (AAs) (Gelernter et al., 2009). The power of that linkage analysis could have been reduced by the presence of genetic heterogeneity owing to differences in admixture among AA families. We hypothesized that by examining a study sample whose genetic ancestry was more homogeneous we could increase the power to detect linkage. To test this hypothesis, we performed ordered subset linkage analysis (OSA) in 384 AA families using admixture proportion as a covariate to identify a more homogeneous subset of families and determine whether there is increased evidence for linkage with AD. Statistically significant increases in lod scores in subsets relative to the overall sample were identified on chromosomes 4 (P=0.0001), 12 (P=0.021), 15 (P=0.026) and 22 (P=0.0069). In a subset of 44 families with African ancestry proportions ranging from 0.858 to 0.996, we observed a genomewide significant linkage at 180 cM on chromosome 4 (lod=4.24, pointwise P<0.00001, empirical genomewide P=0.008). A promising candidate gene located there, GLRA3, which encodes a subunit of the glycine neurotransmitter receptor. Our results demonstrate that admixture proportion can be used as a covariate to reduce genetic heterogeneity and enhance the detection of linkage for AD in an admixed population such as AAs. This approach could be applied to any linkage analysis for complex traits conducted in an admixed population.
linkage; ordered subset linkage analysis; genetic heterogeneity; alcohol dependence; admixture
Understanding genetic influences on both healthy and disordered brain function is a major focus in psychiatric neuroimaging. We utilized task-related imaging findings from an fMRI auditory oddball task known to be robustly associated with abnormal activation in schizophrenia, to investigate genomic factors derived from multiple single nucleotide polymorphisms (SNP’s) from genes previously shown to be associated with schizophrenia. Our major aim was to investigate the relationship of these genomic factors to normal/abnormal brain functionality between controls and schizophrenia patients. We studied a Caucasian-only sample of 35 healthy controls and 31 schizophrenia patients. All subjects performed an auditory oddball task, which consists of detecting an infrequent sound within a series of frequent sounds. Each subject was characterized on 24 different SNP markers spanning multiple risk genes previously associated with schizophrenia. We used a recently developed technique named parallel independent component analysis (para-ICA) to analyze this multimodal dataset (Liu et al., 2008). The method aims to identify simultaneously independent components of each modality (functional imaging, genetics) and the relationships between them. We detected 3 fMRI components significantly correlated with two distinct gene components. The fMRI components, along with their significant genetic profile (dominant SNP) correlations were as follows: 1) Inferior frontal- anterior/posterior cingulate-thalamus-caudate with SNPs from Brain derived neurotropic factor (BDNF) & Dopamine Transporter, (DAT) [r=−0.51; p<0.0001], 2) Superior/middle temporal gyrus-Cingulate-premotor with SLC6A4_PR and SLC6A4_PR_AG (Serotonin transporter promoter; 5HTTLPR) [r=0.27; p=0.03], 3) Default Mode-fronto-temporal gyrus with Brain derived neurotropic factor & Dopamine Transporter (BDNF, DAT) [r=−0.25; p=0.04]. Functional components comprised taskrelevant regions (including PFC, ACC, STG and MTG) frequently identified as abnormal in schizophrenia. Further, gene-fMRI combinations 1 (Z=1.75; p=0.03), 2 (Z=1.84;p=0.03) and 3 (Z=1.67; p=0.04) listed above showed significant differences between controls and patients, based on their correlated loading coefficients. We demonstrate a framework to identify interactions between “clusters” of brain function and of genetic information. Our results reveal the effect/influence of specific interactions, (perhaps epistastatic in nature), between schizophrenia risk genes on imaging endophenotypes representing attention/working memory and goal directed related brain function, thus establishing a useful methodology to probe multivariate genotype-phenotype relationships.
auditory oddball; DAT; BDNF; fMRI; gene; parallel ICA; multivariate; 5HTTLPR
Neuronal nicotinic acetylcholine receptor (nAChR) genes (CHRNA5/CHRNA3/CHRNB4) have been reproducibly associated with nicotine dependence, smoking behaviors, and lung cancer risk. Of the few reports that have focused on early smoking behaviors, association results have been mixed. This meta-analysis examines early smoking phenotypes and SNPs in the gene cluster to determine: (1) whether the most robust association signal in this region (rs16969968) for other smoking behaviors is also associated with early behaviors, and/or (2) if additional statistically independent signals are important in early smoking. We focused on two phenotypes: age of tobacco initiation (AOI) and age of first regular tobacco use (AOS). This study included 56,034 subjects (41 groups) spanning nine countries and evaluated five SNPs including rs1948, rs16969968, rs578776, rs588765, and rs684513. Each dataset was analyzed using a centrally generated script. Meta-analyses were conducted from summary statistics. AOS yielded significant associations with SNPs rs578776 (beta = 0.02, P = 0.004), rs1948 (beta = 0.023, P = 0.018), and rs684513 (beta = 0.032, P = 0.017), indicating protective effects. There were no significant associations for the AOI phenotype. Importantly, rs16969968, the most replicated signal in this region for nicotine dependence, cigarettes per day, and cotinine levels, was not associated with AOI (P = 0.59) or AOS (P = 0.92). These results provide important insight into the complexity of smoking behavior phenotypes, and suggest that association signals in the CHRNA5/A3/B4 gene cluster affecting early smoking behaviors may be different from those affecting the mature nicotine dependence phenotype.
CHRNA5; CHRNA3; CHRNB4; meta-analysis; nicotine; smoke
Multiple substance dependence (MSD) trait comorbidity is common, and MSD patients are often severely affected clinically. While shared genetic risks have been documented, so far there has been no published report using the linkage scan approach to survey risk loci for MSD as a phenotype. A total of 1,758 individuals in 739 families [384 African American (AA) and 355 European American (EA) families] ascertained via affected sib-pairs with cocaine or opioid or alcohol dependence were genotyped using an array-based linkage panel of single-nucleotide polymorphism markers. Fuzzy clustering analysis was conducted on individuals with alcohol, cannabis, cocaine, opioid, and nicotine dependence for AAs and EAs separately, and linkage scans were conducted for the output membership coefficients using Merlin-regression. In EAs, we observed an autosome-wide significant linkage signal on chromosome 4 (peak lod = 3.31 at 68.3 cM; empirical autosome-wide P = 0.038), and a suggestive linkage signal on chromosome 21 (peak lod = 2.37 at 19.4 cM). In AAs, four suggestive linkage peaks were observed: two peaks on chromosome 10 (lod = 2.66 at 96.7 cM and lod = 3.02 at 147.6 cM] and the other two on chromosomes 3 (lod = 2.81 at 145.5 cM) and 9 (lod = 1.93 at 146.8 cM). Three particularly promising candidate genes, GABRA4, GABRB1, and CLOCK, are located within or very close to the autosome-wide significant linkage region for EAs on chromosome 4. This is the first linkage evidence supporting existence of genetic loci influencing risk for several comorbid disorders simultaneously in two major US populations.
comorbidity; multiple substance dependence; fuzzy clustering; chromosome 4
Child abuse is highly prevalent and associated with increased risk for a range of health problems including: cancer, cardiovascular disease, diabetes, psychiatric disorders, and other health problems. Little is currently known about the mechanism by which early adversity confers risk for health problems later in life.
To determine if there are epigenetic differences associated with child maltreatment that may help explain association between adverse childhood experiences and later health problems.
As part of a study examining genetic and environmental factors associated with depression, saliva DNA specimens were collected on 96 maltreated children removed from their parents due to abuse or neglect and 96 demographically-matched control children between 2003 and 2010. In 2011, the Illumina 450K BeadChip was used on stored DNA specimens and analyzed to examine whole-genome methylation differences between maltreated and control children.
After controlling for multiple comparisons, maltreated and control children had significantly different methylation values at 2868 CpG sites (p< 5.0 × 10−7, all sites; average methylation difference per site=17%; range 1%–62%). The gene set contained numerous markers of diseases and biological processes related to the health problems associated with early childhood adversity.
While replication is required, this study suggests that epigenetic mechanisms may be associated with risk for health problems later in life in maltreated children. This study lays the groundwork for future studies examining health and methylation measures to further characterize the role of epigenetic mechanisms in conferring risk for medical problems in individuals with histories of early adversity.
Epigenetic regulation through DNA methylation may influence vulnerability to numerous disorders, including alcohol dependence (AD).
Peripheral blood DNA methylation levels of 384 CpGs in the promoter regions of 82 candidate genes were examined in 285 African Americans (AAs; 141 AD cases and 144 controls) and 249 European Americans (EAs; 144 AD cases and 105 controls) using Illumina GoldenGate Methylation Array assays. Association of AD and DNA methylation changes were analyzed using multivariate analyses of covariance with frequency of intoxication, sex, age and ancestry proportion as covariates. CpGs showing significant methylation alterations in AD cases were further examined in a replication sample (49 EA cases and 32 EA controls) using Sequenom’s MassARRAY EpiTYPER technology.
In AAs, two CpGs in two genes (GABRB3 and POMC) were hypermethylated in AD cases compared to controls (P≤0.001). In EAs, six CpGs in six genes (HTR3A, NCAM1, DRD4, MBD3, HTR2B and GRIN1) were hypermethylated in AD cases compared to controls (P≤0.001); CpG cg08989585 in the HTR3A promoter region showed a significantly higher methylation level in EA cases than in EA controls after Bonferroni correction (P=0.00007). Additionally, methylation levels of six CpGs (including cg08989585) in the HTR3A promoter region were analyzed in the replication sample. Although the six HTR3A promoter CpGs did not show significant methylation differences between EA cases and EA controls (P=0.067–0.877), the methylation level of CpG cg08989585 was non-significantly higher in EA cases (26.9%) than in EA controls (18.6%) (P=0.139).
The findings from this study suggest that DNA methylation profile appears to be associated with AD in a population-specific way and the predisposition to AD may result from a complex interplay of genetic variation and epigenetic modifications.
Illumna GoldenGate Methylation Array; Sequenom MassARRAY EpiTYPER; Promoter CpGs; Alcohol Dependence; Peripheral Blood DNA
The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) will soon replace the DSM-IV, which has existed for nearly two decades. The changes in diagnostic criteria have important implications for research and for the clinical care of individuals with Substance Use Disorders (SUDs).
We used the Semi-Structured Assessment for Drug Dependence and Alcoholism to evaluate the lifetime presence of DSM-IV abuse and dependence diagnoses and DSM-5 mild, moderate, or severe SUDs for alcohol, cocaine, opioids, and cannabis in a sample of 7,543 individuals recruited to participate in genetic studies of substance dependence.
Switches between diagnostic systems consistently resulted in a modestly greater prevalence for DSM-5 SUDs, based largely on the assignment of DSM-5 diagnoses to DSM-IV “diagnostic ophans” (i.e., individuals meeting one or two criteria for dependence and none for abuse, and thus not receiving a DSM-IV SUD diagnosis). The vast majority of these diagnostic switches were attributable to the requirement that only two of 11 criteria be met for a DSM-5 SUD diagnosis. We found evidence to support the omission from DSM-5 of the legal criterion due to its limited diagnostic utility. The addition of craving as a criterion in DSM-5 did not substantially affect the likelihood of an SUD diagnosis.
The greatest advantage of DSM-5 appears to be its ability to capture diagnostic orphans. In this sample, changes reflected in DSM-5 had a minimal impact on the prevalence of SUD diagnoses.
DSM-IV; DSM-5; Substance Use Disorders; Substance Abuse; Substance Dependence
Catechol-O-methyltransferase (genetic locus, COMT) is a major enzyme involved in catecholamine metabolism and has been associated with numerous psychiatric phenotypes. We studied COMT SNPs and haplotypes in cocaine-induced paranoia (CIP) in African-American (AA) and European-American (EA) populations. We genotyped 17 SNPs across the COMT locus in 319 AA pedigrees (848 individuals) and 302 EA pedigrees (707 individuals). Family-controlled association analyses were conducted using FBAT. We found SNP rs737865 to be nominally significantly associated in the AA family population (p=0.05). In EAs, the best-known marker, rs4680 (Val158Met), was nominally significant in additive models (p=0.03). SNP rs174696 also showed nominal significance in additive models (p=0.02). We considered the 3 SNPs (rs737866-rs4680-rs174696) together in haplotype analysis in both family populations, using HBAT. The A-A-T haplotype was significantly associated with CIP in EAs (Z=2.845; p=0.0044, global p=0.020). We then studied COMT SNPs in an additional 738 AA and 404 EA unrelated cocaine dependent individuals with and without paranoia. The A-A-T haplotype was significantly associated to CIP in the AA unrelated population (p=0.0015). Two haplotypes, A-G-C and A-A-C, were significant in the EA unrelated population (p=0.001 and p=0.0003). We also identified rs4680 and three other SNPs, rs933271, rs5993883, and rs740603, as potentially functional variants, as predicted by a signature of positive selection in unrelated EAs and AAs. Based on our robust family-controlled and unrelated-affected analyses, we conclude that COMT is associated with CIP, possibly as a result of its role in the metabolism of dopamine and norepinephrine.
COMT; cocaine-induced paranoia; family-based analysis; haplotype; SNP; positive selection
Childhood adversity has been shown to interact with monoamine
oxidase-A (MAOA) genotype to confer risk for antisocial
behavior. Studies examining this gene-by-environment (G×E)
association, however, have produced mixed results.
Relevant research is reviewed, and results of a study with 114
children (73 maltreated and 41 control subjects) are presented. The
maltreated children represent the extreme on a continuum of adversity and
were assessed at a time of extreme stress—shortly after removal from
their parents’ care due to abuse. Measures of aggressive behavior
were obtained using standard research instruments, and monoamine oxidase-A
MAOA genotypes were obtained from saliva-derived DNA
specimens. Population structure was controlled for using ancestral
proportion scores computed on the basis of genotypes of ancestry informative
Many prior investigations appear to have had reduced power to detect
the predicted G×E interaction because of low base rates of
maltreatment and antisocial behavior in their samples and failure to use
optimal procedures to control for population structure in ethnically diverse
cohorts. In this investigation, a significant interaction was detected
between exposure to moderate trauma and the “low-activity”
MAOA genotype in conferring risk for aggression.
Children with exposure to extreme levels of trauma, however, had high
aggression scores regardless of genotype.
Our study suggests that problems in aggressive behavior in maltreated
children are moderated by MAOA genotype, but only up to
moderate levels of trauma exposure. Extreme levels of trauma appear to
overshadow the effect of MAOA genotype, especially in
children assessed at time of acute crisis.
Aggression; antisocial; child abuse; gene–environment interaction; maltreatment; MAOA
Genetic factors influence the risk for posttraumatic stress disorder (PTSD), a potentially chronic and disabling psychiatric disorder that can arise after exposure to trauma. Candidate gene association studies have identified few genetic variants that contribute to PTSD risk.
We conducted genome-wide association analyses in 1578 European Americans (EAs), including 300 PTSD cases, and 2766 African Americans, including 444 PTSD cases, to find novel common risk alleles for PTSD. We used the Illumina Omni1-Quad microarray, which yielded approximately 870,000 single nucleotide polymorphisms (SNPs) suitable for analysis.
In EAs, we observed that one SNP on chromosome 7p12, rs406001, exceeded genome-wide significance (p = 3.97×10−8). A SNP that maps to the first intron of the Tolloid-Like 1 gene (TLL1) showed the second strongest evidence of association, although no SNPs at this locus reached genome-wide significance. We then tested six SNPs in an independent sample of nearly 2000 EAs and successfully replicated the association findings for two SNPs in the first intron of TLL1, rs6812849 and rs7691872, with p values of 6.3×10−6 and 2.3×10−4, respectively. In the combined sample, rs6812849 had a p value of 3.1 ×10−9. No significant signals were observed in the African American part of the sample. Genome-wide association study analyses restricted to trauma-exposed individuals yielded very similar results.
This study identified TLL1 as a new susceptibility gene for PTSD.
American populations; genome-wide association study; posttraumatic stress disorder; TLL1