Additive Effects of Stress and Alcohol Exposure on Accelerated Epigenetic Aging in Alcohol Use Disorder

BACKGROUND

Stress contributes to premature aging and susceptibility to alcohol use disorder (AUD), and AUD itself is a factor in premature aging; however, the interrelationships of stress, AUD, and premature aging are poorly understood.

METHODS

We constructed a composite score of stress from 13 stress-related outcomes in a discovery cohort of 317 individuals with AUD and control subjects. We then developed a novel methylation score of stress (MS stress) as a proxy of composite score of stress comprising 211 CpGs selected using a penalized regression model. The effects of MS stress on health outcomes and epigenetic aging were assessed in a sample of 615 patients with AUD and control subjects using epigenetic clocks and DNA methylation-based telomere length. Statistical analysis with an additive model using MS stress and a MS for alcohol consumption (MS alcohol) was conducted. Results were replicated in 2 independent cohorts (Generation Scotland, N = 7028 and the Grady Trauma Project, N = 795).

RESULTS

Composite score of stress and MS stress were strongly associated with heavy alcohol consumption, trauma experience, epigenetic age acceleration (EAA), and shortened DNA methylation-based telomere length in AUD. Together, MS stress and MS alcohol additively showed strong stepwise increases in EAA. Replication analyses showed robust association between MS stress and EAA in the Generation Scotland and Grady Trauma Project cohorts.

CONCLUSIONS

A methylation-derived score tracking stress exposure is associated with various stress-related phenotypes and EAA. Stress and alcohol have additive effects on aging, offering new insights into the pathophysiology of premature aging in AUD and, potentially, other aspects of gene dysregulation in this disorder.

Functional Genomic Analysis of Amphetamine Sensitivity in Drosophila

Abuse of psychostimulants, including amphetamines (AMPHs), is a major public health problem with profound psychiatric, medical, and psychosocial complications. The actions of these drugs at the dopamine transporter (DAT) play a critical role in their therapeutic efficacy as well as their liability for abuse and dependence. To date, however, the mechanisms that mediate these actions are not well-understood, and therapeutic interventions for AMPH abuse have been limited. Drug exposure can induce broad changes in gene expression that can contribute to neuroplasticity and effect long-lasting changes in neuronal function. Identifying genes and gene pathways perturbed by drug exposure is essential to our understanding of the molecular basis of drug addiction. In this study, we used Drosophila as a model to examine AMPH-induced transcriptional changes that are DAT-dependent, as those would be the most relevant to the stimulatory effects of the drug. Using this approach, we found genes involved in the control of mRNA translation to be significantly upregulated in response to AMPH in a DAT-dependent manner. To further prioritize genes for validation, we explored functional convergence between these genes and genes we identified in a genome-wide association study of AMPH sensitivity using the Drosophila Genetic Reference Panel. We validated a number of these genes by showing that they act specifically in dopamine neurons to mediate the behavioral effects of AMPH. Taken together, our data establish Drosophila as a powerful model that enables the integration of behavioral, genomic and transcriptomic data, followed by rapid gene validation, to investigate the molecular underpinnings of psychostimulant action.

Maternal posttraumatic stress and FKBP5 Genotype interact to predict trauma-related symptoms in preschool-age offspring

BACKGROUND

Children of parents with posttraumatic stress (PTS) face heightened risk for developing emotional and behavioral problems, regardless of whether they experience a traumatic event themselves. The current study investigates whether child FKBP5, a stress relevant gene shown to interact with child trauma exposure to increase risk for PTS, also moderates the well-established link between maternal PTS and child symptoms.

METHODS

Data are derived from a longitudinal lab-based study for which 205 dyads of trauma-exposed mothers and their preschool-age children from a sample enriched for violence exposure provided DNA samples and completed measures of maternal and child trauma-related symptoms. Hypotheses tested whether child FKBP5 rs1360780 SNP genotype interacts with child trauma exposure and maternal PTS to predict child trauma-related symptoms.

RESULTS

Hypotheses were partially supported, with maternal PTS predicting increased child symptoms for children carrying the minor T-allele (CT/TT), but not those homozygous for the major C-allele.

LIMITATIONS

Study results may not generalize to lower-risk or non-clinical populations, did not assess between-group differences in race/ethnicity, and do not consider other genes that may interact with FKBP5 or contribute to genetic risk for trauma-related impairment.

CONCLUSIONS

These findings provide the first evidence that the robust gene x environment interaction involving FKBP5 and child trauma exposure extends to other environmental perturbations, including maternal PTS. Our results highlight the importance of efforts to address trauma-related psychopathology in caregivers, which may disrupt intergenerational risk processes and improve outcomes for children.

Serotonin system genes contribute to the susceptibility to obesity in Black adolescents

OBJECTIVE

The importance of the central and peripheral serotonin systems in regulating energy balance and obesity development has been highlighted in animal models. Yet, the role of both serotonin systems has not been systematically assessed in humans. The purpose of this study was to investigate the association of genes within both serotonin systems with obesity outcomes in black adolescents.

METHODS

African-American adolescents (n = 1052) whose mothers participated the Memphis New Mother's Study were assessed. In total, 110 polymorphisms mapped to 10 serotonin genes were examined for their associations with standardized body mass index (BMI-z) scores and waist circumferences using generalized estimating equation models.

RESULTS

Over 39% of adolescents were overweight or had obesity. Three single nucleotide polymorphisms (SNPs) within TPH2, HTR3B, and SLC6A4, were significantly associated with BMI-z scores (p < 1.7 × 10-3). Two SNPs in TPH2 were nominally associated with waist circumferences. One SNP in HTR2C was associated with BMI-z scores (p = 0.001) and waist circumferences (p = 0.005) only in girls. Tissue-specific expression indicates that three identified genes are predominantly expressed in the brain.

CONCLUSION

The central serotonin system may play a key role in obesity development in black adolescents. Future studies are warranted to explore additional serotonin system genes and their potential obesogenic mechanisms in humans.

Epigenome-wide association study and multi-tissue replication of individuals with alcohol use disorder: evidence for abnormal glucocorticoid signaling pathway gene regulation

Alcohol use disorder (AUD) is a chronic debilitating disorder with limited treatment options and poorly defined pathophysiology. There are substantial genetic and epigenetic components; however, the underlying mechanisms contributing to AUD remain largely unknown. We conducted the largest DNA methylation epigenome-wide association study (EWAS) analyses currently available for AUD (total N = 625) and employed a top hit replication (N = 4798) using a cross-tissue/cross-phenotypic approach with the goal of identifying novel epigenetic targets relevant to AUD. Results show that a network of differentially methylated regions in glucocorticoid signaling and inflammation-related genes were associated with alcohol use behaviors. A top probe consistently associated across all cohorts was located in the long non-coding RNA growth arrest specific five gene (GAS5) (p < 10-24). GAS5 has been implicated in regulating transcriptional activity of the glucocorticoid receptor and has multiple functions related to apoptosis, immune function and various cancers. Endophenotypic analyses using peripheral cortisol levels and neuroimaging paradigms showed that methylomic variation in GAS5 network-related probes were associated with stress phenotypes. Postmortem brain analyses documented increased GAS5 expression in the amygdala of individuals with AUD. Our data suggest that alcohol use is associated with differential methylation in the glucocorticoid system that might influence stress and inflammatory reactivity and subsequently risk for AUD.

Leptin Gene and Leptin Receptor Gene Polymorphisms in Alcohol Use Disorder: Findings Related to Psychopathology

Comorbidity between alcohol use disorder (AUD) and other addictive and psychiatric disorders is highly prevalent and disabling; however, the underlying biological correlates are not fully understood. Leptin is a peptide hormone known for its role in energy homeostasis and food intake. Furthermore, leptin plays a key role in the activity of the hypothalamic-pituitary-adrenal (HPA) axis and of several neurotransmitter systems that regulate emotionality and behavior. However, human studies that have investigated circulating leptin levels in relation to AUD and affective disorders, such as anxiety and depression, are conflicting. Genetic-based analyses of the leptin gene (LEP) and leptin receptor gene (LEPR) have the potential of providing more insight into the potential role of the leptin system in AUD and comorbid psychopathology. The aim of the current study was to investigate whether genotypic variations at LEP and LEPR are associated with measures of alcohol use, nicotine use, anxiety, and depression, all of which represent common comorbidities with AUD. Haplotype association analyses were performed, using data from participants enrolled in screening and natural history protocols at the National Institute on Alcohol Abuse and Alcoholism (NIAAA). Analyses were performed separately in European Americans and African Americans due to the variation in haplotype diversity for most genes between these groups. In the European American group, one LEP haplotype (EB2H4) was associated with lower odds of having a current AUD diagnosis, two LEPR haplotypes (EB7H3, EB8H3) were associated with lower cigarette pack years and two LEPR haplotypes (EB7H2, EB8H2) were associated with higher State-Trait Anxiety Inventory (STAI-T) scores. In the African American group, one LEP haplotype (AB2H8) was associated with higher cigarette pack years and one LEP haplotype (AB3H2) was associated with lower Fagerström Test for Nicotine Dependence (FTND) scores. Overall, this study found that variations in the leptin and leptin receptor genes are associated with measures of alcohol use, nicotine use, and anxiety. While this preliminary study adds support for a role of the leptin system in AUD and psychopathologies, additional studies are required to fully understand the underlying mechanisms and potential therapeutic implications of these findings.

FAAH and CNR1 Polymorphisms in the Endocannabinoid System and Alcohol-Related Sleep Quality

Sleep disturbances are common among individuals with alcohol use disorder (AUD) and may not resolve completely with short-term abstinence from alcohol, potentially contributing to relapse to drinking. The endocannabinoid system (ECS) is associated with both sleep and alcohol consumption, and genetic variation in the ECS may underlie sleep-related phenotypes among individuals with AUD. In this study, we explored the influence of genetic variants in the ECS (Cannabinoid receptor 1/CNR1: rs806368, rs1049353, rs6454674, rs2180619, and Fatty Acid Amide Hydrolase/FAAH rs324420) on sleep quality in individuals with AUD (N = 497) and controls without AUD (N = 389). We assessed subjective sleep quality (from the Pittsburgh Sleep Quality Index/PSQI) for both groups at baseline and objective sleep efficiency and duration (using actigraphy) in a subset of individuals with AUD at baseline and after 4 weeks of inpatient treatment. We observed a dose-dependent relationship between alcohol consumption and sleep quality in both AUD and control groups. Sleep disturbance, a subscale measure in PSQI, differed significantly among CNR1 rs6454674 genotypes in both AUD (p = 0.015) and controls (p = 0.016). Only among controls, neuroticism personality scores mediated the relationship between genotype and sleep disturbance. Objective sleep measures (sleep efficiency, wake bouts and wake after sleep onset), differed significantly by CNR1 rs806368 genotype, both at baseline (p = 0.023, 0.029, 0.015, respectively) and at follow-up (p = 0.004, p = 0.006, p = 0.007, respectively), and by FAAH genotype for actigraphy recorded sleep duration at follow-up (p = 0.018). These relationships suggest a significant role of the ECS in alcohol-related sleep phenotypes.

TSPO polymorphism in individuals with alcohol use disorder: Association with cholesterol levels and withdrawal severity

The translocator protein (TSPO) transports cholesterol into mitochondria and is involved in steroidogenesis. The TSPO polymorphism rs6971 influences binding of cholesterol and other TSPO ligands including positron-emission tomography (PET) imaging radiotracers. Although it is recognized that alcohol increases plasma high-density lipoproteins (HDLs), its effects on total cholesterol and triglycerides along with its relationship to TSPO genotype have not been assessed. Here, we evaluated whether plasma cholesterol and triglycerides are disrupted in alcohol use disorder (AUD) and their association with rs6971 in 932 AUD participants (DSM IV or 5) and 546 controls. AUD participants compared with controls had significantly higher plasma levels of total cholesterol, HDL, and triglycerides, but not of low-density lipoprotein (LDL). In the AUD group only, TSPO rs6971 had a significant effect on plasma levels of cholesterol, LDL, and triglycerides (AA (n = 62) > AG (n = 319) > GG (n = 551)), but not on HDL levels. Additionally, we showed a significant effect of TSPO rs6971 on withdrawal scores (Clinical Institute Withdrawal Assessment for Alcohol [CIWA]), with higher scores in AA (n = 50) compared with AG (n = 238) and GG (n = 428). CIWA scores in AUD participants correlated negatively with LDL and positively with HDL, but not with total cholesterol or triglycerides. These findings corroborate elevated plasma cholesterol and HDL levels in AUD and document significant increases in triglycerides. We also reveal for the first time an association in AUD participants between TSPO rs6971 genotype and plasma cholesterol, LDL, and triglyceride levels (not for HDL) and with withdrawal severity. Mediation analyses revealed that LDL (but not HDL) influenced the association between TSPO and alcohol withdrawal severity.

Host-parasite interaction associated with major mental illness

Clinical studies frequently report that patients with major mental illness such as schizophrenia and bipolar disorder have co-morbid physical conditions, suggesting that systemic alterations affecting both brain and peripheral tissues might underlie the disorders. Numerous studies have reported elevated levels of anti-Toxoplasma gondii (T. gondii) antibodies in patients with major mental illnesses, but the underlying mechanism was unclear. Using multidisciplinary epidemiological, cell biological, and gene expression profiling approaches, we report here multiple lines of evidence suggesting that a major mental illness-related susceptibility factor, Disrupted in schizophrenia (DISC1), is involved in host immune responses against T. gondii infection. Specifically, our cell biology and gene expression studies have revealed that DISC1 Leu607Phe variation, which changes DISC1 interaction with activating transcription factor 4 (ATF4), modifies gene expression patterns upon T. gondii infection. Our epidemiological data have also shown that DISC1 607 Phe/Phe genotype was associated with higher T. gondii antibody levels in sera. Although further studies are required, our study provides mechanistic insight into one of the few well-replicated serological observations in major mental illness.

Epigenetic aging is accelerated in alcohol use disorder and regulated by genetic variation in APOL2

To investigate the potential role of alcohol use disorder (AUD) in aging processes, we employed Levine's epigenetic clock (DNAm PhenoAge) to estimate DNA methylation age in 331 individuals with AUD and 201 healthy controls (HC). We evaluated the effects of heavy, chronic alcohol consumption on epigenetic age acceleration (EAA) using clinical biomarkers, including liver function test enzymes (LFTs) and clinical measures. To characterize potential underlying genetic variation contributing to EAA in AUD, we performed genome-wide association studies (GWAS) on EAA, including pathway analyses. We followed up on relevant top findings with in silico expression quantitative trait loci (eQTL) analyses for biological function using the BRAINEAC database. There was a 2.22-year age acceleration in AUD compared to controls after adjusting for gender and blood cell composition (p = 1.85 × 10^-5). This association remained significant after adjusting for race, body mass index, and smoking status (1.38 years, p = 0.02). Secondary analyses showed more pronounced EAA in individuals with more severe AUD-associated phenotypes, including elevated gamma-glutamyl transferase (GGT) and alanine aminotransferase (ALT), and higher number of heavy drinking days (all ps < 0.05). The genome-wide meta-analysis of EAA in AUD revealed a significant single nucleotide polymorphism (SNP), rs916264 (p = 5.43 × 10^-8), in apolipoprotein L2 (APOL2) at the genome-wide level. The minor allele A of rs916264 was associated with EAA and with increased mRNA expression in hippocampus (p = 0.0015). Our data demonstrate EAA in AUD and suggest that disease severity further accelerates epigenetic aging. EAA was associated with genetic variation in APOL2, suggesting potential novel biological mechanisms for age acceleration in AUD.

Relations between catechol-O-methyltransferase Val158Met genotype and inhibitory control development in childhood

The Val158Met rs4680 single-nucleotide polymorphism (SNP) at the catechol-O-methyltransferase (COMT) gene, primarily involved in dopamine breakdown within prefrontal cortex, has shown relations with inhibitory control (IC) in both adults and children. However, little is known about how COMT genotype relates to developmental trajectories of IC throughout childhood. Here, our study explored the effects of the COMT genotype (Val/Val, Val/Met, and Met/Met) on IC trajectories between the ages of 5 and 10 years. Children (n = 222) completed a Go/Nogo task at ages 5, 7, and 10; IC was characterized using signal detection theory to examine IC performance (d') and response strategy (RS) (criterion). COMT genotype was not related to initial levels of IC performance and RS at age 5 or change in RS from ages 5 to 10. In contrast, COMT genotype was related to change in IC performance between 5 and 10 years. While Val/Val children did not differ from Val/Met children in development of IC performance, children with the Met/Met genotype exhibited more rapid development of IC performance when compared with Val/Met peers. These results suggest that COMT genotype modulates the development of IC performance in middle childhood.

Working memory reflects vulnerability to early life adversity as a risk factor for substance use disorder in the FKBP5 cortisol cochaperone polymorphism, rs9296158

Early life adversity (ELA) negatively affects health behaviors in adulthood, but pathways from ELA exposure to behavioral outcomes are poorly understood. ELA in childhood and adolescence may translate into adult outcomes by way of modified glucocorticoid signaling. The cortisol cotransporter, FKBP5 has a G-to-A substitution (rs9296158) that hinders cortisol trafficking within target cells, and this impaired glucocorticoid signaling may shape the long-term response to ELA. We used performance on the Stroop test to assess working memory in 546 healthy young adults who had experienced 0, 1, or > 1 forms of ELA in childhood and adolescence and were genotyped for the FKBP5 rs9296158 G-to-A polymorphism. We observed a robust Gene x Environment interaction (F = 9.49, p < .0001) in which increased ELA exposure led to progressively greater Stroop interference in persons carrying AG and AA genotypes of FKBP5 with no such effect in GG carriers. Further work is needed to explore the modification of cognitive function resulting from ELA. Impairments in working memory illustrate how ELA may use glucocorticoid pathways to influence working memory with potential implications for decision-making and risky behavior including substance use disorders.

Early-Life Adversity and Blunted Stress Reactivity as Predictors of Alcohol and Drug use in Persons With COMT (rs4680) Val158Met Genotypes

BACKGROUND

Risk for alcoholism may be enhanced by exposure to early-life adversity (ELA) in persons with genetic vulnerabilities. We examined ELA in the presence of a common variant of the gene for the enzyme catechol-O-methyltransferase (COMT, Val158Met, rs4680) in relation to cortisol reactivity, the onset of early drinking, and experimentation with drugs.

METHODS

Saliva cortisol reactivity to speech and mental arithmetic stress was measured in 480 healthy young adults (23.5 years of age, 50% females) who experienced either 0, 1, or ≥ 2 forms of ELA during childhood and adolescence, provided information on use of alcohol and recreational drugs, and were genotyped for the Val158Met polymorphism.

RESULTS

ELA led to progressively smaller cortisol responses in the Met/Met and Val/Met allele groups but to progressively larger responses in Val homozygotes, F = 3.29, p = 0.011. ELA independently predicted earlier age at first drink, F = 14.2, p < 0.0001, with a larger effect in Met-allele carriers, F = 13.95, p < 0.00001, and a smaller effect in Val homozygotes, F = 4.14, p = 0.02. Similar effects were seen in recreational drug use. Cortisol reactivity was unrelated to drinking behavior or drug experimentation.

CONCLUSIONS

ELA leads to blunted stress reactivity and, independently, contributes to potentially risky drinking and drug-use behaviors in persons carrying 1 or 2 copies of the COMT 158Met allele. The results reinforce the impact of early experience on the stress axis and on risky behaviors, and they point to the 158Met allele as conveying a vulnerability to the early environment.

Methylomic profiling and replication implicates deregulation of PCSK9 in alcohol use disorder

Alcohol use disorder (AUD) is a common and chronic disorder with substantial effects on personal and public health. The underlying pathophysiology is poorly understood but strong evidence suggests significant roles of both genetic and epigenetic components. Given that alcohol affects many organ systems, we performed a cross-tissue and cross-phenotypic analysis of genome-wide methylomic variation in AUD using samples from 3 discovery, 4 replication, and 2 translational cohorts. We identified a differentially methylated region in the promoter of the proprotein convertase subtilisin/kexin 9 (PCSK9) gene that was associated with disease phenotypes. Biological validation showed that PCSK9 promoter methylation is conserved across tissues and positively correlated with expression. Replication in AUD datasets confirmed PCSK9 hypomethylation and a translational mouse model of AUD showed that alcohol exposure leads to PCSK9 downregulation. PCSK9 is primarily expressed in the liver and regulates low-density lipoprotein cholesterol (LDL-C). Our finding of alcohol-induced epigenetic regulation of PCSK9 represents one of the underlying mechanisms between the well-known effects of alcohol on lipid metabolism and cardiovascular risk, with light alcohol use generally being protective while chronic heavy use has detrimental health outcomes.

Association of genetic ancestry with striatal dopamine D2/D3 receptor availability

Despite ethnic differences in allele frequencies of variants in dopaminergic genes associated with dopamine D2/D3 receptor availability (D2R), no study to date has investigated the relationship between genetic ancestry and striatal D2R. Here, we show that ancestry-informative markers significantly predict dorsal striatal D2R in 117 healthy ethnically diverse residents of the New York metropolitan area using Positron Emission Tomography (PET) with [¹¹C]raclopride (P<0.0001), while correcting for age, sex, BMI, education, smoking status, and estimated socioeconomic status (ZIP codes). Effects of ethnicity on D2R were not driven by variation in dopaminergic candidate genes. Instead, candidate gene associations with striatal D2R were diminished when correcting for ancestry. These findings imply that future studies investigating D2 receptor genes should covary for genetic ancestry or study homogeneous populations. Moreover, ancestry studies on human neurobiology should control for socioeconomic differences between ethnic groups.

Effects on gene expression and behavior of untagged short tandem repeats: the case of arginine vasopressin receptor 1a (AVPR1a) and externalizing behaviors

Genome-wide association studies (GWAS) of complex, heritable, behavioral phenotypes have yielded an incomplete accounting of the genetic influences. The identified loci explain only a portion of the observed heritability, and few of the loci have been shown to be functional. It is clear that current GWAS techniques overlook key components of phenotypically relevant genetic variation, either because of sample size, as is frequently asserted, or because of methodology. Here we use arginine vasopressin receptor 1a (AVPR1a) as an in-depth model of a methodologic limitation of GWAS: the functional genetic variation (in the form of short tandem repeats) of this key gene involved in affiliative behavior cannot be captured by current GWAS methodologies. Importantly, we find evidence of differential allele expression, twofold or more, in at least a third of human brain samples heterozygous for a reporter SNP in the AVPR1a transcript. We also show that this functional effect and a downstream phenotype, externalizing behavior, are predicted by AVPR1a STRs but not SNPs.

The Leu72Met Polymorphism of the Prepro-ghrelin Gene is Associated With Alcohol Consumption and Subjective Responses to Alcohol: Preliminary Findings

Aims

The orexigenic peptide ghrelin may enhance the incentive value of food-, drug- and alcohol-related rewards. Consistent with preclinical findings, human studies indicate a role of ghrelin in alcohol use disorders (AUD). In the present study an a priori hypothesis-driven analysis was conducted to investigate whether a Leu72Met missense polymorphism (rs696217) in the prepro-ghrelin gene (GHRL), is associated with AUD, alcohol consumption and subjective responses to alcohol.

Method

Association analysis was performed using the National Institute on Alcohol Abuse and Alcoholism (NIAAA) clinical sample, comprising AUD individuals and controls (N = 1127). Then, a post-hoc analysis using data from a human laboratory study of intravenous alcohol self-administration (IV-ASA, N = 144) was performed to investigate the association of this SNP with subjective responses following a fixed dose of alcohol (priming phase) and alcohol self-administration (ad libitum phase).

Results

The case-control study revealed a trend association (N = 1127, OR = 0.665, CI = 0.44-1.01, P = 0.056) between AUD diagnosis and Leu72Met. In AUD subjects, the SNP was associated with significantly lower average drinks per day (n = 567, β = -2.49, 95% CI = -4.34 to -0.64, P = 0.008) and significantly fewer heavy drinking days (n = 567, β = -12.00, 95% CI = -19.10 to -4.89, P < 0.001). The IV-ASA study further revealed that 72Met carriers had greater subjective responses to alcohol (P < 0.05) when compared to Leu72Leu both at priming and during ad lib self-administration.

Conclusion

Although preliminary, these findings suggest that the Leu72Leu genotype may lead to increased risk of AUD possibly via mechanisms involving a lower response to alcohol resulting in excessive alcohol consumption. Further investigations are warranted.

Short Summary

We investigated whether a Leu72Met missense polymorphism in the prepro-ghrelin gene, is associated with alcohol use disorder, alcohol consumption and subjective responses to alcohol. Although preliminary, results suggest that the Leu72Leu genotype may lead to increased risk of alcohol use disorder possibly via mechanisms involving a lower response to alcohol.

Severity of alcohol dependence is associated with the fatty acid amide hydrolase Pro129Thr missense variant

The endocannabinoid system plays an important role in reward and addiction. One of the two main endocannabinoid neurotransmitters, anandamide, is metabolized by fatty acid amide hydrolase, an enzyme with a functional genetic polymorphism (FAAH Pro129Thr, rs324420). The Thr129 allele has been linked to problem drug and alcohol use, but the association has not been widely replicated and may be stronger for clinical measures of severity rather than categorical diagnosis. In the present study, we sought to determine whether the Thr129 allele was associated with both alcohol dependence (AD) diagnosis and severity in a sample of 1434 European American and African American individuals, 952 of whom were diagnosed with lifetime AD. Participants were genotyped for FAAH rs324420, and ancestry was determined via a genome-wide panel of ancestry informative markers. Subjects participated in Structured Clinical Interviews for psychiatric disorders and 90-day Timeline Followback interviews to assess recent alcohol use. European American participants with current AD had a higher Thr129 allele frequency than non-dependent controls. In European Americans with lifetime AD, there were significantly different distributions of drinking days and binge drinking days between the two genotype groups, with Thr129 carriers reporting a median of 10 fewer abstinent days and 13 more binge drinking days than Pro129/Pro129 homozygotes. In African American participants, there were no significant differences between Thr129 allele frequency in cases and controls and no significant differences in measures of AD severity by genotype. These findings provide evidence that the Pro129Thr missense variant is associated with AD severity in European Americans.

Hepatic, lipid and genetic factors associated with obesity: crosstalk with alcohol dependence?

OBJECTIVES

Alcohol dependence represents a leading cause of mortality and morbidity. Understanding the variables that contribute to this diagnosis and its severity is critical. An overlap between factors that may predispose people to become obese and those that may increase the risk of alcohol dependence may exist. However, data in the literature are not conclusive. Therefore, this study aimed to identify the association between alcohol dependence and obesity-related factors, including biochemical and genetic factors.

METHODS

In a case-control study with 829 participants, factors involved with metabolism and obesity were assessed, including biochemical lipid and liver markers, and the fat mass and obesity-associated (FTO) single nucleotide polymorphism (SNP) rs8050136.

RESULTS

Increased triglycerides, having one or two minor A alleles for rs8050136 and being a smoker were associated with increased risk of alcohol dependence, while increased low-density lipoprotein cholesterol was associated with decreased risk. In addition, having abnormal gamma-glutamyl transferase and being female were factors associated with an increased severity of alcohol dependence.

CONCLUSIONS

Our preliminary findings suggest a link between alcohol dependence and obesity-related biochemical and genetic factors. Future studies are needed to better understand if these factors may play a predictive role and/or may act as biomarkers for treatment response.

Genome-wide association study in essential tremor identifies three new loci

We conducted a genome-wide association study of essential tremor, a common movement disorder characterized mainly by a postural and kinetic tremor of the upper extremities. Twin and family history studies show a high heritability for essential tremor. The molecular genetic determinants of essential tremor are unknown. We included 2807 patients and 6441 controls of European descent in our two-stage genome-wide association study. The 59 most significantly disease-associated markers of the discovery stage were genotyped in the replication stage. After Bonferroni correction two markers, one (rs10937625) located in the serine/threonine kinase STK32B and one (rs17590046) in the transcriptional coactivator PPARGC1A were associated with essential tremor. Three markers (rs12764057, rs10822974, rs7903491) in the cell-adhesion molecule CTNNA3 were significant in the combined analysis of both stages. The expression of STK32B was increased in the cerebellar cortex of patients and expression quantitative trait loci database mining showed association between the protective minor allele of rs10937625 and reduced expression in cerebellar cortex. We found no expression differences related to disease status or marker genotype for the other two genes. Replication of two lead single nucleotide polymorphisms of previous small genome-wide association studies (rs3794087 in SLC1A2, rs9652490 in LINGO1) did not confirm the association with essential tremor.

The abundance of cis-acting loci leading to differential allele expression in F1 mice and their relationship to loci harboring genes affecting complex traits

Background

Genome-wide surveys have detected cis-acting quantitative trait loci altering levels of RNA transcripts (RNA-eQTLs) by associating SNV alleles to transcript levels. However, the sensitivity and specificity of detection of cis- expression quantitative trait loci (eQTLs) by genetic approaches, reliant as it is on measurements of transcript levels in recombinant inbred strains or offspring from arranged crosses, is unknown, as is their relationship to QTL’s for complex phenotypes.

Results

We used transcriptome-wide differential allele expression (DAE) to detect cis-eQTLs in forebrain and kidney from reciprocal crosses between three mouse inbred strains, 129S1/SvlmJ, DBA/2J, and CAST/EiJ and C57BL/6 J. Two of these crosses were previously characterized for cis-eQTLs and QTLs for various complex phenotypes by genetic analysis of recombinant inbred (RI) strains. 5.4 %, 1.9 % and 1.5 % of genes assayed in forebrain of B6/129SF1, B6/DBAF1, and B6/CASTF1 mice, respectively, showed differential allelic expression, indicative of cis-acting alleles at these genes. Moreover, the majority of DAE QTLs were observed to be tissue-specific with only a small fraction showing cis-effects in both tissues. Comparing DAE QTLs in F1 mice to cis-eQTLs previously mapped in RI strains we observed that many of the cis-eQTLs were not confirmed by DAE. Additionally several novel DAE-QTLs not identified as cis-eQTLs were identified suggesting that there are differences in sensitivity and specificity for QTL detection between the two methodologies. Strain specific DAE QTLs in B6/DBAF1 mice were located in excess at candidate genes for alcohol use disorders, seizures, and angiogenesis previously implicated by genetic linkage in C57BL/6J × DBA/2JF2 mice or BXD RI strains.

Conclusions

Via a survey for differential allele expression in F1 mice, a substantial proportion of genes were found to have alleles altering expression in cis-acting fashion. Comparing forebrain and kidney, many or most of these alleles were tissue-specific in action. The identification of strain specific DAE QTLs, can assist in assessment of candidate genes located within the large intervals associated with trait QTLs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2922-9) contains supplementary material, which is available to authorized users.

A Spontaneous Missense Mutation in Branched Chain Keto Acid Dehydrogenase Kinase in the Rat Affects Both the Central and Peripheral Nervous Systems

A novel mutation, causing a phenotype we named frogleg because its most obvious characteristic is a severe splaying of the hind limbs, arose spontaneously in a colony of Sprague-Dawley rats. Frogleg is a complex phenotype that includes abnormalities in hind limb function, reduced brain weight with dilated ventricles and infertility. Using micro-satellite markers spanning the entire rat genome, the mutation was mapped to a region of rat chromosome 1 between D1Rat131 and D1Rat287. Analysis of whole genome sequencing data within the linkage interval, identified a missense mutation in the branched-chain alpha-keto dehydrogenase kinase (Bckdk) gene. The protein encoded by Bckdk is an integral part of an enzyme complex located in the mitochondrial matrix of many tissues which regulates the levels of the branched-chain amino acids (BCAAs), leucine, isoleucine and valine. BCAAs are essential amino acids (not synthesized by the body), and circulating levels must be tightly regulated; levels that are too high or too low are both deleterious. BCKDK phosphorylates Ser293 of the E1α subunit of the BCKDH protein, which catalyzes the rate-limiting step in the catabolism of the BCAAs, inhibiting BCKDH and thereby, limiting breakdown of the BCAAs. In contrast, when Ser293 is not phosphorylated, BCKDH activity is unchecked and the levels of the BCAAs will decrease dramatically. The mutation is located within the kinase domain of Bckdk and is predicted to be damaging. Consistent with this, we show that in rats homozygous for the mutation, phosphorylation of BCKDH in the brain is markedly decreased relative to wild type or heterozygous littermates. Further, circulating levels of the BCAAs are reduced by 70-80% in animals homozygous for the mutation. The frogleg phenotype shares important characteristics with a previously described Bckdk knockout mouse and with human subjects with Bckdk mutations. In addition, we report novel data regarding peripheral neuropathy of the hind limbs.

A Prospective Cohort Study of Influences on Externalizing Behaviors Across Childhood: Results From a Nurse Home Visiting Randomized Controlled Trial

OBJECTIVE

This study investigated genetic and environmental influences on behavior in a cohort of 600 children followed prenatally to 18 years.

METHOD

A randomized controlled trial of prenatal/infancy nurse home visits (NHV) was conducted in 600 predominantly African American mothers and their firstborn children from Memphis, TN. Mothers were assessed in pregnancy for mental health (MH), self-efficacy, and mastery. Mothers reported longitudinally on smoking and alcohol/drug use. The functional polymorphisms SLC6A4 5-HTTLPR, FKBP5 rs1360780 and DRD2/ANKK1 rs1800497 were genotyped together with 186 ancestry informative markers. Composite externalizing disorders (ED) continuous total scores from the mother-report Achenbach Child Behavior Checklist were included as dependent variables in regression analyses for time points 2, 6, 12, and 18 years.

RESULTS

Behaviors at younger ages strongly predicted later behaviors (p < .0001). Children whose mothers had high self-efficacy and had received NHV were better behaved at age 2 years. Poorer maternal MH adversely influenced ED up to 12 years, but at age 18 years, maternal mastery exerted a strong, positive effect (p = .0001). Maternal smoking was associated with worse ED at 6 and 18 years. Main and interactive effects of genetic polymorphisms varied across childhood: FKBP5 rs1360780 up to age 6, 5-HTTLPR from 6 to 12, and DRD2/ANKK1 rs1800497 from 2 to 18 years.

CONCLUSION

Our study suggests that maternal MH and resilience measured in pregnancy have long-lasting effects on child behavior. Maternal smoking across childhood and genetic factors also play a role. NHV had a positive effect on early behavior. Our findings have implications for prevention of pathological behaviors in adulthood. Clinical trial registration information-Age-17 Follow-Up of Home Visiting Intervention; http://clinicaltrials.gov/; NCT00708695.

Association of Superoxide Dismutase 2 (SOD2) Genotype with Gray Matter Volume Shrinkage in Chronic Alcohol Users: Replication and Further Evaluation of an Addiction Gene Panel

BACKGROUND

Reduction in brain volume, especially gray matter volume, has been shown to be one of the many deleterious effects of prolonged alcohol consumption. High variance in the degree of gray matter tissue shrinkage among alcohol-dependent individuals and a previous neuroimaging genetics report suggest the involvement of environmental and/or genetic factors, such as superoxide dismutase 2 (SOD2). Identification of such underlying factors will help in the clinical management of alcohol dependence.

METHODS

We analyzed quantitative magnetic resonance imaging and genotype data from 103 alcohol users, including both light drinkers and treatment-seeking alcohol-dependent individuals. Genotyping was performed using a custom gene array that included genes selected from 8 pathways relevant to chronic alcohol-related brain volume loss.

RESULTS

We replicated a significant association of a functional SOD2 single nucleotide polymorphism with normalized gray matter volume, which had been reported previously in an independent smaller sample of alcohol-dependent individuals. The SOD2-related genetic protection was observed only at the cohort's lower drinking range. Additional associations between normalized gray matter volume and other candidate genes such as alcohol dehydrogenase gene cluster (ADH), GCLC, NOS3, and SYT1 were observed across the entire sample but did not survive corrections for multiple comparisons.

CONCLUSION

Converging independent evidence for a SOD2 gene association with gray matter volume shrinkage in chronic alcohol users suggests that SOD2 genetic variants predict differential brain volume loss mediated by free radicals. This study also provides the first catalog of genetic variations relevant to gray matter loss in chronic alcohol users. The identified gene-brain structure relationships are functionally pertinent and merit replication.

GABBR1 and SLC6A1, Two Genes Involved in Modulation of GABA Synaptic Transmission, Influence Risk for Alcoholism: Results from Three Ethnically Diverse Populations

BACKGROUND

Animal and human studies indicate that GABBR1, encoding the GABAB1 receptor subunit, and SLC6A1, encoding the neuronal gamma-aminobutyric acid (GABA) transporter GAT1, play a role in addiction by modulating synaptic GABA. Therefore, variants in these genes might predict risk/resilience for alcoholism.

METHODS

This study included 3 populations that differed by ethnicity and alcoholism phenotype: African American (AA) men: 401 treatment-seeking inpatients with single/comorbid diagnoses of alcohol and drug dependence, 193 controls; Finnish Caucasian men: 159 incarcerated alcoholics, half with comorbid antisocial personality disorder, 181 controls; and a community sample of Plains Indian (PI) men and women: 239 alcoholics, 178 controls. Seven GABBR1 tag single nucleotide polymorphisms were genotyped in the AA and Finnish samples; rs29220 was genotyped in the PI for replication. Also, a uniquely African, functional SLC6A1 insertion promoter polymorphism (IND) was genotyped in the AAs.

RESULTS

We found a significant and congruent association between GABBR1 rs29220 and alcoholism in all 3 populations. The major genotype (heterozygotes in AAs, Finns) and the major allele in PIs were significantly more common in alcoholics. Moreover, SLC6A1 IND was more abundant in controls, that is, the major genotype predicted alcoholism. An analysis of combined GABBR1 rs29220 and SLC6A1 IND genotypes showed that rs29220 heterozygotes, irrespective of their IND status, had an increased risk for alcoholism, whereas carriers of the IND allele and either rs29220 homozygote were more resilient.

CONCLUSIONS

Our results show that with both GABBR1 and SLC6A1, the minor genotypes/alleles were protective against risk for alcoholism. Finally, GABBR1 rs29220 might predict treatment response/adverse effects for baclofen, a GABAB receptor agonist.

The contribution of rare and common variants in 30 genes to risk nicotine dependence

Genetic and functional studies have revealed that both common and rare variants of several nicotinic acetylcholine receptor subunits are associated with nicotine dependence (ND). In this study, we identified variants in 30 candidate genes including nicotinic receptors in 200 sib pairs selected from the Mid-South Tobacco Family population with equal numbers of African Americans (AAs) and European Americans (EAs). We selected 135 of the rare and common variants and genotyped them in the Mid-South Tobacco Case-Control (MSTCC) population, which consists of 3088 AAs and 1430 EAs. None of the genotyped common variants showed significant association with smoking status (smokers vs non-smokers), Fagerström Test for ND scores or indexed cigarettes per day after Bonferroni correction. Rare variants in NRXN1, CHRNA9, CHRNA2, NTRK2, GABBR2, GRIN3A, DNM1, NRXN2, NRXN3 and ARRB2 were significantly associated with smoking status in the MSTCC AA sample, with weighted sum statistic (WSS) P-values ranging from 2.42 × 10(-3) to 1.31 × 10(-4) after 10(6) phenotype rearrangements. We also observed a significant excess of rare nonsynonymous variants exclusive to EA smokers in NRXN1, CHRNA9, TAS2R38, GRIN3A, DBH, ANKK1/DRD2, NRXN3 and CDH13 with WSS P-values between 3.5 × 10(-5) and 1 × 10(-6). Variants rs142807401 (A432T) and rs139982841 (A452V) in CHRNA9 and variants V132L, V389L, rs34755188 (R480H) and rs75981117 (N549S) in GRIN3A are of particular interest because they are found in both the AA and EA samples. A significant aggregate contribution of rare and common coding variants in CHRNA9 to the risk for ND (SKAT-C: P=0.0012) was detected by applying the combined sum test in MSTCC EAs. Together, our results indicate that rare variants alone or combined with common variants in a subset of 30 biological candidate genes contribute substantially to the risk of ND.

Cortisol Stress Response in Men and Women Modulated Differentially by the Mu-Opioid Receptor Gene Polymorphism OPRM1 A118G

Differences in stress reactivity may affect long-term health outcomes, but there is little information on how these differences arise. The stress axis is regulated by, in part, the endogenous opioid, beta-endorphin, acting on mu-opioid receptors. Persons carrying one or two copies of the G allele of the mu-opioid receptor gene (OPRM1 A118G) may have higher receptor binding for beta-endorphin compared with AA homozygotes that may contribute to individual differences in cortisol reactivity to stress, leading to a relative blunting of cortisol stress reactivity in G allele genotypes. We measured cortisol in 251 young adults (69 GA/GG vs 182 AA genotypes) exposed to mental arithmetic plus public speaking stress relative to a resting control day. Women had smaller cortisol responses than men (F=10.2, p=0.002), and women with GA or GG genotypes (N=39) had an absence of cortisol response relative to AA carriers (N=110) (F=18.4, p<0.0001). Male genotypes had no such difference in response (F=0.29). Cortisol response following mu-opioid receptor blockade using naltrexone in 119 of these subjects unmasked a greater tonic opioid inhibition of cortisol secretion in women (N=64), consistent with their blunted stress reactivity. Compared with men, women may have cortisol stress responses that are more heavily regulated by endogenous opioid mechanisms, and the OPRM1 GA/GG genotypes may affect females differentially relative to males. Diminished cortisol responses to stress may have consequences for health behaviors in women with GA/GG genotypes.

Resting-state functional connectivity and presynaptic monoamine signaling in Alcohol Dependence

Alcohol Dependence (AD) is a chronic relapsing disorder with high degrees of morbidity and mortality. While multiple neurotransmitter systems are involved in the complex symptomatology of AD, monoamine dysregulation and subsequent neuroadaptations have been long postulated to play an important role. Presynaptic monoamine transporters, such as the vesicular monoamine transporter 1 (VMAT1), are likely critical as they represent a key common entry point for monoamine regulation and may represent a shared pathway for susceptibility to AD. Excessive monoaminergic signaling as mediated by genetic variation in VMAT1 might affect functional brain connectivity in particular in alcoholics compared to controls. We conducted resting-state fMRI functional connectivity (FC) analysis using the independent component analysis (ICA) approach in 68 AD subjects and 72 controls. All subjects were genotyped for the Thr136Ile (rs1390938) variant in VMAT1. Functional connectivity analyses showed a significant increase of resting-state FC in 4 networks in alcoholics compared to controls (P < 0.05, corrected). The FC was significantly positively correlated with Alcohol Dependence Scale (ADS). The hyperfunction allele 136Ile was associated with a significantly decreased FC in the Default Mode Network, Prefrontal Cortex Network, and Executive Control Network in alcohol dependent participants (P < 0.05, corrected), but not in controls. Our data suggest that increased FC might represent a neuroadaptive mechanism relevant to AD that is furthermore mediated by genetic variation in VMAT1. The hyperfunction allele Thr136Ile might have a protective effect that is, in particular, relevant in AD by mechanism of increased monoamine transport into presynaptic storage vesicles.

Effect of Functionally Significant Deiodinase Single Nucleotide Polymorphisms on Drinking Behavior in Alcohol Dependence: An Exploratory Investigation

BACKGROUND

Abnormalities of the hypothalamic-pituitary-thyroid (HPT) axis have been reported in alcoholism; however, there is no definitive agreement on the specific thyroid abnormalities and their underlying mechanisms in alcohol dependence. The biological activity of thyroid hormones or the availability of T3 is regulated by the three deiodinase enzymes: D1, D2, and D3. In the context of alcohol use, functionally significant single nucleotide polymorphisms (SNPs) of these deiodinase genes may play a role in HPT dysfunction.

METHODS

This study explored the effect of three functionally significant SNPs (D1: rs2235544, D2: rs225014, and rs12885300) of deiodinase genes on drinking behavior and thyroid-stimulating hormone (TSH) levels in alcohol-dependent (N = 521) and control subjects (N = 288).

RESULTS

Rs225014 was associated with significant differences in the amount of naturalistic alcohol drinking assessed by Timeline Follow Back. Alcohol-dependent subjects had significantly higher TSH levels compared to controls; however, there was no effect of genotype on TSH levels for either group.

CONCLUSIONS

These findings extend previous studies on thyroid dysfunction in alcoholism and provide novel, albeit preliminary, information by linking functionally significant genetic polymorphisms of the deiodinase enzymes with alcohol-drinking behavior.

FKBP5 moderates alcohol withdrawal severity: human genetic association and functional validation in knockout mice

Alcohol withdrawal is associated with hypothalamic-pituitary-adrenal (HPA) axis dysfunction. The FKBP5 gene codes for a co-chaperone, FK506-binding protein 5, that exerts negative feedback on HPA axis function. This study aimed to examine the effects of single-nucleotide polymorphisms (SNPs) of the FKBP5 gene in humans and the effect of Fkbp5 gene deletion in mice on alcohol withdrawal severity. We genotyped six FKBP5 SNPs (rs3800373, rs9296158, rs3777747, rs9380524, rs1360780, and rs9470080) in 399 alcohol-dependent inpatients with alcohol consumption 48 h before admission and recorded scores from the Clinical Institute Withdrawal Assessment-Alcohol revised (CIWA-Ar). Fkbp5 gene knockout (KO) and wild-type (WT) mice were assessed for alcohol withdrawal using handling-induced convulsions (HICs) following both acute and chronic alcohol exposure. We found the minor alleles of rs3800373 (G), rs9296158 (A), rs1360780 (T), and rs9470080 (T) were significantly associated with lower CIWA-Ar scores whereas the minor alleles of rs3777747 (G) and rs9380524 (A) were associated with higher scores. The haplotype-based analyses also showed an association with alcohol withdrawal severity. Fkbp5 KO mice showed significantly greater HICs during withdrawal from chronic alcohol exposure compared with WT controls. This study is the first to show a genetic effect of FKBP5 on the severity of alcohol withdrawal syndrome. In mice, the absence of the Fkbp5 gene enhances sensitivity to alcohol withdrawal. We suggest that FKBP5 variants may trigger different adaptive changes in HPA axis regulation during alcohol withdrawal with concomitant effects on withdrawal severity.

Differential impact of serotonin transporter activity on temperament and behavior in persons with a family history of alcoholism in the Oklahoma Family Health Patterns Project

BACKGROUND

Central serotonergic (5-HT) function is implicated in pathways to alcohol dependence, including dysphoria manifested by symptoms of anxiety and depression. However, little is known about genetic variation in central 5-HT function and its potential impact on temperament and behavior in persons with a family history of alcoholism (FH+).

METHODS

We tested 314 healthy young adults (23.5 years of age, 57% female; 193 FH- and 121 FH+) enrolled in the Oklahoma Family Health Patterns project, a study of alcoholism risk in relation to temperament and behavioral dyscontrol. Dysphoria was assessed using the Eysenck neuroticism and Beck depression scales, and Cloninger's Tridimensional Personality Questionnaire. Risk taking was assessed with the Iowa Gambling Task (IGT) and Balloon Analogue Response Task (BART). All subjects were genotyped for a functional polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene (SLC6A4).

RESULTS

FH+ subjects with the gain-of-function 5-HTTLPR genotype scored higher in neuroticism, harm avoidance, and symptoms of depression (p-values ≤ 0.03). No effect of 5-HTTLPR genotype was seen in FH-. FH+ carriers of the gain-of-function 5-HTTLPR genotype played to minimize their frequency of losses in the IGT, whereas FH- carriers played a balanced strategy (p < 0.003). No 5-HTTLPR effects were seen in the BART. Results were unaffected by sex, education, drug use, and antisocial characteristics.

CONCLUSIONS

The functional 5-HTTLPR polymorphism predicted significant variation in negative moods and poorer affect regulation in FH+ persons, with possible consequences for behavior, as seen in a simulated gambling task. This pattern may contribute to a drinking pattern that is compensatory for such affective tendencies.

Effects of citalopram and escitalopram on fMRI response to affective stimuli in healthy volunteers selected by serotonin transporter genotype

This study was designed to assess whether functional magnetic resonance imaging (fMRI) following antidepressant administration (pharmaco-fMRI) is sufficiently sensitive to detect differences in patterns of activation between enantiomers of the same compound. Healthy adult males (n=11) participated in a randomized, double-blind, cross-over trial with three medication periods during which they received citalopram (racemic mixture), escitalopram (S-citalopram alone), or placebo for 2 weeks. All participants had high expression serotonin transporter genotypes. An fMRI scan that included passive viewing of overt and covert affective faces and affective words was performed after each medication period. Activation in response to overt faces was greater following escitalopram than following citalopram in the right insula, thalamus, and putamen when the faces were compared with a fixation stimulus. For the rapid covert presentation, a greater response was observed in the left middle temporal gyrus in the happy versus fearful contrast following escitalopram than following citalopram. Thus, the combination of genomics and fMRI was successful in discriminating between two very similar drugs. However, the pattern of activation observed suggests that further studies are indicated to understand how to optimally combine the two techniques.

Independent effects of 5' and 3' functional variants in the serotonin transporter gene on suicidal behavior in the context of childhood trauma

The serotonin transporter, encoded by the SLC6A4 gene, influences the synaptic actions of serotonin and is responsive to stress hormones. We hypothesized that 5-HTTLPR, a functional SLC6A4 promoter polymorphism, and two tightly-linked, putatively functional 3' UTR SNPs (rs3813034, rs1042173) might have independent effects on suicidal behavior in the context of childhood trauma (CT). DNA and Childhood Trauma Questionnaire scores were available for a total of 474 African Americans, including 112 suicide attempters and 362 non-suicide attempters. Genotyping was performed for the triallelic 5-HTTLPR polymorphism, 14 SLC6A4 haplotype-tagging SNPs, and 186 ancestry informative markers. There were independent G × E interactive effects of 5-HTTLPR (p = 0.017) and the rs3813034-rs1042173 diplotype (p = 0.011) on suicidal behavior. In individuals exposed to high CT the risk of suicide attempt was 0.52 in carriers of the low activity 5-HTTLPR variant and 0.32 in medium/high activity variant carriers. Likewise, CT exposed carriers of the major rs3813034-rs1042173 ATAT diplotype had an increased risk of suicidal behavior relative to the ATCG/CGCG diplotype carriers (0.40 vs 0.31). Neither the 5' nor the 3' functional variants had an effect in individuals without CT: suicide attempt risk = 0.12-0.22. In individuals exposed to high CT the prevalence of suicide attempt was 0.56 in carriers of both 5' and 3' risk variants, 0.39 in carriers of one risk variant and 0.25 in individuals without either risk variant. Our findings suggest that the 5' and 3'SLC6A4 functional variants have independent effects on the risk for suicidal behavior in CT exposed individuals.

A preliminary study suggests that nicotine and prefrontal dopamine affect cortico-striatal areas in smokers with performance feedback

Nicotine and tonic dopamine (DA) levels [as inferred by catechol-O-methyl tranferase (COMT) Val158Met genotype] interact to affect prefrontal processing. Prefrontal cortical areas are involved in response to performance feedback, which is impaired in smokers. We investigated whether there is a nicotine × COMT genotype interaction in brain circuitry during performance feedback of a reward task. We scanned 23 healthy smokers (10 Val/Val homozygotes, 13 Met allele carriers) during two fMRI sessions while subjects were wearing a nicotine or placebo patch. A significant nicotine × COMT genotype interaction for BOLD signal during performance feedback in cortico-striatal areas was seen. Activation in these areas during the nicotine patch condition was greater in Val/Val homozygotes and reduced in Met allele carriers. During negative performance feedback, the change in activation in error detection areas such as anterior cingulate cortex (ACC)/superior frontal gyrus on nicotine compared to placebo was greater in Val/Val homozygotes compared to Met allele carriers. With transdermal nicotine administration, Val/Val homozygotes showed greater activation with performance feedback in the dorsal striatum, area associated with habitual responding. In response to negative feedback, Val/Val homozygotes had greater activation in error detection areas, including the ACC, suggesting increased sensitivity to loss with nicotine exposure. Although these results are preliminary due to small sample size, they suggest a possible neurobiological mechanism underlying the clinical observation that Val/Val homozygotes, presumably with elevated COMT activity compared to Met allele carriers and therefore reduced prefrontal DA levels, have poorer outcomes with nicotine replacement therapy.

The functional DRD3 Ser9Gly polymorphism (rs6280) is pleiotropic, affecting reward as well as movement

Abnormalities of motivation and behavior in the context of reward are a fundamental component of addiction and mood disorders. Here we test the effect of a functional missense mutation in the dopamine 3 receptor (DRD3) gene (ser9gly, rs6280) on reward-associated dopamine (DA) release in the striatum. Twenty-six healthy controls (HCs) and 10 unmedicated subjects with major depressive disorder (MDD) completed two positron emission tomography (PET) scans with [¹¹C]raclopride using the bolus plus constant infusion method. On one occasion subjects completed a sensorimotor task (control condition) and on another occasion subjects completed a gambling task (reward condition). A linear regression analysis controlling for age, sex, diagnosis, and self-reported anhedonia indicated that during receipt of unpredictable monetary reward the glycine allele was associated with a greater reduction in D2/3 receptor binding (i.e., increased reward-related DA release) in the middle (anterior) caudate (p<0.01) and the ventral striatum (p<0.05). The possible functional effect of the ser9gly polymorphism on DA release is consistent with previous work demonstrating that the glycine allele yields D3 autoreceptors that have a higher affinity for DA and display more robust intracellular signaling. Preclinical evidence indicates that chronic stress and aversive stimulation induce activation of the DA system, raising the possibility that the glycine allele, by virtue of its facilitatory effect on striatal DA release, increases susceptibility to hyperdopaminergic responses that have previously been associated with stress, addiction, and psychosis.

Serotonin transporter genotype differentially modulates neural responses to emotional words following tryptophan depletion in patients recovered from depression and healthy volunteers

Previous studies have suggested that polymorphism in the serotonin transporter gene (5-HTTLPR) influences responses to serotonergic manipulation, with opposite effects in patients recovered from depression (rMDD) and controls. Here we sought to clarify the neurocognitive mechanisms underpinning these surprising results. Twenty controls and 23 rMDD subjects completed the study; functional magnetic resonance imaging (fMRI) and genotype data were available for 17 rMDD subjects and 16 controls. Following tryptophan or sham depletion, subjects performed an emotional-processing task during fMRI. Although no genotype effects on mood were identified, significant genotype*diagnosis*depletion interactions were observed in the hippocampus and subgenual cingulate in response to emotionally valenced words. In both regions, tryptophan depletion increased responses to negative words, relative to positive words, in high-expression controls, previously identified as being at low-risk for mood change following this procedure. By contrast, in higher-risk low-expression controls and high-expression rMDD subjects, tryptophan depletion had the opposite effect. Increased neural responses to negative words following tryptophan depletion may reflect an adaptive mechanism promoting resilience to mood change following perturbation of the serotonin system, which is reversed in sub-groups vulnerable to developing depressive symptoms. However, this interpretation is complicated by our failure to replicate previous findings of increased negative mood following tryptophan depletion.

Oxytocin gene polymorphisms influence human dopaminergic function in a sex-dependent manner

BACKGROUND

Oxytocin, classically involved in social and reproductive activities, is increasingly recognized as an antinociceptive and anxiolytic agent, effects which may be mediated via oxytocin's interactions with the dopamine system. Thus, genetic variation within the oxytocin gene (OXT) is likely to explain variability in dopamine-related stress responses. As such, we examined how OXT variation is associated with stress-induced dopaminergic neurotransmission in a healthy human sample.

METHODS

Fifty-five young healthy volunteers were scanned using [¹¹C]raclopride positron emission tomography while they underwent a standardized physical and emotional stressor that consisted of moderate levels of experimental sustained deep muscle pain, and a baseline, control state. Four haplotype tagging single nucleotide polymorphisms located in regions near OXT were genotyped. Measures of pain, affect, anxiety, well-being and interpersonal attachment were also assessed.

RESULTS

Female rs4813625 C allele carriers demonstrated greater stress-induced dopamine release, measured as reductions in receptor availability from baseline to the pain-stress condition relative to female GG homozygotes. No significant differences were detected among males. We also observed that female rs4813625 C allele carriers exhibited higher attachment anxiety, higher trait anxiety and lower emotional well-being scores. In addition, greater stress-induced dopamine release was associated with lower emotional well-being scores in female rs4813625 C allele carriers.

CONCLUSIONS

Our results suggest that variability within the oxytocin gene appear to explain interindividual differences in dopaminergic responses to stress, which are shown to be associated with anxiety traits, including those linked to attachment style, as well as emotional well-being in women.

Two HPA axis genes, CRHBP and FKBP5, interact with childhood trauma to increase the risk for suicidal behavior

Childhood trauma is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation. Both factors increase risk for suicidal behavior. Corticotropin releasing hormone (CRH) regulates the HPA axis and its actions are moderated by a high-affinity binding protein (CRHBP). We hypothesized that CRHBP variation and interaction with childhood trauma might influence suicidal behavior. Moreover, there might be an additive effect with FKPB5, another HPA axis gene previously associated with suicidality in this dataset. African Americans were recruited: 398 treatment seeking patients with substance dependence (90% men; 120 suicide attempters) and 432 non-substance dependent individuals (40% men; 21 suicide attempters). A total of 474 participants (112 suicide attempters) completed the Childhood Trauma Questionnaire (CTQ). Haplotype-tagging SNPs were genotyped across CRHBP and, for completeness, across CRH, CRHR1 and CRHR2. FKBP5 genotypes were available. Three CRHBP SNPs rs6453267, rs7728378 and rs10474485 showed a nominally significant interaction with the continuous CTQ score to predict suicide attempt; rs7728378 remained significant after FDR correction. There was an additive effect with FKBP5: in the group exposed to high trauma, the prevalence of suicide attempt was 0.35-0.30 in carriers of either the FKBP5 rs3800373 major homozygote or the CRHBP rs7728378 major homozygote and 0.58 in carriers of both major homozygotes. Individuals without either major homozygote were resilient to the effects of childhood trauma (suicide attempt prevalence 0.24). Main effects of CRHBP rs6453267 and CRHR1 rs9900679, both unique to African ancestry, were detected. CRHBP variation may predispose, independently and additively, to suicidal behavior in individuals who have experienced childhood trauma.

BDNF polymorphism-dependent OFC and DLPFC plasticity differentially moderates implicit and explicit bias

This study examined the role of orbitofrontal cortex (OFC) and dorsolateral prefrontal cortex (DLPFC) plasticity in controlling implicit and explicit social biases. Normal controls and patients with varied OFC and DLPFC lesion size and single nucleotide polymorphisms (SNPs) in the brain-derived neurotrophic factor (BDNF) gene, which promotes (methionine-valine [Met/Val] SNP) or stifles (valine-valine [Val/Val] SNP) plasticity in damaged PFC regions, completed measures of implicit and explicit social bias. Patients and controls demonstrated comparable levels of implicit bias, but patients with Met/Val SNPs exhibited less implicit bias when they had smaller OFC lesions compared with Val/Val patients with similar size lesions and those with large OFC lesions. Both patients and controls demonstrated patterns of explicit bias consistent with hypotheses. Patients with Met/Val SNPs exhibited less explicit bias when they had smaller DLPFC lesions sizes compared with Val/Val patients with similar size lesions and those with large DLPFC lesions. OFC lesion size and BDNF SNP type did not moderate explicit bias; DLPFC lesion size and BDNF SNP type did not moderate implicit bias (nor did other medial or lateral regions). Findings suggest that plasticity within specific PFC regions modulates the type and degree of social bias that individuals' exhibit.

BDNF polymorphism predicts general intelligence after penetrating traumatic brain injury

Neuronal plasticity is a fundamental factor in cognitive outcome following traumatic brain injury. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays an important role in this process. While there are many ways to measure cognitive outcome, general cognitive intelligence is a strong predictor of everyday decision-making, occupational attainment, social mobility and job performance. Thus it is an excellent measure of cognitive outcome following traumatic brain injury (TBI). Although the importance of the single-nucleotide polymorphisms polymorphism on cognitive function has been previously addressed, its role in recovery of general intelligence following TBI is unknown. We genotyped male Caucasian Vietnam combat veterans with focal penetrating TBI (pTBI) (n = 109) and non-head injured controls (n = 38) for 7 BDNF single-nucleotide polymorphisms. Subjects were administrated the Armed Forces Qualification Test (AFQT) at three different time periods: pre-injury on induction into the military, Phase II (10-15 years post-injury, and Phase III (30-35 years post-injury). Two single-nucleotide polymorphisms, rs7124442 and rs1519480, were significantly associated with post-injury recovery of general cognitive intelligence with the most pronounced effect at the Phase II time point, indicating lesion-induced plasticity. The genotypes accounted for 5% of the variance of the AFQT scores, independently of other significant predictors such as pre-injury intelligence and percentage of brain volume loss. These data indicate that genetic variations in BDNF play a significant role in lesion-induced recovery following pTBI. Identifying the underlying mechanism of this brain-derived neurotrophic factor effect could provide insight into an important aspect of post-traumatic cognitive recovery.

Functional polymorphism of the mu-opioid receptor gene (OPRM1) influences reinforcement learning in humans

Previous reports on the functional effects (i.e., gain or loss of function), and phenotypic outcomes (e.g., changes in addiction vulnerability and stress response) of a commonly occurring functional single nucleotide polymorphism (SNP) of the mu-opioid receptor (OPRM1 A118G) have been inconsistent. Here we examine the effect of this polymorphism on implicit reward learning. We used a probabilistic signal detection task to determine whether this polymorphism impacts response bias to monetary reward in 63 healthy adult subjects: 51 AA homozygotes and 12 G allele carriers. OPRM1 AA homozygotes exhibited typical responding to the rewarded response--that is, their bias to the rewarded stimulus increased over time. However, OPRM1 G allele carriers exhibited a decline in response to the rewarded stimulus compared to the AA homozygotes. These results extend previous reports on the heritability of performance on this task by implicating a specific polymorphism. Through comparison with other studies using this task, we suggest a possible mechanism by which the OPRM1 polymorphism may confer reduced response to natural reward through a dopamine-mediated decrease during positive reinforcement learning.

A CHRNA5 allele related to nicotine addiction and schizophrenia

Schizophrenia and nicotine addiction are both highly heritable phenotypes. Because individuals with schizophrenia have a higher rate of smoking than those in the general population, one could hypothesize that genes associated with smoking might be overrepresented in schizophrenia and thus help explain their increased smoking incidence. Although a number of genes have been proposed to explain the increased smoking risk in schizophrenia, none of them have been consistently linked to smoking and schizophrenia, and thus difficult to explain the increased smoking in schizophrenia. A functional smoking-related nicotinic acetylcholine receptor α5 subunit gene (CHRNA5) nonsynonymous single nucleotide polymorphism (SNP) rs16969968 (Asp398Asn) has recently been discovered and replicated. As such, we tested whether this variant contributes to smoking in schizophrenia in a sample of 313 schizophrenia patients and 525 controls. The Asp398Asn risk allele is significantly associated with smoking severity independently in schizophrenia patient smokers (P = 0.001) and control smokers (P = 0.029). Furthermore, the same risk allele is significantly associated with schizophrenia in both Caucasian (P = 0.022) and African-American (P = 0.006) nonsmoker schizophrenia patients compared with control nonsmokers. Intriguingly, this SNP was not significantly associated with smoking status (smokers vs. nonsmokers) in either schizophrenia patients or controls. Therefore, our study identifies a genetic variant that is simultaneously linked to smoking and schizophrenia in the same cohort, but whether this SNP contributes to the increased smoking prevalence in schizophrenia patients requires additional studies.

Emotion processing, major depression, and functional genetic variation of neuropeptide Y

CONTEXT

Despite recent progress in describing the common neural circuitry of emotion and stress processing, the bases of individual variation are less well understood. Genetic variants that underlie psychiatric disease have proven particularly difficult to elucidate. Functional genetic variation of neuropeptide Y (NPY) was recently identified as a source of individual differences in emotion. Low NPY levels have been reported in major depressive disorder (MDD).

OBJECTIVE

To determine whether low-expression NPY genotypes are associated with negative emotional processing at 3 levels of analysis.

DESIGN

Cross-sectional, case-control study.

SETTING

Academic medical center.

PARTICIPANTS

Among 44 individuals with MDD and 137 healthy controls, 152 (84%) had an NPY genotype classified as low, intermediate, or high expression according to previously established haplotype-based expression data.

MAIN OUTCOME MEASURES

Healthy subjects participated in functional magnetic resonance imaging while viewing negative (vs neutral) words (n = 58) and rated positive and negative affect during a pain-stress challenge (n = 78). Genotype distribution was compared between 113 control subjects and 39 subjects with MDD.

RESULTS

Among healthy individuals, negatively valenced words activated the medial prefrontal cortex. Activation within this region was inversely related to genotype-predicted NPY expression (P = .03). Whole-brain regression of responses to negative words showed that the rostral anterior cingulate cortex activated in the low-expression group and deactivated in the high-expression group (P < .05). During the stress challenge, individuals with low-expression NPY genotypes reported more negative affective experience before and after pain (P = .002). Low-expression NPY genotypes were overrepresented in subjects with MDD after controlling for age and sex (P = .004). Population stratification did not account for the results.

CONCLUSIONS

These findings support a model in which NPY genetic variation predisposes certain individuals to low NPY expression, thereby increasing neural responsivity to negative stimuli within key affective circuit elements, including the medial prefrontal and anterior cingulate cortices. These genetically influenced neural response patterns appear to mediate risk for some forms of MDD.

Haplotype-based study of the association of alcohol-metabolizing genes with alcohol dependence in four independent populations

BACKGROUND

Ethanol is metabolized by 2 rate-limiting reactions: alcohol dehydrogenases (ADH) convert ethanol to acetaldehyde that is subsequently metabolized to acetate by aldehyde dehydrogenases (ALDH). Approximately 50% of East Asians have genetic variants that significantly impair this pathway and influence alcohol dependence (AD) vulnerability. We investigated whether variation in alcohol metabolism genes might alter the AD risk in four non-East Asian populations by performing systematic haplotype association analyses to maximize the chances of capturing functional variation.

METHODS

Haplotype-tagging SNPs were genotyped using the Illumina GoldenGate platform. Genotypes were available for 40 SNPs across the ADH genes cluster and 24 SNPs across the two ALDH genes in four diverse samples that included cases (lifetime AD) and controls (no Axis 1 disorders). The case control sample sizes were the following: Finnish Caucasians: 232, 194; African Americans: 267, 422; Plains American Indians: 226, 110; and Southwestern American (SW) Indians: 317, 72.

RESULTS

In all four populations, as well as HapMap populations, 5 haplotype blocks were identified across the ADH gene cluster: (i) ADH5-ADH4; (ii) ADH6-ADH1A-ADH1B; (iii) ADH1C; (iv) intergenic; (v) ADH7. The ALDH1A1 gene was defined by 4 blocks and ALDH2 by 1 block. No haplotype or SNP association results were significant after correction for multiple comparisons; however, several results, particularly for ALDH1A1 and ADH4, replicated earlier findings. There was an ALDH1A1 block 1 and 2 (extending from intron 5 to the 3' UTR) yin yang haplotype (haplotypes that have opposite allelic configuration) association with AD in the Finns driven by SNPs rs3764435 and rs2303317, respectively, and an ALDH1A1 block 3 (including the promoter region) yin yang haplotype association in SW Indians driven by 5 SNPs, all in allelic identity. The ADH4 SNP rs3762894 was associated with AD in Plains Indians.

CONCLUSIONS

The systematic evaluation of alcohol-metabolizing genes in four non-East Asian populations has shown only modest associations with AD, largely for ALDH1A1 and ADH4. A concentration of signals for AD with ALDH1A1 yin yang haplotypes in several populations warrants further study.

The influence of GABRA2, childhood trauma, and their interaction on alcohol, heroin, and cocaine dependence

BACKGROUND

The GABRA2 gene has been implicated in addiction. Early life stress has been shown to alter GABRA2 expression in adult rodents. We hypothesized that childhood trauma, GABRA2 variation, and their interaction would influence addiction vulnerability.

METHODS

African-American men were recruited for this study: 577 patients with lifetime DSM-IV single and comorbid diagnoses of alcohol, cocaine, and heroin dependence, and 255 control subjects. The Childhood Trauma Questionnaire (CTQ) was administered. Ten GABRA2 haplotype-tagging single-nucleotide polymorphisms (SNPs) were genotyped.

RESULTS

We found that exposure to childhood trauma predicted substance dependence (p < .0001). Polysubstance dependence was associated with the highest CTQ scores (p < .0001). The African Americans had four common haplotypes (frequency: .11-.30) within the distal haplotype block: two that correspond to the Caucasian and Asian yin-yang haplotypes, and two not found in other ethnic groups. One of the unique haplotypes predicted heroin addiction, whereas the other haplotype was more common in control subjects and seemed to confer resilience to addiction after exposure to severe childhood trauma. The yin-yang haplotypes had no effects. Moreover, the intron 2 SNP rs11503014, not located in any haplotype block and potentially implicated in exon splicing, was independently associated with addiction, specifically heroin addiction (p < .005). Childhood trauma interacted with rs11503014 variation to influence addiction vulnerability, particularly to cocaine (p < .005).

CONCLUSIONS

Our results suggest that at least in African-American men, childhood trauma, GABRA2 variation, and their interaction play a role in risk-resilience for substance dependence.

Association of substance use disorders with childhood trauma but not African genetic heritage in an African American cohort

OBJECTIVE

Genetic variation influences differential vulnerability to addiction within populations. However, it remains unclear whether differences in frequencies of vulnerability alleles contribute to disparities between populations and to what extent ancestry correlates with differential exposure to environmental risk factors, including poverty and trauma.

METHOD

The authors used 186 ancestry-informative markers to measure African ancestry in 407 addicts and 457 comparison subjects self-identified as African Americans. The reference group was 1,051 individuals from the Human Genome Diversity Cell Line Panel, which includes 51 diverse populations representing most worldwide genetic diversity.

RESULTS

African Americans varied in degrees of African, European, Middle Eastern, and Central Asian genetic heritage. The overall level of African ancestry was actually smaller among cocaine, opiate, and alcohol addicts (proportion=0.76-0.78) than nonaddicted African American comparison subjects (proportion=0.81). African ancestry was associated with living in impoverished neighborhoods, a factor previously associated with risk. There was no association between African ancestry and exposure to childhood abuse or neglect, a factor that strongly predicted all types of addictions.

CONCLUSIONS

These results suggest that African genetic heritage does not increase the likelihood of genetic risk for addictions. They highlight the complex interrelation between genetic ancestry and social, economic, and environmental conditions and the strong relation of those factors to addiction. Studies of epidemiological samples characterized for genetic ancestry and social, psychological, demographic, economic, cultural, and historical factors are needed to better disentangle the effects of genetic and environmental factors underlying interpopulation differences in vulnerability to addiction and other health disparities.

Variations in the serotonin-transporter gene are associated with attention bias patterns to positive and negative emotion faces

Both attention biases to threat and a serotonin-transporter gene polymorphism (5-HTTLPR) have been linked to heightened neural activation to threat and the emergence of anxiety. The short allele of 5-HTTLPR may act via its effect on neurotransmitter availability, while attention biases shape broad patterns of cognitive processing. We examined individual differences in attention bias to emotion faces as a function of 5-HTTLPR genotype. Adolescents (N=117) were classified for presumed SLC6A4 expression based on 5-HTTLPR-low (SS, SL(G), or L(G)L(G)), intermediate (SL(A) or L(A)L(G)), or high (L(A)L(A)). Participants completed the dot-probe task, measuring attention biases toward or away from angry and happy faces. Biases for angry faces increased with the genotype-predicted neurotransmission levels (low>intermediate>high). The reverse pattern was evident for happy faces. The data indicate a linear relation between 5-HTTLPR allelic status and attention biases to emotion, demonstrating a genetic mechanism for biased attention using ecologically valid stimuli that target socioemotional adaptation.

Associations of glutamate decarboxylase genes with initial sensitivity and age-at-onset of alcohol dependence in the Irish Affected Sib Pair Study of Alcohol Dependence

BACKGROUND

The relation of gamma-aminobutyric acid (GABA) to alcohol dependence (AD) has been widely studied. Several previous studies suggest that GABA may be involved in alcohol withdrawal, tolerance, and the symptoms that form an AD diagnosis. The genes coding for glutamate decarboxylase (GAD), the rate-limiting enzyme in GABA synthesis, are of potential interest for their association to ethanol consumption and AD. There are two isoforms of GAD, GAD1 and GAD2, which were reported to be associated with AD in males of Han Taiwanese (GAD1) and Russian (GAD2) ancestry. The present study examined the association of the two GAD isoforms with AD and relevant alcohol-related traits in the Irish Affected Sib Pair Study of Alcohol Dependence [Prescott, C.A., Sullivan, P.F., Myers, J.M., Patterson, D.G., Devitt, M., Halberstadt, L.J., Walsh, D., Kendler, K.S., 2005. The Irish Affected Sib Pair Study of Alcohol Dependence: study methodology and validation of diagnosis by interview and family history. Alcohol.-Clin. Exp. Res. 29 (3) 417-429].

METHODS

Participants were recruited in Ireland, including 575 independent cases who met DSM-IV AD criteria and 530 controls, screened for heavy drinking. We first conducted case-control analyses of the GAD genes with AD and, within the cases, examined associations with age at onset of AD, withdrawal symptoms, and two quantitative measures: initial sensitivity and tolerance (based on scales from the Self-Rating of the Effects of Ethanol) [Schuckit, M.A., Smith, T.L., Tipp, J.E., 1997. The self-rating of the effects of alcohol (SRE) form as a retrospective measure of the risk for alcoholism. Addiction 92, 979-988]. A total of 29 SNPs were genotyped for GAD1 and GAD2 using the Illumina GoldenGate protocols. Statistical procedures were implemented to control for false discovery rates (FDR).

RESULTS

Nine of 29 markers with minor allele frequencies less than 0.01 were removed from standard analysis; the remaining 20 markers were all in Hardy-Weinberg equilibrium. Three markers in the intronic regions of GAD1 were associated with initial sensitivity to alcohol (P=0.002); the associations remained significant after a FDR based correction for multiple testing. In addition, one marker located 3kb upstream of GAD1 exhibited association with age at onset of AD (P=0.0001). Gender specific effects were observed in results of both single marker and haplotype analyses.

CONCLUSION

We found no evidence for the association of GAD genes with AD but significant association of GAD1 with initial sensitivity and age at onset of AD. Our findings suggest that the underlying pathophysiology regulated by genes like GAD1 may be more directly related to the component processes that form AD than to the clinical disorder.

GABRG1 and GABRA2 as independent predictors for alcoholism in two populations

The chromosome 4 cluster of GABA(A) receptor genes is predominantly expressed in the brain reward circuitry and this chromosomal region has been implicated in linkage scans for alcoholism. Variation in one chromosome 4 gene, GABRA2, has been robustly associated with alcohol use disorders (AUD) although no functional locus has been identified. As HapMap data reveal moderate long-distance linkage disequilibrium across GABRA2 and the adjacent gene, GABRG1, it is possible that the functional locus is in GABRG1. We genotyped 24 SNPs across GABRG1 and GABRA2 in two population isolates: 547 Finnish Caucasian men (266 alcoholics) and 311 community-derived Plains Indian men and women (181 alcoholics). In both the Plains Indians and the Caucasians: (1) the GABRG1 haplotype block(s) did not extend to GABRA2; (2) GABRG1 haplotypes and SNPs were significantly associated with AUD; (3) there was no association between GABRA2 haplotypes and AUD; (4) there were several common (>or=0.05) haplotypes that spanned GABRG1 and GABRA2 (341 kb), three of which were present in both populations: one of these ancestral haplotypes was associated with AUD, the other two were more common in non-alcoholics; this association was determined by GABRG1; (5) in the Finns, three less common (<0.05) extended haplotypes showed an association with AUD that was determined by GABRA2. Our results suggest that there are likely to be independent, complex contributions from both GABRG1 and GABRA2 to alcoholism vulnerability.

Naltrexone alone and with sertraline for the treatment of alcohol dependence in Alaska natives and non-natives residing in rural settings: a randomized controlled trial

BACKGROUND

Access to specialty alcoholism treatment in rural environments is limited and new treatment approaches are needed. The objective was to evaluate the efficacy of naltrexone alone and in combination with sertraline among Alaska Natives and other Alaskans living in rural settings. An exploratory aim examined whether the Asn40Asp polymorphism of the mu-opioid receptor gene (OPRM1) predicted response to naltrexone, as had been reported in Caucasians.

METHODS

Randomized, controlled trial enrolling 101 Alaskans with alcohol dependence, including 68 American Indians/Alaska Natives. Participants received 16 weeks of either (1) placebo (placebo naltrexone + placebo sertraline), (2) naltrexone monotherapy (50 mg naltrexone + sertraline placebo) and (3) naltrexone + sertraline (100 mg) plus nine sessions of medical management and supportive advice. Primary outcomes included Time to First Heavy Drinking Day and Total Abstinence.

RESULTS

Naltrexone monotherapy demonstrated significantly higher total abstinence (35%) compared with placebo (12%, p = 0027) and longer, but not statistically different, Time to First Heavy Drinking Day (p = 0.093). On secondary measures, naltrexone compared with placebo demonstrated significant improvements in percent days abstinent (p = 0.024) and drinking-related consequences (p = 0.02). Combined sertraline and naltrexone did not differ from naltrexone alone. The pattern of findings was generally similar for the American Indian/Alaska Native subsample. Naltrexone treatment response was significant within the group of 75 individuals who were homozygous for OPRM1 Asn40 allele. There was a small number of Asp40 carriers, precluding statistical testing of the effect of this allele on response.

CONCLUSIONS

Naltrexone can be used effectively to treat alcoholism in remote and rural communities, with evidence of benefit for American Indians and Alaska Natives. New models of care incorporating pharmacotherapy could reduce important health disparities related to alcoholism.