Genetic and environmental contributions to alcohol dependence risk in a national twin sample: consistency of findings in women and men

Bulimic behaviors and alcohol use: shared genetic influences

Bulimic behaviors are frequently associated with alcohol use disorders. However, extant family and twin study findings have been inconsistent with regard to whether these behaviors share etiologic influences. A sample of 292 young adult, female twins was used to examine genetic and environmental factors underlying the association between binge eating and compensatory behaviors (e.g., vomiting)and alcohol use. Binge eating and compensatory behaviors were assessed using the Minnesota Eating Behavior Survey.Alcohol use was measured using the Alcohol Use Disorders Identification Test. Univariate models indicated that the heritability of binge eating, compensatory behaviors, and alcohol use was 41, 28, and 78%, respectively, with the remaining variance due to nonshared environmental effects.Bivariate models indicated that there was a moderate-to-large degree of overlap (genetic correlation = 0.31–0.61) in additive genetic factors between alcohol use and binge eating and compensatory behaviors, and no overlap in environmental effects. Findings suggest that these phenotypes co-aggregate in families and that similar genes or heritable traits may be contributing to their co-occurrence.

Marijuana expectancies and relationships with adolescent and adult marijuana use

BACKGROUND

Outcome expectancy is a central construct in models of addiction and relapse. Much expectancy research has been conducted in the context of alcohol; however, less is known about the structure of expectancies for marijuana and their associations with marijuana use outcomes.

METHODS

The data are taken from waves 3 and 4 of a longitudinal high-risk study of parents and adolescent offspring. Of those families who were retained at wave 3, 225 were high-risk and 205 were matched controls (low-risk). In the present study, we examine the factorial structure of marijuana expectancies (wave 3) in the offspring (using an instrument adapted from the alcohol literature) and test whether expectancies mediate the associations of familial risk for substance use, lifetime marijuana use in adolescence (wave 3) and current use in young adulthood (wave 4; reported approximately 5 years later).

RESULTS

We quantified four marijuana expectancy factors similar to those identified in previous studies when the offspring were adolescents (Mn age=15.2) and results of our mediation models suggest that negative marijuana expectancies (but not positive expectancies) together with lifetime adolescent marijuana use completely mediated the association between familial risk and current use of marijuana during young adulthood (Mn age=20.2).

CONCLUSION

Familial risk for current marijuana use in young adulthood appears to be transmitted through two orthogonal, prospective pathways. One pathway involves marijuana use during adolescence, and the second pathway involves reduced expectancies that using marijuana will result in cognitive and behavioral impairments.

Environmental influences predominate in remission from alcohol use disorder in young adult twins

BACKGROUND

Familial influences on remission from alcohol use disorder (AUD) have been studied using family history of AUD rather than family history of remission. The current study used a remission phenotype in a twin sample to examine the relative contributions of genetic and environmental influences to remission.

METHOD

The sample comprised 6183 twins with an average age of 30 years from the Australian Twin Registry. Lifetime history of alcohol abuse and dependence symptoms and symptom recency were assessed with a structured telephone interview. AUD was defined broadly and narrowly as history of two or more or three or more abuse or dependence symptoms. Remission was defined as absence of symptoms at time of interview among individuals with lifetime AUD. Standard bivariate genetic analyses were conducted to derive estimates of genetic and environmental influences on AUD and remission.

RESULTS

Environmental influences alone accounted for remission in males and for 89% of influences on remission in females, with 11% due to genetic influences shared with AUD, which decreased the likelihood of remission. For women, more than 80% of influences on remission were distinct from influences on AUD, and environmental influences were from individual experiences only. For men, just over 50% of influences on remission were distinct from those on AUD, and the influence of environments shared with the co-twin were substantial. The results for the broad and narrow phenotypes were similar.

CONCLUSIONS

The current study establishes young adult remission as a phenotype distinct from AUD and highlights the importance of environmental influences on remission.

Alcohol dependence in same-sex and opposite-sex twins

Males with a female co-twin are more likely to become alcohol-dependent than males with a male co-twin. According to the twin testosterone transfer model, this finding can be interpreted as indirect evidence for a role of prenatal testosterone in alcohol dependence.

Nur-related receptor 1 gene polymorphisms and alcohol dependence in Mexican Americans

AIM: To investigate the association of polymorphisms of nur-related receptor 1 (Nurr1) and development of alcohol dependence in Mexican Americans.

METHODS: Peripheral blood samples were collected from 374 alcoholic and 346 nonalcoholic Mexican Americans; these two groups were sex- and age-matched. Sample DNA was extracted and genomic DNA was amplified by polymerase chain reaction. The -2922(C) 2-3 polymerase chain reaction products were digested with Sau96I, alleles of 1345(G/C), and -1198(C/G) in the regulatory region as well as Ex+132 (G/T/A/C) and Ex+715(T/-) in exon 3 were studied by sequencing.

RESULTS: The C2/C2, C2/C3, C3/C3 genotype distribution of -2922(C) 2-3 was 34.4%, 38.2% and 27.5% in the nonalcoholic group compared to 23.3%, 51.2% and 25.4% in the alcoholic group (P = 0.001). The C/C, C/G, G/G genotype distribution of -1198(C/G) was 23.5%, 46.1% and 30.3% in the nonalcoholic group compared to 13.9%, 50.9% and 35.3% in the alcoholic group (P = 0.007). However, the -1345 (G/C), Ex3+132(G/T/A/C) and Ex3+715(T/-) alleles were not polymorphic in Mexican Americans, and all those studied had G/G, G/G and T/T genotype for these three alleles, respectively. The -2922(C) 2-3 did not show allele level difference between alcoholic and nonalcoholic individuals, but -1198 (C/G) showed a significant allele frequency difference between alcoholic (39.3%) and nonalcoholic (46.6%) populations (P = 0.005). Excluding obese individuals, significant differences were found at both genotypic and allelic levels for the -2922(C) 2-3 polymorphism (P = 0.000 and P = 0.049) and the -1198 (C/G) polymorphism (P = 0.008 and P = 0.032) between nonobese alcoholics and nonobese controls. Excluding smokers, a significant difference was found only at the genotypic level for the -2922(C) 2-3 polymorphism (P = 0.037) between nonsmoking alcoholics and nonsmoking controls, but only at the allelic level for the -1198(C/G) polymorphism (P = 0.034).

CONCLUSION: Polymorphisms in the regulatory region of Nurr1 are implicated in pathogenesis of alcohol dependence and the Nurr1/dopamine signaling pathway might be important for this dependence development in Mexican Americans.

An Australian twin study of cannabis and other illicit drug use and misuse, and other psychopathology

Cannabis is the most widely used illicit drug throughout the developed world and there is consistent evidence of heritable influences on multiple stages of cannabis involvement including initiation of use and abuse/dependence. In this paper, we describe the methodology and preliminary results of a large-scale interview study of 3,824 young adult twins (born 1972-1979) and their siblings. Cannabis use was common with 75.2% of males and 64.7% of females reporting some lifetime use of cannabis while 24.5% of males and 11.8% of females reported meeting criteria for DSM-IV cannabis abuse or dependence. Rates of other drug use disorders and common psychiatric conditions were highly correlated with extent of cannabis involvement and there was consistent evidence of heritable influences across a range of cannabis phenotypes including early (≤15 years) opportunity to use (h 2 = 72%), early (≤16 years) onset use (h 2 = 80%), using cannabis 11+ times lifetime (h 2 = 76%), and DSM abuse/dependence (h 2 = 72%). Early age of onset of cannabis use was strongly associated with increased rates of subsequent use of other illicit drugs and with illicit drug abuse/dependence; further analyses indicating that some component of this association may have been mediated by increasing exposure to and opportunity to use other illicit drugs.

Treatment of co-occurring posttraumatic stress disorder and substance use disorders

There is a significant need for advanced understanding of treatment of co-occurring posttraumatic stress disorder (PTSD) and substance use disorders (SUD). Approximately half of individuals seeking SUD treatment meet criteria for current PTSD, and individuals with co-occurring PTSD-SUD tend to have poorer treatment outcomes compared with those without such comorbidity. However, there is not sufficient empirical evidence to determine a best course of treatment for these individuals. This paper provides a review of the literature relevant to the treatment of co-occurring PTSD-SUD. To date, treatment studies have focused primarily on non-exposure-based psychosocial treatments, exposure-based psychosocial treatments, and medication trials. The most promising outcome data thus far are for psychosocial treatments that incorporate an exposure therapy component; however, further research is needed, particularly as related to how best to implement these approaches in real-world treatment settings.

Convergence of genome-wide association and candidate gene studies for alcoholism

BACKGROUND

Genome-wide association (GWA) studies have led to a paradigm shift in how researchers study the genetics underlying disease. Many GWA studies are now publicly available and can be used to examine whether or not previously proposed candidate genes are supported by GWA data. This approach is particularly important for the field of alcoholism because the contribution of many candidate genes remains controversial.

METHODS

Using the Human Genome Epidemiology (HuGE) Navigator, we selected candidate genes for alcoholism that have been frequently examined in scientific articles in the past decade. Specific candidate loci as well as all the reported single nucleotide polymorphisms (SNPs) in candidate genes were examined in the Study of Addiction: Genetics and Environment (SAGE), a GWA study comparing alcohol-dependent and nondependent subjects.

RESULTS

Several commonly reported candidate loci, including rs1800497 in DRD2, rs698 in ADH1C, rs1799971 in OPRM1, and rs4680 in COMT, are not replicated in SAGE (p > 0.05). Among candidate loci available for analysis, only rs279858 in GABRA2 (p = 0.0052, OR = 1.16) demonstrated a modest association. Examination of all SNPs reported in SAGE in over 50 candidate genes revealed no SNPs with large frequency differences between cases and controls, and the lowest p-value of any SNP was 0.0006.

CONCLUSIONS

We provide evidence that several extensively studied candidate loci do not have a strong contribution to risk of developing alcohol dependence in European and African ancestry populations. Owing to the lack of coverage, we were unable to rule out the contribution of other variants, and these genes and particular loci warrant further investigation. Our analysis demonstrates that publicly available GWA results can be used to better understand which if any of previously proposed candidate genes contribute to disease. Furthermore, we illustrate how examining the convergence of candidate gene and GWA studies can help elucidate the genetic architecture of alcoholism and more generally complex diseases.

Copy number variations in 6q14.1 and 5q13.2 are associated with alcohol dependence

BACKGROUND

Excessive alcohol use is the third leading cause of preventable death and is highly correlated with alcohol dependence, a heritable phenotype. Many genetic factors for alcohol dependence have been found, but many remain unknown. In search of additional genetic factors, we examined the association between Diagnostic and StatisticalManual of Mental Disorders, Fourth Edition (DSM-IV) alcohol dependence and all common copy number variations (CNVs) with good reliability in the Study of Addiction: Genetics and Environment (SAGE).

METHODS

All participants in SAGE were interviewed using the Semi-Structured Assessment for the Genetics of Alcoholism, as a part of 3 contributing studies. A total of 2,610 non-Hispanic European American samples were genotyped on the Illumina Human 1M array. We performed CNV calling by CNVPartition, PennCNV, and QuantiSNP, and only CNVs identified by all 3 software programs were examined. Association was conducted with the CNV (as a deletion/duplication) as well as with probes in the CNV region. Quantitative polymerase chain reaction (qPCR) was used to validate the CNVs in the laboratory.

RESULTS

CNVs in 6q14.1 (p = 1.04 × 10(-6)) and 5q13.2 (p = 3.37 × 10(-4)) were significantly associated with alcohol dependence after adjusting multiple tests. On chromosome 5q13.2, there were multiple candidate genes previously associated with various neurological disorders. The region on chromosome 6q14.1 is a gene desert that has been associated with mental retardation and language delay. The CNV in 5q13.2 was validated, whereas only a component of the CNV on 6q14.1 was validated by qPCR. Thus, the CNV on 6q14.1 should be viewed with caution.

CONCLUSIONS

This is the first study to show an association between DSM-IV alcohol dependence and CNVs. CNVs in regions previously associated with neurological disorders may be associated with alcohol dependence.

Hypermethylation of OPRM1 promoter region in European Americans with alcohol dependence

The μ-opioid receptor mediates rewarding effects of alcohol and illicit drugs. We hypothesized that altered DNA methylation in the μ-opioid receptor gene (OPRM1) might influence the vulnerability to alcohol dependence (AD). Genomic DNA was extracted from the peripheral blood of 125 European Americans with AD and 69 screened European American controls. Methylation levels of 16 CpGs in the OPRM1 promoter region were examined by bisulfite sequencing analysis. A multivariate analysis of covariance was conducted to analyze AD-associated methylation changes in the OPRM1 promoter region, using days of intoxication in the past 30 days, sex, age, ancestry proportion and childhood adversity (CA) as covariates. Three CpGs (80, 71, and 10 bp upstream of the OPRM1 translation start site) were more highly methylated in AD cases than in controls (CpG-80: P=0.033; CpG-71: P=0.004; CpG-10: P=0.008). Although these sites were not significant after correction for multiple comparisons, the overall methylation level of the 16 CpGs was significantly higher in AD cases (13.6%) than in controls (10.6%) (P=0.049). Sex and CA did not significantly influence OPRM1 promoter methylation levels. Our findings suggest that OPRM1 promoter hypermethylation may increase the risk for AD and other substance dependence disorders.

Common variants in HLA-DRA gene are associated with alcohol dependence in two Caucasian samples

HLA-DRA gene polymorphisms might play an important role in alcohol dependence (AD). We examined genetic associations of 29 single-nucleotide polymorphisms (SNPs) within the HLA-DRA gene with AD using two Caucasian samples-the Collaborative Study on the Genetics of Alcoholism (COGA) sample (660 AD cases and 400 controls) and the Study of Addiction: Genetics and Environment (SAGE) sample (623 cases and 1,016 controls). Logistic regression analysis using PLINK showed that 16 SNPs were associated with AD in the COGA sample and 13 SNPs were associated with AD in the SAGE sample (p < 0.05). The best novel signal was SNP rs2239803 associated with AD in both samples (p = 0.000817 for the COGA sample and p = 0.0026 for the SAGE sample, respectively) while one flanking SNP rs4935356 also showed strong association in both samples (p = 0.00219 and 0.0026 for the COGA and SAGE samples, respectively). Furthermore, these two SNPs revealed stronger associations in meta-analysis of these two samples (p = 8.97 × 10(-6) and 2.02 × 10(-5) for rs2239803 and rs4935356, respectively). In addition, the G-A haplotype from these two SNPs revealed a significant association with AD in both the COGA and SAGE samples (p = 0.0007 and 0.0019, respectively). These findings highlight the novel associations with HLA-DRA that may play an important role in the etiology of AD.

Testing multiple levels of influence in the intergenerational transmission of alcohol disorders from a developmental perspective: the example of alcohol use promoting peers and μ-opioid receptor M1 variation

This study examined the interplay between the influence of peers who promote alcohol use and μ-opioid receptor M1 (OPRM1) genetic variation in the intergenerational transmission of alcohol use disorder (AUD) symptoms while separating the "traitlike" components of AUD symptoms from their age-specific manifestations at three ages from emerging adulthood (17-23 years) to adulthood (29-40 years). The results for males were consistent with genetically influenced peer selection mechanisms as mediators of parent alcoholism effects. Male children of alcoholics were less likely to be carriers of the G allele in single nucleotide polymorphism A118G (rs1799971), and those who were homozygous for the A allele were more likely to affiliate with alcohol use promoting peers who increased the risk for AUD symptoms at all ages. There was evidence for women of an interaction between OPRM1 variation and peer affiliations but only at the earliest age band. Peer influences had stronger effects among women who were G-carriers. These results illustrate the complex ways in which the interplay between influences at multiple levels of analysis can underlie the intergenerational transmission of alcohol disorders as well as the importance of considering age and gender differences in these pathways.

Interaction between serotonin transporter and serotonin receptor 1 B genes polymorphisms may be associated with antisocial alcoholism

Background

Several studies have hypothesized that genes regulating the components of the serotonin system, including serotonin transporter (5-HTTLPR) and serotonin 1 B receptor (5-HT1B), may be associated with alcoholism, but their results are contradictory because of alcoholism’s heterogeneity. Therefore, we examined whether the 5-HTTLPR gene and 5-HT1B gene G861C polymorphism are susceptibility factors for a specific subtype of alcoholism, antisocial alcoholism in Han Chinese in Taiwan.

Methods

We recruited 273 Han Chinese male inmates with antisocial personality disorder (ASPD) [antisocial alcoholism (AS-ALC) group (n = 120) and antisocial non-alcoholism (AS-N-ALC) group (n = 153)] and 191 healthy male controls from the community. Genotyping was done using PCR-RFLP.

Results

There were no significant differences in the genotypic frequency of the 5-HT1B G861C polymorphism between the 3 groups. Although AS-ALC group members more frequently carried the 5-HTTLPR S/S, S/L_G, and L_G/L_G genotypes than controls, the difference became non-significant after controlling for the covarying effects of age. However, the 5-HTTLPR S/S, S/L_G, and L_G/L_G genotypes may have interacted with the 5-HT1B G861C C/C polymorphism and increased the risk of becoming antisocial alcoholism.

Conclusion

Our study suggests that neither the 5-HTTLPR gene nor the 5-HT1B G861C polymorphism alone is a risk factor for antisocial alcoholism in Taiwan’s Han Chinese population, but that the interaction between both genes may increase susceptibility to antisocial alcoholism.

Dopamine transporter (DAT1) VNTR polymorphism and alcoholism in two culturally different populations of south India

It is well established that the central dopaminergic reward pathway is likely involved in alcohol intake and the progression of alcohol dependence. Dopamine transporter (DAT1) mediates the active re-uptake of DA from the synapse and is a principal regulator of dopaminergic neurotransmission. The gene for the human DAT1 displays several polymorphisms, including a 40-bp variable number of tandem repeats (VNTR) ranging from 3 to 16 copies in the 3'-untranslated region (UTR) of the gene. To assess the role of this gene in alcoholism, we genotyped the VNTR of DAT1 gene in a sample of 206 subjects from the Kota population (111 alcohol dependence cases and 95 controls) and 142 subjects from Badaga population (81 alcohol dependence cases and 61 controls). Both populations inhabit a similar environmental zone, but have different ethnic histories. Phenotype was defined based on the DSM-IV criteria. Genotyping was performed using PCR and electrophoresis. The association of DAT1 with alcoholism was tested by using the Clump v1.9 program which uses the Monte Carlo method. In both Kota and Badaga populations, the allele A10 was the most frequent allele followed by allele A9. The genotypic distribution is in Hardy-Weinberg equilibrium in both cases and control groups of Kota and Badaga populations. The DAT1 VNTR was significantly associated with alcoholism in Badaga population but not in Kota population. Our results suggest that the A9 allele of the DAT gene is involved in vulnerability to alcoholism, but that these associations are population specific.

Two-part random effects growth modeling to identify risks associated with alcohol and cannabis initiation, initial average use and changes in drug consumption in a sample of adult, male twins

AIMS

Our aim was to profile alcohol and cannabis initiation and to characterize the effects of developmental and environmental risk factors on changes in average drug use over time.

DESIGN

We fitted a two-part random effects growth model to identify developmental and environmental risks associated with alcohol and cannabis initiation, initial average use and changes in average use.

PARTICIPANTS

1796 males aged 24-63 from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders.

MEASUREMENTS

Data from three interview waves included self-report measures of average alcohol and cannabis use between ages 15 and 24, genetic risk of problem drug use, childhood environmental risks, personality, psychiatric symptoms, as well as personal, family and social risk factors.

FINDINGS

Average alcohol and cannabis use were correlated at all ages. Genetic risk of drug use based on family history, higher sensation seeking, and peer group deviance predicted both alcohol and cannabis initiation. Higher drug availability predicted cannabis initiation while less parental monitoring and drug availability were the best predictors of how much cannabis individuals consumed over time.

CONCLUSION

The liability to initiate alcohol and cannabis, average drug use as well as changes in drug use during teenage years and young adulthood is associated with known risk factors.

Subjective perceptions associated with the ascending and descending slopes of breath alcohol exposure vary with recent drinking history

BACKGROUND

The differentiator model predicts that individuals with a positive family history of alcoholism (FHA) or heavy alcohol consumers will feel more sensitive to the effects of alcohol on the ascending phase of the blood alcohol content while feeling less sedated on the descending phase. This study tested whether subjective perceptions are sensitive to the slope of breath alcohol concentration (BrAC) and whether that sensitivity is associated with an FHA and/or recent drinking history (RDH).

METHODS

Family-history-positive (FHP, n = 27) and family-history-negative (FHN, n = 27) young adult nondependent drinkers were infused intravenously with alcohol in 2 sessions separated by 1 week. After 20 minutes, one session had an ascending BrAC (+3.0 mg%/min), while the other session had a descending BrAC (-1 mg%/min). The BrAC for both sessions at this point was approximately 60 mg%, referred to as the crossover point. Subjective perceptions of intoxication, high, stimulated, and sedation were sampled frequently and then interpolated to the crossover point. Within-subject differences between ascending and descending responses were examined for associations with FHA and/or RDH.

RESULTS

Recent moderate drinkers reported increased perceptions of feeling intoxicated (p < 0.023) and high (p < 0.023) on the ascending slope compared with the descending slope. In contrast, recent light drinkers felt more intoxicated and high on the descending slope.

CONCLUSIONS

Subjective perceptions in young adult social drinkers depend on the slope of the BrAC when examined in association with RDH. These results support the differentiator model hypothesis concerning the ascending slope and suggest that moderate alcohol consumers could be at risk for increased alcohol consumption because they feel more intoxicated and high on the ascending slope. Subjects did not feel less sedated on the descending slope, contrary to the differentiator model but replicating several previous studies.

ASTN1 and alcohol dependence: family-based association analysis in multiplex alcohol dependence families

A previous genome-wide linkage study of alcohol dependence (AD) in multiplex families found a suggestive linkage result for a region on Chromosome 1 near microsatellite markers D1S196 and D1S2878. The ASTN1 gene is in this region, a gene previously reported to be associated with substance abuse, bipolar disorder and schizophrenia. Using the same family data consisting of 330 individuals with phenotypic data and DNA, finer mapping of a 26 cM region centered on D1S196 was undertaken using SNPs with minor allele frequency (MAF) ≥ 0.15 and pair-wise linkage disequilibrium (LD) of r(2) < 0.8 using the HapMap CEU population. Significant FBAT P-values for SNPs within the ASTN1 gene were observed for four SNPs (rs465066, rs228008, rs6668092, and rs172917), the most significant, rs228008, within intron 8 had a P-value of 0.001. Using MQLS, which allows for inclusion of all families, we find three of these SNPs with MQLS P-values < 0.003. In addition, two additional neighboring SNPs (rs10798496 and rs6667588) showed significance at P = 0.002 and 0.03, respectively. Haplotype analysis was performed using the haplotype-based test function of FBAT for a block that included rs228008, rs6668092, and rs172917. This analysis found one block (GCG) over-transmitted and another (ATA) under-transmitted to affected offspring. Linkage analysis identified a region consistent with the association results. Family-based association analysis shows the ASTN1 gene significantly associated with alcohol dependence. The potential importance of the ASTN1 gene for AD risk may be related its role in glial-guided neuronal migration.

The genetic basis of addictive disorders

Addictions are common, chronic, and relapsing diseases that develop through a multistep process. The impact of addictions on morbidity and mortality is high worldwide. Twin studies have shown that the heritability of addictions ranges from 0.39 (hallucinogens) to 0.72 (cocaine). Twin studies indicate that genes influence each stage from initiation to addiction, although the genetic determinants may differ. Addictions are by definition the result of gene × environment interaction. These disorders, which are in part volitional, in part inborn, and in part determined by environmental experience, pose the full range of medical, genetic, policy, and moral challenges. Gene discovery is being facilitated by a variety of powerful approaches, but is in its infancy. It is not surprising that the genes discovered so far act in a variety of ways: via altered metabolism of drug (the alcohol and nicotine metabolic gene variants), via altered function of a drug receptor (the nicotinic receptor, which may alter affinity for nicotine but as discussed may also alter circuitry of reward), and via general mechanisms of addiction (genes such as monoamine oxidase A and the serotonin transporter that modulate stress response, emotion, and behavioral control). Addiction medicine today benefits from genetic studies that buttress the case for a neurobiologic origin of addictive behavior, and some general information on familially transmitted propensity that can be used to guide prevention. A few well-validated, specific predictors such as OPRM1, ADH1B, ALDH2, CHRNA5, and CYP26 have been identified and can provide some specific guidance, for example, to understand alcohol-related flushing and upper GI cancer risk (ADH1B and AKLDH2), variation in nicotine metabolism (CYP26), and, potentially, naltrexone treatment response (OPRM1). However, the genetic predictors available are few in number and account for only a small portion of the genetic variance in liability, and have not been integrated into clinical nosology or care.

Developmental trajectory and environmental moderation of the effect of ALDH2 polymorphism on alcohol use

BACKGROUND

In the aldehyde dehydrogenase 2 (ALDH2) gene, the ALDH2*2 allele, prevalent in East Asian populations, encodes an enzyme with severely reduced activity, thereby disrupting the normal metabolism of alcohol. Possession of the ALDH2*2 allele has been repeatedly shown to be associated with lower risk for alcohol dependence and reduced alcohol use. However, relatively few studies have considered whether the magnitude of the effect of ALDH2 polymorphism upon drinking is related to developmental stage or varies by environmental context.

METHODS

In a longitudinally assessed sample of 356 adopted adolescents and young adults of East Asian descent, we examined the progression over time of the relationship between ALDH2 genotype and multiple measures of drinking behavior. We also sought to determine whether the environmental influences of nonbiological parent and elder sibling alcohol use and misuse, as well as deviant peer behavior, moderated the effect of ALDH2 genotype upon alcohol use.

RESULTS

Across all measures of alcohol use, the association between ALDH2*2 allele possession and reduced drinking went from negligible to moderate between mid-adolescence and early adulthood. A combined index of adoptive parent alcohol use and misuse consistently moderated the protective effect of the ALDH2*2 allele across the measures of quantity and frequency of alcohol use, and symptomology, such that high parental alcohol use and misuse reduced the protective effect of the ALDH2*2 allele, while low parental alcohol use and misuse enhanced the effect of the allele. Neither a combined index of elder sibling alcohol use and misuse, nor deviant peer behavior was consistently related to the effect of ALDH2 genotype.

CONCLUSIONS

The protective effect of the ALDH2*2 allele increases over the course of adolescence and young adulthood and is modified by the environmental influence of parental alcohol use and misuse. As such, ALDH2 provides a model system for exploring the nature of gene-environment interplay across development.

Ambulatory monitoring in the genetics of psychosomatic medicine

Psychosomatic disorders are composed of an array of psychological, biologic, and environmental features. The existing evidence points to a role for genetic factors in explaining individual differences in the development and maintenance of a variety of disorders, but studies to date have not shown consistent and replicable effects. As such, the attempt to uncover individual differences in the expression of psychosomatic disorders as a function of genetic architecture requires careful attention to their phenotypic architecture or the various intermediate phenotypes that make up a heterogeneous disorder. Ambulatory monitoring offers a novel approach to measuring time-variant and situation-dependent intermediate phenotypes. Recent examples of the use of ambulatory monitoring in genetic studies of stress reactivity, chronic pain, alcohol use disorders, and psychosocial resilience are reviewed in an effort to highlight the benefits of ambulatory monitoring for genetic study designs.

Genetic dissection of acute ethanol responsive gene networks in prefrontal cortex: functional and mechanistic implications

Background

Individual differences in initial sensitivity to ethanol are strongly related to the heritable risk of alcoholism in humans. To elucidate key molecular networks that modulate ethanol sensitivity we performed the first systems genetics analysis of ethanol-responsive gene expression in brain regions of the mesocorticolimbic reward circuit (prefrontal cortex, nucleus accumbens, and ventral midbrain) across a highly diverse family of 27 isogenic mouse strains (BXD panel) before and after treatment with ethanol.

Results

Acute ethanol altered the expression of ∼2,750 genes in one or more regions and 400 transcripts were jointly modulated in all three. Ethanol-responsive gene networks were extracted with a powerful graph theoretical method that efficiently summarized ethanol's effects. These networks correlated with acute behavioral responses to ethanol and other drugs of abuse. As predicted, networks were heavily populated by genes controlling synaptic transmission and neuroplasticity.

Several of the most densely interconnected network hubs, including Kcnma1 and Gsk3β, are known to influence behavioral or physiological responses to ethanol, validating our overall approach. Other major hub genes like Grm3, Pten and Nrg3 represent novel targets of ethanol effects. Networks were under strong genetic control by variants that we mapped to a small number of chromosomal loci. Using a novel combination of genetic, bioinformatic and network-based approaches, we identified high priority cis-regulatory candidate genes, including Scn1b, Gria1, Sncb and Nell2.

Conclusions

The ethanol-responsive gene networks identified here represent a previously uncharacterized intermediate phenotype between DNA variation and ethanol sensitivity in mice. Networks involved in synaptic transmission were strongly regulated by ethanol and could contribute to behavioral plasticity seen with chronic ethanol. Our novel finding that hub genes and a small number of loci exert major influence over the ethanol response of gene networks could have important implications for future studies regarding the mechanisms and treatment of alcohol use disorders.

Adolescence and parental history of alcoholism: insights from the sleep EEG

BACKGROUND

Disrupted sleep is a common complaint of individuals with alcohol use disorder and in abstinent alcoholics. Furthermore, among recovering alcoholics, poor sleep predicts relapse to drinking. Whether disrupted sleep in these populations results from prolonged alcohol use or precedes the onset of drinking is not known. The aim of this study was to examine the sleep electroencephalogram (EEG) in alcohol-naïve, parental history positive (PH+), and negative (PH-) boys and girls.

METHODS

All-night sleep EEG recordings in 2 longitudinal cohorts (child and teen) followed at 1.5 to 3 year intervals were analyzed. The child and teen participants were 9/10 and 15/16 years old at the initial assessment, respectively. Parental history status was classified by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria applied to structured interviews (DIS-IV) resulting in 14 PH- and 10 PH+ children and 14 PH- and 10 PH+ teens. Sleep data were visually scored in 30-second epochs using standard criteria. Power spectra were calculated for EEG derivations C3/A2, C4/A1, O2/A1, O1/A2 for nonrapid eye movement (NREM) and rapid eye movement (REM) sleep.

RESULTS

We found no difference between PH+ and PH- individuals in either cohort for any visually scored sleep stage variable. Spectral power declined in both cohorts across assessments for NREM and REM sleep in all derivations and across frequencies independent of parental history status. With regard to parental history, NREM sleep EEG power was lower for the delta band in PH+ teens at both assessments for the central derivations. Furthermore, power in the sigma band for the right occipital derivation in both NREM and REM sleep was lower in PH+ children only at the initial assessment.

CONCLUSIONS

We found no gross signs of sleep disruption as a function of parental history. Modest differences in spectral EEG power between PH+ and PH- children and teens indicate that a marker of parental alcohol history may be detectable in teens at risk for problem drinking.

The dappled nature of causes of psychiatric illness: replacing the organic-functional/hardware-software dichotomy with empirically based pluralism

Our tendency to see the world of psychiatric illness in dichotomous and opposing terms has three major sources: the philosophy of Descartes, the state of neuropathology in late nineteenth century Europe (when disorders were divided into those with and without demonstrable pathology and labeled, respectively, organic and functional), and the influential concept of computer functionalism wherein the computer is viewed as a model for the human mind-brain system (brain=hardware, mind=software). These mutually re-enforcing dichotomies, which have had a pernicious influence on our field, make a clear prediction about how 'difference-makers' (aka causal risk factors) for psychiatric disorders should be distributed in nature. In particular, are psychiatric disorders like our laptops, which when they dysfunction, can be cleanly divided into those with software versus hardware problems? I propose 11 categories of difference-makers for psychiatric illness from molecular genetics through culture and review their distribution in schizophrenia, major depression and alcohol dependence. In no case do these distributions resemble that predicted by the organic-functional/hardware-software dichotomy. Instead, the causes of psychiatric illness are dappled, distributed widely across multiple categories. We should abandon Cartesian and computer-functionalism-based dichotomies as scientifically inadequate and an impediment to our ability to integrate the diverse information about psychiatric illness our research has produced. Empirically based pluralism provides a rigorous but dappled view of the etiology of psychiatric illness. Critically, it is based not on how we wish the world to be but how the difference-makers for psychiatric illness are in fact distributed.

Five-factor personality traits and age trajectories of self-rated health: the role of question framing

We examined the influence of personality traits on mean levels and age trends in 4 single-item measures of self-rated health: general rating, comparison to age peers, comparison to past health, and expectations for future health. Community-dwelling participants (N = 1,683) completed 7,474 self-rated health assessments over a period of up to 19 years. In hierarchical linear modeling analyses, age-associated declines differed across the 4 health items. Across age groups, high Neuroticism and low Conscientiousness, low Extraversion, and low Openness were associated with worse health ratings, with notable differences across the 4 health items. Furthermore, high Neuroticism predicted steeper declines in health ratings involving temporal comparisons. We consider theoretical implications regarding the mechanisms behind associations among personality traits and self-rated health.

Genetics of early cancer detection behaviours in Australian female twins

Early detection of cervical and breast cancers is an important component of women's health strategy. Screening programmes, health professional interventions and preventive behaviours such as breast self-examination provide the means to this end. Our twin study sought to identify the relative influence of environmental and genetic factors on liability to early cancer detection behaviours, including use of cervical smear tests, mammograms, and breast examination. Additive genetic and random environmental effects models gave the best, most parsimonious fit to the data for each early cancer detection behaviour. The heritability of liability to Pap smear use was 66%, mammogram use 50%, breast examination by a doctor or nurse 38% and breast self-examination 37%. Genetic influences were behaviour-specific; there was no evidence for a common genetic influence on the four behaviours. Potential covariates investigated included age, amount of contact between co-twins, educational level and personality traits such as harm avoidance, novelty seeking, reward dependence, neuroticism, anxiety, depression, self-esteem, perceived control, interpersonal dependency and ways of coping. None were significant. The study was carried out before the implementation of national screening programmes with media campaigns to increase participation rates. Hence follow-up investigation, including data on regularity of behaviours, would be informative

Heritability and Stability of Resting Blood Pressure in Australian Twins

In Australian twins participating in three different studies (1979–1996), the contribution of genetic and environmental influences to variation in resting systolic (SBP) and diastolic blood pressure (DBP) was studied. The sample consisted of 368 monozygotic and 335 dizygotic twin pairs with measurements for both individuals. Blood pressure measurements in two studies were available for 115 complete twin pairs, and 49 twin pairs had measurements in three studies. This allowed assessment of blood pressure tracking over an average period of 12 years in the age range of 23 to 45 years. Multivariate analyses showed significant heritability (h2) of blood pressure in all studies (SBP h2= 19%–56%, DBP h2= 37%–52%). In addition, the analyses showed that the blood pressure tracking was explained by the same set of genetic factors. These results replicate an earlier finding in Dutch twins that also showed stability of the contribution of genetic factors to blood pressure tracking.

Age at First Sexual Intercourse and Teenage Pregnancy in Australian Female Twins

Girls who report first sexual intercourse during their early teen years have much higher rates of teenage pregnancy and childbearing than girls who delay sexual onset until older adolescence. In this study, we examine genetic and environmental influences on variation in teenage pregnancy and covariation with age at first sexual intercourse in two cohorts of Australian female twins. In the older twin cohort, born 1893–1964, we observe substantial heritable variation in teenage pregnancy that is largely shared with heritable variation in age at first sexual intercourse, with shared environment contributintablg little to variation in teenage pregnancy. Genetic influences on teenage pregnancy are smaller and nonsignificant in the younger twin cohort, born 1964–1971, where shared environment contributes much more and overlaps entirely with shared environmental variation in age at first intercourse.

Sex-Limited Genome-Wide Linkage Scan for Body Mass Index in an Unselected Sample of 933 Australian Twin Families

Genes involved in pathways regulating body weight may operate differently in men and women. To determine whether sex-limited genes influence the obesity-related phenotype body mass index (BMI), we have conducted a general non- scalar sex-limited genome-wide linkage scan using variance components analysis in Mx (Neale, 2002). BMI measurements and genotypic data were available for 2053 Australian female and male adult twins and their siblings from 933 families. Clinical measures of BMI were available for 64.4% of these individuals, while only self-reported measures were available for the remaining participants. The mean age of participants was 39.0 years of age (SD 12.1 years). The use of a sex-limited linkage model identified areas on the genome where quantitative trait loci (QTL) effects differ between the sexes, particularly on chromosome 8 and 20, providing us with evidence that some of the genes responsible for BMI may have different effects in men and women. Our highest linkage peak was observed at 12q24 (–log10p = 3.02), which was near the recommended threshold for suggestive linkage (–log10p = 3.13). Previous studies have found evidence for a quantitative trait locus on 12q24 affecting BMI in a wide range of populations, and candidate genes for non- insulin-dependent diabetes mellitus, a consequence of obesity, have also been mapped to this region. We also identified many peaks near a –log10p of 2 (threshold for replicating an existing finding) in many areas across the genome that are within regions previously identified by other studies, as well as in locations that harbor genes known to influence weight regulation.

An Integrative Approach for Studying the Etiology of Alcoholism and Other Addictions

Studies of alcoholism etiology often focus on genetic or psy-chosocial approaches, but not both. Greater understanding of the etiology of alcohol, tobacco and other addictions will come from integration of these research traditions. A research approach is outlined to test three models for the etiology of addictions — behavioral undercontrol, pharmacologic vulnerability, negative affect regulation — addressing key questions including (i) mediators of genetic effects, (ii) genotype-environment correlation effects, (iii) genotype x environment interaction effects, (iv) the developmental unfolding of genetic and environmental effects, (v) subtyping including identification of distinct trajectories of substance involvement, (vi) identification of individual genes that contribute to risk, and (vii) the consequences of excessive use. By using coordinated research designs, including prospective assessment of adolescent twins and their siblings and parents; of adult substance dependent and control twins and their MZ and DZ cotwins, the spouses of these pairs, and their adolescent offspring; and of regular families; by selecting for gene-mapping approaches sibships screened for extreme concordance or discordance on quantitative indices of substance use; and by using experimental (drug challenge) as well as survey approaches, a number of key questions concerning addiction etiology can be addressed. We discuss complementary strengths and weaknesses of different sampling strategies, as well as methods to implement such an integrated approach illustrated for the study of alcoholism etiology. A coordinated program of twin and family studies will allow a comprehensive dissection of the interplay of genetic and environmental risk-factors in the etiology of alcoholism and other addictions.

Paternal Alcoholism and Offspring Conduct Disorder: Evidence for the ‘Common Genes’ Hypothesis

Not only are alcoholism and externalizing disorders frequently comorbid, they often co-occur in families across generations; for example, paternal alcoholism predicts offspring conduct disorder just as it does offspring alcoholism. To clarify this relationship, the current study examined the ‘common genes’ hypothesis utilizing a children-of-twins research design. Participants were male monozygotic (MZ) and dizygotic (DZ) twins from the Vietnam Era Twin Registry who were concordant or discordant for alcohol dependence together with their offspring and the mothers of those offspring. All participants were conducted through a structured psychiatric interview. Offspring risk of conduct disorder was examined as a function of alcoholism genetic risk (due to paternal and co-twin alcohol dependence) and alcoholism environmental risk (due to being reared by a father with an alcohol dependence diagnosis). After controlling for potentially confounding variables, the offspring of alcohol- dependent fathers were significantly more likely to exhibit conduct disorder diagnoses than were off- spring of nonalcohol-dependent fathers, thus indicating diagnostic crossover in generational family transmission. Comparing offspring at high genetic and high environmental risk with offspring at high genetic and low environmental risk indicated that genetic factors were most likely responsible for the alcoholism–conduct disorder association. The observed diagnostic crossover (from paternal alcoholism to offspring conduct disorder) across generations in the context of both high and low environmental risk (while genetic risk remained high) supported the common genes hypothesis.

Gene–Environment Interaction Effects on Behavioral Variation and Risk of Complex Disorders: The Example of Alcoholism and Other Psychiatric Disorders

There have been few replicated examples of genotype x environment interaction effects on behavioral variation or risk of psychiatric disorder. We review some of the factors that have made detection of genotype x environment interaction effects difficult, and show how genotype x shared environment interaction (GxSE) effects are commonly confounded with genetic parameters in data from twin pairs reared together. Historic data on twin pairs reared apart can in principle be used to estimate such GxSE effects, but have rarely been used for this purpose. We illustrate this using previously published data from the Swedish Adoption Twin Study of Aging (SATSA), which suggest that GxSE effects could account for as much as 25% of the total variance in risk of becoming a regular smoker. Since few separated twin pairs will be available for study in the future, we also consider methods for modifying variance components linkage analysis to allow for environmental interactions with linked loci.

Longitudinal Genetic Analysis of Plasma Lipids

The consensus from published studies is that plasma lipids are each influenced by genetic factors, and that this contributes to genetic variation in risk of cardiovascular disease. Heritability estimates for lipids and lipoproteins are in the range .48 to .87, when measured once per study participant. However, this ignores the confounding effects of biological variation measurement error and ageing, and a truer assessment of genetic effects on cardiovascular risk may be obtained from analysis of longitudinal twin or family data. We have analyzed information on plasma high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides, from 415 adult twins who provided blood on two to five occasions over 10 to 17 years. Multivariate modeling of genetic and environmental contributions to variation within and across occasions was used to assess the extent to which genetic and environmental factors have long-term effects on plasma lipids. Results indicated that more than one genetic factor influenced HDL and LDL components of cholesterol, and triglycerides over time in all studies. Nonshared environmental factors did not have significant long-term effects except for HDL. We conclude that when heritability of lipid risk factors is estimated on only one occasion, the existence of biological variation and measurement errors leads to underestimation of the importance of genetic factors as a cause of variation in long-term risk within the population. In addition our data suggest that different genes may affect the risk profile at different ages.

Height Discordance in Monozygotic Females is not Attributable to Discordant Inactivation of X-linked Stature Determining Genes

We tested the hypothesis that X-linked genes determining stature which are subject to skewed or non-random X-inactivation can account for discordance in height in monozygotic female twins. Height discordant female monozygotic adult twins (20 pairs) were identified from the Australian Twin Registry, employing the selection criteria of proven monozygosity and a measured height discordance of at least 5 cm. Differential X-inactivation was examined in genomic DNA extracted from peripheral lymphocytes by estimating differential methylation of alleles at the polymorphic CAG triplet repeat of the Androgen receptor gene (XAR). There were 17/20 MZ pairs heterozygous at this locus and informative for analysis. Of these, 10/17 both had random X-inactivation, 5/17 showed identical X-inactivation patterns of non random inactivation and 2/17 (12%) showed discordant X-inactivation. There was no relationship between inactivation patterns and self-report chorionicity. We conclude that non-random X-inactivation does not appear to be a major contributor to intra-pair height discordance in female MZ twins.

Choice of Residential Location: Chance, Family Influences, or Genes?

The choice of where to live would appear to be determined by a combination of economic constraints and personal preferences. We have tested how far this choice is affected by the continuing effects of the environment shared within families, and genetic variation between people, using data from twin studies conducted in Australia. The addresses provided by study participants were categorized as urban, suburban and nonurban, and data were analyzed in three adult age groups. There were significant effects of both shared environment and genes, and the balance between them was affected by both sex and age. Shared environment accounted for some 50% of variation in the youngest group, but only about 10% in the oldest. As shared environmental effects decreased, additive genetic effects increased. These results have implications for internal migration of people within countries and, over the long term, for gene flow within and between populations. They may also be pertinent to the different prevalences of certain psychiatric diseases between city and country locations. Comparisons between countries with different demography are needed to confirm and further characterize these effects.

Heritabilities of Apolipoprotein and Lipid Levels in Three Countries

This study investigated the influence of genes and environment on the variation of apolipoprotein and lipid levels, which are important intermediate phenotypes in the pathways toward cardiovascular disease. Heritability estimates are presented, including those for apolipoprotein E and AII levels which have rarely been reported before. We studied twin samples from the Netherlands (two cohorts;n= 160 pairs, aged 13–22 andn= 204 pairs, aged 34–62), Australia (n= 1362 pairs, aged 28–92) and Sweden (n= 302 pairs, aged 42–88). The variation of apolipoprotein and lipid levels depended largely on the influences of additive genetic factors in each twin sample. There was no significant evidence for the influence of common environment. No sex differences in heritability estimates for any phenotype in any of the samples were observed. Heritabilities ranged from 0.48–0.87, with most heritabilities exceeding 0.60. The heritability estimates in the Dutch samples were significantly higher than in the Australian sample. The heritabilities for the Swedish were intermediate to the Dutch and the Australian samples and not significantly different from the heritabilities in these other two samples. Although sample specific effects are present, we have shown that genes play a major role in determining the variance of apolipoprotein and lipid levels in four independent twin samples from three different countries.

Familial influence and childhood trauma in female alcoholism

BACKGROUND

To assess the role of genetic and environmental factors in female alcoholism using a large population-based twin sample, taking into account possible differences between early and late onset disease subtype.

METHOD

Twins aged 20-47 years from the Swedish Twin Registry (n=24 119) answered questions to establish lifetime alcohol use disorders. Subjects with alcoholism were classified for subtype. Structural equation modeling was used to quantify the proportion of phenotypic variance due to genetic and environmental factors and test whether heritability in women differed from that in men. The association between childhood trauma and alcoholism was then examined in females, controlling for background familial factors.

RESULTS

Lifetime prevalence of alcohol dependence was 4.9% in women and 8.6% in men. Overall, heritability for alcohol dependence was 55%, and did not differ significantly between men and women, although women had a significantly greater heritability for late onset (type I). Childhood physical trauma and sexual abuse had a stronger association with early onset compared to late onset alcoholism [odds ratio (OR) 2.54, 95% confidence interval (CI) 1.53-3.88 and OR 2.29, 95% CI 1.38-3.79 respectively]. Co-twin analysis indicated that familial factors largely accounted for the influence of physical trauma whereas the association with childhood sexual abuse reflected both familial and specific effects.

CONCLUSIONS

Heritability of alcoholism in women is similar to that in men. Early onset alcoholism is strongly association with childhood trauma, which seems to be both a marker of familial background factors and a specific individual risk factor per se.

Levels of explanation in psychiatric and substance use disorders: implications for the development of an etiologically based nosology

The soft medical model for psychiatric illness, which was operationalized in DSM-III, defines psychiatric disorders as syndromes with shared symptoms, signs, course of illness and response to treatment. Many in our field want to move to a hard medical model based on etiological mechanisms. This essay explores the feasibility of this move and asks whether psychiatric disorders have the needed single clear level of explanation for an etiologically based nosology. I propose seven criteria for a good explanation: (i) strength, (ii) causal confidence, (iii) generalizability, (iv) specificity, (v) manipulability, (vi) proximity and (vii) generativity. Applying them to cystic fibrosis, a gene-level approach to etiology performs well across the board. By contrast, a detailed review of alcohol dependence and a briefer review of major depression suggests that psychiatric disorders have multiple explanatory perspectives no one of which can be privileged over others using scientific data alone. Therefore, a move toward an etiologically based diagnostic system cannot assume that one level of explanation will stand out as the obvious candidate on which to base the nosology. This leaves two options. Either a hard medical model will be implemented that will require a consensus about a preferred level of explanation which must reflect value judgments as well as science. To take this approach, we need to agree on what we most want from our explanations. Alternatively, we will need to move away from the traditional hard medical model that requires that we ground our diagnoses in single biological essences, and focus instead on fuzzy, cross-level mechanisms, which may more realistically capture the true nature of psychiatric disorders.

Heritability of problem drinking and the genetic overlap with personality in a general population sample

This study examined the heritability of problem drinking and investigated the phenotypic and genetic relationships between problem drinking and personality. In a sample of 5,870 twins and siblings and 4,420 additional family members from the Netherlands Twin Register. Data on problem drinking (assessed with the AUDIT and CAGE; 12 items) and personality [NEO Five-Factor Inventory (FFI); 60 items] were collected in 2009/2010 by surveys. Confirmatory factor analysis on the AUDIT and CAGE items showed that the items clustered on two separate but highly correlated (r = 0.74) underlying factors. A higher-order factor was extracted that reflected those aspects of problem drinking that are common to the AUDIT and CAGE, which showed a heritability of 40%. The correlations between problem drinking and the five dimensions of personality were small but significant, ranging from 0.06 for Extraversion to −0.12 for Conscientiousness. All personality dimensions (with broad-sense heritabilities between 32 and 55%, and some evidence for non-additive genetic influences) were genetically correlated with problem drinking. The genetic correlations were small to modest (between |0.12| and |0.41|). Future studies with longitudinal data and DNA polymorphisms are needed to determine the biological mechanisms that underlie the genetic link between problem drinking and personality.

School performance and alcohol use problems in early adulthood: a longitudinal study

There is inconsistent evidence about the association between school performance and subsequent use of alcohol and alcohol problems in adolescents and young adults. This study examines whether school performance at 14 years is associated with drinking problems in early adulthood; and whether this association is explained by family and individual factors in childhood and adolescence. Data were from a 21-year follow-up of 3,478 Australian young adults from birth to the age of 21 years when data on use of alcohol were collected. Child school performance (CSP) was assessed at 14 years via self- and maternal report. Alcohol consumption at 21 years was measured via self-report, and alcohol abuse and dependence were assessed by the computerized version of Composite International Diagnostic Interview (CIDI-Auto). Potential confounding factors were prospectively measured between the child's birth and age of 14 years. School performance at 14 years predicted young adults' alcohol consumption and alcohol use disorders (AUDs). After controlling for confounding, children who had lower school performance had increased risk of drinking more than two glasses of alcohol per day in early adulthood (odds ratio=1.7; 95% confidence interval: 1.1-2.6). There was a similar pattern of association between CSP and young adults' alcohol abuse and dependence (AUD) measured by CIDI-Auto. Level of academic performance in high school children predicts their drinking problems as young adults, independently of a selected group of individual and family confounders. Exploration of the pathway linking school performance and alcohol problems in young people may help identify opportunities for preventive interventions.

A meta-analysis of two genome-wide association studies identifies 3 new loci for alcohol dependence

Family, twin and adoption studies have clearly demonstrated that genetic factors are important in modulating the vulnerability to alcohol dependence. Several genome-wide association (GWA) studies of alcohol dependence have been conducted; however, few loci have been replicated. A meta-analysis was performed on two GWA studies of 1283 cases of alcohol dependence and 1416 controls in Caucasian populations. Through meta-analysis we identified 131 SNPs associated with alcohol dependence with p<10(-4). The best novel signal was rs6701037 (p=1.86 × 10(-7)) at 1q24-q25 within KIAA0040 gene while the second best novel hit was rs1869324 (p=4.71 × 10(-7)) at 2q22.1 within THSD7B. The third novel locus was NRD1 at 1p32.2 (the top SNP was rs2842576 with p=7.90 × 10(-6)). We confirmed the association of PKNOX2 at 11q24.4 with alcohol dependence. The top hit of PKNOX2 (rs750338 with p=1.47 × 10(-6)) in the meta-analysis was replicated with the Australian Twin-Family Study of 778 families (p=1.39 × 10(-2)) Furthermore, several flanking SNPs of the top hits in the meta-analysis demonstrated borderline associations with alcohol dependence in the family sample (top SNPs were rs2269655, rs856613, and rs10496768 with p=4.58 × 10(-3), 2.1 × 10(-4), and 2.86 × 10(-3) for KIAA0040, NRD1 and THSD7B, respectively). In addition, ALK, CASC4, and SEMA5A were strongly associated with alcohol dependence (p<2 × 10(-5)) in the meta-analysis. In conclusion, we identified three new loci (KIAA0040, THSD7B and NRD1) and confirmed the previous association of PKNOX2 with alcohol dependence. These findings offer the potential for new insights into the pathogenesis of alcohol dependence.

Race/ethnicity and sex differences in progression from drinking initiation to the development of alcohol dependence

BACKGROUND

Prior studies on the course of alcohol use disorders have reported a "telescoping" effect with women progressing from drinking initiation to alcohol dependence faster than men. However, there is a paucity of population-based analyses that have examined progression to alcohol dependence comparing race/ethnicity subgroups, and little is known about whether the telescoping effect for women varies by race/ethnicity. We examined whether a telescoping effect is present in the general population comparing race/ethnicity subgroups and comparing men and women stratified by race.

METHODS

This study uses data from Wave I of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) to compare a nationally representative sample of White, Black and Hispanic adults 18-44 years of age (n=21,106). Time to event analyses compare the risk of alcohol initiation, onset of alcohol dependence, and the transition from initial use to onset of alcohol dependence in the three race/ethnicity groups and for males and females in each race/ethnicity group.

RESULTS

Whites were younger than Blacks and Hispanics of the same sex at drinking onset and progressed to alcohol dependence at a faster rate than both Blacks and Hispanics. In addition, we found no evidence of a telescoping effect in women for any race/ethnicity group.

CONCLUSIONS

The present study illustrates differences in the course of transition from alcohol initiation to the development of dependence by race/ethnicity but not sex. Our findings highlight the need for additional study of factors resulting in race/ethnicity differences in order to inform culturally relevant prevention and intervention initiatives.

Genome-wide association study identifies loci influencing concentrations of liver enzymes in plasma

Concentrations of liver enzymes in plasma are widely used as indicators of liver disease. We carried out a genome-wide association study in 61,089 individuals, identifying 42 loci associated with concentrations of liver enzymes in plasma, of which 32 are new associations (P = 10(-8) to P = 10(-190)). We used functional genomic approaches including metabonomic profiling and gene expression analyses to identify probable candidate genes at these regions. We identified 69 candidate genes, including genes involved in biliary transport (ATP8B1 and ABCB11), glucose, carbohydrate and lipid metabolism (FADS1, FADS2, GCKR, JMJD1C, HNF1A, MLXIPL, PNPLA3, PPP1R3B, SLC2A2 and TRIB1), glycoprotein biosynthesis and cell surface glycobiology (ABO, ASGR1, FUT2, GPLD1 and ST3GAL4), inflammation and immunity (CD276, CDH6, GCKR, HNF1A, HPR, ITGA1, RORA and STAT4) and glutathione metabolism (GSTT1, GSTT2 and GGT), as well as several genes of uncertain or unknown function (including ABHD12, EFHD1, EFNA1, EPHA2, MICAL3 and ZNF827). Our results provide new insight into genetic mechanisms and pathways influencing markers of liver function.

Birth cohort effects and gender differences in alcohol epidemiology: a review and synthesis

BACKGROUND

Alcohol consumption has demonstrated substantial temporal trends, with some evidence suggesting strong birth cohort effects. The identification of at-risk birth cohorts can inform the interpretation of alcohol trends across age, time, and demographic characteristics such as gender. The present literature review has 2 objectives. First, we conduct a cross-national review of the literature on birth cohort differences in alcohol consumption, disorder, and mortality. Second, we determine the consistency of evidence for birth cohort effects on gender differences.

METHODS

A search was conducted and key data on population characteristics, presence and direction of cohort effects, and interactions with gender compiled. Thirty-one articles were included.

RESULTS

Evidence suggests that younger birth cohorts in North America, especially those born after World War II, are more likely than older cohorts to engage in heavy episodic drinking and develop alcohol disorders, but this cohort effect is not found in Australia and western Europe. Cross-nationally, substantial evidence indicates that women in younger cohorts are at especially high risk for heavy episodic drinking and alcohol disorders.

DISCUSSION

Younger birth cohorts in North America and Europe are engaging in more episodic and problem drinking. The gender gap in alcohol problems is narrowing in many countries, suggesting shifting social norms surrounding gender and alcohol consumption. These trends suggest that public health efforts to specifically target heavy drinking in women are necessary.

A quantitative-trait genome-wide association study of alcoholism risk in the community: findings and implications

BACKGROUND

Given moderately strong genetic contributions to variation in alcoholism and heaviness of drinking (50% to 60% heritability) with high correlation of genetic influences, we have conducted a quantitative trait genome-wide association study (GWAS) for phenotypes related to alcohol use and dependence.

METHODS

Diagnostic interview and blood/buccal samples were obtained from sibships ascertained through the Australian Twin Registry. Genome-wide single nucleotide polymorphism (SNP) genotyping was performed with 8754 individuals (2062 alcohol-dependent cases) selected for informativeness for alcohol use disorder and associated quantitative traits. Family-based association tests were performed for alcohol dependence, dependence factor score, and heaviness of drinking factor score, with confirmatory case-population control comparisons using an unassessed population control series of 3393 Australians with genome-wide SNP data.

RESULTS

No findings reached genome-wide significance (p = 8.4 × 10(-8) for this study), with lowest p value for primary phenotypes of 1.2 × 10(-7). Convergent findings for quantitative consumption and diagnostic and quantitative dependence measures suggest possible roles for a transmembrane protein gene (TMEM108) and for ANKS1A. The major finding, however, was small effect sizes estimated for individual SNPs, suggesting that hundreds of genetic variants make modest contributions (1/4% of variance or less) to alcohol dependence risk.

CONCLUSIONS

We conclude that 1) meta-analyses of consumption data may contribute usefully to gene discovery; 2) translation of human alcoholism GWAS results to drug discovery or clinically useful prediction of risk will be challenging; and 3) through accumulation across studies, GWAS data may become valuable for improved genetic risk differentiation in research in biological psychiatry (e.g., prospective high-risk or resilience studies).

Stable genetic effects on symptoms of alcohol abuse and dependence from adolescence into early adulthood

Relatively little is known about how genetic influences on alcohol abuse and dependence (AAD) change with age. We examined the change in influence of genetic and environmental factors which explain symptoms of AAD from adolescence into early adulthood. Symptoms of AAD were assessed using the four AAD screening questions of the CAGE inventory. Data were obtained up to six times by self-report questionnaires for 8,398 twins from the Netherlands Twin Register aged between 15 and 32 years. Longitudinal genetic simplex modeling was performed with Mx. Results showed that shared environmental influences were present for age 15-17 (57%) and age 18-20 (18%). Unique environmental influences gained importance over time, contributing 15% of the variance at age 15-17 and 48% at age 30-32. At younger ages, unique environmental influences were largely age-specific, while at later ages, age-specific influences became less important. Genetic influences on AAD symptoms over age could be accounted for by one factor, with the relative influence of this factor differing across ages. Genetic influences increased from 28% at age 15-17 to 58% at age 21-23 and remained high in magnitude thereafter. These results are in line with a developmentally stable hypothesis that predicts that a single set of genetic risk factors acts on symptoms of AAD from adolescence into young adulthood.

Common genetic and environmental contributions to post-traumatic stress disorder and alcohol dependence in young women

BACKGROUND

The few genetically informative studies to examine post-traumatic stress disorder (PTSD) and alcohol dependence (AD), all of which are based on a male veteran sample, suggest that the co-morbidity between PTSD and AD may be attributable in part to overlapping genetic influences, but this issue has yet to be addressed in females.MethodData were derived from an all-female twin sample (n=3768) ranging in age from 18 to 29 years. A trivariate genetic model that included trauma exposure as a separate phenotype was fitted to estimate genetic and environmental contributions to PTSD and the degree to which they overlap with those that contribute to AD, after accounting for potential confounding effects of heritable influences on trauma exposure.

RESULTS

Additive genetic influences (A) accounted for 72% of the variance in PTSD; individual-specific environmental (E) factors accounted for the remainder. An AE model also provided the best fit for AD, for which heritability was estimated to be 71%. The genetic correlation between PTSD and AD was 0.54.

CONCLUSIONS

The heritability estimate for PTSD in our sample is higher than estimates reported in earlier studies based almost exclusively on an all-male sample in which combat exposure was the precipitating traumatic event. However, our findings are consistent with the absence of evidence for shared environmental influences on PTSD and, most importantly, the substantial overlap in genetic influences on PTSD and AD reported in these investigations. Additional research addressing potential distinctions by gender in the relative contributions of genetic and environmental influences on PTSD is merited.

Parental depression and offspring psychopathology: a children of twins study

BACKGROUND

Associations between parental depression and offspring affective and disruptive disorders are well documented. Few genetically informed studies have explored the processes underlying intergenerational associations.

METHOD

A semi-structured interview assessing DSM-III-R psychiatric disorders was administered to twins (n=1296) from the Australian Twin Register (ATR), their spouses (n=1046) and offspring (n=2555). We used the Children of Twins (CoT) design to delineate the extent to which intergenerational associations were consistent with a causal influence or due to genetic confounds.

RESULTS

In between-family analyses, parental depression was associated significantly with offspring depression [hazard ratio (HR) 1.52, 95% confidence interval (CI) 1.20-1.93] and conduct disorder (CD; HR 2.27, CI 1.31-3.93). Survival analysis indicated that the intergenerational transmission of depression is consistent with a causal (environmental) inference, with a significant intergenerational association in offspring of discordant monozygotic (MZ) twin pairs (HR 1.39, CI 1.00-1.94). Logistic regression analysis suggested that the parental depression-offspring CD association was due to shared genetic liability in the parents and offspring. No intergenerational association was found when comparing the offspring of discordant MZ twins [odds ratio (OR) 1.41, CI 0.63-3.14], but offspring of discordant dizygotic (DZ) twins differed in their rates of CD (OR 2.53, CI 0.95-6.76). All findings remained after controlling for several measured covariates, including history of depression and CD in the twins' spouses.

CONCLUSIONS

The mechanisms underlying associations between parental depression and offspring psychopathology seem to differ depending on the outcome. The results are consistent with a causal environmental role of parental depression in offspring depression whereas common genetic factors account for the association of parental depression and offspring CD.