Models of treatment seeking for alcoholism: the role of genes and environment

Case-only exome variation analysis of severe alcohol dependence using a multivariate hierarchical gene clustering approach

BACKGROUND

Variation in genes involved in ethanol metabolism has been shown to influence risk for alcohol dependence (AD) including protective loss of function alleles in ethanol metabolizing genes. We therefore hypothesized that people with severe AD would exhibit different patterns of rare functional variation in genes with strong prior evidence for influencing ethanol metabolism and response when compared to genes not meeting these criteria.

OBJECTIVE

Leverage a novel case only design and Whole Exome Sequencing (WES) of severe AD cases from the island of Ireland to quantify differences in functional variation between genes associated with ethanol metabolism and/or response and their matched control genes.

METHODS

First, three sets of ethanol related genes were identified including those a) involved in alcohol metabolism in humans b) showing altered expression in mouse brain after alcohol exposure, and altering ethanol behavioral responses in invertebrate models. These genes of interest (GOI) sets were matched to control gene sets using multivariate hierarchical clustering of gene-level summary features from gnomAD. Using WES data from 190 individuals with severe AD, GOI were compared to matched control genes using logistic regression to detect aggregate differences in abundance of loss of function, missense, and synonymous variants, respectively.

RESULTS

Three non-independent sets of 10, 117, and 359 genes were queried against control gene sets of 139, 1522, and 3360 matched genes, respectively. Significant differences were not detected in the number of functional variants in the primary set of ethanol-metabolizing genes. In both the mouse expression and invertebrate sets, we observed an increased number of synonymous variants in GOI over matched control genes. Post-hoc simulations showed the estimated effects sizes observed are unlikely to be under-estimated.

CONCLUSION

The proposed method demonstrates a computationally viable and statistically appropriate approach for genetic analysis of case-only data for hypothesized gene sets supported by empirical evidence.

Dietary yeast influences ethanol sedation in Drosophila via serotonergic neuron function

Abuse of alcohol is a major clinical problem with far-reaching health consequences. Understanding the environmental and genetic factors that contribute to alcohol-related behaviors is a potential gateway for developing novel therapeutic approaches for patients that abuse the drug. To this end, we have used Drosophila melanogaster as a model to investigate the effect of diet, an environmental factor, on ethanol sedation. Providing flies with diets high in yeast, a routinely used component of fly media, increased their resistance to ethanol sedation. The yeast-induced resistance to ethanol sedation occurred in several different genetic backgrounds, was observed in males and females, was elicited by yeast from different sources, was readily reversible, and was associated with increased nutrient intake as well as decreased internal ethanol levels. Inhibition of serotonergic neuron function using multiple independent genetic manipulations blocked the effect of yeast supplementation on ethanol sedation, nutrient intake, and internal ethanol levels. Our results demonstrate that yeast is a critical dietary component that influences ethanol sedation in flies and that serotonergic signaling is required for the effect of dietary yeast on nutrient intake, ethanol uptake/elimination, and ethanol sedation. Our studies establish the fly as a model for diet-induced changes in ethanol sedation and raise the possibility that serotonin might mediate the effect of diet on alcohol-related behavior in other species.

Characterization of Service Use for Alcohol Problems Across Generations and Sex in Adults With Alcohol Use Disorder

BACKGROUND

There are gaps in the literature on service use (help-seeking and treatment utilization) for alcohol problems among those with alcohol use disorder (AUD). First, policy changes and cultural shifts (e.g., insurance) related to AUD have occurred over the last few decades, making it important to study generational differences. Second, multiple studies have found that females receive fewer services than males, and exploring whether these sex differences persist across generations can inform public health and research endeavors. The current study examined service use for alcohol problems among individuals with AUD. The aims were as follows: (i) to describe service use for alcohol problems; (ii) to assess generational differences (silent [b. 1928 to 1945], boomer [b. 1946 to 1964], generation X [b. 1965 to 1980], millennial [b. 1981 to 1996]) in help-seeking and treatment utilization; and (iii) to examine sex differences across generations.

METHODS

Data were from affected family members of probands who participated in the Collaborative Study on the Genetics of Alcoholism (N = 4,405). First, frequencies for service use variables were calculated across generations. Pearson chi-square and ANOVA were used to test for differences in rates and types of service use across generations, taking familial clustering into account. Next, Cox survival modeling was used to assess associations of generation and sex with time to first help-seeking and first treatment for AUD, and time from first onset of AUD to first help-seeking and first treatment. Interactions between generation and sex were tested within each Cox regression.

RESULTS

Significant hazards were found in all 4 transitions. Overall, younger generations used services earlier than older generations, which translated into higher likelihoods of these behaviors. Regardless of generation, younger females were less likely to use services than males.

CONCLUSIONS

There are generational and sex differences in service use for alcohol problems among individuals with AUD. Policy and clinical implications are discussed.

Familial association of abstinent remission from alcohol use disorder in first-degree relatives of alcohol-dependent treatment-seeking probands

BACKGROUND AND AIMS

Studies that have included family history of alcohol use disorder (AUD) as a predictor of remission from AUD have yielded few significant results. The goals of this study were to estimate the association of persistent AUD, non-abstinent remission and abstinent remission ('AUD/remission status') in a proband with AUD/remission status in a relative and to test whether this association differed in related and unrelated proband-relative pairs.

DESIGN

High-risk family study of alcohol dependence. Probands were recruited from treatment settings and relatives were invited to participate. Baseline assessments occurred between 1991 and 1998 with follow-up between 1996 and 2005. Half of probands were matched with a biological 1st-degree relative with life-time AUD (related group) and half of probands were paired with an unrelated individual with life-time AUD (unrelated group).

SETTING

Brooklyn, New York; Indianapolis, Indiana; Iowa City, Iowa; San Diego, California; Farmington, Connecticut; and St Louis, Missouri, USA.

PARTICIPANTS

A total of 606 probands (25.7% female, mean age 37.7) with baseline and follow-up data and 606 of their 1st-degree relatives who had life-ime AUDs (45.8% female, mean age 36.2 years).

MEASUREMENTS

Persistent AUD, non-abstinent remission and abstinent remission were based on self-report interview data on most recent AUD symptoms and alcohol consumption. Dependent variable was relatives' AUD/remission status. Independent variable was probands' AUD/remission status.

FINDINGS

A total of 34.6% of probands and 20.6% of relatives were abstinent and 11.1% of probands and 22.8% of relatives were in non-abstinent remission. AUD/remission status was correlated significantly in related (r = 0.23, P = 0.0037) but not in unrelated pairs. A significant interaction of probands' abstinent remission with a variable representing related (versus unrelated, P = 0.003) pairs suggested a familial association for abstinent remission. In related pairs, individuals with an abstinent proband were more likely to be abstinent themselves than were individuals whose proband had persistent AUD [relative risk ratio = 3.27, 95% confidence interval (CI) = 1.56-6.85, P = 0.002]; this association was not significant in unrelated pairs.

CONCLUSIONS

The likelihood of abstinent remission among people with alcohol use disorder appears to be more than three times greater for individuals who are related to an abstinent proband versus those related to a proband with persistent alcohol use disorder.

A National Swedish Longitudinal Twin-Sibling Study of alcohol use disorders among males

AIMS

To examine whether genetic influences on the development of alcohol use disorders (AUD) among men during emerging adulthood through mid-adulthood are stable or dynamic.

DESIGN

A twin study modeling developmental changes in the genetic and environmental influences on AUD during three age periods (18-25, 26-33 and 33-41) as a Cholesky decomposition.

SETTING

Sweden.

PARTICIPANTS

Swedish male twin pairs (1532 monozygotic and 1940 dizygotic) and 66 033 full male sibling pairs born less than 2 years apart.

MEASUREMENTS

AUD was identified based on Swedish medical and legal registries.

FINDINGS

The best-fitting model included additive genetic and unique environmental factors, with no evidence for shared environmental factors. Although the total heritability was stable over time, there were two major genetic factors contributing to AUD risk, one beginning at ages 18-25 with a modest decline in importance over time [0.84; confidence interval (CI) = 0.83-0.88], and another of less impact beginning at ages 26-33 with a modest increase in importance by ages 33-41 (0.31; CI = 0.05-0.47).

CONCLUSIONS

The heritability of alcohol use disorders among Swedish men appears to be stable among three age periods: 18-25 years, 26-33 years, and 33-41 years. Two sets of genetic risk factors contribute to alcohol use disorders risk, with one originating during the ages 18-25 years and another coming online at 26-33 years, providing support for the developmentally dynamic hypothesis.

The genetics of alcohol dependence and alcohol-related liver disease

The susceptibility to developing alcohol dependence and significant alcohol-related liver injury is determined by a number of constitutional, environmental and genetic factors, although the nature and level of interplay between them remains unclear. The familiality and heritability of alcohol dependence is well-documented but, to date, no strong candidate genes conferring increased risk have emerged, although variants in alcohol dehydrogenase and acetaldehyde dehydrogenase have been shown to confer protection, predominantly in individuals of East Asian ancestry. Population contamination with confounders such as drug co-dependence and psychiatric and physical co-morbidity may explain the essentially negative genome-wide association studies in this disorder. The familiality and hereditability of alcohol-related cirrhosis is not as well-documented but three strong candidate genes PNPLA3, TM6SF2 and MBOAT7, have been identified. The mechanisms by which variants in these genes confer risk and the nature of the functional interplay between them remains to be determined but, when elucidated, will undoubtedly increase our understanding of the pathophysiology of this disease. The way in which this genetic information could potentially inform patient management has yet to be determined and tested.

Alcohol problem recognition and help seeking in adolescents and young adults at varying genetic and environmental risk

INTRODUCTION

Alcohol use disorder symptoms frequently occur in adolescents and younger adults who seldom acknowledge a need for help. We identified sociodemographic, clinical, and familial predictors of alcohol problem recognition and help seeking in an offspring of twin sample.

METHOD

We analyzed longitudinal data from the Children of Alcoholics and Twins as Parents studies, which are combinable longitudinal data sources due to their equivalent design. We analyzed respondents (n=1073, 56.0% of the total sample) with alcohol use disorder symptoms at the baseline interview. Familial characteristics included perceptions of alcohol problems and help seeking for alcohol problems within the immediate family and a categorical variable indicating genetic and environmental risk. We used logistic regression to examine predictors of alcohol problem recognition and help seeking.

RESULTS

Approximately 25.9% recognized their alcohol problems and 26.7% sought help for drinking. In covariate-adjusted analyses, help seeking among family members predicted problem recognition, several clinical characteristics predicted both problem recognition and help seeking, and familial risk predicted help seeking. Alcohol problem recognition mediated the association between alcohol use disorder symptoms and incident help seeking.

CONCLUSIONS

Facilitating the self-recognition of alcohol use disorder symptoms, and perhaps the awareness of family members' help seeking for alcohol problems, may be potentially promising methods to facilitate help seeking.

Prevention, Use of Health Services, and Genes: Implications of Genetics for Policy Formation

We evaluate the hypothesis that genetic factors influence the use of health services and prevention behaviors in a national sample of adult twins in the United States. The analysis compares the correlation of these outcomes between identical twins, who share all their genes, to the correlation between nonidentical twins, who share, on average, only one-half of their genes. Because the environmental similarities of twins are assumed to be the same for identical and nonidentical twin pairs, researchers can partition the variance in behavioral outcomes that are due to genetic and environmental factors. Using established methods in this field, we find evidence of significant genetic influences on preferences toward prevention, overall prevention effort, routine checkups, and prescription drug use. Use of curative services does not appear to be influenced by genes. Our findings offer several implications for policymakers and researchers and suggest that genetics could be informative for health services and policy research.

The joint effects of ADH1B variants and childhood adversity on alcohol related phenotypes in African-American and European-American women and men

BACKGROUND

The ADH1B gene has consistently been implicated in problem drinking, but rarely incorporated into gene by environment investigations of alcohol phenotypes. This study examined the joint effects of variation in ADH1B and childhood adversity-a well-documented risk factor for alcohol problems and moderator of genetic liability to psychiatric outcomes-on maximum drinks consumed in a 24-hour period (maxdrinks) and alcohol use disorder (AUD) symptoms.

METHODS

Data were drawn from 2,617 African-American (AA) and 1,436 European-American (EA) participants (42% female) in a multisite genetic study of substance dependence. We tested the most significant ADH1B single nucleotide polymorphisms for alcohol dependence from a genomewide association study with this sample, ADH1B-rs1229984 (Arg48His) and ADH1B-rs2066702 (Arg370Cys), in EA and AA subsamples, respectively.

RESULTS

Ordinal regression analyses conducted separately by sex and population revealed significant main effects for childhood adversity for both alcohol phenotypes in AA women and men and for maxdrinks in EA women. A significant rs1229984 by childhood adversity interaction was observed for AUD symptoms in EA men. Unexposed His-allele carriers reported a mean of 3.6 AUD criteria, but adversity-exposed His-allele carriers endorsed approximately the same number (6.3) as those without the protective allele (6.3 and 7.0 for adversity-exposed and -unexposed groups, respectively).

CONCLUSIONS

Results suggest that under conditions of childhood adversity, the His allele does not exert its protective effects in EA men (OR = 0.57, CI: 0.32 to 1.01; p = 0.056). Findings highlight the robust risk effect conferred by childhood adversity and the importance of considering population and sex in genetically informative investigations of its association with alcohol outcomes.

Social contexts of remission from DSM-5 alcohol use disorder in a high-risk sample

BACKGROUND

Measures of social context, such as marriage and religious participation, are associated with remission from alcohol use disorders (AUDs) in population-based and treatment samples, but whether these associations hold among individuals at high familial risk for AUD is unknown. This study tests associations of measures of social context and treatment with different types of remission from DSM-5 AUD in a high-risk sample.

METHODS

Subjects were 686 relatives of probands (85.7% first-degree) who participated in a high-risk family study of alcohol dependence. All subjects met criteria for AUD at baseline and were re-interviewed 5 years later. Follow-up status was categorized as persistent AUD, high-risk drinking, remitted low-risk drinking, and abstinence. Social context measures were defined as stable or changing from baseline to follow-up, and their bivariate and multivariate associations with follow-up status were tested.

RESULTS

At follow-up, 62.8% of subjects had persistent AUD, 6.4% were high-risk drinkers, 22.2% were remitted low-risk drinkers, and 8.6% were abstinent. Birth of first child during the interval was the only measure of social context associated with remitted low-risk drinking and was significant for women only. Abstinent remission was characterized by being stably separated or divorced for women, new marriage for both sexes, experiencing low levels of family support and high levels of friend support, and receiving treatment. High-risk drinkers were more likely than individuals with persistent AUD to have a stable number of children and to have been recently unemployed.

CONCLUSIONS

The social contexts accompanying different types of remission in this high-risk sample resemble those found in population-based and clinical samples. Low-risk drinkers resemble natural remitters from population-based samples who change their drinking habits with life transitions. Abstainers resemble clinical samples in marital context, support from friends, and treatment. High-risk drinkers appear to continue to experience negative consequences of heavy drinking.

μ-Opioid receptor gene (OPRM1) polymorphism A118G: lack of association in Finnish populations with alcohol dependence or alcohol consumption

Aims: The molecular epidemiological studies on the association of the opioid receptor µ-1 (OPRM1) polymorphism A118G (Asn40Asp, rs1799971) and alcohol use disorders have given conflicting results. The aim of this study was to test the possible association of A118G polymorphism and alcohol use disorders and alcohol consumption in three large cohort-based study samples. Methods: The association between the OPRM1 A118G (Asn40Asp, rs1799971) polymorphism and alcohol use disorders and alcohol consumption was analyzed using three different population-based samples: (a) a Finnish cohort study, Health 2000, with 503 participants having a DSM-IV diagnosis for alcohol dependence and/or alcohol abuse and 506 age- and sex-matched controls; (b) a Finnish cohort study, FINRISK (n = 2360) and (c) the Helsinki Birth Cohort Study (n = 1384). The latter two populations lacked diagnosis-based phenotypes, but included detailed information on alcohol consumption. Results: We found no statistically significant differences in genotypic or allelic distribution between controls and subjects with alcohol dependence or abuse diagnoses. Likewise no significant effects were observed between the A118G genotype and alcohol consumption. Conclusion: These results suggest that A118G (Asn40Asp) polymorphism may not have a major effect on the development of alcohol use disorders at least in the Finnish population.

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.

Common genetic contributions to alcohol and cannabis use and dependence symptomatology

BACKGROUND

Despite mounting evidence that use of and dependence on alcohol and cannabis are influenced by heritable factors, the extent to which heritable influences on these phenotypes overlap across the 2 substances has only rarely been explored. In the current study, we quantified cross-substance overlap in sources of variance and estimated the degree to which within-substance associations between use and dependence measures are attributable to common genetic and environmental factors for alcohol and cannabis.

METHODS

The sample was comprised of 6,257 individuals (2,761 complete twin pairs and 735 singletons) from the Australian Twin Registry, aged 24 to 36 years. Alcohol and cannabis use histories were collected via telephone diagnostic interviews and used to derive an alcohol consumption factor, a frequency measure for cannabis use, and DSM-IV alcohol and cannabis dependence symptom counts. Standard genetic analyses were conducted to produce a quadrivariate model that provided estimates of overlap in genetic and environmental influences across the 4 phenotypes.

RESULTS

Over 60% of variance in alcohol consumption, cannabis use, and cannabis dependence symptoms, and just under 50% of variance in alcohol dependence (AD) symptoms were attributable to genetic sources. Shared environmental factors did not contribute significantly to the 4 phenotypes. Nearly complete overlap in heritable influences was observed for within-substance measures of use and dependence symptoms. Genetic correlations across substances were 0.68 and 0.62 for use and dependence symptoms, respectively.

CONCLUSIONS

Common heritable influences were evident for alcohol and cannabis use and for AD and cannabis dependence symptomatology, but findings indicate that substance-specific influences account for the majority of the genetic variance in the cannabis use and dependence phenotypes. By contrast, the substantial correlations between alcohol use and AD symptoms and between cannabis use and cannabis dependence symptoms suggest that measures of heaviness of use capture much of the same genetic liability to alcohol- and cannabis-related problems as dependence symptomatology.

Timing of first alcohol use and alcohol dependence: evidence of common genetic influences

AIMS

To estimate the magnitude of genetic and environmental influences on timing of first alcohol use and alcohol dependence (AD) and to quantify the overlap in these influences across the two alcohol-related outcomes.

PARTICIPANTS

The sample consisted of 5382 twins (2691 complete pairs), aged 24-36 years, from the Australian Twin Registry.

MEASUREMENTS

History of alcohol use and DSM-IV alcohol dependence were assessed by structured telephone interview.

FINDINGS

In both sexes, the relationship between age at first alcohol use and risk for AD followed a linear trend, such that the highest rates of AD were observed in individuals who began drinking at an earlier than average age (14 years or younger). Heritability estimates for timing of first alcohol use and AD were 36% and 53%, respectively. Shared environmental factors accounted for 15% of variance in initiation. There was no evidence of shared environmental influences on AD. The genetic correlation between timing of first alcohol use and AD was 0.59.

CONCLUSIONS

Findings highlight the substantial role of genetics in the development of AD and the early manifestation of that genetic risk in the timing of alcohol use initiation which, unlike AD, is also influenced to a modest degree by shared environmental factors. The considerable overlap in heritable influences-and the virtual absence of overlap in individual-specific environmental influences-on initiation of alcohol use and AD indicates that the association between age at first drink and AD is attributable in large part to common genetic sources of variance.

Alcohol consumption and health among elders

PURPOSE

This article estimates the effects of alcohol consumption on self-reported overall health status, injuries, heart problems, emergency room use, and hospitalizations among persons older than the age of 65.

DESIGN AND METHODS

We analyzed data from the first wave of the National Epidemiologic Survey on Alcohol and Related Conditions, a nationally representative study. We used multivariate regression and instrumental variables methods to study the associations between alcohol consumption (current drinking, binge drinking, and average number of drinks consumed) and several indicators of health status and health care utilization.

RESULTS

Alcohol consumption by women was associated with better self-perceived health status, improved cardiovascular health, and lower rates of hospitalizations. We detected no significant negative or positive associations for older men.

IMPLICATIONS

These findings suggest that light to moderate alcohol use by older women may have beneficial health effects. Experimental trials, however, are needed to more rigorously assess the potential benefits of alcohol use by elders due to the inherent biases of observational studies.

Disentangling the complex association between childhood sexual abuse and alcohol-related problems: a review of methodological issues and approaches

This review describes and evaluates methodological approaches aimed at unraveling the association between childhood sexual abuse (CSA) and later misuse of alcohol, which is complicated by the significant overlap between factors that elevate risk for CSA exposure and those that increase risk for problem alcohol use. We critique methods used to distinguish direct effects of CSA events on alcohol-related outcomes from the effects of risk factors frequently present in families in which CSA exposure occurs (e.g., parental alcohol-related problems). These methods include measurement and adjustment for potentially confounding factors and the use of co-twin designs. The findings across methodological approaches provide support for a CSA-specific risk for alcohol misuse, despite the significant contribution of family background factors to overall risk, but much work remains to be done before a comprehensive model for this association can be proposed. Additional directions for research, including the incorporation of measured genes and the use of longitudinal designs, are proposed to further efforts to model the pathways from CSA to alcohol-related problems.

Searching for an environmental effect of parental alcoholism on offspring alcohol use disorder: a genetically informed study of children of alcoholics

The children-of-twins design was used to isolate a potentially causal environmental impact of having an alcoholic parent on offspring alcohol use disorder, by an examination of whether the children of alcoholics were at a higher risk for alcohol use disorders than were the children of nonalcoholic parents, even after correlated familial factors were controlled. Participants were 1,224 male and female twins from 836 twin pairs selected from the Australian Twin Registry, 2,334 of the twins' 18-39-year-old offspring, and 983 spouses of the twins. Lifetime histories of Diagnostic and Statistical Manual of Mental Disorders (4th ed.) alcohol use disorders were obtained by structured, psychiatric, telephone interviews conducted individually with each of the family members. Comparisons of the offspring of twins who were discordant for alcoholism indicated that there was no longer a statistically significant difference between the children of alcoholics and the children of nonalcoholics after genetic and family environmental factors correlated with having an alcoholic parent were controlled. The results of this study suggest that the direct causal effect of being exposed to an alcoholic parent on offspring alcohol use disorder is modest at best.

Genetic and environmental influences on the rate of progression to alcohol dependence in young women

BACKGROUND

The development of alcohol dependence (AD) involves transitions through multiple stages of drinking behaviors and is shaped by both heritable and environmental influences. We attempted to capture this dynamic process by characterizing genetic and environmental contributions to the rate at which women progressed through 3 significant transitions along the pathway to AD: nonuse to initiation, initiation to onset of first alcohol-related problem, and first problem to onset of AD.

METHODS

The sample consisted of 3,546 female twins from the Missouri Adolescent Female Twin Study. Participants ranged in age from 18 to 29 years. Retrospective reports of alcohol use histories were collected by telephone diagnostic interview and transition times between drinking milestones were coded ordinally. Standard genetic analyses were conducted in Mx to derive a trivariate model that provided estimates of genetic and environmental influences that were common as well as specific to the 3 transition times.

RESULTS

Heritable influences were found for rate of progression across all 3 transitions, accounting for 30 to 47% of the variance in transition times. Shared environmental contributions were evident only in rate of progression from nonuse to initiation (i.e., age at first drink). Heritable contributions to the rate of movement through successive drinking milestones were attributable to a common factor, whereas environmental influences were transition-specific.

CONCLUSIONS

The current study is unique in its use of a genetically informative design to document the rate of movement between drinking milestones in a female sample and to examine genetic contributions to multiple transition times over the course of AD development. Results indicate that an earlier report of heritability for males in rate of progression from regular drinking to AD generalizes to women and to other alcohol stage transitions. Findings also suggest the need to consider stage-specific environmental contributions to alcohol outcomes in developing interventions.

Polymorphisms in the µ-opioid receptor gene (OPRM1) and the implications for alcohol dependence in humans

Twin and adoption studies have shown that alcohol dependence contains a substantial genetic component. In attempts to identify the genetic factors involved, association studies have linked the opioid system to alcohol dependence, with a main focus on the OPRM1 gene encoding the μ-opioid receptor. Our aim was to conduct a systematic review of the literature on the associations between polymorphisms in OPRM1 and alcohol dependence. We addressed findings of 12 studies that met our inclusion criteria. All studies employed a case–control design and included alcohol dependence as a dependent outcome measure. Our review showed that clinical studies do not unequivocally support an association between polymorphisms in OPRM1 and alcohol dependence. Factors that complicate genetic research on alcohol dependence, such as gene–environment interaction, and genetic and clinical heterogeneity, are discussed.

Twin Pair Resemblance for Psychiatric Hospitalization in the Swedish Twin Registry: A 32-year Follow-up Study of 29,602 Twin Pairs

BACKGROUND

Allgulander et al. (Allgulander C, Nowak J, Rice JP (1991) Acta Psychiatr Scand 83, 12) published twin pair analyses of psychiatric hospitalization for like-sex pairs from the Swedish Twin Registry born 1926-1958. As noted in a subsequent letter (Allgulander C, Nowak J, Rice JP (1992) Acta Psychiatr Scand 86, 421), several features of the original study resulted in under-ascertainment of cases and underestimated heritability, particularly for alcoholism. The present report updates the prior results by using 17 additional years of follow-up, including members of opposite-sex twin pairs, and addressing biases arising from cohort effects and from excluding pairs with unknown zygosity.

METHODS

Registry records for 29,602 twin pairs born 1926-1958 were matched against national databases of psychiatric and medical hospitalizations from 1972-2000 to obtain ICD diagnostic codes. Zygosity was known for 10,903 opposite-sex pairs and 15,401 like-sex pairs who participated previously in research. Twin-pair resemblance and genetic and environmental variance proportions were estimated for hospitalization for alcoholism, affective disorders, psychosis, and (in females) anxiety disorders.

RESULTS

Hospitalization rates during the ascertainment window were: alcoholism: males = 3.67%, females = 0.94%; affective disorders: males = 1.99%, females = 2.75%; anxiety disorders: males = 0.46%, females = 0.74%; and psychotic disorders: males = 1.70%, females = 1.96%. Twins from like-sex pairs with unknown zygosity had significantly higher prevalences than those with known zygosity. Tetrachoric correlations and heritability estimates were affected by the method used to model unknown zygosity and cohort effects.

CONCLUSIONS

Inclusion of additional follow-up information, opposite-sex twin pairs, age-adjustment, and use of current ICD definitions yielded higher heritability estimates for alcoholism, anxiety disorders, and psychosis than previously published for this nationally-representative sample of twins from Sweden. The results show that relatively small selection biases can alter twin study results and underscore the importance of addressing under-ascertainment of cases in genetic research based on volunteers.

Challenges in genetic studies of the etiology of substance use and substance use disorders: introduction to the special issue

Misuse of psychoactive substances is associated with substantial costs to users and to society. A growing literature suggests individual differences in vulnerability to develop substance related problems are influenced to a large degree by genetic factors. We review the evidence from genetic epidemiologic and molecular genetic studies of problematic use of alcohol, tobacco, and other drugs, then discuss the challenges for the next generation of studies of genetic influences on substance use. These challenges are addressed in the remaining papers of this special issue. The papers cover a variety of approaches, substances, and non-human as well as human studies, but are united by their focus on going beyond heritability estimates to address the mechanisms and processes underlying the development of substance use and substance related problems, including measurement, precursors of substance abuse, stages of substance involvement, and specificity of genetic influences.

Heritability of SF-36 Among Middle-Age, Middle-Class, Male???Male Twins

OBJECTIVE

We sought to examine the relative importance of genetic and environmental factors for the MOS SF-36; a widely used, valid, and reliable measure of health-related quality of life and to discuss incorporating genetic influences into health services research.

DATA SOURCES

Data are from a nationally distributed, nonclinical cohort of 2928 middle age, middle-class, male-male twin members of the Vietnam Era Twin Registry.

STUDY DESIGN

This was a secondary data analysis, classic twin heritability analysis.

DATA COLLECTION

A telephone survey was used to collect information on alcohol-related problems and health services use, including the SF-36.

PRINCIPAL FINDINGS

Variance component analyses indicated that additive genetic factors accounted for 17% to 33% of the variance for each of the 8 domains of the SF-36. Shared environment accounted for 0% to 12% of the variance for each domain, with the majority of variance for each domain accounted for by nonshared, or unique environment and error. Physical and mental health summary measures indicated that approximately one-third of the variance was accounted for by additive genetic factors and the remainder accounted for by nonshared environment and error. Clinical condition, history of alcohol dependence, had a small-but-significant influence for all domains. Including condition proved to be a better-fitting model. However, confidence intervals temper uniform statistical significance for genetic factors.

CONCLUSIONS

This study assessed the heritability of the SF-36 in a nonclinical, community sample of middle age, middle-class all-male twins. The moderate genetic effects on SF-36 domain and summary measures are new findings and thus may affect interpretations of SF-36 as a measure of health-related quality of life. Ideally, trait-based measures should identify genetic sources of variation and thus help understand any bias of the true effects of SF-36. Still the majority of variance is accounted for by nonshared or unique environmental factors and error. By extension, increased understanding of the importance of genetic and environmental factors that influence either predictors or outcomes of interest will expand the level of scientific debate in health services research and improve predictability.

Heritability of substance dependence in a native American population

OBJECTIVES

To estimate the heritability of substance dependence and associated symptoms in a sample of Southwest California (Mission) Indians.

METHODS

Families from eight contiguous Indian reservations were recruited in order to ascertain information on substance dependence symptoms and diagnoses using a semi-structured diagnostic interview. Dependence diagnoses for alcohol, marijuana, stimulants and a measure of regular tobacco usage, any drug dependence or tobacco usage were obtained. Composite measures of alcohol dependence symptoms for withdrawal, drinking severity, antisocial problems and interpersonal problems were constructed from the nine groups of symptoms summarized in the diagnostic interview. Heritability estimates were calculated using variance component methods, as implemented in SOLAR.

RESULTS

In this population, marijuana dependence (0.38) and regular tobacco use (0.43), alcohol dependence (DSM-III-R 0.19; ICD-10, 0.29) and stimulant dependence (0.25) showed evidence for moderate genetic influences as determined by heritability estimates. Four phenotypes constructed using the composite symptoms of alcohol dependence revealed that withdrawal had the highest heritability estimate (0.71), followed by antisocial problems (0.36) and drinking severity (0.34). Symptom clusters reflecting interpersonal problems did not appear to be highly heritable (0.19).

CONCLUSION

Marijuana dependence, regular tobacco usage and composite phenotypes constructed from alcohol dependence symptoms for antisocial problems, drinking severity and withdrawal generally have patterns of familial aggregation, suggesting that they can be successfully used for linkage analysis in this Southwest California Indian sample.

The Washington University Twin Study of alcoholism

Genetic contributions to the liability to develop alcoholism in males of Northern and Western European ancestry are well-established. However, questions remain concerning the role of genetic variation in the etiology of alcoholism among non-white populations, among women, and the possibility of etiological heterogeneity in subtypes of alcoholism. The answers to these questions are needed to help define phenotypes for molecular genetic studies searching for QTLs for alcoholism. Twins from 295 pairs were consecutively ascertained at inpatient and outpatient psychiatric and alcohol treatment facilities in St. Louis, MO in 1981-1986. Probands and willing cotwins were evaluated by structured psychiatric interviews, psychometric assessment, and lifetime treatment records. One hundred fifty-four probands met criteria for alcohol abuse/dependence (AAD), including twins from 45 MZ, 50 same-sex DZ, and 59 opposite-sex pairs. Twin-pair resemblance was evaluated for AAD and alcohol dependence (AD), as well as for subsets defined by gender, patterns of comorbidity, ethnic background, and clinical features. Among males, heritability of AAD and AD was substantial, with little evidence for common environmental contributions to family resemblance. Pair resemblance among females was also substantial, but similar for MZ and DZ pairs, yielding near-zero heritability estimates. However, based on these sample sizes, the sex differences were not statistically significant. The results confirm prior studies of strong genetic influences on alcoholism in males, but suggest lower genetic influence in females. Power to test other sources of heterogeneity was limited, but the results suggest no evidence for higher heritability for male early onset alcoholism or for alcoholism with comorbid antisocial personality.

Conceptual framework for the etiology of alcoholism: a "kindling"/stress hypothesis

RATIONALE

The rationale for proposing the "kindling"/stress hypothesis is to provide a conceptual basis for the insidious development and maintenance of alcohol abuse.

OBJECTIVE AND RESULTS

An objective of the hypothesis is to emphasize how continued alcohol abuse is linked to progressive neural adaptation. Work has shown that repeated withdrawals from chronic low levels of alcohol sensitize ("kindle") anxiety-like behavior ("anxiety") in rats, a finding consistent with multiple withdrawal kindling of seizure activity. Additionally, stress substitutes for initial cycles of the multiple withdrawal protocol to sensitize withdrawal-induced anxiety, which is indicative that stress is capable of facilitating neuroadaptive processes related to withdrawal. The persistence of adaptation caused by stress and multiple withdrawals is revealed by the appearance of withdrawal-induced anxiety following a future re-exposure to a single 5-day period of alcohol. This persisting adaptation also permits stress to induce anxiety during a period of abstinence--a response not observed in animals without previous exposure to alcohol. Furthermore, stress interacts with repeated withdrawals to enhance voluntary alcohol drinking. Results of other preclinical and clinical studies reported in the literature are integrated with these investigations in support of the proposed hypothesis.

CONCLUSIONS

The "kindling"/stress hypothesis is based on the premise that repeated withdrawals from cycles of chronic alcohol exposure contribute to a progressive development of persisting adaptive change that sensitizes withdrawal-induced anxiety and allows stress to evoke symptoms associated with negative affect during abstinence. Thus, these consequences of repeated withdrawals account for the evolution of major characteristics of alcoholism, which include worsened acute withdrawal symptoms and increased stress-induced negative affect during abstinence, both of which enhance the likelihood of relapse--and with relapse an inability to limit an abusive pattern of alcohol intake. The "kindling"/stress hypothesis provides a clear strategy for future studies to explore the advancing neural adaptation proposed to contribute to the pathogenesis of alcoholism.

Genetic study of alcoholism and novel gene expression in the alcoholic brain

Alcohol dependence may result from neuroadaptation involving alteration of gene expression after long-term alcohol exposure. The systematic study of gene expression profiles of the human alcoholic brain was initiated using the method of polymerase chain reaction (PCR)-differential display and was followed by DNA microarray. To date, more than 100 alcohol-responsive genes have been identified from the frontal cortex, motor cortex and nucleus accumbens of the human brain. These genes have a wide range of functions in the brain and indicate diverse actions of alcohol on neuronal function. This review discusses the current information on the genetic basis of alcoholism and the induction and characterization of these alcohol-responsive genes.

The heritability of alcohol abuse and dependence: a meta-analysis of behavior genetic research

A meta-analysis was performed on 50 family, twin, and adoption studies in which problem drinking and alcohol dependence served as the primary criterion measure. The results showed that far from being an established "fact," the genetic foundations of alcohol misuse are modest and heterogeneous. A weighted mean phi effect size of 0.12 (95% Confidence Interval = 0.11-0.12) was obtained for the total sample of 72 effect sizes. Four potential moderator variables (proband gender, sample nationality, pattern severity, year of publication) were examined with outcomes confirming that the heritability of alcohol misuse is stronger in males and in studies employing more severe definitions of abuse (alcoholism, alcohol dependence). When the effect size measure was restricted to studies using male subjects with more severe diagnoses of alcohol misuse, the unweighted mean phi effect size was only 0.18 (95% Confidence Interval = 0.15-0.21), with an even smaller weighted mean phi effect size of 0.15 (95% Confidence Interval = 0.12-0.18); results which indicate an upper limit of 30-36% for the heritability of alcohol misuse.

A twin study of the association between pathological gambling and antisocial personality disorder

Many individuals with a history of pathological gambling (PG) also have a history of engaging in antisocial behaviors, and this has often been interpreted as a result of the former causing the latter. In a sample of 7,869 men in 4,497 twin pairs from the Vietnam Era Twin Registry, the authors examined (a) the association between PG and antisocial personality disorder (ASPD), (b) the extent to which PG might be differentially associated with childhood conduct disorder (CD) and adult antisocial behavior (AAB), and (c) the contribution of genetic and environmental factors to the association of PG with ASPD, CD, and AAB. PG was significantly associated with all 3 antisocial behavior disorders, and the association of PG with ASPD, CD, and AAB was predominantly explained by genetic factors. The results of this study suggest that the greater-than-chance co-occurrence of PG and antisocial behavior disorders is partially due to their sharing a common genetic vulnerability. The antisocial behavior observed among many individuals with PG probably cannot be interpreted as being simply a consequence of the PG.

Towards a molecular epidemiology of alcohol dependence: analysing the interplay of genetic and environmental risk factors

BACKGROUND

Progress in identifying genetic factors protective against alcohol dependence (AlcD) requires a paradigm shift in psychiatric epidemiology.

AIMS

To integrate analysis of research into the genetics of alcoholism.

METHOD

Data from prospective questionnaire and interview surveys of the Australian twin panel, and from a subsample who underwent alcohol challenge, were analysed.

RESULTS

In men, effects of alcohol dehydrogenase ADH2*1/*2 genotype or high alcohol sensitivity (risk-decreasing), and of history of childhood conduct disorder, or having monozygotic co-twin or twin sister with AlcD (risk-increasing) were significant and comparable in magnitude. Religious affiliation (Anglican versus other) was associated with the ADH2 genotype, but did not explain the associations with AlcD symptoms. No protective effect of the ADH2*1/*2 genotype was observed in women.

CONCLUSIONS

The early onset and strong familial aggregation of AlcD, and opportunity for within-family tests of genetic association to avoid confounding effects, make epidemiological family studies of adolescents and young adults and their families a priority.

Genetic and environmental influences on posttraumatic stress disorder, alcohol and drug dependence in twin pairs

We investigated whether and to what degree genetic and environmental contributions overlap among posttraumatic stress disorder (PTSD), alcohol dependence (AD) and drug dependence (DD). Subjects were 3304 monozygotic and dizygotic male-male twin pair members of the Vietnam Era Twin Registry who participated in 1992 telephone administration of the Diagnostic Interview Schedule Version 3 Revised (DIS-3R). Genetic model fitting was performed to estimate the magnitude of genetic and environmental contributions to the lifetime co-occurrence of DSM-III-R PTSD, AD and DD. The liability for PTSD was partially due to a 15.3% genetic contribution common to AD and DD and 20.0% genetic contribution specific to PTSD. Risk for AD was partially due to a 55.7% genetic contribution common to PTSD and DD. Genetic influences common to PTSD and AD accounted for 25.2% of the total risk for DD. Specific family environmental influence accounted for 33.9% of the total variance in risk for DD. Remaining variance for all three disorders was due to unique environmental factors both common and specific to each phenotype. These results suggest that PTSD, AD and DD each have etiologically distinct components and also have significant genetic and unique environmental contributions in common.

Interrelationship of genetic and environmental influences on conduct disorder and alcohol and marijuana dependence symptoms

Data from the Vietnam Era Twin (VET) Registry were analyzed to explore the degree to which the same genetic and environmental factors contribute to childhood conduct disorder symptoms and to alcohol and marijuana dependence symptoms. Data on conduct disorder and alcohol and marijuana dependence were obtained from administration of the Diagnostic Interview Schedule to 1,856 monozygotic and 1,479 dizygotic male-male twin pair members of the VET Registry. Multivariate genetic models were compared to determine the genetic and environmental influences common and or specific to all three phenotypes. A full model that allowed for common genetic and environmental influences to all three phenotypes gave a good fit to the data, but the best fitting reduced model did not allow for a genetic influence on conduct disorder symptoms. Under the best fitting reduced model, genes explained 44.7% of the variance in risk for alcohol dependence symptoms. The genetic liability for symptoms of marijuana dependence was due to a 36.3% specific contribution and a 7.6% contribution from genes common with alcohol dependence symptoms. Family environmental contributions common to all three phenotypes explained 46.7%, 11.9%, and 21.3% of variance in risk for symptoms of conduct disorder, alcohol dependence, and marijuana dependence, respectively. Common family environmental factors contribute to risk of conduct disorder symptoms and alcohol and marijuana dependence symptoms. Common genetic influences contribute to risk of symptoms of alcohol dependence and marijuana dependence. While our findings suggest genes do not contribute to co-morbid conduct disorder symptoms, comparisons with other twin studies suggest that the role of genes in risk for conduct disorder remains uncertain.

Sex differences in the sources of genetic liability to alcohol abuse and dependence in a population-based sample of U.S. twins

BACKGROUND

There are substantial sex differences in all levels of alcohol involvement among U.S. adults. The goal of this study was to test whether the magnitude and sources of genetic and environmental influences on liability for alcohol abuse and dependence differ for men and women.

METHODS

Structured personal interviews were used to assess DSM-III-R- and DSM-IV-defined alcohol abuse and dependence among 5091 male and 4168 female twins (including 1546 identical, 1128 same-sex fraternal, and 1423 opposite-sex pairs) born in Virginia between 1934 and 1974. Twin correlations were analyzed using structural equation modeling.

RESULTS

The magnitude of twin-pair resemblance was similar across several definitions of alcoholism and was substantially higher among identical than fraternal pairs. The proportion of population variation in liability attributed to genetic factors was substantial among both women (55-66%) and men (51-56%), and we found little evidence of a role of environmental factors shared by family members. In all definitions studied, we could reject a model that the genetic sources of liability in the two sexes overlap completely.

CONCLUSION

In this first population-based study of alcoholism among male and female twins from the U.S., we found that genetic factors play a major role in the development of alcoholism in both sexes, that the magnitudes of genetic influence were equally high for men and women, and that the genetic sources of vulnerability are partially, but not completely, overlapping in men and women.

The heritability of alcoholism symptoms: "indicators of genetic and environmental influence in alcohol-dependent individuals" revisited

There is consistent evidence from twin and adoption studies implicating genetic factors in the etiology of alcoholism, yet few studies have examined the role of genetic influences on individual symptoms of alcoholism. In a previous study of 113 male twins, Johnson et al. (1996a) identified 7 alcoholism symptoms that were more "genetic" and 14 that were more "environmental" (that is, non-genetic) in their etiology by examining symptom concordances among monozygotic and dizygotic twin pairs. The present study represents an attempt to replicate the results of this previous study and extend them by estimating the contribution of genetic factors to the variation in liability for different alcoholism symptoms. Subjects were 3356 male twin pairs from the Vietnam Era Twin Registry. Lifetime histories of alcoholism symptoms were assessed by a structured psychiatric telephone interview. The results of the previous study were not replicated. The correlations between symptom classifications as genetic and non-genetic in the present and previous study were nonsignificant and ranged from -0.27 to 0.11. However, within the present study the correlation between symptom classifications as genetic and non-genetic was statistically significant across random split-half subsamples (r = 0.59); nine alcoholism symptoms were consistently classified as genetic and six symptoms as non-genetic in their etiology. Model-fitting analyses applied to different alcoholism symptoms yielded heritability estimates ranging from 0.03 to 0.53 with broad and overlapping confidence intervals around these estimates, ranging from 0.00 to 0.65. The results of this study highlight the difficulty of identifying more or less heritable phenotypes in twin research, and suggest that it may not be possible to identify specific alcoholism symptoms that are more genetic in their etiology than others. Nevertheless, there appears to be potentially important variation in the relative magnitude of genetic influences for individual alcoholism symptoms, and exploring these differences may lead to further insights into the nosology and etiology of alcohol-related problems.

Long-term reliability and validity of alcoholism diagnoses and symptoms in a large national telephone interview survey

The long-term reliability and validity of telephone lay interview assessments of alcoholism were examined in the context of a large national community-based survey of over 8,000 male Vietnam era veterans. A subsample of 146 men was interviewed twice by telephone using the same structured interview an average of 15 months apart to evaluate the long-term reliability of alcoholism symptoms and diagnoses. In addition, a search of Department of Veterans Affairs patient treatment files of inpatient hospitalizations between 1970 and 1993 yielded a subsample of 89 interviewed men with a past discharge diagnosis of alcohol dependence. The test-retest reliability of alcohol abuse and alcohol dependence diagnoses was good, with kappa coefficients of 0.74 and 0.61, respectively. The reliability of individual alcoholism symptoms was fair to good, with kappas of 0.46 to 0.67. Ninety-six percent of individuals identified by Department of Veterans Affairs patient treatment files as having an alcohol dependence diagnosis were correctly diagnosed by the telephone interview. The results of the present study provide additional evidence for the long-term reliability and validity of lifetime alcoholism diagnoses, and suggest that the reliability and validity of telephone interview assessments of alcoholism are as good as that of an in-person interview. Telephone administration of structured psychiatric interviews appears to be an attractive alternative to in-person interviewing for gathering information about alcoholism and alcohol-related problems.