A twin study of psychomotor and physiological responses to an acute dose of alcohol

Is Asian flushing syndrome a disadvantage in the labor market?

A large fraction of people in East Asia are incapable of digesting alcohol because of a genetic deficiency. This study examines whether the variation in alcohol tolerance contributes to inequality in the labor market. We conduct our original surveys in Japan, Taiwan, and Korea with the measurement of respondents' degree of alcohol tolerance by a bio-marker test. We find that alcohol-tolerant men consume significantly more alcohol, but their earnings and hours worked do not differ from those of alcohol-intolerant men. Despite a prevalent view that drinking alcohol is indispensable to establish good relationships with colleagues and business partners, our results suggest that there is no systematic impact of alcohol tolerance on labor market outcomes.

Genetic Epidemiology of Liability for Alcohol-Induced Blacking and Passing Out

BACKGROUND

Individuals differ in their sensitivity to alcohol's physiological effects, including blacking and passing out. Blackouts are periods of impaired memory formation when an individual engages in activities they later cannot recall, while passing out results in loss of consciousness.

METHODS

The sample consisted of 3,292 adult twins from the Australian Twin Registry. Univariate twin analyses were conducted to examine the contributions of genetic and environmental influences to blacking and passing out occurrence and susceptibility (accounting for frequency of intoxication). Evidence for shared etiology of susceptibility to blacking and passing out was examined using bivariate twin analyses.

RESULTS

Although blacking and passing out were strongly associated (odds ratio (OR) = 4.45, 95% confidence interval (CI): [3.85, 5.14]), the genetic epidemiology was quite different. Genetic (43%) and nonshared environmental (57%) influences contributed to liability for blackout occurrence. For passing out occurrence, there was evidence of sex differences. Among men, genetic (32%) and nonshared environmental (68%) influences contributed, whereas among women, there were shared (29%) and nonshared environmental (72%) influences. After accounting for frequency of intoxication, genetic influences on blackout susceptibility remained significant; in contrast, only nonshared environmental influences were significant for passing out susceptibility. There was evidence for overlapping genetic and nonshared environmental factors influencing susceptibility to blacking and passing out among men; among women, there were overlapping nonshared environmental influences.

CONCLUSIONS

Blacking and passing out are 2 common sedative-like effects of heavy drinking, and people differ considerably in their susceptibility to these effects. This study suggests that differences in blackout susceptibility can be explained by genetic factors in both men and women, while differences in susceptibility to pass out after consuming alcohol may be attributable to environmental influences, particularly among women. These environmental factors may include changing social and cultural norms about alcohol use, drinking context, and the type(s) of alcohol consumed.

Behavior-Genetic Strategies in the Study of Emotion

Behavior-genetic studies of emotionality in rats and human studies of adult personality and childhood temperament provide evidence of genetic effects on emotion-relevant trails. Twin studies of autonomic reactivity suggest that psychophysiologic responses to stress are heritable. Genetic analyses of fears reveal that the magnitude of genetic influence varies across fears and across development. Finally, recent findings in psychiatric genetics shed light on the role of heritable variation in emotional functioning in major psychiatric disorders. Thus, there is evidence from a variety of sources that characteristics relevant to emotion are influenced by genetic factors. However, behavior-genetic methods generally have not been applied in laboratory-based studies of the psychophysiologic, cognitive, or expressive correlates of emotion. Because recent developments in quantitative genetics permit us to go beyond the simple estimation of heritability, a broader application of behavior-genetic strategies to the study of emotion, one which incorporates elicitation of emotion in the laboratory, promises to elucidate the interrelationships among the components of emotional systems.

A Genetic Animal Model of Alcoholism for Screening Medications to Treat Addiction

The purpose of this review is to present up-to-date pharmacological, genetic, and behavioral findings from the alcohol-preferring P rat and summarize similar past work. Behaviorally, the focus will be on how the P rat meets criteria put forth for a valid animal model of alcoholism with a highlight on its use as an animal model of polysubstance abuse, including alcohol, nicotine, and psychostimulants. Pharmacologically and genetically, the focus will be on the neurotransmitter and neuropeptide systems that have received the most attention: cholinergic, dopaminergic, GABAergic, glutamatergic, serotonergic, noradrenergic, corticotrophin releasing hormone, opioid, and neuropeptide Y. Herein, we sought to place the P rat's behavioral and neurochemical phenotypes, and to some extent its genotype, in the context of the clinical literature. After reviewing the findings thus far, this chapter discusses future directions for expanding the use of this genetic animal model of alcoholism to identify molecular targets for treating drug addiction in general.

A twin study of alcohol dependence, binge eating, and compensatory behaviors

OBJECTIVE

Rates of alcohol dependence are elevated in women with eating disorders who engage in binge eating or compensatory behaviors compared with women with eating disorders who do not report binge eating or compensatory behaviors and with healthy controls. Alcohol dependence, binge eating, and compensatory behaviors are heritable; however, it is unclear whether a shared genetic liability contributes to the phenotypic association among these traits, and little information exists regarding this shared liability in men. We investigated genetic and environmental correlations among alcohol dependence, binge eating, and compensatory behaviors in male and female twins.

METHOD

Participants included 5,993 same- and opposite-sex twins from the Australian Twin Registry who completed a modified version of the Semi-Structured Assessment for the Genetics of Alcoholism that assessed lifetime alcohol dependence and binge eating as defined in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised. Compensatory behaviors were assessed via a general health questionnaire in women only. Biometrical twin models estimated genetic and environmental influences on alcohol dependence, binge eating, and compensatory behaviors.

RESULTS

In women, the multivariate twin model suggested that additive genetic and nonshared environmental effects influenced alcohol dependence, binge eating, and compensatory behaviors, with heritability estimates ranging from 38% to 53%. The best-fitting sex-limitation model was a common effects model that equated all genetic and nonshared environmental influences in men and women. The heritability estimates were 50% and 38% for alcohol dependence and binge eating, respectively. Overall, there were significant genetic correlations between alcohol dependence and binge eating, alcohol dependence and compensatory behaviors, and binge eating and compensatory behaviors.

CONCLUSIONS

These findings indicate that common genetic factors may underlie the vulnerability to alcohol dependence and the liability to binge eating and compensatory behaviors.

The genetics of alcohol dependence: advancing towards systems-based approaches

BACKGROUND

Personalized treatment for psychopathologies, in particular alcoholism, is highly dependent upon our ability to identify patterns of genetic and environmental effects that influence a person's risk. Unfortunately, array-based whole genome investigations into heritable factors that explain why one person becomes dependent upon alcohol and another does not, have indicated that alcohol's genetic architecture is highly complex. That said, uncovering and interpreting the missing heritability in alcohol genetics research has become all the more important, especially since the problem may extend to our inability to model the cumulative and combinatorial relationships between common and rare genetic variants. As numerous studies begin to illustrate the dependency of alcohol pharmacotherapies on an individual's genotype, the field is further challenged to identify new ways to transcend agnostic genomewide association approaches. We discuss insights from genetic studies of alcohol related diseases, as well as issues surrounding alcohol's genetic complexity and etiological heterogeneity. Finally, we describe the need for innovative systems-based approaches (systems genetics) that can provide additional statistical power that can enhance future gene-finding strategies and help to identify heretofore-unrealized mechanisms that may provide new targets for prevention/treatments efforts. Emerging evidence from early studies suggest that systems genetics has the potential to organize our neurological, pharmacological, and genetic understanding of alcohol dependence into a biologically plausible framework that represents how perturbations across evolutionarily robust biological systems determine susceptibility to alcohol dependence.

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.

Alcoholic marriage: later start, sooner end

BACKGROUND

Although associations between drinking behavior and marital status are well documented, timing of marital transitions as a function of alcohol use or disorder has received limited empirical attention.

METHODS

We examine the relationship between lifetime history of alcohol dependence (AD) and timing and survival of first marriages in a sample of 3,575 female and 1,845 male adult Australian twins born mostly between 1940 and 1964. Survival analyses were conducted using Cox proportional hazards regression models.

RESULTS

Results indicate moderate delays in marriage associated with AD for both women and men. Among ever-married respondents, AD was strongly predictive of early separation, with similar effects observed for women and men. Heritable sources of covariation were also documented. For women, genetic influences shared between early-onset AD and marital timing were found. Genetic influences shared between AD and marital survival were observed for women without regard to onset and for men with later-onset AD.

CONCLUSIONS

Results confirm the importance of AD as a predictor of both timing and survival of first marriages, with genetic influences contributing to observed associations.

Role of GABRA2 in moderating subjective responses to alcohol

BACKGROUND

Human twin studies have shown that certain responses to alcohol, including subjective perceptions, are genetically influenced. Previous studies have provided evidence that a low level of response to alcohol predicts future alcohol use disorders in humans. Recent genetic studies suggest an association between alcohol dependence and genetic variation in the γ-aminobutyric acid A (GABA(A)) receptor α2 subunit gene (GABRA2). Based on a haplotypic association of alcohol dependence with GABRA2, we investigated whether GABRA2 alleles are associated with the subjective responses to clamped alcohol concentration.

METHODS

One hundred and ten healthy social drinkers (53 men) underwent the alcohol clamp. Fifteen minutes after the start of an intravenous infusion of alcohol, the breath alcohol concentration was clamped at a target of 50 ± 5 mg/dl for 165 minutes. Subjective physiologic responses to alcohol and stimulant and sedative effects of alcohol were measured repeatedly during the alcohol clamp. Because aldehyde dehydrogenase 2 (ALDH2) has been shown to have a great impact on the subjective responses to alcohol, we divided subjects by ALDH2 genotype for further analyses. To examine the role of genetic variation in GABRA2, 7 single nucleotide polymorphisms (SNPs) that were informative in association studies were included as factors in the analysis.

RESULTS

Among these 7 SNPs, 3 SNPs (rs279869, rs279858, and rs279837) located in the middle of the GABRA2 gene showed significant associations with subjective effects of alcohol. Subjects with 1 or 2 copies of the more common allele showed greater subjective responses to alcohol than did individuals homozygous for the alcohol dependence-associated allele regardless of ALDH2 genotype.

CONCLUSIONS

These findings confirm and extend the observation that the GABRA2 alleles affect the subjective responses to alcohol, and suggest that the genetic variations in GABRA2 might play a role in the risk of alcohol use disorders by moderating the subjective effects of alcohol.

Variability in ethanol biodisposition in whites is modulated by polymorphisms in the ADH1B and ADH1C genes

Association between genetic variations in alcohol-related enzymes and impaired ethanol biodisposition has not been unambiguously proven, and the effect of many newly described polymorphisms remains to be explored. The aims of this study are to elucidate the influence of genetic factors in alcohol biodisposition and effects. We analyzed alcohol pharmacokinetics and biodisposition after the administration of 0.5 g/kg ethanol; we measured ethanol effects on reaction time and motor time in response to visual and acoustic signals, and we analyzed 13 single nucleotide polymorphism (SNPs) in the genes coding for ADH1B, ADH1C, ALDH2, and CYP2E1 in 250 healthy white individuals. Variability in ethanol pharmacokinetics and biodisposition is related to sex, with women showing a higher area under the curve (AUC) (P = 0.002), maximum concentration (Cmax) (P < 0.001) and metabolic rate (P = 0.001). Four nonsynonymous SNPs are related to decreased alcohol metabolic rates: ADH1B rs6413413 (P = 0.012), ADH1C rs283413 (P < 0.001), rs1693482 (P < 0.001), and rs698 (P < 0.001). Individuals carrying diplotypes combining these mutations display statistically significant decrease in alcohol biodisposition as compared with individuals lacking these mutations. Alcohol effects displayed bimodal distribution independently of sex or pharmacokinetics. Most individuals had significant delays in reaction and motor times at alcohol blood concentrations under 500 mg/L, which are the driving limits for most countries.

CONCLUSION

Besides the identification of new genetic factors related to alcohol biodisposition relevant to whites, this study provides unambiguous identification of diplotypes related to variability in alcohol biodisposition.

Gene-environment interactions and alcohol use and dependence: current status and future challenges

AIM

To discuss the current status of gene-environment interaction research with regard to alcohol use and dependence. Further, we highlight the difficulties concerning gene-environment studies.

METHODS

Overview of the current evidence for gene-environment interactions in alcohol outcomes, and of the associated challenges in gene-environment studies.

RESULTS

Attention to the causative roles of gene-environment interactions in alcohol use and dependence is increasing. Studies with twin designs are beginning to examine gene-shared environment effects, and animal studies have investigated gene-environment interaction effects on alcohol intake in primates. Thirteen studies incorporated gene-environment interactions in examining alcohol use or dependence in humans. These studies held a variety of candidate genes and environmental risk factors and their heterogeneity made it impossible to draw firm general conclusions.

CONCLUSIONS

Challenges for future gene-environment studies are abundant, and consist of, for example, the development of clear theoretical assumptions about neurobiological mechanisms and the recruitment of large longitudinal samples that already start in childhood. Replication is essential to prevent an overload of false-positive results. Despite the difficulties, it is crucial to include gene-environment interactions in future studies in order to unravel the aetiological factors of human alcohol outcomes.

In vitro and in vivo models of acute alcohol exposure

Alcohol abuse is a global problem due to the financial burden on society and the healthcare system. While the harmful health effects of chronic alcohol abuse are well established, more recent data suggest that acute alcohol consumption also affects human wellbeing. Thus, there is a need for research models in order to fully understand the effect of acute alcohol abuse on different body systems and organs. The present manuscript summarizes the interdisciplinary advantages and disadvantages of currently available human and non-human models of acute alcohol abuse, and identifies their suitability for biomedical research.

Longitudinal stability and change in consumption among female twins: Contributions of genetics

Problem alcohol use among women is increasingly recognized as an important public health and mental health issue. Younger women appear to be at increased risk for heavy drinking and alcohol-related problems compared to women from earlier cohorts. Understanding the sources for inter- and intra-individual differences in alcohol consumption is an important first step in addressing these trends. We studied the sources underlying variation in alcohol consumption in a sample of 2,163 female twins born in Virginia between 1934 and 1970. Measures of past-year alcohol consumption quantity and frequency were obtained on two occasions across a 5-year interval. Quantity and frequency of consumption declined over age, both cross-sectionally and longitudinally. Intra-individual correlations over the interval were substantial for frequency of drinking (r = .62) and quantity consumed per drinking occasion (r = .56) but lower for quantity consumed weekly (r = .22). There was significant intrapair resemblance for all measures, with the drinking behavior of identical twin pairs being more similar than that of fraternal pairs. Twin analyses of patterns of change in consumption over a 5-year interval revealed little within-pair similarity in rate of change, with correlations ranging from .06 to .18, suggesting that among young adult to middle-aged women, determinants of changing alcohol consumption are largely individual-specific. There was some evidence for significant age interactions, with the role of individual-specific sources increasing over age.

Associations of ADH and ALDH2 gene variation with self report alcohol reactions, consumption and dependence: an integrated analysis

Alcohol dependence (AD) is a complex disorder with environmental and genetic origins. The role of two genetic variants in ALDH2 and ADH1B in AD risk has been extensively investigated. This study tested for associations between nine polymorphisms in ALDH2 and 41 in the seven ADH genes, and alcohol-related flushing, alcohol use and dependence symptom scores in 4597 Australian twins. The vast majority (4296) had consumed alcohol in the previous year, with 547 meeting DSM-IIIR criteria for AD. There were study-wide significant associations (P<2.3 x 10(-4)) between ADH1B-Arg48His (rs1229984) and flushing and consumption, but only nominally significant associations (P<0.01) with dependence. Individuals carrying the rs1229984 G-allele (48Arg) reported a lower prevalence of flushing after alcohol (P=8.2 x 10(-7)), consumed alcohol on more occasions (P=2.7 x 10(-6)), had a higher maximum number of alcoholic drinks in a single day (P=2.7 x 10(-6)) and a higher overall alcohol consumption (P=8.9 x 10(-8)) in the previous year than those with the less common A-allele (48His). After controlling for rs1229984, an independent association was observed between rs1042026 (ADH1B) and alcohol intake (P=4.7 x 10(-5)) and suggestive associations (P<0.001) between alcohol consumption phenotypes and rs1693482 (ADH1C), rs1230165 (ADH5) and rs3762894 (ADH4). ALDH2 variation was not associated with flushing or alcohol consumption, but was weakly associated with AD measures. These results bridge the gap between DNA sequence variation and alcohol-related behavior, confirming that the ADH1B-Arg48His polymorphism affects both alcohol-related flushing in Europeans and alcohol intake. The absence of study-wide significant effects on AD results from the low P-value required when testing multiple single nucleotide polymorphisms and phenotypes.

Alcohol dependence and reproductive onset: findings in two Australian twin cohorts

BACKGROUND

Although early alcohol use is a strong predictor of future alcohol problems and adolescent drinking is associated with risky sexual behavior predictive of early childbearing, reproductive dysfunctions associated with delayed childbearing have been reported in adult drinkers. We examine the relationship between lifetime history of alcohol dependence (AD) and timing of first childbirth across reproductive development.

METHODS

Data were drawn from two cohorts of Australian twins born between 1893 and 1964 (3634 female and 1880 male twins) and between 1964 and 1971 (3381 female and 2748 male twins). Survival analyses were conducted using Cox proportional hazards regression models predicting age at first childbirth from AD, with sociodemographic characteristics, regular smoking, history of psychopathology, and family and childhood risks included as control variables in adjusted models.

RESULTS

Results suggest alcoholic women in both cohorts show overall delayed reproduction, with little effect of AD on timing of first reproduction in men. Effects of AD are particularly strong for women in the older cohort, where AD is associated with 73% decreased likelihood of first childbirth after age 29 [hazard ratio (HR) = 0.27, 95% CI: 0.10-0.75]. In adjusted models, effects reduce only slightly (HR = 0.29, 95% CI: 0.11-0.80). For women in the young cohort, AD is associated with delayed reproduction after age 24, with 40% decreased likelihood of first childbirth (HR = 0.60, 95% CI: 0.48-0.75). AD remains predictive in adjusted models, but without age interaction (HR = 0.72, 95% CI: 0.62-0.85).

CONCLUSIONS

Findings of delayed reproductive onset in alcoholic women are consistent with alcohol-related reproductive dysfunctions, although underlying mechanisms remain largely unknown. To better understand AD differences in reproductive onset, continued research on both biological and psychosocial risks is needed.

Effects of GABRA2 variation on physiological, psychomotor and subjective responses in the alcohol challenge twin study

Multiple reports have identified variation in the GABRA2 gene as contributing to the genetic susceptibility to alcohol dependence. However, both the mechanism behind this association, and the range of alcohol-related phenotypes affected by variation in this gene, are currently undefined. Other data suggest that the risk of alcohol dependence is increased by relative insensitivity to alcohol's intoxicating effects. We have therefore tested whether GABRA2 variation is associated with variation in the subjective and objective effects of a standard dose of alcohol in humans. Data on responses to alcohol from the Alcohol Challenge Twin Study (Martin et al., 1985) have been tested against allelic and haplotype information obtained by typing 41 single-nucleotide polymorphisms in or close to the GABRA2 gene. Nominally significant allelic associations (p<.05, without correction for multiple testing) were found for body sway, motor coordination, pursuit rotor and arithmetical computation tasks, and for the personality dimension of Neuroticism. Because of the large number of phenotypes tested, these possibly significant findings will need to be confirmed in further studies.

The role of GABRA2 in alcohol dependence, smoking, and illicit drug use in an Australian population sample

BACKGROUND

Multiple studies have shown that genetic variation in the alpha-2 subunit of the gamma-aminobutyric acid type A (GABA(A)) receptor (GABRA2) is associated with risk for alcohol dependence. Recent reports have suggested that GABRA2 may exert its influence on dependence through factors such as sensitivity to alcohol's intoxicating effects and that GABRA2 may also contribute to a common underlying genetic vulnerability to both alcohol and drug dependence. The present study tested for association between GABRA2 and alcohol dependence, smoking, and illicit drug use within the Australian population.

METHODS

We genotyped 11 single nucleotide polymorphisms (SNPs) within or flanking GABRA2 in 4597 subjects (34.6% males) from 2618 families comprising 814 monozygotic pairs, 1177 dizygotic pairs, and 627 twins whose co-twin did not participate. Family-based association tests were conducted for binary and quantitative measures of alcohol dependence, smoking, and cannabis and other illicit drug use.

RESULTS

We observed evidence of association (p < 0.05) between multiple GABRA2 SNPs and quantitative measures of alcohol dependence, including symptom scores and principal component factor scores from the 9 criteria for DSM-IV alcohol dependence, in the opposite direction to that previously reported. In contrast, GABRA2 was not associated overall with dichotomous measure of alcohol dependence nor with smoking, cannabis, or illicit drug use.

CONCLUSIONS

The GABRA2 allelic associations found in clinical case-control studies have detectable but minor effects on DSM-defined alcohol dependence in the general community. Systematic comparisons of allelic effects on alcohol dependence in clinical cases and in the general community are required.

Ethnic differences in level of response to alcohol between Chinese Americans and Korean Americans

OBJECTIVE

Koreans have higher rates of alcohol-use disorders and family history of alcoholism, compared with Chinese. These differences likely reflect both environmental and genetic influences. One genetically influenced characteristic that may contribute to these ethnic differences is level of response to alcohol. Variant alleles of aldehyde dehydrogenase (ALDH2) and alcohol dehydrogenase (ADH1B) genes are prevalent in individuals of Asian heritage and have been associated with an increased level of response to alcohol and a decreased risk for alcohol dependence. Additionally, a low level of response to alcohol is more common in individuals with a first-degree family history of alcoholism and is predictive of increased risk for this disorder. It also is possible that sociocultural factors have an impact on an individual's response to alcohol. The current study examined self-report level of response to alcohol, ALDH2 and ADH1B, country of origin, and family history of alcoholism in 154 Chinese- and 181 Korean-American college students.

METHOD

Participants were evaluated via in-person interviews and genotyped at the ALDH2 and ADH1B loci.

RESULTS

Ethnicity was significantly related to level of response to alcohol, with Koreans having a lower self-reported level of response than Chinese. This relationship remained significant after considering the effects of gender, height, weight, quantity and frequency of alcohol consumption (over the previous 90 days), ALDH2 genotype, ADH1B genotype, country of origin, and first-degree family history of alcohol dependence.

CONCLUSIONS

The results suggest that a low level of response to alcohol may contribute to the increased risk for alcohol abuse and dependence found in Koreans, relative to Chinese. More research is needed to determine additional factors that may be contributing to the low alcohol response and high rates of alcoholism in Koreans.

Genome-wide scan for blood pressure in Australian and Dutch subjects suggests linkage at 5P, 14Q, and 17P

Large-scale studies estimate the heritability of blood pressure at approximately 50%. We carried out a genome-wide linkage analysis to search for chromosomal loci that might explain this heritability using longitudinal, multiple measures of systolic and diastolic blood pressure obtained in sibling pairs and dizygotic twin pairs from 2 countries (a total of 286 pairs from Australia and 636 pairs from the Netherlands). These pairs and a large number of their parents were genotyped with microsatellite markers. Multivariate linkage analysis of the combined data of both countries, using a variance components approach, showed suggestive linkage for diastolic blood pressure on chromosomes 5p13.1 (logarithm of odds score: 2.48), 14q12 (logarithm of odds score: 2.40) and 17q24.3 (logarithm of odds score: 2.36). The highest logarithm of odds score of 1.21 for systolic blood pressure was observed on chromosome 13q34. These results replicate earlier findings and add to a slowly emerging picture of multiple loci contributing to quantitative blood pressure variation.

Effects of variation at the ALDH2 locus on alcohol metabolism, sensitivity, consumption, and dependence in Europeans

BACKGROUND

The low-activity variant of the aldehyde dehydrogenase 2 (ALDH2) gene found in East Asian populations leads to the alcohol flush reaction and reduces alcohol consumption and risk of alcohol dependence (AD). We have tested whether other polymorphisms in the ALDH2 gene have similar effects in people of European ancestry.

METHODS

Serial measurements of blood and breath alcohol, subjective intoxication, body sway, skin temperature, blood pressure, and pulse were obtained in 412 twins who took part in an alcohol challenge study. Participants provided data on alcohol reactions, alcohol consumption, and symptoms related to AD at the time of the study and subsequently. Haplotypes based on 5 single-nucleotide polymorphisms (SNPs) were used in tests of the effects of variation in the ALDH2 gene on alcohol metabolism and alcohol's effects.

RESULTS

The typed SNPs were in strong linkage disequilibrium and 2 complementary haplotypes comprised 83% of those observed. Significant effects of ALDH2 haplotype were observed for breath alcohol concentration, with similar but smaller and nonsignificant effects on blood alcohol. Haplotype-related variation in responses to alcohol, and reported alcohol consumption, was small and not consistently in the direction predicted by the effects on alcohol concentrations.

CONCLUSIONS

Genetic variation in ALDH2 affects alcohol metabolism in Europeans. However, the data do not support the hypothesis that this leads to effects on alcohol sensitivity, consumption, or risk of dependence.

Genetic associations of alcohol dehydrogenase with alcohol use disorders and endophenotypes in white college students

Associations of alcohol dehydrogenase (ADH) gene polymorphisms (ADH1B*2 and ADH1C*1) with a lifetime alcohol use disorder (AUD) were examined in White college students. Alcohol-related endophenotypes likely to be influenced by elevations in acetaldehyde were also assessed. Individuals with an ADH1B*2 allele had lower rates of AUDs, consumed a lower maximum number of drinks in a 24-hr period, reported a greater level of response to alcohol, were more likely to have experienced alcohol-induced headaches following 1 or 2 drinks, and reported more severe hangovers than those lacking this allele. These findings are consistent with the hypothesis that enhanced sensitivity to alcohol and lower levels of alcohol use reflect the mechanism by which ADH1B*2 protects against developing an AUD.

Alcoholism: the dissection for endophenotypes

Alcohol dependence (alcoholism) is a complex disorder attributed to the interaction of genetic and environmental factors that form a collage of "disease" predisposition, which is not identical for every alcohol-dependent individual. There is considerable evidence to demonstrate that genetic predisposition accounts for roughly half the risk in the development of alcohol dependence. Both family and population studies have identified a number of genomic regions with suggestive links to alcoholism, yet there have been relatively few definitive findings with regard to genetic determinants of alcoholism. This ambiguity can be attributed to a multitude of complications of studying complex mental disorders, such as clinical heterogeneity, polygenic determinants, reduced penetrance, and epistatic effects. Complex mental disorders are clinical manifestations described by combinations of various signs and symptoms. One approach to overcoming the ambiguity in studying the association between genetic risk factors and disease is to dissect the complex, heterogeneous disorder by using intermediate phenotypes--or endophenotypes--to generate more homogeneous diagnostic groupings than an all-encompassing definition, such as the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)-derived term "alcohol dependence" or the commonly used term "alcoholism." The advantage of using endophenotypes is that the number of influential factors that contribute to these characteristics should be fewer and more easily identified than the number of factors affecting the heterogeneous entity of alcohol dependence (alcoholism). A variety of alcohol-related characteristics have been investigated in epidemiological, clinical, and basic research as potential endophenotypes of alcohol dependence. These include phenotypes related to alcohol metabolism, physiological and endocrine measures, neural imaging, electrophysiology, personality, drinking behavior, and responses to alcohol and alcohol-derived cues. This review summarizes the current literature, focused on human data, of promising endophenotypes for dissecting alcoholism.

GABRA2 alleles moderate the subjective effects of alcohol, which are attenuated by finasteride

GABA(A) receptors are involved in the subjective effects of alcohol. Endogenous neuroactive steroids interact with GABA(A) receptors to mediate several behavioral effects of alcohol in rodents. Based on a haplotypic association of alcohol dependence with the gene encoding the GABA(A) receptor alpha-2 subunit (GABRA2), we examined whether GABRA2 alleles are associated with the subjective response to alcohol. We also examined whether finasteride (a 5-alpha steroid reductase inhibitor), which blocks the synthesis of some neuroactive steroids, reduces the subjective response to alcohol. In all, 27 healthy social drinkers (15 males) completed a randomized, double-blind, placebo-controlled study of high-dose finasteride. After being pretreated with study drug, subjects consumed three alcoholic drinks. Subjective effects were measured repeatedly over the ascending blood alcohol curve. To examine the moderating role of genetic variation in GABRA2, a single-nucleotide polymorphism that was informative in association studies was included as a factor in the analysis. Subjects homozygous for the more common A-allele (n=7) showed more subjective effects of alcohol than did individuals with one or two copies of the alcohol dependence-associated G-allele (n=20, including two homozygotes). Among the A-allele homozygotes, there was a greater reduction in several subjective effects during the finasteride session compared to the placebo session. These findings provide preliminary evidence that the risk of alcoholism associated with GABRA2 alleles may be related to differences in the subjective response to alcohol. The effects of finasteride provide indirect evidence for a mediating role of neuroactive steroids in some of the subjective effects of alcohol.

Open field activity and EtOH activation of gamma-PKC null mutants

Null mutants of the neural-specific gamma-isotype of protein kinase C (gamma-PKC) have demonstrated differential responses to acute administration of ethanol in comparison with wild-type animals. Previous studies have shown that the mutants are less sensitive to ethanol-induced loss of righting response. Null mutants also consume more ethanol and exhibit less behavioral inhibition. In order to determine if these sensitivity differences extend to ethanol activation of locomotor activity in an open-field arena, baseline activity and the effect of two low doses of ethanol were assessed in gamma-PKC null mutants and wild-type littermates. Null mutants demonstrated higher levels of baseline activity than did their wild-type counterparts. Further analysis revealed that a 1.0 g/kg dose of ethanol increased locomotor activity in males and females of both genotypes, whereas only null mutant males were activated by a 1.25 g/kg ethanol dose. The current study demonstrates that male gamma-PKC null mutants exhibit increased sensitivity to activating doses of ethanol in contrast to previous findings of decreased sensitivity to higher, depressive doses. This reflects the pleiotropic effects of the gamma-PKC null mutation on the behavioral effects of ethanol.

Subjective intoxication in response to alcohol challenge: heritability and covariation with personality, breath alcohol level, and drinking history

BACKGROUND

Numerous studies have identified differences in subjective response to alcohol in subjects differentiated by family history of alcoholism. Results suggest that genetic influences on individual variation in subjective response to alcohol may be a mechanism for genetic effects on alcohol problems. However, direct evidence for genetic effects on subjective response to alcohol is very limited.

METHODS

In a sample of 99 adult twin pairs, we studied genetic influences on subjective intoxication after alcohol challenge. The twins ingested a standard dose of ethanol (0.70 g/kg for men/0.65 g/kg for women), and two measures of subjective response to alcohol were assessed.

RESULTS

Genetic effects on variation in subjective intoxication reported 1 hr after drinking were significant and substantial: heritability was 0.60 for a 22-item scale and 0.48 for a brief 2-item measure. Self-report measures of neuroticism, psychasthenia, hostility, and family problems shared significant genetic covariation with subjective intoxication. Achieved breath alcohol level, rate of change in breath alcohol on the descending limb, and individual drinking history all shared familial variation with subjective intoxication. No significant genetic effects for subjective intoxication were found 2 hr after drinking, but familial influences remained present, and many of the same personality, drinking history, and breath alcohol variables were predictive of intoxication.

CONCLUSIONS

Subjective response to alcohol is heritable, and genetic effects on subjective intoxication are partly shared with genetic effects on personality.

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.

Biochemical and genetic studies of Caucasian subjects with ethanol-induced flushing reaction

The prevalence of ethanol-induced flushing was investigated in three different Caucasian student populations, namely Irish, Belgian and English. Approximately 45% of all female subjects reported a flushing reaction, while 33%, 17% and 9%, respectively, of male students reported this reaction. There was a high familial incidence of flushing in all groups, suggesting that a specific gene defect might be involved. Our previous investigations had inferred normal ALDH2 in such affected individuals, but low activities of erythrocyte ALDH1.(1) Since the principal role of this cytosolic enzyme may be in the metabolism of biogenic amines, serotonin levels in platelet-rich plasma and urinary adrenaline, noradrenaline and dopamine were assayed in affected individuals after an oral ethanol challenge. No consistent pattern was evident for any of these parameters in any of the subjects at the time intervals investigated. Genotyping for ADH31 and ADH32 showed a higher frequency for ADH3(1) , 58%, than ADH3(2) , 42%. This is comparable to the Caucasian controls and to our previously published data.

Manual performance and laterality in twins of known chorion type

Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8-12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used; dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.

Alcohol reactions in subjects of European descent: effects on alcohol use and on physical and psychomotor responses to alcohol

Self-reports of reactions to small amounts of alcohol, obtained between 1990 and 1992, were compared with reports of alcohol use, obtained in 1990-1992 and also in 1979-1981, in twin subjects of European descent. Data on subjective, physiological, psychomotor, and metabolic responses to a test dose of alcohol, taken in 1979-1981, were also available. Alcohol reactions were more common in women than in men, and were associated with less alcohol use, both at the time that information about reactions was obtained and as recorded on average 12 years previously, in both sexes. Physiological and psychomotor responses to alcohol were similar across the reaction groups, except that deterioration in standing steadiness was greater in those who subsequently reported adverse reactions to alcohol. Contrary to expectation, skin temperature changes after alcohol were less in the subjects who reported always reacting to alcohol than in the other groups. Subjective reports of intoxication were greatest in subjects who subsequently reported alcohol reactions. The pattern of twin pair concordance for reactions suggests low heritability, so alcohol reactions in subjects of European descent are not caused by a single gene of high penetrance of the type found in the Asian alcohol flush reaction.

Alcohol sensitivity and smoking history in men and women

Many studies have found genetic effects to contribute to alcoholism risk in both men and women. Based on preliminary evidence for shared genetic risk between smoking and drinking problems, a reanalysis of alcohol challenge data on 412 Australian twins was performed to explore the possibility that smoking may diminish or moderate the intoxicating effects of alcohol. We found history of smoking to be strongly associated with self-reported intoxication after alcohol challenge in women (women: r = -0.44 +/- 0.08; men: r = -0.21 +/- 0.08), comparable with self-reported average weekly consumption of alcohol, which was more strongly associated in men (women: r = -0.37 +/- 0.07; men: r = -0.54 +/- 0.06). Structural equation model-fitting indicated a strong association between heavy drinking and smoking, but the association between smoking and postalcohol intoxication remained even when the effects of heavy drinking were controlled for. These results prompt the question of whether smoking cigarettes directly influences the transition from moderate to excessive use of alcohol by diminishing feelings of alcohol intoxication.

Is alcohol-related flushing a protective factor for alcoholism in Caucasians?

Although alcohol-related flushing seems to be a genetically influenced protective factor for alcoholism in some Asian groups, little is known about whether this is true for Caucasians. The evidence for alcohol-related flushing as a protective factor for the development of alcoholism was examined in a sample of 5831 Australian twins (2041 men, 3790 women) who were administered a structured psychiatric interview. Twin correlations for self-reported adverse alcohol reactions (e.g., "flushing or blushing" and "feeling very sleepy" after drinking 1 or 2 drinks) were modest, suggesting minimal contribution of genetic factors, but when corrected for reliability of measurement, were consistent with moderate heritabilities. In accord with studies examining Asian samples, we found that individuals who experienced adverse reactions after drinking small amounts of alcohol drank less often and slightly less per drinking occasion than those who did not experience adverse reactions. However, those who experienced adverse reactions were more likely to have symptoms of alcoholism and to report a parental history of alcohol problems. We conclude that self-reported alcohol-related flushing is not a protective factor for alcoholism in Caucasians and may be a risk factor.

Genetic influences on alcohol consumption patterns and problem drinking: results from the Australian NH&MRC twin panel follow-up survey

Self-report questionnaire data from 3,000 adult twin pairs participating in the 1988-1989 follow-up survey of the Australian NH&MRC twin panel were analyzed to determine (1) the contribution of genetic factors to risk of problem drinking in males and females; and (2) the magnitude of the correlation between genetic effects on problem drinking and genetic effects on alcohol consumption level. Significant genetic contributions were found both for average weekly consumption of alcohol and for problem-drinking history. For level of consumption, genetic factors accounted for approximately 58% of the variation in females and 45% of the variation in males. Heritability estimates for problem drinking, though significantly greater than zero, were variable in magnitude, ranging (under different models) from 8-44% in females and 10-50% in males. Likewise, estimates of the magnitude of the genetic correlation, whilst in all cases significantly greater than zero, ranged from 0.42-1.00 in females and 0.45-1.00 in males under different models.

Alcohol sensitivity and dependence

The relationship between the intensity of response to alcohol and the future development of alcohol abuse or dependence was evaluated in 454 18- to 25-year-old drinking but not alcohol dependent subjects. This sample consisted of sons of alcohol dependent fathers and family history negative controls matched on demography as well as alcohol and substance use histories. In response to an alcohol challenge at approximately age 20, 40% of the sons of alcoholics but less than 10% of the controls demonstrated less alcohol-related changes in subjective feelings, physiological measures, and motor performance. An average of 9.3 years later, a successful follow-up of 100% of the first 223 individuals revealed that the diminished response to alcohol was a potent predictor of future alcohol abuse or dependence. Neither the family history of alcoholism nor the intensity of response to alcohol at age 20 predicted drug dependence or major psychiatric disorders during the follow-up period.

Postural sway in children from pedigrees exhibiting a high density of alcoholism

A total of 98 children participated in a study of the neurobehavioral characteristics of individuals from pedigrees in which there was a high density of alcoholism. Two groups of children were evaluated (High and Low Risk) using a sensitive movement platform and a variety of methods to challenge the motor system. High-Risk children showed a greater decrement in postural steadiness when visual input was removed than did Low-Risk children. Additionally, the monopedal stances revealed hemispheric differences in postural sway as a function of risk status. The amount of sway exhibited was correlated with the latency of P300 recorded using a visual task. Both appear to be indicators of neuropathological changes. The present results suggest that postural sway may be a neurobehavioral marker for alcoholism risk.

Does psychomotor sensitivity to alcohol predict subsequent alcohol use?

Data from 42 male and 58 female subjects who participated in the Colorado Alcohol Research on Twins and Adoptees (CARTA) project were subjected to model-fitting analyses. The aim of the present study was to use linear structural equation models to determine whether differences in previously measured psychomotor sensitivity to alcohol predict differences in self-reported alcohol consumption over a 4-year period. LISREL model-fitting results indicate that, for male subjects, only rail walking insensitivity is predictive of alcohol use reported 2 years after their initial CARTA testing. For females, only hand steadiness sensitivity is predictive of alcohol use reported 2 years after their initial CARTA testing. The results for males support a hypothesis that would consider alcohol insensitive individuals at greater risk for alcohol abuse. The female results, however, would argue against such a hypothesis. With only one measure of sensitivity predicting alcohol use at only one out of four time points, in both men and women, the overall results suggest that our three measures of psychomotor sensitivity to alcohol are, in general, poor predictors of alcohol consumption in this sample.

Testing hypotheses about direction of causation using cross-sectional family data

We review the conditions under which cross-sectional family data (e.g., data on twin pairs or adoptees and their adoptive and biological relatives) are informative about direction of causation. When two correlated traits have rather different modes of inheritance (e.g., family resemblance is determined largely by family background for one trait and by genetic factors for the other trait), cross-sectional family data will allow tests of strong unidirectional causal hypotheses (A and B are correlated "because of the causal influence of A on B" versus "because of the causal influence of B on A") and, under some conditions, also of the hypothesis of reciprocal causation. Possible sources of errors of inference are considered. Power analyses are reported which suggest that multiple indicator variables will be needed to ensure adequate power of rejecting false models in the presence of realistic levels of measurement error. These methods may prove useful in cases where conventional methods to establish causality, by intervention, by prospective study, or by measurement of instrumental variables, are unfeasible economically, ethically or practically.

Genetic models for the natural history of smoking: evidence for a genetic influence on smoking persistence

We reanalyze data from the 1981 mailed questionnaire survey of the Australian twin register, to test for a genetic effect on smoking persistence (whether or not a smoker quits smoking). In the young cohort, aged 18-30 years, there are too few ex-smokers to permit resolution of genetic and non-genetic models. In the older cohort, we find a significant and substantial genetic effect on smoking persistence, accounting for 53% of the variance. This genetic effect on smoking persistence is independent of genetic effects on smoking initiation.

Intoxication after an acute dose of alcohol: an assessment of its association with alcohol consumption patterns by using twin data

We examined the hypothesis that genetically determined differences in sensitivity to alcohol explain some of the genetic variation in alcohol consumption pattern. Self-report data on average weekly alcohol consumption and self-ratings of intoxication after a standard dose of ethanol (0.75 g/kg body weight), used as an index of sensitivity, were obtained on 206 Australian twin pairs. Significant genetic covariance between weekly consumption and level of intoxication after alcohol intake was found in males, lower ratings of intoxication being associated with increased consumption. However, when direction of causation models were fitted to the male twin data, the hypothesis that decreased sensitivity was a cause of increased consumption was rejected. The major causal effect was that of weekly consumption on level of sensitivity. A similar, although nonsignificant, trend was observed in females. The strength of the association between self-report of average weekly consumption and level of intoxication after a standard dose of alcohol supports the validity of the former measure.

The effects of age, sex, and genotype on self-report drunkenness following a challenge dose of alcohol

Age is a potential source of variation that contributes to differences between, but not within, twin pairs. In most genetic analyses of twin data, linear and other functions of age are usually removed prior to model fitting. This correction is typically applied only within twin groups of the same sex and zygosity, and no heterogeneity test of age regressions is performed. Here we include age as a variable in the model-fitting procedure and allow for tests of heterogeneity of age regressions across sex and zygosity groups. The LISREL formulation of the approach is illustrated with data collected from Australian twins on subjective impressions of drunkenness following alcohol consumption. The results indicate significant negative covariation of impressions of drunkenness with age. The data support a simple model of additive genetic and unique environmental variation. No evidence was found for sex differences in genetic or environmental components of variation.

Willingness to drive when drunk and personality: a twin study

In a laboratory study of psychomotor sensitivity to alcohol, twins were asked "Would you drive a car now?" at 1, 2, and 3 h after drinking a standard dose of ethanol (0.75 g/kg). Correlations among these binary items, the Eysenck personality scales, and age were investigated using PRELIS and LISREL. Willingness to drive and Extraversion correlate at all three times in both males and females. In males, willingness to drive also correlates with Psychoticism, and in females it correlates negatively with the Lie (or Social Desirability) scale. Most correlations between cotwins in willingness to drive were significant in both monozygotic (MZ) and dizygotic (DZ) male twins but correlations were lower in female twins. Factor and Markovian models were fitted. In males there seem to be both genetic and cultural influences on willingness to drive when drunk. About half the genetic variance seems to be the pleiotropic effects of genes influencing Extraversion. The correlations with Psychoticism, on the other hand, seem to be largely environmental in origin. The small sample size and lack of proper significance tests mean that these results must be interpreted with caution.