Mood-related drinking motives mediate the familial association between major depression and alcohol dependence

BACKGROUND

Major depression and alcohol dependence co-occur within individuals and families to a higher than expected degree. This study investigated whether mood-related drinking motives mediate the association between major depression and alcohol dependence, and what the genetic and environmental bases are for this relationship.

METHODS

The sample included 5,181 individuals from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, aged 30 and older. Participants completed a clinical interview which assessed lifetime major depression, alcohol dependence, and mood-related drinking motives.

RESULTS

Mood-related drinking motives significantly explained the depression-alcohol dependence relationship at both the phenotypic and familial levels. Results from twin analyses indicated that for both males and females, the familial factors underlying mood-related drinking motives accounted for virtually all of the familial variance that overlaps between depression and alcohol dependence.

CONCLUSIONS

The results are consistent with an indirect role for mood-related drinking motives in the etiology of depression and alcohol dependence, and suggest that mood-related drinking motives may be a useful index of vulnerability for these conditions.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Predictors of illicit substance dependence among individuals with alcohol dependence

OBJECTIVE

Individuals with alcohol dependence (AD) are at increased risk for developing dependence on illicit and prescription drugs. The goal of this cross-sectional study was to identify factors associated with drug dependence among individuals with AD.

METHOD

The sample consisted of 855 adults from the Irish Affected Sib Pair Study of Alcohol Dependence who were treated in inpatient or outpatient alcohol treatment programs and met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria for lifetime AD. We studied predictors of dependence on six classes of drugs: cannabis, sedatives, stimulants, cocaine, opioids, and hallucinogens. Potential predictors examined included gender, age, education, and socioeconomic status; the personality traits of extraversion, neuroticism, and novelty seeking; conduct disorder, major depressive disorder, nicotine dependence, age at onset of alcohol use, early illicit drug use, and parental AD.

RESULTS

Nicotine dependence, depression that began before substance use, and drug use before age 19 each increased the risk for dependence on several substance classes. Male gender, younger age, maternal AD, fewer years of education, higher neuroticism scores, conduct disorder, and early alcohol use each increased the risk of dependence on one or more substance classes.

CONCLUSIONS

Among individuals in treatment for AD, cigarette smoking, early onset of major depression, and early drug use were associated with increased risk for drug dependence. These results suggest individuals with these risk factors may benefit from more intensive screening to prevent the onset of or to identify and treat drug dependence.

Using a factor mixture modeling approach in alcohol dependence in a general population sample

Alcohol dependence (AD) is a complex and heterogeneous disorder. The identification of more homogeneous subgroups of individuals with drinking problems and the refinement of the diagnostic criteria are inter-related research goals. They have the potential to improve our knowledge of etiology and treatment effects, and to assist in the identification of risk factors or specific genetic factors. Mixture modeling has advantages over traditional modeling that focuses on either the dimensional or categorical latent structure. The mixture modeling combines both latent class and latent trait models, but has not been widely applied in substance use research. The goal of the present study is to assess whether the AD criteria in the population could be better characterized by a continuous dimension, a few discrete subgroups, or a combination of the two. More than seven thousand participants were recruited from the population-based Virginia Twin Registry, and were interviewed to obtain DSM-IV (Diagnostic and Statistical Manual of Mental Disorder, version IV) symptoms and diagnosis of AD. We applied factor analysis, latent class analysis, and factor mixture models for symptom items based on the DSM-IV criteria. Our results showed that a mixture model with 1 factor and 3 classes for both genders fit well. The 3 classes were a non-problem drinking group and severe and moderate drinking problem groups. By contrast, models constrained to conform to DSM-IV diagnostic criteria were rejected by model fitting indices providing empirical evidence for heterogeneity in the AD diagnosis. Classification analysis showed different characteristics across subgroups, including alcohol-caused behavioral problems, comorbid disorders, age at onset for alcohol-related milestones, and personality. Clinically, the expanded classification of AD may aid in identifying suitable treatments, interventions and additional sources of comorbidity based on these more homogenous subgroups of alcohol use problems.

Genetic and environmental influences on alcohol, caffeine, cannabis, and nicotine use from early adolescence to middle adulthood

CONTEXT

While both environmental and genetic factors are important in the etiology of psychoactive substance use (PSU), we know little of how these influences differ through development.

OBJECTIVE

To clarify the changing role of genes and environment in PSU from early adolescence through middle adulthood.

DESIGN

Retrospective assessment by life history calendar, with univariate and bivariate structural modeling.

SETTING

General community.

PARTICIPANTS

A total of 1796 members of male-male pairs from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders.

MAIN OUTCOME MEASURES

Levels of use of alcohol, caffeine, cannabis, and nicotine recorded for every year of the respondent's life.

RESULTS

For nicotine, alcohol, and cannabis, familial environmental factors were critical in influencing use in early adolescence and gradually declined in importance through young adulthood. Genetic factors, by contrast, had little or no influence on PSU in early adolescence and gradually increased in their effect with increasing age. The sources of individual differences in caffeine use changed much more modestly over time. Substantial correlations were seen among levels of cannabis, nicotine, and alcohol use and specifically between caffeine and nicotine. In adolescence, those correlations were strongly influenced by shared effects from the familial environment. However, as individuals aged, more and more of the correlation in PSU resulted from genetic factors that influenced use of both substances.

CONCLUSIONS

These results support an etiologic model for individual differences in PSU in which initiation and early patterns of use are strongly influenced by social and familial environmental factors while later levels of use are strongly influenced by genetic factors. The substantial correlations seen in levels of PSU across substances are largely the result of social environmental factors in adolescence, with genetic factors becoming progressively more important through early and middle adulthood.

Association of ADH and ALDH genes with alcohol dependence in the Irish Affected Sib Pair Study of alcohol dependence (IASPSAD) sample

BACKGROUND

The genes coding for ethanol metabolism enzymes [alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH)] have been widely studied for their influence on the risk to develop alcohol dependence (AD). However, the relation between polymorphisms of these metabolism genes and AD in Caucasian subjects has not been clearly established. The present study examined evidence for the association of alcohol metabolism genes with AD in the Irish Affected Sib Pair Study of alcohol dependence.

METHODS

We conducted a case-control association study with 575 independent subjects who met Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, AD diagnosis and 530 controls. A total of 77 single nucleotide polymorphisms (SNPs) in the seven ADH (ADH1-7) and two ALDH genes (ALDH1A1 and ALDH2) were genotyped using the Illumina GoldenGate protocols. Several statistical procedures were implemented to control for false discoveries.

RESULTS

All markers with minor allele frequency greater than 0.01 were in Hardy-Weinberg equilibrium. Numerous SNPs in ADH genes showed association with AD, including one marker in the coding region of ADH1C (rs1693482 in exon6, Ile271Gln). Haplotypic association was observed in the ADH5 and ADH1C genes, and in a long haplotype block formed by the ADH1A and ADH1B loci. We detected two significant interactions between pairs of markers in intron 6 of ADH6 and intron 12 of ALDH2 (p = 5 x 10(-5)), and 5' of both ADH4 and ADH1A (p = 2 x 10(-4)).

CONCLUSION

We found evidence for the association of several ADH genes with AD in a sample of Western European origin. The significant interaction effects between markers in ADH and ALDH genes suggest possible epistatic roles between alcohol metabolic enzymes in the risk for AD.

Genomewide linkage survey of nicotine dependence phenotypes

BACKGROUND

A comprehensive understanding of the etiology and neurobiology of nicotine dependence is not available. We sought to identify genomic regions that might contain etiologically-relevant loci using genomewide univariate and bivariate linkage analyses.

METHODS

We conducted secondary data analyses of 626 all possible sibling pairs ascertained in Ireland and Northern Ireland on the basis of alcohol dependence. A set of 1020 short tandem repeat genetic markers were genotyped in all subjects. The phenotypes analyzed were the Fagerström Test for Nicotine Dependence (FTND), a history of nicotine dependence, the number of symptoms of alcohol dependence (AlcSx), and a history of alcohol dependence. Genomewide linkage analyses were conducted with non-parametric and variance components methods.

FINDINGS

For the bivariate variance component analysis of the continuous FTND and AlcSx scores, multipoint LOD scores were >4 in two genomic regions--an 11cM region on chr7 (D7S2252-D7S691, empirical p=0.0006) and an 8cM region on chr18 flanking D18S63 (empirical p=0.0007). These findings did not exceed a conservative estimate of study-wide significance. The remaining sets of findings had considerably smaller or less consistent peak signals. Notably, strong linkage signal at D4S1611 for AlcSx from a prior report (PMID 16534506) was not found when jointly analyzed with FTND.

INTERPRETATION

Replication is required. However, chromosomes 7 and 18 may contain genetic loci relevant to the etiology of nicotine-related phenotypes.

Low extraversion and high neuroticism as indices of genetic and environmental risk for social phobia, agoraphobia, and animal phobia

OBJECTIVE

The authors examined the extent to which two major personality dimensions (extraversion and neuroticism) index the genetic and environmental risk for three phobias (social phobia, agoraphobia, and animal phobia) in twins ascertained from a large, population-based registry.

METHOD

Lifetime phobias and personality traits were assessed through diagnostic interview and self-report questionnaire, respectively, in 7,800 twins from female-female, male-male, and opposite-sex pairs. Sex-limited trivariate Cholesky structural equation models were used to decompose the correlations among extraversion, neuroticism, and each phobia.

RESULTS

In the best-fitting models, genetic correlations were moderate and negative between extraversion and both social phobia and agoraphobia, and that between extraversion and animal phobia was effectively zero. Genetic correlations were high and positive between neuroticism and both social phobia and agoraphobia, and that between neuroticism and animal phobia was moderate. All of the genetic risk factors for social phobia and agoraphobia were shared with those that influence extraversion and neuroticism; in contrast, only a small proportion of the genetic risk factors for animal phobia (16%) was shared with those that influence personality. Shared environmental experiences were not a source of correlations between personality traits and phobias, and unique environmental correlations were relatively modest.

CONCLUSION

Genetic factors that influence individual variation in extraversion and neuroticism appear to account entirely for the genetic liability to social phobia and agoraphobia, but not animal phobia. These findings underline the importance of both introversion (low extraversion) and neuroticism in some psychiatric disorders.

Creating a social world: a developmental twin study of peer-group deviance

CONTEXT

Peer-group deviance is strongly associated with externalizing behaviors. We have limited knowledge of the sources of individual differences in peer-group deviance.

OBJECTIVE

To clarify genetic and environmental contributions to peer-group deviance in twins from midchildhood through early adulthood.

DESIGN

Retrospective assessments using a life-history calendar. Analysis by biometric growth curves.

SETTING

General community.

PARTICIPANTS

Members of male-male pairs from the population-based Virginia Twin Registry personally interviewed in 1998-2004 (n = 1802).

MAIN OUTCOME MEASURE

Self-reported peer-group deviance at ages 8 to 11, 12 to 14, 15 to 17, 18 to 21, and 22 to 25 years.

RESULTS

Mean and variance of peer-group deviance increased substantially with age. Genetic effects on peer-group deviance showed a strong and steady increase over time. Family environment generally declined in importance over time. Individual-specific environmental influences on peer-group deviance levels were stable in the first 3 age periods and then increased as most twins left home. When standardized, the heritability of peer-group deviance is approximately 30% at ages 8 to 11 years and rises to approximately 50% across the last 3 time periods. Both genes and shared environment contributed to individual differences in the developmental trajectory of peer-group deviance. However, while the correlation between childhood peer-group deviance levels and the subsequent slope of peer-group deviance over time resulting from genetic factors was positive, the same relationship resulting from shared environmental factors was negative.

CONCLUSIONS

As male twins mature and create their own social worlds, genetic factors play an increasingly important role in their choice of peers, while shared environment becomes less influential. The individual-specific environment increases in importance when individuals leave home. Individuals who have deviant peers in childhood, as a result of genetic vs shared environmental influences, have distinct developmental trajectories. Understanding the risk factors for peer-group deviance will help clarify the etiology of a range of externalizing psychopathology.

Longitudinal modeling of genetic and environmental influences on self-reported availability of psychoactive substances: alcohol, cigarettes, marijuana, cocaine and stimulants

BACKGROUND

Although an obvious environmental factor influencing drug use, the sources of individual differences in drug availability (DA) are unknown.

METHOD

This report is based on 1788 adult males from the Mid-Atlantic Twin Registry who participated in a structured telephone interview that included retrospective assessments of DA (cigarette, alcohol, marijuana, cocaine and stimulants) between ages 8 and 25. We fitted a biometric dual change score (DCS) model, adapted for ordinal data, to model latent growth and estimate the genetic and environmental components of variance over time.

RESULTS

DA, despite being considered an environmental risk factor, is under both genetic and environmental control. For cigarette, alcohol, marijuana and cocaine availability, there was an overall increase in additive genetic variance and a decline in shared environmental variance over time. Non-shared environmental variance remained steady. Stimulant availability did not follow this pattern. Instead, there was an upswing in shared environmental effects with increasing age.

CONCLUSION

We have modeled the genetic and environmental architecture of changes in DA across adolescence. The rise in additive genetic variance over time coincides with acceleration in the expression of individual differences, probably brought on by an increase in personal freedom and a reduction in social constraints. Understanding the etiology of DA is likely to reveal key components, acting directly or indirectly, in the pathway(s) leading to drug initiation, abuse and dependence.

A genome-wide linkage analysis for the personality trait neuroticism in the Irish affected sib-pair study of alcohol dependence

Neuroticism is a personality trait which reflects individual differences in emotional stability and vulnerability to stress and anxiety. Consistent evidence shows substantial genetic influences on variation in this trait. The present study seeks to identify regions containing susceptibility loci for neuroticism using a selected sib-pair sample from Ireland. Using Merlin regress, we conducted a 4 cM whole-genome linkage analysis on 714 sib-pairs. Evidence for linkage to neuroticism was found on chromosomes 11p, 12q, and 15q. The highest linkage peak was on 12q at marker D12S1638 with a Lod score of 2.13 (-log p = 2.76, empirical P-value <0.001). Our data also support gender specific loci for neuroticism, with male specific linkage regions on chromosomes 1, 4, 11, 12, 15, 16, and 22, and female specific linkage regions on chromosomes 2, 4, 9, 12, 13, and 18. Some genome regions reported in the present study replicate findings from previous linkage studies of neuroticism. These results, together with prior studies, indicate several potential regions for quantitative trait loci for neuroticism that warrant further study.

Factor and item-response analysis DSM-IV criteria for abuse of and dependence on cannabis, cocaine, hallucinogens, sedatives, stimulants and opioids

AIMS

This paper explored, in a population-based sample of males, the factorial structure of criteria for substance abuse and dependence, and compared qualitatively the performance of these criteria across drug categories using item-response theory (IRT).

DESIGN

Marginal maximum likelihood was used to explore the factor structure of criteria within drug classes, and a two-parameter IRT model was used to determine how the difficulty and discrimination of individual criteria differ across drug classes.

PARTICIPANTS

A total of 4234 males born from 1940 to 1974 from the population-based Virginia Twin Registry were approached to participate.

MEASUREMENTS

DSM-IV drug use, abuse and dependence criteria for cannabis, sedatives, stimulants, cocaine and opiates.

FINDINGS

For each drug class, the pattern of endorsement of individual criteria for abuse and dependence, conditioned on initiation and use, could be best explained by a single factor. There were large differences in individual item performance across substances in terms of item difficulty and discrimination. Cocaine users were more likely to have encountered legal, social, physical and psychological consequences.

CONCLUSIONS

The DSM-IV abuse and dependence criteria, within each drug class, are not distinct but best described in terms of a single underlying continuum of risk. Because individual criteria performed very differently across substances in IRT analyses, the assumption that these items are measuring equivalent levels of severity or liability with the same discrimination across different substances is unsustainable. Compared to other drugs, cocaine usage is associated with more detrimental effects and negative consequences, whereas the effects of cannabis and hallucinogens appear to be less harmful. Implications for other drug classes 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.

Lifestyle risk and delaying factors

Research findings suggest that dementia risk is lower in individuals with more extensive education, greater engagement in mentally stimulating leisure activities during adulthood, and higher occupational complexity. Other recent findings support the importance of early-life risk factors, such as socioeconomic conditions, early-life development, and exposure to infection, in explaining individual differences in dementia risk. Life-style variables have been conceptualized as delaying factors, postponing onset of dementia and thereby reducing total population burden of dementia. Using a sample of Swedish twins from the HARMONY study, we found that education significantly affects dementia onset, that is, occurrence and timing of dementia symptoms. In the HARMONY data, we also showed that differences in education are reflected in differences in leisure activities and occupation, suggesting that differences in cognitive engagement begin early and persist over the life course. Such findings point to the importance of taking a life-course perspective to designing interventions to delay or to prevent dementia.

Identification of Susceptibility Loci for Alcohol-Related Traits in the Irish Affected Sib Pair Study of Alcohol Dependence

BACKGROUND

Alcoholism is a phenotypically and probably genetically heterogeneous condition. Thus, one strategy for finding genes influencing liability to alcoholism is to study the components of alcoholism, which may be more directly related to the underlying pathophysiology than is clinical diagnosis. The goal of this study was to identify genomic regions containing susceptibility loci for alcohol-related traits.

METHODS

A 4-cM dense whole-genome linkage study was conducted in the Irish Affected Sib Pair Study of Alcohol Dependence. Probands, affected siblings, and parents were evaluated by structured interview. Variance component linkage analysis was applied to data from 485 families for 5 measures: initial sensitivity and tolerance (based on scales from the self-report of the effects of ethanol; maximum drinks within 24 hours, an empirically derived factor score based on withdrawal symptoms, and age at onset of alcohol dependence.

RESULTS

Evidence for linkage (p<0.005) was found on 9 chromosomes. For age at onset, 2 regions were found on chromosome 9 (highest Lod=2.3, p=0.0005). For initial level of response to alcohol, suggestive regions were on chromosomes 1 and 11 (highest Lod=2.9, p=0.0001 on chromosome 11), while those for tolerance signals were on chromosomes 1, 6, and 22. Maximum drinking was associated with regions on chromosomes 12 and 18. For withdrawal symptoms, the highest peak was on chromosome 2 (Lod=2.2, p=0.0007).

CONCLUSIONS

Using quantitative measures of components of alcohol dependence, we identified several regions of the genome that may contain susceptibility loci for specific alcohol-related traits and merit additional study.

Alcohol dependence is associated with the ZNF699 gene, a human locus related to Drosophila hangover, in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD) sample

Because tolerance is an important aspect of alcohol dependence (AD) in humans, recent evidence showing that the Drosophila gene hang is critically involved in the development of alcohol tolerance in the fly suggests that variation in related human loci might be important in the etiology of alcohol-related disorders. The orthology of hang in mammals is complex, but a number of human gene products (including ZNF699) with similar levels of amino-acid identity (18-26%) and similarity (30-41%), are consistently identified as the best matches with the translated hang sequence. We tested for association between the dichotomous clinical phenotype of alcohol dependence and seven single nucleotide polymorphisms (SNPs) in ZNF699 in our sample of 565 genetically independent cases and 496 siblings diagnosed with AD, and 609 controls. In analyses of genetically independent cases and controls, four of the seven single markers show strong evidence for association with AD (0.00003<Fisher's exact P<0.001), and the most significant single marker, rs7254880, tags an associated haplotype with frequency 0.071 in cases compared to 0.034 in controls (chi2 15.563, P<0.00008, 5000 permutation P<0.001, OR 2.17); inclusion of affected siblings gives similar results. Expression analyses conducted in independent postmortem brain samples show that expression of ZNF699 mRNA is significantly reduced in the dorsolateral prefrontal cortex of individuals carrying this haplotype compared with other observed haplotype combinations.

A Joint Genomewide Linkage Analysis of Symptoms of Alcohol Dependence and Conduct Disorder

BACKGROUND

A large linkage peak for alcohol dependence (AD) was detected on chromosome 4q in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD). Are the susceptibility genes underlying this peak specific for AD or do they increase risk for externalizing disorders more generally? Can we, in the IASPSAD, replicate prior evidence for linkage to conduct disorder (CD)?

METHODS

The 733 all possible sibling pairs in IASPSAD were typed for 1,020 short-tandem-repeat genetic markers. Univariate and bivariate linkage analyses were conducted by the program sequential oligogenic linkage analysis routines (SOLAR), for both the raw and the transformed number of symptoms of AD (ADsx) and number of symptoms of CD (CDsx). In the bivariate analyses, specificity was assessed by the ratio of the variance accounted for in ADsx and CDsx by the quantitative trait locus.

RESULTS

In the univariate linkage analyses, no evidence for linkage to CDsx was found under the 4q peak for ADsx and the largest peaks for CDsx were seen on chromosomes 1q (LOD=3.16) and 14p (LOD=2.36). In the bivariate linkage analysis, the 4q peak had high specificity for AD (AD/CD ratio of 39.9). Several smaller peaks, on chromosomes 1, 7, and 10, had moderate specificity for CD but also impacted on risk for AD, with AD/CD ratios of 0.18 to 0.32.

CONCLUSIONS

Genes under the 4q linkage peak for AD in the IASPSAD impact specifically on risk for AD rather than more broadly on risk for externalizing syndromes. Suggestive linkages were found in several locations for CD, 2 of which broadly replicate prior findings. The bivariate analyses identified genomic locations containing susceptibility loci that impacted on risk for both CDsx and ADsx.

The temporal relationship of the onsets of alcohol dependence and major depression: using a genetically informative study design

BACKGROUND

Although alcohol dependence (AD) and major depression (MD) are highly co-morbid, their causal relationship is unclear. In this longitudinal study, we used a genetically informative population-based twin sample to examine the age-at-onset distributions and the temporal relationship of AD and MD.

METHOD

Our sample included 7477 twins, whose diagnoses of AD and MD and age-at-onset information were obtained from structured interviews. Individual-level survival analyses were conducted based on 2603 monozygotic (MZ) twins, and co-twin diagnosis was included in models as an index of familiar liability to AD and MD.

RESULTS

The age-at-onset distributions of AD and MD differed substantially. Most onsets of AD were in young adulthood, whereas MD had a flatter distribution across age. Most subjects, especially women, had an onset of MD preceding AD. Prior MD significantly affected risk for developing AD, and this risk decreased over time. By contrast, preceding AD had negligible effects on the risk for future MD. Familial risk was transmitted within disorders but there was little evidence of additional familial liability shared across disorders.

CONCLUSIONS

Risk for developing AD was substantially increased by a prior episode of MD. The association was only partially accounted for by familial factors, providing support for a direct causal effect such as self-medication. The etiologic path from AD to MD was insignificant.

The impact of generalized anxiety disorder and stressful life events on risk for major depressive episodes

BACKGROUND

Both generalized anxiety disorder (GAD) and stressful life events (SLEs) are established risk factors for major depressive disorder, but no studies exist that examine the interrelationship of their impact on depressive onsets. In this study, we sought to analyze the joint effects of prior history of GAD and recent SLEs on risk for major depressive episodes, comparing these in men and women.

METHOD

In a population-based sample of 8068 adult twins, Cox proportional hazard models were used to predict onsets of major depression from reported prior GAD and last-year SLEs rated on long-term contextual threat.

RESULTS

For all levels of threat, prior GAD increases risk for depression, with a monotonic relationship between threat level and risk. While females without prior GAD consistently show higher depressive risk than males, this is no longer the case in subjects with prior GAD who have experienced SLEs. Rather, males appear to be more vulnerable to the depressogenic effects of both prior GAD and SLEs.

CONCLUSION

The effects of prior GAD and SLEs jointly increase the risk of depression in both sexes, but disproportionately so in males.

Genomewide linkage study in the Irish affected sib pair study of alcohol dependence: evidence for a susceptibility region for symptoms of alcohol dependence on chromosome 4

Alcoholism is a relatively common, chronic, disabling and often treatment-resistant disorder. Evidence from twin and adoption studies indicates a substantial genetic influence, with heritability estimates of 50-60%. We conducted a genome scan in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD). Most probands were ascertained through alcoholism treatment settings and were severely affected. Probands, affected siblings and parents were evaluated by structured interview. A 4 cM genome scan was conducted using 474 families of which most (96%) were comprised by affected sib pairs. Nonparametric and quantitative linkage analyses were conducted using DSM-IV alcohol dependence (AD) and number of DSM-IV AD symptoms (ADSX). Quantitative results indicate strong linkage for number of AD criteria to a broad region of chromosome 4, ranging from 4q22 to 4q32 (peak multipoint LOD=4.59, P=2.1 x 10(-6), at D4S1611). Follow-up analyses suggest that the linkage may be due to variation in the symptoms of tolerance and out of control drinking. There was evidence of weak linkage (LODs of 1.0-2.0) to several other regions, including 1q44, 13q31, and 22q11 for AD along with 2q37, 9q21, 9q34 and 18p11 for ADSX. The location of the chromosome 4 peak is consistent with results from prior linkage studies and includes the alcohol dehydrogenase gene cluster. The results of this study suggest the importance of genetic variation in chromosome 4 in the etiology and severity of alcoholism in Caucasian populations.

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.

A population-based twin study of the relationship between neuroticism and internalizing disorders

OBJECTIVE

The anxiety and depressive disorders exhibit high levels of lifetime comorbidity with one another. The authors examined how genetic and environmental factors shared by the personality trait neuroticism and seven internalizing disorders may help explain this comorbidity.

METHOD

Lifetime major depression, generalized anxiety disorder, panic disorder, agoraphobia, social phobia, animal phobia, situational phobia, and neuroticism were assessed in over 9,000 twins from male-male, female-female, and opposite-sex pairs through structured diagnostic interviews. Multivariate structural equation models were used to decompose the correlations between these phenotypes into genetic and environmental components, allowing for sex-specific factors.

RESULTS

Genetic factors shared with neuroticism accounted for between one-third and one-half of the genetic risk across the internalizing disorders. When nonsignificant gender differences were removed from the models, the genetic correlations between neuroticism and each disorder were high, while individual-specific environmental correlations were substantially lower. In addition, the authors could identify a neuroticism-independent genetic factor that significantly increased risk for major depression, generalized anxiety disorder, and panic disorder.

CONCLUSIONS

There is substantial, but not complete, overlap between the genetic factors that influence individual variation in neuroticism and those that increase liability across the internalizing disorders, helping to explain the high rates of comorbidity among the latter. This may have important implications for identifying the susceptibility genes for these conditions.

Effects of genetic and procedural variation on measurement of alcohol sensitivity in mouse inbred strains

Mice from eight inbred strains were studied for their acute sensitivity to ethanol as indexed by the degree of hypothermia (HT), indexed as the reduction from pre-injection baseline of their body temperature. Two weeks later, mice were tested for their loss of righting reflex (LRR) after a higher dose of ethanol. The LRR was tested using the "classical" method of watching for recovery in animals placed on their backs in a V-shaped trough and recording duration of LRR. In a separate test, naive animals of the same strains were tested for HT repeatedly to assess the development of rapid (RTOL) and chronic tolerance (CTOL). We have recently developed a new method for testing LRR that leads to a substantial increase in the sensitivity of the test. Strains also have been found to differ in the new LRR test, as well as in the development of acute functional tolerance (AFT) to this response. In addition, our laboratory has periodically published strain difference data on the older versions of the HT and LRR responses. The earlier tests used some of the exact substrains tested currently, while for some strains, different substrains (usually, Nih versus Jax) were tested. We examined correlations of strain means to see whether patterns of strain differences were stable across time and across different test variants assessing the same behavioral construct. HT strain sensitivity scores were generally highly correlated across a 10-23 years period and test variants. The CTOL to HT was well-correlated across studies, and was also genetically similar to RTOL. The AFT, however, was related to neither RTOL nor CTOL, although this may be because different phenotypic end points were compared. The LRR data, which included a variant of the classical test, were not as stable. Measures of LRR onset were reasonably well correlated, as were those taken at recovery (e.g., duration). However, the two types of measures of LRR sensitivity to ethanol appear to be tapping traits that differ genetically. Also, the pattern of genetic correlation between HT and LRR initially reported in 1983 was not seen in current and contemporaneous studies. In certain instances, substrain seems to matter little, while in others, substrains differed a great deal. These data are generally encouraging about the stability of genetic differences.

Mixed-effects variance components models for biometric family analyses

Recent substantive research on biometric analyses of twin and family data has used both a biometric path analysis model (PAM) and a biometric variance components model (VCM). Methodological research on these same topics have suggested benefits of using linear structural equation model algorithms (SEMA) as well as mixed effect multilevel algorithms (MEMA). To better understand the potential similarities and differences among these approaches we first highlight the algebraic equivalence between the standard biometric PAM and the corresponding biometric VCM models for family data. Second, we demonstrate how several SEMA programs based on either the PAM or VCM approach produce equivalent estimates for all phenotypic and biometric parameters. Third, we show how the biometric VCM approach (but not the PAM approach) can be easily programmed using current MEMA programs (e.g., SAS PROC MIXED). We then expand the scope of these different approaches to include measured covariates, observed variable interactions and multiple relatives within each family. MEMA software is compared to SEMA software for programming complex models, including the flexibility of data input, treatment of missing data, inclusion of covariates, and ease of accommodating varying numbers of observations (per family or individual).