General cognitive ability in high school, attained education, occupational complexity, and dementia risk

INTRODUCTION

We address the extent to which adolescent cognition predicts dementia risk in later life, mediated by educational attainment and occupational complexity.

METHODS

Using data from Project Talent Aging Study (PTAS), we fitted two structural equation models to test whether adolescent cognition predicts cognitive impairment (CI) and Ascertain Dementia 8 (AD8) status simultaneously (NCognitive Assessment = 2477) and AD8 alone (NQuestionnaire = 6491) 60 years later, mediated by education and occupational complexity. Co-twin control analysis examined 82 discordant pairs for CI/AD8.

RESULTS

Education partially mediated the effect of adolescent cognition on CI in the cognitive assessment aample and AD8 in the questionnaire sample (Ps < 0.001). Within twin pairs, differences in adolescent cognition were small, but intrapair differences in education predicted CI status.

DISCUSSION

Adolescent cognition predicted dementia risk 60 years later, partially mediated through education. Educational attainment, but not occupational complexity, contributes to CI risk beyond its role as a mediator of adolescent cognition, further supported by the co-twin analyses.

HIGHLIGHTS

Project Talent Aging Study follows enrollees from high school for nearly 60 years. General cognitive ability in high school predicts later-life cognitive impairment. Low education is a risk partially due to its association with cognitive ability.

High school quality is associated with cognition 58 years later

We leveraged a unique school-based longitudinal cohort-the Project Talent Aging Study-to examine whether attending higher quality schools is associated with cognitive performance among older adults in the United States (mean age = 74.8). Participants (n = 2,289) completed telephone neurocognitive testing. Six indicators of high school quality, reported by principals at the time of schooling, were predictors of respondents' cognitive function 58 years later. To account for school-clustering, multilevel linear and logistic models were applied. We found that attending schools with a higher number of teachers with graduate training was the clearest predictor of later-life cognition, and school quality mattered especially for language abilities. Importantly, Black respondents (n = 239; 10.5 percentage) were disproportionately exposed to low quality high schools. Therefore, increased investment in schools, especially those that serve Black children, could be a powerful strategy to improve later life cognitive health among older adults in the United States.

Nature, Nurture, and the Meaning of Educational Attainment: Differences by Sex and Socioeconomic Status

Estimated heritability of educational attainment (EA) varies widely, from 23% to 80%, with growing evidence suggesting the degree to which genetic variation contributes to individual differences in EA is highly dependent upon situational factors. We aimed to decompose EA into influences attributable to genetic propensity and to environmental context and their interplay, while considering influences of rearing household economic status (HES) and sex. We use the Project Talent Twin and Sibling Study, drawn from the population-representative cohort of high school students assessed in 1960 and followed through 2014, to ages 68-72. Data from 3552 twins and siblings from 1741 families were analyzed using multilevel regression and multiple group structural equation models. Individuals from less-advantaged backgrounds had lower EA and less variation. Genetic variance accounted for 51% of the total variance, but within women and men, 40% and 58% of the total variance respectively. Men had stable genetic variance on EA across all HES strata, whereas high HES women showed the same level of genetic influence as men, and lower HES women had constrained genetic influence on EA. Unexpectedly, middle HES women showed the largest constraints in genetic influence on EA. Shared family environment appears to make an outsized contribution to greater variability for women in this middle stratum and whether they pursue more EA. Implications are that without considering early life opportunity, genetic studies on education may mischaracterize sex differences because education reflects different degrees of genetic and environmental influences for women and men.

A longitudinal study shows stress proliferation effects from early childhood adversity and recent stress on risk for depressive symptoms among older adults

Objectives: We evaluated whether the effects of recent stressful life events (SLEs) and early childhood adversities (ECAs) on depressive symptoms are consistent between men and women and across older age, and whether there was evidence for the following: stress sensitization, whereby the psychological impact of SLEs is greater for individuals with ECAs compared with those without; or stress proliferation effect, whereby those with ECAs are more likely to report more SLEs than those without ECAs to effect depressive symptoms.Method: ECAs, SLEs in the past two years, and current depressive symptoms through a modified CES-D were obtained from 11,873 individuals participating in a population representative study of older adults, yielding 82,764 observations. Mixed-effects regression models on depressive symptoms were constructed to control for multiple observations per participant and evaluate within-person effects over time, thereby reducing bias from reverse causation.Results: Results suggest a stress proliferation effect and do not support stress sensitization. ECAs contribute to vulnerability for depressive symptoms, with a dosage effect for each additional ECA. Recent SLEs result in greater depressive symptom risk, with stable effects over age and dosage effects for each additional SLE that were smaller than the effects of ECAs among men, but not women. Belonging to an ethnic minority group, having less education, and less household income at baseline were associated with greater depressive symptom risk.Conclusions: Findings suggest the importance of addressing early childhood adversity and sociodemographic factors, among at-risk older adults to mitigate life-course stress proliferative processes and thereby reduce disparate risk for depression in older age.

Financial strain moderates genetic influences on self-rated health: support for diathesis-stress model of gene-environment interplay

Data from the Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium were used to examine predictions of different models of gene-by-environment interaction to understand how genetic variance in self-rated health (SRH) varies at different levels of financial strain. A total of 11,359 individuals from 10 twin studies in Australia, Sweden, and the United States contributed relevant data, including 2,074 monozygotic and 2,623 dizygotic twin pairs. Age ranged from 22 to 98 years, with a mean age of 61.05 (SD = 13.24). A factor model was used to create a harmonized measure of financial strain across studies and items. Twin analyses of genetic and environmental variance for SRH incorporating age, age², sex, and financial strain moderators indicated significant financial strain moderation of genetic influences on self-rated health. Moderation results did not differ across sex or country. Genetic variance for SRH increased as financial strain increased, matching the predictions of the diathesis-stress and social comparison models for components of variance. Under these models, environmental improvements would be expected to reduce genetically based health disparities.

The Project Talent Twin and Sibling Study: Zygosity and New Data Collection

The Project Talent Twin and Sibling (PTTS) study includes 4481 multiples and their 522 nontwin siblings from 2233 families. The sample was drawn from Project Talent, a U.S. national longitudinal study of 377,000 individuals born 1942-1946, first assessed in 1960 and representative of U.S. students in secondary school (Grades 9-12). In addition to the twins and triplets, the 1960 dataset includes 84,000 siblings from 40,000 other families. This design is both genetically informative and unique in facilitating separation of the 'common' environment into three sources of variation: shared by all siblings within a family, specific to twin-pairs, and associated with school/community-level factors. We term this the GIFTS model for genetics, individual, family, twin, and school sources of variance. In our article published in a previous Twin Research and Human Genetics special issue, we described data collections conducted with the full Project Talent sample during 1960-1974, methods for the recent linking of siblings within families, identification of twins, and the design of a 54-year follow-up of the PTTS sample, when participants were 68-72 years old. In the current article, we summarize participation and data available from this 2014 collection, describe our method for assigning zygosity using survey responses and yearbook photographs, illustrate the GIFTS model applied to 1960 vocabulary scores from more than 80,000 adolescent twins, siblings and schoolmates and summarize the next wave of PTTS data collection being conducted as part of the larger Project Talent Aging Study.

IGEMS: The Consortium on Interplay of Genes and Environment Across Multiple Studies - An Update

The Interplay of Genes and Environment across Multiple Studies (IGEMS) is a consortium of 18 twin studies from 5 different countries (Sweden, Denmark, Finland, United States, and Australia) established to explore the nature of gene-environment (GE) interplay in functioning across the adult lifespan. Fifteen of the studies are longitudinal, with follow-up as long as 59 years after baseline. The combined data from over 76,000 participants aged 14-103 at intake (including over 10,000 monozygotic and over 17,000 dizygotic twin pairs) support two primary research emphases: (1) investigation of models of GE interplay of early life adversity, and social factors at micro and macro environmental levels and with diverse outcomes, including mortality, physical functioning and psychological functioning; and (2) improved understanding of risk and protective factors for dementia by incorporating unmeasured and measured genetic factors with a wide range of exposures measured in young adulthood, midlife and later life.

MEDIATORS OF GENETIC AND ENVIRONMENTAL MECHANISMS ON SELF-RATED HEALTH

Self-rated health (SRH), an individual’s assessment of their own health status, is associated with older adults’ chronic and acute health conditions, as well as mortality. Assessments of SRH indicate individual’s global health is likely multifaceted. Level of education, particularly amount of post-secondary schooling, is associated with better SRH. Other indices of socioeconomic status (SES) such as income and wealth, have varying associations with SRH partly dependent on relative deprivation (e.g. Gini Index). The current study utilized data from 2,500 members of the Project Talent Twin and Sibling (PTTS) Study interviewed as adolescents in 1960 and followed up 54 years later. In 2014, participants were, on average, 70 years of age. Women comprised about 54% of the sample. We examined rearing family wealth, years of education, and functional independence as mediators of variance in SRH. Mean-level results indicated small positive associations between SES and SRH. Activities of Daily Living (ADL) accounted for about a quarter of variance in SRH, with higher functional independence predicting better SRH. Biometric analyses indicated that family wealth had small mediation effects on SRH via familial-environment (S) influences. Education mediated individual-specific (E) environmental influences. Functional independence (measured by ADL) mediated SRH via both additive genetic (A) and E influences. After adjusting for overall effects of sex, age, and specified mediators, a large portion of remaining variation in SRH was due to individual-specific (E) environmental influences. Current results suggest complex underlying genetic and environmental mechanisms contributing to an older adult’s assessment of their own health.

Frailty Index associates with GRIN2B in two representative samples from the United States and the United Kingdom

The concept of frailty has been used in the clinical and research field for more than two decades. It is usually described as a clinical state of heightened vulnerability to poor resolution of homeostasis after a stressor event, which thereby increases the risk of adverse outcomes, including falls, delirium, disability and mortality. Here we report the results of the first genome-wide association scan and comparative gene ontology analyses where we aimed to identify genes and pathways associated with the deficit model of frailty. We used a discovery-replication design with two independent, nationally representative samples of older adults. The square-root transformed Frailty Index (FI) was the outcome variable, and age and sex were included as covariates. We report one hit exceeding genome-wide significance: the rs6765037 A allele was significantly associated with a decrease in the square-root transformed FI score in the Discovery sample (beta = -0.01958, p = 2.14E-08), without confirmation in the Replication sample. We also report a nominal replication: the rs7134291 A allele was significantly associated with a decrease in the square-root transformed FI score (Discovery sample: beta = -0.01021, p = 1.85E-06, Replication sample: beta = -0.005013, p = 0.03433). These hits represent the KBTBD12 and the GRIN2B genes, respectively. Comparative gene ontology analysis identified the pathways ‘Neuropathic pain signalling in dorsal horn neurons’ and the ‘GPCR-Mediated Nutrient Sensing in Enteroendocrine Cells’, exceeding the p = 0.01 significance in both samples, although this result does not survive correction for multiple testing. Considering the crucial role of GRIN2B in brain development, synaptic plasticity and cognition, this gene appears to be a potential candidate to play a role in frailty. In conclusion, we conducted genome-wide association scan and pathway analyses and have identified genes and pathways with potential roles in frailty. However, frailty is a complex condition. Therefore, further research is required to confirm our results and more thoroughly identify relevant biological mechanisms.

Genome-wide scan of depressive symptomatology in two representative cohorts in the United States and the United Kingdom

Unlike the diagnosed Major Depressive Disorder, depressive symptomatology in the general population has received less attention in genome-wide association scan (GWAS) studies. Here we report a GWAS study on depressive symptomatology using a discovery-replication design and the following approaches: To improve the robustness of the phenotypic measure, we used longitudinal data and calculated mean scores for at least 3 observations for each individual. To maximize replicability, we used nearly identical genotyping platforms and identically constructed phenotypic measures in both the Discovery and Replication samples. We report one genome-wide significant hit; rs58682566 in the EPG5 gene was associated (p = 3.25E-08) with the mean of the depression symptom in the Discovery sample, without confirmation in the Replication sample. We also report 4 hits exceeding the genome-wide suggestive significance level with nominal replications. Rs11774887, rs4147527 and rs1379328, close to the SAMD12 gene, were associated with the mean depression symptom score (P-values in Discovery sample: 4.58E-06, 7.65E-06 and 7.66E-06; Replication sample: 0.049, 0.029 and 0.030, respectively). Rs13250896, located in an intergenic region, was associated with the mean score of the three somatic items of the depression symptoms score (p = 3.31E-07 and 0.042 for the Discovery and Replication samples). These results were not supported by evidence in the literature. We conclude that despite the strengths of our approach, using robust phenotypic measures and samples that maximize replicability potential, this study does not provide compelling evidence of a single genetic variant's significant role in depressive symptomatology.

Genetic variants specific to aging-related verbal memory: Insights from GWASs in a population-based cohort

Verbal memory is typically studied using immediate recall (IR) and delayed recall (DR) scores, although DR is dependent on IR capability. Separating these components may be useful for deciphering the genetic variation in age-related memory abilities. This study was conducted to (a) construct individual trajectories in IR and independent aspects of delayed recall, or residualized-DR (rDR), across older adulthood; and (b) identify genetic markers that contribute to four estimated phenotypes: IR and rDR levels and changes after age 60. A cognitively intact sample (N = 20,650 with 125,164 observations) was drawn from the U.S. Health and Retirement Study, a nationally representative study of adults aged 50 and older. Mixed effects regression models were constructed using repeated measures from data collected every two years (1996–2012) to estimate level at age 60 and change in memory post-60 in IR and rDR. Genome-wide association scans (GWAS) were conducted in the genotypic subsample (N = 7,486) using ~1.2 million single nucleotide polymorphisms (SNPs). One SNP (rs2075650) in TOMM40 associated with rDR level at the genome-wide level (p = 5.0x10^-08), an effect that replicated in an independent sample from the English Longitudinal Study on Ageing (N = 6,898 with 41,328 observations). Meta-analysis of rDR level confirmed the association (p = 5.0x10^-11) and identified two others in TOMM40 (rs71352238 p = 1.0x10^-10; rs157582 p = 7.0x10^-09), and one in APOE (rs769449 p = 3.1 x10^-12). Meta-analysis of IR change identified associations with three of the same SNPs in TOMM40 (rs157582 p = 8.3x10^-10; rs71352238 p = 1.9x10^-09) and APOE (rs769449 p = 2.2x10^-08). Conditional analyses indicate GWAS signals on rDR level were driven by APOE, whereas signals on IR change were driven by TOMM40. Additionally, we found that TOMM40 had effects independent of APOE e4 on both phenotypes. Findings from this first U.S. population-based GWAS study conducted on both age-related immediate and delayed verbal memory merit continued examination in other samples and additional measures of verbal memory.

Genomewide Association Study of Alcohol Dependence Identifies Risk Loci Altering Ethanol-Response Behaviors in Model Organisms

BACKGROUND

Alcohol dependence (AD) shows evidence for genetic liability, but genes influencing risk remain largely unidentified.

METHODS

We conducted a genomewide association study in 706 related AD cases and 1,748 unscreened population controls from Ireland. We sought replication in 15,496 samples of European descent. We used model organisms (MOs) to assess the role of orthologous genes in ethanol (EtOH)-response behaviors. We tested 1 primate-specific gene for expression differences in case/control postmortem brain tissue.

RESULTS

We detected significant association in COL6A3 and suggestive association in 2 previously implicated loci, KLF12 and RYR3. None of these signals are significant in replication. A suggestive signal in the long noncoding RNA LOC339975 is significant in case:control meta-analysis, but not in a population sample. Knockdown of a COL6A3 ortholog in Caenorhabditis elegans reduced EtOH sensitivity. Col6a3 expression correlated with handling-induced convulsions in mice. Loss of function of the KLF12 ortholog in C. elegans impaired development of acute functional tolerance (AFT). Klf12 expression correlated with locomotor activation following EtOH injection in mice. Loss of function of the RYR3 ortholog reduced EtOH sensitivity in C. elegans and rapid tolerance in Drosophila. The ryanodine receptor antagonist dantrolene reduced motivation to self-administer EtOH in rats. Expression of LOC339975 does not differ between cases and controls but is reduced in carriers of the associated rs11726136 allele in nucleus accumbens (NAc).

CONCLUSIONS

We detect association between AD and COL6A3, KLF12, RYR3, and LOC339975. Despite nonreplication of COL6A3, KLF12, and RYR3 signals, orthologs of these genes influence behavioral response to EtOH in MOs, suggesting potential involvement in human EtOH response and AD liability. The associated LOC339975 allele may influence gene expression in human NAc. Although the functions of long noncoding RNAs are poorly understood, there is mounting evidence implicating these genes in multiple brain functions and disorders.

Latent classes of alcohol problems in Mauritian men: Results from the Joint Child Health Project

INTRODUCTION AND AIMS

The purpose of this study was to identify latent classes of alcohol problems and their sociodemographic correlates in the east African nation of Mauritius.

DESIGN AND METHODS

Participants were from the Joint Child Health Project, a longitudinal study of a 1969-1970 birth cohort of 1795 individuals. In mid-adulthood (M = 37 years), all available participants (n = 1206; 67% of the original cohort) were assessed for demographic characteristics, and lifetime drinkers were assessed for alcohol-related problems. Given the low endorsement of problems by women, only male lifetime drinkers (n = 520) were included in the latent class analyses.

RESULTS

Analyses indicated the best-fitting model contained four classes of drinkers: Non-problematic (66%), Moderate (16%), Hazardous (11%) and Severe (6%). Lower education and occupation were associated with Moderate and Severe problem classes, whereas higher education and occupation were associated with the Hazardous class. Being Hindu, Tamil and Creole were differentially predictive of class membership, but being Muslim was not.

DISCUSSION AND CONCLUSIONS

Our findings provide evidence of a distinct Hazardous drinking class that has unique demographic correlates and may represent a cluster of problems that is more bound by cultural factors. We also found problem classes on a severity continuum from none to moderate to severe problems. This study highlights the importance of examining societal, subgroup and person-level factors to produce a more nuanced understanding of distinct classes of alcohol-related problems. [Luczak SE, Prescott CA, Venables PH. Latent classes of alcohol problems in Mauritian men: Results from the Joint Child Health Project.

Anxiety trajectories in the second half of life: Genetic and environmental contributions over age

Clinically significant anxiety symptoms are prevalent among the elderly, yet knowledge about the longitudinal course of anxiety symptoms in later life remains scarce. The goals of this study were to (a) characterize age trajectories of state anxiety symptoms in the second half of life, and (b) estimate genetic and environmental contributions to individual differences in the age trajectory of state anxiety. This study was based on data from 1,482 participants in the Swedish Adoption/Twin Study of Aging who were aged 50 and older at their first occasion (512 complete twin pairs, 458 singletons) and had up to 6 measurement occasions spanning 11 years. Consistent with life span developmental theories of age-related emotional change, anxiety symptom levels declined during the transition from midlife to the mid-60s, followed by a mild increase that gradually plateaued in the 80s. There were substantial individual differences in the age trajectory of anxiety. After accounting for effects of sex, cohort, mode of testing, and proximity to death, this longitudinal variation was partitioned into biometric sources. Nonshared environmental variance was highest in the late 60s and declined thereafter, whereas genetic variance increased at an accelerated pace from approximately age 60 onward. There was no evidence for effects of rearing or other shared environment on anxiety symptoms in later life. These findings highlight how the etiology of anxiety symptoms changes from midlife to old age.

Effects of Recent Stress and Variation in the Serotonin Transporter Polymorphism (5-HTTLPR) on Depressive Symptoms: A Repeated-Measures Study of Adults Age 50 and Older

Depending on genetic sensitivity to it, stress may affect depressive symptomatology differentially. Applying the stress-diathesis hypothesis to older adults, we postulate: (1) recent stress will associate with increased depressive symptom levels and (2) this effect will be greater for individuals with at least one short allele of the serotonin transporter gene promoter region (5-HTTLPR). Further, we employ a design that addresses specific limitations of many prior studies that have examined the 5-HTTLPR × SLE relation, by: (a) using a within-person repeated-measures design to address fluctuations that occur within individuals over time, increase power for detecting G × E, and address GE correlation; (b) studying reports of exogenous stressful events (those unlikely to be caused by depression) to help rule out reverse causation and negativity bias, and in order to assess stressors that are more etiologically relevant to depressive symptomatology in older adults. The sample is drawn from the Health and Retirement Study, a U.S. population-based study of older individuals (N = 28,248; mean age = 67.5; 57.3 % female; 80.7 % Non-Hispanic White, 14.9 % Hispanic/Latino, 4.5 % African American; genetic subsample = 12,332), from whom measures of depressive symptoms and exogenous stressors were collected biannually (1994-2010). Variation in the 5-HTTLPR was characterized via haplotype, using two single nucleotide polymorphisms (SNPs). Ordered logit models were constructed to predict levels of depressive symptoms from 5-HTTLPR and stressors, comparing results of the most commonly applied statistical approaches (i.e., comparing allelic and genotypic models, and continuous and categorical predictors) used in the literature. All models were stratified by race/ethnicity. Overall, results show a main effect of recent stress for all ethnic groups, and mixed results for the variation in 5-HTTLPR × stress interaction, contingent upon statistical model used. Findings suggest there may be a differential effect of stressors and 5-HTTLPR on depressive symptoms by ethnicity, but further research is needed, particularly when using a haplotype to characterize variation in 5-HTTLPR in population-based sample with a diverse ethnic composition.

Contemporary Modeling of Gene × Environment Effects in Randomized Multivariate Longitudinal Studies

There is a great deal of interest in the analysis of Genotype × Environment interactions (G×E). There are some limitations in the typical models for the analysis of G×E, including well-known statistical problems in identifying interactions and unobserved heterogeneity of persons across groups. The impact of a treatment may depend on the level of an unobserved variable, and this variation may dampen the estimated impact of treatment. Some researchers have noted that genetic variation may sometimes account for unobserved, and hence unaccounted for, heterogeneity. The statistical power associated with the G×E design has been studied in many different ways, and most results show that the small effects expected require relatively large or nonrepresentative samples (i.e., extreme groups). In this article, we describe some alternative approaches, such as randomized designs with multiple measures, multiple groups, multiple occasions, and analyses, to identify latent (unobserved) classes of people. These approaches are illustrated with data from the Aging, Demographics, and Memory Study (part of the Health and Retirement Study) examining the relations among episodic memory (based on word recall), APOE4 genotype, and educational attainment (as a proxy for an environmental exposure). Randomized clinical trials (RCTs) and randomized field trials (RFTs) have multiple strengths in the estimation of causal influences, and we discuss how measured genotypes can be incorporated into these designs. Use of these contemporary modeling techniques often requires different kinds of data be collected and encourages the formation of parsimonious models with fewer overall parameters, allowing specific G×E hypotheses to be investigated with a reasonable statistical foundation.

Effects of ALDH2∗2 on alcohol problem trajectories of Asian American college students

The variant aldehyde dehydrogenase allele, ALDH2∗2, consistently has been associated with protection against alcohol dependence, but the mechanism underlying this process is not known. This study examined growth trajectories of alcohol consumption (frequency, average quantity, binge drinking, maximum drinks) and problems over the college years and then tested whether the ALDH2 genotype mediated or moderated the relationship between alcohol consumption and problems. Asian American college students (N = 433) reported on their drinking behavior in their first year of college and then annually for 3 consecutive years. Alcohol consumption and problems increased over the college years for both those with and without ALDH2∗2, but having an ALDH2∗2 allele was associated with less of an increase in problems over time. A mediation model was supported, with ALDH2∗2 group differences in problems fully accounted for by differences in frequency of binge drinking. Findings also supported a moderation hypothesis: All four alcohol consumption variables were significant predictors of subsequent alcohol problems, but these relationships were not as strong in those with ALDH2∗2 as in those without ALDH2∗2. Our findings suggest that the interplay between ALDH2∗2 and drinking-related problems is complex, involving both mediation and moderation processes that reduce the likelihood of developing problems via reduction of heavy drinking as well as by altering the relationship between alcohol consumption and problems. Results of this longitudinal study provide evidence that what seems like a relatively straightforward effect of a diminished ability to metabolize alcohol on drinking behavior is actually dependent on behavior and developmental stage.

Drinking experience uncovers genetic influences on alcohol expectancies across adolescence

AIMS

To test whether drinking onset moderates genetic and environmental contributions to individual differences in the etiology of alcohol expectancies across adolescence.

DESIGN

Longitudinal twin design.

SETTING

Community sample from Los Angeles, CA, USA.

PARTICIPANTS

A total of 1292 male and female twins, aged 11–18years, were assessed at 1 (n = 440), 2 (n = 587) or 3 (n = 265) occasions as part of the risk factors for the Antisocial Behavior Twin Study.

MEASUREMENTS

Social behavioral (SB) alcohol expectancies were measured using an abbreviated version of the Social Behavioral subscale from the Alcohol Expectancy Questionnaire for adolescents (AEQ-A). Drinking onset was defined as >1 full drink of alcohol.

FINDINGS

Alcohol expectancies increased over age and the increase became more rapid following onset of drinking. The importance of genetic and environmental influences on SB scores varied with age and drinking status, such that variation prior to drinking onset was attributed solely to environmental influences, whereas all post-onset variation was attributed to genetic influences. Results did not differ significantly by sex.

CONCLUSION

Only environmental factors explain beliefs about the social and behavioral consequences of alcohol use prior to drinking onset,whereas genetic factors explain an increasing proportion of the variance in these beliefs after drinking onset.

Childhood cognitive measures as predictors of alcohol use and problems by mid-adulthood in a non-Western cohort

This study examined the relationship between childhood cognitive functioning and academic achievement and subsequent alcohol use and problems in a non-Western setting. We examined longitudinal data from a birth cohort sample (N = 1,795) who were assessed at age 11 years on cognitive measures and then approximately 25 years later on lifetime alcohol use and alcohol use disorder symptom count. The sample was from Mauritius (eastern Africa), which allowed us to examine these relationships in a non-Western society with a different social structure than is typical of prior cognitive studies on primarily White samples in Western societies. Poorer performance on the Trail Making Test B-A in childhood predicted being a lifetime drinker, even after covarying for gender, childhood psychosocial adversity, and Muslim religion. Lower academic achievement and verbal IQ, but not performance IQ, were predictive of subsequent alcohol problems after including demographic covariates; the relationship between verbal IQ and alcohol problems was stronger in females than males. A nonlinear relationship emerged for Trails, suggesting that only more extreme impairment on this measure was indicative of later alcohol problems. Results of this study provide evidence that verbal deficits and poor academic performance exist in a general cohort sample by age 11 years (when 99% were nondrinkers) for those who go on to develop alcohol problems. (PsycINFO Database Record

Multiple mechanisms influencing the relationship between alcohol consumption and peer alcohol use

BACKGROUND

Alcohol consumption is typically correlated with the alcohol use behaviors of one's peers. Previous research has suggested that this positive relationship could be due to social selection, social influence, or a combination of both processes. However, few studies have considered the role of shared genetic and environmental influences in conjunction with causal processes.

METHODS

This study uses data from a sample of male twins (N = 1,790) who provided retrospective reports of their own alcohol consumption and their peers' alcohol-related behaviors, from adolescence into young adulthood (ages 12 to 25). Structural equation modeling was employed to compare 3 plausible models of genetic and environmental influences on the relationship between phenotypes over time.

RESULTS

Model fitting indicated that one's own alcohol consumption and the alcohol use of one's peers are related through both genetic and shared environmental factors and through unique environmental causal influences. The relative magnitude of these factors, and their contribution to covariation, changed over time, with genetic factors becoming more meaningful later in development.

CONCLUSIONS

Peers' alcohol use behaviors and one's own alcohol consumption are related through a complex combination of genetic and environmental factors that act via correlated factors and the complementary causal mechanisms of social selection and influence. Understanding these processes can inform risk assessment as well as improve our ability to model the development of alcohol use.

Religious factors associated with alcohol involvement: results from the Mauritian Joint Child Health Project

BACKGROUND

The purpose of this study was to examine religious factors associated with alcohol involvement in Mauritius. The three main religions on the island, Hinduism, Catholicism, and Islam, promote different views of the appropriate use of alcohol. Based on reference group theory, we hypothesized that both the content of a religion's alcohol norms and an individual's religious commitment would relate to alcohol use behavior.

METHODS

Participants were from the Joint Child Health Project, a longitudinal study that has followed a birth cohort of 1.795 individuals since 1972 when they were 3 years old. All available participants (67%; 55% male) were assessed in mid-adulthood on religious variables, lifetime drinking, and lifetime alcohol use disorders.

RESULTS

Across religions, individuals who viewed their religion as promoting abstinence were less likely to be drinkers. Religious commitment was associated with reduced probability of drinking only in those who viewed their religion as promoting abstinence. Among drinkers, abstention norms and religious commitment were not associated with lower likelihood of alcohol use disorders. In Catholics who viewed their religion as promoting abstinence and still were drinkers, high religious commitment was associated with increased risk for alcohol use disorders.

CONCLUSIONS

Predictions based on reference group theory were largely supported, with religious norms and commitment differentially related to alcohol use and problems both across religions and among individuals within religions. Findings highlight the importance of examining multiple aspects of religion to better understand the relationship of religion with alcohol behaviors.

Neuropsychological deficits in major depression reflect genetic/familial risk more than clinical history: a monozygotic discordant twin-pair study

Neuropsychological deficits have been associated with major depression (MD) and persist in some individuals even after symptom remission. However, it is unclear if the deficits are a consequence of MD or are pre-existing and reflect MD vulnerability. We addressed this issue by studying 117 twins from monozygotic (MZ) pairs discordant for lifetime history of DSM-III-R defined MD and 41 twins from MZ pairs in which neither twin had experienced MD. Our assessment included a structured clinical interview and measures from the WMS-III and WAIS-III. The "unaffected" twins from discordant pairs showed the same pattern of performance as their affected cotwins on measures of attention, working memory, verbal memory, and visuo-spatial processing. Compared to twins from pairs with no MD history, twins in discordant pairs had lower performance in the domains of attention, memory, visuo-spatial processing, and general knowledge. However, after adjusting for sex and age, the groups differed only on attention and general knowledge. The similar performance of twins in pairs discordant for MD suggests that familial risk for MD has a greater influence on neuropsychological functioning than individual MD history. Findings of impairment in individuals euthymic for MD are more consistent with pre-existing deficits than scarring effects of MD.

A polygenic risk score associated with measures of depressive symptoms among older adults

It has been suggested that depression is a polygenic trait, arising from the influences of multiple loci with small individual effects. The aim of this study is to generate a polygenic risk score (PRS) to examine the association between genetic variation and depressive symptoms. Our analytic sample included N = 10,091 participants aged 50 and older from the Health and Retirement Study (HRS). Depressive symptoms were measured by Center for Epidemiological Studies-Depression scale (CESD) scores assessed on up to nine occasions across 18 years. We conducted a genome-wide association analysis for a discovery set (n = 7,000) and used the top 11 single-nucleotide polymorphisms, all with p < 10(-5) to generate a weighted PRS for our replication sample (n = 3,091). Results showed that the PRS was significantly associated with mean CESD score in the replication sample (β = .08, p = .002). The R(2) change for the inclusion of the PRS was .003. Using a multinomial logistic regression model, we also examined the association between genetic risk and chronicity of high (4+) CESD scores. We found that a one-standard-deviation increase in PRS was associated with a 36 percent increase in the odds of having chronically high CESD scores relative to never having had high CESD scores. Our findings are consistent with depression being a polygenic trait and suggest that the cumulative influence of multiple variants increases an individual's susceptibility for chronically experiencing high levels of depressive symptoms.

Measurement invariance of internalizing and externalizing behavioral syndrome factors in a non-Western sample

This study examined the measurement structure of Child Behavior Checklist internalizing and externalizing syndrome scales in 1,146 eleven-year-old children from a birth cohort in Mauritius. We tested for measurement invariance at configural, metric, and scalar levels by gender and religioethnicity (Creole, Hindu, Muslim). A pared-down model representing five primary factors and two secondary factors met all three forms of invariance, supporting the validity of their use for group comparisons among Mauritian children. As rated by their parents, girls were higher than boys on Somatic Complaints and lower on Aggressive Behavior, Attention Problems, and Externalizing. Creoles were higher than Muslims and Hindus on all seven factors. Hindus were higher than Muslims on Somatic Complaints and lower on Aggressive Behavior. To our knowledge, this is the first study to demonstrate strict invariance of a Child Behavior Checklist-based internalizing and externalizing factor structure among subgroups within a society.

Reexamining the association between fertility and longevity: testing the disposable soma theory in a modern human sample of twins

The disposable soma theory proposes a trade-off between fertility and longevity but existing findings on this association have been mixed. This study used data from 15,622 twins born between 1901 and 1925 ascertained from the population-based Swedish Twin Registry to test the child-longevity association and whether it is accounted for by individual-level factors or by genetic and environmental factors shared by family members. Based on survival analysis, both women and men with children had significantly longer survival relative to the childless, with a slightly higher relative advantage in men. Adjustments for demographic factors and cotwin fertility did not mediate the parenting-survival association, indicating that this association is attributable to individual-level factors associated with fertility rather than family-level environmental or genetic factors shared by cotwins. These results, derived from a large, population-based sample, are inconsistent with the disposable soma theory as applied to modern human populations.

Evidence for multiple genetic factors underlying the DSM-IV criteria for alcohol dependence

To determine the number of genetic factors underlying the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for alcohol dependence (AD), we conducted structural equation twin modeling for seven AD criteria, plus two summary screening questions, in 7133 personally interviewed male and female twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders, who reported lifetime alcohol consumption. The best-fit twin model required three genetic and two unique environmental common factors, and criterion-specific unique environmental factors. The first genetic factor was defined by high loadings for the probe question about quantity and frequency of alcohol consumption, and tolerance criterion. The second genetic factor loaded strongly on the probe question about self-recognition of alcohol-related problems and AD criteria for loss of control, desire to quit, preoccupation and activities given up. The third genetic factor had high loadings for withdrawal and continued use despite the problems criteria. Genetic factor scores derived from these three factors differentially predicted patterns of comorbidity, educational status and other historical/clinical features of AD. The DSM-IV syndrome of AD does not reflect a single dimension of genetic liability, rather, these criteria reflect three underlying dimensions that index risk for: (i) tolerance and heavy use; (ii) loss of control with alcohol associated social dysfunction and (iii) withdrawal and continued use despite problems. While tentative and in need of replication, these results, consistent with the rodent literature, were validated by examining predictions of the genetic factor scores and have implications for gene-finding efforts in AD.

Shared genetic contributions to early-onset drinking and drinking to cope motives

INTRODUCTION

Recent evidence from empirical studies indicates that individuals who begin drinking at an early age may be more likely to use alcohol to cope with negative mood states and stress; however, the mechanisms underlying this association are unclear. One possibility is that early drinking directly increases risk for drinking to cope (DTC). Alternatively, the association between early drinking and DTC may be indirect, attributable to overlapping genetic or environmental factors. No prior genetically informative study has investigated the sources of covariation underlying the early-onset drinking-DTC association.

METHOD

Early-onset drinking (before age 15) was assessed using structured clinical interviews in a sample of 7130 male and female participants aged 19-56 years from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders (VATSPSUD, Kendler & Prescott, 2006). DTC was assessed using the mood management scale of the alcohol use inventory (Horn & Wanberg, 1983). The sources of the covariation between early first drink and DTC were estimated using bivariate twin modeling.

RESULTS

Early drinking onset was reported by 28% of males and 16% of females and was associated with significantly higher DTC scores (phenotypic correlation: males = .19, females = .22). Results from bivariate twin models indicated that the association between early-onset drinking and DTC was completely attributable to shared genetic factors that contribute to both behaviors.

CONCLUSIONS

Greater DTC among early-onset drinkers may not reflect a direct causal process, as shared biological pathways may explain vulnerability to stress-related drinking seen among early-onset drinkers.

Interactive effects of childhood maltreatment and recent stressful life events on alcohol consumption in adulthood

OBJECTIVE

Childhood maltreatment is associated with early alcohol use initiation, alcohol-related problem behaviors, and alcohol use disorders in adulthood. Heavy drinking risk among individuals exposed to childhood maltreatment could be partly attributable to stress sensitization, whereby early adversity leads to psychobiological changes that heighten sensitivity to subsequent stressors and increase risk for stress-related drinking. We addressed this issue by examining whether the association between past-year stressful life events and past-year drinking density, a weighted quantity-frequency measure of alcohol consumption, was stronger among adults exposed to childhood maltreatment.

METHOD

Drinking density, stressful life events, and child maltreatment were assessed using structured clinical interviews in a sample of 4,038 male and female participants ages 20-58 years from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. Stress sensitization was examined using hierarchical multiple regression analyses to test whether stressful events moderated the association between maltreatment and drinking density. Analyses were stratified by sex and whether the impact was different for independent stressful events or dependent stressful events as related to a participant's actions.

RESULTS

Independent stressful events were associated with heavier drinking density among women exposed to maltreatment. In contrast, drinking density was roughly the same across independent stressful life events exposure among women not exposed to maltreatment. There was little evidence for Maltreatment × Independent Stressor interactions in men or Maltreatment × Dependent Stressor interactions in either gender.

CONCLUSIONS

Early maltreatment may have direct effects on vulnerability to stress-related drinking among women, particularly in association with stressors that are out of one's control.

Meta-analyses of genome-wide linkage scans of anxiety-related phenotypes

Genetic factors underlying trait neuroticism, reflecting a tendency towards negative affective states, may overlap genetic susceptibility for anxiety disorders and help explain the extensive comorbidity amongst internalizing disorders. Genome-wide linkage (GWL) data from several studies of neuroticism and anxiety disorders have been published, providing an opportunity to test such hypotheses and identify genomic regions that harbor genes common to these phenotypes. In all, 11 independent GWL studies of either neuroticism (n=8) or anxiety disorders (n=3) were collected, which comprised of 5341 families with 15 529 individuals. The rank-based genome scan meta-analysis (GSMA) approach was used to analyze each trait separately and combined, and global correlations between results were examined. False discovery rate (FDR) analysis was performed to test for enrichment of significant effects. Using 10 cM intervals, bins nominally significant for both GSMA statistics, P(SR) and P(OR), were found on chromosomes 9, 11, 12, and 14 for neuroticism and on chromosomes 1, 5, 15, and 16 for anxiety disorders. Genome-wide, the results for the two phenotypes were significantly correlated, and a combined analysis identified additional nominally significant bins. Although none reached genome-wide significance, an excess of significant P(SR)P-values were observed, with 12 bins falling under a FDR threshold of 0.50. As demonstrated by our identification of multiple, consistent signals across the genome, meta-analytically combining existing GWL data is a valuable approach to narrowing down regions relevant for anxiety-related phenotypes. This may prove useful for prioritizing emerging genome-wide association data for anxiety disorders.

The effects of age at drinking onset and stressful life events on alcohol use in adulthood: a replication and extension using a population-based twin sample

BACKGROUND

A study by Dawson and colleagues (Alcohol Clin Exp Res 2007; 31:69) using data from National Epidemiologic Survey on Alcohol and Related Condition found earlier drinking onset age, and higher levels of past-year stressful life events (SLE) were associated with higher past-year alcohol consumption. The aims of our study were as follows: (i) to attempt to replicate this interaction; (ii) to extend it by examining sex and event dependence as potential moderators of the effect; and (iii) to estimate the roles of genetic and environmental factors in mediating the overlap of early drinking onset and SLE in their relations with alcohol consumption.

METHODS

Data were from 1,382 female and 2,218 male drinkers interviewed as part of the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. Regression models were used to evaluate the main and interactive effects of early drinking onset and moderate or severe past-year SLE on past-year drinking density (PYDD), a weighted quantity-frequency measure of alcohol consumption. Analyses adjusted for demographic covariates and were stratified by sex and whether SLE were independent or dependent on the person's actions, as rated by interviewers. Structural twin models were used to estimate the degree to which early drinking onset, SLE, and their interaction accounted for additive genetic, common environmental and individual-specific variance in PYDD.

RESULTS

We replicated the prior finding of a main effect of higher alcohol consumption among individuals reporting earlier drinking onset. Age at drinking onset accounted for about 5% of the variation in PYDD, and this association was mostly attributable to overlapping genetic influences. Evidence for an interaction between onset age and SLE was generally weak, possibly because of lower power and other methodological differences from Dawson and colleagues' study. However, there was some evidence consistent with an interaction of higher PYDD among early drinking men who experienced independent SLE and early drinking women with dependent SLE.

CONCLUSIONS

We confirmed prior findings of an association between early age at drinking onset with higher past-year drinking among young- and middle-aged adults and found limited evidence supporting a replication for higher stress-related drinking among early-onset drinkers. The association is consistent with early onset and stress-related drinking being attributable to overlapping genetic liability. Among early drinkers, our results suggest sex differences in consumption with regard to event dependence.

Clarifying the relationship between religiosity and psychiatric illness: the impact of covariates and the specificity of buffering effects

Previous analyses in a large population-based sample of female twins indicated that three dimensions of religiosity – personal devotion, personal conservatism and institutional conservatism – were, in different ways, significantly related to current depressive symptoms and substance use and lifetime psychiatric and substance use disorders. Furthermore, personal devotion, but neither personal conservatism nor institutional conservatism, buffered the depressogenic effects of stressful life events (SLEs). We here explore further these results, using linear, logistic and Cox regression models. Eight personality and six demographic variables had distinct patterns of association with the three dimensions. Personal devotion was positively associated with years of education, age, and optimism and negatively correlated with neuroticism. Personal conservatism was negatively associated with education, income, age, mastery and positively correlated with neuroticism. Institutional conservatism was negatively correlated with self-esteem and parental education. Covarying for these 14 variables produced little change in their association with psychiatric and substance use outcomes. The impact of the dimensions of religiosity differed as a function of the SLE category. High levels of both personal devotion and institutional conservatism protected against the depressogenic effects of death and personal illness. High levels of personal conservatism were associated with increased sensitivity to relationship problems. These results suggest that the association between religiosity and low risk for symptoms of depression and substance use may be in part causal. The relationship between dimensions of religiosity and response to SLEs is complex but probably of importance in clarifying the nature of the coping process.

The Differential Heritability of Regular Tobacco Use Based on Method of Administration

Several large studies have demonstrated that the liability to smoke cigarettes is strongly genetically influenced. However, the role of genetic and environmental risk factors in the use of other common forms of tobacco use has yet to be studied. Data on the regular use of cigarettes, cigars, pipes, dip (moist snuff), and chewing tobacco from 2634 male twins were analyzed with ACE structural equation models. Twin similarity for regular cigarette and dip use was largely genetic in origin. However, twin resemblance for chewing tobacco was just about equally the result of genes and shared environment, and twin similarity for use of pipes and cigars was entirely the result of shared environmental factors. Thus, the genetic influences on the liability for regular tobacco use appear to vary based on tobacco type. The causes for the use of different forms of tobacco are complex and worthy of further study.

Different phenotypic and genotypic presentations in alcohol dependence: age at onset matters

OBJECTIVE

Several theoretical typology models have been proposed to classify alcoholism into more homogeneous subtypes using various criteria, for which age at onset of alcohol dependence is shared across many models. We investigated the evidence for the distinction between early- versus late-onset alcoholism by examining relevant phenotypic and genotypic variables.

METHOD

Data are from 1,248 individuals with alcohol dependence, who were interviewed to collect detailed clinical information. Early versus late onset of alcohol dependence was defined by the age at onset of 22 years. Odds ratio (OR) and Cohen's d were calculated as effect size for comparisons of clinical features between the two groups. We adjusted interviewed age and gender in logistic regression models. Case-control genetic analyses were conducted for the association between HTR1B, SLC6A4, DRD2, and OPRμ1 genes and subgroups of alcohol dependence using a sample of 530 controls screened for alcohol problems.

RESULTS

Early-onset alcoholism exhibited significantly (p < .01) different clinical characteristics from late-onset alcoholism, including higher severity in alcohol dependence symptoms (d = 0.22) and maximum drinking quantity within 24 hours (d = 0.40), more rapid progression from regular drinking to meet alcohol dependence diagnosis (d = 1.73), higher expectancies for alcohol (d = 0.22-0.47), more comorbidity with externalizing disorders (ORs = 2.8-2.9), and greater prevalence of family alcohol use problems (d = 0.26-0.43). In addition, markers in the HTR1B and OPRμ1 genes showed genetic associations with subgroups of alcohol dependence (ORs = 1.5-2.4).

CONCLUSIONS

Our findings support that subgroups of alcohol dependence defined by onset age have phenotypic and genetic differences. The early-onset subgroup had more severe features for almost every aspect we examined. Coupled with genetic association findings, age at onset of alcohol dependence may serve as a simple but important clinical marker with implications for future etiological research and intervention.

A twin association study of nicotine dependence with markers in the CHRNA3 and CHRNA5 genes

Twin and family studies have provided overwhelming evidence for the genetic basis of individual differences in tobacco initiation (TI), regular smoking (RS) and nicotine dependence (ND). However, only a few genes have been reliably associated with ND. We used a finite mixture distribution model to examine the significance and effect size of the association of previously identified and replicated specific variants in the CHRNA5 and CHRNA3 receptor genes with ND, against the background of genetic and environmental risk factors for ND. We hypothesize that additional phenotypic information in relatives who have not been genotyped can be used to increase the power of detecting the genetic variant. The nicotine measures were assessed by personal interview in female, male and opposite sex twin pairs (N = 4,153) from the population-based Virginia Twin Registry. Three SNPs in the CHRNA5 and CHRNA3 receptor genes, previously shown to be significantly associated with ND in this sample, were replicated in the augmented analyses; they accounted for less than one percent of the genetic variance in liability to ND, which is estimated to be over 50% of the phenotypic variance. The significance of these effects was increased by adding twins with phenotype but without genotype data, but gains are limited and variable. The SNPs associated with ND did not show a significant association with either TI or RS and appear to be specific to the addictive stage of ND, characterized by current smoking and smoking a large amount of cigarettes per day. Furthermore, these SNPs did not appear to be associated with the remaining items comprising the FTND scale. This study confirmed a significant contribution of the CHRNA receptor on different forms of tobacco dependence. However, the genetic variant only accounted for little of the total genetic variance for liability to ND. Including phenotypic data on ungenotyped relatives can improve the statistical power to detect the effects of genetic variants when they contribute to individual differences in the phenotype.

The influence of gene-environment interactions on alcohol consumption and alcohol use disorders: a comprehensive review

Since 2005, a rapidly expanding literature has evaluated whether environmental factors such as socio-cultural context and adversity interact with genetic influences on drinking behaviors. This article critically reviews empirical research on alcohol-related genotype-environment interactions (GxE) and provides a contextual framework for understanding how genetic factors combine with (or are shaped by) environmental factors to influence the development of drinking behaviors and alcohol use disorders. Collectively, evidence from twin, adoption, and molecular genetic studies indicates that the degree of importance of genetic influences on risk for drinking outcomes can vary in different populations and under different environmental circumstances. However, methodological limitations and lack of consistent replications in this literature make it difficult to draw firm conclusions regarding the nature and effect size of alcohol-related GxE. On the basis of this review, we describe several methodological challenges as they relate to current research on GxE in drinking behaviors and provide recommendations to aid future research.

The influence of gene-environment interactions on alcohol consumption and alcohol use disorders: a comprehensive review

Since 2005, a rapidly expanding literature has evaluated whether environmental factors such as socio-cultural context and adversity interact with genetic influences on drinking behaviors. This article critically reviews empirical research on alcohol-related genotype-environment interactions (GxE) and provides a contextual framework for understanding how genetic factors combine with (or are shaped by) environmental factors to influence the development of drinking behaviors and alcohol use disorders. Collectively, evidence from twin, adoption, and molecular genetic studies indicates that the degree of importance of genetic influences on risk for drinking outcomes can vary in different populations and under different environmental circumstances. However, methodological limitations and lack of consistent replications in this literature make it difficult to draw firm conclusions regarding the nature and effect size of alcohol-related GxE. On the basis of this review, we describe several methodological challenges as they relate to current research on GxE in drinking behaviors and provide recommendations to aid future research.

Toward a comprehensive developmental model for alcohol use disorders in men

The multiple risk factors for alcohol use (AU) and alcohol use disorders (AUDs) are interrelated through poorly understood pathways, many of which begin in childhood. In this report, the authors seek to develop an empirical, broad-based developmental model for the etiology of AU and AUDs in men. We assessed 15 risk factors in four developmental tiers in 1,794 adult male twins from the Virginia population based twin registry. The best fitting model explained 39% of the variance in late adolescent AU, and 30% of the liability to lifetime symptoms of AUD. AU and AUDs can be best understood as arising from the action and interaction of two pathways reflecting externalizing genetic/temperamental and familial/social factors. Peer group deviance was important in each pathway. Internalizing symptoms played a more minor role. Familial/social factors were especially important influences on AU, while genetic/temperamental factors were more critical for AUDs. We conclude that AU and AUDs in men are complex traits influenced by genetic, family, temperamental, and social factors, acting and interacting over developmental time.

Heritability of Parkinson disease in Swedish twins: a longitudinal study

Previous twin studies report no heritability of Parkinson's disease (PD) based on cross sectional information. Here, we apply a longitudinal design and re-evaluate cross sectional data in the population-based Swedish Twin Registry (STR) using clinical as well as hospital discharge and cause of death diagnoses. In the longitudinal analyses (based on 46,436 individuals), we identified 542 twins with PD and 65 twins with Parkinsonism. Concordance rates for PD were 11% for monozygotic and 4% for same-sexed dizygotic twin pairs, with a heritability estimate of 34%. Concordance rates for PD or parkinsonism were 13% for monozygotic and 5% for same-sexed dizygotic twin pairs, with a heritability estimate of 40%. In the cross sectional analyses (based on 49,814 individuals), we identified 287 twins with PD and 79 twins with parkinsonism. Concordance rates for PD were 4% for monozygotic and same-sexed dizygotic twin pairs and 0 for opposite-sexed twin pairs. Concordance rates for PD or parkinsonism were somewhat higher but the heritability estimate was nonsignificant. Our longitudinal analyses demonstrate that PD and parkinsonism are modestly heritable.

Accounting for the association between childhood maltreatment and alcohol-use disorders in males: a twin study

BACKGROUND

An association between childhood maltreatment and subsequent alcohol abuse and/or dependence (AAD) has been found in multiple studies of females. Less is known about the association between childhood maltreatment and AAD among males, and the mechanisms that underlie this association in either gender. One explanation is that childhood maltreatment increases risk for AAD. An alternative explanation is that the same genetic or environmental factors that increase a child's risk for being maltreated also contribute to risk for AAD in adulthood.

METHOD

Lifetime diagnosis of AAD was assessed using structured clinical interviews in a sample of 3527 male participants aged 19-56 years from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. The sources of childhood maltreatment-AAD association were estimated using both a matched case-control analysis of twin pairs discordant for childhood maltreatment and bivariate twin modeling.

RESULTS

Approximately 9% of participants reported childhood maltreatment, defined as serious neglect, molestation, or physical abuse occurring before the age of 15 years. Those who experienced childhood maltreatment were 1.74 times as likely to meet AAD criteria compared with males who did not experience childhood maltreatment. The childhood maltreatment-AAD association largely reflected environmental factors in common to members of twin pairs. Additional exploratory analyses provided evidence that AAD risk associated with childhood maltreatment was significantly attenuated after adjusting for measured family-level risk factors.

CONCLUSIONS

Males who experienced childhood maltreatment had an increased risk for AAD. Our results suggest that the childhood maltreatment-AAD association is attributable to broader environmental adversity shared between twins.

Neurotransmitter and neuromodulator genes associated with a history of depressive symptoms in individuals with alcohol dependence

BACKGROUND

Depressive symptoms are common among individuals with alcohol use disorders and impact treatment outcome. Substantial overlap exists among the neurobiological systems proposed in the pathophysiology of depressive and alcohol use disorders; however, specific genetic effects contributing to risk for depressive comorbidity remain poorly understood.

METHODS

This study examines the association of depressive symptom scores for lifetime depression (the sum of DSM-IV major depression co-endorsed criteria for lifetime depression) with markers in 120 candidate genes in 554 alcohol-dependent individuals. The candidate genes code for molecules involved in dopamine, serotonin, glutamate, gamma-aminobutyric acid (GABA), and opioid neurotransmission, cell signaling, pharmacokinetics, stress biology, and behavioral control. Analyses were conducted at the single marker level with experimentwise permutation to control for multiple testing.

RESULTS

Results revealed nominal associations for markers in 20 genes. Following experimentwise permutation, markers in the corticotropin-releasing hormone-binding protein (CRHBP) the μ-opioid receptor (OPRM1) and the β1 subunit of GABA A (GABA(A)) receptors (GABRB1) met or exceeded the significance threshold. None of the markers associated with depressive symptom scores were significantly associated with alcohol dependence symptom scores.

CONCLUSION

These findings suggest potential risk genes for depressive symptoms in alcohol-dependent individuals.

Limited associations of dopamine system genes with alcohol dependence and related traits in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD)

BACKGROUND

Over 50 years of evidence from research has established that the central dopaminergic reward pathway is likely involved in alcohol dependence (AD). Additional evidence supports a role for dopamine (DA) in other disinhibitory psychopathology, which is often comorbid with AD. Family and twin studies demonstrate that a common genetic component accounts for most of the genetic variance in these traits. Thus, DA-related genes represent putative candidates for the genetic risk that underlies not only AD but also behavioral disinhibition. Many linkage and association studies have examined these relationships with inconsistent results, possibly because of low power, poor marker coverage, and/or an inappropriate correction for multiple testing.

METHODS

We conducted an association study on the products encoded by 10 DA-related genes (DRD1-D5, SLC18A2, SLC6A3, DDC, TH, COMT) using a large, ethnically homogeneous sample with severe AD (n = 545) and screened controls (n = 509). We collected genotypes from linkage disequilibrium (LD)-tagging single nucleotide polymorphisms (SNPs) and employed a gene-based method of correction. We tested for association with AD diagnosis in cases and controls and with a variety of alcohol-related traits (including age-at-onset, initial sensitivity, tolerance, maximum daily drinks, and a withdrawal factor score), disinhibitory symptoms, and a disinhibitory factor score in cases only. A total of 135 SNPs were genotyped using the Illumina GoldenGate and Taqman Assays-on-Demand protocols.

RESULTS

Of the 101 SNPs entered into standard analysis, 6 independent SNPs from 5 DA genes were associated with AD or a quantitative alcohol-related trait. Two SNPs across 2 genes were associated with a disinhibitory symptom count, while 1 SNP in DRD5 was positive for association with the general disinhibitory factor score.

CONCLUSIONS

Our study provides evidence of modest associations between a small number of DA-related genes and AD as well as a range of alcohol-related traits and measures of behavioral disinhibition. While we did conduct gene-based correction for multiple testing, we did not correct for multiple traits because the traits are correlated. However, false-positive findings remain possible, so our results must be interpreted with caution.

The relationship between genetic influences on alcohol dependence and on patterns of alcohol consumption

BACKGROUND

Genetic factors impact substantially both on alcohol consumption (AC) and on the risk for alcohol dependence (AD). However, we know little about the degree to which measures of AC index the genetic risk for AD.

METHODS

We assessed a lifetime history of AD by DSM-IV criteria and four measures of AC at the time of heaviest drinking (drink frequency, regular quantity, maximum quantity, and drunk frequency) in 5,073 adult twins from same-sex pairs from the Virginia Twin Registry. Structural models were fitted using Mx.

RESULTS

We found evidence for different genetic structure in the sexes. In women, genetic risk for AD and for the four measures of AC was entirely shared. In men, the AC measures captured 85% of the genetic risk for AD. In women, the genetic relationship with AD was strongest for drunk frequency and in men for both drunk frequency and regular quantity.

CONCLUSIONS

In a population-based sample of twins, four relatively simple measures of AC obtained for the time of lifetime heaviest drinking were able to capture all (in women) or a very large proportion (in men) of the genetic risk for the complex multi-dimensional construct of AD. If replicated, these results have practical implications for studies aiming to assess genetic risk for AD.

A systematic gene-based screen of chr4q22-q32 identifies association of a novel susceptibility gene, DKK2, with the quantitative trait of alcohol dependence symptom counts

Studies of alcohol dependence (AD) have consistently found evidence of linkage on chromosome 4q21-q32. A genome-wide linkage scan in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD) sample also provided its strongest evidence of linkage on chromosome 4q22-q32 using an index of AD severity based on the count of DSM-IV AD symptoms (ADSX; LOD = 4.59). We conducted a systematic, gene-centric association study using 518 LD-tagging single nucleotide polymorphisms (SNPs) in the 65 known and predicted genes within the 1-LOD interval surrounding the linkage peak. Case-only regression analysis with the quantitative variable of ADSX was performed in the 562 genetically independent cases; nominal support for association was demonstrated by 32 tagging SNPs in 14 genes. We did not observe study-wide significance, but gene-wise correction for multiple testing with the Nyholt procedure yielded empirical evidence of association with two genes, DKK2 (dickkopf homolog 2) (P = 0.007) and EGF (epidermal growth factor) (P = 0.025) in the IASPSAD sample. Three SNPs in DKK2 (rs427983; rs419558; rs399087) demonstrated empirical significance. Assessment of possible replication in 847 cases of European descent from a large independent sample, the Collaborative Study of the Genetics of Alcoholism, yielded replication for DKK2 but not EGF. We observed genotypic and phenotypic replication for DKK2 with the three SNPs yielding significant association with ADSX in the IASPSAD sample. Haplotype-specific expression measurements in post-mortem tissue samples suggested a functional role for DKK2. This evidence notwithstanding, replication is needed before confidence can be placed in these findings.

Empirically defined subtypes of alcohol dependence in an Irish family sample

Alcohol dependence (AD) is clinically and etiologically heterogeneous. The goal of this study was to explore AD subtypes among a sample of 1221 participants in the Irish Affected Sib Pair Study of Alcohol Dependence, all of whom met DSM-IV criteria for AD. Variables used to identify the subtypes included major depressive disorder, antisocial personality disorder, illicit drug dependence (cannabis, sedatives, stimulants, cocaine, opioids, and hallucinogens), nicotine dependence, the personality traits of neuroticism and novelty seeking, and early alcohol use. Using latent class analysis, a 3-class solution was identified as the most parsimonious description of the data. Individuals in a Mild class were least likely to have comorbid psychopathology, whereas a severe class had highest probabilities of all comorbid psychopathology. The third class was characterized by high probabilities of major depression and higher neuroticism scores, but lower likelihood of other comorbid disorders than seen in the severe class. Overall, sibling pair resemblance for class was stronger within than between classes, and was greatest for siblings within the severe class, suggesting a stronger familial etiology for this class. These findings are consistent with the affective regulation and behavioral disinhibition subtypes of alcoholism, and are in line with prior work suggesting familial influences on subtype etiology.

The Norwegian Institute of Public Health twin study of mental health: examining recruitment and attrition bias

All Norwegian twin pairs born 1967-1974 and still living in Norway in 1992 were invited to a health questionnaire study (Q1). 2,570 pairs (65%) participated. These cohorts and the twin cohorts born 1967-1979 were invited to a new questionnaire study (Q2) in 1998. This time 3,334 pairs (53%) participated. Almost all pairs having participated in the 1998 study were invited to an interview study of mental health (MHS), taking place 1999-2004. 1,391 complete pairs (44%) participated. The questionnaire studies included extensive data on somatic health with fewer items on mental health and demography. Health-related and demographic information available from the Medical Birth Registry on all invited twins was applied to predict participation to the first study. A few registry variables indicating poor health predicted nonparticipation in Q1. Health information and demography from Q1 were tested as predictors of participation in the follow-up study (Q2). Monozygosity, female sex, being unmarried, having no children, and high education predicted participation, whereas few indicators of poor mental and somatic health and unhealthy lifestyle moderately predicted nonparticipation in Q2. No health indicators reported in Q2 predicted further participation. Standard genetic twin analyses of indicators of various mental disorders from Q2, validated by diagnostic data from the MHS, did not indicate differences in genetic/environmental covariance structures between participants and nonparticipants in MHS. In general the results show a moderate selection towards good mental and somatic health. Attrition from Q2 to the MHS does not appear to affect twin analyses of mental health related variables.