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Genes associated with educational attainment may be related to or interact with adolescent alcohol, tobacco and cannabis use. Potential gene–environment interplay between educational attainment polygenic scores (EA-PGS) and adolescent alcohol, tobacco, and cannabis use was evaluated with a series of regression models fitted to data from a sample of 1871 adult Australian twins. All models controlled for age, age2, cohort, sex and genetic ancestry as fixed effects, and a genetic relatedness matrix was included as a random effect. Although there was no evidence that adolescent alcohol, tobacco or cannabis use interacted with EA-PGS to influence educational attainment, there was a significant, positive gene–environment correlation with adolescent alcohol use at all PGS thresholds (ps <.02). Higher EA-PGS were associated with an increased likelihood of using alcohol as an adolescent (ΔR2 ranged from 0.5% to 1.1%). The positive gene–environment correlation suggests a complex relationship between educational attainment and alcohol use that is due to common genetic factors.
Prior research has documented shared heritable contributions to non-suicidal self-injury (NSSI) and suicidal ideation (SI) as well as NSSI and suicide attempt (SA). In addition, trauma exposure has been implicated in risk for NSSI and suicide. Genetically informative studies are needed to determine common sources of liability to all three self-injurious thoughts and behaviors, and to clarify the nature of their associations with traumatic experiences.
Multivariate biometric modeling was conducted using data from 9526 twins [59% female, mean age = 31.7 years (range 24–42)] from two cohorts of the Australian Twin Registry, some of whom also participated in the Childhood Trauma Study and the Nicotine Addiction Genetics Project.
The prevalences of high-risk trauma exposure (HRT), NSSI, SI, and SA were 24.4, 5.6, 27.1, and 4.6%, respectively. All phenotypes were moderately to highly correlated. Genetic influences on self-injurious thoughts and behaviors and HRT were significant and highly correlated among men [rG = 0.59, 95% confidence interval (CI) (0.37–0.81)] and women [rG = 0.56 (0.49–0.63)]. Unique environmental influences were modestly correlated in women [rE = 0.23 (0.01–0.45)], suggesting that high-risk trauma may confer some direct risk for self-injurious thoughts and behaviors among females.
Individuals engaging in NSSI are at increased risk for suicide, and common heritable factors contribute to these associations. Preventing trauma exposure may help to mitigate risk for self-harm and suicide, either directly or indirectly via reductions in liability to psychopathology more broadly. In addition, targeting pre-existing vulnerability factors could significantly reduce risk for life-threatening behaviors among those who have experienced trauma.
Two major challenges to conducting a community-based twin study of pathological gambling (PG) disorder are that: (a) it is relatively rare, and (b) individuals with the disorder in the community may be difficult to locate and recruit. We describe a new study of 4,764 individuals recruited from the Australian Twin Registry in which we attempt to effectively deal with the first challenge and examine the impact of the second challenge. The lifetime prevalence of DSM-IV PG in this Australian twin sample was 2.2%, which is 400–500% higher than has been obtained in prevalence surveys conducted in the United States. A number of predictors of non-participation were identified, including a lifetime PG disorder diagnosis, but these did not have a large net effect on the estimated number of individuals with PG or related characteristics in the twin sample. Results of biometric modeling suggested that the effect of genetic, shared family environmental, and nonshared environmental influences on the propensity to engage in 11 different specific forms of gambling (e.g., playing the lottery, betting on horse or dog races, playing electronic gaming machines) were generally moderate, low, and moderate, respectively, with mean parameter estimates obtained of 43%, 10%, and 46%. An intriguing comparison with results from a 1963 US adolescent twin study conducted by Loehlin and Nichols (1976) suggests that: (a) propensity genes for gambling involvement may be more likely to be expressed in the heavy-gambling Australian culture, or that (b) the family environment has a transient effect on the gambling behavior of young people.
Questionnaire surveys, while more economical, typically achieve poorer response rates than interview surveys. We used data from a national volunteer cohort of young adult twins, who were scheduled for assessment by questionnaire in 1989 and by interview in 1996-2000, to identify predictors of questionnaire non-response. Out of a total of 8536 twins, 5058 completed the questionnaire survey (59% response rate), and 6255 completed a telephone interview survey conducted a decade later (73% response rate). Multinomial logit models were fitted to the interview data to identify socioeconomic, psychiatric and health behavior correlates of non-response in the earlier questionnaire survey. Male gender, education below University level, and being a dizygotic rather than monozygotic twin, all predicted reduced likelihood of participating in the questionnaire survey. Associations between questionnaire response status and psychiatric history and health behavior variables were modest, with history of alcohol dependence and childhood conduct disorder predicting decreased probability of returning a questionnaire, and history of smoking and heavy drinking more weakly associated with non-response. Body-mass index showed no association with questionnaire non-response. Despite a poor response rate to the self-report questionnaire survey, we found only limited sampling biases for most variables. While not appropriate for studies where socioeconomic variables are critical, it appears that survey by questionnaire, with questionnaire administration by telephone to non-responders, will represent a viable strategy for gene-mapping studies requiring that large numbers of relatives be screened.
The aim of this study was to investigate familial influences and their dependence on sex for panic disorder and/or agoraphobia, social phobia, generalized anxiety disorder and major depression. Data from Australian (N = 2287) and Dutch (N = 1185) twins and siblings who were selected for a linkage study and participated in clinical interviews to obtain lifetime Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) diagnoses were used. In a liability model, tetrachoric correlations were estimated in sibling pairs and sex differences between sibling correlations were tested. For each diagnosis, the sibling correlations could be constrained to be equal across the Australian and Dutch samples. With the exception of panic disorder and/or agoraphobia, all sibling correlations were the same for brother, sister and opposite-sex sibling pairs and were around .20. For panic disorder and/or agoraphobia, the correlation was .23 in brother and sister pairs, but absent in opposite-sex sibling pairs. From these results it can be concluded that upper heritability estimates, based on twice the correlations in the sibling pairs, vary between 36% (major depression) and 50% (social phobia). Furthermore, different genetic risk factors appear to contribute to the vulnerability for panic disorder and/or agoraphobia in men and women. No other sex differences were found.
Multivariate modelling of anxiety and depression data in twins has suggested that the two phenotypes are largely underpinned by one genetic factor, while other studies have indicated a relationship between these disorders and the neuroticism personality trait. As part of a study to identify quantitative trait loci for anxiety and depression, questionnaire responses and interviews of 15 027 Australian twins and 11 389 of their family members conducted during the past 20 years were reviewed to identify individuals with neuroticism, anxiety and depression scores in the upper or lower deciles of the population. This information was then used to identify extreme discordant and concordant (EDAC) sib pairs. 1373 high-scoring and 1571 low-scoring subjects (2357 sib pairs) were selected for participation, and extremely high participation rates were achieved, with over 90% of contactable prospective participants completing the interview phase, and over 90% of these providing blood or buccal samples. Participation bias arising from the nature of the selection variables was minimal, with only a small difference between rates of interview participation among prospective participants with high and low selection scores (89.4% vs 91.6%). The interview permitted the diagnosis of depression and several anxiety disorders (OCD, agoraphobia, panic disorder, generalised anxiety disorder) in this sample according to DSM-IV criteria. The methodology for selection of prospective subjects was demonstrated to be extremely successful, with highly significant differences in depression and anxiety disorder prevalence rates between individuals in the two selection groups. The success of this EDAC sampling scheme will enhance the power for QTL linkage and association analysis in this sample. Twin Research (2000) 3, 299–309.
Background. This study examined the relationships between self-reported childhood sexual abuse (CSA) and drug-related outcomes in an Australian twin panel.
Method. A semi-structured psychiatric interview was conducted in 1996–2000 by telephone with young adult Australian twins (mean age 29·9 years). Data reported here are from 6050 twins who responded to both CSA and drug-related items.
Results. A history of CSA was associated with significant risk for subsequently occurring regular smoking and use of each illicit drug class. Further CSA-associated risk was found among regular users, for nicotine and alcohol dependence, and among illicit drug users, for abuse/dependence of most drug classes. In same-sex discordant pairs, significant risk for regular smoking and illicit drug use was found in twins with a history of CSA compared to their non-abused co-twins. Similar analyses for abuse/dependence found significant risk for opioids, any illicit drug, and any non-cannabis illicit drug. CSA was associated with significantly earlier drug use. Despite the association of CSA with risk for early-onset cannabis use and regular smoking, risks for illicit drug outcomes associated with CSA and with either form of early-onset use combine in near-additive fashion.
Conclusions. CSA is associated with risk for subsequently occurring regular smoking and illicit drug use and abuse/dependence. Risks for drug use are mildly attenuated with control for familial contributions; similar risks for abuse/dependence remain significant for opioids and for illicit drugs combined across classes. Although we found evidence of earlier onset drug use with CSA, risks associated with CSA and with early-onset use combine in a largely additive manner.
Background. Whether current criteria used to define nicotine dependence are informative for genetic research is an important empirical question. The authors used items of the DSM-IV and of the Heaviness of Smoking Index to characterize the nicotine dependence phenotype and to identify salient symptoms in a genetically informative community sample of Australian young adult female and male twins.
Method. Phenotypic and genetic factor analyses were performed on nine dependence symptoms (the seven DSM-IV substance dependence criteria and the two Heaviness of Smoking Index (HSI) items derived from the Fagerström Tolerance Questionnaire, time to first cigarette in the morning and number of cigarettes smoked per day). Phenotypic and genetic analyses were restricted to ever smokers.
Results. Phenotypic nicotine dependence symptom covariation was best captured by two factors with a similar pattern of factor loadings for women and men. In genetic factor analysis item covariation was best captured by two genetic but one shared environmental factor for both women and men; however, item factor loadings differed by gender. All nicotine dependence symptoms were substantially heritable, except for the DSM-IV criterion of ‘giving up or reducing important activities in order to smoke’, which was weakly familial.
Conclusions. The salient behavioral indices of nicotine dependence are similar for women and men. DSM-IV criteria of tolerance, withdrawal, and experiencing difficulty quitting and HSI items time to first cigarette in the morning and number of cigarettes smoked per day may represent the most highly heritable symptoms of nicotine dependence for both women and men.
It is widely believed that people can remember the age at which they
first had sexual intercourse. Questions about age at onset are routinely asked
in population sexual behaviour surveys and in clinical history-taking.
However, there are limited test–retest data, especially with regard to
individual differences in unreliable recall. In this study, telephone
interviews and follow-ups an average of 15 months later were conducted with
570 non-virgin subjects aged between 28 and 73 years. Test–retest correlations
for recalled age at first intercourse were 0·85 for females and 0·91 for
males. Consistency was slightly
lower among older people and women with a history of sexual abuse. There were
associations between consistency of recall and measures of personality,
educational background or history of alcohol dependence and depression.
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