Michael P. Dunne

Common genetic risk factors for conduct disorder and alcohol dependence

The association between retrospectively reported childhood conduct disorder (CD) and a history of alcohol dependence (AD) was examined in a sample of 2,682 male, female, and unlike-sex adult twin pairs. There was a strong association between CD and AD in both men (tetrachoric r = .34, odds ratio = 2.8) and women (tetrachoric r = .53, odds ratio = 9.9). Genetic factors accounted for most of the association between CD and AD liability in men and women, with the remainder of the association being due to nonshared individual-specific environmental factors. Genetic influences common to CD and AD accounted for 17% and 35% of the genetic variation in AD liability in men and women, respectively, and accounted for 11% and 23% of the total variation in AD liability in men and women, respectively. The results suggest that there are common genetic risk factors for CD and AD or that CD itself is an important genetically influenced risk factor for AD.

Modeling genetic and environmental influences in the etiology of conduct disorder: a study of 2,682 adult twin pairs.

The etiology of conduct disorder (CD) was examined retrospectively in a sample of 2,682 male, female, and unlike-sex adult twin pairs from the community-based Australian Twin Register. Model-fitting analyses indicated a substantial genetic influence on risk for CD, accounting for 71% of the variance (95% confidence interval [CI] = 32-79%). There was not a statistically significant effect of the shared environment in the best-fitting model of CD, but a modest effect of the shared environment on the risk for CD could not be rejected (95% CI = 0-32%). The magnitude of genetic and environmental influences for CD liability did not vary significantly for boys and girls, and the specific genetic and environmental mechanisms important for the development of CD appeared to be largely the same for both sexes. The fit of a multiple-threshold model raises the possibility that CD may not necessarily be a discrete entity but rather an extreme of the normal variation in conduct-disordered behavior found in the general population.

Measurement Models for Sexual Orientation in a Community Twin Sample

Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18–52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings), providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.

The assessment of alcoholism in surveys of the general community: What are we measuring? Some insights from the Australian twin panel interview survey

The majority of cases identified by commonly used alcoholism criteria in general community surveys are mild ones, with few alcohol-related problems. We illustrate this using data on 2088 Australian male twins aged 28–89 (mean age = 42.7), including 1846 who reported more than minimal alcohol exposure when surveyed by telephone in 1992–3. Using latent class analysis of alcoholism symptoms reported by these twins, we identify five classes of respondent: those with no alcohol-related problems (49% of the sample, if we include those with minimal alcohol exposure); excessive drinkers (33%); and individuals with a history of mild (14%), moderate (3%) or severe problems (1%). Symptom endorsement profiles associated with these different classes are illustrated. The two most severe classes constitute a substantial majority of those reporting alcoholism treatment, but a minority of those reporting alcohol-related auto accidents or injuries, recurrent hazardous alcohol use, or alcohol-related arrests. The excessive ...

The consistency of recalled age at first sexual intercourse

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 no significant associations between consistency of recall and measures of personality, educational background or history of alcohol dependence and depression.