Stephen H. Dinwiddie

Suicidal behaviour : an epidemiological and genetic study

BACKGROUND Psychiatric history, familial history of suicide attempts, and certain traumatic life events are important predictors of suicidal thoughts and behaviour. We examined the epidemiology and genetics of suicidality (i.e. reporting persistent suicidal thoughts or a plan or suicide attempt) in a large community-based sample of MZ and DZ twin pairs. METHOD Diagnostic telephone interviews were conducted in 1992-3 with twins from an Australian twin panel first surveyed in 1980-82 (N = 5995 respondents). Data were analysed using logistic regression models, taking into account twin pair zygosity and the history of suicidality in the respondents co-twin. RESULTS Lifetime prevalence of suicidal thoughts and attempts was remarkably constant across birth cohorts 1930-1964, and across gender. Major psychiatric correlates were history of major depression, panic disorder, social phobia in women, alcohol dependence and childhood conduct problems. Traumatic events involving assault (childhood sexual abuse, rape or physical assault) or status-loss (job loss, loss of property or home, divorce), and the personality trait neuroticism, were also significantly associated with suicide measures. Prevalence of serious suicide attempts varied as a function of religious affiliation. After controlling for these variables, however, history of suicide attempts or persistent thoughts in the respondents co-twin remained a powerful predictor in MZ pairs (odds ratio = 3.9), but was not consistently predictive in DZ pairs. Overall, genetic factors accounted for approximately 45% of the variance in suicidal thoughts and behaviour (95% confidence interval 33-51%). CONCLUSIONS Risk of persistent suicidal thoughts and suicide attempts is determined by a complex interplay of psychiatric history, neuroticism, traumatic life experiences, genetic vulnerability specific for suicidal behaviour and sociocultural risk or protective factors.

Early sexual abuse and lifetime psychopathology: a co-twin-control study

BACKGROUND This study was designed to determine lifetime prevalence of psychiatric disorders among twins who reported childhood sexual abuse (CSA), and to compare these rates with those among non-abused co-twins. The contribution of familial and individual-specific factors to reported sexual abuse was also examined. METHOD Information about lifetime psychopathology and substance use was obtained by structured telephone interviews with 5995 Australian twins. Twins who reported a history of childhood sexual abuse (CSA) were contrasted on lifetime psychopathology with subjects without such a history; in addition, comparisons were made between same-sex twin pairs discordant for CSA. RESULTS A history of CSA was reported by 5.9% of the women and 2.5% of the men. In the sample as a whole, those reporting CSA were more likely to receive lifetime diagnoses of major depression, conduct disorder, panic disorder and alcoholism, and were more likely to report suicidal ideation and a history of suicide attempt. Abused women, but not men, were also more likely to report social phobia. When comparisons were restricted to non-abused co-twins, no differences in psychopathology were seen. However, rates of major depression, conduct disorder and suicidal ideation were higher if both co-twins were abused than if the respondent alone reported CSA. Model-fitting indicated that shared environmental factors influenced risk for reported CSA in women, but not in men. CONCLUSION The association between CSA and psychopathology arises at least in part through the influence of shared familial factors on both risk of victimization and risk of psychopathology.

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.

Genetic and Environmental Contributions to Variance in Age at First Sexual Intercourse

Little is known about the relative importance of genetic and environmental factors as determinants of age at first sexual intercourse In this study, subjects were 5,080 individuals from the Australian Twin Registry (3,310 females, I 770 males, age range 27-70 years, median 40 years) who completed a semistructured interview by telephone in 1992-1993 Self-reported age at first intercourse correlated higher for identical (monozygotic) twins than for nonidentical (dizygotic) twins Structural equation model fitting found that the genetic contribution to variance was considerably greater among twins aged 40 years or less (72% for males and 49% for females) than for those aged from 41 to 70 years (0% for males and 32% for females) Among the older cohort, there was evidence that somewhat different aspects of the shared social environment influenced age at onset in males and females In a more laissez-faire social climate in recent decades, it is likely that biological and psychological characteristics that are partly under genetic control significantly influence the age at which a person commences sexual activity

Psychiatric diagnoses of self-reported child abusers.

In order to evaluate lifetime psychiatric diagnoses and prevalence of dyssocial behaviors among self-reported child abusers, three large databases of clinical, community, and family study subjects were examined. Subjects who had acted as parents and who reported any episodes of child battery were compared to those without any history of child battery on prevalence of psychiatric disorders and dyssocial behaviors. Overall, 4% of subjects from the community sample reported child abuse. Abusers not selected through alcoholism treatment were more likely to receive diagnoses of alcoholism, antisocial personality disorder, and major depression. Those selected through alcoholism treatment were more likely to have antisocial personality disorder. Abusers in general were found to have a history of disciplinary problems, property destruction, and as adults to engage in other violent behaviors. It was concluded that self-identified child abusers have increased lifetime rates of antisocial personality disorder, alcoholism, and depression. The association between child abuse and other violence is not explained by selection of cases through the medical or legal systems.

Psychiatric disorders among wife batterers

Sixty-one male spouse batterers were identified from a population of relatives of treated alcoholics and compared to 319 married or formerly married men without a reported history of battering on lifetime psychiatric diagnoses and antecedent behaviors. Batterers had higher lifetime rates of alcoholism, antisocial personality disorder, and depression than nonbatterers, but not other psychiatric disorders. While batterers and nonbatterers could not be differentiated based on violent behaviors occurring before the age of 15, 95% of batterers reported other fighting as an adult. Batterers also were more likely to have been divorced two or more times and to report repeated infidelity. Implications for treatment of batterers and identifying groups at high risk for battering are discussed.

Psychopathology and HIV risk behaviors among injection drug users in and out of treatment

To replicate prior descriptions of injection drug users (IDUs), 158 IDUs recruited via a street-outreach program were compared to 320 non-IDUs on measures of substance use, lifetime psychopathology, and HIV risk behavior. IDUs were more likely to receive a diagnosis of antisocial personality disorder, but not other psychiatric diagnoses, and to report dependence on multiple substances. IDUs reported more HIV risk behaviors, but perceived HIV risk did not differ from non-IDUs. Compared to IDUs who declined treatment, IDUs willing to accept treatment did not differ on drug-related problems, lifetime psychopathology, or perceived HIV risk.

Solvent use as a precursor to intravenous drug abuse

Intravenous drug abuse (IVDA) is a significant public health threat, and ways of identifying individuals at high risk for IVDA are needed to plan strategies for intervention and treatment. Previous work had identified similarities in psychiatric diagnosis and patterns of drug use in IVDAs and solvent users. Using the same population, we found that 59 of 179 IVDAs (33.0%) reported a history of solvent use, which preceded the onset of IVDA in 41 of the 59. IVDAs with a history of solvent use were more likely to receive diagnoses of alcoholism and antisocial personality disorder (ASP) than IVDAs without solvent use. Even allowing for these coexisting psychiatric disorders, a reported history of solvent use increased the likelihood of also reporting IVDA by a factor of 3.2. Although the magnitude of risk is likely to differ in other populations, a history of solvent use may indicate individuals at high risk for IVDA, and youths who have used solvents should be considered at high risk for severe drug abuse, including IVDA.

Prediction of intravenous drug use

Information about lifetime intravenous drug use (IVDU) was obtained from 1,062 relatives of hospitalized alcoholics, felons, and control subjects, of whom 92 had a history of IVDU and an additional 230 had a history of substantial, but non-IV drug use. The IVDUs were significantly more likely than all other subjects to have reported experiencing numerous behavioral and social difficulties relating to conduct difficulties, early initiation of substance use, and disrupted living situation before the age of 15. They were also more likely to have exhibited conduct problems than other drug users. In multivariate analyses, four symptoms (fighting in school, juvenile arrest, initiation of cannabis use before 15, or initiation of sexual activity before 15) differentiated IVDUs. A history of greater numbers of these problems was associated with increasing risk for IVDU, both when compared with the total sample and when compared with other drug users.