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
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 respondent's co-twin
remained a powerful predictor in MZ
pairs (odds ratio=3·9), but was not consistently predictive in DZ
Overall, genetic factors
accounted for approximately 45% of the variance in suicidal thoughts and
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.